Endocrine

Endocrine System — Important Details Only

Hormones

  • Endocrine system — Controls body functions through hormones.

  • Hormones — Chemical messengers carried by blood.

  • Homeostasis — Maintains a stable internal environment.

  • Steroid hormones — Made from cholesterol.

  • Nonsteroid hormones — Mainly proteins, peptides, and amines.

  • Direct gene activation — Steroid and thyroid hormones affect DNA to produce proteins.

  • Second-messenger system — Protein/peptide hormones act through membrane receptors and messengers like cAMP.

  • Negative feedback — Stops or reduces hormone release when levels are sufficient.

Stimuli for Hormone Release

  • Hormonal — One hormone triggers another gland.

  • Humoral — Changes in blood nutrients or ions trigger release.

  • Neural — Nerve signals trigger hormone release.

Major Glands and Hormones

Hypothalamus and Pituitary

  • Hypothalamus — Links nervous and endocrine systems.

  • Anterior pituitary — Produces six major hormones.

  • Posterior pituitary — Stores and releases hypothalamic hormones.

  • GH — Bone and muscle growth.

  • PRL — Milk production.

  • FSH — Follicle development and sperm production.

  • LH — Ovulation and testosterone production.

  • TSH — Stimulates thyroid.

  • ACTH — Stimulates adrenal cortex.

  • ADH — Kidney water reabsorption; decreases urine.

  • Oxytocin — Uterine contractions and milk let-down.

Pineal Gland

- Melatonin — Regulates sleep-wake cycle.

Thyroid and Parathyroids

  • T3 and T4 — Increase metabolism; support growth and development.

  • Calcitonin — Decreases blood calcium.

  • PTH — Increases blood calcium.

Thymus

- Thymosin — Supports immune-cell maturation.

Adrenal Glands

  • Aldosterone — Retains sodium and water; removes potassium; increases blood pressure.

  • Cortisol — Increases blood glucose; long-term stress response; reduces inflammation.

  • Epinephrine and norepinephrine — Fight-or-flight response; increase heart activity and blood glucose.

Pancreas

  • Beta cells → Insulin — Lowers blood glucose.

  • Alpha cells → Glucagon — Raises blood glucose.

  • Key point — Insulin and glucagon have opposite effects.

Gonads

  • Estrogen — Female reproductive development and secondary sex characteristics.

  • Progesterone — Prepares uterus for implantation; supports pregnancy.

  • Testosterone — Male reproductive development and sperm production.

Other Important Hormones

  • ANP (heart) — Helps lower blood volume and pressure.

  • hCG (placenta) — Helps maintain early pregnancy.

  • hPL (placenta) — Helps prepare breasts for lactation.

  • Relaxin (placenta) — Relaxes pelvic ligaments for childbirth.

Must-Memorize Comparisons

  • Insulin ↓ blood glucose | Glucagon ↑ blood glucose

  • PTH ↑ blood calcium | Calcitonin ↓ blood calcium

  • Anterior pituitary produces hormones | Posterior pituitary stores and releases hormones

  • Adrenal cortex = aldosterone, cortisol, sex hormones

  • Adrenal medulla = epinephrine and norepinephrine

  • Menopause — Declining ovarian function; increased risk of osteoporosis and heart disease.