Bio ch. 44

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Terrestrial animals are

osmoregulators that must obtain water from the environment

Birds, insects, and many reptiles excrete nitrogenous waste in the form of uric acid, which

reduces water loss compared to other nitrogenous wastes, but requires more metabolic energy to produce

Freshwater fish excrete nitrogenous wastes as



The urethra is identified by the letter

Urine formed by a kidney collects in the ___before being drained from the kidney by the___and transported to the____

renal pelvis….ureter….urinary bladder


Filtrate is formed as fluid is forced through the walls of the glomerulus and, initially, collects in the structure indicated by the letter

The____are the major blood vessels transporting blood to the kidneys

renal arteries

The outer part of the kidney is the


What is the functional unit of a kidney?


An appropriate group of animals to examine to observe a Malpighian tubule would be

the insects

As a result of the non-selectivity of the kidney’s filtration of small molecules

useful substances must be selectively reabsorbed

The movement of substances out of the glomerulus and into Bowman’s capsule is referred to as


The movement of substances from the blood into the proximal tubule is known as


What is reabsorbed from filtrate?

sodium chloride, glucose, water and amino acids

As filtrate moves down the loop of Henle, the surrounding interstitial fluid becomes____ concentrated than the filtrate, so____leaves the filtrate


The most abundant solute in urine is

urea (and other nitrogenous wastes)

Glucose is removed from filtrate by

active transport

Increases water reabsorption

ADH secretion, dehydration due to inadequate water intake, sweating, eating salty food

Increases both water and Na+ reabsorption

aldosterone release, blood loss, severe diarrhea

Does not increase water or Na+ reabsorption

diabetes insipidus, alcohol consumption, caffeine consumption

Under the influence of antidiuretic hormone (ADH), _____ is produced

more concentrated urine

Antidiuretic hormone (ADH) makes the____permeable to water

collecting duct

The kidneys are paired organs that

regulate water and electrolyte balance in terrestrial vertebrates

What is the correct sequence of flow through the nephron?

renal corpuslce>proximal tubule>loop of Henle>distal tubule>collecting duct

What is the driving force for the filtration of blood by the renal corpuscle?

higher pressure in glomerular capillaries than in surrounding Bowman’s capsule

Which regions of the nephron function independently of hormonal control for the most part?

renal corpuscle, proximal tubule, and loop of Henle

In which region of the nephron is a steep osmotic gradient created?

loop of Henle

Which of the following statements best describes the actions of the hormone ADH of the nephron?

ADH causes the collecting duct to increase water reabsorption by the surrounding tissue under conditions of dehydration

Osmoregulation regulates

solute concentrations and balances the gain and loss of water

Osmolarity determines the

movement of water across a selectively permeable membrane

Osmoconformeers are

isoosmotic with their surroundings and do not regulate their osmolarity

Osmoregulators expend

energy to control water uptake and loss in a hyper osmotic or hypo osmotic environment

Osmoregulation in marine fish

gain of water and salt ions from food through mouth; excretion of salt ions from gills; osmotic water loss through gills and other parts of body surface; excretion of salt ions and small amounts of water in scanty urine from kidneys

Osmoregulation in a freshwater fish

gain of water and some ions in food; uptake of salt ions by gills, osmotic water gain through gills; excretion of salt ions and large amounts of water in dilute urine from kidneys

Osmoregulatory mechanisms of freshwater fish include

salt uptake in gills and water excretion in urine

Osmoregulators must

expend energy to maintain osmotic gradients

The fluid with the highest osmolarity is

seawater in a tidal pool

Water balance is affected by

type of wastes, quantity of waste products

Animals that excrete nitrogenous wastes as

ammonia need access to lots of water

Mammals and most adult amphibians convert ammonia to

the less toxic urea; produced in the liver and carried to the kidneys

Pros and Cons of Urea

pros: less toxic, requires less water cons: energetically expensive

Insects, land snails, and many reptiles including birds mainly excrete

uric acid

Uric acid is

relatively nontoxic and does not dissolve readily in water

Uric acid is more

energetically expensive produce than urea

What nitrogenous waste has the greatest number of nitrogen atoms?

uric acid

Nitrogenous wastes excreted depend on

an animal’s evolutionary history, habitat, environment of the animal egg

The amount of nitrogenous waste is coupled to

the animal’s energy budget

Adaptations of desert animals do not likely include

nitrogenous waste excreted as ammonia

An aquatic animal with an internal solute concentration of 500 mOsm/L is placed in a fluid with solute concentration of about 700 mOsm/L. To osmoregulate and survive, the animal must

pump out salts to keep tissue at 500 mOsm/L.

Excretory systems regulate

solute movement between internal fluids and the external environment

Most excretory systems produce

urine by refining a filtrate derived from body fluids

Kidneys, the excretory organs of vertebrates

function in both excretion and osmoregulation

The filtrate produced in Bowman’s capsule contains

salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

Molecules are transported actively and passively from the filtrate into the

interstitial fluid and then capillaries

Some toxic materials are actively

secreted into the filtrate

As the filtrate passes through the proximal tubule

materials to be excreted become concentrated

Reabsorption of water continues through

channels formed by aquaporin proteins

Movement is driven by the

high osmolarity of the interstitial fluid, which is hyper osmotic to the filtrate

What is able to diffuse from the tubule into the interstitial fluid

salt but not water; filtrate becomes increasingly dilute

The distal tubule regulates the

K+ and NaCl concentrations of body fluids, the controlled movement of ions contributes to pH regulation

The collecting duct carries

filtrate through the medulla to the renal pelvis

Urine is hypersomotic to

body fluids

The mammalian kidneys ability to

conserve water is a key terrestrial adaptation

Hyperosmotic urine can be

produced only using energy to transport solutes against concentration gradients

The two primary solutes affecting osmolarity are

NaCl and urea

In the proximal tubule,

filtrate volume decreases but its osmolarity remains the same

The countercurrent multiplier system involving

the loop of Henle maintains a high salt concentration in the kidney

Considerable energy is expended to maintain

the osmotic gradient between the medulla and cortex

The collecting duct conducts filtrate

through the osmolarity gradient, and more water exits the filtrate by osmosis

Urea diffuses out of the

collecting duct as it traverses the inner medulla

Urea and NaCl form the osmotic gradient that

enables the kidney to produce urine that is hyper osmotic to the blood

The juxtamedullary nephron is

key to water conservation in terrestrial animals

Mammals in dry environment have

long loops of Henle

Mammals in fresh water have

relatively short loops

Birds have shorter loops of Henle but

conserve water by excreting uric acid instead of urea

Other reptiles have

only optical nephrons but also excrete nitrogenous waste as uric acid

Freshwater fishes conserve

salt in their distal tubules and excrete large volumes of dilute urine

Kidney function in amphibians is similar

to freshwater fishes

Marine bony fishes are

hypo osmotic compared with their environment; their kidneys have small glomeruli and some lack glomeruli entirely; filtration rates are low, and very little urine is excreted

The counter current multiplier system in the nephrons of mammalian kidneys allows the development of a concentration gradient of salt and urea in the medullary fluid that is

high enough to develop hyper osmotic urine

The primary nitrogenous waste excreted by mammals is

urea, which is less toxic than ammonia

The osmolarity of the urine is regulated by

nervous and hormonal control

Antidiuretic hormone (ADH) increases the

permeability of the collecting duct epithelium to water; water osmolarity increases, this triggers the release of ADH, which helps to conserve water

The renin-angiotensin-aldosterone system (RAAS) is part of a

complex feedback circuit that functions in homeostasis

A drop in blood pressure near the glomerulus causes the

juxtaglomerular apparatus (JGA) to release the enzyme renin

Renin triggers the formation

of the peptide angiotensin 2

Angiotensin 2

raises blood pressure and decreases blood flow to the kidneys; stimulates the release of the hormone aldosterone, which increases blood volume and pressure

ADH and RAAS both increase

water reabsorption, but only RAAS will respond to a decrease in blood volume

Atrial natriuretic peptide (ANP)

opposes the RAAS; ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin

The two solute model explaining urine production in the nephron states that

the transport epithelium in the ascending loop of Henle is relatively impermeable to water

A decrease in the volume of urine excreted would be expected following

an increase in aquaporin channels in collect duct

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