Renal Structure and Function Part 1 Flashcards
where do renal arteries branch from
the abdominal artery
what does the ureter do
it is the tube carrying urine to the bladder
what does the urethra do
the tube carrying the urine from the bladder to the outside
describe what the renal arteries pass into and divide into
the renal arteries pass into the interloper vessel and divide into the small arcuate arteries in the renal cortex
where do the arcuate arteries end
= they terminate in a clump of capillaries in a cortex in a structure called the glomerulus
what is each capillary glomerulus enclosed by
- it is enclosed inside a bag of tissue called the bowman capsule
what are the stages of urine formation
- plasma is filtered from the glomerular capillaries into the space of the capsule
1. blood enters the glomerulus of the nephron int he afferent arteriole and leaves through the efferent arterioles, afferent has a larger diameter than efferent this causes a drop in pressure between eh afferent and efferent arterioles and this makes the filtration pressure which forces the fluid through the endothelium into the capsular space
2. the fluid leaves bowman capsule and enters the proximal convoluted tubule then it enters the loop of gene then the distal convoluted tubule and then the collecting duct which drains in the ureter
what is the difference between the afferent arterioles and efferent arterioles
- afferent has a larger diameter than efferent
- afferent brings blood in whereas efferent removes the blood
what is the filtration fraction
it is normally 20%
- this is the proportion of the blood plasma that is filtered through glomerulus into the bowman capsule which enters in the proximal tubule
a greater filtration fraction will…
- make the blood in the efferent arteriole too viscous as it would have too high a haematocrit
describe the capillary structure in the glomerulus
- they are fenestrated - this means that they have gaps between the endothelial cells
- covered on the outside by podocytes
- podocytes have gaps between them which help form the filtration mechanism this allows certain molecules to enter the urine and certain molecules to stay in the plasma
what happens to the podocytes in renal disease
- in renal disease - the podocytes become inflamed and enlarged therefore the gaps between them get larger which enables more solutes to enter the urine
- proteinuria is therefore a sign of glomerular inflammation
what is the nephron
- this is the complete set of tubes from the bowman capsule to the collecting duct
- it is the unit of kidney function
what supplies oxygenated blood to the glomerulus
- efferent arterioles
- wraps around and forms a plexus
what part of the nephron is in the medulla
- loop of Henle
what part of the nephron is in the cortex
- glomerulus
- proximal convoluted tubule
several distal tubules….
enter into one collecting duct
what part of the nephron can vary in size
- loop of Henle
- in desert animals it is long so they don’t loose much water but have heavily concentrated urine
- in water animals it is short so they loose a lot of water and don’t have heavily concerted urine
what happens int he proximal convoluted tubule
- reabsorption into the pertiubular capillaries
- substances are transported out of the capillaries and secreted into the tubular fluid
- filtration
How do you work out the amount of material excreted
amount filtered + amount secreted - amount reabsorbed
what is the filtration of water into the capsule controlled by in an healthy individual
- balance between constriction of the afferent and efferent arterioles
what is the normal physical pressure in the glomerular capillaries
55 mmHg
How do you work out the net filtration
hydrostatic pressure - osmotic pressure
what is the net filtration pressure
10 mmHg
describe cardiac output to the kidneys
- just under a quarter of CO goes to the capillary, this is 1.2 Lt/min
Define the glomerular filtration rate
- this is the total amount of fluid filtered through all the glomeruli in both kidneys
- usually 120-125 ml/min
what is urine flow
1ml/min
- almost all of the fluid filtered by the glomeruli is reabsorbed
what is the renal plasma flow
- 680 ml/min
what is used clinically to assess the health of the kidney
Glomerular filtration ate GFR
where is the water reabsorbed
- 2/3 reabsorbed int he proximal tubule
- some reabsorbed in the collecting duct
how does reabsorption of water in the proximal tubule happen
- tubule is lined with epithelial cells and the basal membranes of these cells contain sodium pumps that move the sodium from the proximal tubule into the interstitial fluid against the concentration gradient this creates a low concentration gradient in the proximal tubule
- in the luminal membrane of the proximal tubule there are sodium channels and sodium therefore diffuses down the concentration gradient into the proximal tubule (this is a symport mechanism and brings glucose with it)
- water is then reabsorbed down an osmotic gradient from the lumen into the cells and then out into the interstitial fluid (it flows the sodium pathway)
- when the sodium is taken out of the proximal tubule there is a negative voltage so the chloride is pulled out as well
How do you measure GFR
- Measured by clearance
define clearance
- it is the effective volume of plasma completely cleared of a substance per minute
if 100% blood component is filtered through the glomerulus ..
- this means that material goes into the proximal tubule at the same rate as the water in the plasma, therefore the clearance of the substance will be the same as the glomerular filtration rate which is 125 ml/min
if 100% of the blood component is filtered through the glomerulus and all of it is reabsorbed ..
- no blood will be cleared of the material
- clearance is o
that 100 % of the material is filtered and in addition all of the material in the efferent arteriolar blood is secreted into the urine
- renal venous blood will have no material in it and all the blood passing through the kidney will have been cleared of the material
- the clearance will then equal the renal plasma flow
what can clearance be equal to
Not removed at all by kidney: Clearance = zero
Removed at same rate as water passes through glomeruli: Clearance = GFR
Completely removed from blood passing through kidney: Clearance = RPF
what happens to the GFR and RPF if the kidney is damaged
GFR will decrease
RPF will be normal
what is the formula of clearance
urine concentration/ plasma concentration x urine flow (volume of urine per minute)
how do you measure the clearance of a substance
- measure the concentration of the substance in the plasma
- collect the urine for a fixed period to get the urine flow
- measure the concentration of the substance in the collected urine
what do you use to measure GFR
- inulin - completely filtered from the plasma and is not reabsorbed, have to iV inulin over a period of hours until you reach a steady plasma concentration - not clinically practical as it takes too long
- Clinically use creatinine to measure GFR, produced naturally by the Body and is filtered by the glomerulus and is also secreted by the peritubular capillaries in the small amounts, it is already at a steady state concentration in the blood so it takes much shorter to measure
what does the secretion of creatinine by the peritubular capillaries do
- means that the creatinine clearance overestimates the GFR by 10-20%
what is creatinine
it is the product of creatine metabolism
how does urine collection work
- a 24 hour urine collection is usually undertaken from empty bladder one morning to the contents of the bladder the following morning
- blood test for creatinine then taken
how can you get an approximation of kidney function
from blood creatinine concentration
what can clearance also be used to measure
renal plasma flow
how can clearance be used to measure renal plasma flow
if all of a particular substance is filtered along with water and addition of all material int he efferent arteriolar blood is secreted into the urine than the renal venous blood will have no material in it
- all the blood passion through the kidney will have been cleared of the material
- therefore ether clearance will then equal the renal plasma flow
what material is used to use clearance to measure the renal plasma flow
- PAH
- PAH infused until steady concentration in arterial blood is reached
- urine is collected for 24 hours and urien flow and PAH concentration is measured
what is the normal GFR
120-125 ml/min
What is the norml RPF
600-700 ml/min
name the 5 stages of chronic kidney disease
stage 1 greater but equal to 90 stage 2 (mild) 60-89 stage 3 (moderate) 30-59 stage 4 (severe) 15-29 stage 5 (kidney failure) less than 15
the GFR in kidneys is…
autoregulated which means that it does not change over a wide range of blood pressures
what does auto regulation of the GFR mean
- means the the GFR does not change over a wide range of blood pressures
why are the EPO relasing cells in the kidney
- the renal blood flow is constant and the oxygen consumption of the kidney is constant the oxygen saturation of kidney interstitum is a measure of the oxygen delivery to the kidney and therefore the oxygen carrying capacity of the blood
how is the GFR auto regulated
- by the balance of constriction in the smooth muscle of the afferent and efferent arterioles
what happens if the afferents relax and what happens if the afferents constrict
- if the afferents relax and dilate this increases the filtration pressure and increases the GFR
- if the afferents constrict this lowers the filtration pressure and the GFR
what is auto regulation of the GFR controlled by
- the Juxtaglomerular apparatus
- this is the point at where the distal tubules folds back and contacts the glomerulus at the point where the afferent and efferent arterioles enter
what are the 3 structures of the juxtaglomerular apparatus
- afferent arteriole
- efferent arteriole
- distal tubule
what lines the wall of the distal tubules
- macula densa
what are macula densa
- sodium sensors
- release local chemicals which modulate the contraction of smooth muscle around the afferent arteriole
why does a low sodium level indicate a low GFR
Sodium is removed (by reuptake) from the proximal tubule at a fixed rate.
If the flow is slow (low GFR) , more sodium has been removed by time the fluid has reached the end of the tubule and the remaining concentration will be low . Conversely, if the flow is fast (high GFR) , more sodium is flowing past the uptake sites than they can manage, so the concentration remains high.
With low distal tubule sodium, the macula densa cells release local chemical factors which relax the smooth muscle in the afferent arteriole, thus increasing the filtration pressure and increasing GFR. Conversely, if the sodium level is too high, the macula densa cells release chemical factors which constrict the the afferent arteriole, decrease filtration pressure and reduce GFR.
