SUGER Flashcards
what is the blood filtering component of the kidney?
renal corpuscle
what comprises the glomerular filtering barrier?
fenestrated capillary endothelium
glomerular basement membrane (double thickness)
podocyte foot processes
which protein maintains filtration slits?
nephrin
why is the glomerular basement membrane negative?
heparin sulfate
which repels negative molecules e.g albumin
what percentage of the cardiac output do the kidneys receive?
20%
about 1L/min
do glomerular filtrate and plasma have the same concentration?
yes, except albumin
what is the charge of the glomerular basement membrane (GBM)?
negative
why does the GBM repel proteins?
both proteins and the GBM have a negative charge
what comprises the renal corpuscle?
glomerular tuft and Bowman’s capsule
as well as afferent and efferent arteriole
what is the glomerular tuft?
convoluted, interconnected glomerular capillaries protruding into Bowman’s capsule
what can pass through the filtration barrier?
glucose
water
urea
creatinine
ions
amino acids
name cells comprising the glomerulus
endothelial cells and mesangial cells
what are mesangial cells?
modified smooth muscle cells
specialised renal pericytes
which stain shows mesangial cells?
PAS
which pressures affect glomerular filtration?
hydrostatic pressure out of Bowman’s capsule
hydrostatic pressure out of capillary
oncotic pressure in capillary
what is the net filtration pressure (NFP)?
total pressure that promotes filtration
determined by:
hydrostatic pressure out of the capillary
hydrostatic pressure out of Bowman’s capsule
oncotic pressure in capillary (determined by albumin)
which is the only protein that should be found in urine and why?
Tamm Horsfall
renal origin - produced in LOH
what is the approximate glomerular filtration rate (GFR)?
120 ml/min
how is GFR measured in a clinic, and why is this substance used?
creatinine
not metabolised
freely filtered
not absorbed in tubules
only a small about secreted by tubules
what is renal clearance?
how quickly a particular substance is removed from the plasma by the kidney and excreted in urine
so something with a high renal clearance means that it will be quickly removed from the blood, and vice versa
how is GFR increased?
dilation of afferent arteriole
constriction of efferent arteriole (these opposite effects are intuitive - it makes sense that constricting the efferent arteriole causes a back of up fluid in the glomerulus)
how is GFR decreased?
constriction of aa
dilation of ea
what is tubuloglomerular feedback?
adaptive mechanism that links the rate of glomerular filtration to the concentration of salt in the tubule fluid at the macula densa
maintains constant GFR
what is the rate of renal blood flow?
1 L/minute
what is the juxtaglomerular apparatus?
involved in tubuloglomerular feedback
is tubuloglomerular feedback intrinsic or extrinsic?
intrinsic - not dependent on neural systems
what detects fall in NaCl?
macula densa in DCT
what detects fall in blood pressure?
granular cells in afferent arteriole
what is the effect of a fall in NaCl or blood pressure?
renin secreted from granular cells to act on RAAS
angiotensin II is produced
- ADH released
- aldosterone released
- increases blood pressure
how is GFR usually reported?
ml/min/surface area
is GFR measured directly?
no
use creatinine
where does bulk reabsorption occur?
PCT mainly
what does the PCT reabsorb?
glucose, amino acids, lactate, Na+, phosphate, hydrogencarbonate ions, H+, water, Cl-
what does the PCT secrete?
organic ions
in the PCT, how are water and solutes reabsorbed?
bulk transport
what is the difference between glomerular filtrate and plasma?
blood plasma contains suspended cells, proteins, and big molecules, but glomerular filtrate typically does not. proteins cannot pass through the glomerular capillary membranes
what size molecule can fit through the filtration barrier?
less than 10kDa
how do you calculate GFR?
GFR = NFP x kF
what determines blood oncotic pressure?
albumin
how many times is plasma filtered a day?
60 times in 24h
how many L of plasma do we have?
3L
how many mL of plasma is filtered a day?
180L in 24h
what structure initiates tubuloglomerular feedback?
juxtaglomerular apparatus
describe tubuloglomerular feedback
by juxtaglomerular apparatus
renin is secreted from granular cells to act on RAAS
this is due to:
- a fall in NaCl detected by macula dense in DCT
- a fall in blood pressure detected by granular cells in afferent arteriole
- sympathetic activation
where are macula densa cells?
DCT
what are the types of cells in the juxtaglomerular apparatus?
macula densa - DCT
juxtaglomerular cells/ granular cells - afferent arteriole
extraglomerular mesangial cells
what is reabsorbed at the PCT?
glucose, amino acids, lactate, Na+, phosphate, HCO3-
what is secreted at the PCT?
organic ions
describe the process of sodium reabsorption in the PCT
- driven by Na/ K+ ATPase on the basolateral membrane
- Na+ is actively transported out of the proximal convoluted tubule epithelial cell via the Na+/ K+ ATPase pump (3Na out, 2K in) into the interstitial fluid
- this lowers the concentration of Na+ intracellularly
- thus Na+ moves from tubular lumen into cell lining PCT
- Na+ cotransports glucose or phosphate (secondary active transport)
or - Na+ anti ported with H+ to maintain electrical charge
- once in cell, Na is pumped into interstitium as described before
- water follows by osmosis
the Na/ K ATPase is energy dependent
what is the basolateral membrane in renal physiology?
cell membrane which is oriented away from the lumen of the tubule
what is the apical membrane in renal physiology?
apical or luminal membrane refers to the cell membrane which is oriented towards the lumen
describe bicarbonate reabsorption
involves that reversible equation that keeps coming up
dependent on secretion of H+ whilst removing Na from the lumen
H+ combines with bicarbonate (HCO3-) to produce H2CO3 (carbonic acid) - carbonic anhydrase
carbonic acid dissociates into water and carbon dioxide
carbon dioxide diffuses through cell membrane
water reabsorbed through osmosis through AQP1 channels
inside the cell, water and carbon dioxide combine to form carbonic acid which again dissociates into bicarbonate and H+
H+ recycled through this sequence
2 methods of bicarbonate transport across the basolateral membrane:
- co-transported with Na+ into interstitium and then into blood
- pumped passively in exchange for an anion
how many bicarbonates are are cotransported per sodium ion?
3
which limb of the Loop of Henle is thicker?
ascending
is the descending limb permeable to water and ions?
permeable to water, not to ions
is the ascending limb permeable to water and ions
impermeable to water, permeable to ions
