Lecture: Salt, Electrolyte, and Acid-Base Balance Flashcards
Describe fluid movement in the human body.
body fluids are distributed into fluid compartments, areas separated by selectively permeable membranes and differing from each other in chemical composition;
fluids continually exchanged by capillary walls and plasma membranes;
Describe the major fluid compartments of the body.
intracellular (2/3 of fluid);
-low sodium and chloride content
-high potassium and phosphate content
extracellular (1/3 of fluid);
-25% interstitial (tissue)
-8% plasma and lymph
-2% transcellular fluid ("catch-all")
-high sodium and chloride content
-most protein found in plasmaDefine: fluid (water) balance.
equilibrium between fluid intake and output or between the amounts of fluid contained in the body’s different fluid compartments
Define: metabolic water.
water produced as a by-product of dehydration synthesis reactions and aerobic respiration
Define: preformed water.
water ingested in food and drink
Define: obligatory water loss.
water output that is relatively unavoidable: expired air, cutaneous transpiration, sweat, fecal moisture, and minimum urine output
Define: cutaneous transpiration.
water that diffuses through the epidermis and evaporates (not the same as sweat)
What physiological responses does dehydration cause?
increased osmolarity: stimulates release of ADH;
decreased BP: stimulates renin-angiotensin system
Explain the regulation of water intake. What physiological responses does dehydration cause?
governed by thirst;
increased osmolarity: stimulates release of ADH;
decreased BP: stimulates renin-angiotensin system;
both responses stimulate thirst center in hypothalamus
Explain the regulation of water output. What physiological responses does dehydration cause?
controlled by variations in urine volume;
dehydration causes slow rate of water and electrolyte loss and release of ADH
What are the electrolytes referred to by the phrase “electrolyte balance?”
all salts, acids, and bases;
usually refers to salt balance
What 3 conditions do salts enable?
1) neuromuscular excitability
2) secretory activity
3) membrane permeability
Explain the importance of sodium balance.
sodium = most important solute determining total body water and distribution of fluid in compartments;
sodium gradients provide potential energy for cotransport;
generates resting membrane potentials of cells;
cellular inflow of sodium essential for depolarization
What 4 variables do changes in sodium levels affect?
1) plasma volume
2) BP
3) ICF volume
4) interstitial fluid volume
Define: hyponatremia. How does this condition stimulate aldosterone secretion?
decreased plasma sodium levels;
directly stimulates adrenal cortex to release aldosterone
Define: hyperkalemia. How does this condition stimulate aldosterone secretion?
increased plasma potassium levels;
directly stimulates adrenal cortex to release aldosterone
Define: hypotension. How does this condition stimulate aldosterone secretion?
decreased blood volume & BP; stimulates aldosterone secretion indirectly by way of renin-angiotensin system
Explain the importance of potassium balance.
potassium = most abundant cation in ICF;
generates resting membrane potentials of cells;
essential cofactor in protein synthesis;
part of buffer system;
potassium imbalance = most dangerous of all electrolytes;
How is potassium balance maintained?
rise in potassium concentration stimulates adrenal cortex to secrete aldosterone;
aldosterone stimulates renal secretion of potassium
Explain the importance of calcium balance.
calcium = most abundant mineral;
- bones
- neurotransmitter release
- second-messenger systems
- muscle contraction
How is calcium homeostasis maintained?
parathyroid hormone (PTH): enhances calcium reabsorption from filtrate; calcitonin: removes calcium from plasma via osteoblasts (causes deposition of calcium in bone matrix)
Explain the importance of acid-base balance.
acid-base balance = major challenge of homeostasis;
-maintaining H+ concentration of bodily fluids;
optimal pH differs in various fluids;
H+ produced via metabolic rxns
The homeostasis of H+ concentration within a normal range depends on what 3 mechanisms?
1) chemical buffer systems
2) respiratory control
3) renal control
Explain how buffer systems help to maintain H+ concentration within a normal range. Name the 3 buffer systems present in the body.
mechanism that resists changes in pH by converting strong acid or base to a weak one;
1) bicarbonate buffer system
2) phosphate buffer system
3) protein buffers
Explain the bicarbonate buffer system.
CO2 + H2O ⇆ H2CO3 ⇆ HCO3− + H+
kidneys aid in removal of HCO3;
lungs aid in removal of CO2
Explain the phosphate buffer system.
H2PO4− ⇆ HPO42– + H+
Explain protein buffers.
proteins are more concentrated than either bicarbonate or phosphate buffers;
proteins can absorb extra protons when needed, or release them when needed, in order to maintain pH;
amino (NH2) group of AA binds to or releases H+
Explain how respiratory control helps to maintain H+ concentration within a normal range.
relates to bicarbonate buffering system: lungs remove CO2 from the body
rising [CO2] stimulates chemoreceptors to increase ventilation so that CO2 gets rapidly removed;
removal of CO2 leads to reduced [H+];
stronger buffering system than chemical buffers
Explain how renal control helps to maintain H+ concentration within a normal range.
kidneys can neutralize more acid or base than either the respiratory system or the chemical buffers;
renal tubules secrete H+ into tubular fluid
Rank the 3 buffer systems from most effective to least effective.
1) renal control
2) respiratory control
3) chemical buffer systems
