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Physiology > lecture 12 - renal physiology 2 > Flashcards

lecture 12 - renal physiology 2 Flashcards

1
Q

process in the formation of urine?

A

filtration

reabsorption

secretion

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2
Q

what is the total amount excreted?

A

amount filtered - amount reabsorbed + amount secreted

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3
Q

specialised epithelial cells of the nephron

A

whole length is lined by specialised epithelial cells
specialisation changes along the tube

thin limb - flat epithelial cells
• don’t have many mitochondria or organelles as aren’t active
• allow reabsorption of water - passive process

collecting ducts - different cell types

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4
Q

what is reabsorption?

A

movement of solutes/fluid out of filtrate and into capillaries, via epithelial transport mechanisms

from the lumen, across epithelial cells, into ECF into peritubular capillary

different mechanisms dependent on the solute being moved

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5
Q

epithelial transport mechanisms

A

route taken by solute depends on their electrochemical gradient and permeability of epithelial junctions

can either be moved by: 
• epithelial transcellular transport 
• paracellular transport pathway 
• passive transport 
• active transport
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6
Q

epithelial transcellular transport

A

substances cross apical and basolateral membranes of the tubule epithelial cells

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7
Q

paracellular transport pathway

A

substances pass through the cell-cell junction between 2 adjacent cells

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8
Q

passive transport

A

diffusion
leak channels
paracellular transport

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9
Q

active transport

A 
membrane channels 
transporters 
co-transporters 
pumps 
carriers
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10
Q

proximal convoluted tubule

A

structure specialised for:
• reabsorption
• secretion

microvilli on apical surface maximise SA available for reabsorption

ER, Golgi, lysosomes and vacuoles all for synthesis of membrane proteins

interdigitations of the basolateral membrane shorten distance to mitochondria - active transport

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11
Q

Na+ reabsorption at PCT

A

conc of Na+ is higher in filtrate than the cells so passive movement of Na+ into the cells

Na+ is the main solute reabsorbed

electrochemical gradient changes due to Na+ moving, so Cl- moves to equalise it and water move to maintain osmotic gradient

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12
Q

what are the 3 main mechanisms for Na+ transport into the cell

A

sodium-potassium pump

sodium-glucose transporter

sodium-proton pump

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13
Q

water reabsorption at PCT

A

paracellular route via osmosis

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14
Q

glucose reabsorption at PCT

A

co-transport at apical membrane

carrier at basolateral membrane

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15
Q

urate reabsorption at PCT

A

organic anion transporters

paracellular route

passively transcellular route

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16
Q

low molecule weight proteins / amino acid reabsorption at PCT

A

endocytosis at apical membrane

breakdown in lysosome

release of amino acid

17
Q

what is renal threshold?

A

plasma concentration of substrate at transport maximum

18
Q

diabetes mellitus

A

excessive glucose concentration saturates number of carriers and excess glucose appears in urine

some will pass into the nephron and out in the urine as the threshold is exceeded

19
Q

secretion at PCT

A

transport of molecules from peritubular capillaries into tubule - active process

20
Q

how much reabsorption occurs in the PCT?

A

around 66%

tubular fluid leaving PCT is isometric with plasma = ~300mOsm

21
Q

how does osmolarity change through the nephron?

A

isosmotic fluid leaving PCT becomes more concentrated in the defending limb

removal of solute in the thick ascending lim creates a hypo osmotic fluid

permeability to water and solutes in DCT and collecting duct is regulated by hormones

final urine osmolarity depends on reabsorption in the collecting duct

22
Q

formation of urine

A
  • descending limb permeable to water and impermeable to solutes
  • NaCl transport from ascending limb into interstitial
  • thick ascending limb impermeable to water
  • collecting duct relatively impermeable to water and permeable to urea
  • dilute urine produced
23
Q

formation of concentrated urine

A

increase water reabsorption

ADH makes collecting duct permeable to water

countercurrent systems maintain osmotic gradient in the medullary interstitium

24
Q

properties of countercurrent exchange systems

A
  • 2 flows in opposite directions
  • vessels anatomically close
  • passive transfer of molecules from 1 vessel to another
  • water reabsorbed from collecting duct results in concentrated urine
25
Q

what is a countercurrent multiplier system?

A

countercurrent exchange enhanced by active transport of solutes

eg. loop of henle and vasa recta

26
Q

whats different peritubular capillaries and vasa recta?

A

peritubular capillaries are around cortical nephrons

vasa recta are around juxtamedullary nephrons

27
Q

what happens in the descending loop of the limb?

A

water reabsorption

increased filtrate osmolarity

28
Q

what happens in the ascending loop of the limb?

A

active solute reabsorption

decreased filtrate osmolarity

29
Q

what happens in the descending limb of the vasa recta?

A

water reabsorption

solute uptake

increased blood osmolarity

30
Q

what happens in the ascending limb of the vasa recta?

A

water reabsorption

decreased blood osmolarity

31
Q

how is NaCl actively reabsorbed by the thick ascending limb?

A

sodium and potassium cotransported with chlorine

sodium/potassium pump used

no paracellular transport

32
Q

how is pH tightly regulated?

A

buffers

respiratory adjustment - CO2

renal adjustment

33
Q

buffers used to regulate pH

A

cellular proteins

haemoglobin

HPO4 2-

HCO3-

34
Q

renal adjustment to regulate pH

A

directly by excreting or reabsorbing H+

indirectly by excreting or reabsorbing HCO3-

acidosis

alkalosis

35
Q

what is acidosis

A

alpha (type A) intercalated cells in collecting duct excrete H+ and reabsorb HCO3-

36
Q

what is alkalosis

A

beta (type B) interacted cells in the collecting duct excrete HCO3- and reabsorb H+

37
Q

what happens in acidosis?

A

high H+ concentration

presence of large amounts of carbonic anhydrase

produces H+ & HCO3-

hydrogen ATPase pumps H+ into the collecting duct to be excreted

HCO3- go back into the extracellular fluid to combine with H+ to prevent pH changing

38
Q

what happens in alkalosis?

A

low H+ concentration

similar process to acidosis - channels are flipped around

HCO3- exchange on the apical membrane & HCO3- excreted

H+ actively moved into ECF to increase H+ concentration to increase pH

Physiology (29 decks)

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