Fluid and electrolyte balance Flashcards
What are the 4 parameters in which homeostatic mechanisms maintain fluid/electrolyte balance
-Fluid volume
-Osmolarity
-Concentrations of individual ions
-pH
Describe fluid and electrolyte balance
How does ECF osmolarity affect cell volume
How is fluid and electrolyte balance an integrative process
Describe water balance
How do kidneys conserve water
How does the renal medulla create concentrated urine
How does vasopressin control water reabsorption
Describe vasopressin induced aquaporin insertion
What stimuli control vasopressin secretion?
Explain vasopressin (AVP) production and secretion
Secretion:
-Increased osmolarity
-Decreased blood volume
-Decreased blood pressure
What creates the hyperosmotic interstitium and why isn’t it reduced as water is reabsorbed?
What is the renal countercurrent exchange system
What is the function of the counter current multiplier (loop of henle)
What is the function of the counter current exchanger (vasa recta)
Explain active transport in the loop of Henle
How does urea contribute to the osmolarity of the medullary intersitium
Summarize the components involved in water balance
Explain homeostatic responses to salt ingestion
How does aldosterone help control Na+ balance
Explain how aldosterone acts on principle cells
Explain aldosterone secretion
Explain the Renin-Angiotensin pathway
What are the effects of angiotensin II
How do pharmaceutical companies treat hypertension
Use ACE inhibitors
-Preventing the conversion of ANGI to ANGII leads to relaxation of the vasculature and lower blood pressure
-other options include AT receptor antagonists and renin inhibitors
What is atrial natriuretic peptide (ANP) and how does it promote Na+ and water excretion?
-Peptide hormone produced and secreted by specialized myocardial cells primarily in the atria of the heart
-increased blood volume causes increased stretch of the atria, causing the specialized myocardial cells to release ANP
-Some produced in cardiac ventricles and some neurons in the brain (BNP) brain natriuretic peptide (used as biological marker)
Explain the importance of potassium balance
what are the behavioural mechanisms of salt and water balance
-Behavioural responses are critical in restoring the normal state, particularly when ECF volume decreases or osmolarity deviates
-Drinking water is normally the only way to replace lost water and eating salt is the only way to raise the body’s Na+ content
-The act of drinking relieves thirst, water does not actually have to be absorbed
-unknown receptors in the mouth/pharynx respond to water by decreaseing thirst and decreasing AVP release
Explain 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 behavioural mechanisms resond to both \
- eating salty foods and drinking liquids at the same time, net results = ingestion of hypertonic saline (salt>water)
-Need to excrete solute and liquid to match what was taken in - If salt and water ingested is equivalent to isotonic solution
- Drinking pure water without ingesting solute
-Kidneys cannot excrete pure water, so some solute would be lost in this situation, compensation is imperfect - Eating salt without drinking water, increases ECF osmolarity shifting water from cells to ECF
-Triggers intense thirst and kidneys make concentrated urine - 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 - Dehydration could be due to heavy excercise (water loss from lungs can double, sweat loss can increase from 0,1-5L) or diarrhea (excessive fluid loss in feces)
-can results in inadequate perfusion (decreased blood volume) and cell dysfunction
-Increase water intake - Hemorrhage, need blood transfusion or ingestion of isotonic solution
- May result from incomplete compensation for dehydration but is uncommon
What are the physiological responses triggered by decreased blood pressure/volume
What are the physiological responses triggered by increased blood pressure
What are the physiological responses triggered by increased and decreased osmolarity
Why is aldosterone not secreted when decreased ECF volume (blood pressure) is caused by 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
Explain the function of each mechanism involved in homeostatic response to severe dehydration
Results in:
1. 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
