L16*-Physiology of the renal system II-Glomerular filtration Flashcards
(20 cards)
What is a nephron?
It is the fundamental functional unit of the kidney.
What is a capillary tuft in the nephron ?
and
State the functions of afferent and efferent arterioles in the nephron.
Same as the glomerulus
- tangled network of tiny blood vessels(capillaries)
-Blood enters the glomerulus through afferent arteriole. these capillary walls are highly permeable, allowing water, electrolytes and small solutes to pas into the Bowman’s capsule while preventing larger solutes like protein and blood cells from escaping.
-The efferent arteriole carries blood away but has a smaller diameter than the afferent arteriole. this creates high hydrostatic pressure in side the glomerulus forcing fluid and solutes out, which forms glomerular filtrate.
Define Glomerular ultrafiltration, formation of Bowman’s capsule. What is the process for filtration? diffusion or …?
-Filtration in the kidney occurs in the glomerulus, where a semi-permeable membrane separates the cells and plasma in the capillaries from the filtrate which forms the Bowmans capsule. The filtration involves bulk flow.
What are the 2 forces which drive the flow in the nephron ? these 2 forces are also identical to the those forces determining movement in all capillary beds. and what happens to the osmotic force along the capillary?
- Hydrostatic pressure - higher hydrostatic pressure int he capillaries drives fluid out, much higher in most capillaries.
- Osmotic/oncotic pressure - higher osmotic pressure in the capillaries( due to plasma proteins) impedes (slows down/blocks) the flow. The osmotic force👆se along the length of the capillaries, but equilibrium is not normally achieved in people.
Define more about osmotic/oncotic pressure.
AND
How to calculate osmotic pressure.
The total osmotic pressure of plasma is very high due to the proteins levels being too low.
However, most of the constituents of plasma are of LOW MOLECULAR MASS and size and hence the equal distribution across the glomerular capillaries, it is the osmotic pressure of the proteins (oncotic pressure) that affects the driving force.
- Morse equation,
Osmotic pressure = nCRT where,
nC = osmolality (0.28osm.kg-1),
R=ideal gas constant (0.082 L.atm.mol-1.K-1), T=temperature (310 K).
How does he filtration pressure differs along peritubular capillaries after the efferent capillaries leave the glomerulus ?
Once the efferent capillary leaves the glomerulus, it enters a portal vein and travels to a second capillary bed surrounding the Loop of Henle; here, the hydrostatic pressure is much more similar to a systemic capillary,
while the osmotic (oncotic) pressure is much higher.
What are the 3 layers separating the blood from the lumen of Bowman’s capsule ? and explain each of them.
- Endothelial cells of the glomerular capillaries - The endothelial cells have small fenestrations between them.
-The endothelial cells have a -vely charged glycocalyx, which creates a charge barrier that is particularly effective for proteins. - Glomerular basement membrane - The basement membrane also consists of fixed, -vely charged proteins ( ie : collagen)
- Epithelial cells of Bowman’s capsule
What are podocytes in the Nephron?
-the epithelial cells of Bowman’s capsule.
* From these cells, small processes (pedicels; foot processes) project and interdigitate with their neighbours to form another barrier to the movement of fluid (see images on the next few slides).
Compare 1.bulk flow and 2.diffusion.
-Most of the movement of substances through the filtration barrier is by bulk flow rather than diffusion.
1. Bulk flow/bulk transport/advection - Is the movement of solutions from an area of high pressure to an area of low pressure. As the solvent(water) moves, it carries any solutes dissolved in it. This process is sometimes described by the term solvent drag.
2. Diffusion : the movement of a substance from an area of [higher] to [lower] (a macroscopic, emergent property) as a result of Brownian motion.
The glomerular barrier is sufficiently tortuous and the distance sufficiently great, that diffusion alone cannot explain glomerular filtration.
What are the 2 main ways to control the glomerular hydrostatic pressure or GFR ?
-dilate the afferent arteriole
-contract the efferent arteriole
consider a leaky hose-pipe
How to measure GFR ?
-measured using substances that are small enough to be freely filtered, but the neither secreted nor reabsorbed over the length of the tubules.
ie:- such substance can either be injected intravenous(insulin) or be produced by the body at a steady rate (creatinine).
Why is the [Creatinine] in the Bowman’s space is the same as the [Creatinine] in the plasma ?
Bc creatinine is freely filtered around.
Why is GFR X Ccr.p = Ccr.uV.
The rate at which Creatinine is filtered must be equal to the rate at which is found in the urine because we know that Creatinine isn’t reabsorbed or secreted along the tubule system.
So how do we measure GFR based on Creatinine ? write the equation in the book.
[Creatinine} in the urine divided by the [Creatinine] in the plasma and times the rate at which urine is produced.
GFR = ( Ccr.u / Ccr.p ) x V.
Since we cant do 24hr collection to measure GFR, we use a estimate equation. What is it and why is it linked to age ?
eGFR = (140-age) x mass x C / Ccr.p
Bc GFR declines with age as well as [Creatinine]
Define renal plasma flow rate.
The plasma flow rate at which its flowing into the kidney.
Define GFR
the rate at which the kidneys filter blood to remove waste and excess fluids
Explain proximal/afferent constriction and distal/efferent constriction
THEN
Explain proximal/afferent dilation and distal/efferent dilation
- Proximal/afferent constriction
When we stand on the leak, we 👇se hydrostatic pressure so less of a leak. In the kidney if we vasoconstrict an afferent arteriole(blood vessel heading INTO the glomerulus) the hydrostatic pressure 👇ses so less glomerular filtration. - Distal/efferent constriction
If we stand on the far side which increase the resistance to flow downstream, the fluid pressure will increase where the link is. This 👆se in hydrostatic pressure where the leak is will cause my leak to leak even more. In the kidney if we vasoconstrict the efferent arteriole (heading OUT), the hydrostatics pressure in the capillaries 👆se, which 👆ses the glomerular filtration rate. - Proximal/afferent dilation
If we turn the tap on more wider to stop the resistance flowing from the water supply and to open up the lumen.
or if we dilate an afferent arterioles there will be an 👆se in hydrostatic pressure > 👆se in the GFR. - Distal/efferent dilation
If we have a gun at the end of the hose, and if dilate the efferent arteriole the hydrostatic pressure drops within the glomerulus > GFR falls.
What 2 mechanisms in the body controls the diameter of afferent and efferent arteriole in the kidney ?
There is both neural and hormonal mechanisms for regulating the diameter of both afferent and efferent blood vessels.
What is nephrotic syndrome and name a type.
-when we find proteins in the urine 😡 😔
- glomerulonephritis
