Fluid Homeostasis & Acid-Base Balance

Question 1

Fluid inside cell

Answer 1

• 2/3 is fluid
• cytosol

Question 2

Fluid outside cell

Answer 2

• 1/3 fluid
• interstitial fluid (80%)
• blood plasma (20%)

Question 3

Plasma membrane

Answer 3

Cell separates intracellular fluid from interstitial fluid

Question 4

Blood vessel walls

Answer 4

divide interstitial fluid from blood plasma

Question 5

Capillary walls

Answer 5

thin enough to allow exchange of water & solutes between blood plasma & interstitial fluid

Question 6

Net filtration process

Answer 6

hydrostatic pressure in capillaries - hydrostatic pressure in ECF

Question 7

Oncotic pressure

Answer 7

colloid osmotic pressure exerted by proteins in fluid

Question 8

ADH & Diabetes insipidus

Answer 8

• central diabetes insipidus: inadequate secretion of ADH
• Nephrogenic diabetes insipidus: inability of kidneys to respond to ADH

Question 9

Atrial Natriuretic Peptide (ANP)

Answer 9

• Increase in blood volume –> ANP release when atrial walls are stretched
• stimulates to excrete more salt –> more water
• decrease blood volume & blood pressure

Question 10

B-type Natriuretic Peptide (BNP)

Answer 10

• released by ventricles
• secreted in response to increased volume in ventricles, acts like ANP to promote diuresis
• increases congestive heart failure, so measuring it helps diagnose CHF

Question 11

Sodium ion

Answer 11

• most abundant cation in extracellular fluid
• Used for impulse transmission, muscle contraction, fluid, & electrolyte balance
• Level is controlled by aldosterone, ADH, & ANP

Question 12

Chloride ion

Answer 12

• major extracellular anion
• Helps regulate osmotic pressure between compartments
• Forms HCl in stomach
• Regulation of Cl- balance is controlled by aldosterone

Question 13

Potassium ion

Answer 13

• most abundant cation in intracellular fluid
• Involved in fluid volume, impulse conduction, muscle contraction, & regulating pH
• Mineralocorticoids (mainly aldosterone) regulate plasma level

Question 14

Bicarbonate ion

Answer 14

• important plasma ion
• Major membrane of plasma acid-base buffer system
• Kidneys reabsorb or secrete it for final acid-base balance

Question 15

Magnesium ion

Answer 15

• intracellular cation
• Activates enzymes involved in carbohydrate & protein metabolism
• Used in myocardial function, transmission in CNS, & operation of sodium pump

Question 16

Calcium ion

Answer 16

• most abundant mineral in body
• Structural component of bones & teeth
• Used for blood coagulation, neurotransmitter release, muscle tone, excitability of nerves & muscles
• Level in plasma regulated by parathyroid hormone

Question 17

Phosphate ion

Answer 17

• occurs as calcium phosphate salt
• Used in buffer system
• Regulated by parathyroid hormone & calcitrol

Question 18

Protein buffer system

Answer 18

• most abundant in intracellular fluid & blood plasma
• pH rises > COOH group dissociates, acts like an acid
• pH calls > free amino group dissociates, acts like a base

Question 19

Hemoglobin in red blood cells

Answer 19

• when oxygen dissociates from oxygen, attaches to hydrogen > neutralizing acidic hydrogen ion

Question 20

Carbonic acid-bicarbonate buffer system

Answer 20

• based on bicarbonate ion (HCO3-) which acts as a weak base, carbonic acid (H2CO3) acts as weak acid
• pH falls > HCO3- removes excess H+
• pH rises > H2CO3 can provide H+ & HCO3- (bicarbonate ion)

Question 21

Phosphate buffer system

Answer 21

• dihydrogen phosphate (H2PO4-) & monohydrogen phosphate (HPO42-)
• pH rises: H+ attaches to HPO42- > H2PO4 (acid)
• pH falls: OH- + H2PO4 > H2O + HPO42- (base)

Question 22

Exhaling/Retaining of CO2

Answer 22

• mixes with water in blood to form carbonic acid
• exhaling: less acid production & pH rise
• retaining: more acid production & pH drop

Question 23

Excretion of H+

Answer 23

• removes nonvolatile acids
• Proximal convoluted tubules & collecting ducts of kidneys secrete H+ into tubular fluid
• Some H+ secreted into tubular fluid of collecting duct is buffered by HPO42- & NH3. Buffers are excreted in urine

Question 24

Respiratory acidosis

Answer 24

• blood pH drops due to excessive retention of CO2 leading to excess H2CO3, decreased pH
• Renal: increased excretion of H+; increased reabsorption of HCO3-
• If compensation is complete, pH will be within normal range but PCO2 will be high

Question 25

Respiratory alkalosis

Answer 25

• blood pH rises due to excessive loss of CO2 as in hyperventilation, increased pH
• Renal: decreased excretion of H+; decreased reabsorption of HCO3
• If compensation is complete, pH will be within normal range but PCO2 will be low

Question 26

Metabolic acidosis

Answer 26

-arterial blood levels of HCO3- falls, decreased pH
- Respiratory: hyperventilation increases loss of CO2
- If compensation is complete, pH will be within normal range but HCO3- will be low

Question 27

Metabolic alkalosis

Answer 27

• arterial blood levels of HCO3- rises, increased pH
• Respiratory: hypoventilation, which slows loss of CO2
• If compensation is complete, pH will be within normal range but HCO3- will be high

Question 28

Loop diuretics

Answer 28

• most powerful diuretic
• inhibits salt transport out of ascending loop of Henle
• can inhibit up to 25% of water resorption

Question 29

Osmotic diuretics

Answer 29

• reduce reabsorption of water by adding extra solutes to filtrate
• can occur as side effect of diabetes

Question 30

Potassium-sparing diuretics

Answer 30

• aldosterone receptor antagonists block reabsorption of Na+ & secretion of K+