physio

1. Water and Electrolytes

2. Key concepts involving water Body water is contained in two major body compartments (intracellular fluid compartment and extracellular fluid compartment) Fluid balance is maintained when input and output are equal The primary source of intakeis water ingestion (eating and drinking) …60% from drinking In addition, digestion and metabolism of carbohydrates, proteins, and fats provides another source of intake

3. Key concepts involving water

4. Compartments Intracellular fluid (ICF) represents the fluid inside the cells and is the largestcompartment (2/3 of body water) Extracellular fluid (ECF) represents the fluid outside the cells and is 1/3 of total. ECF is further divided into interstitial (ISF) and is the plasma.

5. ECF divisions ISF occupies the space between cells and consists of 15% of total body fluid or ¾ of ECF Plasma is the fluid portion of the blood and is 4% of total body fluid or ¼ of ECF

6. ICF ECF 60-kg man TBW = 0.6 x 60 kg = 36 L ICF = 0.4 x 60 kg = 24 L ECF = 12 L P IS 3L 9L 20% TBW 40% TBW BODY FLUIDS Distribution of Body Fluids

7. Water balance In a healthy person, the fluid ingested balances the fluids excreted If you have a daily intake of 2500 ml, you should have an output of 2500 ml Water regulation is associated with sodium regulation Primary regulatoris thirst-- alerts body to a fluid deficit

8. Water loss Regulation of water loss is by ADH which increases the permeability of the distal convoluted tubule and collecting duct to water Water loss from kidneys is primary source(urine 60%) evaporation through skin and respiratory system (also called insensible is 28%), sweat-6%, gastrointestinal (feces 6%) diarrhea, vomiting are additional sources occasionally

9. Disturbances of water homeostasis Water disturbances involve Gain or loss extracellular fluid volume Gain or loss of solute Four examples of water disturbances Hypervolemia Overhydration Hypovolemia Dehydration

10. Hypervolemia occurs when too much water and solute taken at the same time. Extracellular fluid volume increases and normal plasma osmolarity Overhydration occurs when too much water taken without solute. Volume increases and osmolarity decreases Hypovolemia occurs when water and solute lost at the same time. Loss of plasma volume. Osmolarity remain normal Dehydration occurs when water is lost, volume decreases and plasma osmolarity increases

11. Mechanisms of fluid balance Antidiuretic hormone (ADH) Thirst Aldosterone Sympathetic nervous system

12. ADH (Antidiuretic Hormone) Made in hypothalamus; water conservation hormone Stored in posterior pituitary gland Acts on renal collecting tubule to regulate re-absorption or elimination of water If blood volume decreases, then ADH is released & water is reabsorbed by kidney. Urine output will be lower

13. Effect of ADH Losing water through sweating results increase solute concentration in the plasma and thus blood become more osmotic and this results in tissue osmotic pressure increase Then ADH is released & water is reabsorbed by kidney. Urine output will be lower but concentration will be increased.

14. THIRST Mechanism Major factor that determines fluid intake Saliva production decreases. Impulses from the mouth and throat to the thirst centre in the hypothalamus. Increase in osmotic pressure of body fluids stimulate the osmoreceptor in the thirst centre of hypothalamus Decrease blood volume stimulate the release of renin which stimulate thirst center

15. Effect of Aldosterone Reduce blood volume leads to reduced blood pressure This stimulate release of renin which leads to release Aldosterone

17. Aldosterone can be also released when K concentration in the blood is high Presence of Aldosterone, Na reabsorbed in the plasma and K secreted in the urine This leads to increase blood pressure

18. Sympathetic nervous system When blood pressure is low baroreceptor in the heart, aortic arch and carodit arteries send sensory information to the medulla, which increase the sympathetic impulses to the kidney Smooth muscle cell constrict causing a decrease in blood flow into glomerulus