The endocrine system is a network of glands that secrete hormones directly into the blood. These hormones regulate growth, metabolism, reproduction, and many vital body functions. Unlike exocrine glands, they do not have ducts → they are called ductless glands.

1. Pituitary Gland – Master Gland

• Location: Base of the brain, below hypothalamus.
• Divisions: Anterior lobe, Posterior lobe.

Hormones & Functions:

• Anterior lobe (adenohypophysis):
  • Growth hormone (GH) → growth of bones & muscles.
  • TSH (Thyroid Stimulating Hormone) → stimulates thyroid.
  • ACTH (Adrenocorticotropic Hormone) → stimulates adrenal cortex.
  • FSH & LH → control reproductive functions.
  • Prolactin → stimulates milk production.
• Posterior lobe (neurohypophysis):
  • ADH (Antidiuretic Hormone) → water balance (reabsorbs water in kidneys).
  • Oxytocin → contraction of uterus during childbirth, milk ejection.

2. Thyroid Gland

• Location: Neck, in front of trachea.
• Hormones:
  • Thyroxine (T₄) & Triiodothyronine (T₃) → regulate metabolism, growth, development.
  • Calcitonin → lowers blood calcium.
• Disorders:
  • Goiter (enlargement due to iodine deficiency).
  • Hyperthyroidism → weight loss, anxiety.
  • Hypothyroidism → weight gain, lethargy, cretinism in children.

3. Parathyroid Glands

• Location: 4 small glands on the back of thyroid.
• Hormone:
  • Parathyroid Hormone (PTH) → increases blood calcium by breaking down bone.

4. Adrenal Glands – Emergency Glands

• Location: On top of each kidney.
• Parts: Cortex & Medulla.

Cortex (outer):

• Cortisol → stress hormone, regulates metabolism.
• Aldosterone → maintains sodium & potassium balance.
• Sex hormones (small amounts).

Medulla (inner):

• Adrenaline (epinephrine) → “fight or flight” response.
• Noradrenaline → maintains blood pressure.

5. Pancreas (Islets of Langerhans)

• Location: Behind stomach.
• Hormones:
  • Insulin → lowers blood sugar (stores glucose as glycogen).
  • Glucagon → raises blood sugar (breaks down glycogen).
• Disorder: Diabetes mellitus (insulin deficiency).

7. Thymus Gland

• Location: Behind sternum, in chest (large in children, shrinks in adults).
• Hormone:
  • Thymosin → development of immune system (T-lymphocytes).

8. Gonads (Sex Glands)

Testes (in males):

• Testosterone → male secondary sexual characters, sperm production.

Ovaries (in females):

• Estrogen → female secondary sexual characters, menstrual cycle.
• Progesterone → prepares uterus for pregnancy.

Summary Table

Gland	Hormones Secreted	Major Functions
Pituitary	GH, TSH, ACTH, FSH, LH, Prolactin, ADH, Oxytocin	Master control of other glands, growth, reproduction
Thyroid	T₃, T₄, Calcitonin	Metabolism, growth, calcium regulation
Parathyroid	PTH	Increases blood calcium
Adrenal	Cortisol, Aldosterone, Adrenaline, Noradrenaline	Stress response, metabolism, water balance
Pancreas	Insulin, Glucagon	Blood sugar regulation
Pineal	Melatonin	Sleep-wake cycle
Thymus	Thymosin	Immunity development
Testes	Testosterone	Male reproduction
Ovaries	Estrogen, Progesterone	Female reproduction