Kidney physiology Flashcards
Name the five main processes that happen in the kidneys
- Filtration by glomerulus
- Obligatory absorption and secretion by the PCT
- Generation of osmotic gradient at loop of Henle
- Regulated absorption and secretion by DCT
- Regulation of water uptake by collecting ducts
Control of glomerular filtrate
- Endothelial lining of capillaries
- Basement membrane of capillaries
- Foot processes of epithelial cells (podocytes)
Triple barrier
Free passage of solutes up to 60KDa
Opposes movement of solutes and large solutes
negatively charged molecules filtered less easily than positively charged molecules
Balance of Sterling’s pressures giving a filtrate
Pushing fluid out of capillaries into tubule
Hydrostatic pressure 55mmHg
No oncotic pressure
Opposing forces pushing back into blood
Oncotic pressure -30mmHg
Hydrostatic pressure -15mmHg
Net movement of 10mmHg - GFR
Myogenic autoregulation
Afferent arterioles - dilation increases GFR
Efferent arterioles - dilation decreases GFR
Renal blood flow essentially constant normally
What are two different types of nephron?
Superficial - high up in cortex
Juxtamedullary - go right the way down into pyramids
Tubuloglomerular feedback
High flow rate inDCT of juxto-medullary complex means high Na - signal of adenosine goes to afferent arterioles to decrease flow rate (causes afferent arterioles to constrict)
Extrinsic hormonal factors influencing GFR and RBF
Dec afferent blood flow (VC)
- Symp nerves releasing NA
- Circulating NA
- Ang II (also efferent VC)
Inc afferent flow (VD)
- PGs
- ANP
Tubular reabsorption and excretion
Tubular reabsorption highly selective
Glucose and AA reabsorption is almost complete so excretion is zero
Na, Cl and bicarb are also highly reabsorbed but rates of reabsorption and excretion are highly variable and controlled
Waste products such as urea and creatinine are poorly absorbed and excreted in large amounts
How is sodium transported form lumen into blood?
Active transport epithelial cells into blood to allow electrical gradient for na to diffuse from lumen into epithelial cells
Why does no glucose appear in urine?
SGLT1/2 transporters - secondary active transport - Na diffuses across which provides energy for one or two glucose molecules to be transported out of the tubule
What happens in PCT?
65% of filtered sodium and water reabsorbed here
High capacity for reabsorption with high metabolically active cells
Sodium pump driven, a lot of co-transport
Secretion also occurs
What happens at loop of Henle?
20% of filtered water and 25% of filtered Na, K and Cl reabsorbed
Thin descending segment permeable to water diffusion
Thick ascending impermeable to water - has active transporters and absorbs Na, K and Cl (loop diuretics work here)
What happens in DCT?
5% of filtered sodium reabsorbed
Pumps/absorbs Na, K and Cl just like ascending limb of loop of Henle
Impermeable to water
Urine becomes more dilute
Two cell types - principal cell type absorb water and na ions, intercalated cell type absorb K and secrete H+
Thiazides, aldosterone ants and Na channel blockers act on these receptors
Collecting ducts
Absorbs less than 10% of filtered water and sodium
Determine urine output - dilute or conc
Impermeable to water unless ADH present
permeable to urea and has urea transporters
can secrete H+ so plays a role in acid/base balance
Aldosterone effects
Released from adrenal cortex
Important regulator of Na reabsorption and K excretion
Principal cells of cortical collecting duct is major site
Stimulates Na-K ATPase pump
Increases Na permeability of luminal side of principal membrane
