89. Pituitary gland – functional morphology. Hormones of the posterior pituitary gland – physiologic effects, control of secretion. PDF

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Theoretical Exam Essay 89. Pituitary gland – functional morphology. Hormones of the posterior pituitary gland – physiologic effects, control of secretion....

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Physiology theoretical exam!

ENDOCRINE SYSTEM

89. Pituitary gland – functional morphology. Hormones of the posterior pituitary gland – physiologic effects, control of secretion. - The hypothalamus is part of the brain, the pituitary gland is an endocrine gland! - The hypothalamus links the nervous system to the endocrine system via the pituitary gland!

- The hypothalamus and pituitary gland are connected via a think stalk (infundibulum)!

- If the pituitary stalk is cut above the pituitary gland but the entire hypothalamus is left intact, the posterior pituitary hormones continue to be secreted normally!

- The pituitary gland consists of 2 lobes: anterior & posterior! - Anterior pituitary:! - Also known as adenohypophysis! - Communicates with the hypothalamus through blood vessels → hypophyseal portal system

- Several neurohormones produced by the hypothalamus are secreted into the portal system to reach the anterior pituitary !

- Posterior pituitary:! - Also known as neurohypophysis! - Communicates with the hypothalamus through a bundle of nerve fibers!

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Physiology theoretical exam!

ENDOCRINE SYSTEM

Posterior pituitary = Neurohypophysis

Hormones of the posterior pituitary Hormones are produced in the hypothalamus and stored in the posterior pituitary! 2 hormones are stored in the posterior pituitary:! 1. Oxytocin # ➝ uterine contractions during labor! 2. Antidiuretic Hormone (ADH)# ➝ produced in response to low levels of water in the blood (low blood pressure)) ➝ triggers nephron to reabsorb water!

Oxytocin • Oxytocin neurons have their cell bodies in the paraventricular nuclei of the hypothalamus • Actions of oxytocin:! • Milk ejection ➝ oxytocin causes contraction of the myoepithelial cells lining the ducts of the mammary gland ➝ milk flows out of the nipple! • Uterine contractions (powerful rhythmic contractions of uterine smooth muscle) • Sexual behaviour ➝ may have a role in the maintenance of relationships • Control of secretion: • Suckling of the breast → stimulates oxytocin release! • Sight, sound or smell of the infant → stimulate oxytocin release! • Dilation of the cervix during labor and orgasm → stimulate oxytocin release! • Opioids (endorphins) → inhibit oxytocin release!

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Physiology theoretical exam!

ENDOCRINE SYSTEM

Antidiuretic Hormone (ADH) / Vasopressin • ADH neurons have their cell bodies in the supraoptic nuclei of the hypothalamus • Actions of ADH:! • Increase in water permeability ➝ increased water permeability allows water to be reabsorbed by the collecting ducts of the nephron ➝ makes the urine concentrated! • Contraction of vascular smooth muscle • Control of secretion: • Increased plasma osmolarity → stimulate ADH release! Someone doesn’t have access to water → serum osmolarity will increase → osmoreceptors in hypothalamus detect increase → action potentials initiated by cell bodies of ADH neurons → ADH secreted from nerve terminals in posterior pituitary !

• Decreased plasma osmolarity → inhibit ADH release! • Decreased ECF (extracellular) volume → stimulate ADH release! Decreased ECF volume of 10% or more → decreased arterial blood pressure → detected by baroreceptors in left atrium, carotid artery & aortic arch → info send to hypothalamus → hypothalamus directs increase of ADH secretion → ADH stimulates water reabsorption in collecting ducts kidney!

• Pain, nausea, hypoglycaemia, drugs (nicotine, opiates) → stimulate ADH release!

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