Endocrine System Overview

What is the Endocrine System?

• Collection of cells and glands that produce and release hormones
• Hormones: Chemicals that enter the bloodstream to affect distant areas
• Communication network like the nervous system, but different
  • Nervous system: Fast, direct, short-acting
  • Endocrine system: Slow, indirect, long-lasting

Main Components

Hypothalamus

• Location: Base of the brain, below the thalamus
• Master regulator of the endocrine system
• Produces hormones to control other endocrine glands
  • Five Key Hormones:
    • Thyrotropin releasing hormone (TRH)
    • Corticotropin releasing hormone (CRH)
    • Growth hormone releasing hormone (GHRH)
    • Prolactin releasing hormone (PRH)
    • Gonadotropin releasing hormone (GnRH)

Structural Connections

• Anterior Pituitary Gland: Connected by blood supply
  • Hormones travel to anterior pituitary to release separate hormones
• Posterior Pituitary Gland: Connected by nerves
  • Direct nervous signaling for hormone release

Anterior Pituitary Gland

• Hormones Released:
  1. Thyroid Stimulating Hormone (TSH)
  2. Adrenocorticotropic Hormone (ACTH)
  3. Growth Hormone (GH)
  4. Prolactin (PRL)
  5. Gonadotropins: Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH)

Target and Effects

• TSH: Stimulates thyroid to release T3 (tri-iodothyronine) and T4 (thyroxine)
  • Functions: Metabolism, development, and catecholamine release
  • Calcitonin: Lowers blood calcium
• ACTH: Stimulates adrenal cortex to release cortisol and aldosterone
  • Cortisol: Increases blood glucose, suppresses immune system, stimulates fight or flight
  • Aldosterone: Increases sodium reabsorption, raises blood pressure by increasing blood volume
• GH: Stimulates growth, protein synthesis, metabolic activities
• PRL: Stimulates milk production
• LH/FSH in Gonads:
  • Females: LH stimulates progesterone and ovulation; FSH stimulates follicle maturation and estrogen production
  • Males: LH stimulates Leydig cells to produce testosterone; FSH stimulates Sertoli cells for spermatogenesis

Posterior Pituitary Gland

• Hormones: Oxytocin and Anti-Diuretic Hormone (ADH, Vasopressin)
  • Oxytocin: Uterine contractions, milk ejection, relationship building
  • ADH: Reduces urination to maintain hydration

Thyroid Gland

• Produces T3, T4, and Calcitonin
  • T3/T4: Key in metabolism, development, catecholamine release
  • Calcitonin: Lowers blood calcium levels

Parathyroid Gland

• Produces Parathyroid Hormone (PTH)
  • PTH: Increases blood calcium, opposing calcitonin

Adrenal Glands

• Consists of cortex and medulla
  • Cortex: Produces cortisol, aldosterone, androgens
  • Medulla: Produces norepinephrine and epinephrine

Pancreas

• Both endocrine and exocrine functions
  • Endocrine Hormones: Insulin and glucagon
  • Insulin: Lowers blood glucose levels
  • Glucagon: Raises blood glucose levels

Kidneys

• Produce renin and erythropoietin
  • Renin: Works with aldosterone to increase blood pressure
  • Erythropoietin: Stimulates red blood cell production

General Function

• The endocrine system works to maintain homeostasis and proper physiological function through hormone release.