Kidney and Body Fluids 4

Nota:

• Anatomy of the piping of the nephrons.

1. Proximal Tubules

   Nota:

   • Most reabsorption occurs here. i.e Glucose, amino acids, at least 2/3 Na Cl and h2o (aquaporin 1) in isosmotic amounts. Most HCo3 Most K  2/3 of Ca 30% of Mg 80% of phosphate 50% of urea. lactate citrate and other kerb's cycle intermediates and vitamins Uptake of filtered proteins (multiligands or endocytic ligands) Synthesis of ammonium
   1. Segments

      Nota:

      • Divided into 3 segments S1- ? S2- secrete organic acids and bases S3 - Straight proximal tubules Early segments have loads of microvilli, hence rapid transcullular transport, paracellular pathway is leakier. Later segments have slower rates of transcelullar reabsorption and paracellular pathways are tighter. i.e opposite.
   2. Peritubular Reabsorption

      Nota:

      • Much lower than glomerular filtration
   3. Glomerulotubular Balance

      Nota:

      • Constantcy of the fraction of sodium reabsorbed by proximal tubule despite changes in GFR Due to change in peritubular Starling's forces. Changes in filtered load of glucose and amino acids.
2. Loop of Henle
   1. Thin
      1. Thin Descending Limb

         Nota:

         • Very permeable to H20 due to AQP1 Maybe permeable to NaCL or urea. Therefore, as stuff pass thru, water leaves lumen and osmolality increases. In cortical nephrons 600mOSM/kg Justamedullary 1200mOSM/kg
      2. Thin ascending limb

         Nota:

         • Impermeable to water Highly permeable to NAcl and moderately permeable to urea. No active transort. Fluid becomes more dilute.
   2. Thick Ascending

      Nota:

      • Impermeable to water, low urea permeability Active NaCl transport. Reabsorb Hco3 by H+ secretion Low osmolality at end of thick aLH
3. Distal Convoluted Tubule and Connecting Tubule

   Nota:

   • Similar in function, connecting tubule is sensitive to several hormones They are water impermeable,  low urea permeability, active NaCL reabsorption.
4. Collecting Duct

   Nota:

   • Made up of 2 cell types Principal cell: Light cells Na reabsorption and K secretion Responds to aldosterone and ADH Intercalated cells: Dark cells a intercalated cells reabsorb K and secrete H b intercalated cells secretes Hco3
   1. Permeablity

      Nota:

      • Water: Without ADH, no water goes. If ADH water goes into/ UreaL Only papillary segment is permeable to urea. via UTA1 and UTA3 urea transporters Stimulated by ADH
5. Water Balance

   Nota:

   • Water inputs from food, oxidation of food or liquid intake. Water outputs form insensible loss, sweat, faeces, urine Water balance is regulated by, thirst and drinking, the kidneys, inhibit or stimulate ADH
   1. Thirst

      Nota:

      • REgulated in specific areas in hypothalamus, with aid from cerebral cortex Stimulated by increased osmolality Fall in extracellular volume Renin0angiotensin Dryness of mouth and throat.
   2. Urine

      Nota:

      • Dilute rine is achieved by taking solute out and leaving water behind. From thin ascending loop of hence. If there no ADH in collecting duct, it is water impermeable.  Thin/thick alb and DCT are always water impermeable. To make a concentrated urine, it must have ADH and high medullary osmolalityh, so it makes collecting tubule collect water.