Kidneys and Body Fluids 6

Nota:

• Excretion is decreased by: Renin angiotensin Aldosterone Noradrenaline Excretion is increased by ANP and prostaglandins.

1. Hormones Affecting Balance
2. Renin-Angiotensin System

   Nota:

   • Decreases sodium excretion by increasing aldosterone Direct effect on proximal tubular epithelium Renal vasoconstriction due to reduced medullary flow which increase medullary osmotic gradient and passive NA reabsorption in thin ascending limb
   1. Direct Effects
   2. Aldosterone

      Nota:

      • Steroid from the adrenal cortex. Increases Na reabsorption with K and H secretion. Acts on principal cells of collecting ducts. Immediate genomic effects to increase permeability to K
      1. Stimuli

         Nota:

         • Stimulated by Angiotensin A rise in plasma k very sensitive. Afall in plasma NA ACTH

Nota:

• Atrial natriuretic peptide. 28 amino acids long Produced in Atrail myocytes, available also as BNP and CNP They react with receptors to produce effects such as Natriuresis and diureis. Lowers BP by causing vasodilation Reduce smooth muscle responsiveness Decrease levels of renin, aldosterone and AVP.

Nota:

• As potassium is the most prevalent cation. Normalization is needed due to electrical polarisation and for normal intracellular function. 3.5 to 5.5 mmol/l are the ranges, any less or more is bad.

1. Control

   Nota:

   •  baklancStorage is due to physiology and pathophysiology. Insulin, adrenaline and  aldosterone enables the physiology to keep the  balance balanced. Pathophysiology: acid-base balance, plasma osmolality, cell lysis and exercise
   1. Renal Handling

      Nota:

      • Freely filtered. Net reabsorption... In the collecting duct, K is reabsorbed by intercalated duct and secreted by principal cells according to need.
2. 4 Main determinants

   Nota:

   • A :concentration of K in the cytoplasm in principal cells B: Conc of K in tubular fluid C; Transepithelial Potential Difference D: Permeability of luminal membrane to K
   1. Factors influencing K secretion

      Nota:

      • Aldosterone A C D K Intake A C Aldosterone Distal Nephron Flow Rate B Distal nephron Na delivery C and Flow rate Impermeant anions Via C in tubular fluid
3. Systemic Acid-Base Status

   Nota:

   • In acute Alcalosis. K secretion increase. increase in pH makes it more permeable and hence secretion increase While decrease, i.e acute acidosis K is retained. chronic acidosis. Secretion increases due to inhibition of  proximal reabsorption.