water balance U.4 L.15

  • the average adult loses 2.5 L of water per day, 1% decrease in body water causes thirst, 5% causes extreme pain and collapse, 10% decrease causes death

  • water balance is regulated with antidiuretic hormone (ADH)

    • what : increases water reabsorption in kidney

    • how : makes collecting duct permeable to water

    • why : regulates osmostic pressure of body fluids

    • where : produced in the hypothalamus, stored and released from the posterior pititary gland

  • maintaining homeostasis : lower water level in bloodm increased blood solutes/osmotic pressure

  • water moves out of cells into the bloodstream hypothalamic osmoreceptors shrink (posterior pituitary releases ADH, ADH travels to the collecting ducts, collecting ducts become permeable to water, H2O reabsoption

  • increased water reabsorption = increased urine concentration

  • 85% of the water in the filtrate is reabsorbed from the nephron

    • with ADH - collecting duct permeable to water and remaining 15% reabsorbed

    • without ADH - the remaining 15% will not be reabsorbed

  • increased fluid loss results in lower blood pressure

  • BP receptors in the juxtaglomerular apparatus detects low BP

  • lower blood pressure releases renin (kidney) which cinverts angiotensinogen (liver) into angiotensis

  • functions of angiotensin : constriction of blood vessels, stimulates release of aldosterone

  • aldosterone from adrenal glands acts on dsital tubule to increase NaCl reabsoption

    • increased osmotic gradient, water absorption and blood pressure

  • pH balance :

    • between 7.3-7.5

    • buffer system

    • extra h+ absorbed and screted by kidneys

    • bicarbonate ions act as a buffer

    • CO2 controlled by lungd