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4. Hormone Release & Regulation

  • Release control: mainly negative feedback (hormone effects inhibit further release).

  • Endocrine stimuli:

    • Humoral: changing blood levels of ions/nutrients (e.g., Ca2+ → PTH release).

    • Neural: nerve fibers stimulate hormone release (e.g., sympathetic nervous system → adrenal medulla → norepinephrine and epinephrine).

    • Hormonal: one hormone stimulates another gland (e.g., hypothalamus → anterior pituitary → thyroid).



5. Hypothalamus & Pituitary Gland

  • Hypothalamus: link between nervous and endocrine systems, controls pituitary gland.

  • Pituitary gland: “master gland,” located in sella turcica of sphenoid bone. Two lobes:

Posterior Pituitary (neurohypophysis)

  • Stores and releases hormones made in hypothalamus.

  • Composed of pituicytes and nerve fibers

  • Hormones:

    • Oxytocin: stimulates uterine contractions during labor, milk ejection; positive feedback loop.

    • Antidiuretic Hormone (ADH/vasopressin): stimulates kidney water reabsorption; inhibited by alcohol; deficiency → diabetes insipidus; excess → SIADH.

    • Hyposecretion → diabetes insipidus (extreme thirst, dilute urine).

    • Hypersecretion → SIADH (fluid retention, low sodium).

  • Action potentials travel down the axons of hypothalamic neurons causing hormone release from their axon terminals in the posterior pituitary 

Anterior Pituitary (adenohypophysis)

  • Controlled by hypothalamic releasing/inhibiting hormones.

  • Composed of glandular tissue (true endocrine gland)

  • Hormones:

    • Growth Hormone (GH): Stimulates growth of bones and muscles. Increases protein synthesis, fat breakdown.

    • Disorders:

      • Excess in children → gigantism.

      • Excess in adults → acromegaly.

      • Deficiency → pituitary dwarfism.Gene


    • Thyroid-Stimulating Hormone (TSH): stimulates thyroid hormone release.

    • Adrenocorticotropic Hormone (ACTH): stimulates adrenal cortex → cortisol.

    • Follicle-Stimulating Hormone (FSH): gamete production (egg/sperm).

    • Luteinizing Hormone (LH): triggers ovulation/testosterone production.

Prolactin (PRL): milk production; excess → inappropriate lactation, infertility