lecture 3- water balance

essential functions of water

nutrient transport and waste removal, chemical reactions, temperature regulation, joint lubrication and organ cushioning, support for secretions

ideal transport vehicle for nutrients and wastes

water soluble nutrients (except lipids), water acts to transport nutrients to the cells of the body, waste products dissolve in water and exit the body as urine

a medium for many chemical reactions of human metabolism

when carbs, lipids, and proteins are metabolized as sources of energy, water is one of the by-products, this metabolic water contributes to the maintenance of fluid balance in the body

metabolic water

water formed as a by-product of carbs, lipids, and protein metabolism

body temperature regulation

water molecules are polar, which attract each other os it takes a lot of energy to separate them, therefore water resists rapid changes in temperature

what percentage of the body is water?

50 to 70 percent

when you get overheated

your body secretes fluids in the form of perspiration which evaporates through pores in your skin, as the water in pores evaporates, heat energy is removed from the skin, cooling your body in the process

increased body temp causes blood vessels to

dilate (open more), allowing greater water loss through perspiration

each quart of perspiration that evaporates

represents 600 kcal of heat energy lost from the skin and surrounding tissues

energy released from heat

60% turned into body heat and 40% converted to forms of energy the cell can use (ATP)

water based secretions are produced by

the digestive tract, respiratory tract, urogenital tract, eyes, and skin

saliva

acts as a lubricant, allowing food to pass through the esophagus to the stomach

mucus

provides a protective coating throughout the digestive tract, lungs are coated with a layer of mucus that provides an important immunologic function

water helps

form the lubricant found in knees and other joints of the body

the spinal cord and brain

are cushioned by cerebrospinal fluid

amniotic fluid

functions as a shock absorber surrounding the growing fetus in the mothers womb, water is the basis

water intake

AI for women- 2.7L and men- 3.7L, this includes from both foods and water; from just water women-2.2L and men- 3.0L

water output

urinating is the majority of water output, average loss per day is 1950mL, minimum of 500mL of urine produced each day

perspiration and respiration

another source of water output, insensible because it can’t be measured easily

lung respiration

some water is lost from the lungs in the form of water vapor in exhaled air

water lost in feces

small amount, the small intestine absorbs as much as 99% of the water filtered each day

other influences on water loss

altitude, ambient temperature, humidity, physical activity, caffeine, and alcohol intake

fluid conservation

blood pressure and concentration of solutes in the blood are closely monitored by receptors in the kidneys, blood vessels, and brain

shortage of available water

increases fluid conservation

antidiuretic hormone (ADH)

a hormone secreted by the pituitary gland when blood concentration of solutes id high. It causes the kidneys to decrease water excretion, which increases blood volume

angiotensin

hormone produced by the liver and activated by enzymes from kidneys. It signals the adrenal glands to produce aldosterone and directs kidneys to conserve sodium, increasing blood volume

aldosterone

hormone produced by the adrenal gland glands when blood volume is low. It acts on the kidneys to conserve sodium, increasing blood volume

hypothalamus

senses the concentration of solutes in the blood. When blood concentration of slots is high, hypothalamus signals pituitary gland to release ADH

kidneys

respond to ADH by reducing urine production and output

low blood pressure

triggers the release of hormones that tell the kidney to retain more sodium and more water via osmosis, increasing the blood pressure back to normal

losing 1 to 2% of body weight in fluids

will be thirsty, and experience lack of appetite and hemoconcentration. Feel tired and dizzy and experience headaches

hemoconcentration

decrease in plasma volume, causing an increase in the concentration of RBCs and other constituents of the blood

losing 4% of body weight in fluids

muscles loose significant strength and endurance, central nervous system function is negatively effected

losing 10% of body weight in fluids

heat tolerance is decreased and weakness results. If not addressed dehydration will lead to kidney failure, coma, and death

kidney stones

when urine production is lower than 500mL per day the urine is concentrated increasing the risk of kidney stone formation is susceptible people

water toxicity

as water intake increases moderately above the AI, kidneys process the excess fluid and excrete a more dilute urine, leads to over-hydration and sodium dilution

hyponatremia

dangerously low blood sodium levels

when hyponatremia occurs

blood volume increases, which rapidly dilutes the blood. Tissues swell and body functions that rely on sodium and potassium are impaired

hard water

contains high levels of calcium and magnesium

soft water

water that contains low levels of calcium and magnesium