Session 3 - Renal Blood Flow And GFR Flashcards
Name the blood vessels through which blood must pass to reach the glomerulus from the aorta.
Aorta —> Renal artery —> Segmental artery —> Interlobar artery —> Arcuate artery —> Interlobular artery —> Afferent arteriole —> Glomerular capillary
What are the two types of nephron?
Cortical
Juxtamedullary
Where in the kidney are cortical and juxtamedullary nephrons found?
Cortical nephron - outer part of cortex, extends just into the medulla
Juxtamedullary nephron - inner part of cortex next to medulla, extends deeper into the medulla
Do cortical and juxtamedullary nephrons have large or small glomeruli?
Cortical nephron - small
Juxtamedullary nephron - large
What are the differences between the loop of Henle of the cortical and juxtamedullary nephrons?
Cortical nephron - loop of Henle is shorter, mainly in cortex, just reaches into the medulla.
Juxtamedullary nephron - loop of Henle is longer, reaches into the inner part of the medulla.
How do the diameters of the afferent and efferent arterioles differ in the cortical and juxtamedullary nephrons?
Cortical nephron: afferent arteriole > efferent arteriole
Juxtamedullary nephron: afferent arteriole = efferent arteriole
How does the amount of sympathetic nerve innervation to cortical nephrons differ from juxtamedullary nephrons?
Cortical nephron - rich sympathetic nerve innervation
Juxtamedullary nephron - poor sympathetic nerve innervation
How does the concentration of renin present differ between the cortical and juxtamedullary nephrons?
Cortical nephron - high concentration of renin
Juxtamedullary nephron - almost no renin
What is the percentage of cortical and juxtamedullary nephrons present in the kidney?
Cortical nephron - 90%
Juxtamedullary nephron - 10%
What is the average renal blood flow rate?
~ 1.1 L/min
How do you calculate renal plasma flow?
Volume percentage of plasma in blood (1 - percentage volume of haematocrit) x renal blood flow
E.g. percentage plasma volume = 0.55
RBF = 1.1 l/min
0.55 x 1.1 l/min = 605 mL/min of plasma = renal plasma flow
What percentage of blood passing through the glomerulus is actually filtered?
20% of blood from the renal artery is filtered at any one time. 80% of blood arriving exits unfiltered via the efferent arteriole.
What makes up the renal corpuscle?
The glomerulus and Bowman’s capsule
What is the function of the renal corpuscle?
To produce ultrafiltrate
What sort of epithelium s the parietal layer of the Bowman’s capsule made of?
Simple squamous epithelium
What cells make up the visceral layer of the Bowman’s capsule?
Podocytes
What three layers make up the filtration barrier in a renal corpuscle?
Capillary endothelium
Basement membrane
Podocytes
What molecules can be filtered from the glomerulus into the lumen of the Bowman’s capsule?
Water, salts and small molecules. Cells and large proteins can’t be filtered.
How does the composition of ultrafiltrate produced in the renal corpuscle differ to the composition of blood?
Endometrium product of filtration is identical to plasma without the large proteins and cells.
What is the basement membrane composed of?
It is an acellular gelatinous layer of collagen and glycoproteins.
Negative charge of glycoproteins helps to repel large proteins.
What charge does the filtration barrier have and why?
Filtration barrier is negatively charged. Due to negative charge of glycoproteins in basement membrane.
Why can cationic molecules pass through the filtration barrier more easily than anionic molecules?
Negative filtration barrier, attracts cation but repels anions.
In many disease processes the negative charge on the filtration barrier is lost so that proteins are more readily filtered. What condition will this result in?
Proteinuria
Which forces favour filtration and which forces oppose filtration?
Forces favouring filtration:
- hydrostatic pressure of plasma in glomerulus
Forces opposing filtration:
- hydrostatic pressure of ultrafiltrate in tubule
- oncotic pressure in glomerulus
What is renal autoregulation?
Feedback mechanisms intrinsic to the kidney that keep renal blood flow (RBF) and glomerular filtration rate (GFR) constant.
What mechanisms are involved in renal autoregulation?
Myogenic mechanisms
Tubuloglomerular feedback
Why is autoregulation of GFR needed?
Without autoregulation a slight change in blood pressure would cause a significant change in glomerular filtration rate.
Outline the myogenic response to an increase in renal blood pressure.
Increase in blood pressure —> afferent arteriole constricts —> GFR unchanged
Outline the myogenic response to a decrease in blood pressure.
Decrease in blood pressure —> afferent arteriole dilates —> GFR remains unchanged
Where are macula densa cells located?
Distal convoluted tubule, where the tubule comes into contact with the glomerulus.
Describe what happens in tubular glomerular feedback.
1) A change in GFR causes a change in tubular flow rate and therefore changes the amount of NaCl that reaches the distal tubule.
2) Macula densa cells detect luminal [NaCl] in the distal convoluted tubule.
3) This stimulates the juxtaglomerular apparatus to release either adenosine (to reduce GFR) or prostaglandins (to increase GFR).
How do macula densa cells monitor NaCl concentrations in the distal convoluted tubule?
Through concentration-dependent salt uptake via NaKCC co-transporters in the apical membrane of macula densa cells.
What affect does adenosine have when released from the juxtaglomerular apparatus?
Acts on A1 receptors which cause constriction of afferent arteriole near the glomerulus, and A2 receptors which cause dilation of efferent arteriole.
Works to reduce glomerular filtration rate.
What affect do prostaglandins have when released from the glomerulus?
Vasodilate the afferent arteriole.
Works to increase glomerular filtration rate.
What is the role of glomerulotubular balance?
It reduces the amount of sodium excreted when GFR becomes to high despite the action of the myogenic response and tubular glomerular feedback. It does this by reabsorbing more of the filtered sodium.
