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Endocrine 1

Hormones

Definition

  • Chemical messengers secreted by endocrine glands and transported in the blood.

  • Control metabolism, growth, and reproduction.

Major Endocrine Organs

  • Hypothalamus

  • Pituitary Gland

  • Parathyroid

  • Thyroid

  • Adrenals

  • Ovaries

  • Testes

  • Pancreas

Types of Hormones

  • Most are amino acids (proteins), except for sex & adrenal hormones which are steroids synthesized from cholesterol.

  • Act on specific receptors in tissue.

Pituitary Gland (Hypophysis)

  • Size: About the size of a pea.

  • Known as the "Master Gland" for its role in controlling other glands.

  • Secretes 9 hormones (probably more).

Structure

  • Comprised of 2 lobes connected to the hypothalamus via the infundibulum (stalk).

  • Posterior Pituitary (Neurohypophysis):

    • Stores neurohormones made in the hypothalamus.

    • Contains neural tissue.

  • Anterior Pituitary (Adenohypophysis):

    • Glandular tissue that manufactures & releases many hormones.

Control of Secretion

  • Negative Feedback: Inhibits hormone release when the desired effect occurs.

  • Positive Feedback: Stimulates hormone release when the desired effect occurs.

  • Signals sent via:

    • Blood (Humoral)

    • Nerve impulse (Neural)

    • Hormonal (from target endocrine glands)

Hormonal Properties

  • Half-Life (t1/2): Specific effectiveness period before deactivation.

  • Duration of Action: Ranges from seconds to hours.

  • Synergy: Combined effects of hormones greater than individual effects.

  • Antagonism: One hormone opposes the effect of another.

Control of Pituitary Hormone Release (Hypothalamic-Pituitary Axis)

  • Hypothalamus regulates pituitary function for homeostasis.

  • Links:

    • Posterior Pituitary: Linked via nerves.

    • Anterior Pituitary: Linked via blood vessels (hypothalamo-hypophyseal portal system).

Anterior Pituitary Hormones

  • All proteins:

    • Growth Hormone (GH)

    • Thyroid Stimulating Hormone (TSH)

    • Adrenocorticotropic Hormone (ACTH)

    • Follicle Stimulating Hormone (FSH)

    • Luteinizing Hormone (LH)

    • Prolactin (PRL)

Growth Hormone (GH)

  • Stimulates cell growth and muscle mass.

  • Metabolic effects: Mobilizes fat for fuel and promotes growth.

  • Regulation:

    • Growth Hormone Releasing Hormone (GHRH)

    • Growth Hormone Inhibiting Hormone (GHIH)

Posterior Pituitary Hormones

  • Directly linked to the hypothalamus.

  • Key Hormones:

    • Oxytocin

    • Antidiuretic Hormone (ADH)

Oxytocin

  • Stimulates contractions during childbirth (positive feedback).

  • Triggers milk release with suckling.

Antidiuretic Hormone (ADH)

  • Inhibits urine production, promotes water reabsorption.

  • Stimuli for release: Pain, low blood pressure.

  • Inhibitors: Alcohol, diuretic drugs.

  • Consequences of Deficiency: Diabetes insipidus (not related to glucose).