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141 Cards in this Set
- Front
- Back
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TBW constitutes about what percentage of body weight in men and in women?
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60% in men
50% in women |
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What percentage of TBW is intracellular fluid?
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60-66%
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what percentage of TBW is extracellular fluid?
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33-40%
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in the ECF, what percentage is interstitial fluid?
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80%
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in the ECF, what percentage is plasma water?
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20%
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what is a typical TBW in L?
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42L
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what is a typical ICF (L)?
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25-28L
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what is typical ECF (L)?
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14-17L
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what is typical plasma water (L)?
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3 L
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what is the one major solute in intracellular fluid?
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K+ salts
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what is the one major solute in extracellular fluid?
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Na+ salts
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what is the major solute in plasma?
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proteins, particularly albumin
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water moves btn the plasma and interstitial compartments in response to what?
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net pressure difference
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what are capillary membranes usually very permeable to?
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water
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water moves between the interstitial and intracellular compartments in response to what?
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difference in osmotic pressure
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increase ECF effective osmolality --> ?
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cellular dehydration
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decrease ECF effective osmolaltiy --> ?
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cellular overhydration
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what are the major extracellular solutes?
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Na+ salts
glucose urea |
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plasma [Na+] = ?
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137-143 mosm/kg H2O
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fasting plasma [glucose] = ?
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60-100 mg/dL
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BUN = ?
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10-20 mg/dL
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because glucose and urea contribute < 5% to total Posm, Posm = ?
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2 x plasma [Na+]
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normal cell function is dependent on control of what?
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cell volume
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regulation of ECF osmolality, and thus intracellular volume is achieved by?
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regulating water balance
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balance = ?
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intake - output
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what are some sources of water intake?
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ingestion of water, food, metabolism
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what are some routes of excretion?
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urine, skin, lungs, feces
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what is the role of hypothalamic osmoreceptors?
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sense Posm - can detect changes in Posm as small as 1%
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what sends signals to supraoptic and parventricular nuclei of the hypothalamus as well as to the hypothalamic thirst center?
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hypothalamic osmoreceptors
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What neurons synthesize ADH?
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suproptic (SO) and paraventricular (PV)
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where is ADH stored and released from?
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posterior pituitary (neurohypophysis)
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what is the threshold for ADH secretion and what happens below this level?
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280 mosm/kg - below this level, there is little or no circulating ADH - and the urine is maximally dilute
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what is the Uosm when urine is maximally dilute?
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50 mosm/kg H2O
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What happens in response to a rise in Posm (>280 mosm/kg H2O)?
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1. stimulation of hypothalamic osmoreceptors --> secretion of ADH from neurohypophysis --> increased water reabsorption in collecting tubules
2. stimulation of the thirst center --> ingestion of water |
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what are some other factors that stimulate ADH secretions? (inappropriate)
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hypovolemia
stress nausea hypoglycemia drugs |
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what drugs stimulate ADH secretion?
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opioids, carbamazepine, thiothixene, haloperidol, amitryptiline, MAOIs, fluoxetine
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what factors inhibit ADH secretions (inappropriate)?
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hypervolemia
drugs - ethanol, phenytoin |
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what is the definition of hyponatremia?
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PNa+ < 135 mEq/L
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what usually, but not always, reflects hypo-osmolality?
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hyponatremia
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what are the consequences of decreased ECF osmolality?
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net water movement into cells
symptoms largely neurologic |
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what are the neurologic symptoms associated with hyponatremia?
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nausea, malaise, HA, lethargy, seizures and coma possible with PNa+ below 110-115 meq/L
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what is hyponatremia most often caused by?
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excess total body water
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what is excess body water caused by?
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increased ADH secretion and impaired water excretion
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what are some etiologies of hyponatremia?
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hypovolemia
diuretics SIADH |
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why can hypovolemia cause hyponatremia?
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overrides normal response to decreased Posm
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what do thiazides do?
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promote sodium excretion in excess of water excretion
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what is a treatment for SIADH?
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water restriction
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what is pseudohyponatremia?
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decreased PNa+ with normal Posm
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what can pseudohyponatremia be seen with?
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hyperlipidemia and hyperproteinuria
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why is Posm normal is pseudohyponatremia?
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osmometer measures the osmotic activity of plasma water, which is not altered
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when can decreased PNa+ with increased Posm occur?
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with addition to the ECF of an effective osmol other than Na+, eg mannitol
-water movement out of cells causes reduction in PNa+ |
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hypernatremia represents?
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hyperosmolality
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what are neurologic symptoms of hypernatremia?
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lethargy, weakness, irritability, twitching, seizures, coma (can occur with severe hypernatremia)
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what is sheehan's syndrome?
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occurs as result of ischemic pituitary necrosis due to severe post-partum hemorrhage
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what are the normal body defenses against hypernatremia?
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thirst and increased ADH secretion
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what is the most common cause of hypernatremia?
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water loss in excess of Na+
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what are some causes of water loss?
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diabetes insipidus
osmotic diuresis (poorly controlled diabetes mellitus with glucosuria) |
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what are the two types of DI?
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central DI
nephrogenic DI |
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what is a diminished renal responsiveness to ADH?
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nephrogenic DI
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what is reduced or absent ADH secretion?
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central DI
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what is that part of the ECF that is contained in the vascular space and is effectively perfusing the tissues?
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effective circulating volume
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why is effective circulating volume not a measurable entity?
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refers to the rate of perfusion of the capillaries (the sites of exchange between blood and tissue cells)
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does effective circulating volume varies directly or indirectly with ECF volume?
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directly
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maintenance of effective circulating volume is essential for what?
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delivery of adequate O2 and energy substrates to tissues and for removal of CO2 and metabolic end-products
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what is maintenance of effective circulating volume closely linked to?
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regulation of Na+ balance
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what does Na+ loading lead to?
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volume expansion
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what does Na+ loss lead to?
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volume depletion
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response to variations in effective circulating volume involves what two steps?
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1. volume change is sensed by multiple receptors
2. activation of effector mechanisms that act together to restore normovolemia |
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where are the primary volume receptors located?
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carotid sinuses and aortic arch
atria of heart afferent arterioles in the kidney (JG cells) |
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what is the variable being sensed for volume receptors?
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pressure (stretch) - pressure and volume are directly related
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rate of discharge in nerve endings is proportional to what?
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degree of stretch
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volume receptors afferent activity is directed where?
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to the vasomotor centers in the medulla and to the paraventricular nuclei (ADH secretion) in the hypothalamus
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renin secretion from the JG cells of afferent arteriole is _____________ to degree of stretch of the anteriolar wall
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inversely related to
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what does volume depletion that reduces afferent arteriole stretch lead to?
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increased renin secretion - which increases AII production and aldosterone release
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volume expansion tends to increase filling and stretch --> ?
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reflex decrease in ADH secretion; release of ANP into the circulation
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what does volume expansion suppress?
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renin secretion
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what is sympathetic outflow from the medulla vasomotor center regulated by?
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peripheral baroreceptors (inverse relationship)
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volume expansion reduces sympathetic output from vasomotor centers to do what?
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minimize changes in CO and BP and to facilitate Na+ excretion
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secretion of renin from JG cells of afferent arteriole?
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renin-angiotensin system
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renin-angiotensis system is influenced by?
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sympathetic NS - direct relationship
degree of stretch of afferent arteriole -- inverse relationship |
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what are the actions of angiotensin II?
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1. potent vasoconstrictor
2. stimulates secretion of aldosterone from the adrenal cortex -- promote Na reabsorption in principal cells of the CCT 3. stimulates Na+ reabsorption in PCT |
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when are renin secretion and angiotensin II enhanced?
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hypovolemic states such as sodium restriction/loss, hemorrhage, or decompensated heart failure
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renal sodium excretion varies directly with what?
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effective circulating volume
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what are adjustments in Na+ excretion primarily due to?
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adjustments in Na+ reabsorption by the tubules
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what are factors that affect Na+ reabsorption?
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1. aldosterone
2. atrial natriuretic peptide 3. filtration fraction |
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what promotes Na+ reabsorption in cortical collecting tubules?
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aldosterone
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what inhibits Na+ reabsorption in medullary collecting tubule?
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atrial natruiretic peptide
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what does increased filtration fraction enhance?
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proximal tubular Na+ reabsorption - decreased FF has opposite effect
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ECF volume is determined by?
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absolute amounts of Na+ and water present
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ECF osmolality is determined by?
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the ratio of solutes (primarily Na+ salts) to water
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sweating leads to loss of hypoosmotic fluid --> ?
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rise in Posm and fall in ECF volume
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infusion of isotonic saline --> ?
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rise in ECF volume but no change in Posm
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what is osmoregulation achieved by?
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regulation of water balance, Na+ is not directly affected unless there are concurrent changes in ECF volume
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what is volume regulation achieved by?
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primarily by regulation of Na+ excretion - the hypovolemic stimulus for ADH secretion, however, also promotes water retention to help restore normovolemia
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what do crystalloid solution contain?
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water and electrolytes, no colloids
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what is the replacement of blood loss with crystalloids?
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ratio of 3:1 or 4:1
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what is the most physiological replacement fluid?
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LR, though slightly hypotonic
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what is the purpose of LR containing lactate?
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converted to bicarbonate
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what are other names for LR?
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plasmalyte, normosol
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what solution is isotonic and isoosmotic?
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normal saline (0.9% NaCl)
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what electrolyte concentration in normal saline is higher than that of ECF and what can this result in?
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higher cholride concentration - can cause hypercholoremic (non AG) metabolic acidosis
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when is normal saline a preferred replacement fluid over LR?
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patients with brain injury, hyperkalemia, or hypochloremic metabolic alkalosis
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what is 3% saline used for?
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treatment of severe symptomatic hyponatremia
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why have 3% and 7.5% saline solutions been used to treat hypovolemic shock?
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mobilize intracellular H2O to maintain intravascular volume
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what solution is hypotonic (253 msom/kg H2O)?
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5% dextrose in water (D5W)
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what colloid's colloid osmotic pressure is approximately 20 mmHg?
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5% albumin, 5% plasma protein fraction
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what solution has an average polymer MW of 70,000?
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dextran 70
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what is dextran 40 used for?
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used in vascular surgery to reduce blood viscosity, improve microcirculatory blood flow, and prevent thrombosis
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what has antiplatelet activity and can increase bleeding time?
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dextrans
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what is a synthetic colloid that is a very effective plasma volume expander and less expensive than albumin and nonantigenic?
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hydroxyethyl starch
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what is a 6% hydroxyethyl starch in normal saline?
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hespan
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what is a 6% hyroxyethyl starch in a solution that contains electrolytes, glucose, and lactate?
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hextend
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what may interfere with clotting and raise PTT?
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hespan
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what is normal extracellular H+ concentration?
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about 40 nmol/L
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what is the range of ECF H+ concentration that is compatible with life?
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16-160 nmol/L or pH 6.8 - 7.8
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what is pH of skeletal and smooth muscle cells?
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7.06
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intracellular H+ conc is greater than or less than extracellular fluid?
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greater than (pH is lower)
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what is the pH of the proximal convoluted tubule cells?
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7.13
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H+ are highly chemically reactive, especially with?
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proteins
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activities of many cellular enzymes is?
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pH dependent
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regulation of ECF H+ concentration involves what three processes?
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1. chemical buffering by extracellular and intracellular buffers
2. control of blood PCO2 by adjustments in alveolar ventilation 3. control of plasma HCO3- concentration by adjustments in renal H+ secretion/excretion |
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daily oxidative metabolism produces how many millimoles of CO2?
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15,000 millimoles
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what prevents large changes in ECF and intracellular pH by taking up or releasing H in response to H addition or depletion?
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buffers
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what is the predominant ECF buffer?
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CO2/HCO3 system
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what is normal plasma [HCO3] = ?
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24 mM
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what is normal plasma [CO2] = ?
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40 mm Hg
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what is the normal ratio of HCO3 to CO2?
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20
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what are two other EC buffers?
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phophate, plasma proteins
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what are some intracellular buffers?
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proteins, including hemoglobin in erythrocytes
organic and inorganic phosphates |
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where is as much as 40% of an acute acid load buffered by?
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bone
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what is responsible for eliminating the 15,000 mmoles of CO2 produced daily by oxidative metabolism?
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lungs
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what percentage of filtered HCO3 is reaborbed and where?
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90% in the PCT
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what occurs as a result of H secretion in PCT and collecting tubules?
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urine H excretion
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in the PCT and CCT secreted H are buffered by?
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weak acids in the tubular fluid
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how much H+/day is excreted as titratable acidity?
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10-40 mmol
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how is NH3 in the PCT produced?
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produced from the oxidative deamination of glutamine, NH3 can combine with H+ in PCT cells and be secreted as NH4
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how much H+/day is excreted in the form of NH4?
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40-60 mmol
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pH at end of PCT is?
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6.80
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what happens to pH in loop and distal tubule?
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remains relatively steady
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where does pH fall to the lowest value?
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medullary collecting tubules
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what is the minimum urine pH in humans?
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4.5 represents a H concentration that is nearly 1000x greater than that of plasma
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