Glomerular filtration

Question 1

Glomerulus structure

Answer 1

Capillary knot
Supplied by afferent, drained by efferent arteriole
Enveloped in capsule of epithelium = Bowmans capsule

Question 2

Glomerular capillaries

Answer 2

Fenestrated
Highly permeable to water
Low permeability to proteins
High hydrostatic pressure 
Surrounding mesanglial cells = modified smooth muscle

Question 3

Perm-selectivity

Answer 3

Size
Shape
Charge

Question 4

Permeability barrier

Answer 4

Endothelial layer of capillaries
Basement membrane, lots of - charged glycosaminoglycans
Epithelial podocytes = have pedicels, inter-digitate to produce split pores

Question 5

Driving forces for filtration

Answer 5

Hydrostatic pressure in capillary/ Bowmans state

Oncotic pressure in capillary/ Bowmans space

Question 6

Oncotic pressure

Answer 6

Created from the presence of proteins

In Bowmans space = 0

Question 7

Hydrostatic pressure

Answer 7

In Bowmans space should be low and remain constant, as the PCT acts as a sink

Question 8

Net filtration pressure

Answer 8

Pressure out - Pressure in

hydrostatic capillary + oncotic bowmans) - (hydrostatic bowmans + oncotic capillary

Question 9

GFR

Answer 9

Rate of formation of filtrate
GFR = Kf (permeability x SA) x net filtration pressure
{can also be calculated as urine conc. / plasma conc.}

Question 10

Factors affecting GFR

Answer 10

Hydrostatic pressure in capillary is most important variable
Varies with blood pressure, resistance in arterioles controlled by SNS, angiotensin and tubuloglomerular feedback

Question 11

Clearance

Answer 11

Volume of plasma from which substance X is completely removed
Use inulin and creatine
GFR measured at about 125 ml/min using markers
Calculated by (urine conc x urine flow rate)/ plasma conc

Question 12

Autoregulation of GFR

Answer 12

Myogenic = increased pressure stretches arteriole smooth muscle, causes contraction of smooth muscle and increases afferent arteriole resistance
Tubuloglomerular feedback = detected by macula densa of DCT, if flow rate increases, adenosine released to constrict afferent arteriole and lower GFR

Question 13

driving force for filtration

Answer 13

hydrostatic pressure

Question 14

hydrostatic pressure in glomerulus

Answer 14

filtration occurs when blood hydrostatic pressure exceeds pressure in glomerular capsule

Question 15

pressures

Answer 15

P = hydrostatic (in BC/ GC)
Pi = oncotic (BC/GC)
- oncotic in BS = 0
- hydrostatic in BS = low, PCT acts as sink

Question 16

pressures in arterioles

Answer 16

normal:

resistance in efferent>afferent to create high pressure in capillaries

Question 17

use of clearance

Answer 17

assess GFR if it is assumed the the amount of X removed from the blood = amount appearing in urine
marker needs to be:
- freest filtered, not reabsorbed, not metabolised