Kidney: tubular processing of Glomerular filtrate

Question 1

Enumerate mechanisms of tubular transport in the kindey

Answer 1

• Active transport:
  1. Primary active
  2. Secondary Active:
  -Co transport & Counter transport
• Passive transport

Question 2

Example of primary active transport in tubular proccessing

Answer 2

Sodium reabsorption across Proximal tubular epithelium

Question 3

decribe primary active transport of sodium at basolateral border of tubular epithelium

Answer 3

• Sodium potassium pump pumps 3 sodium out of cell into ISF & 2 Potassium in
• Creating a negtive potential inside the cell (-70mV) & lowering Intracellular Na+ concentration

Question 4

decribe primary active transport of sodium at luminal border of tubular epithelium

Answer 4

due to electrochemical gradient, Sodium diffuses from lumen into Tubular epithelium

Question 5

enumerate types of Secondary active transport

Answer 5

• Co transport
• Counter transport

Question 6

example of Co transport (of secondary Active transport)

Answer 6

Glucose reabsorption (via passive aborption of Sodium)

Question 7

Describe the Co transport of Glucose at the luminal Border

Answer 7

• Sodium diffuses from lumen into tubular epithelium down electrochemical gradient
• Glucose & sodium bind to a common Carrier called Sodium glucose transporter 2 (SGLT-2)

Question 8

Describe the Co transport of Glucose at the Basolateral Border

Answer 8

• Sodium is pumped out by sodium potassium pump into ISF
• Glucose is transported by Facilitated diffusion into ISF via GLUT-2

Question 9

Difenition & example of Counter transport in tubular processing

Answer 9

when reabsorption of a substance is linked to Secretion of another substance

• Example: secondary Active secretion of H+, by Sodium-hydrogen counter transport

Question 10

Enumerate examples of Passive Reabsorption

Answer 10

1. Passive reabsorption of Chloride
2. Osmosis of water
3. Passive reabsorption of Urea

Question 11

Describe passive reabsorption of Chloride

Answer 11

Paracellular
1. Reabsorption of Na+ Creates a negatively charged lumen & positively charged tubular cell
2. Causing Chloride to diffuse passively From Lumen to Cells down electrical gradient

Question 12

Describe osmosis of Water from lumen

Answer 12

Paracellular route
1. reabsorption of solutes causes decrease in their concentration in lumen & increase their concentration in Interstitium
2. This creates concentration gradient for water to diffuse out from lumen into ISF

Question 13

Describe passive reabsorption of urea

Answer 13

• Reabsorption of water creates Concentration gradient favouring 50% Urea reabsorption

Question 14

Enumerate Laws of Tubular Transportation

Answer 14

• Tubular Transport maximum (for actively transported substances): is the maximum transport rate for actively transported substances (mg/ minute), when carrier systems are saturated, there is no further increase in transport, this causes a Threshold concentration of these substances in plasma, below which, non of these substances appear in urine, And above which, they appear in urine
• Gradient-time transport (for substances reabsorbed by diffusion): detremined by Electro-chemical gradient & tubular flow rate

Question 15

Explain why sodium (Na+) obeys gradient-time transport law in PCT despite being actively transported

Answer 15

• At the baslateral border, there are many & more than enough Sodium potassium pump Carriers
• therefore Active transportation at the Basolateral Broder Is non-limiting
• Instead the limiting will be Diffusion at the Luminal Border

Question 16

Froces favouring reabsorption by peritubular capillaries

Answer 16

• Colloidal osmotic pressure of peritubular capillaries (32mmHg)
• Hydrostatic Pressure in ISF (6 mmHg)
• Total= 38mmHg

Question 17

Forces opposing Reabsorption by peritubular capillaries

Answer 17

• Hydrostatic pressure inside peritubular capillaries (13mmHg)
• Colloidal osmotic pressure inside ISF (15mmHg)
• Total=28mmHg

Question 18

Net reabsorptive force of Peritubular capillaries

Answer 18

38(favoring)- 28(opposing)= 10mmHg favouring