lecture 29

Question 1

true or false: GFR changes very little over a wide range of blood pressures

Answer 1

true because GFR is maintained by regulating renal blood flow

Question 2

vasoconstriction and vasodilation of afferent arteriole

Answer 2

• VC will increase resistance, decrease blood flow into glomerulus, Ph and GFR
• VD will decrease resistance, increase blood into glomerulus, Ph and GFR

Question 3

vasoconstriction of efferent arteriole

Answer 3

• blood will pool in the glomerulus because efferent is constricted therefore pH and GFR will be higher

Question 4

what are some mechanisms to keep GFR constant over a wide range of blood pressure

Answer 4

• we can vasoconstrict or vasodilate to regulate blood flow into the glomerulus and dictate the driving force behind GFR

Question 5

Mechanisms of auto regulation of GFR (How will we vasoconstrict or vasodilate)

Answer 5

Myogenic autoregulation is a self regulating machanism
- when flow is to high or when stretch on the wall of the vessel is to high that leads to reflexive vasoconstriction because mechanically gated channels on vascular smooth muscle membrane will open and let cations in therefore cell will depolarize and cause opening of voltage gated calcium channels to open. Ca2+ in smooth muscle will cause more cross bridge cycling and increase contraction which will increase arteriole resistance therefore decreasing blood flow which will decrease pressure through vessel

Question 6

Tubuloglomerular feedback

Answer 6

• stimulus: GFR is to high, flow into glomerular is above 180 L/day
• More fluid through bowman’s space, along proximal tubule and through nephron
• Macula densa cells sense flow and secrete paracrines that will act on afferent arteriole and will cause afferent arteriole to vasoconstrict
• Afferent arteriole resistance increases therefore hydrostatic pressure in glomerulus decreases and GFR decreases

Question 7

The juxtaglomerular apparatus

Answer 7

Region where the ascending limb of loop of henle passes between afferent and efferent arterioles

Question 8

filtration

Answer 8

movement from blood to lumen

Question 9

reabsorption

Answer 9

from lumen to blood

Question 10

secretion

Answer 10

from blood to lumen

Question 11

excretion

Answer 11

from lumen to outside of the body

Question 12

most reabsorption occurs in ______

Answer 12

the proximal tubule

Question 13

why is reabsorption primarily driven by Na+ movement

Answer 13

because Na+ will be reabsorbed by active transport (sodium-potassium pump) and will create and electrochemical gradient and driving force for anion reabsorption (when Na+ goes Cl- goes) and then following solute reabsorption water will move by osmosis

Question 14

on which membrane of the epithelial cell would you need an active transporter for Na as it is reabsorbed

Answer 14

• we would need it on the basolateral membrane because Na+ ions would move from and area of low to high concentration

Question 15

Sodium reabsorption (primary active transport)

Answer 15

• In the tubule lumen there is a higher concentration of Na+ than in the proximal tubule cell therefore Na+ will cross the apical membrane with epithelium Na+ channels (ENaC), moving down it electrochemical gradient
• now in proximal tubule the concentration of Na+ is less than in the ECF therefore Na+ is pumped out of basolateral side using sodium-potassium pump
• Na+ is reabsorbed

Question 16

sodium-linked secondary active transport

Answer 16

• in the tubule lumen there is a high concentration of Na+ and a low concentration of glucose
• Na+ would move down its electrochemical gradient across the apical membrane and use this energy to pull glucose in against its concentration gradient
• once inside glucose will leave out of the basolateral side using GLUT
• and Na+ is pumped out of the basolateral side by the sodium potassium pump

Question 17

what causes reabsorption in peritubular caprillaries

Answer 17

• colloid osmotic pressure is higher in peritubular capillaries than afferent arteriole therefore there is a strong driving force for reabsorption of substances into the peritubular capillaries and therefore they go back into circulation

Question 18

secretion

Answer 18

• H+ and K+ important in homeostatic regulation
• urea, uribilinogen, creatinine, NH4+, drugs (anything toxic)
• increasing secretion increase nephron excretion

Question 19

excretion

Answer 19

• at the end of the collecting duct when filtrate can no longer be modified
• output = urine
• shouldn’t contain anything useful that was filtered (glucose, amino acids, or useful metabolites)