Filtration

Question 0

Explain the role of active transport and co-transport in tubular reabsorption and secretion

Answer 0

Na+/K+ATPase (3Na out, 2K in)
Co-transport:
SGLUT, GLUT2 of glucose (renal threshold 200mg/100ml)
Amino acids
Organic cation secretion:
H+-OC+ exchanger (driven by Na-H antiporter

Question 1

Describe glomerular filtration, tubular reabsorption, pumps leak systems and fluid uptake by the peritubular region

Answer 1

Glomerular filtration:
Capillary endothelium - filtrate moves between cells
Basement membrane - acellular, gelatinous layer of collagen/glycoproteins, negative charge
Podocyte - pseudopodia interdigitate –> filtration slits
Plasma filtration:
Hydrostatic pressure in capillary
Hydrostatic pressure in Bowman’s
Osmotic pressure difference
Tubular reabsorption:
PCT - main site (ions, water, glucose, amino acids)
LoH - further reabsorption of salts
DCT - reabsorption of electrolytes, removes NaCl, actively secreted H+

Question 2

Describe the concept of clearance and be able to calculate clearance

Answer 2

Clearance - volume of plasma from which any substance is completely removed by the kidney in a given amount of time
65ml/min
Clearance rate = urine conc. of substrate x flow rate/plasma conc. of substrate

Question 3

Describe renal processes including renal blood flow and GFR

Answer 3

Renal plasma flow = 550ml/min

GFR = 90-125ml/min (20% of renal plasma flow)

Question 4

Describe the regulation of renal blood flow and GFR

Answer 4

Autoregulation
Myogenic response - increased BP –> afferent constriction
Tubular glomerular feedback (macula densa cells) - increased BP –> increased NaCl –> adenosine –> vasoconstriction, decreased BP –> decreased NaCl –> prostaglandins –> vasodilation

Question 5

Describe how GFR and clearance are related

Answer 5

Clearance rate calculates GFR

Question 6

Define the term ‘renal threshold’

Answer 6

Plasma concentration of substrate at which Tm is reached