Renal Physiology Part II Flashcards
Describe the mechanisms underlying the reabsorption of solute from the renal tubules into the blood.
Na+ K+ pump drives gradient of Na+ from lumen into PCT cells, but has to bring other things along with it - secondary active transport of glucose, AAs, some ions, vitamins alongside Na+ from lumen into PCT cells
Describe the mechanism underlying the reabsorption of water from the renal tubules into the blood. What effect does the reabsorption of water have on solute?
Water moves via osmosis from lumen of PCT through PCT cells’ aquaporins on both sides and then into bloodstream, which increases [solute] that’s left behind, which then allows them to move down their concentration gradient: lipid-soluble substances, some ions, urea
Regulation of reabsorption of sodium and water:
the location of active sodium reabsorption
Regulation of reabsorption of sodium and water:
the pumps involved in active sodium reabsorption
links between the reabsorption of sodium and water and the establishment of renal concentration gradients
the relationship between sodium reabsorption and glucose reabsorption
the relationship between sodium reabsorption and water reabsorption
antidiuretic hormone (ADH)
reduces urine volume:
fluid osmolarity in hypothalamus increases > posterior pituitary gland releases ADH into circulation > bloodstream > renal tubules > aquaporins inserted in apical surface of principal cells in collecting duct > increase water reabsorption, ADH also increases reabsorption urea
atrial natriuretic peptide (ANP)
released from walls of atria in response to high BP, reduce blood sodium levels by decreasing activity of Na-K pumps and increasing loss of sodium > increase water loss > decrease blood volume and BP
aldosterone
part of RAAS, released to increase BP, high levels of angiotensin II > adrenal cortex releases aldosterone > targets DCT and CDs (principal cells) to conserve water in bloodstream, increases sodium and potassium leak channels and pumps, increase Na+ (and Cl-) reabsorption, increase K+ secretion
parathyroid hormone (PTH)
released from parathyroid gland when blood calcium levels drop, acts on DCT to increase calcium reabsorption, keeps Ca2+ in blood instead of allowing loss through urine,
Describe the importance of tubular secretion using specific examples of secreted substances.
movement from peritubular capillaries into tubules, secretions need to either be removed or are regulating blood composition: K+, NH4+, creatinine, organic acids and bases, drugs, metabolites, urea, uric acid, H+ and HCO3-
Describe the medullary osmotic gradient
kidneys have to maintain osmolarity of body fluids at about 300 mOsm so that it’s isotonic for our body’s cells, countercurrent multiplier and exchanger work together to establish MOG, as you move away from cortex and pyramids’ base and towards renal papilla, higher the osmolarity of IS fluids (300-1200 mOsm)
Explain the mechanism of countercurrent exchange and its importance in renal function.
preserve medullary gradient because vasa recta’s hairpin turns ensures it doesn’t carry too much solute away from interstitium, able to reabsorb water and solute without destroying gradient
Describe the consequences of overhydration
overhydration: low ADH, low number of aquaporins in collecting duct, can’t reabsorb water, lose effects of medullary osmotic gradient and can’t concentrate urine, end up with large volume of very dilute urine
Define diuretic. List several examples of diuretics and explain their effects on urine production.
inhibit ADH from being released from the posterior pituitary (alcohol) or anything that keeps salt in filtrate (coffee, htn drugs), some drugs also inhibit NKCC2 symporter and inhibit active transport of salt out of filtrate, also inhibits water moving out of filtrate, more solute like glucose in filtrate like in a diabetic patient
Define renal clearance. Explain its clinical importance and how it is measured.
volume of plasma from which kidneys remove particular substance in a given time, C=UV/P
Differentiate chronic renal disease and renal failure.
What is reabsorbed during tubular reabsorption?
almost all organic nutrients, water and ions (regulated hormonally)
facultative water reabsorption
aquaporins inserted in collecting ducts if ADH present
What’s reabsorbed in PCT?
glucose, AAs, other nutrients, Na+ and HCO3- and many other ions, water
What’s secreted into PCT?
some drugs, NH4+, H+ to balance acid-base
thin descending limb of loop of Henle permeability
highly permeable to water, so water leaves filtrate and enters surrounding tissues
kinda permeable to solute - mostly salt, some solute enters
thin ascending limb of loop of Henle permeability
not permeable to water, passively permeability to solute, solute leaving filtrate, urea entering
thick ascending limb of loop of Henle permeability
pulling a ton of solute from filtrate:
active transport of solute NKCC2 symporter - moves Na+ K+ and two Cl- from filtrate in tubule into surrounding tissue: Na+ H+ antiporter, Na+ out of filtrate and H+ into filtrate
Explain countercurrent multiplication and its importance in renal function.
establishes medullary osmotic gradient, concentration changes a lot in loop of henle, single effect is movement of salt out of ascending limb into IF, & equilibrium established between descending limb and interstitium, gradient increases at each adjacent segment,
D=I > A by a max of 200 mOsm, goal is concentrated urine
urea recycling
helps form medullary gradient, enters thin ascending limb down its concentration gradient into filtrate, filtrate has higher [urea] on its way to collecting duct, increases as water leaves collecting duct, super concentrated urea leaves collecting duct and enters interstitium driven by ADH because more permeability to urea in collecting duct walls when ADH present, then [urea] in interstitium is high, then it reenters the thin ascending limb, and the cycle starts over
Describe the consequences of dehydration.
more ADH released by posterior pituitary gland, more ADH and more aquaporins in collecting duct, filtrate grows more and more concentrated in collecting duct because water is allowed to leave, increase [urea] to contribute to gradient, low volume of concentrated urine
inulin
plant polysaccharide that’s injected and freely filtered, neither secreted nor absorbed, so it’s a good measure of how well the kidneys are moving substances through (alternatively use creatinine as a rough estimate)
chronic renal disease
GFR < 60 ml/min lasting for at least 3 months, leading causes are diabetes mellitus and htn
renal failure
hemodialysis is temp fix until transplant, GFR <15 ml/min at any point, uremia aka “urine in blood” as filtration formation essentially stops, “uremic frost” crystals may form on skin as body tries to rid itself of excess urea through sweat
Which part of the nephron is responsible for reabsorbing most water and nutrients from renal filtrate?
proximal convoluted tubule
Once the filtrate reaches the ____, reabsorption becomes dependent upon the body’s needs and regulated by hormones.
distal convoluted tubule
ADH promotes reabsorption of what?
water
Aldosterone promotes reabsorption of what?
sodium
parathyroid hormone promotes reabsorption of what?
calcium
nephron loops are the site of ___ secretion
only urea molecules
what two places in nephron secrete only K+?
DCTs and collecting ducts
what is absorbed in nephron loops?
H20, Na+, K+, Cl-, Ca2+, Mg2+
The reabsorption of sodium in the DCT is regulated primarily by __________
Aldosterone increases Na+ reabsorption, and atrial natriuretic peptide (ANP) inhibits Na+ reabsorption.
Filtrate in a typical healthy nephron will NEVER include
blood cells and proteins
When the macula densa detects an increase in NaCl concentration in the renal filtrate, what happens to the glomerular filtration rate (GFR)?
GFR decreases
If the osmotic pressure in the glomerular capillaries increased from 28 mmHg to 35 mmHg due to dehydration, would net filtration increase or decrease?
net filtration would decrease
Where in the nephron can secretion take place?
proximal tubule, distal tubule, collecting duct
What can be accurately said about the relationship between glucose in the blood and the amount of glucose filtered through the glomerular membrane?
The higher the blood glucose concentration, the more glucose is filtered through the glomerular membrane. Glucose passes freely through the glomerular membrane, so the amount of glucose in the glomerular filtrate correlates with the amount of glucose in the blood.
Urea transport into the medullary collecting duct is enhanced by ___
ADH
