Chapter 18: Endocrine System

Comparison of Control by the Nervous and Endocrine Systems

• Collaboration: Nervous and endocrine systems work together to coordinate body functions.

• Hormones vs. Neurotransmitters:

  • Hormones: Chemical signaling molecules (can be proteins, lipids, or cholesterol-based).

  • Neurotransmitters: Generally proteins that act locally.

Control of Hormone Secretion

• Released in short bursts when needed.

• Regulation influenced by:

  • Nervous system signals.

  • Blood chemical changes.

  • Other hormone levels.

Glands Overview

• Definition: Glands are organs that produce/release substances for specific functions, differing between secretion (useful) and excretion (waste).

• Types:

  • Exocrine Glands: Secrete products into ducts (e.g., sweat, saliva).

  • Endocrine Glands: Secrete hormones into the bloodstream (e.g., pituitary, thyroid).

Endocrine Gland Locations

• Main glands: Pituitary, Thyroid, Parathyroid, Suprarenal (adrenal), Pineal.

• Other organs: Hypothalamus, thymus, pancreas, ovaries, testes, kidneys.

Hormone Activity

• Hormones affect specific target cells with receptors.

• Receptors can up-regulate/down-regulate based on hormone concentration.

Hormone Signaling Types

• Endocrine: Hormones act at distant sites via blood.

• Paracrine: Local hormones affecting nearby cells.

• Autocrine: Hormones affecting the same cell that secretes them.

Hormones by Chemical Class

• Lipid-Soluble Hormones: Steroids and thyroid hormones needing transport proteins in blood.

• Water-Soluble Hormones: Amine, peptide, and protein hormones circulating freely in plasma.

Mechanisms of Hormone Action

• Lipid-soluble Hormones: Bind to receptors inside target cells, altering gene expression.

• Water-soluble Hormones: Bind to membrane receptors, activating signaling pathways.

Control of Hormone Secretion

• Most regulation via negative feedback; positive feedback in cases like childbirth (oxytocin).

Hypothalamus and Pituitary Gland

• Regulation: Governs other endocrine glands via the infundibulum.

• Hormonal Influence: Hypothalamus hormones influence anterior pituitary secretion.

• Posterior Pituitary: Stores hormones (ADH, oxytocin) from the hypothalamus.

Hormones from the Anterior Pituitary

• Secretes several hypothalamic-regulated hormones:

  • Growth hormone (GH)

  • Prolactin (PRL)

  • Thyroid-stimulating hormone (TSH)

  • Adrenocorticotropic hormone (ACTH)

  • Follicle-stimulating hormone (FSH)

  • Luteinizing hormone (LH)

  • Melanocyte-stimulating hormone (MSH)

Summary of Anterior Pituitary Hormones

• Growth Hormone (GH): Stimulates growth and metabolism.

• TSH: Stimulates thyroid hormone release.

• ACTH: Stimulates adrenal cortex.

Posterior Pituitary Hormones

• ADH: Regulates body water balance.

• Oxytocin (OT): Promotes uterine contractions and milk ejection during breastfeeding.

Thyroid Gland Overview

• Located below the larynx, produces T3 and T4 hormones, increases BMR, and influences growth.

Parathyroid Glands

• Contains chief cells producing parathyroid hormone (PTH), maintains calcium homeostasis with calcitonin.

Suprarenal (Adrenal) Glands

• Located atop kidneys; divided into cortex (mineralocorticoids, glucocorticoids) and medulla (epinephrine, norepinephrine).

Pancreatic Islets

• Contain glucagon (raises blood glucose) and insulin (lowers blood glucose).

Gonadal Hormones

• Ovaries: Hormones for female reproductive health.

• Testes: Produce testosterone for male reproductive health.

Pineal Gland and Thymus

• Pineal Gland: Secretes melatonin for regulating the biological clock.

• Thymus: Produces hormones for T cell maturation.

Eicosanoids and Growth Factors

• Derived from fatty acids; involved in local signaling and tissue repair.

Stress Response

• Eustress: Beneficial stress; Distress: Harmful stress.

• Key hormones: cortisol and catecholamines (epinephrine, norepinephrine).

Aging and the Endocrine System

• Hormone levels shift with age; some increase, others decrease, and endocrine tissues may become fibrous.

Disorders of the Endocrine System

• Common disorders include:

  • Diabetes Mellitus (insulin deficiency)

  • Cushing’s Syndrome (excess cortisol)

  • Addison’s Disease (cortisol and aldosterone deficiency)