Renal structure and function Flashcards
What do renal arteries branch from?
The abdominal Aorta
Function of ureter
Carries urine to bladder
Function of urethra
Carries urine away from bladder to be excreted
Describe the course of renal arteries in the kidneys
- They pass into interlobar vesseles than branch into arcuate arteries in the renal cortex then terminate in the glomerulus (in the cortex). Each capillary glomerulus is enclosed inside bowmans capsule
What is bowmans capsule?
A bag of tissue which encloses a glomerulus capillary
What is the firsts stage or urine formation?
Blood plasma enters the glomerulus capillaries via afferent arterioles, this plasma enters bowmans capsule and is filtered. Blood leaves the glomerular capillaries via efferent arterioles, it then empties in the proximal tubule.
How does blood enter and leave the glomerulus?
Blood enters- Afferent arterioles
Blood laves- Efferent arterioles
What is the filtration pressure? How is it created?
Rate at which kidneys filter blood- From capillaries into the capsule space
Created by the drop in pressure between the afferent and efferent arteriole
What is the filtration fraction? What is the normal value?
Amount of plasma filtered into Bowman’s capsule
Normal- 20%
What would happen to the blood if the filtration fraction was too high?
Blood in efferent arteriole would be too viscouse
Haematocrit would be too high
Describe the morphology of the capillaries in the glomerulus
They are fenestrated (have gaps between the endothelial cells)
The outside is covered in podocytes which have slits
Explain the structure and function of podocytes. What happens to them during renal disease
Podocytes cover the outside of the glomerulus capillaries
They contain slits which form the filtration mechanism
During renal disease- Slits become large and inflammed- podocytes enable proteins (solutes) to enter the urine (proteinuria).
How does proteinuria occur?
When podocyte slits become large and enflammed enabling proteins to filter into the urine.
Describe the course of fluid after it leaves bowmans capsule
- Fluid leaves Bowman’s capsule and enters the proximal convoluted tubule.
- Then it enters the ‘Loop of Henle’.
- After the loop it enters the distal convoluted tubule.
- It leaves the distal tubule and enters the collecting duct.
- The collecting ducts drain into the ureter.
What is the nephron?
The complete set of tubes, from Capsule to Collecting Duct
Where is the glomerulus & proximal tubule located?
Renal cortex
Where is the loop of Henle located
Renal medulla
How would you calculate the amount of fluid excreted?
The amount filtered plus the amount secreted minus the amount reabsorbed
How is the cause of physical pressure in the glomerula controlled? What is the normal value for physical pressure?
Cause- balance between constriction of the afferent and efferent arterioles
Normal value- 55 mm Hg
How does starlings principal apply to establishing the net filtration pressure? (net outward pressure)
Starling’s principle applies. The net filtration pressure is the physical (hydrostatic) pressure in the capillaries minus an osmotic pressure.
The physical pressure of fluid in the capsule is about 15mm Hg, and the osmotic pressure is nearly zero (no proteins) so the net filtration pressure is about 10 mmHg.
What is is the Glomerular Filtration Rate? What is the normal value? Why dont we pee this much?
The Glomerular Filtration Rate is the total amount of fluid filtered through ALL the glomeruli in BOTH kidneys
Normal value- 120-125ml/min
We only pee out 1 ml/min. The rest is reabsorbed
Where is most of the filtered water from the glomerulus rebasorbed? Explain how absorbtion is possible at this location?
2/3 is absorbed in the proximal tubule
Sodium channel located in the lumen of the the proximal tubules transport sodium out of the lumen into the tubule cells down its concentration gradient, glucose is carried with it
Basal membranes of the cells at proximal tubule contain sodium pumps also which extrude sodium from the tubule cell into the interstitial fluid.
Water follows the sodium and is aborved down this osmotic gradient into the interstitial fluid.
Tubule lumen—-> cells—–> interstital fluid
How is the GFR measured and assessed? When will the clearence be the same as the GFR?
Clearence of a selected molecule (liters/min)
It is the volume of plasma completly cleared of a substance in 1min
If 100% of a blood compound is filtered through the glomerulus, and is removed at the same rate as water passes through the glomeruli and
all of the filtered compound appears in the urine (not rebaosrbed) then its clearnce will be the same as the glomerular filtration rate
Where does secretion of additional substances to be excreted occure?
Efferent arteriolar blood- substances secreted into tubular fluid
When is the clearnace of materials 0?
This will happen if 100% of a blood component is filtered through the glomerulus and all of this filtered material is reabsorbed
no blood will be ‘cleared’ of the material as it is all reabsorbed
When is clearance equal to renal plasma flow
Material in the efferent arteriolar blood is secreted into the urine.
All the blood passing through the kidney will have been cleared of the material.
What happens to GFR when kidneys are damaged?
It will decrease
Renal plasma flow may stay normal
What is the formula for clearnace? How is it calculated?
Urine concentration/ plasma concentration X volume of urine per minute
1) measure the concentration of the substance in the plasma,
2) collect urine for a fixed period to get the urine flow (ml/min)
3) measure the concentration of the substance in the collected urine
What is the gold standard for measuring GFR using clearance? Why is it the cold standard? Why is it impractical?
Assessing the clearance of INULIN (polysaccharide)
Why is it gold? It is completely filtered from the plasma and not reabsorbed.
Impractical? Inuline has to be infused over time using an IV to obtain constant plasma concentrtion
How is GFR measured clinically? Why is this method a better alternative to inuline? What is the disadvanatge also?
creatinine is used
Advanatges -Produced natutally by the body (break down proudct of creatinine in muscle)
-Freely filtered by the but also actively secreted by the peritubular capillaries in small amounts.
Already at a steady concentration in the blood
Disadvanatges- secreted by the peritubular capillaries in small amounts so creatinine clearance overestimates actual GFR by 10-20%.
What is the procedure for GFR creatinine clearance assessment? State an alternative to this procedure.
- 24 hour urine collection is undertaken, from empty-bladder one morning to the contents of the bladder the following morning,
- Blood test for creatinine then taken.
Alternative- get an approximation of kidney function from blood creatinine concentration
How can Clearance be used to measure RENAL PLASMA FLOW? Name of substance used, the procedure and the formula. What is the formal value?
Substance which is filtered out with water, and all material in efferent arteriolar blood is secreted into the urine. NO material in venous blood.
Molecule- PAH (para-amino-hippuric acid)
Procedure- infused until a steady concentration in (arterial) blood is reached
infused until a steady concentration in (arterial) blood is reached
Formula: Clearance= (urine concentration x urine flow)/plasma concentration
Normal value (both kidneys)- 600-700 ml/min
How is autoregulation of GFT controlled?
by the juxtaglomerular apparatus (JGA).
Distal tubule folds back and contacts the glomerulus at the point where the afferent and efferent arterioles enter.
Where in the nephron is fluid rebasorbed?
Where in the nephron is fluid secreted?
Proximal tubules-into peritubulat capillaries
Secreted out of capillaries into the tubular fluid
What is the normal creatin clearance value?
women 88-128 mL/min:
men 97 to 137 mL/min.
What is the meaning of the term GFR autoregulation? What effect does this have on renal blood flow?
GFR it does not change over a wide range of blood pressures
Autoregulation of GFR means that renal blood flow also does not change over a wide range of blood pressures.
Where will you find erythropoietin releasing cells? Why are thye found here?
In the kidneys
metabolic rate of the kidney (i.e. its oxygen consumption) is constant
How can the afferet and efferent artiroles effect GFR hence filtration pressure?
GFR will be increased if the the afferents relax and dilate, as this will increase filtration pressure
Conversely if the afferents constrict, this lowers filtration pressure and thus GFR.
What controls the Autoregulation of GFR?
the juxtaglomerular apparatus (JGA)
What does the the juxtaglomerular apparatus (JGA) consist of?
Three structures;
afferent arteriole,
efferent arteriole, &
distal tubule.
Which cells line the distal tubules and what is there function?
Macula densa cells-
Sodium sensors-
they release chemicals to control the contraction of smooth mucles around the afferent artiriole
How do sodium levels in the distal tubule effect GFR?
If sodium is low GFR is low- Sodium at the promal tubule is removed at a fixed rate. If this rate is slow meaning of GFR is slow then more soidum will be taken up as there will be more time for this to happen so the sodium at the distal tubule will be low.
This is the same for if the GFR is fast, then the sodium concentration at the distal tubule will be high.
How is low sodium rectified in the kidneys?
The mecula densa cells will release chemicals wich relax the smooth muscles of the afferent arteriole therefore increasing the filtration presure hence GFR
If sodium levels are too high mecula densa cells will release factors to constrict the afferent arteriols therefore decreasing filtration pressure, gence GFR
