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What is the excretory system? |
The excretory system is the kidneys. -Its function is to excrete liquid and solute waste (e.g., excess water, excess salts, nitrogenous wastes, etc.) maintain pH, Osmolarity, and blood pressure. |
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The Excretory System (The kidneys): |
Excrete liquid and solute waste (e.g., excess water, excess salts, nitrogenous wastes, etc.) -Maintain pH, Osmolarity, and Blood Pressure. |
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Draw a kidney and label the following: |
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Draw a nephron and label the following: |
See labeled diagram below. In vivo, Bowman’s capsule is in contact with a portion of the distal tubule rather than directed away from it as shown. The juxtaglomerular apparatus is made up of a patch of cells on the distal tubule and a patch of cells on the afferent arteriole—where the two structures meet. The patch of cells on the distal tubule is called the macula densa, and the cells on the afferent arteriole are called juxtaglomerular cells (don’t memorize these names). Together, these cells constitute the juxtaglomerular apparatus. In Figure 2 the distal tubule is labeled C. The macula densa are magenta and labeled #7. The juxtaglomerular cells are green and labeled #6. Flow through the afferent arteriole is demonstrated by #9. |
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Describe the function of each of the items labeled on your diagram, focusing on the role each component plays in the concentration of the filtrate, exchange of ions, etc. |
-The glomerulus is a fenestrated (Penetrated, perferated) capillary bed that strains the blood—allowing fluids, ions, and molecules the approximate size of glucose or smaller to pass through into Bowman’s capsule. Blood cells and larger blood components remain within the capillaries and exit via the efferent arteriole which eventually empties into the renal vein. -Bowman’s capsule is a spherical enclosure around the glomerulus that catches the filtrate as it is formed and funnels it into the proximal tubule. -The proximal convoluted tubule (PCT) is the section of the nephron between Bowman’s capsule and the descending limb of the Loop of Henle. Along the PCT sodium is reabsorbed via active transport and glucose is reabsorbed via secondary active transport through a symporter identical to the one used to absorb glucose from the small intestine. Water follows the solutes via facilitated diffusion. However, because water and solutes are reabsorbed in the same ratio, the filtrate remains isotonic (i.e., the volume of filtrate decreases, but its concentration remains constant). -The descending Loop of Henle travels into the very hypertonic medulla. This section of the nephron is impermeable to salts, but very permeable to water. Water therefore flows out of the filtrate and into the medulla, concentrating the urine. -The ascending Loop of Henle carries the filtrate out of the medulla and back into the cortex. This portion of the loop is impermeable to water and actively transports ions out of the filtrate and into the medulla. This continuous "dumping" of salts into the medulla accounts for its hypertonicity. At the top of the ascending loop the filtrate is actually less concentrated due to the removal of these ions. -The distal convoluted tubule (DCT) is the section of the nephron between the top of the ascending loop of Henle and the collecting duct. Recall that this segment passes directly by the opening to Bowman’s capsule where the juxtaglomerular apparatus is located. The distal convoluted tubule regulates calcium, sodium and hydrogen concentrations—although for the MCAT we suggest you focus only on its sodium reabsorption function as regulated by the hormone Aldosterone. Recall that aldosterone stimulates increased sodium reabsorption at the DCT and the collecting duct. Less important, but worth remembering, is the fact that the DCT also reabsorbs calcium in response to parathyroid hormone (PTH). When the juxtaglomerular apparatus detects decreased blood pressure in the afferent arteriole, it secretes Renin, setting into motion the renin-angiotensin pathway whose ultimate result is increased blood volume and blood pressure (This increased blood pressure would provide negative feedback inhibition to the juxtaglomerular apparatus). A number of DCTs from a number of different nephrons dump into a shared collecting duct. The collecting duct carries the filtrate through the medulla toward the renal pelvis. The collecting duct becomes very permeable to water in the presence of ADH from the posterior pituitary. If ADH is present the filtrate will be further concentrated as water flows out into the very salty medulla. |
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Loop of Henle |
It is a counter current exchange. The downward section of the loop is excreting water, increasing the osmolarity of the interior. It starts with a molarity of about 300 and then once it reaches the bottom, the molarity peaks around 1200. -For the right side of the loop of Henle, the part that is going upwards, it is excreting NaCl, or salt. This side is decreasing the osmolarity of the inside of the tube and the molarity is decreasing from about 1200 to around 300. Towards the top of the tube, where the tube gets thicker, it begins to actually pump the NaCl out of the tube. |
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Collecting Duct: |
Once in the collecting duct, the water has become urine. This is where we control whether we let water out or not. We do that using a hormone, known as Antidiuretic Hormone, or ADH. The ADH is released from the posterior Pituitary Gland, and acts on the collecting duct and tells the duct that it can let water through. This will then allow water to flow out of the duct and back into the capillaries and into our interstitial fluid. If we dont need to let water out of the collecting duct, we then decrease the ADH hormone and dont let water out. The water instead just fows through the duct out into our urine. |
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What is a medulla? |
The inner region of an organ or tissue. Esp. when it is distinguishable from the outer region or cortex. |
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What is a cortex? |
An outer layer of an organ or body part, such as the brain or the kidney. |
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What is an antidiuretic? |
An Anti-diuretic is a Hormone that has us hold onto water |
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What is the gradient in the Loop of Henle and what is its primary purpose? |
The gradient begins at around 300 and then once it reaches the bottom of the loop, it reaches 1200. Once it begins to flow back up, it comes back to 300. Finally, once it begins to flow through the Collecting Duct, the amount of ADH hormone controls the amount of water that is secreted from the collecting duct. If water is needed, then a lot of ADH is released and it will release water, increasing the osmolarity of the duct. If water is not needed, then the amount of ADH is decreased, decreasing the amount of water that is released, and allowing it to flow through the collecting duct out as urine. |
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The "Hilus": |
The "Hilus" is present on the concave side of the Kidney, through which the Uriters are attached to the kidney. The part of the kidney where the Renal Artery and Renal Vain enter. |
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The 2 zones of the Kidney: |
The kidney is distinguished into 2 groups: -The Cortex – an outer Dark Red Zone -The Medulla – an inner pale red zone. |
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Uriniferous Tubules: |
Each kidney is made up of millions of functional units known as ‘Uriniferous Tubules.’ Each Tubule is made up of a Nephron and a Collecting Tubule. |
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The parts of the nephron: |
A Nephron can be split into different parts i.e., Renal Tubule, which can be split into 3 parts, The Proximal Convoluted Tubule (PCT), the Loop of Henle, and the Distal Convoluted Tubule (DCT). |
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IMPORTANT NOTE: |
It is easy to confuse the Ureters and the Urethra. The Ureters carry urine from the renal pelvis portion of the kidneys to the bladder. The Urethra carries urine from the bladder to the external urinary orifice. You have 2 Uriters, but you only have 1 Urethra. |
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What role does aldosterone play? |
Aldosterone increases sodium reabsorption in the Distal Convoluted Tubule and the Collecting Duct |
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Describe the interplay between: |
The diagram below outlines the renin-angiotensin pathway in more than sufficient detail for the MCAT. We do NOT believe the MCAT would ever require memorized knowledge of this pathway, but it has shown up multiple times and a strong familiarity with it would have made several moderately difficult questions quite easy. |
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Juxtoglomerular Apparatus: |
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Glomerular Histology: |
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Hormonal Regulation of Kidney Function: |
Aldosterone acts on the distal tubule causing an increase in sodium uptake. Aldosterone also causes reabsorption of Na+ out of the collecting duct via the insertion of Na+ channels, K+ channels, and NA+/K+ ATPases in the cellst that line the collecting duct. This increases the osmolarity of the cells lining the distal, causing water to flow out of the filtrate and into the cells. Aldosterone also causes reabsorption of Na+ out of the collecting duct via the insertion of Na+ channels, K+ channels, and Na+/K+ ATPases in the cellst that line the collecting duct. The net effect = water retention and increased blood pressure ADH (Antidiuretic Hormone) acts on the collecting duct, making it permeable to water. In the absence of ADH the collecting duct is impermeable to water. Because the collecting duct passes through the highly-concentrated Medulla, as soon as the membrane becomes permeable there is a large net flow of water out of the filtrate, concentrating the urine. The net effect = water retention and increased blood pressure. |
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Glomerular Filtration: |
This is a picture of GLomerular Filtration through the Glomerular capsular membrane which creates Glomerular filtrate. The wall of the glomerulus acts as a strainer and determines which substituents flow through the walls, and which remain in the glomerulus and flow out the efferent arteriole. The only blood substituents that do not move into Bowmans Capsule are the larger molecules such as blood cells and most plasma proteins, which exit the efferent arteriole. |
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Renal Capsule: |
Distal Convoluted Tubule: -Made of Macula Densa Cells, which represent modified smooth muscle cells. -Purpose is to communicate with Juxtaglomerular Cells on the Afferent Arteriole. -Monitor osmolarity of the filtrate and the flow rate. (If flow rate too slow, they will signal afferent arteriole to dialate and let more blood in to be filtered. If flow rate too fast, Macula Densa cells will signal Afferent Arteriole to constrict, which will limit amount of blood coming in, which will slow down flow rate. |
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What exactly is the Filtrate? |
The filtrate is all of the fluid within the Excretory system. All of the fluid within the Bowmans Capsule, Glomerulus, Proximal Convoluted Tubule, Loop of Henle, Collecting Duct etc. |
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Osmolarity explanation of the Loop of Henle: |
Proximal Convoluted Tubule: -Reabsorption/ Pumping out of Sodium, Potassium and Chlorine (buddies, always follow eachother), and Water (follows everything). Descending Loop of Henle: -Water is being reabsorbed – moving from filtrate, out into the blood. This increases the Osmolarity. The excreted water is then picked up by the blood Ascending loop of Henle: -Ions are reabsorbed (salts are being actively pumped from the filtrate back to the blood, but water isnt allowed to follow). Osmosis cannot happen! Osmolarity in the filtrate then decreases. -The filtrate is then Hypoosmotic at the top of the ascending loop of henle and into the Distal Convoluted Tubule. The entire goal of the Loop of Henle Structure is to create the environment for the collecting duct to sit in. |
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What is the entire goal of the Loop of Henle structure? |
The entire goal is to create an environment for the collecting duct to sit in. |
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Osmolarity changes at the bottom of the Loop of Henle: |
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Collecting Duct at work: |
Collecting Duct: -Allows Nephrons to control how dilute and how much volume of urine to produce. Collecting Duct (Left): -Water Conserving Mode -Water wants to leave the filtrate because it sees the saltiness outside, it is allowed to leave through the aquaporins. -As water leaves, the filtrate gets saltier and saltier and can actually be as salty as the surrounding environment. -Urine output will then be very concentrated. -The volume of uring excreted will also be low. Collecting Duct (Right): -Wants to get rid of excess water from the body. – The water wants to leave the filtrate, it still sees the same saltiness in the environment, but is not allowed to leave because the collecting duct is SELECTIVELY PERMEABLE to water, so the Aquaporins in the collecting duct are closed, not allowing the water to leave. -This then excretes urine that is as dilute as 100 mOsM. |
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The Collecting Duct and its messenger signals: |
Key: Hormone Vasopresin (used to be called ADH) -When Vasopressin is secreted, there is a second messenger signal, with cyclical AMP (cAMP) as a second messenger, which causes storage vasicals, which have aquaporins attached to them, to exocytose. Here is where the water channels are exposed and the water is then allowed to go in the direction that it wants, which is into the blood. -So the collecting duct is the key, it is the regulated part, it is what allows us to be able to excrete at a minimum. The Obligatory production is at leasts 400 cc’s per day, all the way up to 20-23 mL per day. |
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What are aquaporins? |
Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins (MIP) that form pores in the membrane of biological cells.[1] Aquaporins are "the plumbing system for cells," said Agre. Every cell is primarily water. "But the water doesn’t just sit in the cell, it moves through it in a very organized way. The process occurs rapidly in tissues that have these aquaporins or water channels." |
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The Respiratory System: |
Function: -Primary Function is gas exchange. Inhalation and expiration are necessary functions to deliver air to the alveoli where gas exchange can occur. Oxygen diffuses down its concentration gradient into the blood, and carbon dioxide diffuses down its concentration gradient out of the blood and back into the lungs. |
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The Respiratory System: |
Path of Air = Mouth/nose > pharynx >larynx>trachea>bronchi>bronchioles>alveoli |
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Provide a conceptual definition for the following terms: tidal volume, reserve volume, residual volume, and vital capacity. |
-The tidal volume (TV) is the volume of air that enters and exits the lungs during an average, unforced respiration. -There are two reserve volumes, an inspiratory reserve volume (IRV) and an expiratory reserve volume (ERV). This is the volume of additional air that can be exhaled or inhaled after a normal, unforced expiration or inhalation. -The residual volume (RV) is the amount of air left in the lungs after a forced, maximal exhalation. -Vital capacity (VC) is the total volume of air the lungs can hold at maximum inflation, minus the residual volume. |
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Respiratory System Pathway: |
Path of Air = Mouth/nose > pharynx >larynx>trachea>bronchi>bronchioles>alveoli -At the top of the Respiratory System, the nostrils bring air into the nose. -Cilia protect the nasal passage ways and other parts of the respiratory tract and filter out dust and other particles that enter the nose through the breathed air. -Air is also breathed in through the mouth. Pharynx: -Where the nose and the mouth meet up. -Located at the back of the throat. -Carries both food and air and is used for digestion and respiration. Esophagus: -1 Path of the Pharynx that is for food. It leads to the stomach. Epiglotis: -Small flap of tissue that covers the trachea, the air only pathway, when we swallow. This stops food and liquid from going into the lungs. Larynx: – a.k.a. Voicebox -Located at the top of the trachea, the air only pathway. -This is where our vocal cords are Trachea: -Side of the Pharynx that is for air travel. – 2-3 cm tube. -Extends downward from the bottom of the larynx for about 12 cm. -Walls of Trachea are made strong by stiff rings of cartilage that keep it open. -Also lined with tiny hairs, which sweep foreign particles and fluids out of the airway, keeping them from entering the lungs. -The Trachea divides into 2 branches, each one entering one of the two lungs of the body. Right and Left Main Stem Bronchus: -Each of these branches resemble the limb of a tree – dividing into smaller – finer branches called Bronchioles Bronchioles: -The Bronchioles are the small tree branch structures that come off of the left and right Main Stem Bronchus. – The Bronchioles end in tiny air sacs called Alveoli. Alveoli: – Alveoli are tiny air sacs at the end of the Bronchioles in the lungs. -They resemble grapes. -They enable fresh air to get to the air sacs, which are surrounded by tiny blood vessels or capillaries. |
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Laryngitis is the loss of one’s normal voice due to inflammation of the vocal cords. A common home remedy suggests that drinking honey soothes and hydrates the vocal cords, speeding recovery. Does the anatomy of the respiratory system support or refute this proposed remedy? |
If we assume—as seems to be implied—that this home remedy works because coating the vocal cords with honey hydrates and soothes these structures, then the remedy is entirely debunked by the anatomy of the respiratory system. At the back of the throat, near the base of the tongue, the pharynx essentially ends at a fork. The more posterior fork is the esophagus, which leads to the stomach. The more anterior fork is the larynx, which houses the vocal cords, and then continues on to the trachea, bronchi and lungs. The epiglottis is an upward-oriented cartilaginous flap that folds down over the opening to the larynx creating a one-way only route down the esophagus during swallowing. Thus, if honey or some honey concoction is consumed, it would coat the pharynx, epiglottis and esophagus, but be entirely separated from the vocal cords. To coat the vocal cords the honey would have to be inhaled—which would be very painful. At best, if any remedy does exist it would have to be the result of vapors given off by the honey in the throat reaching the vocal cords. |
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How the Respiratory System actually works: |
Hemoglobin: -Hemoglobin, also spelled haemoglobin and abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates (with the exception of the fish family Channichthyidae) as well as the tissues of some invertebrates. Hemoglobin in the blood carries oxygen from the respiratory organs (lungs or gills) to the rest of the body (i.e. the tissues) where it releases the oxygen to burn nutrients to provide energy to power the functions of the organism in the process called metabolism. -Oxygen bonds to Iron in the Hemoglobin. -The Hemoglobin are running through the capillaries and taking the Oxygen from the Alveoli. -Hemoglobin is actually red because it is literally rusting, when bonded to the O2. Carbon Dioxide: -The Carbon dioxide isnt actually in the red blood cell. -Instead, it is first converted to bicarbonate. -Bicarbonate is produced from carbon dioxide + water. -A lot of the bicarbonate will be in the plasma of the blood. -Carbon dioxide then gets released from red blood cells and back into the alveoli and eventually exhaled out of the body. |
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What are Hemoglobin? |
Hemoglobin; also spelled haemoglobin and abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates (with the exception of the fish family Channichthyidae) as well as the tissues of some invertebrates. Hemoglobin in the blood carries oxygen from the respiratory organs (lungs or gills) to the rest of the body (i.e. the tissues) where it releases the oxygen to burn nutrients to provide energy to power the functions of the organism in the process called metabolism. |
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How is Carbon Dioxide exhaled out of the body? |
Carbon Dioxide: -The Carbon dioxide isnt actually in the red blood cell. -Instead, it is first converted to bicarbonate. -Bicarbonate is produced from carbon dioxide + water. -A lot of the bicarbonate will be in the plasma of the blood. -Carbon dioxide then gets released from red blood cells and back into the alveoli and eventually exhaled out of the body. |
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Difference Between Pharynx, Larynx, and Trachea: |
Pharynx: -Where the nose and the mouth meet up. -Located at the back of the throat. -Carries both food and air and is used for digestion and respiration. Larynx: – a.k.a. Voicebox -Located at the top of the trachea, the air only pathway. -This is where our vocal cords are Trachea: -Side of the Pharynx that is for air travel. – 2-3 cm tube. -Extends downward from the bottom of the larynx for about 12 cm. -Walls of Trachea are made strong by stiff rings of cartilage that keep it open. -Also lined with tiny hairs, which sweep foreign particles and fluids out of the airway, keeping them from entering the lungs. -The Trachea divides into 2 branches, each one entering one of the two lungs of the body. |
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The Diaphragm: |
Be careful, students frequently get the following confused: 1) The Diaphragm moves DOWN when it is FLEXED and moves UP when it is RELAXED. 2) The Diaphragm moves DOWN during INHALATION and UP during EXHALATION |
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Gas Exchange: |
Hemoglobin = quaternary protein made of four protein chains, two alpha and two beta. -Each Protein has an Fe-containing "heme" group at its center. Each "heme" can hold one O2 molecule. |
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How many oxygen atoms are carried on one molecule of "Hb" at 100% saturation? |
Each hemoglobin molecule has four subunits, each with one heme. Each heme can hold one O2 molecule. Therefore, at 100% saturation a hemoglobin molecule can hold 8 oxygen atoms. |
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How CO2 is carried in the blood: |
(you must know and understand the following equation:) * (CO2) + (H2O) > (HCO3-) + (H+) |
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The equation: |
The two equations whose net equation is given in the outline are: CO2 + H2O ⇔ H2CO3 H2CO3 ⇔ HCO3- + H+ |
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Draw a hemoglobin binding curve. Show the shape of the curve for both O2 binding and CO binding. Demonstrate the effect of [CO2], [H+], [BPG], and temperature on the O2 binding curve. |
The MCAT has demonstrated that they clearly expect prior knowledge of this curve as demonstrated by their asking stand-alone questions that cover these concepts without presenting an example of the curve or discussing it in a passage. It would be logical to expect future questions on all aspects of this curve, especially trends related to pH, carbon dioxide concentration, and temperature. One question asked previously about BPG, but some helpful information was given in the stem. |
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The Cardiovascular System: |
Function: Deliver oxygen and nutrients to the cells and tissues of the body; pick up CO2 and waste products and deliver them to the lungs and kidneys. |
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Heart Valve: |
The Heart has 4 Valves. -Each valve is like a one way door that keeps the blood in the heart flowing in the same direction. -The valves are made up of 2 or 3 small, but strong, pieces of tissue, called leaflets. -The leaflets open to allow blood to flow through the valve and close to prevent blood from flowing backwards. -The opening and closing of the valve is controlled by the blood pressure changes within each heart chamber. |
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Oxygen Binding Curve |
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Tricuspid Valve: |
Positioned in the Hearts right side between the right Atrium and the right Ventricle. -The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, between the right atrium and the right ventricle. The function of the valve is to prevent back flow of blood into the right atrium. |
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Pulmonic Valve: |
The Pulmonic Valve separates the right ventricle from the Pulmonary Artery. -The pulmonary valve (sometimes referred to as the pulmonic valve) is the semilunar valve of the heart that lies between the right ventricle and the pulmonary artery and has three cusps. Similar to the aortic valve, the pulmonary valve opens in ventricular systole, when the pressure in the right ventricle rises above the pressure in the pulmonary artery. At the end of ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonary valve. |
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Mitral Valve: |
The Mitral Valve is positioned in the hearts left side between the left Atrium and the left Ventricle. -The mitral valve (also known as the bicuspid valve or left atrioventricular valve) is a dual-flap (bi- from the Latin, meaning double, and mitral- from the Latin, meaning shaped like a mitre) valve in the heart that lies between the left atrium (LA) and the left ventricle (LV). The mitral valve (not to be confused with the congenital bicuspid aortic valve) and the tricuspid valve are known collectively as the atrioventricular valves because they lie between the atria and the ventricles of the heart and control the flow of blood. -During diastole, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). As atrial pressure increases above that of the left ventricle, the mitral valve opens. Opening facilitates the passive flow of blood into the left ventricle. Diastole ends with atrial contraction, which ejects the final 20% of blood that is transferred from the left atrium to the left ventricle. This amount of blood is known as end diastolic volume (EDV), and the mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow. |
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The Heart: |
See the diagram below. You do NOT need to memorize the heart valves for the MCAT (but they are pretty easy to remember if you would like to know them. Think of Traveling to Bolivia, abbreviated: TRV BLV = Tricuspid Right Ventricle, Bicuspid Left Ventricle. The other two are named after what they lead to: pulmonary valve and aortic valve). |
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Coronary Blood Vessels: |
The Blood Vessels that provide the Heart and its cells with the necessary blood, oxygen, and nutrients. Blue vessels = Veins Red Vessels = Arteries (Fall under the Systemic Flow) |
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The Heart: |
Blood flows from the left ventricle, through the Arteries, Arterioles, Capillaries, Venules, Veins, Vena Cava and back to the right Atrium. |
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The Heart: |
Blood flows from the right Ventricle through the pulmonary arteries to the lungs and back through the pulmonary veins to the left atrium. |
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Arteries and Veins: |
Arteries leave the heart and Veins return to the heart. -The naming of blood vessels is NOT based on whether they carry oxygenated or de-oxygenated blood. Rather, it is based on the direction of flow: either toward or away from the heart. |
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Name at least one Artery and one Vein that carry oxygenated blood. Name at least one Artery and one Vein that carry deoxygenated blood. |
The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. The veins of the systemic circulation all carry deoxygenated blood from the capillaries back to the right atrium. The pulmonary veins carry oxygenated blood from the lungs back to the left atrium. The arteries of the systemic circulation all carry oxygenated blood from the left ventrical to the capillaries. |
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Electrical System of the Heart: |
The electrical signal originates at the SA node, then spreads across both atria to the AV node. There is a slight delay, then the signal travels from the AV node down the bundle of His and through the Purkinje fibers. At the end of the Purkinje fibers the signal travels cell to cell through gap junctions. |
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Sympathetic vs Parasympathetic Nervous Systems: |
Sympathetic Nervous System activity Increases heart rate and blood pressure. Parasympathetic Nervous System activity Decreases heart rate and blood pressure |
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Blood Vessels: |
Arteries -> Arterioles -> Capillaries -> Venules – > Veins -Arteries: muscular, thick-walled vessels that push blood through via rhythmic contraction. Pressure system. -Veins: thin-walled vessels with little to no musculature that rely on a valve system to move blood back toward the heart. |
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Arterioles, Venules, and Capillaries: |
-An Arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. -A venule is a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 7 to 50μm in diameter. Veins contain approximately 70% of total blood volume, 25% of which is contained in the venules. Venules are blood vessels that drain blood directly from the capillary beds. Many venules unite to form a vein. -Capillaries: Capillaries /ˈkæpɨlɛriz/ are the smallest of a body’s blood vessels and are parts of its microcirculation. Their endothelial linings are only one cell layer thick. These microvessels, measuring around 5 to 10 micrometre in diameter, connect arterioles and venules, and they help to enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste chemical substances between blood and the tissues[3] surrounding them. |
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Capillaries: |
Capillaries are the smallest of a body’s blood vessels and are parts of its microcirculation. Their endothelial linings are only one cell layer thick. These microvessels, measuring around 5 to 10 micrometre in diameter, connect arterioles and venules, and they help to enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste chemical substances between blood and the tissues[3] surrounding them. |
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Decribe how the interplay of hydrostatic and osmotic pressure accounts for the flow of fluid into and out of the capillary beds: |
On the arterial side of the capillary bed the hydrostatic pressure is at its maximum. At this same point, the osmolarity of the blood is greater than that of the interstitial fluid, creating an osmotic pressure that would drive fluid into the capillary. These two influences oppose one another, but the hydrostatic pressure is greater than the osmotic pressure, yielding a net filtration pressure (13 mmHg, driving fluid out of the capillary and into the interstitial fluid). -On the venous side of the capillary bed the differences in osmolarity are about the same, but the hydrostatic pressure has decreased significantly. This makes the net filtration pressure negative and fluid flows out of the interstitial fluid and into the capillary (-7 mmHg). Note, however, that the net pressure on the arterial side is slightly greater than the net pressure on the venous side. As a result, about 10 percent of the fluid that exits on the arterial side does NOT re-enter the capillary on the venous side. What happens to that 10%? That is one of the primary functions of the lymphatic system—to pick up extra interstitial fluid from the capillary beds and return it to the venous system. |
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Draw a graph for each of the following: a) cross-sectional area vs. blood vessel type (aorta/arteries/arterioles/capillaries/venules/veins/vena cava) b) velocity vs. blood vessel type c) blood pressure vs. blood vessel type |
See diagram below. Diagram intended to show general theoretical trends and is not drawn to scale. Q = AV explains the inverse relationship between the red and green lines. |
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Important NOTE: |
Blood gases and blood pH are very frequent MCAT topics. Questions usually ask you to predict changes to blood pH based on the partial pressure of CO2, [CO2] in the blood, hyperventilation, breathing into a bag, difficulty exhaling, blockage of a pulmonary vein or artery, and so on. For example, "If the pulmonary artery became blocked, what would be the immediate short-term effects on blood pH?" What if the pulmonary vein were blocked? What if the capillary walls became impermeable to CO2? What if the alveoli were impermeable to CO2? |
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Blood: |
Functions: -Transport nutrients, gases, waste products and hormones o and from cells -Regulate the extracellular environment -Help maintain homeostasis -Repair injuries -Protect the body from foreign bodies (i.e., antigens). |
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Blood: |
Contents: -White Blood Cells (a.k.a. WBC’s or leukocytes, -Red Blood Cells (a.k.a. RBC’s or erythrocytes) -Antibodies (a.k.a. immunoglobins) -Clotting Factors (e.g., fibrinogen) -Transport proteins (e.g., albumin) and platelets. |
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Blood is an example of which type of tissue? |
Blood is a connective tissue. |
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Blood: |
-a.k.a. Red Blood Cells Sacks of hemoglobin and not much else. Immature RBC’s start out with a nucleus and organelles but these disappear as the cell matures. *Mature RBC’s have no nucleus or other organelles. |
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Do erythrocytes undergo mitosis? Y/N |
Erythrocytes do NOT undergo mitosis because they lack nearly all of the cellular machinery to do so. Recall that red blood cells do not have nuclei or organelles. They are essentially membrane-bound sacks of hemoglobin. |
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Blood: |
No Hemoglobin. Normal cells with all their organelles that are involved in the immune system (we’ll discuss WBC’s in more detail with the immune system). -Granulocytes: Neutrophils, eosinophils, and basophils. *These cells live for hours to days. -Agranulocytes: monocytes (become macrophages) and lymphocytes. *These cells live for months to years. |
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Blood: |
Tiny membrane-bound drops of cytoplasm. They are sticky when exposed to injured epithelium and non-sticky to healthy epithelium. If they encounter injured epithelium, they release chemicals that activate other platelets and clotting factors. -Platelets are derived from Megakaryocytes, a type of blood cell that remains in the bone marrow. Mature Megakaryocytes produce small fragments, which they release into the circulating blood. These cellular fragments are platelets. -All blood cells develop from stem cells (undifferentiated cells) in the bone marrow; a process called Hematopoiesis. |
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Where do all blood cells develop from? What is this process called? |
All blood cells develop from stem cells (undifferentiated cells) in the bone marrow; a process called "Hematopoiesis." |
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Blood Typing: |
Four Phenotypes: A, B, AB, and O. The letters A and B indicate the Antigens that are present on that individuals blood cell membranes: A = A antigens only B = B antigens only AB = Both A & B antigens O = Neither A or B antigens |
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Blood type is an example of what kind of genetic inheritance pattern? |
Blood type is an example of co-dominance because both alleles are expressed equally in a heterozygote. A person with the AB genotype, for example, has both A and B antigens. In other words, both the A and B phenotypes are expressed simultaneously. |
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Important Note: |
To avoid mistakes on blood-typing questions, always focus on the recipient. If a person’s immune system sees any protein it does not have on its own blood cell membranes, it will attack it and coagulation/rejection will result. Thus, a patient with type A blood is fine with A antigens on donated blood cells, but will attack B antigens, whether from an AB, or a B donor. Type O blood can be donated to anyone because it has no A or B antigens. A person with blood type AB can receive from anyone because no donor will have any antigens this person’s immune system hasnt seen previously. |
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What type of blood can be universally donated to anyone? |
-Type O blood can be donated to anyone because it has no A or B antigens. -A person with blood type AB can receive from anyone because no donor will have any antigens this person’s immune system hasnt seen previously. |
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The Lymphatic System: |
Function: -Gather excess interstitial fluid and return it to the blood. -Remove from the interstitial spaces proteins and other molecules too big to be taken up by the capillaries -Monitor the blood and lymph for infection. |
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What is the Lymphatic System responsible for? |
The Lymphatic System: -It is responsible for the removal of interstitial fluid from tissues -It absorbs and transports fatty acids and fats as chyle from the digestive system -It transports white blood cells to and from the lymph nodes into the bones -The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated. |
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The Lymphatic System: |
Lymph Nodes: Lymph nodes are filled with lymphocytes. These immune system cells monitor the blood for foreign antigens and fight infections (covered more in "Immune System in Bio 4) Lymph Vessels: Lymphatic Vessels are a lot like veins; many – but not all – contain one-way valves used to move the lymph; single cells overlap slightly creating a trap door that allows things in, but not back out. The entire lymph system eventually drains into two main vessels, the right lymphatic duct and the thoracic duct, which both dump back into the blood stream by merging with large veins in the lower portion of the neck. |
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Hardeining of the arteries (arteriosclerosis) is often accompanied by hypertension primarily because: A) Smooth muscle lining the arteries is weakened and cannot contract. |
Answer A is false because this would increase the diameter of the vessel and decrease blood pressure. Answer B would also decrease blood pressure per the equation P = F/A. Answer D describes a process that does not occur in the human body. Answer C is therefore correct. Blood pressure is primarily a function of cardiac output and vascular resistance. |
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The Nervous System: |
Definition: The Nervous System includes the brain, spinal cord, peripheral nerves, neural support cells (astrocytes, Schwann Cells, Ependymal Cells, etc.) and sensory organs such as the eyes and ears. |
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Neuron Anatomy: |
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The Nervous System: |
A Neuron is a specialized cell that can carry an electrochemical signal (i.e., action potential). Remember that Neurons: 1) Are frozen in G0 phase (unable to divide) 2) Depend entirely on glucose for energy 3) Dont require insulin for glucose uptake 4) Have very low glycogen & Oxygen storage capability and thus require high perfusion (blood flow) |
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Draw a Neuron and label the following: |
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Describe the Function and Significance of each item labeled in your diagram: |
-A dendrite is a finger-like projection from the cell body that receives signal information from an upstream neuron with which it forms a synapse. The signal will be received from the previous neuron via binding of a neurotransmitter on the dendrite portion of the membrane (i.e., postsynaptic membrane). -The cell body is the main part of the neuron where the nucleus is located. -The axon hillock is the area where the axon joins the cell body. This region has a very high concentration of voltage-gated sodium channels. This makes it both sensitive to action potentials and capable of regenerating a strong action potential for transmission down the axon. -The terminal button (a.k.a., axon terminal) is a projection at the end of the axon that synapses with the dendrite of another neuron or with the effector. -The axon is the long, narrow, tube-like extension between the cell body and the terminal button. Human axons can be up to 1.5 meters long! -Along the axon are specialized neural support cells called Schwann cells. These cells contain high levels of fat and wrap themselves around the axon multiple times creating an insulating myelin sheath. -There are small gaps between Schwann cells, called the nodes of Ranvier. A signal is able to "Jump" from one node to another without progressing along the entire length of the axon—dramatically increasing transmission speed. |
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Important Note: |
A stimulus (i.e., the action potential) starts at the dendrites and passes through the cell body to the axon hillock. The axon hillock then generates a new stimulus only if the initial stimulus is above a certain threshold. Thus, the action potential that arrives at the terminal button is NOT the same stimulus that began at the dendrites; it is a new, regenerated stimulus. Also remember, impulses can only flow down the axon in one direction: cell body to synapse. |
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Axon Hillock Function: |
The axon hillock is a specialized part of the cell body (or soma) of a neuron that connects to the axon. The axon hillock is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon. |
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What is the resting potential within a neuron? |
-70 mV (Millivolts) |
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Sodium/Potassium Pump |
The sodium-Potassium Pump is an active transport mechanism. (meaning it requires energy) The transport protein is open towards the inside of the cell and has active sites that are designed for certain ions to bind to it. -3 sodium ions bind to the protein channel and an ATP provides the energy to change the shape of the channel that in turn drives the ions through the channel. -One phosphate group from the ATP remains bound with the channel. -The sodium ions are then released to the outside of the cell. -The new shape of the cell now has a high affinity for Potassium ions and two of these ions then bind to the channel. -This binding of the potassium ions again causes a change in the shape of the protein channel, which makes the channel open back up into the inside of the cell and release the Potassium ions into the cell. -The protein channel then finds more Sodium ions to bond with it, along with an ATP, and it then repeats the process again. The important part of this cycle is that both Sodium (Na) and Potassium (K) are moving from an area of low concentration to an area of high concentration. |
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Nervous System: |
Action Potential: A disturbance (i.e., a dramatic change) in the resting electrical potential (i.e., voltage) across the membrane of a nerve cell. Once an action potential is created, it will propagate along the cell membrane to neighboring portions of the neurons. As it does, the areas where it originally started gradually return to the normal resting potential (see below). Resting Potential: -70 mV. This is the potential difference (i.e., voltage) across the membrane |
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Resting Potential: |
Resting Potential: -70 mV. This is the potential difference (i.e., voltage) across the membrane when an action potential is NOT present (e.g., one has not yet occurred, or it has already passed). Know the exact value: -70mV. This is the only exact value that is used consistently in most textbooks. The other values given below vary from source to source and you only need to know their sign and approximate value. |
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Sodium/Potassium Pump: |
An ATP pump that actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell per cycle. The net effect is more positive charge outside the cell and a progressively more negative charge inside the cell. |
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Voltage-Gated sodium channels.: |
Integral Proteins that change shape ("open") in response to a disturbance in the resting potential (i.e., voltage) across the membrane. In their "open state", they allow the rapid flow of sodium back into the cell. |
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Depolarization: |
The opening of the voltage-gated sodium channels causes a sudden spike in the membrane potential, from -70mV to somewhere around +40 mV. This process is referred to as "depolarization." |
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Threshold Potential: |
This is the minimum stimulus that must be exerted upon the membrane to initiate the full action potential. It is usually reported as somewhere around -55mV. If a stimulus depolarizes the membrane above this threshold, the entire action potential will follow. If not, the membrane potential will return to -70mV. |
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What is the "threshold" that a stimulus must exert upon a membrane or the axon hollock in order for it to initiate from -70mV? |
The threshold potential is usually reported as somewhere around -55mV. |
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Voltage-Gated Potassium Channels: |
These are also integral proteins that respond to a change in the membrane potential. However, their threshold for responding is much higher than that for the voltage-gated sodium channels. As a result, they only react following the very large change in membrane potential caused by depolarization. *Just before maximum depolarization is reached, the Na+ channels begin to close and the K+ channels begin to open. |
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Repolarization: |
Because there are more potassium ions inside the cell (due to the Na+/K+ pump), opening of the potassium channels causes K+ ions to flow out of the cell. This results in a sudden decrease in the membrane potential from +40mV back down to -70 mV, and is referred to as "repolarization." |
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Hyperpolarization: |
The potassium channels are somewhat slow to close as the membrane potential approaches -70mV. Thus, the membrane potential actually dips to around -90mV before gradually returning to the resting potential. |
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Provide a definition for the "absolute refractory period" and the "relative refractory period." Why does it take a stronger stimulus than normal to cause an action potential during the relative refractory period? |
The absolute refractory period is a portion of time during which an action potential cannot be initiated regardless of the strength of the stimulus. This time period occurs during the progression of a previous action potential. The progression of an action potential involves the depolarization of the membrane and a second stimulus cannot be initiated until the membrane is repolarized. The relative refractory period is a portion of time during which the membrane is hyperpolarized (i.e., is more negative than at normal resting potential). During this time a second action potential can be initiated, but a stronger-than-normal stimulus will be required. This makes sense because the firing of an action potential is an all-or-nothing event dependent on the polarity of the membrane reaching the threshold potential. During hyperpolarization there is a greater voltage difference between the present state of the membrane and the threshold potential—thus a larger stimulus is required to reach that threshold. |
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Graph and label the entire action potential as Voltage vs. Time. Include resting potential, threshold stimulus, absolute refractory period, relative refractory period |
See the labeled diagram below. The potassium channels open at some positive potential, before the sodium channels close. The sodium channels close at the peak of depolarization. Note that some stimuli fail to result in an action potential because they fall short of the threshold stimulus. In this diagram it is also easy to see why a greater-than normal stimulus would be necessary to reach the threshold during the hyperpolarization phase (i.e., relative refractory period). |
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The Synapse: |
There are two kinds of synapses: electrical and chemical. Transmission across the synapse is by far the slowest part of signal transmission. Electrical Synapses: Gap junctions between cells that allow electrical signals to pass very quickly from cell to cell. In humans they are found only in specific locations: the retina, smooth muscle, cardiac muscle, and the CNS. Chemical Synapses: This is the traditional synapse you probable think of when you hear the word. It is the small gap between the terminal button and either: 1) the dendrite of a subsequent neuron 2) The membrane of a muscle or other target (called the "effector"). |
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Describe the process by which the signal is transmitted from the terminal button, across the synaptic cleft, to the subsequent neuron or effector. Include definitions and explanations of function for the following: presynaptic membrane, Ca2+ ions, calcium channels, neurotransmitters, neurotransmitter bundles, exocytosis, postsynaptic membrane, and protein receptors. |
When an action potential arrives at the presynaptic membrane it triggers voltage-gated calcium channels to open, allowing calcium ions to flow into the cell. Inside of the terminal button are numerous neurotransmitter bundles—vesicles filled with neurotransmitter. The presence of calcium initiates a cascade that results in these bundles fusing with the presynaptic membrane and dumping their contents into the synaptic cleft. These neurotransmitter molecules diffuse across the gap and bind to protein receptors on the postsynaptic membrane. These receptors are usually associated with sodium channels so that the binding of neurotransmitter opens the sodium channel allowing sodium ions to flow into the cell. If enough sodium ions flows into the cell the voltage will reach the threshold stimulus and an action potential will be generated in the second neuron. |
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Stopping the Signal: |
The post-synaptic membrane will be continuously stimulated as long as a neurotransmitter is present. Specialized enzymes in the synaptic cleft must break down the neurotransmitter to interrupt its action. The most common one is Acetylcholinesterase (AChE). The MCAT loves to ask about Acetylcholinesterase. They often ask about Acetylcholinesterase activators or inhibitors. Agonist is another term for an activator and antagonist is another term for an inhibitor. |
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What do Agonist and Antagonist mean? |
Agonist is another term for an activator and Antagonist is another term for an inhibitor. |
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What is the name of the common enzyme that stops the neurotransmitters from continuing to the post-synaptic membrane and transferring the signal? |
It is called the Acetylcholinesterase (AChE) and it breaks down the neurotransmitters in the synapses. |
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Name several possible effects caused by a drug that acts as an acetylcholinesterase antagonist at the neuromuscular junction. |
An acetylcholinesterase antagonist would impede the normal activity of this enzyme, which breaks down acetylcholine. Decreased breakdown of the neurotransmitter would allow more of it to be present in the synaptic cleft, and to be present for a longer period of time—causing hyperstimulation of the subsequent neuron. Hyperstimulation of neurons could cause any number of problems depending on the effector with which a neuron is communicating. Muscle rigor, cramping, ticks, and pain would be logical possibilities. The drug effect would not necessarily be negative. An increase in the concentration of certain neurotransmitters in the brain has been shown to combat depression and therefore many antidepressants are actually acetylcholinesterase inhibitors (i.e., fluoxetine [Prozac], sertraline [Zoloft] and amitriptyline [Elavil]). If the drug were an agonist it would have the opposite effect, resulting in increased breakdown of acetylcholine and therefore decreased stimulation of neurons. |
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Neural Support Cells: |
These cells are not neurons that conduct electrical potentials, but cells in the nervous system that provide support to neurons. Schwann cells (oligodendricytes in the CNS), cells lining the cerebrospinal fluid cavities (ependymal cells) and structural support cells (astrocytes) are a few prominent examples. |
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What is the name of the cells that line the cerebrospinal fluid cavities? What type of cells are they? |
They are called Ependymal Cells. They are Neural Support Cells. They arent neurons that conduct electrical potentials, but cells in the nervouse system that provide support to neurons. |
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Neuron Functions: |
Sensory (Afferent) Neurons: Receive sensory signals from sensory cells. Motor (Efferent) Neurons: Carry signals to a muscle or gland to respond to the stimulus. Interneurons: Connect afferent and efferent neurons. They also transfer and process signals. The brain and 90% of all other neurons are interneurons. |
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What are the 3 types of Neurons and what are their jobs? |
1: Sensory (Afferent) Neurons: Receive sensory signals from sensory cells. 2: Motor (Efferent) Neurons: Carry signals to a muscle or gland to respond to the stimulus. 3: Interneurons: Connect afferent and efferent neurons. They also transfer and process signals. The brain and 90% of all other neurons are interneurons. |
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If a concentrated saline solution were to be injected at the proximal end of one of the collecting ducts of the kidney, what changes would be expected to urinary output and blood pressure, respectively? A) urinary output would increase and blood pressure would decrease |
Without the presence of the hormone ADH, the collecting ducts of the kidney remain impermeable to water and thus no change in urinary output or water retention could occur. However, considering the injection itself would join with the urine, it is logical to say that urinary output would increase slightly. Answer D is thus correct. |
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All of the following changes to the physiology of the cell membrane of a neuron would decrease the sensitivity of that neuron to the propagation of a new action potential, EXCEPT: A) a complete inhibition of ATP production and availability in the cell |
If there were no ATP at all, the sodium-potassium pump would stop functioning and all ions would equilibrate. Upregulaton of that same pump would make the cytosol more negative than resting membrane potential and a larger stimulus would be required. Similarly, increased diffusion of potassium would also make the cytosol more negative. Increased permeability to sodium, however, would cause sodium to flow into the cell, moving resting potential closer to the threshold. It would then be easier to propagate a new stimulus. Answer C is therefore correct. |
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Nervous System Organization: |
The nervous system is divided into the CNS and the PNS. CNS: The brain and spinal cord; interneurons only. No subdivisions. PNS: All neurons outside of the CNS; both sensory and motor neurons. Contains "somatic" and "autonomic" divisions. |
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Somatic and Autonomic Divisions: |
Somatic: Voluntary; innervates skeletal muscle; contains both sensory and motor subdivisions. Autonomic: Involuntary (done without control); innervates (supplies with nerves) cardiac muscle, smooth muscle, and glands; contains both sensory and motor subdivisions. |
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Subdivisions of the Autonomic Nervous System: |
Sensory (a.k.a. afferent): The sensory subdivision of the autonomic nervous system is not well developed, explaining why visceral pain is ofter referred (i.e., felt at a location other than the actual source) and poorly localized. Motor: The motor subdivision of the autonomic nervous system contains the "sympathetic" and "parasympathetic" divisions with which you are likely familiar. –Sympathetic: "Fight or Flight." Cell bodies located far from the effectors. Neurotransmitters: acetylcholine only, at both the ganglia norepinephine at the effector. –Parasympathetic: "Rest and Digest." Cell bodies located very close to, or inside, the effector. Neurotransmitters: acetylcholine only, at both the ganglia and the effector. -A common misconception is that the Sympathetic stimulates and the Parasympathetic inhibits. This is false. They both stimulate and inhibit, depending on the situation. Always rely on "Fight or Flight" and "Rest and Digest" to predict what they will do. |
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Describe the effect of: |
-The pupils dilate in response to sympathetic stimulation and constrict in response to parasympathetic stimulation; -Heart rate is increased by sympathetic stimulation and decreased by parasympathetic stimulation; -Blood pressure is increased by sympathetic stimulation and decreased by parasympathetic stimulation -Blood flow to the skeletal muscles is increased by sympathetic stimulation and decreased by parasympathetic stimulation; -Blood flow to the digestive organs is decreased by sympathetic stimulation and increased by parasympathetic stimulation; -Blood flow to the brain is increased by sympathetic stimulation and decreased by parasympathetic stimulation; -Blood flow to the skin is decreased by sympathetic stimulation and increased by parasympathetic stimulation. *Basically, the parasympathetic is responsible to calming down every stimulation caused by the sympathetic nervous system. |
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Draw a flow chart (i.e., algorithm) demonstrating the hierarchical organization of the human nervous system. At a minimum, include all of the bolded terms from the previous section. |
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Sensory Organs: |
Rods = highly sensitive, perceive black and white only. Cones = less sensitive, perceive color. |
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Draw a diagram of the human eye and label the following: Cornea, Sclera, Pupil, Iris, Aqueous Humor, Vitreous humor, Lens, Ciliary muscles, Retina, and Optic Nerve. |
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The Eye: |
The lens of the human eye is a "Converging Lens" and therefore always produces a PRI image -Light Rays are bent most by the cornea, and subsequently adjusted by the lens. -As a review from physics, you should be able to describe the factors that determine when a person is near-or far-sighted. Where is the image formed in both cases? What type of lens is needed to correct each condition? |
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Describe the factors that determine when a person is near-or far-sighted. Where is the image formed in both cases? What type of lens is needed to correct each condition? |
A near-sighted person can see close objects but not objects farther away. A far-sighted person can see objects far away, but not closer objects. -For a near-sighted person the light rays are being bent (i.e., diffracted) too much, resulting in a focal point and image that is in front of the retina. Placing a diverging lens in front of an eye with this condition spreads the rays apart, increasing the distance between the lens and the focal point (i.e., the place where the rays will meet). -For a far-sighted person they cannot see close objects because the light is diffracted too little, resulting in a focal point and image that is behind the retina. Placing a converging lens in front of an eye with this condition brings the rays closer together so that the focal length decreases and lands on the retina. |
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What happens to the eye as you attempt to focus on a book very near your face? Do the ciliary muscles contract or relax? Does the curvature of the lens increase or decrease? Does the focal point move outward or inward (i.e., increase or decrease)? Does the power of the lens of the eye increase or decrease? |
To answer this question one must first understand that when the ciliary muscles contract the lens becomes more spherical (i.e., smaller radius of curvature). For an object near the eye the light rays must be bent (i.e., diffracted) more sharply than rays from distant objects (for distant objects light rays are assumed to be parallel). A lens with a smaller radius of curvature bends light more sharply. Therefore, the ciliary muscles contract to increase the curvature of the lens, bend the light more sharply and thereby land the image on the retina. The focal point will decrease (i.e., move closer to the lens) as the radius of curvature of the lens decreases. The power of a lens is the inverse of the focal point: P = 1/f. Therefore, as the lens of the eye focuses on a nearby object that lens becomes more powerful. |
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What is Rhodopsin and what does it do? |
Rhodopsin is the protein at the top or tip of the cones and rods at the back of the eye. The Rhodopsin reacts to light entering the eye. When it is confronted by light, the Rhodopsin then changes shape and sends an action potential down the rod to the Optic Nerve, which sends a signal to the Brain. |
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Ear Diagram: |
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The Ear: |
Outer Ear: Includes the Pinna (earlobe) and auditory Canal. Middle Ear: Includes the tympanic membrane (eardrum), and the three middle ear bones (in this order outside to inside: malleus, incus and stapes. Inner Ear: includes the cochlea, semicircular canals, and the vestibulocochlear nerve. |
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Draw and label all of the parts of the inner ear. Also draw a cross-section of the cochlea showing the three compartments and the organ of Corti. |
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Glands/Hormones/Action |
Pineal Gland – (small tip in center) secretes Melatonin. Only secreted at night. If the eyes are open, then no Melatonin is secreted. When eyes are closed, it is then released and Melatonin acts on the part of the brain that tells the time of day and season of the year. This sets up our Circadian Rhythm, or internal clock. Anterior Pituitary Gland – (little green object dangling. Anterior is the front part) – Gives off growth hormone. The growth hormone is relased and floats through the rest of the body, through the circulatory system or interstitial fluid, and basically causes cells to grow. Posterior Pituitary Gland – (Back section of the dangling green object.) – Gives off ADH, which as we know from the kidneys, is used to balance water reabsorbance. Thyroid Gland – ( Purple sheath at the throat) – secretes T3 and T4. It basically just regulates Metabolism. When T3 and T4 are given off by the Thyroid Gland, they then speed up Metabolism inside our body. So if you have a hyperactive Thyroid, then you have a high metabolism. If you have an inactive Thyroid, then you will have a really slow Metabolism. -The Thyroid also secretes Calcitonin. The amount of Calcium within the body, within the blood stream, is very important. So when Thyroid secretes Calcitonin, it lowers the blood Calcium. Some of the calcium is secreted back into the kidneys, but the majority is absorbed back into the bones. Parathyroid – The red dots that sit on the outside of the Thyroid gland. The Parathyroid glands secrete the Parathyroid Hormone, or PTH. PTH raises the blood calcium if it gets too low. -The thyroid and parathyroid work together to keep the calcium concentration in the blood at a normal level. |
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Glands/Hormones/Action: |
Pancreas – (Grean leaflet behind the stomach.) – empties enzymes into the Duodenum (green tip on the kidneys) – on the surface of the pancrease it has Alpha and Beta cells that are going to secrete Insulin and Glucagon. Insulin is secreted if we need to lower the blood sugar, it allows the cells to take in that blood sugar, and Glucagon is secreted if we need to raise the blood sugar, it releases more insulin from the glycogen found in the liver. Kidneys – on the top of the kidneys we have the Adrenal Glands, which have a cortex and a medulla. The Adrena Cortex (outside of the Adrenal Gland) secretes Glucocorticoids, which is an antiinflammatory. The Adrenal Medulla secretes Epinephrine – which is Adrenaline, it goes throughout your body and triggers that fight or flight response. |
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Glands/Hormones/Action Part 3: |
Ovary – in females – release Estrogen – which are responsible for female sex characteristics. Testes – in males – release Testosterone – which are responsible for male sex characteristics. Once you go through puberty, either the Testes or the Ovaries get a signal from the pituitary gland that tell them that it is now time to make these sex horomones |
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The Endocrine System: |
The Endocrine System includes the "endocrine glands" and the fluids and ducts into which they are released. -Exocrine Glands: release enzymes or other liquids into the external environment (which includes the digestive tract and epithelial-lined orifices; substances released include sweat, oil, mucus, digestive enzymes, etc.) -Endocrine Glands: release hormones into the internal fluids of the body (e.g., blood, lymph, etc.) |
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Endocrine Hormones: |
You need to know each hormone, its function, whether it is a peptide, steroid, or tyrosine derivative, the organ that secretes it, and where that endocrine organ is located in the body. |
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Endocrine Hormones: |
-Anterior Pituitary: FSH, LH, ACTH, hGH, TSH & Prolactin -Posterior Pituitary: ADH and Oxytocin. –The anterior and posterior pituitary are both regulated by "__________stimulating/releasing" hormones from the hypothalamus. -Parathyroid: PTH (Parathyroid Hormone) -Pancreas: Glucagon and Insulin (also releases several digestive enzymes, but this is an exocrine function, not an endocrine function.) Thyroid: Calcitonin Embryo/Placenta: hCG (Human Chorionic Gonadotropin.) |
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Endocrine Hormones: |
-Adrenal Cortex: Cortisol and Aldosterone -Gonads: Estrogen, Progesterone & Testosterone |
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Endocrine Hormones: |
-Thyroid – T3 (Triiodothyronine) & T4 (Thyroxine) -Adrenal Medulla: Epinephrine and Norepinephrine |
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Hormone Transport and Action at the Effector: |
Transport: Lipid-soluble hormones require a protein carrier or a micelle/vesicle. Peptide hormones are water soluble and dissolve in the blood readily. Target: Lipid-soluble hormones act almost exclusively by binding to a receptor on or inside the nucleus and influenceing transcription; Peptide hormones, by contrast, act at a variety of cell locations. Membrane Permeability: Lipid-Soluble hormones diffuse easily through the lipid center of the membrane and thus do NOT require a cell membrane receptor. They still require a receptor eventually, wherever they act inside the cell. Peptide Hormones are hydrophilic and cannot dissolve through the membrane; thus they require a membrane receptor. |
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Second Messenger Systems: |
You must know what a second messenger system is and how it works. It usually occurs via a cascade. In a cascade, one hormone activates another hormone, enzyme, or other signaling molecule. The signal recipient then activates another member of he cascade, with the size of the reaction and the number of molecules involved increasing with each step. Review: During BIology 1 lesson we discussed the function of G-Proteins. G-Proteins are a prime example of a second messenger system. As a review from Biology 1 (and a good test of whether or not you are truly mastering and retaining the content as required) attempt to answer the following question asked of you previously in Biology 1. Attempt to do so from memory, without consulting the internet, the study links, or any other resources. |
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Give a generalized description of a G-protein cascade. Include terms such as G-protein-coupled receptor (GPCR), alpha/beta/gamma subunits, GDP, GTP, adenylyl cyclase, cAMP, and Protein Kinase A (Hint: Many enzymes are activated by phosphorylation). |
https://www.youtube.com/watch?v=V_0EcUr_txk First, a hormone or signal molecule binds to an integral protein on one of its extracellular domains—this protein is called a G-protein-coupled receptor or GPCR. This causes a conformational change that activates a cytosolic domain of that same integral protein. Near the GPCR, or at least along the cytosolic face of the membrane, is a G protein made up of an alpha, beta and gamma subunit. The alpha subunit binds both GTP and GDP. When GDP is bound the protein is "off" and when GTP is bound it is "on." Usually, but not always, the activated receptor protein acts as a catalyst for the replacement of GDP by GTP, activating the alpha subunit of the G protein. Usually, the activated alpha subunit then separates from the beta and gamma subunits. The activated alpha subunit acts as an agonist for another enzyme, often adenylyl cyclase. Adenylyl cyclase is an enzyme that catalyzes the conversion of ATP to cAMP and 2Pi. Cyclic AMP just happens to be an agonist for Protein Kinase A, which phosphorylates proteins—usually enzymes. Many enzymes are turned on or off through being phosphorylated or dephosphorylated. The cascade can be shut down in various ways. Often the beta and gamma subunits rebind with the alpha subunit deactivating it. In other cases GPCR is phosphorylated one or more times which deactivates it. DO NOT MEMORIZE THIS. The MCAT will not test you on names or other specifics. However, it does illustrate how cascades work and having a general familiarity with G protein signaling pathways will be a tremendous help on any passages or questions about G proteins—which have been fairly common. |
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Predicting Hormone Levels: |
This is a very frequent MCAT question! *Remeber: Hormones always act to return to homeostatic, or "normal," conditions. They never cause a drift away from normal. |
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Recalling that glucagon stimulates the release of glucose into the bloodstream and insulin stimulates the uptake and storage of glucose, answer the following: -Patient A has high blood glucose levels. Which hormone is likely to be found in highest concentration in her blood? -Patient B has low blood glucose levels. Which hormone is likely to be in highest concentration in his blood? |
-Patient A has high blood glucose. The body’s hormonal reaction to this condition will be to attempt to re-establish homeostasis. High blood glucose levels stimulate the cells of the pancreas to secrete insulin. Insulin stimulates cells to import glucose, decreasing blood glucose levels. This would return the blood toward homeostasis and therefore insulin is expected in high levels. (Note: Some students resist this logic by claiming that high blood glucose is a potential indication of diabetes—a disease resulting from a lack of insulin or insulin resistance. However, there is nothing in this question that would lead you to suspect that a disease condition is present. The MCAT does not test you on disease symptoms. On the MCAT you should always assume normal physiology unless specifically told otherwise.) -Patient B has low blood glucose levels. Glucagon—also secreted by the pancreas—stimulates the liver to breakdown glycogen to release glucose into the blood. In this case, more glucose would be necessary to reach homeostasis and therefore high glucagon levels would be expected. |
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Recalling that parathyroid hormone causes the breakdown (a.k.a., resorption) of bone and a concomitant release of calcium into the blood; and that calcitonin causes the buildup of bone matrix with a concomitant decrease in blood calcium, answer the following: Patient A has ingested a large dose of a calcium supplement. Which hormone will be found in highest concentration in her blood? Patient B suffers from calcinuria, a condition marked by low blood calcium. Which hormone will be found in highest concentration in his blood? |
Using the same logic as described for the previous question, Patient A is expected to have high levels of the hormone calcitonin because this hormone decreases calcium blood levels. -Patient B has low blood calcium, so we expect him to have high levels of parathyroid hormone because its effect is to breakdown bone and release calcium into the blood. |
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The Hormone Chart: |
Your new friend: At the end of this lesson you will find a color-coded chart highlighting every major hormone you must know for the MCAT-including its class and function, the gland that secretes it, and the location of that gland in the body. Make "The Hormone Chart" your new best friend. You will need to know it in and out and upside down to do well on the MCAT. Many students find it helpful to make copies of the blank chart provided on a subsequent page and attempt to fill it out from memory – repeating as necessary until they can do so easily. |
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The Hormone Chart Study Hints: |
1) Try to go two or three steps beyond basic memorization. Dont just memorize hormones individually. Memorize them by type, function, permeability and by the gland that secretes them. After you have memorized the entire chart, try to obtain a more conceptual understanding of each hormone in terms of how it acts, how it could be either inhibited or upregulated, and what physiological effects might result from either action. 2) Notice that every gland (with one exception) secretes only one kind of hormone (Steroid, peptide, or tyrosine derivative), but any given kind of hormone could come from various glands (e.g., the pituitary gland secretes only peptide hormones, but an unknown peptide hormone could have been secreted by the anterior or posterior pituitary, parathyroid, thyroid, pancreas, or the egg/placenta). 3) The notable exception mentioned in #2 above is the thyroid. It secretes both a tyrosine derivative and a peptide hormone. |
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The Hormone Chart: |
Name all of the glands that secrete peptide hormones Name all of the glands that secrete steroid hormones Name all of the glands that secrete tyrosine derivatives Hormone X is water-soluble. What glands could have secreted it? Hormone X is lipid-soluble. What gland could have secreted it? Hormone X is secreted by the pituitary. What is its solubility? Hormone X is secreted by the gonads. What is its solubility? Hormone X is secreted by the pancreas. What is its solubility? T/F The adrenal gland secretes only lipid-soluble hormones. T/F Steroid hormones are always lipid-soluble. T/F Tyrosine derivatives hormones are always lipid-soluble. |
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Polycystic Ovary Syndrome results in numerous follicles, or fluid-filled egg sacs, forming on the surface of a womans ovaries. Ovulation is greatly inhibited or irregular and multiple cysts build up over time. A researcher has discovered that female lab animals who are given high levels of "male hormones," called androgens, exhibit almost identical symptoms. The researcher hopes to develop a drug that associates with the androgens in a woman’s body and prevents them from binding to their receptors. To be effective, it is important that the drug: A) be lipid-soluble |
The androgen targeted is most likely testosterone, a male steroid hormone that is lipid soluble. Because testosterone is lipid-soluble and the researcher wants the drug to associate with it, the drug should most likely also be lipid-soluble. This makes A the best possible answer. Answer C and D would both tend to inhibit the ability of the drug to reach and permanently bind its target. |
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Hormones: |
Location: Anterior Pituitary Class: Peptide/water-soluble Function: Stimulates the adrenal cortex to release stress hormones called "Glucocorticoids" |
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Hormones: |
Location: Anterior Pituitary Class: Peptide/Water-soluble Function: Surges in LH causes ovulation; stimulates the secretion of the sex hormones estrogen and testosterone |
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Hormones: |
Location: Anterior Pituitary Class: Peptide/water-soluble Function: Stimulates growth of the follicle during menstrual cycle and production of sperm. |
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Hormones: |
Location: Anterior Pituitary Class: Peptide/Water-soluble Function: Stimulates release of T3/T4 from the thyroid, which stimulates the metabolism of almost every tissue in the body. |
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Hormones: |
Location: Anterior Pituitary Class: Peptide/Water-soluble Function: Stimulates growth throughout the body. |
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Hormones: |
Location: Anterior Pituitary Class: Peptide/Water-soluble Function: Stimulates milk production in the breasts |
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Hormones: |
Location: Posterior Pituitary Class: Peptide/Water-Soluble Function: Causes the collecting duct of the kidney to become highly permeable to water, concentrating the urine. |
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Hormones: |
Location: Posterior Pituitary Class: Peptide/Water-soluble Function: Stimulates contractions during child birth and milk secretion during nursing. |
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Hormones: |
Location: Parathyroid Class: Peptide/ Water-soluble Function: Increases blood calcium by stimulating proliferation of Osteoclasts, uptake of Ca2+ in the gut, and reabsorption of Ca2+ in the kidney. |
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Hormones: |
Location: Pancreas Class: Peptide/Water-soluble Function: Stimulates uptake and storage of glucose from the blood. |
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Hormones: |
Location: Pancreas Class: Peptide/Water-Soluble Function: Stimulates Gluconeogenesis and release of glucose into the blood |
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The relationship between Insulin and Glucagon: |
Insulin acts when blood sugar is too high and it stores the glucose, which is in the blood, into Glycogen. Glucagon then acts when the blood sugar is too low. It activates the stored Glycogen to release glucose into the blood, increasing the blood sugar level. |
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What is Gluconeogenesis? |
Gluconeogenesis is the biosynthesis of new glucose, (i.e. not glucose from glycogen). This process is frequently referred to as endogenous glucose production (EGP). The production of glucose from other carbon skeletons is necessary since the testes, erythrocytes and kidney medulla exclusively utilize glucose for ATP production. The brain also utilizes large amounts of the daily glucose consumed or produced via gluconeogenesis. The primary carbon skeletons used for gluconeogenesis are derived from pyruvate, lactate, glycerol, and the amino acids alanine and glutamine. The liver is the major site of gluconeogenesis, however, as discussed below, the kidney and the small intestine also have important roles to play in this pathway. Synthesis of glucose from three and four carbon precursors is essentially a reversal of glycolysis. The relevant features of the pathway of gluconeogenesis are diagrammed below: |
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