Week 17 Physiology - Renal I Flashcards
What makes up a nephron?
Individual renal tubule and its glomerulus (1.3 million per kidney)
What is the basic structure of a glomerulus?
Its a tuft of capillaries invaginated into the blind end of a nephron (Bowman’s Capsule). Involves afferent arteriole supplying blood to, and efferent from the glomerulus.
What layers separate the blood and the filtrate in Bowman’s Capsule?
- Capillary endothelium
- Podocytes
What is the glomerular basement membrane formed by?
Podcytes and mesangial cells
What are the different components of the nephron?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
What is the filtration fraction?
The proportion of the fluid reaching the kidneys that passes into the renal tubules. It is normally about 20%.
Which portion of the nephron is most permeable to H2O?
Thin descending loop of Henle
Which parts of the nephron are impermeable to water?
Ascending loop of hence (thick and thin)
Describe major structural features of PCT?
15mm long
Brush border
Where is the juxtaglomerular apparatus located?
Between where the thick ascending limb passes next to the glomerulus associated with that nephron
(Also marks the transition point to the DCT)
What are the cell types of the JGA?
Granular cells –> Secrete Renin
Macula densa –> sense Na+ concentration in filtrate, then stimulate granular cells to secrete renin
Mesangial cells
How long is the DCT?
5mm
What are the 2 cells types of the collecting duct, and their function?
P cells = Na+ reabsorption and ADH stimulated water reabsorption
I cells = more microvilli, mitochondria, concerned with Acid secretion and HCO3- transport
Which solutes are generally completely reabsorbed?
Glucose
Amino acids
Where do the blood vessels that supply the nephron originate from?
Efferent arteriole (which supplies peritubular capillaries)
What direction does the vasa recta run?
Descending vasa recta is parallel to ascending LOH
Ascending vasa recta is parallel to descending LOH
What is the renorenal reflex?
Increase in ureter pressure of one kidney leads to decrease in efferent nerve activity of the other –> increased sodium and water in the contralateral kidney
How much blood do the kidneys receive per minute?
1.2-1.3L/min of blood (25% cardiac output)
Between what systolic pressures does kidney autoregulation operate optimally?
90-220mmHg
Describe renal blood flow autoregulation:
Mediated by response to stretch of the smooth muscle of afferent arterioles, works to maintain constant rate of renal blood flow
I.e. if increased blood pressure, afferent constricts to limit, or dilates if low to allow increased flow to glomerulus
What substance can be used to measure renal plasma flow?
What about GFR?
P-amino-hippuric acide (PAH) –> has a high extraction ratio, therefore can be used to compare amount in urine versus plasma (in relation to haematocrit)
Inulin –> freely filtered, not reabsorbed, not metabolised
What is renal plasma clearance?
Volume of plasma from a substance is cleared per unit time
What factors affect the GFR?
- Size of capillary bed
- Permeability of GFR
- Hydrostatic and osmotic pressure gradients across capillary wall
Therefore:
- Changes in renal blood flow
- Changes in systemic blood pressure/hypovolaemia
- Changes in glomerular capillary permeability/surface area due to glomerular disease
What substances are more easily filtered across glomerular membrane?
Size: <4nm (neutral)
Charge: cationic/neutral
Membrane is negatively charged, therefore will lead to repelling of negatively charged particles
What transporter is primarily responsible fore glucose reabsorption in the kidney?
SGLT-2 (Sodium dependent glucose transporter) –> secondary active form of transport as requires sodium to be pumped out of the interstitium to maintain concentration gradients
What is the transport maximum for glucose?
375mg/min in men, 300mg/min in women
What causes mesangial cell contraction?
Endothelins
Angiotensin II
ADH
Noradrenaline
Leukotrienes
Histamine
**Leads to reduced GFR
What causes mesangial cell relaxation?
ANP
Dopamine
PDE2
cAMP
**Leads to increased GFR
Briefly describe the process of a solute (i.e. Na+) getting from tubular fluid back into renal interstitium?
Travels from tubular space across apical membrane, usually via osmotic/passive transport/co-transporters then requiring active transport across basal membrane to the interstitium
What solutes are couple to sodium reabsorption?
Sodium
H+
Glucose
PO4
What is the most important mechanism/transporter across apical membrane for sodium in proximal tubule?
Na+/H+ exchanger –> facilitates first step of Na+ moving across apical membrane into tubular epithelial cell
What is the most important mechanism/transporter across apical membrane for sodium in thick ascending limb?
Na+/K+/2Cl- cotransporter
By location, what is the different portion of sodium reabsorption?
PCT: 60%
Thick ascending limb: 30%
DCT: 7%
Collecting duct: 3%
Describe the process by which glucose is reabsorbed?
SGLT-2 transports across apical membrane into tubular epithelium.
Glucose then removed from cell via GLUT-2 transporter
Where is H2O primarily reabsorbed in the nephron?
70% PCT
20% Thin descending limb LOH
Remainder in collecting ducts
How does ADH affect H20 reabsorption?
Secreted in response to low plasma volume or high osmolality.
ADH causes increased aquaporin channel expression on principal cells and allows reabsorption of H20.
