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Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter 18<br />

Pituitary Function<br />

Jan A. Mol<br />

Department <strong>of</strong> <strong>Clinical</strong> Sciences <strong>of</strong> Companion <strong>Animals</strong><br />

Faculty <strong>of</strong> Veterinary Medicine<br />

Utrecht University<br />

Utrecht, The Netherlands<br />

Björn P. Meij<br />

Department <strong>of</strong> <strong>Clinical</strong> Sciences <strong>of</strong> Companion <strong>Animals</strong><br />

Faculty <strong>of</strong> Veterinary Medicine<br />

Utrecht University<br />

Utrecht, The Netherlands<br />

I. HYPOTHALAMUS-PITUITARY SYSTEM<br />

A. Anatomical Considerations<br />

B. Regulation <strong>of</strong> Pituitary Functions<br />

II. ANTERIOR LOBE AND<br />

INTERMEDIATE LOBE<br />

A. Proopiomelanocortin-Derived Peptides<br />

B. Glycoprotein Hormones<br />

C. Somatomammotropic Hormones<br />

III. NEUROHYPOPHYSIS<br />

A. Vasopressin<br />

B. Oxytocin<br />

IV. ASSESSMENT OF PITUITARY FUNCTION<br />

A. Adenohypophysis<br />

B. Neurohypophysis<br />

REFERENCES<br />

I . HYPOTHALAMUS-PITUITARY SYSTEM<br />

The hypothalamic-pituitary system is a preeminent example<br />

<strong>of</strong> the integration <strong>of</strong> neural and endocrine control. It<br />

consists <strong>of</strong> three major systems: (1) a neuroendocrine system<br />

connected to an endocrine system by a portal circulation,<br />

(2) a neurosecretory pathway, and (3) a direct neural<br />

regulation <strong>of</strong> endocrine secretion ( Fig. 18-1 ).<br />

The neuroendocrine system involves clusters <strong>of</strong> peptideand<br />

monoamine-secreting cells in the anterior and midportion<br />

<strong>of</strong> the ventral hypothalamus. Their products reach<br />

the median eminence by axonal transport. From there they<br />

are released into the capillary vessels <strong>of</strong> the hypothalamicpituitary<br />

portal system and transported to the pituitary to<br />

regulate the secretion <strong>of</strong> hormones from the anterior lobe<br />

(AL) <strong>of</strong> the adenohypophysis ( Amar and Weiss, 2003 ).<br />

Hypophysiotropic<br />

hormones<br />

GHRH<br />

TRH<br />

GnRH<br />

CRH<br />

Others<br />

IL<br />

NL<br />

FIGURE 18-1 Schematic representation<br />

<strong>of</strong> the relationship between the<br />

hypothalamus and the pituitary in a<br />

generalized mammal. The hypothalamus<br />

exerts control over the anterior<br />

lobe (AL) by releasing and inhibiting<br />

factors. These hormones reach the<br />

AL cells via capillaries <strong>of</strong> the pituitary<br />

portal system. The neural lobe<br />

(NL) <strong>of</strong> the pituitary is a downward<br />

projection <strong>of</strong> the hypothalamus. The<br />

intermediate lobe (IL) is under direct<br />

neurotransmitter control.<br />

AL<br />

Pituitary hormones<br />

ACTH GH PRL TSH LH FSH α MSH VP OT<br />

<strong>Clinical</strong> <strong>Biochemistry</strong> <strong>of</strong> <strong>Domestic</strong> <strong>Animals</strong>, 6th <strong>Edition</strong> 561<br />

Copyright © 2008, Elsevier Inc.<br />

All rights reserved.

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