Chapter2WaterandElectrolytesBalanceandimbal水电解质平衡.doc

Chapter 2 Water and Electrolytes Balance and imbalance 一．Water balance: water is taken into the body by two major sources:one is from the ingestion in the from of liquids or water in the food; the other is from the mebabolism in the body following oxidation of carbohydrates. Four pathways for water output:①insensible water loss②evaporation from respiratory tract③sweating④through kidneys Mechanisms for regulation of body fluid and electroyte balance-----in nervous and hormonal systems. ㈠The sensation of thirst ㈡Antidiuretic hormone(ADH) ADH is produced in the supraoptic and paraventricular nuclei of the hypothalamus, transported along the nerves from hypothalamus and stored in the posterior hypophysis.When osmolarity of the body fluids increases above normal,the posterior pituitary gland secrets more ADH into the circulatory system. The main target sites of ADH are the distal tubuls and collecting ducts in the kidney.Binding of ADH to V2 receptor in the basolateral membrane of the principle cells in the collecting ducts stimulates the cAMP and protein kinase A systems,which in turn causes the reversible translocation of stored aquaporin2(AQP2) in intracellular vesicles to the apical membrane of the principle cells, where AQP works as a water channel. Factors that regulate ADH release Increase ADH secretionDecrease ADH secretionBlood pressure↓Blood pressure↑Plasma osmolality↑Plasma osmolality↓Blood volume↓Blood volume↑NauseaHypoxia Arterial pressure↓↓ Syspathetic nervous system↓ Plasma sodium content Glomerulus ㈢Renin - angiotensin - aldosterone system(RAAS) AngⅡ Ang Ⅰ Angiotensinogen Renin + — Renal artery pressure↑ ECF volume ↑ Renal retention of sodium Increase in potassium of hydrogen secretion Aldosterone Adrenal glands Angiotensin converting enzyme (lung) ECF ↑potassium content ECF↓ sodium content + generate (四) The natriuretic peptide family (ANP) Increased levels of natriu