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what are the three layers of the filtration membrane?
capillary endotheslium, basement membrane, foot processes of podocyte
what happens to the macromolecules that gets stuck in the filtration membrane?
engulfed by glomerular mesangial cells
what allows the plamsa to maintain some water?
what are the pressures that affect filtration?
- outward: hydrostatic (glomerular blood pressure)
- inward: hydrostatic pressure in capsular space andcolloid osmotic pressure in capillaries
what is net filtration pressure?
- pressure responsible for filtrate formation (10mm Hg)
- main controllable factor determinating glomerular filtration rate (GFR)
what is glomerular filtration rate?
volume of filtrate formed per minute by both kidneys (normal=120-125ml/min)
what is the GFR proportional to?
- total surface area available for filtration (glomerular mesangial cells control by contracting)
- filtration membrane permeability
what are the two types of renal autoregulation (intrinsic) that acts to maintain normal GFR despite fluctuations in bp?
- myogenic mechanism: vacular smooth muscle contracts when stretched
- tubuloglomerular feeback: directed by macula densa cells of juxtaglomerular complex; respond to filtrate NaCl concentration
what happens to the myogenic mechanism when bp is high?
- muscle stretch causing constriction of afferent arterioles, restricts blood flow to glomerulus (protects glomeruli from damaing high BP)
- decrease in blood pressure, dilation of afferent arterioles
how does the tubuloglomerular feedback mechanism work?
increase in GFR, filtrate flow rate increases, decrease in reabsorption time, high filtrate NaCl levels causes constriction of afferent arteriole, decrease in NFP and GFR, more time for NaCl reabsorption
what are the extrinsic control of GFR
- extrinsic controls take precedence over intrinsic controls if system BP is less than 80 (worried more about maintaining bp)
- nervous system (NE released by sympathetic system, epinephrine released by adrenal medulla)
- endocrine system (renin angiotensin aldosterone)
how does the nervous system control the GFR?
- systemic vasoconstriction: increased blood pressure
- contriction of afferent arterioles: decrease in GFR, increased blood volume and pressure (less taken out of blood)
what are the extrinsic endocrine mechanisms?
- three pathways of renin release by granular cells
- -direct stimulation of granular cells by sympathetic nervous system (relaxed granular cell: reduced stretch means low BP)
- -stimulation by macula densa cells when filtrate NaCl is low
what are the two routes where reabsorption in the DCT can occur?
most occurs via the transcellular route (include both active and passive), some may occur in the paracellular route
what does hyperglycemia mean?
high blood glucose levels exceed transcellular transport systems, glucose in urine
what does the PCT reabsorb?
- all glucose, amino acids, and other organic nutrients
- 65% of water and soidum
- ionic reabosrption of Na+, K+, Ca2+, MG2+, HCO3-
- all uric acid, 1/2 urea, later secreted back into filtrate
how much of the water and solute is abosrbed before filtrate reaches DCT?
80% water and 85% solutes
what is the role of aldosterone?
- targets collecting ducts and distal DCT
- promotoes synthese of Na+ and K+channels, for Na+reabsorption; water follow
- absence of aldosterone: losts of 2% filtered Na+ could kill you
atrial natriureti peptide
- reduce blood Na+, decreased blood volume and pressure
- released by cardiac atrial cells
what is the function of the parathyroid hormone
acts on DCT to increase Ca+2 reabsorption