renal phys- filtrate modification, clearance, water and solute movement through the nephron Flashcards
how does diet intake affect K+ homeostasis
- herbivores consume much larger quantities of K+ than carnivores
- chronic dietary K+ overload or underload will affect the rate of its excretion
how does the body prevent a dangerous rise in the extracellular fluid of K+ levels from the addition of K+ to the body
K+ can be shifted from ECF into the cells
K+ is maintained at high levels within the cells by the activity of ____
Na+, K+ - ATPase enzyme
(moves K+ into the cells and Na+ out_
the activity of Na+, K+ - ATPase is regulated by:
- insulin - stimulates - increases the entry of K+ into the cell
- catecholamines and aldosterone - similar to insulin
- changes in blood pH
- acedemia (pH<7.4) - release of K+ by cells into ECF
- alkalemia (pH>7.4) - release in cellular uptake of K+ from ECF
the kidney is responsible for maintaining external:
K+ balance and total body K+
the external balance between dietary K+ intake and output is maintained primarily by:
the daily renal excretion of K+
is it normal for a small portion (10%) of K+ is loss by extrarenal routes such as the GI system
yes; in disease states large amounts can be lost from extrarenal routes
K+ is freely filtrated at
glomerulus
90% of K+ is reabsorbed where?
in the proximal tubule and thick ascending lumb of the loop of henle
K+ is secreted into urine by:
- more distal nephron segments
- distal tubules
- cortical collecting ducts
- fitst part of outer medullary collecting ducts
almost all urine K+ comes from:
secretion
K+ transport in the proximal tubule
- K+ is passively reabsorbed form the tubular lumen by a paracellular route
- K+ is reasorbed with water in the proximal tubule through thr lateral intercellular spaces by solvent drag
- in the late proximal tubule, some passive reabsorption of K+ may occur through K+ channels in the luminal and peritubular membranes
are the thin segments of the loop of henle involved in K+ reabsorption
no
K+ transport in the thick ascending limb of the loop of henle
- paracellular route is the primary mode of K+ reabsorption in the TAL
- the presence of a K+ channel in the luminal membrane and a positive electrical potential in the lumen favor K+ reabsorption passively down its electrochemical gradient
K+ transport in the late distal tubule and collecting duct
the presence of two cell types (principal and intercalated cells) account for K+ movement
the ultimate rate of renal excretion of K+ and its concentration in the urine is determined by efficiency of: (2)
- K+ secretion by principal cells
- K+ reabsorption by intercalated cells
net reabsorption or net secretion of K by the kidney is influence by
decreasing or increasing the intake of K+
increased K+ intake results in:
an increased quantity and activity of Na+,K+ - ATPase pumps and amplification of principal cell basolateral membrane
dietary K+ intake reduced:
net reabsorption of K+ by the intercalated cells sultrs rather than secretion by principal cells
secretion of K+ is enhanced by increased levels of such mineralocorticoids as:
aldosterone
changes in Na+ balance directly influence:
K+ balance
H+ balance regulation of K+ excretion
K+ secretion is reduced by acute increases in H+ and enhanced by acute decreases in H+
regulation of K+ excretion - urine flow rate
high urinary flow rate past sites of K+ secretion prevents the buildup of K+ concentration in the tubular fluid, favoring the secretion of K+
regulation of K+ excretion - drugs and toxins
- diuretics - alter the urinary excretion of water, Na+ adn Cl-, which alters K+ excretion
- poisonous heavy metals inhibit Na+,K+ ATPase
what are the physiological processes that require Ca2+, Mg2+ and PO4
- cell division and growth
- muscle contraction
- neurotransmitter release
- coagulation of blood
- hormonal response
- bone formation
the amount of calcium excreted by the kidneys and absorbed by the intestines determines:
the total body Ca2+
what are the two forms that Ca2+, Mg2+, and PO4 in plasma exist in
- as free solutes
- inthe complexes with plasma proteins
bulk reabsorption of Ca2+ and PO4 occurs in:
the proximal tubule
(Ca2+ also gets reabsorbed in the thick ascending limb of the loop of henle)
what is the mechanism of Ca2+, Mg2+, and PO4 reabsorption
- active transport via Na+ - PO4 co-transporter
- passive diffusion along chemical and electrochemical gradients
- passive transport via solvent drag
bulk reabsorption of Mg2+ occurs in the
thick ascending limb of the loop of henle
Ca2+ and Mg2+ reabsorption in the thick ascending limb of the look of henle parallels:
Na+ reabsorption since Ca2+ and Mg2+ reabsorption in these segments occurs secondary to Na+ reabsorption
what do loop diuretics (durosemide) do
- inhibit sodium chloride reabsorption in the thick ascending limb of the loop of henle by competing for the Cl site on the Na+,K+-2Cl- cotransporter
- results in decrease in lumen positive electrochemical gradient that drives passive Ca2+ transport and its reabsorption
the ability to increase Ca2+ excretion makes loop diuretics a:
key component of therapy for hypercalemia
renal loss of Mg2+ and hypomagnesemia
- mutation in tight junction claudin paracellin-1 prevent Mg2+ reabsorption and result in the loss of Mg2+ with the urine and hypomagnesemia
- cattle and sheep - loss of Mg2+ in milk production with insufficient alimentary Mg2+ acts to increase the efficacy of Mg2+ reabsorption - to a max physiological limit. beyond this limit - hypomagnesemia leads to grass tetany
distal nephron - Ca2+, Mg2+, and PO4
- small amounts of filtered Mg2+ and PO4 are reabsorbed in the DCT and cortical CD
- almost all remaining Ca2+ is reabsorbed along the distal nephron
fractional excretion of Ca, Mg, PO4
small amounts are excreted in the final urine
<5% - Ca
10% - Mg
20% - PO4
what hormone is the major regulator of renal excretion of Ca, Mg PO4
parathyroid hormone
what is PTH
a polypeptide which is produced by and secreted form the parathyroid glands
PTH is secreted in response to: (2)
- decreased plasma concentrationsof Ca
- decreased plasma concentrations of Mg
what is the net effect of PTH
restoration in plasma levels of Ca and Mg
what is the net effect of PTH
restoration in plasma levels of Ca and Mg
PTH also stimulates the enzymatic conversion of VD to the active form ____ via the activation of ____ that catalizes the final hydroxylation of VD
calcitriol; 1-hydroxylase
what are two important functions of calcitriol
- stimulate intestinal absorption of calcium and phosphate
- increase renal tubular Ca reabsorption by the distal tubule
kidneys regulate the (HCO3-) by:
- conserving or excreting the HCO3- present in the glomerular ultrafiltrate
- producing new HCO3- which enters the body fluids as the kidneys excrete ammonium salts and titratable acids
the kidneys generate new HCO3- through:
- urinary excretion of ammonium (NH4) salts
- urinary excretion of titratable acids
what is the net result of proximal tubule reabsorption of bicarbonate
NaHCO3 disappears form the lumen and appears in the blood-side of the proximal tubule cells
proximal re-absorption of HCO3 is stimulated by (2)
- decreases in cell pH
- high levels of angiotensin II
what is the major buffer in the urine
phosphate
where does secretion of titratable acids occur
proximal tubules and collecting ducts
the rate of urinary excretion of TA depends on
- the urine pH
- efficiency of Na/H antiporter
- the rate of excretion of buffers
what happens in acidosis
TA
TA excretion is enhanced due to the low urine pH and a small increase in phosphate excretion
what is net acid excretion
- the sum of the NH4+ excretion and the TA excreted minus the bicarbonate that might escape in the urine
- equals the milliequivalents of new bicarbonate produced by the kidneys to restore the buffer reserves of the body fluids
what are the physiological significances of regulating water excretion in the kidney
- concentration or dilution of the urine leads to changes in plasma osmolality. changes in osmality of the plasma and extracellular fluid have significant effects on the volume of the cell (shrink or swell)
- concentration and dilution of the urine leads to alteration in blood volume and consequently to changes in cardiac function, blood pressure and perfusion of tissue
diuresis
when the renal excretion of water is increased and the urine flow is greater than normal
antidiuresis
when the renal excretion of water is decreased and the urine flow is less than normal
hypoosmotic
urine with an osmolality less than that of plasma
hyperosmotic
urine with an osmolality greater than that of plasma
water is freely filtered in
glomeruli
the proximal tubule is responsible for the reabsorption of the bulk of
filtered solutes
the peritubular capillary plexus collects:
water and solutes from proximal tubule
what are the conditions in the proximal plexus
- low capillary wall resistance
- low volume of plasma
- high protein concentration
- encourage bulk movement of water and solutes from the interstitium around PCT into the blood
water further moves from the interstitial fluid to the bloodstream of peritubular capillaries because:
of high oncotic pressure of blood plasma (starling’s forces) and low hydrostatic pressure within capillaries
what are the two types of nephrons
- cortical (short loop of henly)
- medullar (long loop of henle)
concentration or dilution of urine is ____ a result of ____ reabsorption or secretion of water
not; active
in the renal tubule, the movement of water to areas of high osmolality allowas for its:
passive reabsorption
what are the 3 components of the urinary concentrating system
- countercurrent multiplier system of the loop of henle
- countercurrent exchange system of the vasa recta
- antidiuretic hormone (ADH) and its effects on the permeability of the distal tubule and the collecting duct
where does the countercurrent multiplier sustem reside
in the loop of henle
what are the 3 differences between the limbs of the loop of henle
- thin decending limb (TDL) is permeable to water but not NaCL. water goes to the interstitial tissue, urine concentrates
- the thin ascending limb is permeable to NaCl but not water. NaCl goes to the interstitial tissue, urine dilutes
- the thick ascending limb (TAL) - impermeable to water actively pumps NaCl out of the tubule fluid and into the interstitium
what is the net result of the differences between the limbs of the loop of henle
form a osmotic gradient
the longer the loop of henle:
the greater the magnitude of the osmotic gradient (which enhances the ability to concentrate the urine)
the presence of absence of ____ determines wheter the urine is concentrated or dilute
vasopressin (ADH)
what happens in the absence of ADH
the DCT and CD are impermeable to water, preventing water movement out of the tubule into the hypertonic interstitium
what happens if ADH is present
the late DCT and CD are permeable to water - water will passively diffuse from the tubular lumen into the interstitium
the basic strategy for maintaining proper water balance is to regulate two elements:
- water output (regulated in part by ADH)
- water input (regulated through the sensation of thirst and behavioral response to this sensation)
secretion of ADH and sensation of thirst are regulated primarily in response to changes in:
plasma volume and osmolality
changes in plasma volume are monitored by:
- baroreceptors in the left atrium
- baroreceptors in the carotid sinus and aortic arch monitor arterial pressure
changes in plasma osmolality are monitored by:
osmoreceptors near the hypothalamus
what happens when plsama volume and/or arterial pressure decreases and/or plasma osmolality increases
an increase in thirst intensity occurs
what transporters are in the PCT
- Na+ H+ antiporter
- Na+ HCO3- cotransporter
what transporters are in the ascending loop of henle
Na+K+2Cl- cotransporter
what transporters are in the DCT
Na+Cl- cotransporter
what transporters are in the collectin ducts
- V2 receptor
- AQP2
- Na+K+ antiporter (also this is everywhere)
