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Kin110_Chapter 8 Water & Electrolytes.docx

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Biomedical Physio & Kines
BPK 110
Gina Whitaker

Chapter 8 Water & Electrolytes Water in the Body The most important macronutrient 60% of body weight -2/3 intracellular (inside cells), 1/3 extracellular (outside cells) Water content of intra/extracellular spaces depends on -solute concentrations (proteins, sodium, potassium, etc) -water moves by osmosis to achieve proper solute concentrations -blood pressure (the amount of force exerted by the blood against the walls of arteries), which moves water through blood vessels and into tissues Water Balance Water intake is about 2950ml or 12.5 cups per day 500ml food 2200ml drink 250ml metabolism Water output is also about 2950ml or 12.5 cups per day 200ml feces 1650ml urine 1100ml evaporation and sweat Water, Blood Volume & Blood Pressure Adequate water levels maintain blood volume, which helps maintain blood pressure -maintaining blood pressure is critical for nutrient delivery Water levels are maintained by regulating water intake and output Water intake is regulated by thirst sensations Water output is regulated at the kidneys by 3 hormones a) Antidiuretic Hormone (ADH) b) Angiotensin II c) Aldosterone Regulation of Water Intake Thirst sensations in response to low H2O -dryness in the mouth -signals from the brain Thirst is a powerful urge but often lags behind the need for water, we don’t or can’t always drink when we are thirsty therefore thirst alone cannot be relied on to maintain water balance Regulation of Water Output The kidneys are responsible for maintaining water balance by regulating output in urine 1-2L of urine per day depending on the amount of water consumed and amount of waste needed to be excreted The amount of water excreted by the kidneys is regulated by the 3 hormones Regulation of Water Balance Antidiuretic Hormone (ADH) also called vasopressin Secreted by the pituitary gland in response to ↓ blood pressure ↓ blood volume ↑ salt concentration of the extracellular fluid Increases blood volume and blood pressure by a) stimulating thirst b) stimulating the kidneys to reabsorb water c) promoting vasoconstriction The diuretic (a substance that increases the amount of urine passed from the body) effects of caffeine and alcohol are due to their inhibition of ADH release Angiotensin II Cells in the kidney detect decrease in the blood pressure and secrete an enzyme called renin Renin is an enzyme necessary for the activation of the hormone Angiotensin II Angiotensin increases blood volume and blood pressure by a) vasoconstriction b) stimulates thirst c) stimulates synthesis and release of aldosterone which increases sodium re-absorption which leads to water being re-absorbed Aldosterone Released in response to stimulation by Angiotensin II when blood volume and blood pressure are low Increases blood volume and blood pressure by -increasing sodium retention in the kidneys -increased water is also reabsorbed (follows the osmotic gradient created by the sodium retention) All three hormones work together to restore blood volume and pressure Water Functions Acts as a solvent: solutes (for example: glucose, proteins, minerals) dissolve in water Participates in chemical reactions Transports nutrients, oxygen, waste materials, hormones, etc. as the main component of blood Protects and cushions body structures Regulates pH and temperature How water regulates body temperatures Blood carries heat from the body’s core to the capilleries near the surface of the skin Heat is released from the skin to the environment Water in sweat evaporates from the skin causing heat to be lost Evaporation cools the skin and the blood at the skin’s surface Cooled blood returns to the body’s core Dehydration-a state that occurs when not enough water is present to meet the body’s needs Water Intoxication Rare Can lead to hyponaturemia -too much water in relation to sodium in body = drop in Na+ concentration Water moves into tissues, leading to swelling -can cause disorientation, convulsions, nausea, muscle cramps, slurred speech, confusion Meeting Water Needs 3.7L for men, 2.7L for women Needs increased based on -increased activity -increased temperature -decreased humidity -low calorie diet (increased ketone & urea production) -high salt diet -high fiber diet -high protein diet -alcohol & caffeine intake -pregnancy & lactation Minerals-inorganic elements found in the periodic table, throughout nature More than 20 essential minerals found in plants/animals Major minerals – need > 100mg/day Trace minerals – need < 100mg/
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