Renal system

Question 1

Define glomerulus, peritubular capillaries and juxtaglomerular apparatus

Answer 1

Glomerulus: ball like network of capillaries inside the Bowman’s capsule of the nephron: site of filtration

Peritubular capillaries surround the tubule and dip into the medulla with the loop of Henle (then called vasa recta)

Juxtaglomerular apparatus: twisted portion ascending loop which passes through afferent/efferent arterioles
- Contains macula densa cells of the ascending loop which sense flow and send paracrine signals to adjacent arterioles (constrict or relax)
- Granular cells in afferent arterioles secrete renin

Question 2

3 Filtration barriers and how it is regulated

Answer 2

3 barriers: glomerular capillary endothelium, basement membrane, Bowman’s capsule epithelium

Endothelium is fenestrated with glycocalyx (lattice) protein net
and basement membrane - coarse sieve for most plasma proteins

Podocytes of Bowman’s epithelium have foot processes that wrap around the glomerular capillaries to make filtration slits
Mesangial cells contract to control opening of slits

Question 3

GFR and coefficient of filtration definition

Answer 3

Glomerular filtration rate (GFR) = volume of fluid which filters into Bowman’s capsule per unit time

Influenced by net filtration pressure and coefficient of filtration

Coefficient = surface area and permeability of filtration slits (controlled by mesangial cells)

Question 4

OAT transporters main points

Answer 4

OAT transporters allow for transport of a variety of organic substrates (ex. penicillin)

Basolateral NaDC cotransporter used to concentrate dicarboxylates (TCA) intracellularly

Basolateral Na-K ATP used to maintain low intracellular Na+ balance to drive NaDC cotransport

Basolateral OAT transports organic anions into cell and dicarboxylates out to ECM

Apical OAT4 secretes organic anion and regains dicarboxylate intracellularly