Fluid, Electrolyte and Acid/Bases Flashcards
1
Q
body water content
A
- infants- 73% or more water (low body fat, low bone mass)
- adult males- 60% water
- adult females- 50% water (higher fat content, less skeletal muscle mass)
- water content declines to about 45% in old age
- daily recommended amount- 8 cups
2
Q
total body water
A
- 40L - 60% body weight
- intracellular fluid- 25L- 40%
- interstitial fluid- 12L- 80 of ECF
- extracellular fluid- 15L- 20% body weight
- plasma- 3L- 20% ECF
3
Q
extracellular and intracellular fluids
A
- each fluid compartment has a distinctive pattern of electrolytes
- ICF- major cation is K and major anion is HPO42-
- ECF- major cation is Na and major anion is Cl
4
Q
fluid movement among compartments
A
- regulated by osmotic and hydrostatic pressures
- water moves freely by osmosis
- osmolarities of all body fluids are almost always equal
- change in solute concentration of any compartment leads to net water flow
- increase in ECF solate -> water moves out of cells
- decrease in ECF solate -> water moves into cells
5
Q
regulation of water intake
A
- thirst mechanism is the driving force for water intake
- the hypothalamic thirst center osmoreceptors are stimulated by:
- increase in osmolality of 1-2% activates receptors
- angiotensin 2 or baroreceptor input
- dry mouth - less saliva
- substantial decrease in blood volume or pressure
6
Q
regulation of water output
A
- obligatory water losses:
- insensible water loss- from lungs and skin
- feces
- minimum daily sensible water loss of 500 ml in urine to excrete wastes
- body water and Na content are regulated in tandem by mechanisms that maintain cardiovascular function and blood pressure
- thirst is not always a reliable indicator of need (the last straw)
7
Q
regulation of water output: influence of ADH
A
- hypothalamic osmoreceptors trigger or inhibit ADH release (inc in ECF solute concentration)
- decrease in ADH -> dilute urine and decrease volume of body fluids
- increase ADH -> concentrated urine
- conserves water in body
- water reabsorption in collecting ducts is proportional to ADH release
- other factors may trigger ADH release via large changes in blood volume or pressure
8
Q
electrolyte balance
A
- electrolytes are salt, acids, and bases
- salts enter the body by ingestion and are lost via perspiration, feces, and urine
- salts:
- controlling fluid movement, osmotic relations between cells
- excitability; neuromuscular excitability
- secretory activity
- membrane permeability
- eat a meal high in salt will cause a temporary increase in blood volume
- electrolyte balance usually refers only to salt balance
9
Q
central role of sodium
A
- most abundant cation in the ECF (90-95%)
- highest in blood plasma
- exerts the most significant osmotic pressure
- regulation of sodium linked to BP
- sodium is a water magnet
- aldosterone regulates salt
10
Q
regulation of sodium balance: aldosterone
A
- if blood volume and BP is low then aldosterone is released
- renin-angiotensin mechanism is the main trigger for aldosterone release
- granular cells of JGA secrete renin in response to:
- sympathetic nervous system stimulation
- decrease filtration osmolality
- decrease stretch (due to decreased blood pressure)
11
Q
regulation of sodium balance: ANP atrial natriuretic peptide
A
- released by atrial cells in response to stretch (if BP is high)
- decrease BP and blood volume:
- decrease ADH, renin and aldosterone production
- increase excretion of sodium and water
- promotes vasodilation
12
Q
cardiovascular system baroreceptors
A
- if an increase in blood volume and pressure:
- baroreceptors alert the cardiovascular centers in brain
- sympathetic nervous system impulses to the kidneys decline
- afferent arterioles dilate
- GFR increases
- Na and water output increase (less reabsorption)
- blood volume and pressure decrease
- baroreceptors provide information on the fullness or volume of the circulation that is critical for maintaining CV homeostasis
13
Q
regulation of potassium balance
A
- importance of potassium:
- affects RMP (resting metabolic potential) in neurons and muscle cells (especially cardiac muscle)
- K balance is controlled by the kidney
- over 80% of K is reabsorbed at the prox tubule
- potassium is part of bodys buffer system
- shift of H+ shift in and out of cells induce corresponding shifts in K in the opposite direction to maintain cation balance
- Na is reabsorbed at collecting ducts never excreted, K can be excreted at ducts
- the collecting ducts control the amount of K secreted back into filtrate
- ***high K content of ECF favors secretion of K
- when K levels are low, the kidneys conserve K by reducing its excretion
14
Q
influence of aldosterone on potassium balance
A
- stimulates K secretion (and Na reabsorption)
- increased K in the adrenal cortex causes:
- release of aldosterone
- potassium secretion
- amount of K in ECF determines how much will be secreted in kidney
15
Q
regulation of caclium
A
- calcium role in ECF- neuromuscular excitability, blood clotting, cell membrane permeability, secretory activities
- hypocalcemia -> causes muscle tetany
- hypercalcemia -> increase heart rate and contractility but very high calcium levels may cause heart arrhythmias
- calcium balance is controlled by parathyroid hormone (PTH) and calcitonin
16
Q
influence of PTH parathyroid hormone on calcium
A
- bones are the largest reservoir for Ca and phosphates
- PTH promotes increase in calcium levels in blood by targeting bones, kidneys, and small intestine (indirectly through vitamin D)
- calcium reabsorption and phosphate excretion go hand in hand
17
Q
regulation of anions
A
- Cl- is the major anion in the ECF
- helps maintain the osmotic pressure of the blood
- follows Na ions out of filtrate
18
Q
an increase in the ECF solute content causes ______
A
- water to move into the cell
- solute to move out of the cell
- water to move out of the cell*
- both a and b
19
Q
you would expect blood levels of ANP to increase when _____
A
- blood pressure is increased
- there is an increase in preload
- the walls of the atria are stretched
- all of the above occur*
- a and c only
20
Q
acid-base balance
A
- pH affects all functional proteins and biochemical reactions
- normal pH of body fluids:
- arterial blood- pH 7.4
- venous blood- pH 7.35
- alkalosis or alkalemia- arterial blood pH > 7.45
- acidosis or acidemia- arterial pH < 7.35