H1v: Outline the functions of the kidney

BP Regulation

  • Kidneys maintain homeostasis of blood volume by regulating H2O & electrolytes long term
  • ∴have a direct determination of control of BP longT
  • RENIN is formed & stored in GRANULAR CELLS of JUXTAGLOM APPARATUS
  • ↓NaCl delivery to macula densa/↑symp activity/↓intrarenal BP → release of RENIN →
Renin Cleaves

production

  • Aldosterone = ↑Na+ retention in kidneys
  • ANP = ↑Na+ loss in kidneys
  • Which affects total circulating volume & ∴BP

Water & Electrolyte Balance

  • PRIMARY FUNCTION of kidneys in regulation of fluid & electrolytes
  • High BF → 180L/day of ultrafiltrate produced
  • Normal urine output 1500mL/day → ∴large amount of reabsorption of H2O & electrolytes
  • 60% Na+ reabsorbed at PCT with H2O following
  • Final volume & composition of urine is regulated by factors controlling glom. filtration, tubular reabsorption & tubular secretion
  • But via counter-current mechanism can concentrate urine up to 1400 mOsm to ↓water loss
  • Each day 2.5L ingested (food, drink, metabolic processes)
  • 900mL of insensible loss → balance is achieved by renal urine output

Basolateral membrane = blood side

Apical membrane = urine side

Regulation of Plasma Osmolality

  • Plasma osmolality is regulated within 1 – 2% of normal range
  • Osmoreceptors of hypothalamus monitor ECF tonicity
  • Hypothalamus then controls thirst & ADH secretion
  • ADH works on V2 receptors on BLM of collecting duct principle cells via GPCR → ↑ Aquaporin H2O channel insertion on APICAL MEMBRANE → ↑H2O permeability & ↑water reabsorption
  • Requires maintenance of a medullary interstitial osmotic gradient by kidneys
  • Kidney is constantly ∆ H2O & solute input & output in response to OSMORECEPTOR info

Endocrine Function

  • Produces active form of Vitamin D (1,25 dihydroxyvitamin D3)
  • Secretes EPO in response to ↓PO2 to stimulate RBC production
  • Stores & produces & secretes RENIN which makes up the RAAS system → aldosterone & AII have profound effects in the kidneys
  • Kallikrein secreted by kidneys → production of BK in circulation → VD

Regulation of Acid/Base

  • Reabsorbs all filtered HCO3–
  • Excretion of fixed & non-volatile acids (phosphate, ammonium), secretion of H+

Excretion of Waste & Foreign Substances

  • Filtration & removal of metabolic waste
    • Urea from protein
    • Uric acid from nucleic acids
    • Creatinine from muscle creatine
  • Filtration & removal of drugs
  • Hepatic metabolism → makes drugs water soluble → allowing renal excretion

Gluconeogenesis

  • Renal cortex contains glucose-6-phosphatase
  • ∴during fast can synthesis & release glucose