Compensatory Mechanisms

Question 1

Hypovolemic Shock

Answer 1

• Shock is a condition in which the cardiovascular system fails to perfuse tissues adequately
• Impaired CO or blood volume can lead to compromised blood flow to tissues

Question 2

Hypovolemic shock physiology

Answer 2

Cells switch from aerobic to anaerobic metabolism
• ↑ lactic acid production
• ↓ decreased cell function and ↑ membrane permeability
• Na+/K+ pump impaired
• Mitochondrial damage
• Cell death

• Loss of circulatory volume → ↓venous return → ↓decreased SV → ↓CO

Question 3

Automatic Nervous System receptors

Answer 3

Sympathetic
a1 blood vessels
a2 digestive tract, CNS
b1 heart
b2 airways, some blood vessels

Parasympathetic
M vagus nerve
N sympathetic, parasympathetic ganglia adrenal gland

Question 4

Compensatory mechanism: Sympathetic Nervous System

Answer 4

• SNS – Neurohormonal response stimulated by baroreceptors
• ↑ HR
• ↑ contractility
• ↑ vasoconstriction

Question 5

Blood Pressure regulation - hypotension

Answer 5

1. Baroreceptors signal the medulla that BP is too low
   2a. The medulla signals to the heart to increase rate, which increases cardiac output
   2b. The medulla signals blood vessels to constrict (vasoconstriction)
   2c. This also increases venous return, which increases Cardiac Output
2. This raises blood pressure

Question 6

Compensatory mechanism: Adrenal response

Answer 6

Renin-angiotensin system
• ↓ renal perfusion → ↑ release of renin
• ↑ angiotensin I → ↑ angiotensin II
• angiotensin II is a potent vasoconstrictor
• angiotensin II → ↑ aldosterone
• Aldosterone stimulates kidneys to retain sodium → ↑ fluid retention

Question 7

Blood pressure and The Renin-Angiotensin-Aldosterone System

Answer 7

1. Blood pressure falls
2. Renin is released and acts upon angiotensinogen which forms angiotensin I.
3. Angiotensin converting enzyme joins to form angiotensin II.
4. Acts on the adrenal cortex to release aldosterone, which in turn acts on the kidneys to increase sodium and fluid retention

Question 8

Compensatory mechanism: Antidiuretic Response

Answer 8

• Osmoreceptors in hypothalamus → ↑ antidiuretic hormone (ADH) release by posterior pituitary gland

• ADH has vasopressor effect to increase
BP

• ADH acts on renal tubules to retain water

Question 9

Compensatory mechanism: Adrenal Cortex

Answer 9

• Anterior pituitary releases adrenocorticotropic hormone (ACTH)
• ACTH stimulates adrenal cortex to release glucorticoids
• ↑ BGL to meet increased metabolic needs

Question 10

Compensatory mechanism: Respiratory System

Answer 10

• ↓ PO2 sensed by peripheral chemoreceptors → ↑ respiratory rate → ↑ FiO2 and → ↑ pH (less CO2-induced H+)

Question 11

What are the three lines of defense against changes in non-CO2 induced [H+] to maintain the [H+] of body fluids at a nearly constant level:

Answer 11

• Chemical buffer system – immediate response
• Respiratory compensation – few-minute delay
• Renal compensation – hours to days delay