Lecture: Salt, Electrolyte, and Acid-Base Balance

Question 1

Describe fluid movement in the human body.

Answer 1

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;

Question 2

Describe the major fluid compartments of the body.

Answer 2

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 plasma

Question 3

Define: fluid (water) balance.

Answer 3

equilibrium between fluid intake and output or between the amounts of fluid contained in the body’s different fluid compartments

Question 4

Define: metabolic water.

Answer 4

water produced as a by-product of dehydration synthesis reactions and aerobic respiration

Question 5

Define: preformed water.

Answer 5

water ingested in food and drink

Question 6

Define: obligatory water loss.

Answer 6

water output that is relatively unavoidable: expired air, cutaneous transpiration, sweat, fecal moisture, and minimum urine output

Question 7

Define: cutaneous transpiration.

Answer 7

water that diffuses through the epidermis and evaporates (not the same as sweat)

Question 8

What physiological responses does dehydration cause?

Answer 8

increased osmolarity: stimulates release of ADH;

decreased BP: stimulates renin-angiotensin system

Question 9

Explain the regulation of water intake. What physiological responses does dehydration cause?

Answer 9

governed by thirst;
increased osmolarity: stimulates release of ADH;
decreased BP: stimulates renin-angiotensin system;
both responses stimulate thirst center in hypothalamus

Question 10

Explain the regulation of water output. What physiological responses does dehydration cause?

Answer 10

controlled by variations in urine volume;

dehydration causes slow rate of water and electrolyte loss and release of ADH

Question 11

What are the electrolytes referred to by the phrase “electrolyte balance?”

Answer 11

all salts, acids, and bases;

usually refers to salt balance

Question 12

What 3 conditions do salts enable?

Answer 12

1) neuromuscular excitability
2) secretory activity
3) membrane permeability

Question 13

Explain the importance of sodium balance.

Answer 13

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

Question 14

What 4 variables do changes in sodium levels affect?

Answer 14

1) plasma volume
2) BP
3) ICF volume
4) interstitial fluid volume

Question 15

Define: hyponatremia. How does this condition stimulate aldosterone secretion?

Answer 15

decreased plasma sodium levels;

directly stimulates adrenal cortex to release aldosterone

Question 16

Define: hyperkalemia. How does this condition stimulate aldosterone secretion?

Answer 16

increased plasma potassium levels;

directly stimulates adrenal cortex to release aldosterone

Question 17

Define: hypotension. How does this condition stimulate aldosterone secretion?

Answer 17

decreased blood volume & BP; stimulates aldosterone secretion indirectly by way of renin-angiotensin system

Question 18

Explain the importance of potassium balance.

Answer 18

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;

Question 19

How is potassium balance maintained?

Answer 19

rise in potassium concentration stimulates adrenal cortex to secrete aldosterone;
aldosterone stimulates renal secretion of potassium

Question 20

Explain the importance of calcium balance.

Answer 20

calcium = most abundant mineral;

• bones
• neurotransmitter release
• second-messenger systems
• muscle contraction

Question 21

How is calcium homeostasis maintained?

Answer 21

parathyroid hormone (PTH): enhances calcium reabsorption from filtrate;
calcitonin: removes calcium from plasma via osteoblasts (causes deposition of calcium in bone matrix)

Question 22

Explain the importance of acid-base balance.

Answer 22

acid-base balance = major challenge of homeostasis;
-maintaining H+ concentration of bodily fluids;
optimal pH differs in various fluids;
H+ produced via metabolic rxns

Question 23

The homeostasis of H+ concentration within a normal range depends on what 3 mechanisms?

Answer 23

1) chemical buffer systems
2) respiratory control
3) renal control

Question 24

Explain how buffer systems help to maintain H+ concentration within a normal range. Name the 3 buffer systems present in the body.

Answer 24

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

Question 25

Explain the bicarbonate buffer system.

Answer 25

CO2 + H2O ⇆ H2CO3 ⇆ HCO3− + H+
kidneys aid in removal of HCO3;
lungs aid in removal of CO2

Question 26

Explain the phosphate buffer system.

Answer 26

H2PO4− ⇆ HPO42– + H+

Question 27

Explain protein buffers.

Answer 27

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+

Question 28

Explain how respiratory control helps to maintain H+ concentration within a normal range.

Answer 28

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

Question 29

Explain how renal control helps to maintain H+ concentration within a normal range.

Answer 29

kidneys can neutralize more acid or base than either the respiratory system or the chemical buffers;
renal tubules secrete H+ into tubular fluid

Question 30

Rank the 3 buffer systems from most effective to least effective.

Answer 30

1) renal control
2) respiratory control
3) chemical buffer systems