Renal Physiology And Bp: Nephron Flashcards
Nephron structure consists of:
Bowman’s capsule
Glomerulus
PCT
Loop of Henley
DCT
Collecting duct
NEPHRON STRUCTURE main steps:
- Filtration
- Reabsorption
- Secretion
Summary of nephron function
- Filtration at the glomerular capillaries in the renal corpuscle
- Active removal of ions, glucose and amino acids at the PCT
- Water reabsorption in the PCT and descending lib of LOH increase filtrate conc.
- Active transport of Na+ and Cl- from ascending limb
- Reabsorption and secretion in the DCT
- Final reabsorption of water In collecting duct
Mech. For reabsorbing ions
Combination of diffusion, osmosis and carrier mediated transport
Solutes such as glucose and ions are reabsorbed, water follows by osmosis
Renal tubule made up of polarised epithelial cells = advantage of this?
Distinctly different membranes - APICAL and BASOLATERAL
Microvili increase the SA of absorption
Apical vs basolateral membrane
Apical= in contact with tubular fluid
Basolateral= in close proximity to the peritubular capillaries
Largest site of water reabsorption happens?
In PCT
60-70% by osmosis
Two main mechanism of Na reabsorption in the PCT are through?
Sodium-hydrogen exchanger (NHE) and through sodium glucose transporters (SGLT)
SGLT
UPATKES sodium and glucose together in the cell
Other transporters on basolateral membrane which allow passage of them
Gliflozins are?
SGLT2 inhibitors
Useful in treatment of diabetes as they prevent reabsorption of glucose from filtrate and so it is excreted in the urine= lowers blood glucose
NHE
Sodium is reabsorbed in exchange for H ions
Dapagliflozin mechanism
Competitive reversible inhibitor = blocks SGLT2 proteins
And is highly selective
=prevents uptake of glucose, so some Na+/glucose is trapped in the urine which means you aren’t reabsorbing as much water = wee it out
Descending limb vs ascending limb
Descending limb is impermeable to solutes, but permeable to water
Ascending= permeable to solutes but impermeable to water
Countercurrent multiplication is?
Positive feedback loop that exist in the LOP
(When filtrate becomes more concentrated providing a gradient for NA and Cl to be pumped out )
Countercurrent multiplication EXPALINED
Na+ and Cl- are pumped out of the ascending limb- elevates the osmotic conc. around the descending limb
Provides osmotic gradient for water to leave descending limb
=increases conc. of solutes in the descending limb which then arrive in the ascending limb and accelerates the transport of Na+ and Cl-
NKCC transporter
Na/K/2Cl
NKCC transporter is the site of action for?
Loop diuretics
What is happening in The ascending loop of Henle?
Na+ and Cl- are actively reabsorbed
NKCC at the apical membrane
Moves one Na+ , one K+ and 2 Cl- ions out of the filtrate into the cell every time it pumps
2 further carriers on basolateral membrane ( the peritubular side, close to the capillaries) role
K-Cl cotransporter that removes one of each ion with every pump and there is a Na-K exchange pump
Activity of these pumps = net loss of Na and Cl, but not K as the levels maintained by the Na/K exchanger
Loop diuretics site of action
NKCC cotransporter along ascending limb of the LOH in nephrons of the kidneys
NCC
Na/Cl transporter
Carries out one NA and one Cl- ion
What transporter in DCT?
NCC
Thiazide diuretics tend to be first one of treatment for?
Hypertension
Site of action for thiazide diuretics
Primarily DCT
Inhibit the NCC co-transporter
In DCT Na+ and Cl- actively reabsorbed by?
Activity of the NCC transporter
NCC located?
So the apical (tubular side) moves one Na+ and Cl-ion out of the cell with each pump
Na+ in the peritubular space. What happens?
Exchange for K at the basolateral membrane by the Na/K pump
Cl- leaves by Cl -channels on the basolateral membrane
Epithelial Na+ channels on collecting duct reabsorb?
Na+
These channels are sensitive to aldosterone
Function of aquaporins in collecting duct
Reabsorb water
Sensitive to Vasopressin (ADH)
Reabsorption mechanism : in PCT
NHE - sodium hydrogen exchanger
SGLT- glucose and sodium
Reabsorption mechanism : LOH
NKC- sodium, potassium and 2 Chloride
Reabsorption mechanism : DCT
NCC- Sodium and 2 chloride
Reabsorption mechanism : collecting duct
ENaC- sodium channel aquaporins - water channels
