Chapter 44: Osmoregulation and Excretion

Question 1

Osmolarity is

Answer 1

the unit of measurement for solute concentration, the number of moles of solute per liter of solution

Question 2

Isoosmotic solutions are

Answer 2

solutions with the same osmolarity

Question 3

Water flows via osmosis from a ____smotic solution to a _____

Answer 3

from hypoosmotic to hyperosmotic

Question 4

What is an osmoconformer?

Answer 4

an animal that is isoosmotic with its surroundings, no tendency to gain or lose water. All osmoconformers are marine animals.

Question 5

What is an osmoregulator?

Answer 5

Controls internal osmolarity independent of its environment.

Question 6

In a hypoosmotic
environment, an osmoregulator must ____excess
water. In a hyperosmotic environment, it must___
in water to offset osmotic loss

Answer 6

In a hypoosmotic
environment, an osmoregulator must discharge excess
water. In a hyperosmotic environment, it must instead take
in water to offset osmotic loss

Question 7

Transport epithelia are responsible for

Answer 7

osmoregulation and metabolic waste in most animals
they are 1+ layers of epithelial cells specialized for moving solutes in specific directions

Question 8

Transport epithelia are typically arranged

Answer 8

into tubular networks withe extensive surface areas

Question 9

The movement of salt from the surrounding water to the
blood of a freshwater fish requires the expenditure of
energy in the form of ATP. Why?

Answer 9

Because the salt is moved against its concentration gradient, from low
concentration (fresh water) to high concentration (blood)

Question 10

Why aren’t any freshwater animals osmoconformers?

Answer 10

A freshwater
osmoconformer would have body fluids too dilute to carry out life’s
processes.

Question 11

What is ammonia?

Answer 11

a toxic metabolite produced by the dismantling of nitrogenous molecules such as proteins and nucleic acids

Question 12

Why does the type and quantity of an animal’s waste products have a large impact on its water balance?

Answer 12

Because most metabolic wastes must be dissolved in water to be excreted from the body

Question 13

Why is ammonia so toxic?

Answer 13

its ion, ammonium, can interfere with oxidative phosphorylation

Question 14

TorF: ammonia molecules (NH3 and NH4+), easily pass through membranes and are lost by diffusion to surrounding water due to their high solubility

Answer 14

true

Question 15

What is urea? why is it advantageous for waste excretion? What are its disadvantages

Answer 15

urea: product of a cycle that combines ammonia with CO2 in the liver
advantageous for nitrogeneous waste excretion are its low toxicity and high solubility is water
disadvantages: animals must expend energy to produce urea from ammonia

Question 16

Uric acid is typically excreted by

Answer 16

insects, land snails, reptiles, birds

Question 17

How is uric acid different from urea? How is it similar?

Answer 17

different: does not readily dissolve in water, excreted as a paste, more energetically expensive
similar: relatively nontoxic/low toxicity

Question 18

What advantage does uric acid offer as a nitrogenous waste
in arid environments?

Answer 18

Because uric acid is largely insoluble in water, it can be excreted as a semisolid
paste, thereby reducing an animal’s water loss.

Question 19

The key steps of the excretory system are:

Answer 19

filtration, reabsorption, secretion, excretion

Question 20

Filtration is driven by ___ ____. Water and small solutes (such as: ) cross the membrane, forming a solution called __.

Answer 20

driven by hydrostatic pressure
solutes such as salts, sugats, amino acids, and nitrogeneous wastes
filtrate

Question 21

Describe the process of reabsorption

Answer 21

filtrate converted to a fluid. Reabsorption recovers useful molecules and water and returns them to the body fluid. Valuable solutes are reabsorbed via active transport.

Question 22

Describe the process of secretion

Answer 22

after reabsorbtion, nonessential solutes are left in filtrate or added to it via active transport

Question 23

Nearly all of the fluid in the filtrate is reabsorbed into surrounding blood vessels and exits the kidney in the ____. The reamining fluid..

Answer 23

renal vein
remaining fluid leaves the excretory tubules as urine, collected in renal pelvis, and exits the kidney

Question 24

Juxtamedullary nephrons differ from cortical nephrons because

Answer 24

they extend deep into the medulla. They produce urine that is hyperosmotic to body fluids

Question 25

Each nephron consists of a single long tubule as well as a
ball of capillaries called the ____. The blind end of
the tubule forms a cup-shaped swelling, called ___, which surrounds the glomerulus.

Answer 25

Each nephron consists of a single long tubule as well as a
ball of capillaries called the glomerulus. The blind end of
the tubule forms a cup-shaped swelling, called Bowman’s
capsule, which surrounds the glomerulus. F

Question 26

Filtrate is formed when

Answer 26

blood pressure forces fluid from the blood in the glom-
erulus into the lumen of Bowman’s capsule

Question 27

Processing occurs
as the filtrate passes through three major regions of the nephron:

Answer 27

Processing occurs
as the filtrate passes through three major regions of the nephron: the proximal tubule, the loop of Henle (a hairpin
turn with a descending limb and an ascending limb), and the
distal tubule

Question 28

A collecting duct receives processed filtrate
from…

Answer 28

A collecting duct receives processed filtrate
from many nephrons and transports it to the renal pelvis.

Question 29

Each nephron is supplied with blood by an ____ ____

Answer 29

afferent arteriole

Question 30

An afferent arteriole is…
An efferent arteriole is…

Answer 30

Afferent arteriole: an offshoot of the renal artery that branches and forms the
capillaries of the glomerulus
An efferent arteriole: capillaries converge as they leave the glomurelus

Question 31

Describe what happens when filtrate goes through the proximal tubule

Answer 31

Critical for recapture of important molecules
Na+ ions transferred to interstitial fluid by active transport, Cl- out of tubule via passive
As salt goes from filtrate to interstitial, water follows, reducing filtrate volume. Then go to peritubular capillaries
helps maintain pH, cells of transport epithelium secrete H+ into the lumen AND synthesize/secrete ammonia. Also reabsorb HCO3-
As filtrate passes through, materials to be excreted become concentrated

Question 32

The more acidic the filtrate is, the more ammonia the cells
_____, and a mammal’s urine usually contains
some ammonia from this source (even though most nitrog-
enous waste is excreted as urea)

Answer 32

The more acidic the filtrate is, the more ammonia the cells
produce and secrete, and a mammal’s urine usually contains
some ammonia from this source (even though most nitrog-
enous waste is excreted as urea)

Question 33

Describe what occurs when filtrate goes through the descending limb of the loop of Henle

Answer 33

Further reduces filtrate volume
In first portion, aquaporins make transport epithelium freely permeable to water. There are no channels for salt and other small solutes

Question 34

For water to move out of the tubule by osmosis, the interstitial fluid must be ____osmotic to the filtrate. How is this condition met?

Answer 34

hyper
This condition is met along the entire length of the
descending limb because the osmolarity of the interstitial
fluid increases progressively from the cortex through the
medulla. Filtrate loses water and increases solute concentration

Question 35

What occurs when filtrate passes through the ascending limb of the loop of henle

Answer 35

The transport epithelium LACKS WATER CHANNELS. Impermeable to water
Two regions: thin segment and thick segment
In the thin segment, NaCl diffuses out into the interstitial fluid
In the thick segment, the movement of NaCl continues, but it is actively transported. Filtrate become more dilute

Question 36

Although the loop of Henle has a small net effect on filtrate composition, it is a major site for the recovery of water
(____ loop) and salt (____ loop) from the filtrate

Answer 36

Although the loop of Henle has a small net effect on filtrate composition, it is a major site for the recovery of water
(descending loop) and salt (ascending loop) from the filtrate

Question 37

Describe what occurs when filtrate goes through the distal tubule

Answer 37

regulates K+ and NaCl

Question 38

Describe what occurs when filtrate passes through the collecting duct

Answer 38

Processes filtrate into urine, carries to renal pelvis
hormone control of permeability determines the extent to which urine becomes concentrated

Question 39

If blood pressure in the afferent arteriole leading
to a glomerulus decreased, how would the rate of blood fil-
tration within Bowman’s capsule be affected? Explain.

Answer 39

A decline in blood pressure in the afferent arteriole would
reduce the rate of filtration by moving less material through the vessels

Question 40

ADH molecules
released from the _____ bind
to and activate membrane receptors on
the surface of _____cells. The
activated receptors initiate a _____that directs insertion of
___ ___ into the membrane
lining the collecting duct

Answer 40

ADH molecules
released from the posterior pituitary bind
to and activate membrane receptors on
the surface of collecting duct cells. The
activated receptors initiate a signal trans-
duction cascade that directs insertion of
aquaporin proteins into the membrane
lining the collecting duc

Question 41

What happens to blood osmolarity and ADH secretion if you drink a large amount of water?

Answer 41

Blood osmolarity
falls below the normal range, causing a drop in ADH secretion
to a very low level. The resulting decrease in permeability of
the collecting ducts reduces water reabsorption, resulting in
discharge of large volumes of dilute urine

Question 42

Mutations that prevent ADH production or that inactivate the ADH receptor gene disrupt homeostasis by…..

Answer 42

Mutations that prevent ADH production or that inacti-
vate the ADH receptor gene disrupt homeostasis by block-
ing the insertion of additional aquaporin channels in the
collecting duct membrane

Question 43

The release of ADH is a response to an ____in blood osmolarity

Answer 43

The release of ADH is a response to an increase in blood osmolarity

Question 44

The RAAS responds to a drop
in blood volume and pressure by …..

Answer 44

The RAAS responds to the drop
in blood volume and pressure by increasing water and Na +
reabsorption.

Question 45

The RAAS involves the juxtaglomerular apparatus
(JGA), which is a…

Answer 45

The RAAS involves the juxtaglomerular apparatus
(JGA), a specialized tissue consisting of cells of and around
the afferent arteriole, which supplies blood to the glomeru-
lus.

Question 46

When BP or volume drops in the afferent arteriole, the JGA releases

Answer 46

renin

Question 47

Renin initiates…

Answer 47

a sequence of
steps that cleave a plasma protein called angiotensino-
gen, ultimately yielding a peptide called angiotensin II

Question 48

Angiotensin II is a peptide that triggers____, which ___ BP and ____ blood flow. It also stimulates the adrenal glands to release a hormone called ____

Answer 48

vasoconstriction
increase BP, decrease blood flow
hormone aldosterone

Question 49

Aldosterone, released by the ___ ___, causes the nephrons distal tubules and collecting duct to

Answer 49

reabsorb more Na+ and water, increasing blood volume and pressure

Question 50

Atrial Natriueretic Peptid, ANP, _____ RAAS. It is released by _____ in response to an increase in blood volume and pressure.

Answer 50

opposes RAAS
walls of atria

Question 51

ANP inhibits the release of ____ from the JGA, lowering ____ and ____

Answer 51

renin
lowers blood volume and pressure

Question 52

How does alcohol affect regulation of water balance in the
body

Answer 52

Alcohol inhibits the release of ADH, causing an increase in urinary water loss
and increasing the chance of dehydration.

Question 53

Conn’s syndrome is a condition caused by tumors
of the adrenal cortex that secrete high amounts of aldoste-
rone in an unregulated manner. What would you expect to
be the major symptom of this disorder?

Answer 53

high blood pressure

Question 54

Which process in the nephron is least selective?
(A) filtration
(B) reabsorption
(C) active transport
(D) secretion

Answer 54

filtration

Question 55

The high osmolarity of the renal medulla is maintained by
which of the following?
(A) active transport of salt from the upper region of the
descending limb.
(B) the loose packing of juxtamedullary nephrons.
(C) diffusion of urea into the collecting duct.
(D) diffusion of salt from the descending limb of the loop of
Henle

Answer 55

diffusion of salt from the descending limb of the loop of
Henle

Question 56

African lungfish, which are often found in small, stagnant
pools of fresh water, produce urea as a nitrogenous waste. What
is an advantage of this adaptation?
(A) Urea takes less energy to synthesize than ammonia.
(B) Small, stagnant pools do not provide enough water to dilute
ammonia, which is toxic.
(C) Urea forms an insoluble precipitate.
(D) Urea makes lungfish tissue hypoosmotic to the pool.

Answer 56

Small, stagnant pools do not provide enough water to dilute
ammonia, which is toxic