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).