1. three types of homeostatic balance

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BIOS 256 week 5

• three types of homeostatic balance

–Answer

• fluid balance
• electrolyte balance
• acid-base balance
• cellular function requires

–Answer

• a fluid medium with carefully controlled composition
• main fluid in body is water
• balances maintained by

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• collective action of urinary, respiratory, digestive, integumentary, endocrine, nervous,

cardiovascular, and lymphatic systems

• fluid balance

–Answer

• body water percentages varies

> newborn baby's body weight is about 75% water > young men average 55% to 60% water > women average slightly less

• adipose tissue is nearly free of water

> obese and elderly people as little as 45% by weight

• total body water (TBW) of a 70-kg (150lbs) young male

–Answer 40L > needs to be maintained by homeostasis > varies from person to person 1 / 3

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• major fluid compartments of the body

–Answer

• 65% intracellular fluid (within cells)
• 35% extracellular fluid (outside cells)

> 25% tissue (interstitial) fluid (between cells) > 8% blood plasma and lymphatic fluid > 2% transcellular fluid "catch-all" category

• CSF, synovial, peritoneal, pleural, and pericardial fluids
• vitreous and aqueous humors of the eye
• fluids of the digestive, urinary, and reproductive tracts
• fluid compartments

–Answer

• fluid continually exchange between compartments

> intracellular and extracellular osmolarity are equal

• osmosis from one fluid compartment to another is determined by the relative

concentrations of solutes in each compartment > most solute particles are electrolytes

• sodium salts in ECF
• potassium salts in ICF
• electrolytes play the principle role in governing the body's water distribution and total

water content > electrolytes determine where water goes > wherever electrolytes go - water will follow

• water gain and loss

–Answer

• fluid balance

> daily gains and losses are equal (about 2,500 mL/day)

• gains come from two sources

> preformed water (2,300 mL/day)

• ingested in food (700 mL/day) and drink (1,600 mL/day)

> metabolic water (200 mL/day)

• formed by aerobic metabolism and dehydration synthesis
• C6H12O6 + 6 O2 ---> 6 CO2 + 6 H2O
• sensible water loss is observable 2 / 3

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> 1,500 mL/day is in urine > 200 mL/day is in feces > 100 mL/day is sweat in resting adult

• insensible water loss is unnoticed

> 300 mL/day in expired breath > 400 mL/day is cutaneous transpiration > loss varies greatly with environment and activity

• obligatory water loss

> output that is relatively unavoidable > expired air, cutaneous transpiration, sweat, fecal moisture, and minimum urine output (400 mL/day)

• regulation of fluid intake

–Answer

• dehydration

> reduces blood volume and blood pressure > increases blood osmolarity

• osmoreceptors in hypothalamus

> respond when BP drops > respond to rise in osmolarity of ECF (too many solutes and not enough water)

• hypothalamus produces antidiuretic hormone

> promotes water conservation (negative feedback loop)

• cerebral cortex produces conscious sense of thirst

> intense sense of thirst with 2% to 3% increase in plasma osmolarity or 10% to 15% blood loss > thirst mainly governs fluid intake

• long-term inhibition of thirst

> absorption of water from small intestine reduces osmolarity of blood

• short-term inhibition of thirst

> cooling and moistening of mouth quenches thirst > distension of stomach and small intestine (stretches with water) > short-term response designed to prevent overdrinking

• regulation of fluid output

–Answer

• only way to control water output significantly is through variation in urine volume

> kidneys cannot replace water or electrolytes > can only slow rate of water and electrolytes loss until water and electrolytes can be

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