054 Glomerular Filtration Flashcards
Which organ has the lowest arteriovenous O2 difference of any organs and why?
Kidney because they have high O2 uptake but blood flow is so high. The arteriovenous difference is 10%.
What is the diameter of glomerulus?
200microns
How many nephrons do we have in our kidneys?
2 millions
What is nephrin?
Protein found in the diaphgram of the filtration slit
What charge do the components of the filteration barrier carry?
-ve charge due to glycoproteins. This repels -ve charged solutes and attracts positively charged solutes. However for small solutes, the charge doesnt matter. Only plasma proteins (-ve) are repelled.
What are the two factors of glomerular filtreation?
Electrical charge (+ve) Molecular weight (smaller)
Which can be filtrated more? Albumin or haemaglobin?
Haemaglobin because it is not as negatively charged.
What occurs to renal blood flow and glomerular filtration rate during afferent arteriolar constriction?
Both renal blood flow and glomerular filtration rate decreases due to lower hydrostatic pressure
What occurs to renal blood flow and glomerular filtration rate during efferent arteriolar constriction?
Increase in hydrostatic pressure causing glomerular filtration rate
What is the effect of adenosine on arterioles in glomerulus?
Constricts the afferent arteriole, lowering filtration
What is an example of a molecule that is able to constrict efferent arteriole constriction?
Angiotensin II
What occurs when you block angiotensin II?
Efferent arteriolar dilation
What occurs to renal blood flow and glomerular filtration rate during efferent arteriolar dilation?
High blood flow but low hydrostatic pressure, causing lower glomerular filtration.
What occurs to renal blood flow and glomerular filtration rate during afferent arteriolar constriction?
High blood flow and higher hydrostatic pressure, causing higher glomerular filtration.
How do prostaglandins and NO affect glomerular capillaries?
Dilate afferent arterioles
What is the best way to test function of kidneys?
Total glomerular filtration rate. Using substance that can be 1. freely filtered, not reabsorbed and not secreted. One example is inulin, but we use creatinine clinically because there is no need for IV
What is the typical value of renal blood flow?
1.2l/min
What is the significance of autoregulatory change?
Keeping renal blood flow along with glomerular filtration constant despite changes in MAP
Describe the myogenic mechanism of autoregulation?
Increase in blood pressure -> afferent arterial stretch -> non-specific cation channels open -> depolarization -> Ca2+ channels open -> afferent arteriole contracts
What are two mechanisms of autoregulation of glomerular capillaries?
Myogenic mechanism
Tubuloglomerular feedback
What is the MAP range of autoregulation?
90-180mmHg
During haemorrhage, what occurs to the regulation of kidney vessels?
Reduced renal blood flow by sympathetic nerves. Circulating adrenaline acts similarly.
What is tubuglomerular feedback?
A type of autoregulation mechanism. Macula densa cells sense changes in Na+ delivery and increased filtration associated with it. This stimulates release of adenosine, causing vasoconstriction of the afferent arteriole through paracrine mechanism.
Why does tubuglomerular occur?
It is to protect against Na+ and fluid loss, resulting in a lower renal blood flow and so lower hydrostatic pressure.
How much of total body weight do kidneys make up?
<0.05%
What is the formula for net ultrafiltration pressure?
Net hydrostatic pressure - net oncotic pressure (oncotic pressure in bowman capsule 0)
What is typical value for renal blood flow
1200mL/min
What is the typical value for renal plasma flow
650mL/min
What is typical GFR value?
120ml/min (20% filtration fraction)
Describe the mechanism of tubuloglomerular feedback
Macula densa cells in the distal tube will detect changes in the Na+ absorbed, signalling hormones to constrict or dilate afferent arterioles e.g. adenosine to cause paracrine vasoconstriction.
What are the renal consequences of an increased filtration rate?
Causes efferent blood to be more viscous. Decrease in circulating renin by both macula densa signals and also the viscous sluggish efferent blood flow.
What are the consequences of GFR of an increased protein filtration?
Oncotic pressure of fluid in Bowmans capsule becomes significant, increasing fluid filtration.
How much renal blood flow supplies the cortex?
More than 90%
What substance can be used to measure renal plasma flow?
PAH
How may the concept of renal clearance be used to estimate renal plasma flow?
At a low plasma PAH concentration, filtered level of PAH is low and PAH will be efficiently secreted into proximal tubule, thus PAH in renal vein will be 0. Hence renal plasma flow = clearance of PAH.
