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Harry E. SAROINSONG

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Neuroendocrinology is the study of the

interactions between the nervous system and

the endocrine system. The concept arose from

the recognition that the secretion of hormones

from the pituitary gland was closely controlledby the brain especially by the hypothalamus.

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Hypothalamus and Pituitary

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Hypothalamus and Pituitary Gland

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Hypothalamus and Pituitary

The hypothalamus-pituitary unit is the mostdominant portion of the entire endocrine system.

The output of the hypothalamus-pituitary unit

regulates the function ofthe thyroid, adrenal andreproductive glands and also controls somaticgrowth, lactation, milk secretion and watermetabolism.

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Pituitary function depends on thehypothalamus and the anatomicalorganization of the hypothalamus-pituitaryunit reflects this relationship.

The pituitary gland lies in a pocket of boneat the base of the brain, just below thehypothalamus to which it is connected bya stalk containing nerve fibers and bloodvessels.

The pituitary is composed to two lobes--anterior and posterior

Hypothalamus and Pituitary

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Posterior Pituitary:

neurohypophysis

Posterior pituitary: an outgrowth of thehypothalamus composed of neural tissue.

Hypothalamic neurons pass through the

neural stalk traverse the median eminenceand reach the posterior pituitary.

The upper portion of the neural stalkextends into the hypothalamus and is

called the median eminence.

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Hypothalamus and

posterior pituitary

Midsagital view illustratesthat magnocellular neuronsfrom paraventricular and

supraoptic nuclei secreteoxytocin and vasopressindirectly into capillaries in theposterior lobe

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Synthesis, storageand release ofposterior pituitary

hormone

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Anterior pituitary: adenohypophysis

Anterior pituitary: connected to thehypothalamus by the superiorhypophyseal artery.

The anterior pituitary is an amalgam ofhormone producing glandular cells.

The anterior pituitary produces six peptidehormones: prolactin, growth hormone

(GH), thyroid stimulating hormone(TSH), adrenocorticotropic hormone(ACTH), follicle-stimulating hormone(FSH), and luteinizing hormone (LH).

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Hypothalamus andanterior pituitary

Midsagital viewillustrates parvicellularneurosecretory cellssecrete releasing factorsinto capillaries of the

pituitary portal system atthe median eminencewhich are thentransported to theanterior pituitary glandto regulate the secretion

of pituitary hormones.

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Hypothalamic andpituitary hormones

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Hypothalamic releasing factors foranterior pituitary hormones

Travel to adenohypophysis viahypophyseal-portal circulation

Travel to specific cells in anterior pituitaryto stimulate synthesis and secretion oftrophic hormones

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Hypothalamic releasing hormones

Hypothalamic releasinghormone

Effect on pituitary

Corticotropin releasinghormone (CRH)

Stimulates ACTHsecretion

Thyrotropin releasing

hormone (TRH)

Stimulates TSH and

Prolactin secretionGrowth hormone releasinghormone (GHRH)

Stimulates GH secretion

Somatostatin Inhibits GH (and otherhormone) secretion

Gonadotropin releasinghormone (GnRH) a.k.aLHRH

Stimulates LH and FSHsecretion

Prolactin releasing hormone(PRH)

Stimulates PRL secretion

Prolactin inhibiting hormone(dopamine)

Inhibits PRL secretion

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Hypothalamus-Pituitary Axis

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Axis

Anterior Pituitary

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The HPA Axis Structure

The way physiologists see the

HPA axis

Adopted from the Williams

Textbook of Endocrinology, 10th

edition, p. 113.

Ed. by Larsen P., Kronenberg

H., Melmed S., and Polonsky K.

ISBN 0-7216-9184-6

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Hypothalamus/Pituitary

Axis

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Feedback regulation of

hypothalmus/pituitary

A prominent feature of each of the hormonalsequences initiated by the hypothalamic

releasing hormones is negative feedbackexerted upon the hypothalamic-pituitarysystem by the hormones whose productionare stimulated in the sequence.

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N ti F db k C t l

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Negative Feedback Controls:Long & Short Loop Reflexes

Figure 7-14: Negativefeedback loops in the

hypothalamicanteriorpituitary pathway

Negati e Feedback Controls

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Negative Feedback Controls :Long & Short Loop Reflexes

Figure 7 15: Control pathway for cortisol secretion