Structure & function of the renal tubule

Question 1

Renal tubule

Answer 1

Segments - filtered fluid is converted to urine

Question 2

Glomerular filtrate

Answer 2

Same composition as plasma except no cells and very little protein

Question 3

What happens to the Glomerular filtrate?

Answer 3

Modifications which take place along the tubule by the transport of solutes and water into and out of tubule.

Question 4

Reabsorption

Answer 4

Tubular lumen to peritubular plasma

Question 5

Secretion

Answer 5

Peritubular plasma to the tubular lumen

Question 6

When does reabsorption take place

Answer 6

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

Question 7

When does secretion take place?

Answer 7

When movement is in the opposite direction from the peritubular plasma into the tubular lumen

Question 8

Active transport

Answer 8

Moving molecules/ion against conc gradient
Operates against an electrochemical gradient
Requires energy - driven by ATP

Question 9

Passive transfer

Answer 9

Passive movement down concentration gradient (requires suitable route)
Active removal of one component = concentrates other components

Question 10

Symport

Answer 10

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

Question 11

Anti-port

Answer 11

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

Question 12

Co transport

Answer 12

Movement of one substance down its concentration gradient = generates energy = allows transport of another substance against its concentration gradient

Question 13

Transport in tubule

Answer 13

Combination of active and passive mechanisms = transcellular transport over luminal & basolateral membranes in either direction

Question 14

What are the 2 types of nephron

Answer 14

Cortical nephron (DO NOT EXTEND INTO THE MEDULLA)
Juxta-medullary nephron (BETTER AT CONCENTRATING URINE)

Question 15

What are the key differences in the nephrons?

Answer 15

Cortical - 85% short LoH

Juxta-medullary - 15% Long LoH

Question 16

Proximal convoluted tubule

Answer 16

Directly adjacent to bowman’s capsule

High capacity for reabsorption

Question 17

What is Fancoi’s syndrome?

Answer 17

All PCT reabsorptive mechanisms deffective

Question 18

What is Fancoi’s syndrome?

Answer 18

All PCT reabsorptive mechanisms defective

Question 19

What are the characteristics of the PCT?

Answer 19

Highly metabolic, numerous mitochondria for active transport

Extensive brush border o luminal side = large surface area for rapid exchange

Question 20

Functions of Loop of Henle

Answer 20

LoH critical role in concentrating/diluting urine - adjusting rate if water secretion/absorption

Question 21

What are the 3 segements of the Loop of Henle?

Answer 21

Thin descending
Thin ascending - thin epithelial cells no brush border, few mitochondria and low metabolic activity
Thick ascending - Thick epithelial cells, extensive lateral intercellular folding, few microvilli, many mitochondria

Question 22

Medullary osmotic gradient

Answer 22

The gradient from cortex to inner medulla and the osmolality decreases

Question 23

What maintains the counter medullary osmotic gradient?

Answer 23

Countercurrent and Vasa Recta

Question 24

What can change the gradient in the Vasa recta?

Answer 24

Change in blood flow

Question 25

What does the vasa recta do?

Answer 25

Acts as a counter-current exchangbe system. As the VS descends into the medulla water diffuses out and salts diffuse in The reverse occurs when ascending

Question 26

DCT (Distal Convoluted Tubule)

Answer 26

``` 1st part (macula densa) linked to juxtaglomerular complex 2nd part very convoluted ```

Question 27

Connecting tubule

Answer 27

Connects end of DCT to collecting duct - mainly in the outer cortex Similar functions to 2nd part of DCT

Question 28

Functions of the DCT

Answer 28

Solute reabsorption continues, w/out water reabsorption Low water permeability High Na+, K+- ATPase activity in the basolateral membrane Further dilution of tubular fluid ADH can exert actions Role in acid-base balance

Question 29

What are the two types of cells in the collecting duct?

Answer 29

Intercalated cells- involved in acidification of urine and acid-base balance Principal cells role to play in Na balance & ECF volume regulation

Question 30

What is the main function of ADH?

Answer 30

Conserve body water by reducing the loss of water in the urine

Question 31

What are the functions of the collecting duct ?

Answer 31

The medullary collecting duct is permeable to urea.

Question 32

How is the solute concentration built up in the medulla

Answer 32

1. Active transport of Na+ and co-transport of K+ & Cl- of thick ascending limb into the medullary interstitium 2. AT of ions from collecting ducts into medullary interstitium 3. Facilitated diffusion of large amounts of urea from collecting ducts into the medullary interstitium 4. Very little diffusion of water from ascending limbs of tubules interstitium