Physiology of Adrenaline and Noradrenaline

Adrenaline and Noradrenaline

• Noradrenaline serves as a postganglionic neurotransmitter within the sympathetic division of the autonomic nervous system.
• Both adrenaline and noradrenaline are released into the bloodstream from the adrenal medulla during sympathetic activation.
• The hormones from the adrenal medulla enhance and prolong sympathetic nervous system stimulation.

The Pancreas

• Functions as both an endocrine and exocrine organ.
• Contains three main types of cells in the pancreatic islets:
  • Alpha cells produce glucagon.
  • Beta cells, which are the most abundant, secrete insulin.
  • Delta cells release somatostatin (GHRIH).

Blood Glucose Regulation

• Normal blood glucose levels range from 3.5 to 8 mmol/litre (63 to 144 mg/100 mL).
• Insulin and glucagon have opposing effects on blood glucose:
  • Glucagon increases blood glucose levels.
  • Insulin decreases blood glucose levels.

Hormonal Functions in the Pancreas

• Insulin:

  • Lowers elevated blood nutrient levels (glucose, amino acids, fatty acids).
  • Supports nutrient storage, particularly when there's an excess.

• Glucagon:

  • Increases blood glucose by stimulating glycogenolysis (conversion of glycogen to glucose) in the liver and muscles.
  • Secretion is triggered by low blood glucose and exercise, and inhibited by somatostatin and insulin.

• Somatostatin (GHRIH):

  • Inhibits the secretion of both insulin and glucagon.
  • Also suppresses growth hormone (GH) release from the anterior pituitary.

Pineal Gland

• A small endocrine gland in the brain, approximately 10 mm long and reddish-brown in color.
• Often atrophies after puberty and may calcify with age.

Melatonin

• Secreted by the pineal gland.
• Promotes sleepiness and helps regulate the body's biological clock.

Thymus Gland

• Located in the upper mediastinum; birth weight: 10-12 g, increases to 20-30 g during childhood, reduces to 3-6 g in old age.

Thymosin

• Hormones from the thymus promote proliferation and maturation of T cells, which combat microbes and foreign substances.
• Thymic hormones may also aid in slowing down aging processes.

Ovaries and Testes (Gonads)

• Ovaries:

  • Female gonads located in the pelvic cavity.
  • Secrete estrogens and progesterone, which develop female sexual characteristics and regulate reproductive systems.
  • Produce relaxin to soften connective tissues for childbirth.

• Testes:

  • Male gonads located in the scrotum.
  • Secrete testosterone and other hormones responsible for male sexual characteristics and reproductive functions.

Adrenal Glands

• Paired adrenal glands are positioned above the kidneys, measuring around 4 cm long and 3 cm thick.
• Comprised of the adrenal cortex (essential for life) and adrenal medulla (non-essential).

Hormones of the Adrenal Gland

• Adrenal Cortex:

  • Produces steroids from cholesterol called adrenocorticosteroids.
  • Three main groups:
    • Glucocorticoids (e.g., cortisol, cortisone).
    • Mineralocorticoids (e.g., aldosterone).
    • Sex hormones (androgens).

• Adrenal Medulla:

  • Produces adrenaline (epinephrine) and noradrenaline (norepinephrine).

Glucocorticoids

• Cortisol is the primary glucocorticoid and is vital for metabolism and stress response.
• Stimulated by ACTH from the anterior pituitary and stress levels.
• Has anti-inflammatory properties.