Renal Physiology Part II

Question 1

Describe the mechanisms underlying the reabsorption of solute from the renal tubules into the blood.

Answer 1

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

Question 2

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?

Answer 2

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

Question 3

Regulation of reabsorption of sodium and water:

the location of active sodium reabsorption

Question 4

Regulation of reabsorption of sodium and water:

the pumps involved in active sodium reabsorption

Question 5

links between the reabsorption of sodium and water and the establishment of renal concentration gradients

Question 6

the relationship between sodium reabsorption and glucose reabsorption

Question 7

the relationship between sodium reabsorption and water reabsorption

Question 8

antidiuretic hormone (ADH)

Answer 8

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

Question 9

atrial natriuretic peptide (ANP)

Answer 9

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

Question 10

aldosterone

Answer 10

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

Question 11

parathyroid hormone (PTH)

Answer 11

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,

Question 12

Describe the importance of tubular secretion using specific examples of secreted substances.

Answer 12

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-

Question 13

Describe the medullary osmotic gradient

Answer 13

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)

Question 14

Explain the mechanism of countercurrent exchange and its importance in renal function.

Answer 14

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

Question 15

Describe the consequences of overhydration

Answer 15

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

Question 16

Define diuretic. List several examples of diuretics and explain their effects on urine production.

Answer 16

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

Question 17

Define renal clearance. Explain its clinical importance and how it is measured.

Answer 17

volume of plasma from which kidneys remove particular substance in a given time, C=UV/P

Question 18

Differentiate chronic renal disease and renal failure.

Answer 18

Question 19

What is reabsorbed during tubular reabsorption?

Answer 19

almost all organic nutrients, water and ions (regulated hormonally)

Question 20

facultative water reabsorption

Answer 20

aquaporins inserted in collecting ducts if ADH present

Question 21

What’s reabsorbed in PCT?

Answer 21

glucose, AAs, other nutrients, Na+ and HCO3- and many other ions, water

Question 22

What’s secreted into PCT?

Answer 22

some drugs, NH4+, H+ to balance acid-base

Question 23

thin descending limb of loop of Henle permeability

Answer 23

highly permeable to water, so water leaves filtrate and enters surrounding tissues
kinda permeable to solute - mostly salt, some solute enters

Question 24

thin ascending limb of loop of Henle permeability

Answer 24

not permeable to water, passively permeability to solute, solute leaving filtrate, urea entering

Question 25

thick ascending limb of loop of Henle permeability

Answer 25

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

Question 26

Explain countercurrent multiplication and its importance in renal function.

Answer 26

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

Question 27

urea recycling

Answer 27

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

Question 28

Describe the consequences of dehydration.

Answer 28

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

Question 29

inulin

Answer 29

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)

Question 30

chronic renal disease

Answer 30

GFR < 60 ml/min lasting for at least 3 months, leading causes are diabetes mellitus and htn

Question 31

renal failure

Answer 31

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

Question 32

Which part of the nephron is responsible for reabsorbing most water and nutrients from renal filtrate?

Answer 32

proximal convoluted tubule

Question 33

Once the filtrate reaches the ____, reabsorption becomes dependent upon the body’s needs and regulated by hormones.

Answer 33

distal convoluted tubule

Question 34

ADH promotes reabsorption of what?

Answer 34

water

Question 35

Aldosterone promotes reabsorption of what?

Answer 35

sodium

Question 36

parathyroid hormone promotes reabsorption of what?

Answer 36

calcium

Question 37

nephron loops are the site of ___ secretion

Answer 37

only urea molecules

Question 38

what two places in nephron secrete only K+?

Answer 38

DCTs and collecting ducts

Question 39

what is absorbed in nephron loops?

Answer 39

H20, Na+, K+, Cl-, Ca2+, Mg2+

Question 40

The reabsorption of sodium in the DCT is regulated primarily by __________

Answer 40

Aldosterone increases Na+ reabsorption, and atrial natriuretic peptide (ANP) inhibits Na+ reabsorption.

Question 41

Filtrate in a typical healthy nephron will NEVER include

Answer 41

blood cells and proteins

Question 42

When the macula densa detects an increase in NaCl concentration in the renal filtrate, what happens to the glomerular filtration rate (GFR)?

Answer 42

GFR decreases

Question 43

If the osmotic pressure in the glomerular capillaries increased from 28 mmHg to 35 mmHg due to dehydration, would net filtration increase or decrease?

Answer 43

net filtration would decrease

Question 44

Where in the nephron can secretion take place?

Answer 44

proximal tubule, distal tubule, collecting duct

Question 45

What can be accurately said about the relationship between glucose in the blood and the amount of glucose filtered through the glomerular membrane?

Answer 45

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.

Question 46

Urea transport into the medullary collecting duct is enhanced by ___

Answer 46

ADH