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Renal system 2 (PCT (Cells (Na reabsorption (Loop of Henle (25%), Distal…
Renal system 2
PCT
Transcellular transport
- Movement of substances across epithelial cell
Paracelluar transport
- Movement of substances between epithelial cells
Tubular reabsorption
- Substances move from tubule into blood
Tubular secretion
- Substances move from blood into tubule
Peritubular capillary:
- low hydrostatic prewssure
- High colloid pressure
Cells
- Sodium: down conc gradient into cells of PCT up till equilibrium
- NaK ATPase: sodium outside cells to maintain conc gradient. K into PCT cells
- Na pulls glucose + AA + Cl diffuse into interstitial fluid into bloodstream: complete re absorption of glucose
- Water pulled across cells in interstitial fluid and peritubular capillary
- H+ (byproduct of respiration): from peritibular capillary to tubular fluid carbonic acid
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Loop overview
Fluid in PCT isoosmotic balance with blood (300)
- Go down loop of Henle: water take out tubular filtrate: 300 to 600 to 900 to 1200 as you pull more water out
- Ascending: more permeable to salt
CCM
Blood flow and tubular filtrate flow in opposite directions
Variable permeability maintains gradient
- Thick: loaded with Na and Cl: into interstitial space, into blood
- Lot of salt been pulled out before it passes thick ascending limb
- Potassium used to drive the last Na and Cl
- blood then passes thin descending limb which is permeable to water: water into salty blood
Thin descending limb (permeable to water, impermeable to solutes)
Thick ascending limb (impermeable to water, active solute transport)
Thick ascending limb
Potassium (in tubular filtrate) to interstitial space with 2 Cl- and Na+
potassium pumped back out (NaK ase)
LOOP OF HENLE
CONC urine
Descending limb
Permeable to water, less permeable to Na/CL and impermeable to urea
Ascending limb
Impermeable to water, very permeable to Na.Cl and moderate permeable to urea
Acid base maintenance
- Blood maintains constant pH
- pH is conc of free H+
Mixture of H+ ions and HCO3-
- Correct of pH is maintained by keeping ratio of hydrogen ions to bicarbonate in blood constant
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pH correction
- Reabsoprtion of filtered bicarbonate
- Excretion of daily acid load
- HCO3- reabsorption
- H+ secretion
- Ammonium secretion
Bicarbonate reabsorption
- Mostly in PCT 80%-90% (reclaimed bicarbonate) (CO2 and H2O) and then CO2 back to bicarbonate ions
- Rest in DCT and collecting duct: De novo constructed:
No hydrogen and bicarbonate transporters in DCT
Distal tubule
- Macula desna (tubular filtrate) sense low fluid or low Na+ conc
- Juxtaglomerular cells: renin into blood (liver releases angiotensinogen)
Ang 1 (ACE) Ang 2 (widespread vasoconstriction) to adrenal cortex to aldosterone to reabsorption of Na+ (and then water)
ADH
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- Osmorecepetors in hypothalamus sense Na conc of blood
- Nerve endings of osmoreceptors are located in posterior pituitary gland and secrete ADH
- If NA conc blood = high: Secretion of ADH
- Na conc blood low = no secretion ADH
Homeostasis
Overhydrated
- No ADH secreted
- Decrease aquaporins
- Decrease Reabsoprtion in collecting duct
Dehydrated
- ADH secretion
- Increase aquaporins
- Increase reabsorption in collecting duct
Urinary buffering
- Process where secreted H+ are buffered in urine by combining with weak acids or with NH3 to be excreted
- Major adaptation to an increased acid load is increased ammonium secretion
- Ammonium production also has role in further generation of HCO3-
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Reabsorption
- Once inside lumen of nephron: small molecules (ions, glucose and AA) reabsorbed from filtrate back into circulation
Transporters:
- Co- transporters (Na/Glucose)
- Active transporters
- Osmosis
- Solvent drag
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Secretion
- Secretion of substances into the lumen of tubule
- NH3 is screted from plasma into proximal tubule lumen
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