Renal System Flashcards
external anatomy of kidney
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
lobes of kidney
- ~8-12 lobes in human kidneys (i.e. multilobar)
- one triangular section that extends out form medullary pyramids, including cortex and capsule
path of urine drainage
nephron → collecting duct → papillary duct → calyces (minor → major) → renal pelvis → ureter
path of bloodflow
- 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
filtration membrane
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
functions of kidney
- 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
fluid distribution in the body
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)
sources of water gain
- beverages → 64% (i.e. 1600mL)
- foods→ 28% (i.e. 700mL)
- metabolism → 8% (i.e. 200mL)
- total → 2500mL
sources of water loss
- urine → 60% (i.e. 1500mL)
- skin → 24% (i.e. 600mL)
- lungs → 12% (i.e. 300mL)
- feces → 4% (i.e. 100mL)
net filtration pressure
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
autoregulation of glomerular filtration
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
neural control of glomerular filtration
- baroreflex → increased sympathetic nerve activity → vasoconstriction of afferent arterioles
- decreased glomerular capillary pressure → decreased glomerular filtration rate
ANP
- 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
urine output
- directly proportional to renal/mean arterial blood pressure
- despite blood flow and glomerular filtration rate being relatively constant
reabsorption in proximal convoluted tubule
- 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)
reabsorption in descending loop of Henle
- 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)
reabsorption in ascending loop of Henle
- 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)
reabsoprtion in distal convoluted tubule
- 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
countercurrent mechanism
- vasa recta blood flows in opposite direction to tubular filtrate flow
- blood removes water extracellular fluid, maintains high concentrations of NaCl in extracellular fluid
primary mechanism of ADH release
- 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
secondary mechanism of ADH release
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
threshold of ADH release
~280 mOsm
threshold for thirst sensation
~295 mOsm
plasma ADH vs plasma osmolarity
- 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
