Renal system

• Renal system


  The system responsible for regulating the water balance, electrolyte balance and acid-base balance of the body, as well as the excretion of metabolic wastes

  
• Kidneys


  • Homeostatic function: Regulation of the water balance, electrolyte balance and acid-base balance
  • Excretory function: Excretion of metabolic wastes, urea, creatinine, toxins, drugs, excess minerals, water
  • Endocrine secretory function: Secretion of renin, erythropoietin and prostaglandins
  • Endocrine metabolic function: Conversion of Vitamin D3 in active 1,25-dihydroxycholecalciferol
• Urine formation


  1. Filtration from glomerular capillaries into Bowman's capsule

  2. Reabsorption of organic nutrients, ions and water

  3. Secretion of waste products

  
• Glomerular filtration rate


  Volume of filtrate/min, 180 L/day
• Nutritional substances are completely reabsorbed from the tubules and do not appear in the urine
• Substances that must be cleared from the blood (e.g. urea, creatinine, uric acid) are poorly reabsorbed and excreted in large amounts in the urine

  
• Tubular transport


  1. Reabsorption and secretion of substances

  2. In loop of Henle: Descending limb is permeable to water, ascending limb is impermeable to water but permeable to solutes
• Urine concentration


  1. Continuing to secrete solutes while increasing water reabsorption

  2. Requires high level of ADH and highly osmolar renal medullary interstitium
• Plasma osmolality


  Measure of osmotically active solutes in plasma, normal range 282-295 mOsm/kg H2O
• Alterations in plasma osmolality

  Can cause swelling or shrinking of cells, leading to cell death

  
• ADH mechanism of action

  ADH acts on collecting duct cells, stimulating insertion of water channels (aquaporins) to promote water reabsorption
• High plasma osmolality


  Increases ADH secretion, leading to more water reabsorption and less water excretion
• Low plasma osmolality


  Decreases ADH secretion, leading to less water reabsorption and more water excretion
• Blood pressure


  The pressure blood exerts on the arterial walls, determined by cardiac output and total peripheral resistance
• Kidneys regulate blood pressure

  By regulating extracellular fluid volume through excretion of variable amounts of sodium and water
• RAAS (Renin-Angiotensin-Aldosterone System)


  1. Renin converts Angiotensinogen into Angiotensin I. ACE converts Angiotensin l into Angiotensin II->Aldosterone

  2. Increases water and sodium reabsorption, leading to increased blood pressure
• Anatomy of the renal system

  • kidneys
  • renal artery and vein
  • ureter
  • bladder
  • urethra
• Anatomy of the kidneys:

  • capsule
  • cortex
  • medulla
  • calyx
  • renal pelvis
  • ureter
• Urine in the kidneys:

  • Urine is formed from the arterial blood that enters the kidney via renal artery
  • Urine is collected in the calyx, leads to the renal pelvis and finally the ureter
  • Filtered blood leaves the kidney through renal vein
• Anatomy of the nephron:

  • Bowman's capsule
  • loop of henle
  • proximal convoluted tubule
  • distal convoluted tubule
  • collecting duct
• Anatomy of Bowman's capsule:

  • afferent and efferent arterioles
  • glomerulus
  • podocytes
  • proximal convoluted tubule