Endocrine Organs and Glands

Pineal Gland

• Location: Posterior epithalamus, near the third ventricle of the brain.
• Function: Secretes melatonin.
  • Melatonin makes us drowsy and regulates sleep-wake cycles by increasing production at night.

Thyroid Gland

• Location: Inferior to the thyroid cartilage and anterior to the trachea.
• Structure: Butterfly-shaped with left and right lobes connected by an isthmus.
• Hormones:
  • Thyroid Hormone: Increases cellular metabolism.
  • Calcitonin: Reduces blood calcium by inhibiting osteoclasts and increasing calcium loss in urine.
• Cell Types:
  • Thyroid Follicles: Produce thyroid hormone.
  • Parafollicular Cells (C cells): Secrete calcitonin.

Parathyroid Glands

• Location: Posterior surface of the thyroid gland.
• Structure: Usually four small glands per person.
• Cell Types:
  • Chief Cells: Secrete parathyroid hormone (PTH) which raises blood calcium levels.
• PTH Mechanism:
  • Increases osteoclast activity.
  • Kidneys retain calcium.
  • Small intestine increases calcium absorption.

Thymus

• Location: Within the mediastinum, superior to the heart, posterior to the sternum.
• Function:
  • Large in children, small in adults.
  • Regulates body immunity and maturation of white blood cells.

Pancreas

• Location: Between the duodenum and the spleen, posterior to the stomach.
• Functions:
  • Exocrine: Pancreatic acini produce alkaline secretions for digestion.
  • Endocrine: Pancreatic islets (Islets of Langerhans) secrete hormones.
• Cell Types:
  • Alpha Cells: Secrete glucagon which raises blood glucose.
  • Beta Cells: Secrete insulin which lowers blood glucose.

Adrenal Glands

• Location: On superior borders of the kidneys.
• Structure:
  • Cortex: Produces corticosteroid hormones affecting stress and immune responses.
  • Medulla: Secretes norepinephrine and epinephrine involved in the fight or flight response.

Gonads

• Testes:
  • Leydig Cells: Produce testosterone affecting reproductive organ development and behavior.
• Ovaries:
  • Follicular Cells: Produce estrogen affecting reproductive organ development.
  • Corpus Luteum: Produces progesterone maintaining uterine lining.

Other Organs with Endocrine Function

• Heart:
  • Atrial Natriuretic Peptide (ANP): Increases sodium and water excretion, lowers blood pressure.
• Kidneys:
  • Regulate electrolytes, erythrocyte production, blood volume, and blood pressure.
  • Calcitriol: Stimulates calcium uptake in the intestine.
  • Erythropoietin: Raises red blood cell production.
  • Renin: Forms angiotensin II for water conservation.
• Gastrointestinal Tract: Secretes hormones that regulate digestive activities.