Physiology of the renal system

Question 1

Describe the process of Glomelular filtration in terms of forces !

Answer 1

• Hydrostatic pressure = pressure on walls of the capillaries = fluid pushed out = pushing
• Oncotic pressure = pressure by proteins on the walls of compartment = pulling

NFP = Hydrostatic pressure of glomerulus -. Hydrostatic of BC- oncotic pressure of glomerular capillary protein

Question 2

layers of filtration In glomerulus :

Answer 2

• Endothelium = fenestrated ( lets everything through except from RBC)
• Basement membrane (stop filtration of large proteins )
• Podocytes = part x bowmans capsule =>pedicles = narrow slits between them = only allow small molecules

( charge selective = everything is negative so negative molecules = hard tp go through , hence albumin doesn’t go through )

Question 3

describe renal blood flow
how is it controlled ?
how is it measured in humans ?
(4)

Answer 3

Autoregulation via myogenic vasoconstriction
1- Para- Aminohippuric acid (PAH) –>90% extracted by kidney in one circuit , inert , doesn’t effect kidney function
BUT its confined to the plasma so it doesn’t directly measure the renal blood flow
2- measure the clearance = volume of plasma delivered to kidney every min = renal plasma flow
3- Renal blood flow = renal plasma flow / 1- haematocrit

Clearance of PAH = Urine of PAH x Urine flow rate / Arterial plasma of PAH

Question 4

Describe how the glomerular filtration rate can be measure in humans *****

Answer 4

GFR = assesses if a person has kidney impairment

GFR= Urine x urine flow /Plasma

Question 5

Where does renal reabsorption occur ?

modes of transport ?

Answer 5

1) Everywhere through the epitheliums but mainly PCT

Between cells = paracellular 
Transcellular :
-diffusion 
-faciltated diffusion 
-active transport ( primary and secondary )

Question 6

outline the tubular reabsorption of glucose

Answer 6

97% reabsorbed in PCT
from filtrate to the epithelium –>SGLT2 ( sodium + glucose transporter ) –>GLUT2

If you have too much glucose in blood (diabetes) = SGLT2 inhibitors work here

Question 7

Tubular reabsorption of Amino Acids

2

Answer 7

Tend to be transported with Na+ , or Cl-

95% of AA = reabsorbed mainly in PCT

Question 8

Reabsorption of Na

• Transporters
• What drugs act on each section
• DCT + Ducts expression of the receptor is controlled by ——-

Answer 8

1) Na+ + glucose transporter PCT
2) Na+/K+/2CL- pump Ascending loop of Henle
3) DCT= Na+ ,Cl- + normal Na+ channel
4) Collecting ducts Na+/K+ pump

DRUGS :

1) PCT = SGLT2 inhibitors
2) Loop of henle = Loop diuretics
3) DCT = Thiazides
4) Ducts = Spironolactone

In the DCT, Ducts = Aldosterone controls the Na/K pump expression

Question 9

Reabsorption of water

Answer 9

Water follows Na+ 
Paracellular = between cells = gap junctions 
Transcellular = Osmosis through cell
Mostly reabsorbed by PCT 
BUT changes with levels of ADH

Counter -Current Multiplier :
Opposing direction of Flow of the Vasa recta and loop of henle ****

Question 10

Excretion of Urea

Answer 10

PCT = simple diffusion of urea into the blood
Loop= Urea transporter puts Urea back into Tubule = 50% excreted
Ducts = reabsorbed 80% back to blood
Only 20% is acc excreted

Question 11

Tubular secretion pumps in collecting ducts

Answer 11

1) Na/K pump
2) Na/H pump
3) Urea pump
4) Creatinine pump
5) NSAID = excreted here

Remember PAH measures renal filtration