lecture 26/27 objectives Flashcards
Describe the normal routes of body fluid entry and loss, and explain how changes in water intake/loss can disrupt osmolarity homeostasis.
Entry:
Oral intake of fluids (main source)
Food (contains water)
Metabolic water (produced during cellular respiration)
Loss:
Urine (major route)
Sweat
Feces
Exhaled air (water vapor)
Skin evaporation (insensible loss)
Disruption of Osmolarity Homeostasis:
Increased water intake → lowers plasma osmolarity → water enters cells → risk of cell swelling or hyponatremia
Dehydration/loss of water → increases plasma osmolarity → water leaves cells → cell shrinkage → stimulates thirst and ADH release
describe the mechanisms that control thirst
Increased plasma osmolarity (detected by osmoreceptors in hypothalamus)
Decreased blood volume/pressure (detected by baroreceptors and renin-angiotensin system)
Angiotensin II acts on the hypothalamus to increase thirst
Dry mouth and throat stimulation also contribute
State the normal pH range for arterial blood and the pH range that is compatible with life.
o Normal arterial blood pH: 7.35–7.45
o Compatible with life: ~6.8 to ~7.8
(Outside this range → enzyme malfunction, death)
Describe the major buffer systems of the body (e.g., bicarbonate buffer system, protein buffer system) and their locations (e.g., extracellular fluid) in the body. - bicarbonate buffer system
Location: Extracellular fluid (plasma)
HCO₃⁻ + H⁺ ⇌ H₂CO₃ ⇌ CO₂ + H₂O
Describe the major buffer systems of the body (e.g., bicarbonate buffer system, protein buffer system) and their locations (e.g., extracellular fluid) in the body. - protein buffer system
Location: Intracellular fluid and plasma (e.g., hemoglobin in RBCs, plasma proteins)
Amino acid side chains accept/release H⁺
Describe the major buffer systems of the body (e.g., bicarbonate buffer system, protein buffer system) and their locations (e.g., extracellular fluid) in the body. - phosphate buffer system
Location: Intracellular fluid, kidney tubules
HPO₄²⁻ + H⁺ ⇌ H₂PO₄⁻
Explain the relationship between transport of carbon dioxide in the blood and the bicarbonate buffer system in the plasma.
o CO₂ enters blood, combines with H₂O → forms H₂CO₃ → dissociates into H⁺ and HCO₃⁻
o Most CO₂ is transported as bicarbonate (HCO₃⁻) in plasma
o This reaction is catalyzed by carbonic anhydrase in red blood cells
Using the equation CO2 + H2O ↔ H+ + HCO3- , explain what happens to pH when arterial blood PCO2 and HCO3- concentrations change.
o ↑CO₂ (hypoventilation) → shift right → ↑H⁺ → ↓pH (acidosis)
o ↓CO₂ (hyperventilation) → shift left → ↓H⁺ → ↑pH (alkalosis)
o ↑HCO₃⁻ → binds H⁺ → ↑pH (alkalosis)
o ↓HCO₃⁻ → less buffering → ↓pH (acidosis)
Explain the relationship between changes in alveolar ventilation (i.e., hypoventilation and hyperventilation), arterial blood PCO2, arterial blood pH, and arterial blood HCO3-.
o Hypoventilation: ↑PCO₂ → ↑H⁺ → ↓pH → respiratory acidosis
o Hyperventilation: ↓PCO₂ → ↓H⁺ → ↑pH → respiratory alkalosis
o Effect on HCO₃⁻: In chronic conditions, kidneys will adjust HCO₃⁻ levels to compensate
Explain the mechanisms by which the nephron secretes or retains filtered bicarbonate ions/makes new bicarbonate ions
o Reabsorption of filtered HCO₃⁻ in the proximal tubule
o Secretion of H⁺ in exchange for Na⁺ in the distal tubule
o Generation of new HCO₃⁻ via:
Glutamine metabolism → ammonium excretion + HCO₃⁻ generation
Define acidosis and alkalosis.
o Acidosis: pH < 7.35
o Alkalosis: pH > 7.45
metabolic and respiratory causes of pH imbalances. - respiratory acidosis
Respiratory acidosis
Cause - Hypoventilation → ↑CO₂
Primary change – ↑PCO₂
Compensation - Kidneys ↑HCO₃⁻
Low pH, the kidneys compensate by retaining bicarbonate (HCOs) - buffer
metabolic and respiratory causes of pH imbalances. - respiratory alkalosis
Respiratory alkalosis
Cause - Hyperventilation → ↓CO₂
Primary change - ↓PCO₂
Compensation - Kidneys ↓HCO₃⁻
High pH, the kidneys compensate by eliminating bicarbonate (HCO3) – buffer. By decreasing the amount of bicarbonate the body can lower pH and decrease the buffers.
metabolic and respiratory causes of pH imbalances. - metabolic acidosis
Metabolic acidosis
Cause - Loss of HCO₃⁻ or ↑H⁺ (e.g., diarrhea, DKA)
Primary change - ↓HCO₃⁻
Compensation - Lungs ↑ventilation (↓CO₂)
Low pH, the lungs will compensate by blowing of CO2
metabolic and respiratory causes of pH imbalances. - metabolic alkalosis
Metabolic alkalosis
Cause - Loss of H⁺ or ↑HCO₃⁻ (e.g., vomiting)
Primary change - ↑HCO₃⁻
Lungs ↓ventilation (↑CO₂)
High pH, the lungs will compensate by letting CO2 build up
Describe the concept of compensation in relation to disruption of pH homeostasis.
Respiratory compensation (fast, minutes): Lungs alter CO₂ levels
Renal compensation (slow, hours to days): Kidneys adjust H⁺ and HCO₃⁻
Given arterial blood values for PCO2, pH and HCO3-, determine whether a patient is in acidosis or alkalosis and whether the cause of the pH disturbance is metabolic or respiratory.
Given:
pH: Normal (7.35–7.45)
PCO₂: Normal (35–45 mmHg)
HCO₃⁻: Normal (22–26 mEq/L)
Steps:
Check pH → acidic or alkaline?
Check PCO₂ → respiratory component
Check HCO₃⁻ → metabolic component
Determine cause and whether compensation is present
Example:
- pH = 7.28, PCO₂ = 50 mmHg, HCO₃⁻ = 24 → Respiratory acidosis
- pH = 7.28, PCO₂ = 40, HCO₃⁻ = 18 → Metabolic acidosis
the intake of fluid is
- Driven by thirst receptors
o Stimuli: hypothalamus osmoreceptors decrease salivary secretion, decrease BP - Dehydration: too much fluid loss
- Hyponatremia: too much fluid intake
how does the urinary system specifically help with pH regulation
- Alkaline: same as basic (high pH)
- Acidic: low pH
- Lungs and kidneys work together to regulate pH
o respiratory and metabolic (acidosis or alkalosis) - Respiratory: the more CO2 you have in your system the more acidic your blood pH
- Renal: hold on to bicarbonate when too acidic, secrete when too alkaline
o Bicarbonate binds to H+
