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MEDSCI 142 > Renal System > Flashcards

Renal System Flashcards

1
Q

external anatomy of kidney

A

renal capsule
- innermost
- physical barrier
- protection against trauma
- maintains the shape of kidneys
adipose capsule
- middle
- padding
- physical protection
- maintains the position of the kidneys
renal fascia
- outermost
- anchors the kidneys to surrounding structures

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2
Q

lobes of kidney

A
  • ~8-12 lobes in human kidneys (i.e. multilobar)
  • one triangular section that extends out form medullary pyramids, including cortex and capsule
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3
Q

path of urine drainage

A

nephron → collecting duct → papillary duct → calyces (minor → major) → renal pelvis → ureter

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4
Q

path of bloodflow

A
  • renal artery → interlobar artery → arcuate artery → interlobular artery → afferent arteriole → glomerulus → efferent arteriole
  • efferent arteriole → peritubular capillaries of cortex → interlobular vein
  • efferent arteriole → descending vasa recta → peritubular capillaries of medulla → ascending vasa recta → interlobular vein
  • interlobular vein → arcuate vein → renal vein → inferior vena cava → heart
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5
Q

filtration membrane

A

fenestrated endothelium
- fenestrations/pores in glomerular capillaries
- small enough to stop red blood cells from escaping
- large enough to allow other components of plasma to pass through
basal lamina
- endothelial cells and podocytes both secrete basement membrane
- fuse to form basal lamina
- prevents filtration of larger proteins
slit membrane / diaphragm
- between interdigitating pedicels / foot processes of podocytes
- prevents filtration of medium-sized proteins

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6
Q

functions of kidney

A
  • maintaining homeostasis (i.e. a constant internal environment)
  • regulates water and electrolyte/ion balance
  • maintains blood osmolarity
  • regulates blood volume
  • regulates blood pressure
  • excretes metabolic waste products (e.g. urea/creatinine) or foreign chemicals (e.g. pesticides, drugs, food additives) from the body
  • regulates blood pH (e.g. via regulation of H+ and HCO3-)
  • regulates erythrocyte production
  • regulates hormone production (e.g. calcitriol/vitamin D)
  • regulates blood glucose levels
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7
Q

fluid distribution in the body

A

60% (i.e. 42L) fluid
intracellular → 2/3 of fluid (i.e. 28L)
extracellular → 1/3 of fluid (i.e. 14L)
- plasma → 20% of extracellular fluid (i.e. 2.8L, 55% of blood)
- interstitial → 80% of extracellular fluid (i.e. 11.2L)

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8
Q

sources of water gain

A
  • beverages → 64% (i.e. 1600mL)
  • foods→ 28% (i.e. 700mL)
  • metabolism → 8% (i.e. 200mL)
  • total → 2500mL
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9
Q

sources of water loss

A
  • urine → 60% (i.e. 1500mL)
  • skin → 24% (i.e. 600mL)
  • lungs → 12% (i.e. 300mL)
  • feces → 4% (i.e. 100mL)
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10
Q

net filtration pressure

A

determines glomerular filtration rate
~10 mmHg
GBHP + COP - CHP - BCOP
GBHP -> ~55 mmHg, mechanical pressure within the glomerulus, halfway between the afferent and efferent arterioles
COP -> ~0 mmHg, can be ignored
CHP -> ~15 mmHg, pressure exerted on plasma filtrate by the elastic recoil of the glomerular capsule, does not usually change
BCOP -> ~30 mmHg, the osmotic force of the proteins left in the plasma

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11
Q

autoregulation of glomerular filtration

A

myogenic mechanism
- increased blood pressure → increased stretching of smooth muscle fibres in afferent arteriole walls
- stretched smooth muscle fibres contract → narrow lumen of afferent arterioles
- decreased glomerular capillary pressure → decreased glomerular filtration rate
tubuloglomerular feedback
- increased glomerular filtration rate → increased tubular flow rate → increased tubular Na+, Cl- and water content
- sensed by macula densa cells in distal convoluted tubule → activity sensed by juxtaglomerular cells in afferent arteriole wall → decreased release of NO (i.e. nitric oxide, relaxes smooth muscle)
- afferent arteriole vasoconstriction → decreased glomerular filtration rate

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12
Q

neural control of glomerular filtration

A
  • baroreflex → increased sympathetic nerve activity → vasoconstriction of afferent arterioles
  • decreased glomerular capillary pressure → decreased glomerular filtration rate
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13
Q

ANP

A
  • atrial natriuretic peptide
  • stretching of atria of heart → secretion of ANP
  • relaxation of mesangial cells between capillaries → increases surface area available for filtration → increased glomerular filtration rate
  • acts to reduce renin, ADH and aldosterone release
  • reduces Na+ and water reabsorption
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14
Q

urine output

A
  • directly proportional to renal/mean arterial blood pressure
  • despite blood flow and glomerular filtration rate being relatively constant
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15
Q

reabsorption in proximal convoluted tubule

A
  • sodium-glucose symporter and sodium-hydrogen antiporter in apical membrane of cell → pumps Na+ into cell, brings glucose and water into cell
  • sodium potassium pump (i.e. Na/K ATPase) in basal membrane of cell → pumps Na+ out of cell, creates concentration gradient (i.e. low Na+ in cell)
  • glucose diffuses down its concentration gradient out of cell
  • osmolarity of filtrate is similar to plasma (i.e. 290 mOsmol)
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16
Q

reabsorption in descending loop of Henle

A
  • low permeability to ions and urea, high permeability to water
  • high salts and urea concentration in extracellular fluid of medulla (i.e. ~2-4x more concentrated than glomerular filtrate)
    • due to reabsorption of ions in ascending loop
  • water moves out into extracellular fluid
  • concentrates filtrate, higher osmolarity than plasma (i.e. 1200 mOsmol)
17
Q

reabsorption in ascending loop of Henle

A
  • impermeable to water, high permeability to ions
  • Na/K/Cl symporter in apical membrane of cell → pumps K+ into cell, Na+ and Cl- follows
  • sodium potassium pump (i.e. Na/K ATPase) in basal membrane of cell → pumps Na+ out of cell, creates concentration gradient (i.e. low Na+ in cell)
  • Cl- passively diffuses down its concentration gradient out of cell
  • dilutes filtrate, lower osmolarity than plasma (i.e. 100mOsmol)
18
Q

reabsoprtion in distal convoluted tubule

A
  • sodium potassium pump (i.e. Na/K ATPase) in basal membrane of cell → pumps Na+ out of cell, creates concentration gradient (i.e. low Na+ in cell)
  • Na+ passively diffuses into cell
  • water permeability depends on presence of ADH (i.e. antidiuretic hormone/vasopressin)
  • in absence, water permeability decreases → dilute urine (i.e. 100 mosmol)
    • alcohol inhibits ADH → dilute urine → dehydration
  • in dehydrated state, ADH is present → concentrated urine
19
Q

countercurrent mechanism

A
  • vasa recta blood flows in opposite direction to tubular filtrate flow
  • blood removes water extracellular fluid, maintains high concentrations of NaCl in extracellular fluid
20
Q

primary mechanism of ADH release

A
  • osmoreceptors
  • innervate the hypothalamus
  • have stretch-activated sodium channels
  • shaped like pyramid, has tethered arms
  • when ECF is hypertonic water is drawn out of cells
  • cell shrinks → cell wall in arms is stretched → sodium channels open
  • sodium enters cells → triggers action potential
  • sense small increases in Na+ concentration / osmolarity (i.e. high salt consumption / low water intake)
  • sends signal to posterior pituitary → ADH released into bloodstream
21
Q

secondary mechanism of ADH release

A

increase in blood pressure/volume
- significant increase in plasma volume / blood pressure (i.e. 10-15%)
- increased firing rate of baroreceptors in atrium and large vessels
- inhibits release of ADH from posterior pituitary → bloodstream
decrease in blood pressure/volume
- significant decrease in plasma volume / blood pressure (i.e. 10-15%)
- decreased firing rate of baroreceptors in atrium and large vessels
- stimulates release of ADH from posterior pituitary → bloodstream

22
Q

threshold of ADH release

A

~280 mOsm

23
Q

threshold for thirst sensation

A

~295 mOsm

24
Q

plasma ADH vs plasma osmolarity

A
  • plasma ADH increases as plasma osmolarity increases
  • normal plasma osmolarity is 290 mOsm, usually some ADH present
  • sensitivity of ADH release is affected by blood volume
  • increased blood volume → decreased sensitivity
  • decreased blood volume → increased sensitivity
25
Q

action of ADH

A
  • acts on last part of convoluted distal tubule and collecting duct in renal medulla
  • acts on ADH receptors on basal membrane of principal cells
  • stimulates insertion of aquaporin-2 (i.e. water channel) containing vesicles into apical membrane
  • water can now move from tubule into cell
  • water moves through relatively permeable basolateral membrane via osmosis (i.e. ECF in medulla has high solute concentration)
  • facilitates reabsorption of water (i.e. water retention) into blood → decreased plasma osmolarity, increased blood volume → negative feedback on osmoreceptors
  • concentrated urine (i.e. max 1200mOsm, depends on amount of ADH), small volume
26
Q

triggers for renin release

A
  • low filtrate Na+ content, low blood pressure, low blood volume
  • macula densa cells sense decrease in filtrate Na+ → increased prostaglandin release → stimulates renin release
  • decreased perfusion pressure in juxtaglomerular cells → stimulates renin release
  • low blood pressure/volume → increase in sympathetic activity → decrease in afferent arteriole pressure → stimulates renin release
27
Q

renin -> angiotensin

A

renin converts angiotensinogen → angiotensin I
- rate limiting step
- angiotensinogen is a circulating precursor, made by liver
ACE converts angiotensin I → angiotensin II
- ACE is angiotensin converting enzyme, released by lungs

28
Q

actions of angiotensin II

A

maintains glomerular filtration rate
- potent vasoconstrictor
- causes constriction of both afferent and efferent arterioles
- tubuloglomerular feedback counters effect of Ang II on afferent arteriole (i.e. dilates), so preferentially constricts efferent arterioles
- afferent arteriole → effect of tubuloglomerular feedback dominates
- efferent arteriole → effect of angiotension II dominates
increases Na+ reabsorption in the proximal tubule
- upregulates Na+/H+ cotransporters in basolateral membrane
- improves reabsorption of sodium into blood
- more Na+ and water retained
increases aldosterone release
act centrally to stimulate thirst and salt intake, release ADH, increase sympathetic activity

29
Q

aldosterone

A

release
- from adrenal cortex
- in response to angiotensin II
actions
- acts on last part of convoluted distal tubule and collecting duct (i.e. same as ADH)
- increases production of Na+/K+ ATPase in basolateral membrane
- increases Na+ reabsorption and K+ excretion
- water reabsorption may also increase via osmosis, depends on presence of ADH
- more Na+ (and water) retained

30
Q

timescale of what body restores

A
  1. blood pressure (i.e. baroreceptors)
  2. osmolarity (i.e. minutes → capillary-fluid shift; hours → hormonal, ADH, aldosterone)
  3. blood volume (i.e. same as above)
  4. blood cells

MEDSCI 142 (6 decks)

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