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54 Cards in this Set

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How much of the body is made of water?
45-75%
Why would an obese person have a lower water composition than someone of normal weight?
Adipose tissue only contains roughly 10% water where other tissues can hold up to 75%.
How much water is found intracellularly and extracellularly in an average male?
28 liters intracellularly and 14 liters extracellularly.
Where is extracellular water found?
25% in plasma, 1-3% in CSF, aqueous humor, etc. The remainder in lymph and interstitial fluid.
What is an electrolyte?
A substance that conducts charge when dissolved in water.
What is the main cation found intracellularly?
Potassium.
What is the main cation found extracellularly?
Sodium.
What two main anions are found in extracellular fluid?
Chloride and bicarbonate.
What is molarity?
Moles of substance per liter of solution.
What is molality?
Moles of substance per kg of solvent.
What is osmolarity?
Moles of osmotically active solute per liter of solution.
What is osmolality?
Moles of osmotically active solute per kg of solvent.
Why aren't molarity and osmolarity always the same?
Some substances such as NaCl dissociate into two or more osmotically active species thus increasing the osmolarity.
What is an electrochemical equivalence?
The atomic weight of an atom divided by it's valence. Therefore Na has equivalence of 1.
How many equivalents of cations and anions are found in the body?
Typically 155 mEq of cations and anions.
What is the main driving factor in determining the amount of fluid intracellularly and extracellularly?
The amount of solute associated with each. Water follows the solutes.
How would excessive water intake affect fluids found intra and extracellularly?
Excess fluid intake would lower the osmolality and water would move into the cells (which is now hypertonic to the fluid). ADH would then be inhibited and excess urine would form.
How would excess salt intake affect fluids in the body?
Sodium would increase the fluid osmolality and would dehydrate cells. This would stimulate thirst.
What is metabolic water?
Water formed from the oxidation of glucose.
Why is most water excreted through urine even if the majority of water might be ingested through food?
Water is almost completely reabsorbed in the small intestine.
What are the two stimuli for thirst?
1. Increased plasma osmolality as detected by osmoreceptors in the hypothalamus.
2. Via volume loss as detected by baroreceptors found in aortic and carotid bodies.
What area of the brain that might be related to increased thirst when associated with hypovolemia?
It is believed that angiotensin II might at on the subfornical organ of the diencephalon.
What hormone is antagonistic (in effect) of aldosterone?
Atrial natriuretic factor.
What is the difference between nephrogenic diabetes insipidus and hypothalamic diabetes insipidus?
Nephrogenic is the result of mutation in ADH receptor (V2) gene aquaporin II. Hypothalamic is the result of decreased ADH secretion and could be caused by a number of factors.
How does the body detect volume loss and what is the effect on ADH secretion?
Via baroreceptors in the aortic and carotid bodies, it would increase ADH secretion so as to increase retained fluid.
What is alcohol's effect on ADH?
Alcohol inhibits the release of ADH thus producing a dilute urine.
How does the body detect increased plasma osmolality and what is the effect on ADH secretion?
It is registered via osmoreceptors in the hypothalamus and would increase the release of ADH so as to retain more water and lower plasma osmolarity. Realize these are different than the osmoreceptors found in the subfornical organ of the diencephalon that are associated with thirst when stimulated by hypovolemia.
What is the effect of excess water intake?
Osmoreceptors in the hypothalamus swell which inhibits the secretion of ADH and leads to a dilute urine.
What happens when a person sweats excessively (in terms of fluid and response)?
Sweat is hypotonic to body fluid (mostly water). This essentially dehydrates body fluid (makes it hypertonic) which will stimulate thirst as well as secretion of ADH to retain more water.
Where is the majority of sodium expelled?
Urine. Minor amounts are expelled through feces and sweating.
What is a positive sodium balance called?
Hypernatremia.
What is hypernatremia?
Excess salt intake can lead to water retention, weight gain, skin puffiness and long term high blood pressure.
What is hyponatremia?
A condition associated with excess sodium loss via skin, feces, kidneys. There is typically a loss of extracellular fluid which can lead to hypovolemia and hypotension.
What is salt appetite?
Hypovolemia can trigger a craving for salt. It is potentially caused by angiotensin II and aldosterone.
How does filtration rate affect sodium excretion?
Filtration rate will affect how much passes into the tubule and therefore excreted.
How does aldosterone affect sodium excretion?
Acting on the distal convoluted tubule and collecting duct, aldosterone increases salt reabsorption and potassium excretion.
How does atrial natriuretic factor affect sodium excretion?
Atrial natriuretic factor acts on the distal convoluted tubule and collecting duct to increase salt excretion and potassium reabsorption. It does this increasing glomerular filtration rate and decreasing sodium permeability in the collecting duct.
Where is the majority of all potassium found in the body?
Intracellularly.
What is hyperkalemia?
Excess potassium in blood.
Where is the majority of potassium secreted?
90% from urine. 10% in feces.
If the majority of potassium is reabsorbed in the proximal convoluted tubule, how does urine act as the main source of excretion?
It is excreted into the collecting duct.
What is the effect of increased plasma potassium levels?
This will lead to an increase in aldosterone secretion which will in turn expel more potassium from the blood.
What are the effects of hyperkalemia?
A reduction in membrane potential, it makes all nerves more excitable. This can lead especially to cardiac dysrhythmias or arrest.
What are the effects of hypokalemia?
This leads to hyperpolarization of cells and can lead to muscle weakness or possible paralysis.
How can Cushing's syndrome indirectly lead to paralysis?
Cushing's syndrome is over excretion of glucocorticoid cortisol. In high concentrations cortisol mimics aldosterone (similar chemical structure) which will increase potassium expulsion. This can lead to hypokalemia which has the ability of locking cells into hyperpolarization.
What areas and processes of the body is calcium associated with?
Large component in bones in teeth. Directly involved in muscle contraction (binds to troponin) and blood clotting. Used in neurotransmitters and intracellular signaling. Also critically important in regulating sodium permeability in cell membranes.
What is the function of phosphate in the body?
Used in buffer systems. A component of calcium phosphate in bone. Used in nucleic acids, phospholipids, ATP.
How is phosphate utilized in urine?
As a buffer, HPO3 binds to a proton to buffer thus stopping pH from falling too far.
What are the three main hormonal controls of calcium?
Parathyroid hormone, calcitonin (might not be important) and calcitriol derived from Vitamin D3.
Low blood calcium levels will stimulate what?
Secretion of parathyroid hormone.
What is associated affect of calcium reabsorption via parathyroid hormone?
Phosphate excretion.
How does parathyroid hormone indirectly affect calcium absorption in the gut?
It stimulates conversion of 25-hydroxy Vitamin D3 to calcitriol in the kidney. This stimulates calcium absorption in the gut.
What is effect of hypocalcemia?
Via hypoparathyroidism and Vitamin D3 deficiency, can lead to muscle twitches, cramps, tetany, cardiac dysrhythmias.
What is effect of hypercalcemia?
Via hyperparathyroidism, parathryoid adenoma, D3 overdose or excess calcium ingestion, can lead to lethargy, nausea, constipation.