Endocrine System Overview

Study Notes

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

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

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

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