Structure and function of the renal tubule

Question 1

What occurs at the Bowman’s capsule and glomerulus?

Answer 1

Large amounts of plasma are filtered

Question 2

What occurs at the renal tubule?

Answer 2

Filtered fluid is converted to urine

Question 3

Difference between glomerular filtrate and plasma?

Answer 3

Glomerular filtrate has the same composition as plasma except there are no cells and very little protein

Question 4

When does urine formation begin?

Answer 4

When large amounts of fluid (that is virtually free of protein) is filtered from the glomerular capillaries into the bowman’s capsule

Question 5

What is glomerular filtrate?

Answer 5

An ultrafiltrate of plasma

Question 6

What is the rate at which glomerular filtrate is formed?

Answer 6

At 120 ml/min

Question 7

What is the rate of urine flow?

Answer 7

~ 1ml/min

Question 8

How does modification of glomerular filtrate occur?

Answer 8

• The filtration process is relatively non-selective
• Modification occurs along the tubule by the process of reabsorption and secretion of water and various solutes via tubular transport

Question 9

What is the direction of movement when reabsorption is occurring?

Answer 9

When the direction of movement is from the tubular lumen into the peritubular capillary plasma it is called reabsorption

Question 10

What is the direction of movement when secretion is occurring?

Answer 10

When the movement is in the opposite direction to reabsorption i.e. peritubular plasma into tubular lumen, it is called secretion

Question 11

Excretion

Answer 11

Clearing unwanted substances by excretion into urine

Question 12

Reabsorption

Answer 12

Returning wanted substances

Question 13

What barriers must substances cross to be reabsorbed?

Answer 13

it must first cross:

• the luminal membrane
• diffuse through the cytosol
• across the basolateral membrane & into the blood (transcellular transport).
• Vice versa for secretion

Question 14

What are two physiological processes involved with reabsorption/secretion?

Answer 14

1. Active transfer

2. Passive transfer

Question 15

Cellular composition of the tubule?

Answer 15

Tubule has a single cell layer wall

Question 16

Basolateral membrane

Answer 16

Away from the lumen

Question 17

Luminal/apical membrane

Answer 17

Towards the lumen

Question 18

Describe the movement of molecules via active transfer/primary active transport

Answer 18

Moving molecules/ions against their concentration gradient (from low to high)

• Operates against electrochemical gradient

Question 19

What does active transfer/primary active transport require?

Answer 19

Requires energy: driven by ATP

Question 20

Describe movement of molecules via passive transfer

Answer 20

Passive movement down concentration gradient (from high to low conc)
- requires suitable route

Question 21

How does passive transfer occur?

Answer 21

Active removal of one component: concentrates other components

Question 22

Describe movement of molecules via co-transport/secondary active transport

Answer 22

Movement of one substance down its concentration gradient: generates energy
- Allows transport of another substance against its concentration gradient

Question 23

Why does co-transport/secondary active transport require?

Answer 23

Carrier proteins

Question 24

What are the two types of co-transport/secondary active transport?

Answer 24

1. Symport

2. Anti-port

Question 25

Symport

Answer 25

Transported species move in the same direction, e.g. Na+-glucose

Question 26

Antiport

Answer 26

Transported species move in opposite directions e.g. Na+-H+ anti port

Question 27

What is counter-transport?

Answer 27

When substance to be transported along with Na binds to carrier protein from inside of cell and comes out