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Physiology > Lecture 28 Kidneys > Flashcards

Lecture 28 Kidneys Flashcards

1
Q

Functions of the Kidneys

A
  1. osmoregulation = water and solute balance (ECF osmolarity -290mOsm and volume total H20
  2. ion (electrolyte) balance (Na+, K+, Ca2+, etc.)
  3. acid-base regulation (H+, HCO3-)
  4. excretion - urea + other soluble waste products
  5. endocrine function - erythropoietin
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2
Q

Regions

A

Cortex
medulla
renal pelvis -> ureter

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3
Q

Nephron

A

functional unit of the kidney

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4
Q

Renal corpuscle

A

glomerulus

glomerular (Bowman’s) capsule

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5
Q

Renal Tubule

A

proximal convoluted tubule (PCT)
loop of Henle - descending limb, ascending limb
distal convoluted tubule
collecting duct

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6
Q

Blood Supply

A

glomerulus - afferent arteriole
glomerular capsule- efferent arteriole
renal tubule- peritubular capillaries
PCT - vasa recta

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7
Q

cortical nephrons

A

mostly in cortex, short loops of henle

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8
Q

juxtamedullary nephrons

A

long loops of Henle extend deep into the medulla

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9
Q

three primary processes of the Nephron

A

filtration
reabsorption
secretion

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10
Q

Filtration: Glomerulus and Glomerular Capsule

A

formation of protein-free filtrate

filtrate contains H20 + small to medium sized solutes (ions, glucose, urea, etc.)

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11
Q

Filtration membrane

A

consists of three layers
fenestrated capillaries
basement membrane
filtration slits of podocytes

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12
Q

Net filtration pressure

A

Blood pressure 55mm Hg (in glomerular capillaries)

  • C.O.P -30 mm Hg (from plasma proteins in cap.)
  • Tissue P -15mm Hg (fluid backpressure in glomerulacap)

=NFP 10 mm Hg

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13
Q

Glomerular filtration rate

A

GFR = 125 mL/min

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14
Q

GFR

A

can be estimated by measuring clearance of a substance that is filtered into the nephron but not reabsorbed or secreted. e.g. inulin, creatinine
GFR= insulin clearance = [inulin]urine X urine flow (mL/min) / [inulin]plasma

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15
Q

Reabsorption: PCT

A

“mass reabsorption” in the PCT, isosmotic with ECF (300 mOsm)
approx. 70% filtered fluid is reabsorbed from the PCT into the ECF (peritbular capillaries)

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16
Q

Epithelial Transport in the PCT

A 
transport proteins (pumps, carriers, channels) in apical and basolateral membranes 
microvilli on apical surface face into lumen of tubule (increase surface area)
17
Q

Transport mechanisms

Na+

A

diffusion through channels in the apical membrane

primary active transport: Na+/K+ ATPase in the basolateral mambrane

18
Q

Transport mechanisms glucose

A 
secondary active transport with Na+ (SGLT) across apical membrane 
facilitated diffusion (GLUT) across basolateral membrane
19
Q

Transport mechanisms amino acids

A

cotransport with Na+ similar to glucose

20
Q

Transport mechanisms H20

A

via osmosis, follows movement of solutes

21
Q

Glucose reabsorption in the PCT

A

normally, all glucose filtered into nephrons is reabsorbed

at very high glucose levels, glucose transporters become saturated

22
Q

transport maximum

A

maximal rate of glucose reabsorption

23
Q

renal plasma threshold

A

minimum plasma [glucose] at which glucose appears in urine

24
Q

normal plasma

A

normal plasma [glucose] 90 mg/dL &laquo_space;renal plasma threshold - 180 mg/dL

25
Q

in diabetes mellitus

A

high plasma [glucose] > renal plasma threshold -> glucose in urine
-> osmotic diuresis

26
Q

Vertical Osmotic Gradient: Loop of Henle

A

Counteractive multiplier mechanism
active transport of NaCl
osmotic movement of H20

27
Q

Active transport of NaCl

A

NaCl pumped out of ascending limb (thick region)

decrease osmolarity of tubular fluid and increase osmolarity of surrounding ECF

28
Q

Osmotic movement of H20

A

H20 moves out of descending limb due to increase ECF osmolarity
differential permeability properties along the loop of Henle:
descending limb : permeable to H20, impermeable to NaCl Ascending limb: impermeable to H20, permeable to NaCl (active transport)

29
Q

Countercurrent flow

A 
opposite direction of flow in descending and ascending limbs 
concentrated fluid (1200 mOsm) formed at base of loop and surrounding ECF 
dilute fluid (100 mOsm) at top of ascending limb enters DCT
vasa recta around loop of Henle helps maintain vertical osmotic gradient
30
Q

Tubular secretion: PCT and DCT

A

active transport of ions and waste products (H+, K+, organic acids) into tubules
occurs in the PCT and DCT

31
Q

Collecting Duct: Regulated Reabsorption of H20

A 
hypotonic fluid (100 mOsm) enters collecting duct (CD) from DCT 
as CD passes down the medulla, it encounters high osmolarity of surrounding ECF 
permeability of the CD to H20 is variable and regulated
32
Q

Antidiuretic Hormone

A

(ADH)(vasopressin)
secreted by the posterior pituitary gland
ADH stimualtes insertion of aquaporins into the membrane of the CD epithelial cells
promotes reabsorption of H20 from the CD back into the ECF

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