Endocrine System Overview

Endocrine System

• Involved in critical long-term processes including growth, development, and reproduction
• Utilizes chemical messengers (hormones) to communicate between cells
• Regulates activities by influencing cellular metabolism

Endocrine System Organs and Tissues

• Hypothalamus:
  • Produces antidiuretic hormone (ADH), oxytocin, and regulatory hormones
• Pineal Gland:
  • Secretes melatonin
• Pituitary Gland:
  • Anterior Lobe: Produces ACTH, TSH, GH, PRL, FSH, LH, and MSH
  • Posterior Lobe: Releases oxytocin and ADH
• Parathyroid Glands:
  • Located on the posterior surface of the thyroid gland
  • Secretes parathyroid hormone (PTH)
• Thyroid Gland:
  • Produces thyroxine (T4), triiodothyronine (T3), and calcitonin (CT)
• Adrenal Glands:
  • Adrenal Medulla: Secretes epinephrine (E) and norepinephrine (NE)
  • Adrenal Cortex: Produces cortisol, corticosterone, aldosterone, and androgens
• Pancreas (Pancreatic Islets):
  • Secretes insulin and glucagon
• Organs with Secondary Endocrine Functions:
  • Heart: Secretes natriuretic peptides (ANP and BNP)
  • Thymus: Secretes thymosins
  • Adipose Tissue: Secretes leptin
  • Digestive Tract: Secretes hormones involved in coordinating system functions, glucose metabolism, and appetite
  • Kidneys: Secretes erythropoietin (EPO) and calcitriol
  • Gonads:
    • Testes (Male): Secretes androgens (especially testosterone) and inhibin
    • Ovaries (Female): Secretes estrogens, progestins, and inhibin

Intercellular Communication

• Direct Communication:
  • Exchange of ions and molecules between adjacent cells through gap junctions
  • Occurs between cells of the same type
  • Highly specialized and relatively rare
• Paracrine Communication:
  • Uses chemical signals (local regulators) to transmit information between cells within the same tissue
  • Most common form of intercellular communication
• Endocrine Communication:
  • Endocrine cells release hormones into the bloodstream
  • Alters metabolic activities of many tissues and organs simultaneously
• Synaptic Communication:
  • Ideal for rapid communication in emergencies
  • Occurs across synaptic clefts
  • Chemical messenger used is a neurotransmitter
  • Limited to a very specific area

Hormones

• Classes of Hormones:
  • Amino Acid Derivatives: Small molecules structurally related to amino acids
    • Derivatives of Tyrosine: Include thyroid hormones
  • Peptide Hormones: Chains of amino acids
  • Lipid Derivatives: Derived from fatty acids or cholesterol
• Secretion and Distribution:
  • Hormones circulate freely or bind to specialized carrier proteins

Amino Acid Derivatives

• Derivatives of Tyrosine:
  • Thyroid hormones