Functions of Adrenal Medullary Hormones and Regulation

Question 1

What are the hormones secreted by adrenal medulla?

Answer 1

Hormones secreted by adrenal medulla are called catecholamines;

a) adrenaline / epinephrine
b) noradrenaline / norepinephrine
c) dopamine

Question 2

What are the roles of adrenal medullar hormones?

Answer 2

a) enhance the sympathetic nervous system
b) prepare the body for stressful events
c) ‘fight or flight’ response

Question 3

What are the effects of catecholamines on the heart?

Answer 3

a) EP binds to both alpha and beta-1 receptors
b) NE binds to alpha receptors
c) NE and EP both increase the force and rate of contraction of the isolated heart. The responses are mediated by beta-1 receptors. Catecholamines cause;
- heart rate (chronotropic effect)
- force of contraction (inotropic effect)
- excitability of heart muscle (bathmotropic effect)
- conductivity in heart muscle (dromotropic effect)

Question 4

What are the effects of catecholamines on the blood vessels?

Answer 4

• NE causes vasoconstriction through alpha receptors; increases TPR
• EP also causes vasoconstriction but vasodilation in 3 major organs; skeletal muscle, liver and heart through beta-2 receptors. This vasodilation balances the vasoconstriction caused by EP in elsewhere. -> TPR decreased
• Catecholamines need the presence of cortisol hormones for vascular effects

Question 5

What are the effects of catecholamines on the blood pressure?

Answer 5

• NE -> vasoconstriction -> increases TPR -> increases DBP
• NE increases SBP slightly by its actions on heart
• Hypertension stimulates baroreceptors(in carotid and aortic sinuses) -> produces reflex bradycardia (prevents abnormal increases in BP)
• CO per minute decreases
• EP increases SBP (by increasing force of contraction of heart and cardiac output)
• Decreases DBP (by reducing TPR - caused by vasodilation in 3 major organs)
• Widening of pulse pressure (SBP - DBP)
• Insufficient baroreceptor stimulation -> increases heart rate and cardiac output
• Action of catecholamine son blood pressure needs presence of glucocorticoids (cortisols)
• hypersecretion of catecholamines causes hypertension

Question 6

How does stress stimulate the adrenal glands?

Answer 6

Short term stress: (adrenal medulla)

• Stress -> stimulates hypothalamus -> stimulates nerve impulses -> spinal cord -> preganglionic nerve fibers reach the adrenal medulla -> secrete catecholamines -> short term stress response:
  a) increased heart rate
  b) increased BP
  c) Liver converts glycogen -> glucose (increases blood glucose level)
  d) changes blood flow patterns (leading to increased alertness, decreased digestive system activity, reduced urine output)
  e) increased metabolic rate

Long term stress: (adrenal cortex)
- Stress -> activation of hypothalamus -> hypothalamus secretes CRH (corticotropin-releasing hormone) -> activates corticotrope cells of anterior pituitary -> releases ACTH -> activates adrenal cortex -> secretes cortisol