1- Epithelial transport in the glomerulus

Question 1

describe the body fluid compartments of a 70kg man

Answer 1

• total volume = 42L
• intracellular volume = 28L (2/3), extracellular volume = 14L
• plasma volume = 3L, interstitial volume = 11L

Question 2

describe the distribution of the major free ions

Answer 2

• Na - extracellular: 135mM, intracellular: 10mM
• K - extracellular: 4.5mM, intracellular: 145mM
• Cl - extracellular 95mM, intracellular: 4.2mM
• Ca2+ - extracellular: 2.5mM, intracellular¨: 10^-7

Question 3

describe the different parts of the nephron

Answer 3

1. glomerulus: tuft of capillaries between an afferent and efferent arteriole
2. tubule:
   
   • bowman´s capsule
   • proximal convoluted tubule
   • loop of Henle - descending and ascending limbs
   • distal convoluted tubule
   • collecting duct

Question 4

what is the role of tight junctions in the nephron?

Answer 4

1. separate the extracellular fluid surrounding apical and basolateral membranes of polarised epithelial cells - required for transport functions
2. prevent diffusion of membrane proteins and glycolipids between apical and basolatera regions of plasma membrane
3. creates varying permeability of epithelial barrier for paracellular transport

Question 5

where does the greatest amount of paracellular transport occur in the nephron? explain why

Answer 5

in the PCT (1/3 of all its transport):

• leaky epithelium with low transepithelial resistance (TER)
• high peritubular protein conc. and renal hydrostatic pressure
• NO, prostaglandings and cAMP increase paracellular permeability

Question 6

name 3 examples of primary active transport in the nephron

Answer 6

1. Na/K ATPase (basolateral)
2. PMCA (basolateral)
3. H+ ATPase (apical)