Renal Blood Flow and GFR Flashcards
Through which vessels does blood need to travel to get to the glomerulus from the aorta?
Abdominal aorta Renal artery Segmental artery Lobular artery Arcuate artery Interlobular artery Afferent arteriole Glomerulus
After blood leaves the glomerulus, what vessels does it have to pass through to get into the inferior vena cava?
Glomerulus Efferent arteriole Peritubular capillaries/vasa recta Interlobular vein Arcuate vein Lobular vein Segmental vein Renal vein IVC
What are the two types of nephron?
Cortical and juxtamedullary
Describe the differences in the loop of henle between the cortical and juxtamedullary nephrons
Cortical: Short loop of henle, only just penetrates medulla
Juxtamedullary: Long loop of henle, penetrates deep into the medulla
Describe the differences in the capillaries between the cortical and juxtamedullary nephrons
Cortical: efferent arterioles go on to form peritubular capillaries
Juxtamedullary: efferent arterioles go on to form vasa recta
What is the difference in location between cortical and juxtamedullary nephrons?
Cortical: outer part of cortex
Juxtamedullary: inner part of cortex, next to medulla
What is the difference in diameter of AA/diameter of EE between cortical and juxtamedullary nephrons?
Cortical: AA>EA
Juxtamedullary: AA=EA
Which is the most common type of nephron?
Cortical
How much of the blood from the renal artery is filtered at any one time?
20%
What is the renal corpuscle?
The glomerulus and bowman’s capsule
What is the function of the renal corpuscle?
To produce ultra filtrate of plasma
What epithelia does the partietal layer of bowman’s capsule consist of?
Simple squamous
What are podocytes?
Podocytes are cells in the Bowman’s capsule in the kidneys that wrap around capillaries of the glomerulus
What is the filtration barrier produced by?
Fenestrated capillary endothelium and visceral layer of bowman’s capsule
How many layers make up the filtration barrier?
3
What are the layers of the filtration barrier?
1) Capillary endothelium - permeable to water, salts, glucose - filtrate moves between cells
2) Basement membrane - acellular - permeable to small proteins
3) Podocyte layer - pseudopodia interdigitate forms filtrations slits - provide a defined gap
What are the layers of the bowman’s capsule?
1) Parietal layer (simple squamous epithelia)
2) Bowman’s space - between parietal and visceral layers where filtrate enters after passing through the filtration slits
3) Visceral layer - made up of podocytes
4) Filtration barrier
Why is the basement membrane of the filtration barrier impermeable to most proteins?
It’s made up of glycoproteins which are negatively charge so these repel protein movement
What effective molecular radius does a substance need to be under to get through the filtration barrier?
Radius less than 1.48nm will pass through
What is the effect of charge on the passage of substances through the filtration barrier?
Positively charged - better clearance (even a substance thats a bit bigger will clear better than a smaller substance that is less positive)
Negatively charged - does not pass through as well (due to glycoproteins in the basement membrane)
How can a nephrotoxic substance lead to proteinuria?
It can strip the negative charge from the basement membrane layer and allow the passage of negatively charged proteins which end up in the urine
What are the 3 forces involved in plasma filtration?
1) Hydrostatic pressure in the capillary - regulated (Pgc)
2) Hydrostatic pressure in bowman’s capsule (Pbc)
3) Oncotic pressure difference between capillary and tubular lumen (πgc)
Which ways are the forces moving in plasma filtration? Thus, what is the net filtration direction?
1) Hydrostatic pressure in capillary - moves plasma into bowman’s capsule
2) Hydrostatic pressure in bowman’s capsule - moves plasma into capillary
3) Oncotic pressure difference - moves plasma into capillary
Net movement = capillary into bowmans because the hydrostatic pressure in the capillary is greater than the other forces
In what ways is renal autoregulation achieved?
Myogenic mechanisms and tubuloglomerular feedback
What is the myogenic mechanism?
The myogenic mechanism is how arteries and arterioles react to an increase or decrease of blood pressure to keep the blood flow within the blood vessel constant.
If someone has a decreased GFR, how does the kidney respond?
Attempts to increase GFR
Dilate AA, Constrict EA
If someone has an increased GFR, how does the kidney respond?
Attempts to decrease GFR
Constrict AA, Dilate EA
How does the dilation of afferent arterioles/constriction of efferent arterioles help to increase GFR?
Dilation of AA - allows more blood to come in
Constriction of EA - keeps blood there for longer
This all increases hydrostatic pressure in the capillary
How do auto-regulatory mechanisms keep GFR within normal limits?
Increase in blood pressure leads to afferent arteriole constriction, so GFR remains unchanged
(would go up otherwise)
Decrease in blood pressure leads to afferent arterioles dilation, so GFR remains unchanged
(would go down otherwise)
What does the mechanism of TG feedback link?
Sodium and chloride concentration at the macula densa with control of renal arteriolar resistance
What does TG feedback act in response to
Acute perturbations in the delivery of fluid and solutes to the JGA
What cells sense the tubular flow rate as a result of changes in GFR?
Macula densa cells
How do the macula densa cells sense changes in GFR?
Eg increased GFR leads to an increase in [Na+] and [Cl-] in the DCT
Senses changes of NaCl in DCT via a concentration-dependent salt uptake via NaKCC co-transporter in the apical membrane of MD cells (detects increased Cl-)
What happens when the macula densa cells detect too little flow through the nephron?
Assumes a decrease in GFR, responds to attempt to increase GFR
Stimulates JGA to release chemicals
Prostaglandins vasodilate afferent arterioles
Increased glomerular capillary hydrostatic pressure
GFR goes up
What happens when the macula densa cells detect an increase in NaCl in the DCT?
Respond by trying to decrease GFR
Stimulates JGA to release chemicals
Adenosine works on A1 receptors to constrict afferent arterioles and works on A2 receptors to vasodilate efferent arterioles
Decreased glomerular capillary hydrostatic pressure
GFR goes down
Which transporter detects the increase in Cl-?
NaKCC in apical membrane of MD cells
Aside from the myogenic response and TG feedback, what is the third autoregulatory mechanism?
Glomerulotubular balance - blunts sodium excretion by always reabsorbing 67% of the filtered load
How do you calculate filtered load?
Filtered load = GFR x concentration
