Endocrine System and Hormonal Regulation: Key Concepts and Hypothalamic-Pituitary Interactions

**Endocrine System

Body system that uses hormones released into the bloodstream to regulate long‑term processes such as growth, metabolism, reproduction, and homeostasis**

**Relationship Between Nervous and Endocrine Systems

Nervous system sends rapid electrical signals; endocrine system sends slower but longer‑lasting hormonal signals; hypothalamus links the two**

**Hypothalamus

Brain region that receives neural signals and controls endocrine function through the pituitary gland**

**Hypophyseal Portal Vein

Specialized blood vessel system carrying hypothalamic hormones directly to the anterior pituitary**

**Hormone

Chemical messenger released by endocrine glands that travels through blood to target cells with specific receptors**

**Lipid‑Soluble Hormones

Hormones that dissolve in fats, cross cell membranes, bind intracellular receptors, and alter gene expression**

**Water‑Soluble Hormones

Hormones that dissolve in water, cannot cross membranes, bind surface receptors, and activate second messenger systems**

**Steroid Hormones

Lipid‑soluble hormones such as cortisol, estrogen, and progesterone**

**Thyroid Hormones (T3/T4)

Lipid‑soluble hormones that regulate metabolism**

**Peptide Hormones

Water‑soluble hormones such as insulin, glucagon, GH, ADH, and oxytocin**

**Catecholamines

Water‑soluble hormones such as epinephrine and dopamine**

**Humoral Stimulation

Hormone release triggered by changes in blood levels of ions or nutrients**

**Hormonal Stimulation

One hormone stimulates another endocrine gland to release its hormones**

**Neural Stimulation

Nerve impulses trigger hormone secretion**

**GHRH (Growth Hormone Releasing Hormone) Hypothalamus Hormones

Triggered by low blood glucose; stimulates anterior pituitary to release hGH**

**GHIH (Growth Hormone Inhibiting Hormone) Hypothalamus Hormones

Triggered by high blood glucose; inhibits release of hGH**

**TRH (Thyrotropin Releasing Hormone) Hypothalamus Hormones

Triggered by low T3/T4; stimulates release of TSH**

**CRH (Corticotropin Releasing Hormone) Hypothalamus Hormones

Triggered by stress; stimulates release of ACTH**

**GnRH (Gonadotropin Releasing Hormone) Hypothalamus Hormones

Triggered by low estrogen/testosterone; stimulates release of FSH and LH**

**PRH (Prolactin Releasing Hormone) Hypothalamus Hormones

Triggered by pregnancy; stimulates prolactin release**

**PIH (Prolactin Inhibiting Hormone / Dopamine) Hypothalamus Hormones

Triggered by high prolactin or non‑lactation state; inhibits prolactin release**

**Oxytocin Posterior Pituitary

Triggered by uterine stretching or suckling; targets uterus and mammary glands; causes contractions and milk ejection**

**ADH (Antidiuretic Hormone / Vasopressin) Posterior Pituitary

Triggered by high osmotic pressure or low blood volume; increases water reabsorption and raises blood pressure**

**hGH (Human Growth Hormone) Anterior Pituitary

Triggered by GHRH; targets bones, muscles, and body cells; stimulates growth and protein synthesis**

**PRL (Prolactin) Anterior Pituitary

Triggered by PRH or decreased PIH; stimulates and maintains milk production**

**FSH (Follicle Stimulating Hormone) Anterior Pituitary

Triggered by GnRH; stimulates egg follicle development and estrogen secretion; stimulates sperm production in males**

**LH (Luteinizing Hormone) Anterior Pituitary

Triggered by GnRH; triggers ovulation and progesterone secretion; stimulates testosterone production in males**

**TSH (Thyroid Stimulating Hormone) Anterior Pituitary

Triggered by TRH; stimulates thyroid gland to release T3 and T4**

**ACTH (Adrenocorticotropic Hormone) Anterior Pituitary

Triggered by CRH and stress; stimulates adrenal cortex to release cortisol and glucocorticoids**

**MSH (Melanocyte Stimulating Hormone) Anterior Pituitary

Triggered by excess CRH; affects pigmentation and brain activity**