Renal Physiology Lecture 1: Process of Renal Secretion and Excretion

Question 1

What is renal secretion?

Answer 1

Transfer from circulation to renal tubules

• Movement of substances from the capillaries to renal interstitium
  
  • Transport to the lumen for excretion
• Involves membrane transporters
• Facilitates ion balance, waste excretion
• Enhances excretion of substances not required by the body

Question 2

What kind of process is secretion?

Answer 2

An active process

• Transport of substances against concentration gradients demands energy
• i.e. Organic anion transporters (OATs)
  
  • Transport a wide variety of wastes
    
    • i.e.bilesalts. Chemicals. drugs

Question 3

Process of renal secretion

Answer 3

Sodium potassium ATPase maintains low intracellular sodium concentration. Sodium electrochemical gradient facilitates the concentration of dicarboxylate such as alpha ketoglutarate (akg) in the tubular epithelial cell by the action of a sodium dicarboxylate cotransporter (NaDC) on the apical and bass lateral membranes in the proximal tubule. Organic anion transporters then use the energy generated by dicarboxylate moving out of the cell down its concentration radiant to move an organic anion against its concentration gradient into the epithial cell. Once the organic anion is sufficiently concentrated in the epithelial cell facilitated diffusion by anion exchangers can transfer to lumen where it is destined for excretion.

Question 4

What does excretion of a substance depend on?

Answer 4

• Filtration rate → and how it is handled as it passes through the tubule
• Reabsorption
• Secretion

Question 5

What is renal clearance help with?

Answer 5

Renal clearance of substances can help estimate GFR

• Assessment of renal function

Question 6

What is renal clearance?

Answer 6

Rate at which a substance is lost from the body by excretion or metabolism

• Higher the plasma concentration the more of a substance will filter into the tubule, and the higher the GFR the more plasma is filtered at the glomerular capillaries so higher amount of substance enters the tubule and in final urine

Question 7

What is often used to estimate renal clearance?

Answer 7

inulin

• Substances only cleared by excretion, clearance is the volume of plasma flowing through kidneys that is totally cleared of that substance in a certain period of time. Inulin can be used because it is freely filtered and not reabsorbed or secreted so can estimate clearance or GFR. Clearance is equivalent to GFR
• creatinine sometimes used clinically but only small amount is secreted

Question 8

Renal clearance calculation

Answer 8