renal 8 Flashcards
what is the integrated control of volume and osmolarity?
-the CV system responds to changes in blood volume and pressure, the renal system responds to changes in blood volume and/or osmolarity and behavioral mechanisms respond to both
-normally can be kept within a narrow range but under certain circumstances becomes out of balance
-osmolarity and blood volume can change independently resulting in different scenarios
what is increased volume and increased osmolarity (1)?
increased volume and osmolarity
-may occur with eating salty foods and drinking liquids at the same time, net results=ingestion of hypertonic saline (salt>water)
-need to therefore excrete the solute and liquid to match what was taken in
what is increased volume, no change in osmolarity (2)?
-if salt and water ingested is equivalent to isotonic solution
what is increased volume and decrease osmolarity (3)?
-simply drinking pure water without ingesting solute
-the kidneys cannot excrete pure water, so some solute would be lost in this situation, compensation is imperfect
what is no volume change and increased osmolarity (4)?
-eating salt without drinking water
-increases ECF osmolarity, shifting water from cells to ECF
-triggers intense thirst and kidneys make concentrated urine
what is no change in volume and decreased osmolarity (5)?
-water and solutes would be lost in sweat but only water is replaced
-can lead to hypokalemia or hyponatremia
-sports drinks help to replace fluid and solutes lost
what is decreased volume and increased osmolarity (6)?
-dehydration could be due to heavy exercise (water loss from lungs can double, sweat loss can increase from 0.1-5L) or diarrhea (excessive fluid loss in feces)
-can result in inadequate perfusion (decreased blood volume) and cell dysfunction
-increase water intakes
what is decreased volume and no change in osmolarity (7)?
-hemorrhage, need blood transfusion or ingestion of isotonic solution
what is decreased volume and decreased osmolarity (8)?
-may result from incomplete compensation for dehydration, but is common
what is the graph of responses triggered by decreased blood pressure/volume?
what is the graph of responses triggered by increased blood pressure?
what is the graph of responses triggered by increased and decreased osmolarity?
what are the three factors that mechanisms aim to restore when there is severe dehydration?
severe dehydration results in a loss of ECF volume, decrease in blood pressure and an increased in osmolarity, the compensatory mechanisms aim to restore these three factors by:
1. conserving fluid to prevent additional loss
2. trigger cardiovascular reflexes to increase blood pressure
3. stimulate thirst so normal fluid volume and osmolarity can be restored
four compensatory mechanisms with redundant overlap ovecome the symptoms of dehydration:
- cardiovascular mechanisms
- renin-angiotensin system
- renal mechanisms
- hypothalamic mechanisms
what is worth noting in regard to severe dehydration?
-during severe dehydration decreased ECF volume (blood pressure) would signal to increase aldosterone release but at the same time an increased osmolarity inhibits aldosterone release
-osmolarity control in this situation reigns and aldosterone is not secreted, if it were that would cause Na reabsorption which would worsen the already high osmolarity
how does the carotid and aortic baroreceptors signal CVCC?
a. heart rate goes up as SA node control shifts from parasympathetic to sympathetic
b. force of ventricular contraction increases from sympathetic stimulation
c. sympathetic input to arterioles increases peripheral resistance
d. sympathetic vasoconstriction of afferent arterioles in kidney decreases GFR, conserving fluid
e. increased sympathetic activity at granular cells increases renin secretion
what is the homeostatic compensation for severe dehydration?
- decreased blood pressure directly decreases GFR
- paracrine feedback at macula densa cells causes granular cells to release renin
- granular cells respond to decreased blood pressure by releasing renin
- decreased blood pressure, volume, increased osmolarity, and increased ANGII all stimulate vasopressin and the thirst centers of the hypothalamus. ANGII reinforces CV response
what do the homeostatic compensations result in?
- rapid attempt by the CVCC to maintain blood pressure (depending on volume loss CVCC response may not completely restore pressure)
- restoration of volume by water conservation and fluid intake
- restoration of normal osmolarity by decreased Na reabsorption and increased water reabsorption and intake
