Lecture 31

Question 1

How is GFR regulated?

Answer 1

changing the hydrostatic pressure by regulating flow through arterioles
increasing resistance of afferent arteriole (majority)= less blood flow, decreased BP/GFR
increasing resistance of efferent arteriole = blood pooling in glomerulus, less blood flow but increased GFR and BP

Question 2

Describe the two methods of autoregulation of GFR

Answer 2

1) Myogenic
stretch-activated cation channels in smooth muscle activated by increase in pressure, depolarization leads to contraction
2) Tubuloglomerular
in the juxtaglomerular apparatus, macula densa cells ascending limb of loop of Henle sense increased BP, increased concentrations of Na and Cl, release paracrine signals that act on afferent arteriole to constrict

Question 3

What are some extrinsic factors that regulate GFR

Answer 3

hormones –> angiotensin II, epinephrine
Sympathetic neurons
norepinephrine acts on α1 receptors, activates causes vasoconstriction of both afferent (main) and efferent arterioles

Question 4

What are the two methods of reabsorption

Answer 4

1) transepithelial –> crosses both apical and basolateral membranes
2) paracellular –> crosses tight junctions

Question 5

What drives reabsorption, and how does it work?

Answer 5

Na movement –> goes down electrochemical gradient, anions follow, water follows through osmosis
1) primary
sodium flows down concentration gradient through a channel into proximal tubule cell, then gets pumped against concentration gradient through basolateral membrane via Na-K-ATPase, K leaves via leak channel
2) secondary
sodium cotransports another molecule, other molecule leaves via diffusion, sodium leaves through ATPase

Question 6

How does reabsorption work in the peritubular capillaries?

Answer 6

hydrostatic pressure has decreased such that colloid osmotic pressure wins out

Question 7

Describe the micturition reflex

Answer 7

bladder is made of smooth muscle, there are 2 sphincters (internal vs external). Internal is passively contracted while external is contracted through tonic signalling of motor neurons. Through stretch receptors and either CNS input, conscious/unconscious, signal sent via parasympathetic neurons that cause smooth muscle of bladder to contract. This wave forces open the internal sphincter. the somatic motor neurons stop firing, relaxing the external sphincter.