Structure & function of the renal tubule Flashcards
Renal tubule
Segments - filtered fluid is converted to urine
Glomerular filtrate
Same composition as plasma except no cells and very little protein
What happens to the Glomerular filtrate?
Modifications which take place along the tubule by the transport of solutes and water into and out of tubule.
Reabsorption
Tubular lumen to peritubular plasma
Secretion
Peritubular plasma to the tubular lumen
When does reabsorption take place
When the direction of movement is from the tubular lumen into peritubular capillary plasma
When does secretion take place?
When movement is in the opposite direction from the peritubular plasma into the tubular lumen
Active transport
Moving molecules/ion against conc gradient
Operates against an electrochemical gradient
Requires energy - driven by ATP
Passive transfer
Passive movement down concentration gradient (requires suitable route)
Active removal of one component = concentrates other components
Symport
Transported species move in same direction e.g. Na+ - glucose
Anti-port
Transported species move in opposite directions e.g. Na+-H+ antiport
Co transport
Movement of one substance down its concentration gradient = generates energy = allows transport of another substance against its concentration gradient
Transport in tubule
Combination of active and passive mechanisms = transcellular transport over luminal & basolateral membranes in either direction
What are the 2 types of nephron
Cortical nephron (DO NOT EXTEND INTO THE MEDULLA) Juxta-medullary nephron (BETTER AT CONCENTRATING URINE)
What are the key differences in the nephrons?
Cortical - 85% short LoH
Juxta-medullary - 15% Long LoH
Proximal convoluted tubule
Directly adjacent to bowman’s capsule
High capacity for reabsorption
What is Fancoi’s syndrome?
All PCT reabsorptive mechanisms deffective
What is Fancoi’s syndrome?
All PCT reabsorptive mechanisms defective
What are the characteristics of the PCT?
Highly metabolic, numerous mitochondria for active transport
Extensive brush border o luminal side = large surface area for rapid exchange
Functions of Loop of Henle
LoH critical role in concentrating/diluting urine - adjusting rate if water secretion/absorption
What are the 3 segements of the Loop of Henle?
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
Medullary osmotic gradient
The gradient from cortex to inner medulla and the osmolality decreases
What maintains the counter medullary osmotic gradient?
Countercurrent and Vasa Recta
What can change the gradient in the Vasa recta?
Change in blood flow
What does the vasa recta do?
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
DCT (Distal Convoluted Tubule)
1st part (macula densa) linked to juxtaglomerular complex 2nd part very convoluted
Connecting tubule
Connects end of DCT to collecting duct - mainly in the outer cortex
Similar functions to 2nd part of DCT
Functions of the DCT
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
What are the two types of cells in the collecting duct?
Intercalated cells- involved in acidification of urine and acid-base balance
Principal cells role to play in Na balance & ECF volume regulation
What is the main function of ADH?
Conserve body water by reducing the loss of water in the urine
What are the functions of the collecting duct ?
The medullary collecting duct is permeable to urea.
How is the solute concentration built up in the medulla
- Active transport of Na+ and co-transport of K+ & Cl- of thick ascending limb into the medullary interstitium
- AT of ions from collecting ducts into medullary interstitium
- Facilitated diffusion of large amounts of urea from collecting ducts into the medullary interstitium
- Very little diffusion of water from ascending limbs of tubules interstitium
