I. The Endocrine System

• The endocrine system regulates metabolism, growth, and tissue function.

• Endocrine glands secrete hormones into the bloodstream.

II. The Hypothalamus and Pituitary

A. Hypothalamus

• Coordination center of the endocrine system, located in the forebrain.

• Integrates signals from the CNS, synthesizes oxytocin and vasopressin.

• Regulates the anterior pituitary.

B. Anterior Pituitary

• Receives releasing factors from the hypothalamus via blood vessels.

• Secretes tropic hormones that target other endocrine glands.

C. Posterior Pituitary

• Contains axon terminals from the hypothalamus.

• Secretes hormones synthesized in the hypothalamus.

III. Neuronal vs. Hormonal Signaling

• Neuronal Signaling: Uses neurotransmitters; affects nearby cells.

• Hormonal Signaling: Hormones travel through blood; small amounts can have significant effects.

  • Extracellular hormones bind receptors producing secondary messengers.

  • Nuclear hormones enter the nucleus and activate transcription factors.

IV. Hormones and Target Tissues

• Hypothalamus sends hypothalamic hormones to the anterior and posterior pituitary.

• Hormones from pituitary target adrenal cortex, thyroid, ovaries/testes.

• Many target tissues including muscle, liver, mammary glands.

V. Hormone Classification

• Endocrine: Released into blood (e.g., insulin, glucagon).

• Paracrine: Diffuse to neighboring cells (e.g., eicosanoids).

• Autocrine: Affect the secreting cells (e.g., interleukins).

VI. Insulin and Glucagon

• Insulin:

  • Synthesized in b-cells (70% of pancreatic islets).

  • Responds to high glucose levels, binds to receptors in various tissues.

• Glucagon:

  • Synthesized in a-cells (20% of pancreatic islets).

  • Acts to increase blood glucose levels.

VII. Pro-Hormones

• Pro-opiomelanocortin (POMC) can yield multiple products that regulate various physiological functions.

VIII. Oxytocin and Vasopressin

• Oxytocin: Promotes uterine contractions and milk release.

• Vasopressin: Involved in water retention and increases blood pressure.

IX. Catecholamines (Epinephrine and Norepinephrine)

• Produced in adrenal glands; involved in