Renal Physiology Lecture 1: The Basic Renal Processes

Question 1

What are the basic renal processes?

Answer 1

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion

Question 2

How much filtration occurs daily?

Answer 2

~180L/day (total plasma volume filtered over 60X/day)

• Protein-free fluid

Question 3

Filtrate subject to both …..?

Answer 3

Filtrate subject to both reabsorption or secretion

Question 4

Tubular reabsorption vs. secretion

Answer 4

Reabsorption:

• Water & solutes move from lumen to circulation
• Via peritubular capillaries or vasa recta

Secretion:

• Selective removal of substances from the circulation into the tubular filtrate
• Destined for excretion

Question 5

How do renal processes serve the body’s needs?

Answer 5

• Essential substances are conserved → i.e. water, salt, glucose
  
  • Enter circulation at the renal vasculature, reaches the heart for systemic circulation
• Substances not required remain in tubule lumen → Enter final urine for excretion

Question 6

What is filtrate initially similar to?

Answer 6

Filtrate is initially similar in composition to plasma

• ‘isosmotic’ → of or having the same or equal osmotic pressure. (2) A condition in which the total number of solutes (i.e. permeable and impermeable) in a solution is the same or equal to the total solutes in another solution.

Question 7

Filtrate processing at the proximal tubule

Answer 7

• 70% filtrate volume reabsorbed
• Solutes actively reabsorbed
  
  • Water follows by osmosis
• Both solute and water are reabsorbed
  
  • Filtrate remains isosmotic

Question 8

Filtrate processing at Loop of Henle

Answer 8

• Descending limb facilitates water reabsorption
  
  • Relatively impermeable to solute
• Ascending limb facilitates active solute reabsorption
  
  • Relatively impermeable to water
• Diluted filtrate leaves the loop of Henle

Question 9

What parts of loop of Henle are impermeable to solute/ water?

Answer 9

• descending → relatively impermeable to solute
• ascending → relatively impermeable to water

Question 10

Filtrate processing at the distal tubule and collecting duct

Answer 10

• Hormone-sensitive
• Site of salt & water regulation
• Varying permeability to salt & water based on body needs

Question 11

Amount of solute excreted = ??

Answer 11

• Volume and concentration of final urine varies according to body needs
  
  • Average volume is about 1.5 L after 24 hrs once it leaves the collecting duct but it’s can vary widely
• Fluid reaching the renal pelvis is destined for excretion