After filtration, __________ is subject to reabsorption and secretion
tubular fluid
what are the 2 modes of transport for molecules in the tubular fluid?
transcellular
paracellular
in ________ transport, molecules move through tubular cells
transcellular
in ________ transport, molecules move between tubular cells
paracellular
________ diffusion requires a specific membrane protein
facilitated
what types of transporter proteins are used for facilitated diffusion?
uniporter
symporter
antiporter
65% of all filtered Na+ will be reabsorbed in the ____________
proximal tubule
20% of all filtered Na+ will be reabsorbed in the ____________
thick ascending limb
only ___% of the initial Na+ that was filtered remains once the filtrate reaches the collecting duct
3
what percentage of the Na+ that is initially filtered ends up being excreted?
less than 1%
what molecules are reabsorbed with Na+ in the proximal tubule?
glucose and amino acids are rebsorbed with Na+
what type of transporter is used to reabsorb glucose and amino acids from the proximal tubule?
symporters
use Na+ to pull glucose and AAs
what keeps intracellular Na+ low in the walls of the proximal tubule?
Active transport on basal side of the PT cells
the Na+/K+ antiporter
in the PT (proximal tubule), ________ move via paracellular transport
Water (and solutes)
how are small proteins reabsorbed in the PT? how is this accomplished?
Small proteins reabsorbed via endocytosis
requires ATP (active transport)
what is reabsorbed in the proximal tubule using a Na+/H+ antiporter?
Bicarbonate ions
reabsorption is NOT direct- coupled to the Na+/H+ exchanger
what reaction produces H+ and HCO3- in tubule cells?
Carbonic Anhydrase (CA) reaction
T/F: Organic ions are commonly bound to plasma proteins so they are not filtered at the glomerulus
true
how does the proximal tubule secrete organic ions?
The proximal tubule has organic cation and organic anion transporters to secrete these molecules into the tubular fluid
by the end of the proximal tubule, how much of the initial Na+, Cl-, and water are reabsorbed?
2/3 of Na+, Cl-, and water reabsorbed
small proteins too
in the proximal tubule, K+ and divalent cations are reabsorbed by __________
solvent drag
In the loop of Henle, __% of filtered NaCl and ___% of water is reabsorbed
25% of filtered NaCl and 15% of water is reabsorbed
the Descending thin limb is impermeable to ______, but permeable to ______
impermeable to salt, but permeable to water
the Ascending thin limb is impermeable to _____, but permeable to ______
impermeable to water, but permeable to salt
reabsorption in the Ascending and Descending thin limbs is a _______ process
passive
T/F: fluid in the ascending THICK limb is diluted
true
in the ascending thick limb, Na+ K+ 2Cl- symporter are found in the ______ membrane
apical
in the ascending thick limb, Na+ K+ ATPase transporters are found in the ________ membrane
basolateral
T/F: paracellular transport of monovalents and divalents in the ascending thick limb is due to solvent drag
FALSE
tubular fluid becomes positive when what is reabsorbed?
Cl-
Fluid leaving loop of henle is _________
hyposmotic
what establishes an osmotic gradient required for formation of hyperosmotic urine in the loop of henle?
the renal countercurrent mechanism
where is the “vasa recta” found?
at the bottom of the peritubular capillaries
most concentrated solute area
where does ADH work in the nephron? what does its absence cause?
ADH works on the collecting duct
absence of ADH causes a LARGE amount of DILUTE urine
in the DISTAL tubule, there is a Na+ Cl- symporter in the ______ membrane, and a Na+ K+ ATPase in _________ membrane
Na+/Cl- symporter on the apical membrane
Na+ K+ ATPase on the basolateral membrane
principal cells of the distal tubule have ___________ channels that reabsorb Na+ and secrete K+
epithelial sodium channels (ENaC)
what drives paracellular Cl- reabsorption in the distal tubule?
Na+ reabsorption drives paracellular Cl- reabsorption
how is K+ secreted in the distal tubule?
K+ secreted due to Na+ K+ ATPase
A positive or negative shift in water balance shifts extracellular volume away from _______ (normal)
euvolemia
___________ is released from the posterior pituitary, and helps control kidney volume regulation
Vasopressin or antidiuretic hormone (ADH)
at what osmolarity is vasopressin (ADH) released?
respond to osmolality above a set point of 275-290 mOsm/kg H2O
T/F: vasopressin release can be stimulated by changes in blood volume/pressure
true
what kind of baroreceptors respond to a decrease in blood pressure?
high pressure baroreceptors in aortic arch and carotid sinus
what kind of baroreceptors respond to a decrease in blood volume?
low pressure baroreceptors in left atrium and large pulmonary vessels
what effect does ADH have on the nephron?
ADH increases the permeability of the late distal tubule and the collecting duct to water
ADH (vasopressin) causes insertion of _______ into the apical membrane of the nephrons
aquaporins
ADH (vasopressin) increases permeability of medullary collecting duct to ______
urea
what happens when ADH levels are low?
solutes reabsorbed in distal tubule and collecting duct, but no water reabsorption; urine as dilute as 50 mOsm/kg H2O
what is the result of high ADH levels?
water reabsorbed as fluid passes through collecting duct; urine can be concentrated up to 1200 mOsm/kg H2O
_______________ and __________ stimulate events which increase sodium and water reabsorption
Angiotensin II and aldosterone
when is renin released?
renin released in response to:
1) a drop in perfusion pressure
2) decreased NaCl delivery to macula densa
3) sympathetic input to juxtaglomerular cells
what converts angiotensinogen into angiotensin 1?
Renin
what molecule is responsible for the conversion of angiotensin 1 into angiotensin 2?
ACE
angiotensin converting enzyme
where is ACE produced?
Endothelial cells of the lung and kindey
angiotensin 2 will stimulate _______ and ___________ secretion
aldosterone and ADH
how does aldosterone (from the adrenal cortex) Increase NaCl reabsorption?
increase NaCl reabsorption in the distal tubule and collecting duct by increasing transport protein synthesis
Natriuretic peptides are secreted when what occurs?
the heart dilates (during volume expansion)
what are the effects of natriuretic peptides? (theres 4 of them)
1) vasodilation of AFFERENT arterioles
2) vasoconstriction of EFFERENT arterioles
3) inhibits renin (and aldosterone)
4) inhibits ADH secretion
what is the net effect of natriuretic peptide release?
increases the excretion of NaCl and water
- does this by REDUCING reabsorption
during volume expansion, where in the nephron is the reabsorption of Na+ and Cl- actually increased?
- Thick ascending limb*
- Distal tubule
______ is a major determinant of membrane resting potential
potassium (K+)
____________ will depolarize Vm, while ____________ will hyper-polarize Vm
hyperkalemia will depolarize
hypokalemia will hyper-polarize
the kidneys typically excrete ________% of ingested K+
90-95%
In the _________ K+ is freely filtered
glomerulus
in the ______________ about 67% of filtered K+ is reabsorbed, mostly by paracellular route
proximal tubule
how is most K+ reabsorbed in the proximal tubule
mostly by paracellular route
how is K+ reabsorbed in the thick ascending limb of the nephron?
reabsorption by Na+K+2Cl- symporter and paracellular transport
K+ is secreted by principal cells of what nephron structures?
late distal tubule
and
collecting duct
what determines K+ secretion or reabsorption in the late distal tubule, and collecting duct?
depends on: - ATPase activity - K+ gradient and/or - apical K+ permeability
what 2 factors affect excretion of potassium?
1) plasma concentrations of K+
2) flow rate of tubular fluid
how do plasma potassium concentrations affect excretion?
- increased K+ stimulates aldosterone release
- aldosterone increases Na+ K+ ATPases in principal cells
how does the flow rate of tubular fluid affect the excretion of potassium?
increased flow rate increases K+ secretion
local response to bending cilium
increased _____ reabsorption will favor K+ secretion
Na+
which nephron segments will reabsorb potassium (K+) when plasma concentrations are low?
distal tubule
cortical collecting duct
if plasma concentrations of potassium are high, which structures will begin increasing secretion of potassium?
distal tubule
cortical collecting duct