Hypothalamus and Pituitary Notes

Hypothalamus and Pituitary

Introduction to Endocrine Physiology

  • Learning Objectives:

    • Name hormones associated with the posterior pituitary (neurohypophysis).

    • Name an example of an endocrine disorder.

Endocrine Glands

  • The following are examples of endocrine glands in the body:

    • Parathyroid glands

    • Thyroid gland

    • Pineal gland

    • Hypothalamus

    • Pituitary

    • Skin

    • Small intestine

    • Pancreas

    • Adrenal gland

    • Kidney

    • Adipose tissue

    • Liver

    • Stomach wall

    • Ovary

    • Placenta

    • Testes

Pituitary Gland

  • The pituitary gland has 3 lobes:

    • Anterior lobe

    • Posterior lobe

    • Intermediate lobe

  • Hypothalamic-hypophyseal Tract

Neurohypophysis

  • Axons originate in paraventricular and supraoptic nuclei and end in posterior pituitary.

  • Antidiuretic hormone (ADH) and oxytocin are the 2 main hormones released.

  • VP = vasopressin = ADH

Structures of ADH and Oxytocin

  • Antidiuretic Hormone (ADH):

    • Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-GlyNH2

  • Oxytocin:

    • Cys-Tyr-lle-Gln-Asn-Cys-Pro-Leu-GlyNH2

Oxytocin

  • Roles of oxytocin:

    • Milk ejection by contraction of myoepithelial cells of mammary gland

    • Contraction of myometrium of uterus

    • Sperm transport

    • Prolactin synthesis

    • Release of PGF2a from corpus luteum and endometrium

Oxytocin Release

  • Teat stimulation leads to:

    • Activation of nerve pathway

    • Stimulation of supraoptic and paraventricular nuclei of hypothalamus

    • Neurohypophysis releases oxytocin into blood.

    • Contraction of myoepithelial cells (smooth muscle) around alveoli resulting in milk ejection.

Anti-diuretic Hormone

  • Stimuli of ADH release:

    • Decreased blood volume

    • Increased blood osmolality

  • Responses:

    • Increase volume to normal.

    • Decrease osmolality to normal.

    • Retain water.

    • The heart contains volume receptors, and the posterior pituitary releases vasopressin in response to changes in blood volume or osmolality. The kidney is the target organ for vasopressin.

Stimuli of ADH Secretion

  • Changing blood volume

  • Changing osmolality

  • Graph shows ADH secretion increases with decreasing blood volume and increasing osmolality

Diseases

  • Low ADH: diabetes insipidus

    • Large volume tasteless urine.

    • Unable to conserve water when water deprived.

  • High ADH: idiopathic ADH syndrome

    • Retain fluid, hyponatremic, hypoosmolal.

    • Rare

Diabetes Insipidus

  • Central diabetes insipidus:

    • No secretion of ADH from hypothalamus

  • Nephrogenic diabetes insipidus:

    • ADH secreted from hypothalamus, but kidney fails to respond (usually due to lack of receptors)

Stimuli of ADH Secretion

  • ADH secretion increased by:

    • Barbiturates

    • Ether

    • Chloroform

    • Morphine

    • Acetylcholine

    • Nicotine

    • Pain

Inhibition of ADH Secretion

  • ADH secretion inhibited by:

    • Alcohol