Urinary System 2 Flashcards
what is paracellular transport
movement of substances between epithelial cells within tubule
what is transcellular trasnport
movement of substances from one end of a cell to the other
must cross both luminal and basolateral membrane
what do transport proteins embedded within luminal and basolateral membranes do
control movement of various substances
can have pumps, carriers, and channels
what are the pressures like in the peritubular capillaries after glomerular filtration
low hydrostatic pressure and high colloid osmotic pressure
both facilitate reabsorption of substances from filtrate back into the peritubular capillaries
where does most reabsorption occur and why
in the proximal convoluted tubule (PCT)
this portion of the tubule has lots of microvilli on the cells’ luminal surfaces (created more surface area for absorption)
what is the transport maximum (Tm)
maximum rate of substance that can be reabsorbed or secreted across tubule epithelium per a certain time
if you have more substance than transport proteins, excess is excreted in the urine
explain how glucose is reabsorbed at the proximal converted tubule
sodium moves down its concentration gradient through a sodium/glucose symporter
it moves from tubular fluid into tubule cell, creating energy
this energy moves glucose up its concentration gradient into the cell through that same symporter
glucose moves down its concentration gradient by facilitated diffusion through a glucose uniporter
moves into blood
what is renal threshold
maximum plasma concentration value where the transport maximum is not exceeded
what is glucosuria
excretion of glucose in the urine
occurs when amount of glucose in the tubule is more than the transport maximum
glucose pulls water into tubular fluid with it which causes loss of fluid in urine
ex. diabetes
what two substances are typically 100% reabsorbed into the blood
nutrients
filtered plasma proteins
explain how filtered plasma proteins are reabsorbed
proteins are moved into tubular cell by receptor-mediated endocytosis
proteins are digested by lysosomes into amino acids
amino acids are released by exocytosis into the blood
what is renal disease
when kidney is not degrading or reabsorbing proteins
what would higher than normal filtration of plasma proteins indicate
damage to filtration membrane or high systemic blood pressure
too much protein, left over lost in urine (proteinuria)
blood concentration of plasma proteins decreases
what would lower than normal filtration of plasma proteins indicate
changes that accompany chronic kidney disease
results in a decrease in filtration of small proteins and their degradation within tubules
too many in the blood
which substances undergo regulated reabsorption
sodium
water
potassium
biocarbonate
calcium
how is sodium reabsorbed into the blood in the proximal convoluted tubule
sodium moves down its concentration gradient from the tubular fluid into the cell through a sodium transport protein
it then moves through sodium/potassium pump into the interstitial fluid
finally it moves into the blood
how does aldosterone effect sodium reabsorption into the blood in the collecting tubules and ducts
produced by adrenal cortex
stimulates making of sodium channels and sodium potassium pumps
increase sodium reabsorption
how does atrial natriuretic peptide effect sodium reabsorption into the blood in the collecting tubules and ducts
inhibits reabsorption of sodium by inhibiting release of aldosterone
more sodium excreted in urine, increases GFR
explain how water is reabsorbed in the proximal convoluted tubule
water follows sodium and moves from tubular fluid into cell by aquaporin
it then moves by osmosis through another aquaporin to the blood
ADH would increase water absorption
explain how water is reabsorbed in the nephron loop
water follows sodium and moves from tubular fluid into cell by aquaporin
it then moves by osmosis through another aquaporin to the blood
water moves from the descending limb of loop into vasa recta
which portions of the system are impermeable to water
ascending limb and distal convoluted tubule
explain how water is reabsorbed in the collecting tubules and ducts
controlled by aldosterone and antidiuretic hormones
aldosterone: increases sodium/potassium channels which increase sodium and water reabsorption
antidiuretic hormone: binds to ADH receptors, increases migration of vesicles containing aquaporins which adds channels to increase water reabsorption, less urine produced
what is obligatory water reabsorption
water follows sodium by osmosis
what is facultative water reabsorption
tubular reabsorption of water in response to ADH
what happens during dehydration
more ADH causes more water reabsorption
less urine, darker yellow
what happens during overhydration
less ADH, less water being reabsorpbed
more urine, less concentrated, paler color
how is potassium moved in the proximal convoluted tubule
sodium is reabsorbed with water to create a gradient
potassium moves down the gradient from fluid into the blood by the paracellular route
how is potassium moved in the nephron loop
intercalated cells reabsorb potassium
principals cells secrete potassium
what is the most powerful stimulant for aldosterone
elevated potassium
what regulates the absorption of calcium and phosphate
parathyroid hormone
inhibits potassium reabsorption in PCT
stimulates calcium reabsorption in DCT
