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# Lecture 19

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### Lecture 19

1. 1. Water and Electrolytes <br />
2. 2. Key concepts involving water<br />Body water is contained in two major body compartments (intracellular fluid compartment and extracellular fluid compartment)<br />Fluid balance is maintained when input and output are equal<br />The primary source of intakeis water ingestion (eating and drinking) …60% from drinking<br />In addition, digestion and metabolism of carbohydrates, proteins, and fats provides another source of intake <br />
3. 3. Key concepts involving water<br />
4. 4. Compartments<br />Intracellular fluid (ICF) represents the fluid inside the cells and is the largestcompartment (2/3 of body water)<br />Extracellular fluid (ECF) represents the fluid outside the cells and is 1/3 of total.<br />ECF is further divided into interstitial (ISF) and is the plasma. <br />
5. 5. ECF divisions<br />ISF occupies the space between cells and consists of 15% of total body fluid or ¾ of ECF<br />Plasma is the fluid portion of the blood and is 4% of total body fluid or ¼ of ECF<br />
6. 6. ICF<br />ECF<br />60-kg man<br />TBW = 0.6 x 60 kg = 36 L<br />ICF = 0.4 x 60 kg <br />= 24 L<br />ECF <br />= 12 L<br />P<br />IS<br />3L<br />9L<br />20% TBW<br />40% TBW<br />BODY FLUIDS<br />Distribution of Body Fluids <br />
7. 7. Water balance<br />In a healthy person, the fluid ingested balances the fluids excreted<br />If you have a daily intake of 2500 ml, you should have an output of 2500 ml<br />Water regulation is associated with sodium regulation<br />Primary regulatoris thirst-- alerts body to a fluid deficit<br />
8. 8. Water loss<br />Regulation of water loss is by ADH which increases the permeability of the distal convoluted tubule and collecting duct to water<br />Water loss from kidneys is primary source(urine 60%)<br /> evaporation through skin and respiratory system (also called insensible is 28%), sweat-6%, gastrointestinal (feces 6%)<br />diarrhea, vomiting are additional sources occasionally<br />
9. 9. Disturbances of water homeostasis <br />Water disturbances involve<br />Gain or loss extracellular fluid volume<br />Gain or loss of solute<br />Four examples of water disturbances<br />Hypervolemia<br />Overhydration<br />Hypovolemia<br />Dehydration<br />
10. 10. Hypervolemia occurs when too much water and solute taken at the same time. Extracellular fluid volume increases and normal plasma osmolarity<br />Overhydration occurs when too much water taken without solute. Volume increases and osmolarity decreases<br />Hypovolemia occurs when water and solute lost at the same time. Loss of plasma volume. Osmolarity remain normal<br />Dehydration occurs when water is lost, volume decreases and plasma osmolarity increases<br />
11. 11. Mechanisms of fluid balance<br />Antidiuretic hormone (ADH)<br />Thirst<br />Aldosterone<br />Sympathetic nervous system<br />
12. 12. ADH (Antidiuretic Hormone)<br />Made in hypothalamus; water conservation hormone<br />Stored in posterior pituitary gland<br />Acts on renal collecting tubule to regulate re-absorption or elimination of water<br />If blood volume decreases, then ADH is released & water is reabsorbed by kidney. Urine output will be lower<br />
13. 13. Effect of ADH<br />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<br />Then ADH is released & water is reabsorbed by kidney. <br />Urine output will be lower but concentration will be increased.<br />
14. 14. THIRST Mechanism<br />Major factor that determines fluid intake<br />Saliva production decreases. Impulses from the mouth and throat to the thirst centre in the hypothalamus. <br />Increase in osmotic pressure of body fluids stimulate the osmoreceptor in the thirst centre of hypothalamus <br />Decrease blood volume stimulate the release of renin which stimulate thirst center <br />
15. 15. Effect of Aldosterone<br />Reduce blood volume leads to reduced blood pressure <br />This stimulate release of renin which leads to release Aldosterone <br />
16. 16.
17. 17. Aldosterone can be also released when K concentration in the blood is high<br />Presence of Aldosterone, Na reabsorbed in the plasma and K secreted in the urine<br />This leads to increase blood pressure<br />
18. 18. Sympathetic nervous system<br />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<br />Smooth muscle cell constrict causing a decrease in blood flow into glomerulus<br />