Water, Electrolyte, and acid base balance: Water Balance
How much of our body weight is due to fluids?
55-60%, depending on age, sex, body mass and body fat
What is water intake controlled by and how does BP and blood osmolarity affect it?
A hypothalamic "thirst center" that responds to dehydration, falling BP will trigger angiotensin II to be released, rising blood osmolarity will trigger the release of ADH, increasing osmolarity of ECF will be detected by osmoreceptors
What is hypovolemia caused by?
Hemorrhage, severe burns, chronic vomitting/diarrhea
What is water intoxication?
If the body replaces water without replacing sodium, the ECF become hypotonic and water moves into tissues causing them to swell!
What is fluid loss due to?
Obligatory water loss, insensible water loss (expired breath, sweating, cutaneous transpiration, defecation), sensible water loss (urine 60%)
What is hypovolemia?
Occurs when body eliminates water and sodium without equally replacing them, total body water declines, osmolarity is stable
How much water in the body is in the extracellular fluid and where is it distributed?
One third, it is distributed among the interstitial fluid, blood plasma....
How does water movement between ICF and ECF maintain homeostasis?
Osmosis, the gradients are short lived
How does cold weather affect fluid balance?
Raises urinary out put because the blood vessels constrict to conserve heat, but it raises blood pressure, which inhibits ADH secretion and stimulates ANP secretion, dry and clod air also increases water loss during respiration
How much water in the body is intracellular fluid?
Two thirds
What is water output controlled by and how does ADH play a roll?
Variations in urine volume that are usually linked to sodium reabsorption, ADH allows kidneys to reabsorb more water and produce less urine
What is dehydration and what is it cause by?
When body eliminates more water than sodium, and caused by diabetes mellitus, diabetes insipidus, profuse sweating, overuse of diruetic
When, under normal condidtions, does water balance occur?
When fluid intake equals fluid output
When does fluid deficiency occur?
When water output exceeds water input over a long period of time
What is fluid sequestration?
occurs if excess fluid accumulates in interstitial spaces
What is fluid gain due to?
preformed water from ingested food/liquids, and metabolic water from chemical reactions in cells
