3 - Clearance And Filtration Flashcards
What acts as the filter in the kidney?
The glomerulus.
Where in each nephron is the glomerulus found?
Only in the cortex.
Does the glomerulus filter all of the blood from the renal artery?
No. Only 20% of the blood from the afferent arteriole (which branches off from the renal arteries) can be filtered at any one time. The rest exits via the efferent arteriole.
What are the types of nephron?
Cortical and juxtamedullary.
Do the two types of nephrons differ in their levels of filtration?
No. Functionally they are exactly the same and have the same ability for filtration (20% of blood from renal artery). Structurally they differ.
How do the two types of nephron differ structurally?
They have a different arrangement of peritubular capillaries.
Is everything filtered at the glomerulus?
No. Cells and large proteins are not filtered. However, water, salts and small molecules pass through the glomerulus.
What are the layers of the glomerulus?
- Capillary endothelium permeable: will filter water, salts and glucose. Filtrate moves between cells.
- Basement membrane: permeable to small proteins; acellular gelatinouws layer of collagen / glycoproteins - the latter repel protein movment due to their - charge.
- Podocyte layer: pseudopodia interdigitate forms filtration slits.
How are molecules filtered by the barrier?
Size: small molecular weight and radius <1.48nm
Charge: charged proteins will normally not be filtered. May be if -ve charge on the glycoprotein’s of the barrier is lost - leading to proteinuria.
What are the three physical forces involved in filtering the plasma?
ENTERING the Bowman’s Capsule:
Hydrostatic pressure in the glomerular capillaries
EXITING the Bowman’s Capsule:
Hydrostatic pressure in the Bowman’s capsule
Osmotic pressure difference between the capillary and tubular lumen
Once the plasma has been filtered, what is the fluid known as?
Ultrafiltrate.
Which of the forces involved in filtering the plasma is regulated?
Hydrostatic pressure in the capillary (pushes fluid into the Bowman’s Capsule)
What is the net filtration pressure (in mmHg)? Which direction does this go? Do you know the pressure of each of the forces involved in filtering plasma?
50mmHg - hydrostatic pressure in capillary (ENTERING)
MINUS
15mmHg - hydrostatic pressure in the tubule
25mmHg - osmotic pressure difference between capillary and tubular lumen (both EXITING)
EQUALS
10mmHg ENTERING the Bowman’s Capsule.
What is GFR?
Glomerular filtration rate, is the rate at which plasma is filtered in the glomerulus. It is normally around 125ml/min.
What is autoregulation?
Autoregulation keeps GFR within normal limits when blood pressure is within physiological limits (80-180mmHg).
How does autoregulation work?
Through vasomodulation.
If blood pressure is high, there is afferent arteriole constriction.
If blood pressure is low, there is afferent arteriole dilatation.
If blood pressure is outside the physiological limit (80-180mmHg) then GFR will be compromised.
What is TGF?
Tubular glomerular feedback, is the change in tubular flow as a result of changes in GFR. NaCl levels are important in this process.
What will happen if arterial pressure exceeds its physiological limit?
If GFR is high what will happen to the levels of NaCl in the nephron?
A raised GFR will decrease NaCl reabsorption. This will mean more NaCl reaches the distal convoluted tubule. This must be resolved.
How does the nephron correct changes to NaCl levels in the distal convoluted tubule?
The macula densa cells (which are proximal to the glomerulus) are sensors of luminal [NaCl] (in the late thick ascending limb). They have a NaK2Cl transporter on their apical membrane which can adjust salt uptake, dependent on {NaCl].
If there is high {NaCl] then the macula densa cells will try to decrease GFR via vasoconstriction of afferent arteriole. Adenosine is released.
If there is low [NaCl} then the macula densa cells will try to increase GFR via vasoconstriction of afferent arteriole. Prostaglandins are released.
Does tubular glomerular feedback apply in long term changes in GFR?
No. It is a response that only applies in acute changes.
Describe the blood supply to the kidney.
Abdominal aorta –> Renal artery (L1-L2) –> Segmental arteries –> Interlobar arteries –> Arcuate arteries –> Interlobular arteries –> Afferent arterioles –> Glomerular capillaries –> Efferent arterioles –> Peritubular capillaries –> Interlobular veins –> Arcuate veins –> Interlobar veins –> Renal veins
Are the renal arteries the same length?
No. The right renal artery is longer (the abdominal aorta is slightly to the left of the midline and the right renal artery must pass the IVC) and more inferior.
What does the vasa recta do?
It is a group of capillaries that run parallel to the loop of Henle. They are a branch of the efferent arterioles in juxtamedullary nephrons. They are important in maintaining countercurrent exchange - which allows the kidney to produce concentrated urine.
