Hormones

These are chemical substances that are secreted into the body fluids by one cell or a group of cells and have a physiological control effect on other cells of the body. Hormones act by binding to specific receptors in the target organ.


Functions of hormones

  1. Help to control the internal environment by regulating its chemical composition and volume.
  2. Transport substances through the cell membrane.
  3. Play a key role in growth and development.
  4. Contribute to the basic processes of reproduction, fertilization, nourishment of the embryo, and delivery of newborns.
  5. Regulate metabolism and energy balance in the body.
 

Types

1. Local hormones: These have specific local effects on the body.
Example: Acetylcholine, secretin, and Cholecystokinin.
2. General hormones: These affect body cells far away from their points of secretion. A few general hormones affect all the cells of the body, such as growth hormone and thyroid hormone. On the other hand, some hormones affect only target cells because they have specific receptors for the hormone. Example: ACTH, estrogen, and progesterone.

CLASSIFICATION OF HORMONE

BASED ON THE SITE OF PRODUCTION

1. Anterior pituitary gland

  • Growth hormone (somatotropin)
  • Thyroid-stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Follicular stimulating hormone (FSH)
  • Prolactin
  • Luteinizing hormone (LH)

2. Posterior pituitary gland

  • Vasopressin or Antidiuretic hormone (ADH)
  • Oxytocin

3. Adrenal cortex

  • Mineralocorticoids (Aldosterone)
  • Glucocorticoids (Cortisol)
  • Sex hormone (Adrenal androgens)

4. Adrenal medulla

  • Epinephrine (adrenaline)
  • Norepinephrine (noradrenaline)

5. Thyroid gland

  • Thyroxin (T4)
  • Triiodothyronine (T3)
  • Calcitonin

6. Parathyroid gland

  • Parathyroid hormone (Parathormone)

7. Islets of Langerhans

Pancreas

  • Insulin (Beta cells)
  • Glucagon (Alpha cells)
  • Somatostatin (Delta cells)

8. Testes

  • Testosterone

9. Ovaries

  • Estrogen
  • Progesterone
  • Relaxin

10. Placenta

  • Estrogen
  • Progesterone
  • Human chorionic gonadotropin (HCG)
  • Human somatomammotropin
  • Relaxin