RENAL Renal blood flow and glomerular filtration Flashcards
How much do kidneys weigh in males and females?
150g in male and 135g in female
How many nephrons are there in each kidney?
1 million nephrons in each kidney
What is the blood flow rate in the kidneys?
1.1L/min
What is part of the tubular structure of the nephron?
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting ducts
What is the structure of the proximal convoluted tubule?
Cells with numerous mitochondria, apical tight junction and numerous microvilli
What type of cells does the descending loop of henle have?
Descending – thin permeable cells
What type of cells does the ascending loop of henle have?
Ascending - thick cells with numerous mitochondria
What cells is the juxtaglomerular apparatus made up of?
Macula Densa + Lascis cells + Granular cells of Afferent arteriole
What are the 2 types of cells in collecting duct?
-Principal cells
-Intercalated cells
What is the structure of principal cells and what are they responsible for?
tall, responsible for sodium absorption and vasopressin action
What is the structure of intercalated cells and what are they responsible for?
more microvilli, numerous mitochondrion and responsible for acid secretion
What is the size of the glomerulus in the corpuscle?
220 μm
What is the corpuscle?
Ball of capillaries supplied by afferent and efferent arterioles
What structure is the corpuscle surrounded by and what does this structure hold?
Surrounded by Bowmans capsule which holds filtered fluid (urine)
What is the total area of the corpuscle?
0.8m^2
What cells are found in the corpuscle?
Mesangial cells(pericytes)
What do mesangial cells reduce when they contract?
Contract to reduce glomerular volume
What do mesangial cells secrete?
Secretes extracellular matrix
What are the 3 layers in the glomeluar filtration barrier?
- Endothelium
- Basement membrane
- Podocytes
What is the size of endothelial fenestration?
70-90nm
What are podocytes also known as and what is there size?
-Filtration slit
-25nm
Up to what sized molecules does the glomerulus allow free movement?
Glomerulus allows free movement <4nm [7000
Da]
Above what sized molecule does the glomerulus stop free movement?
stops everything >8 nm [60,000 Da]
What rate of blood flow does the kidney receive?
Kidneys receive 1.1L/min
What % of the cardiac output do the kidneys receive
20% of cardiac output
What is the renal cortical blood flow rate?
5ml/g/min
What is the renal cortical arterio-venous oxygen difference and PO2?
14ml/L; pO2=50 mmHg
What is the renal medulla blood flow rate and PO2 ?
2.5ml/g/min pO2=15 mmHg
What drives the fluid out to make filtrate in the glomerulus?
In the glomerulus the capillary hydrostatic
pressure drives the fluid out to make the filtrate
What drives solutes into the descending vasa recta?
In the descending vasarecta the osmotic
pressure drives solutes in
What vertebrae level is the sympathetic preganglionic supply for renal blood vessels from?
Sympathetic preganglionic is from T10-L2
Where do the postganglionic neurons lie which supply renal blood vessels?
Postganglionic neurons lie in superior mesenteric and renal artery ganglion
What are sympathetic fibers distributed through in the kidney?
Sympathetic fibres are distributed through the afferent arterial, efferent arterial
and juxtaglomerular apparatus
What type of innovation happens at the loop of henle?
Noradrenergic innovation also happens at the loop of Henle
What do nociceptive afferents run parallel to?
Nociceptive afferents run parallel to sympathetic fibres
What is the renorenal-reflex in ureteric obstruction?
Ureteric obstruction –> Decrease efferent nerve stimulation –> Increase Na/Water excretion
What is the effect of norepinephrine on renal blood flow?
Constriction
What is the effect of dopamine on renal blood flow?
Dilation
What is the effect of angiotensin 2 on renal blood flow?
Constriction
What is the effect of prostaglandin 1 on renal blood flow?
Dilation
What is the effect of acetylcholine on renal blood flow?
Dilation
What is the effect of a high protein diet on renal blood flow?
Increase renal blood flow
What is the effect of increasing renal nerve stimulation when norepinephrine acts on juxtaglomerular apparatus?
Increase in renin
What is the effect of increasing renal nerve stimulation when norepinephrine acts on PCL, TALH, DCT ?
Increase in sodium absorption
What is the effect of increasing renal nerve stimulation when norepinephrine acts on alpha 1 and alpha 2 receptors?
Reduce renal blood flow
What does the glomerulus preserve during auto-regulation and what is this in response to?
The glomerulus can autoregulate its blood supply in response to systemic blood pressure changes to preserve the filtration pressure
What are the steps involved in the renin angiotensin aldosterone axis?
- Renin released from juxtaglomerular apparatus converts angiotensinogen into angiotensin 1
- Angiotensin 1 converted into angiotensin 2 by ACE
- Angiotensin 2 acts on adrenal cortex which releases aldosterone.
- Aldosterone causes:
-Decreased Na+(and water) excretion –> Increased extracellular fluid volume –> Increased renal arterial mean pressure, decreased discharge of renal nerves
What may a sudden increase in blood pressure do to the glomerulus?
Sudden increases in blood pressure increases glomerular blood flow
and GFR potentially, may damage the glomerulus
What prevents a sudden increase in blood pressure to glomerulus which could potentially increase GFR?
This is prevented by the “myogenic reflex”
How does the myogenic reflex work when theres an increased blood pressure?
-There’s an increase in stretch
-This results in depolarisation
-This causes opening of voltage gated calcium channels causing an increasing in calcium
-Results in muscle contraction of the afferent artery to reduce blood flow
What autoregulation happens to the GFR in response to increased flow in tubule, what is this orchestrated by and what is this feedback called?
-In response to increased flow in the tubule the GFR decreases
-This is orchestrated at the juxtaglomerular apparatus
-This is called ‘tubo-glomerular feedback
What is the juxtaglomerular apparatus?
The JG apparatus is a special structure in the nephron at the junction of distal tubule with it own afferent artery
How does the juxtaglomerular feedback work?
-Mechanism increased Na entry into macula densa cells
-Leads to more AYP breakdown
-This causes adenosine secretion which results in Calcium release
-Resulting in vasoconstriction of afferent artery
What is renal blood flow calculated from?
Calculatef rom renal plasma flow and haematocrit
What is used to measure renal plasma flow?
Renal plasma flow is measured using p-aminohippuric acid clearance
What is the equation for renal blood flow?
Blood flow = Arterial concentration - venous concentration
What can cause a decreased GFR?
-Constricted afferent artery
-Dilated efferent artery
What can cause an increased GFR?
-Constricted efferent artery
-Dilated afferent artery
What are the 2 targets in systemic hypotension that are autoregulated in kidneys?
-Afferent arteriolar vasodilation
-Efferent arteriolar vasoconstriction
What is afferent arteriolar vasodilation mediated and prevented in what groups?
-Mediated by prostaglandin
-Prevented in old age, diabetes, NSAIDS
What is efferent arteriolar vasconstriction mediated by and prevented by?
-Mediated by angiotensin II
-Prevented by ACEi, ARB
What can prevention of afferent arteriolar vasodilation and efferent arteriolar vasoconstriction predispose and cause?
Prevention of afferent arteriolar vasodilatation and efferent arteriolar vasoconstriction predisposes and causes AKI
What is the equation renal plasma flow?
Renal plasma flow = Upah x V/Arterial pah
Why is venous PAH zero in measurement of renal plasma flow?
Venous PAH is zero as all of it is removed
Why is it effective to use PAH as an effective way to measure effective renal plasma flow?
p-amino hippuric acid [PAH] and most (90%) of it removed in single passage through kidney, leaving nothing in renal vein;
and if it is not metabolized, stored, or produced by the kidney and does not itself affect blood flow
What equation is used to estimate actual renal plasma flow?
Estimate actual renal plasma flow = [effective renal plasma flow]/0.9
What equation is used to estimate renal blood flow?
Estimate renal blood flow = [actual renal plasma]/1-haematocrit
What is the equation for clearance of a substance?
Clearance of a substance = Urine conc X urine flow
