Ion + Water Balance Flashcards
What can environment refer to in animal physiology?
the external world for the entire organism
the extracellular fluid for a cell
the cytoplasm for intracellular enzymes
What are the 3 homeostatic processes of body fluid regulation?
osmotic regulation
ionic regulation
nitrogenous waste excretion
What is osmotic regulation?
regulation of the osmotic pressure of body fluids
What is ionic regulation?
the regulation of specific ion concentrations in body fluids
What is nitrogenous waste excretion as a process of body fluid regulation?
the excretion of urea and uric acid (end products of protein metabolism) from the body
What are the major ions in salt and freshwater?
sodium
chloride
magnesium
sulfate
calcium
potassium
bicarbonate
Which major ions are most highly concentrated in seawater vs. freshwater?
seawater:
- Na
- Cl
- Mg
- Sulfate
fresh:
- bicarbonate
- Ca
- Na
How does the concentration of Na compare in seawater to freshwater?
seawater 470 mM > 0.35 mM fresh
sea > > fresh
How does the concentration of Cl compare in seawater to freshwater?
sea > > fresh
How does the concentration of bicarbonate compare in seawater to freshwater?
sea > fresh
sea = 2, fresh = 1.72
T or F: all of the major ions are concentrated more heavily in seawater than fres h
true
bicarbonate is the only one that comes close in freshwater to seawater concentrations
How does the osmolarity of seawater compare to that of freshwater?
seawater > > freshwater
sea ~1100 mOsm/L
fresh 0.5-10 mOsm/L
What is osmolarity?
the number of solute particles per 1L of solvent
How does the RATIO of concentration of major ions (Na, Cl, K) in the intracellular and extracellular fluid of squid axons compare to mammalian muscles?
squid axons have lower ratios of ions in/out than mammals
How does the osmolarity of major ions (Na, Cl, K) in the intracellular and extracellular fluid of squid axons compare to mammalian muscles?
squid axons have much higher osmolarity than mammalian muscles
What osmotic and ionic challenges do animals face in marine environments?
the environmental conditions (high osmolarity) make it easy to gain salts and easy to lose water
What osmotic and ionic challenges do animals face in freshwater environments?
the low osmolarity conditions make it easy to lose salts and easy to gain water
What osmotic and ionic challenges do animals face in terrestrial environments?
less water outside body than inside = easy to lose water
What is the osmoregulatory and ionoregulatory strategy of marine arthropods?
isosmotic
no ionoregulation
What is the osmoregulatory and ionoregulatory strategy of marine molluscs (ex. squid)?
slightly hyperosmotic
ionoregulation
What is the osmoregulatory and ionoregulatory strategy of marine fish, amphibians, reptiles, mammals, birds?
hyposmotic
ionoregulation
What is the osmoregulatory and ionoregulatory strategy of freshwater arthropods?
hyperosmotic
ionoregulate
What is the osmoregulatory and ionoregulatory strategy of freshwater molluscs (ex. clams)?
slightly hyperosmotic
ionoregulate
What is the osmoregulatory and ionoregulatory strategy of freshwater fish, amphibians, reptiles, mammals, birds?
hyperosmotic
ionoregulate
generally, all aquatic animals except ____ have strategies for ionoregulation
except marine arthropods and hagfish
What is hyposmotic?
when the organism has lower internal osmotic pressure than the external environment
What is hyperosmotic?
when the animal has higher internal osmotic pressure than the external environment
What is isosmotic?
when the animal has the same internal osmotic pressure as the external environment (does not regulate)
generally, all aquatic animals except ____ have a strategy for osmoregulation
except marine arthropods
Most freshwater animals are ___osmotic?
hyperosmotic (higher osmolarity internally)
What are the 2 strategies for overcoming osmotic challenges?
osmoconformer
osmoregulator
What is an osmoconformer? give an example
animals that do not regulate their internal osmotic pressure and internal osmolarity matches the external environment
ex. marine invertebrates (arthropods)
What is an osmoregulator? give an example
animals that regulate internal osmolarity to be different than that of the external environment
ex. most vertebrates
Most marine vertebrates are ____osmotic?
hyposmotic (lower internal osmolarity than external)
What are the 2 strategies for ionic regulation?
ionoconformer
ionoregulator
What is an ionoconformer? give an example
animals that don’t regulate their ionic concentrations and match that of the external environment
ex. marine invertebrates (marine organisms only)
What is an ionoregulator? give an example
animals that maintain ionic concentrations different from that of the external environment
ex. most vertebrates
Organisms in what environment are the only examples of ionoconformers?
only marine animals
ex. many marine invertebrates
T or F: some freshwater animals are ionoconformers
false, only some marine animals are known to be ionoconformers
What is ECF?
extracellular fluid
How do cells control cell volume?
water is moved in and out of cells via osmosis (follows solutes) through aquaporins
cells transport solutes in and out of ECF and water follows solutes
What is osmosis?
the flow of water from an area of low solute concentration to high solute concentration
basically, water follows the flow of solutes
How does water move through the hydrophobic cell membrane?
through aquaporins
Why do animal cells need to regulate the composition of ECF?
to provide cells with an external solution that allows them to have the right cell volume
What causes a change in cell volume?
environmental osmotic stress
What happens to cells in hypotonic environments?
HYPOtonic = external environment has lower solute concentration than in cells
water follows concentration of solutes= water flows into the cell
cell swells and can explode
What happens to cells in hypertonic environments?
HYPERtonic = external environment has higher solute concentration than inside cells
water flows out of cells causing cells to shrink and die
How do cells control their volume?
by regulating solutes across their membrane
How do cells regulate volume increase?
by importing ions
import of ions brings influx of water
How do cells regulate volume decrease?
by exporting ions
export of ions allows efflux of water
What ion channels or transporters are involved in regulatory volume increase?
to swell cells:
Cl- and Na+ channels open (influx)
Na+, K+, 2Cl- cotransporter brings in these ions
Na+/H+ exchanger brings in Na+ in exchange for H+
What ion channels or transporters are involved in regulatory volume decrease?
to shrink cells
K+ and Cl- channels open = efflux
K+/Cl- cotransporter active
3Na+ / Ca2+ exchanger pumps out 3 Na+ for 1 Ca2+
Na+/K+ ATPase pumps out 3 Na+ for 2 K+
Who won the Nobel Prize for chemistry in 2003 for the discovery of water channels (aquaporins)?
Peter Agre, Johns Hopkins
What is the function of epithelial tissues? what is an example?
they are the outermost layer of an animal and they form a barrier between the animal’s internal environment and an external environment
external surfaces: ex. integument
internal surfaces: ex. lumen of digestive system, kidney, respiratory tract
What physiological functions do epithelial tissues have?
respiratory
digestive
ion and water regulation
How do animals limit water movement across body surface?
- by limiting permeability of the epithelial tissues (integument)
- layers of hydrophobic molecules on external surfaces
By what factor do aquaporins increase water permeability of a membrane?
by 100x
How do animals limit permeability of integument to water?
reducing concentration of aquaporins on the integument
What type of hydrophobic molecules might animals use to layer integument to reduce water flux?
mucus cells
Cornified stratum corneum with keratin
cuticle made of chitin
What are examples of animals that use mucus cells to create a protective hydrophobic barrier around their integument?
lungfish
frogs
What are examples of animals that use cornified stratum corneum with keratin to create a protective hydrophobic barrier around their integument?
animals with skin
What is the cornified stratum corneum?
a hydrophobic barrier composed of keratin and lipids
(skin)
What are examples of animals that use a cuticle to create a protective hydrophobic barrier around their integument?
animals with chitin exoskeletons such as insects, spiders, crustaceans
What composes an arthropods cuticle layer?
chitin
Describe the structure of an epithelial cell
apical membrane (faces external environment) has ion transporters
between epithelial cells, tight junctions prevent water from moving between cells
within cell, many mitochondria
basolateral membrane (faces internal environment) has ion transporters and contacts basement membrane
T or F: epithelial cells play an important role in ion transport
true for digestive tract, kidneys, gills
What are the 4 major features of epithelial cells involved in ion transport?
- asymmetrical membrane transporters
- tight junctions between cells
- high cell diversity within tissue
- abundant mitochondria
What is important about the asymmetry of transporters on epithelial cells?
solutes are transported selectively across the membrane
What is important about the tight junctions between epithelial cells?
this forms an impenetrable sheet of tissues and prevents leakage between cells
What is important about the high abundance of mitochondria in epithelial cells?
they have a large energy supply
What are the 2 main routes of ion transport for epithelial cells?
transcellular
paracellular
Describe transcellular transport
movement of ions through a cell across membranes
describe paracellular transport
movement of ions between cells through leaky or tight gap junctions
what 4 types of transporters exist on epithelial cells?
Na/K ATPase and other ATPases
ion channels (Cl, K, Na)
electroneutral cotransporters
electroneutral exchangers
T or F: epithelial cells are massive consumers of ATP - why/why not?
true because they have a high abundance of mitochondria so they need a lot of ATP
What are the 2 types of epithelial cells in fish gills?
chloride cells
pavement cells
What are chloride cells? describe them
a type of epithelial cell on fish gills
they are large mitochondria-rich cells
aka PNA+ cells
What is PNA?
peanut lectin agglutin
a glycoprotein that binds carbohydrates on chloride cells
What type of cells in fish gills have PNA?
only the chloride cells
Which fish gill cells are PNA+? PNA-?
chloride cells are PNA+
pavement cells are PNA- (no PNA)
What are pavement cells? describe them
a type of epithelial cell found on fish gill surfaces
flatter, smaller cells usually with less mitochondria than chloride cells
do NOT have PNA
What are the functions of the chloride and pavement cells in fish gills?
to mediate transport of ions
T or F: all pavement cells are mitochondria rich, but not all are PNA-
false
all pavement cells are PNA-
some are mitochondria-rich
some are mitochondria-poor
Which of the epithelial cells in fish gills are more likly to do ion transport?
mitochondria rich chloride and mitochondria-rich pavement cells
What does the direction of ion transport depend on?
water salinity
Describe the direction of ion transport across a freshwater fish gill via mitochondria-rich pavement and chloride cells
pavement cells:
- ions (ex. Na+) are transported across the apical membrane from the external environment inside the pavement cells
- Na+
pavement cells:
- low external salinity, Na+ ions transported across apical membrane into cell
- basolateral side: Na+ and HCO3- transported across basolateral membrane, K+, Cl-, CO2 transported into cell
chloride cells:
- Ca2+ and Cl- transported across apical membrane into cell
HCO3- transported to external environment
- Ca+ x2, Na+, H+ transported across basolateral membrane out of cell
- Na+, K+, CO2 transported across basolateral membrane into cell
What ions are transported into the pavement cells across the apical membrane of freshwater fish?
Na+
from the environment
What ions are transported into the pavement cells across the basolateral membrane of freshwater fish?
K+
Cl-
CO2
from internal environment
What ions are transported out of the pavement cells across the basolateral membrane of freshwater fish?
Na+
HCO3-
from inside the cell to the internal environment
What ions are transported into the chloride cells across the apical membrane of freshwater fish?
Ca2+
Cl-
from external environment
What ions are transported out of the chloride cells across the apical membrane of freshwater fish?
HCO3- from inside the cell to the external environment
What ions are transported into the chloride cells across the basolateral membrane of freshwater fish?
Na+
K+
CO2
from internal environment into the cell
What ions are transported out of the chloride cells across the basolateral membrane of freshwater fish?
Ca+ x2
Na+
H+
from inside cell to internal environment
What ions are transported out the pavement cells across the apical membrane of freshwater fish?
H+
from inside cell to external environment
What ions are transported into the chloride cells across the apical membrane of marine fish?
NONE
only influx transport across basolateral membrane
What ions are transported out of the chloride cells across the apical membrane of marine fish?
Cl-
from inside cell to external environment
What ions are transported into the chloride cells across the basolateral membrane of marine fish?
2K+
Na+
2Cl-
from internal environment into cell
What ions are transported out of the chloride cells across the basolateral membrane of marine fish?
Na+
K+
from inside cell to internal environment
What ions are transported from internal environment directly to external without membrane transporters? how?
Na+ can diffuse out of the internal environment between chloride and pavement cells of fish gills
What is a diadromous animal?
an animal that can migrate between seawater and freshwater throughout its life
What is anadromous? what is an example?
when the animal spends most of its adult life in marine environment and returns to freshwater to spawn and die
ex. salmon
How do juvenile salmon adapt their physiology to prepare for the change from freshwater to seawater?
smoltification
What is smoltification?
the process of reorganizing the ion-pumping properties to prepare juvenile salmon for entering seawater from freshwater
and changes to the GI tract and kidney to adjust ion-water balance regulation
What mediates smoltification in salmon?
a growth hormone, insulinlike growth factor 1 and cortisol mainly
What happens to adult salmon gills when preparing to migrate into different salinity?
transitions from ion-secreting to ion-absorbing epithelium for moving into freshwater or vice versa for moving into salt water
genes coding for Na/K ATPase change in isoform
a1a increase for freshwater (ion-absorption)
a1b increase for saltwater (ion secretion)
Where are water and salts from drinking and food transported?
across digestive epithelial cells
What type of transport is involved in digestive epithelium?
transcellular and paracellular
What happens to the water and salts that are transported across digestive epithelia?
they enter bloodstream
What organ is key for maintaining ion and water balance in vertebrates?
the kidney
What are the 6 major homeostatic roles of vertebrate kidneys?
ion balance
osmotic and water balance
blood pressure
pH balance
excretion of nitrogenous wastes and toxins
hormone production
describe the structure of the mammalian kidney
bean shaped
What are the layers of the mammalian kidney?
renal cortex: outermost
renal medulla: inner layer
What are the structures within the mammalian kidney?
renal cortex - outermost layer
renal medulla - inner layer consisting of the renal pyramids and renal papilla
renal pelvis
minor calyx
major calyx
renal artery and vein
ureter - tube that drains kidney into urinary bladder
What drains urine into the ureters from the kidneys? where does that urine drain to?
minor calyxes drain urine into major calyx which drains urine into a ureter which drains into the bladder
How many kidneys do mammals have?
2
= 2 ureters drain into 1 bladder and 1 urethra
What is the functional unit of the kidney?
nephrons
~how many nephrons per kidney?
~1 million
What composes the nephron?
renal corpuscle (composed of the Glomerulus, Bowman’s capsule)
renal tubules
What composes the renal corpuscle of a nephron?
Glomerulus and Bowman’s capsule
What is the Glomerulus?
a ball of capillaries within the Bowman’s capsule = the renal corpuscle of a nephron
What is the Bowman’s capsule?
a capsule lined with epithelial cells that surround the capillary ball (glomerulus) in the nephrons of a kidney
What are the renal tubules?
part of a nephron
they are lined with transport epithelial cells and are segmented with specific transport functions
What layer of the kidney are Bowman’s capsule and glomerulus located?
in the renal cortex
What part of a nephron is located in the renal medulla?
the loop of Henle and collecting duct
What are the 4 functions of neurons (ie, renal processes)?
filtration of blood
reabsorption of filtrate
secretion of wastes and toxins
excretion of nitrogenous waste
Where in the nephron does the filtration of blood occur?
blood filtrate formed at glomerulus (in Bowman’s capsule)
How much blood is filtered per day in an adult human?
~180 L/day
~7.5L/hr
What do nephrons reabsorb?
the filtrate is reabsorbed after specific molecules have been removed
How much filtrate is reabsorbed by nephrons?
~99% (including water)
What is secreted by nephrons?
the specific molecules removed from blood are added to the filtrate
ex. K+, H+, NH4+, urea, phamaceuticals, drugs, toxins
What is excreted by nephrons?
nitrogenous wastes - urine
How much urine is excreted by nephrons?
75 ml/hr
~1% of the filtrate
Describe filtration in nephrons
liquid components of blood flow into the bowman’s capsule through the glomerulus (coated in capillaries)
water and small solutes transport across glomerular wall but NOT blood cells or large macromolecules
podocytes and foot processes on outside of capillaries form filtration structure
filtrate flows from Bowman’s into proximal tubule
What controls the blood pressure and filtration within the glomerulus?
mesangial cells
T or F: glomerular capillaries are very leaky
true
they are only coated with spread out podocytes and foot processes which allow filtrate to leak out of glomerulus
What type of solutes cross the glomerular wall into the bowman’s capsule?
water and small solutes
NOT blood cells or macromolecules
Where does the filtrate that leaked from the glomerulus into the Bowman’s capsule go next?
to the proximal tubule
What type of transporters is the proximal tubule epithelia rich in?
Na/K ATPAse
ion transporters (Na+, glucose)
some ion channels (Cl-)
Does the apical membrane of a nephron face tubular fluid or peritubular space?
tubular fluid (inside the nephron)
Does the basolateral membrane of a nephron face tubular fluid or peritubular space?
peritubular space
what is the renal threshold?
the saturation limit of the transporters on epithelial cells of a nephron
Describe the renal threshold graph for plasma [glucose] x vs. glucose flux y
as glucose levels increase in the blood:
amount of glucose filtered by kidneys = the amount of glucose reabsorbed by kidneys (linear increase)
until saturation (renal threshold)
at which point,
glucose will continue to be filtered but reabsorption will plateau and the concentration of glucose in urine will increase
What happens to glucose flux when reabsorption of glucose is less than the filtration of glucose?
if glucose concentration increases past the renal threshold
the transporters are saturated and no more glucose can be reabsorbed by the nephrons of the kidney, so more glucose is filtered out and enters the urine
= higher glucose levels in urine
What is primary urine?
the initial filtrate that is filtered in the Bowman’s capsule which is isosmotic to blood (same ion concentrations)
Describe reabsorption
most of the water, salt and glucose in the primary urine is reabsorbed via transport proteins and energy
each segment of a nephron has specific transporters for specific solutes
T or F: reabsorption of water, salts and glucose from primary urine requires energy input
true
What limits the rate of reabsorption by nephrons?
the number of transporters on the epithelial cells
What are the 4 segments of the nephron involved in reabsorption?
proximal tubule
loop of Henle
distal tubule
collecting duct
What does the proximal tubule of a nephron reabsorb?
most of the solute (salt, glucose) and water
What does the loop of Henle of a nephron reabsorb?
the descending limb reabsorbs water
the ascending limb reabsorbs ions
What does the distal tubule of a nephron reabsorb?
completes the reabsorption of solutes and water
What is the function of the collecting duct?
it regulates the final urine composition
it collects urine from multiple nephrons and drains into the renal pelvis of the kidney
T or F: there’s only one nephron per collecting duct
false, multiple nephrons can drain into a single collecting duct
Where does the collecting duct bring urine to?
the renal pelvis of the kidney to be drained through the ureter into the bladder
What allows for the differences in transport and permeability along a nephron’s tubule?
the different epithelial cells lining the tubule
Where does most of the reabsorption in the tubules of a nephron occur?
in the proximal tubule
What type of transporters are on the epithelial cells of the proximal tubule? what kind of solutes do they transport?
Na+ contransporters of:
glucose
lactate
AAs
water-soluble vitamins
phosphates
water follows these by osmosis
What molecules does the proximal tubule secrete?
organic anions (ex. cAMP)
organic cations (ex. norepinephrine, ACh)
drugs and toxins
absorb from the blood stream and secrete into the lumen of the nephron to be moved with filtrate
What is the descending limb permeable to? / what does it reabsorb?
water
What occurs in the descending limb of henle?
water is reabsorbed = the volume of primary urine in the nephron lumen decreases and becomes more concentrated
What is the ascending limb permeable to?
ions
What happens in the ascending limb of henle?
ions are reabsorbed
primary urine in the lumen of a nephron becomes dilute
water does not move, this limb is impermeable to water
What happens as the reabsorbed ions accumulate in the interstitial fluid via the ascending limb of the loop of henle?
it creates an osmotic gradient in the renal medulla to allow for the reabsorption of water
Describe the osmotic gradient created by the loop of henle
it is counter current
as tubular fluid enters the proximal tubule and drains down the descending limb, the osmolarity is low
as tubular fluid flows down the descending limb and water is reabsorbed from the primary urine, osmolarity increases (more concentrated urine)
as tubular fluid flows up the ascending limb and ions are reabsorbed but no flow of water, the tubular fluid becomes more dilute
the tubular fluid that enters the distal tubule is more diluted
How does the osmolarity of the tubular fluid compare at the proximal tubule v. the Loop of Henle v. the distal tubule?
at the proximal tubule, the primary urine is both high in water and ion concentration = low osmolarity
at the bottom of the loop of henle, water has been reabsorbed = very high osmolarity
at the distal tubule, ions have been reabsorbed, = low osmolarity
Where does the loop of henle occur?
in the renal medulla
Where are the proximal and distal tubules?
in the renal cortex
What occurs in the distal tubule?
more reabsorption of salts and water from primary urine
secretion of potassium into primary urine
What regulates the transport in distal tubules and collecting ducts?
hormones:
parathormone
aldosterone
vassopressin
What does parathormone do?
increase Ca2+ reabsorption by the distal tubule and collecting duct
What does aldosterone do?
increase Na+ reabsorption and K+ secretion by the distal tubule and collecting duct
What does vassopressin do?
increase water reabsorption by the distal tubule and collecting duct
What type of response (slow/fast) do steroid hormones have on kidney function?
steroid hormones like aldosterone have a slow response on kidney function because they affect transcription and translation
What type of response (slow/fast) do peptide hormones have on kidney function?
peptide hormones like vassopressin and parathormone have a rapid response on kidney function
Which of the 3 hormones mentioned that affect kidney function have fast responses? slow?
fast: vassopressin and parathormone
slow: aldosterone
What part of the kidney do hormones (vasopressin, parathormone, aldosterone) effect?
distal tubules and collecting duct
What determines the filtration rate of the glomerulus (GFR)?
the pressure across the glomerular wall
What are the 3 main forces that cause pressure changes to the glomerular wall which effect GFR?
glomerular capillary hydrostatic pressure
bowman’s capsule hydrostatic pressure
oncotic pressure = osmotic pressure created by protein concentration in blood
What is hydrostatic pressure?
the pressure exerted by a fluid at equilibrium due to gravity
What are the regular directions and pressures of the GFR?
the blood pressure in the glomerulus is at 60 mmHg
the fluid in the bowman’s capsule lumen has hydrostatic pressure of 15 mmHg
= blood filtrate is pushed out of glomerulus into lumen of bowman’s capsule
= fluid in lumen is pushed out of bowman’s capsule into glomerulus
the glomerulus has protein (oncotic) pressure of 30 mmHg and filtrate pumped into lumen has lower oncotic pressure than blood so it is pumped into the glomerulus
What is the net GFR?
60 out of glomerulus
30 + 15 in glomerulus
net = 15
What direction does the blood filtrate flow between glomerulus and BC?
filtrate is pumped out of glomerulus into bowman’s capsule
What direction does fluid in the lumen of the BC flow between that and the glomerulus?
fluid in lumen pumped into glomerulus
what are the 3 pathways for intrinsic regulation of GFR?
myogenic
tubuloglomerular feedback
mesangial control
Describe myogenic regulation of GFR
constriction and dilation of afferent arterioles control hydrostatic pressure and flow of fluids
Describe tubuloglomerular feedback of GFR
in the juxtaglomerular apparatus:
- macula densa cells in the distal tubule
- juxtaglomerular cells in the afferent arteriole
macula densa cells control the diameter of the afferent arteriole
Describe mesangial regulation of GFR
mesangial cells alter the permeability of the glomerulus
they also increase/decrease of flow into glom by stretching or constricting capillaries
Both myogenic and tubuloglomerular feedback involve changes in ________, whereas mesangial control involves changes to ____ of the filter
filtration pressure
surface area
How are mesangial cells involved in the negative feedback of GFR?
when arterial blood pressure increases
mesangial cells in the capillaries around the glomerulus stretch = causes them to contract
contraction reduces SA of the filter = brings GFR back to normal
stretch = contract = decreased GFR
What type of feedback are the intrinsic pathways of regulating GFR?
negative feedback to create a narrow range of blood pressure
describe tubuloglomerular feedback in the distal tubule
macula densa sense increased urine flow in distal tubule and signal juxtaglomelular cells of the afferent arteriole to cause vasoconstriction = decreased hydrostatic pressure = decreased GFR
vasoconstriction = decreased pressure = decreased GFR
describe myogenic regulation of GFR
increased arterial blood pressure will raise GFR
increased BP stretches smooth muscle cells in the afferent arteriole = stretch-sensitive ion channels activated = depolarization = contraction of smooth muscles = vasoconstriction = decreased blood flow = decreased hydrostatic pressure = decreased GFR
Which hormone is antidiuretic?
vasopressin (ADH)
What other peptide hormones can affect urinary function?
renin-angiotensin - can be slow or rapid
How does vasopressin affect kidney function?
increases water reabsorption by the collecting ducts and distal tubules by increasing number of aquaporins
Where is vasopressin produced? where is it released?
hypothalamus and released by posterior pituitary
Describe the steps of vasopressin increasing water absorption in the distal tubules and collecting ducts
hypothalamus receives signal of increased osmolarity = produces ADH (vasopressin)
posterior pituitary gland releases ADH
ADH binds to G-protein coupled receptor on nephron epithelial cells to activate it
triggers adenylate cyclase, cAMP, PKA pathway
cytoskeletal and vesicle proteins are phosphorylated
translocation of vesicles to the cells for the membrane to be inserted with aquaporins
T or F; the collecting duct does not normally absorb water
true
What stimulates the release of vasopressin?
osmoreceptors of the hypothalamus receive signal of increased plasma osmolarity
What inhibits the release of vasopressin?
increased blood pressure detected by the stretch receptors of the atria and baroreceptors in the carotid and aortic bodies
What is aldosterone?
a mineralcorticoid that controls ion excretion
What produces aldosterone?
adrenal cortex
How does aldosterone affect kidney function in the distal and collecting duct?
it stimulates Na+ reabsorption from urine and K+ secretion into urine
stimulates production of Na/K ATPase for the basolateral membrane
stimulates production of Na+ and K+ channels for the apical membrane
What are the steps of aldosterone increasing Na+ reabsorption?
the adrenal cortex is stimulated by:
- angiotensin II
- High K+
- ACTH
- decreased BP detected by stretch receptors in atria
to release aldosterone
aldosterone diffuses across cell membrane and binds to transcription factors in the nucleus
aldosterone activates transcription factor and stimulates transcription of genes for Na+ transporters
new transporters are made in the ER and transported to cell membrane via vesicles
describe the RAA (renin-angiotensin-aldosterone) pathway
juxtaglomerular cells secrete the enzyme renin
What enzyme do juxtaglomerular cells secrete?
renin
What 3 ways is renin secretion regulated?
baroreceptors
sympathetic neurons
macula densa
How do baroreceptors in the juxtaglomerular cells regulate renin secretion?
they stimulate the release of renin when there’s low BP
How do sympathetic neurons regulate renin secretion?
in the cardiovascular control center (medulla oblongota) stimulate secretion in response to low BP
How do macula densa cells regulate renin secretion?
in the distal tubule, the macula densa release paracrine signal to stimulate juxtaglomerular cells to release renin when BP is low
when is renin secreted?
when BP is low or GFR is low
What happens after renin is released?
renin catalyzes the conversion of angiotensinogen (released by liver) to angiotensin I
angiotensin I is cleaved by angiotensin converting enzyme (ACE) on the endothelial cells of blood vessels into angiotensin II
What happens when angiotensin II is produced?
release of aldosterone from adrenal cortex
release of vasopressin
vasoconstriction of arterioles
binds to GPCR
all of this brings BP back to normal rates
