glomerulus, GFR and clearance

Question 1

how does the glomerular filtrate barrier create ultrafiltrate

Answer 1

multiple layers that act together to selectively filter blood:
- endothelium = fenestrated with small holes called fenestrae
- glomerular basement membrane - proteins in a mesh
- epithelium = podocytes of bowmans capsule = finger like projections that wrap around the capillaries

Question 2

which factor does NOT significantly change as you move along the glomerular capilary

Answer 2

hydrostatic pressure

Question 3

what is the primary force that favours filtration in the glomerulus

Answer 3

hydrostatic pressure

Question 4

how does filtration from the glomerulus to bowmans capsule occur

Answer 4

filtration from the glomerulus into bowmans capsule follows the same principles as any other capillaries:
- hydrostatic pressure pushes fluid through and favours filtrations
- the fluid formed is nearly protein free so doesnt have any real rotein-osmotic pressure

Question 5

define glomerular filtration rate

Answer 5

the amount of fluid filtered from the glomerular capillaries into bowmans space per minute
- product of the net filtration pressure across the glomerular membrane and the filtration coefficient. the filtration coefficient represents the permeability of the membrane and the filtration area
- GFR = Kf x net filtration pressure

Question 6

Is GFR higher in a horse or a dog. why

Answer 6

varies proportionally to metabolic body mass so will be higher in a horse than in a dog

Question 7

how is the glomerular filtration rate regulated

Answer 7

renal blood flow and hydrostatic pressure are controlled by arterial blood pressure and the resistance of the afferenct and efferent arterioles. the total resistance of efferent and afferent arterioles determines renal blood pressure at any given blood pressure
autoregulation, angiotensin and neural regulation all affect constriction and dilation of afferent and efferent arterioles

Question 8

why is GFR important

Answer 8

important as is directly proportional to renal mass (how many functional nephrons there are)
if nephrons are damaged or destroyed GFR will decrease
decreased GFR = less ability for the kidney to filter blood

Question 9

what is renal clearance

Answer 9

numerical expression for the ability of the kidneys to clear the plasma of different substances
volume of plasma cleared of a substance in a unit of time
= how much of a substance appears in urine at that time

Question 10

what makes a good substance to measure when assessing GFR

Answer 10

• levels should be stable in the body
• freely filtered
• not resorbed or secreted

if these are true in steady state then the renal clearance would be equal to GFR

Question 11

what substances are used to measure GFR. what are the pitfalls or benefits to measuring this substance

Answer 11

• blood urean nitrogen (BUN). not constant, higher after protein meals and elevated by GI bleeding (blood digested), starvation infection or fever can also increase via tissue catabolism, as can certain drugs
• serum creatinine: as GFR goes down blood creatiniine levels go up. affected by age (low in young) weight and muscle mass and old age. also not very sensitive
• SDMA: early marker –> will change before creatinine levels change
• FGF-23