Chapter 50 Flashcards
Water in a multicellular animal’s body is distributed between
the intracellular and extracellular compartments
What kind of cells facilitate the exchange of water and electrolytes between the body and the environment?
specialized epithelial cells
What is the major cation in extracellular fluids?
Na+
What is the major anion in extracellular fluids?
Cl-
What are three other important ions?
Ca2+; Mg2+; K+
What is osmosis?
diffusion of water across a semipermeable membrane
What is osmotic pressure?
measure of a solution’s tendency to take in water by osmosis; is the amount of pressure needed to balance the pressure created by water movement
What is the relationship between the concentration of a solution and its osmolarity?
solution with higher concentration exerts more osmotic pressure
What is osmolarity?
number of osmotically active moles of solute per liter solution
How does osmolarity differ from molarity?
if a substance dissociates in solution, there are multiple osmotically active particles - ex 1 M NaCl is 2 Osm because of Na+ and Cl-
What is the tonicity of a solution?
measure of solutions’ ability to change the volume of a cell by osmosis
Give two examples of isotonic solutions used in medical settings.
normal saline; 5% dextrose
Normal saline and 5% dextrose are what kind of solution?
isotonic solutions
What are normal saline and 5% dextrose used for?
used to bathe exposed tissue
Describe the osmolarity of body fluids in marine invertebrates.
same as that of seawater (except Mg2+ concentrations aren’t the same)
What is the consequence of marine invertebrate body fluids having the same osmolarity as seawater?
no osmotic gradient exists, so therefore no net movement of water
What are osmoconformers?
animals that maintains the osmotic concentration of its body fluids at the same level of the medium in which they live
Which vertebrates are strict osmoconformers?
primitive hagfish
Are sharks/Chondrichthyes osmoconformers?
they are isotonic to seawater even though their blood NaCl level is lower than that of seawater
How do Chondrichthyes make up the difference in NaCl between their blood and the surrounding seawater?
made up by retaining urea
What are osmoregulators?
animals that maintain relatively constant blood osmolarity in any environment
Which animals are osmoregulators?
all other vertebrates other than primitive hagfish
Describe the osmolarity of freshwater vertebrates.
hypertonic to environment
What is the consequence of hypertonicity of freshwater vertebrates?
water tends to enter their bodies, so they have adapted ways to eliminate excess water
Freshwater vertebrates tend to lose what particles?
tend to lose inorganic ions to environment, so they must actively transport these ions back into their bodies
Describe the osmolarity of marine vertebrates.
most are hypotonic to environment; body fluids are 1/3 the osmolarity of surrounding water
What is the consequence of the hypotonicity of marine vertebrates?
water tends to leave their bodies, so they have adapted ways to retain water
How exactly do marine vertebrates retain water/avoid excessive water loss?
they drink seawater and eliminate excess ions through kidneys and gills
Describe the osmolarity of terrestrial vertebrates.
hypertonic to environment
What is the consequence of the hypertonicity of terrestrial vertebrates?
tend to lose water to air by evaporation from skin and lungs
The catabolism of amino acids and nucleic acids produces
nitrogen-containing by-products called nitrogenous waste
What is the immediate by-product of amino acid/nucleic acid catabolism?
ammonia
In bony fishes/aquatic vertebrates, ammonia is converted to
ammonia isn’t converted into anything, but is eliminated directly
Ammonia is eliminated directly in
bony fishes/aquatic vertebrates
In mammals, amphibians, and cartilaginous fish, ammonia is converted to
urea
Ammonia is converted to urea in
mammals, amphibians, cartilaginous fish
Draw the structure of urea.
draw
In reptiles, birds, and insects, ammonia is converted to
uric acid
Ammonia is converted to uric acid in
reptiles, birds, insects
Draw the structure of uric acid.
draw
Why does ammonia have to be quickly removed?
because it is toxic
How do bony fishes/aquatic vertebrates eliminate ammonia?
eliminate most of it by diffusion through the gills, less through excretion in very dilute urine
Is urea more or less toxic than ammonia?
Urea is less toxic than ammonia.
Describe the solubility of urea.
urea is soluble in water
What is the consequence of urea being water-soluble?
large amounts can be excreted in urine
Where is urea synthesized in mammals?
liver
Describe the solubility of uric acid.
slightly soluble in water
What is the consequence of the solubility of uric acid?
uric acid precipitates
What is guano?
pasty white material in bird droppings that is made of uric acid
Describe the energetics of synthesizing uric acid.
Costs animal energy to synthesize uric acid, but this is offset by the conservation of water
Why is the insolubility of uric acid important for embryonal development?
as a solid precipitate, uric acid is unable to affect the embryo’s development even though it’s still in the egg
(T/F) Mammals do not produce uric acid.
False, mammals do produce uric acid.
In what context do mammals produce uric acid?
waste product of purine nucleotide degradation (not from amino acids)
How do most mammals deal with uric acid?
uricase converts uric acid into allantoin, which is more soluble
Which mammals lack uricase?
humans, apes, Dalmatian dog
How do mammals that lack uricase deal with uric acid?
directly excrete uric acid
What is gout?
excessive accumulation of uric acid in the joints
In animals, the removal of water/salt is coupled to
the removal of metabolic wastes through the excretory system
How do single-celled protists get rid of excretory waste?
contractile vacuoles
How do sponges get rid of excretory waste?
contractile vacuoles
What are the excretory tubules found in flatworms?
protonephridia
Where are protonephridia found?
flatworms
Protonephridia branch throughout the flatworm’s body into
bulblike flame cells
Flatworm flame cells are open to
the outside, but are not open to the inside of the flatworm’s body
How are substances brought into the inside of the flatworm’s body?
movement of cilia within the flame cells draw in bodily fluids
Which organism has tubules that open to the outside but are closed to the inside?
flatworms
What are the excretory tubules in earthworms?
nephridia
How do nephridia obtain fluid from the body?
fluid is filtered through nephrostomes
Nephridia are found in
earthworms
What are nephrostomes?
funnel-shaped structures that filter bodily fluids into nephridia
Why is the term “filtration” used?
fluid is formed under pressure passes through small openings such that molecules larger than a certain size are excluded
Describe the concentration of the filtered fluid in earthworms.
filtered fluid is isotonic to coelom fluid
What happens to the filtered fluid in earthworms as it passes through the nephridia tubules?
NaCl is removed from fluid via active transport
Most invertebrates have what kind of excretory tubules?
nephridia
Define reabsorption.
transport out of tubule and into the surrounding body fluids
What are antennal glands?
excretory organs of crustaceans
What organ in the mollusks produce urine?
kidneys of mollusks
What is the excretory organ in insects?
Malphigian tubules
What are Malphigian tubules?
extensions of the digestive tract that branch off anterior to the hindgut
(T/F) Urine is formed in insects in the Malphigian tubules.
False, urine is NOT formed in the Malphigian tubules.
Why can’t urine be formed by filtration in the Malphigian tubules?
there is no pressure difference between the blood in the body cavity and the Malphigian tubule
If urine/waste isn’t formed in the Malphigian tubule, how does it get into the Malphigian tubule?
waste and K+ ions are secreted into the Malphigian tubule by active transport
What type of transport is used to transport waste into the Malphigian tubules?
active transport
How does the flatworm expel waste that is brought into protonephridia?
expelled through pores that open to outside of body
Most invertebrates have which type of excretory tubules?
most invertebrates use nephridia
What is the opposite of reabsorption?
secretion
What is secretion in the context of insect Malphigian tubules?
ions/molecules are transported from body fluid into Malphigian tubule
What causes osmosis in Malphigian tubules?
secretion of K+ into tubules creates osmotic gradient that draws water into tubules via osmosis
What happens to most of the water/K+ brought into the Malphigian tubules?
reabsorbed into circulatory system through epithelium of hindgut
What kinds of wastes are ultimately excreted from an insect?
small molecules; waste products; feces
Generally speaking, what do the kidneys of vertebrates do?
create a tubular fluid by filtering blood under pressure
Which biomolecule is too large to be filtered from blood plasma?
proteins
Why would vertebrates filter everything except proteins from blood and then spend energy to reabsorb it?
because selective reabsorption provides great flexibility and allows vertebrates to reabsorb molecules that are especially valuable in certain conditions
What is the main unit in the vertebrate kidney?
nephrons
Describe the overall flow of fluid in the vertebrate kidney.
capillaries > glomerulus > Bowman’s capsule > proximal arm > loop of Henle > distal arm > collecting duct
What is considered the beginning of the tubule system in the vertebrate kidney?
Bowman’s capsule
The glomerulus retains
blood cells; proteins; most other large molecules
The glomerulus lets which molecules pass into the nephron?
water; small molecules dissolved in the water; wastes dissolved in the water
What kinds of transport mechanisms are used in the nephron?
active and passive transport
Draw out the Figure 50.6 on page 1043, which is titled “Organization of the vertebrate nephron.”
draw
Describe the concentration of glomerular filtrate relative to blood in vertebrates.
original glomerular filtrate is isotonic to blood
Describe the possible concentrations of urine relative to blood in vertebrates.
urine is isotonic to blood because of reabsorption of water/ions in equal proportions; urine is hypotonic to blood by reabsorbing less water
(T/F) Vertebrates cannot produce urine that is hypertonic to blood.
False, birds and mammals can produce urine that is hypertonic to blood.
Which vertebrates can produce urine hypertonic to blood?
birds, mammals
How do birds/mammals produce urine that is hypertonic to blood?
by reabsorbing more water
Kidneys are thought to have evolved among the
freshwater teleosts = bony fishes
Describe the concentration of body fluids in freshwater fish relative to the surrounding water.
body fluids of freshwater fish are hypertonic to surrounding water
What are the two problems that freshwater fish face with regards to their urinary systems?
water tends to enter body from environment; solutes tend to leave the body and enter environment
How do freshwater fish solve the problem of water entering their body from the environment?
by not drinking water and excreting a large volume of dilute urine
Describe the urine excreted by freshwater fish.
hypotonic to their body fluids
How do freshwater fish solve the problem of solutes leaving their bodies?
reabsorb ions across nephron tubules (from the glomerular filtrate back into blood); actively transport ions across gill surface from surrounding water into blood
What is another name for marine bony fishes?
teleosts
Where did teleosts evolve from?
freshwater ancestors
Describe the concentration of body fluids of marine bony fishes relative to surrounding water.
body fluids are hypotonic to seawater
What is the problem that marine bony fishes face with regards to their urinary systems?
water tends to leave their bodies across gills
How do marine bony fishes solve their major problem?
by drinking large amounts of seawater
What happens to divalent ions in seawater that is consumed by marine bony fishes?
remain in the digestive tract and are eliminated through the anus
What kinds of ions are reabsorbed in marine bony fishes?
some divalent ions and some monovalent ions like K+/Na+/Cl-
How are monovalent ions excreted in marine bony fishes?
actively transported across gill surfaces
How are divalent ions excreted in marine bony fishes?
secreted into nephron tubules and excreted through urine
Describe the concentration of the urine excreted by marine bony fishes relative to its body fluids.
urine is isotonic relative to body fluids
Describe the concentration of the urine excreted by marine bony fishes relative to the urine produced by freshwater fishes.
urine of marine bony fishes is MORE concentrated than urine of freshwater bony fishes
Describe the concentration of the urine excreted by marine bony fishes relative to the urine produced by birds/mammals.
urine of marine bony fishes is LESS concentrated than urine of birds/mammals
Describe the glomerulus in freshwater fish.
large glomerulus
Describe the glomerulus in marine fish.
glomerulus is reduced or absent
Generally speaking, what happens in the nephrons of freshwater fish?
active tubular reabsorption of Na+ and Cl-
Generally speaking, what happens in the kidneys of freshwater fish?
excretion of dilute urine
Generally speaking, what happens in the gills of freshwater fish?
active absorption of Na+ and Cl-; water enters osmotically
Generally speaking, what happens in the nephrons of marine fish?
active tubular secretion of Mg2+ and SO42-
Generally speaking, what happens in the stomach of marine fish?
passive reabsorption of water, Na+, Cl-
Generally speaking, what happens in the gills of marine fish?
active secretion of Na+, Cl-; water loss
Generally speaking, what happens in the kidneys of marine fish?
excretion of urea, little water, Mg2+, SO42-
What are the intestinal wastes produced by marine fish?
Mg2+, SO42-, feces
What are the most common types of Chondrichthyes?
sharks, rays
How do elasmobranchs solve the osmotic problem?
instead of continuously drinking seawater for hypotonic body fluids, they reabsorb urea from nephron tubules to maintain blood urea concentration that is 100x that of mammals
What is the blood urea concentration in elasmobranchs?
100x that of mammals
What is the consequence of elasmobranchs reabsorbing urea?
makes elasmobranchs’ blood isotonic to surrounding sea, which prevents water loss; no need to drink seawater; kidneys and gills don’t have to get rid of large amounts of ions
What needed to evolve in elasmobranchs to tolerate high urea concentrations?
enzymes and tissues of cartilaginous fish have evolved to tolerate high urea concentrations
What were the first terrestrial vertebrates?
amphibians
The amphibian kidney is identical to
the kidney of the freshwater fish
Amphibians spend most of their time in what kind of water?
freshwater
Amphibians produce what kind of urine?
very dilute urine
How do amphibians compensate for Na+ loss?
by actively transporting Na+ across skin from the surrounding water
Marine reptiles face what problem?
they tend to lose water and take in salts
(T/F) Marine reptiles drink seawater.
True
What kind of urine do marine reptiles produce?
isotonic urine
How do marine reptiles get rid of excess salt?
through salt glands located near the nose/eye
What is a cloaca?
common exit of the digestive and urinary tracts
How do terrestrial reptiles adapt to dry environments in terms of reabsorption?
they reabsorb most of the salt and water in their nephron tubules
What kind of urine do terrestrial reptiles produce?
urine cannot be more concentrated than blood plasma
How do terrestrial reptiles excrete urine?
urine isn’t excreted, instead it is emptied into cloaca where additional water is reabsorbed, then waste is excreted with feces
In humans, how much more concentrated can urine be relative to plasma?
Urine can be up to 4.2 times as concentrated as blood plasma
Which mammals produce the most concentrated urine, and how much more concentrated is it relative to their blood plasma?
camels - 8x; gerbils - 14x; pocket mice - 22x
Which mammal has the most efficient kidney system?
kangaroo rats/Dipodomys
(T/F) Kangaroo rats drink water.
False, they don’t even need to drink water because they get everything they need from food and cellular respiration
In which organisms is the loop of Henle found?
only in mammals and birds
What produces hypertonic urine in mammals/birds?
loop of Henle
What is the relationship between the urine concentration and the loop of Henle?
the degree of urine concentration depends on the length of the loop of Henle
Describe the nephrons found in birds.
very few/no nephrons with long loops
What is the consequence of birds not having nephrons with long loops?
they can’t produce urine that is as concentrated as that of mammals - at max, urine is 2x more concentrated than blood
How do marine birds solve the problem of water loss?
drinking salt water and then excreting excess salt from salt glands near eyes
How is urine eliminated from the bird?
urine is delivered to cloaca along with feces, additional water is reabsorbed, white paste/pellet is left behind and excreted
Where are the kidneys located in humans?
lower back
Each kidney receives blood from which structure?
renal artery
From the kidney, where does urine go?
drains out of kidney through ureter, which carries urine to urinary bladder, and urine is passed out of body via urethra
What is the urethra?
tube that carries urine from the bladder to the exterior of mammals
What are the three basic functions of the kidney?
filtration; reabsorption; secretion
What happens during filtration in the mammalian kidney?
fluid in blood, which contains most solutes except large proteins and cells; is filtered into tubule system
What is reabsorption in the mammalian kidney?
selective movement of important solutes (e.g. glucose, AAs, inorganic ions) back into the bloodstream
What kinds of transport mechanisms are used in reabsorption in the mammalian kidney?
active or passive transport mechanisms
What happens in secretion in the mammalian kidney?
movement of substances from blood to extracellular fluid, then into filtrate in tubule system
How are reabsorption and secretion different?
reabsorbed substances from the tubules are sent back into the bloodstream; secreted substances into the tubules are excreted along with wastes
Which structure carries blood into the glomerulus?
afferent arteriole
Which structure carries blood out of the glomerulus?
efferent arteriole
The kidney contains about how many nephrons?
1 million nephrons
What are the two types of nephrons in mammalian kidneys?
juxtamedullary nephrons; cortical nephrons
Describe juxtamedullary nephrons.
have long loops that dip deeply into medulla
Describe cortical nephrons.
shorter loops
What is the glomerulus?
cluster of capillaries enclosed by Bowman’s capsule
What is the Bowman’s capsule?
bulbous unit of nephrons that surrounds the glomerulus
What happens to blood components (i.e. proteins, cells) that are not filtered into the glomerulus?
blood is drained into efferent arteriole, which empties into the peritubular capillaries
What are the peritubular capillaries?
bed of capillaries that surrounds the tubules
What structure surrounds the loop of Henle?
vasa recta
What is the vasa recta?
capillaries that surround the loop of Henle
Why are the peritubular capillaries needed?
needed for secretion and reabsorption
From the Bowman’s capsule, where does the filtrate go?
enters the proximal convoluted tubule
Where is the proximal convoluted tubule located in the kidney?
located in the cortex of the kidney
In a cortical nephron, where does the filtrate go after the proximal convoluted tubule?
filtrate flows through loop of Henle
In cortical nephrons, the loop of Henle
dips only minimally into the medulla before ascending back to the cortex
Contrast water reabsorption in juxtamedullary and cortical nephrons.
more water can be reabsorbed from juxtamedullary nephrons than in cortical nephrons
In juxtamedullary nephrons, the loop of Henle
extends much deeper into the medulla before ascending back to the cortex
After leaving the loop of Henle, where does the fluid go?
fluid goes to the distal convoluted tubule
Where is the distal convoluted tubule located in the kidney?
cortex
After leaving the distal convoluted tubule, where does the fluid go?
fluid drains into collecting duct
Where does the collecting duct lead to?
descends into medulla where it merges with other collecting ducts to empty urine into renal pelvis
In humans, how much blood passes through the kidneys each day?
2000 L of blood
In humans, how much water leaves blood and enters the glomerulus as filtrate each day?
180 L
Water is first reabsorbed by which structure in the nephron?
proximal convoluted tubule
How is water reabsorbed in the collecting duct?
water reabsorption in the collecting duct is driven by an osmotic gradient created by the loop of Henle
The reabsorption of biomolecules such as glucose and amino acids is driven by what transport mechanism?
glucose/AA reabsorption is driven by active transport/secondary active transport
Where are renal glucose carriers located?
proximal convoluted tubule
When does saturation of the renal glucose carriers occur?
saturation occurs when [glucose] in blood is at 180mg/100mL
What happens if a person has a blood [glucose] greater than 180 mg/100 mL?
glucose remaining in filtrate is expelled in urine; indicative of untreated diabetes mellitus
What is a diagnostic test used to diagnose diabetes mellitus?
testing for glucose presence in urine
Why does penicillin have to be administered in high doses/several times per day?
because it is secreted rapidly into the nephrons and is eliminated in one pass
(T/F) Urine has a low H+ concentration because it is basic.
False, urine has a high H+ concentration and its pH is between 5 and 7.
Why is urine’s high H+ concentration important?
helps maintain acid-base balance of blood within the pH range of 7.35 to 7.45.
What is the relationship between volume of urine and blood pressure?
the larger the volume of urine excreted, the lower the blood volume, and the lower the BP
Virtually all nutrient molecules are reabsorbed into the bloodstream via what structure?
proximal convoluted tubule
What fraction of NaCl and water that is filtered into the Bowman’s capsule is reabsorbed by the proximal convoluted tubule?
2/3 of NaCl and water are immediately reabsorbed by the proximal convoluted tubule
What drives the reabsorption of water in the proximal convoluted tubule?
active transport of Na+ out of filtrate means Cl- follows passively because of chemical attraction and water follows because of the concentration difference
The water remaining after reabsorption by the proximal convoluted tubule is reabsorbed by
the collecting duct
What fraction of water is reabsorbed by the collecting duct?
1/3 - 2/3 of it was already reabsorbed by the proximal convoluted tubule
What is the primary function of the loop of Henle?
to create a gradient of increasing osmolarity from the cortex to the medulla
The gradient created by the loop of Henle allows for
water to be reabsorbed by osmosis in collecting duct as it runs down into the medulla past the loop of Henle
How do the descending and ascending portions of the loop of Henle differ?
differ in structure and in permeability to ions/water
Which part of the loop of Henle is impermeable to water?
entire ascending limb is impermeable to water
The ascending limb of the loop of Henle is impermeable to
water
What does the thick portion of the ascending limb do?
active transport of Na+ out of tubule and Cl- passively follows
What does the thin portion of the ascending limb do?
permeable to both Na+ and Cl-, which move out by diffusion
Is the descending limb thick or thin?
The descending limb is thin.
Describe the permeability of the descending limb.
permeable to water; impermeable to NaCl
In which part of the loop of Henle are ions lost?
ascending limb
In which part of the loop of Henle is water lost?
descending limb
Why/how does water leave from the descending limb?
Because ions are leaving from the ascending limb which creates an osmotic gradient, so water leaves, too
Compare the osmolarity of the interstitial fluid and the fluid in the descending limb.
Osmolarity of interstitial fluid is higher because Na+ and Cl- ions are coming into the interstitial fluid
What is the consequence of water loss on the concentration of fluid in the loop of Henle as we move from the descending to the ascending loop?
the concentration multiplies/increases; in humans, the [filtrate] at the top is 300 mOsm whereas at the bottom of the loop it is >1200 mOsm
What is the relationship between the length of the loop of Henle and the concentration of fluid in the loop of Henle.
longer loop of Henle means greater total concentration that can be achieved
What happens to the Na+/Cl- pumped out of the ascending limb?
reabsorbed into the loops of the vasa recta
What kind of exchange is used in the vasa recta?
countercurrent exchange
Why is countercurrent exchange important in the vasa recta?
prevents flow of blood through its capillaries from destroying the loop of Henle’s osmotic gradient
What is the countercurrent multiplier system?
action of loop of Henle creating a hypertonic renal medulla
Which substances contribute to the overall “saltiness”/osmolarity of the renal medulla?
Na+, Cl-, and urea
Which structures of the nephron are permeable to urea?
Descending limb and collecting duct are permeable to urea
Describe the concentration nature of the fluid that arrives at the distal convoluted tubule.
hypotonic, with a concentration of 100 mOsm
What happens after the fluid reaches the distal convoluted tubule?
fluid plunges down into the medulla via the collecting duct
What happens to the fluid while in the collecting duct?
the interstitial fluid is hypertonic, so an osmotic gradient pulls water out of the collecting tubule
What controls the permeability of the distal convoluted tubule and collecting duct?
antidiuretic hormone (ADH)
What happens hormonally if an animal needs to conserve water?
more ADH is secreted, which increases the number of water channels in the collecting duct cells - increases permeability
Describe the relationship between ADH levels and the need for water conservation.
If more water needs to be conserved, more ADH will be secreted.
What secretes ADH?
posterior pituitary gland
Where is K+ reabsorbed?
proximal convoluted tubule
Where is K+ secreted?
distal convoluted tubule
Why is K+ reabsorbed and then secreted?
to maintain homeostasis
How do kidneys maintain acid-base balance?
by excreting H+ into urine and reabsorbing HCO3-
Where is HCO3- reabsorbed?
proximal convoluted tubule
Where is H+ secreted?
distal convoluted tubule
What does aldosterone do, generally?
controls reabsorption of NaCl in the distal convoluted tubule and collecting duct
The reabsorption of NaCl in the distal convoluted tubule and collecting duct is controlled by
aldosterone
Which two hormones influence the distal convoluted tubule/collecting duct?
antidiuretic hormone and aldosterone
What produces ADH?
hypothalamus
What is the primary stimulus for ADH secretion?
increase in osmolarity of blood plasma
ADH stimulating water reabsorption is what kind of feedback loop?
negative feedback loop
What is the name for the water channels present in the cells of the distal convoluted tubule/collecting duct?
aquaporins
On a molecular level, how does ADH stimulate water reabsorption?
stimulates fusion of vesicle membrane with plasma membrane such that aquaporins are in place to allow water to flow through
When secretion of ADH is reduced, what happens on a molecular level?
plasma membrane pinches in to form new vesicle that contains aquaporins; aquaporins no longer in place
Under conditions of maximal ADH secretion, how much concentrated urine is released by a person?
600 mL of highly concentrated urine per day
What is diabetes insipidus?
condition characterized by a lack of ADH due to pituitary damage
What are the effects of diabetes insipidus?
severe dehydration; low blood pressure
What two common drugs also inhibit ADH?
ethanol; caffeine
What is the major solute in blood plasma?
Na+
If blood [Na+] falls, what else falls?
blood osmolarity also falls
A drop in blood Na+ is compensated for by
aldosterone
What secretes aldosterone?
adrenal cortex
What senses decreased blood flow?
juxtaglomerular apparatus
What is the juxtaglomerular apparatus?
a group of cells that recognize decreased blood flow
Where is the juxtaglomerular apparatus located?
between the distal convoluted tubule and afferent arteriole
In response to low blood flow, what does the juxtaglomerular apparatus do?
secretes renin
What does renin do?
catalyzes production of angiotensin I from angiotensinogen
What does angiotensin I do?
is converted to angiotensin II, which stimulates blood vessel constriction and the secretion of aldosterone
Homeostasis of blood volume/pressure can be maintained by activating the
renin-angiotensin-aldosterone system
What else does aldosterone do, in addition to Na+ reabsorption?
stimulates K+ secretion into the distal convoluted tubule and collecting duct
Which hormone opposes aldosterone?
atrial natriuretic hormone (ANH)
ANH is secreted by
the right atrium of the heart
What does ANH do? (2)
promotes excretion of salt and water in urine; lowers blood volume
