Human Anatomy, Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2002

Special Part
Endocrine glands (ductless glands), glandulae endocrinae (glandulae sine ductibus)
Central Regulatory Organs — Hypothalamus

The Hypothalamus (hypothalamus) is a central neuroendocrine organ that transforms nerve impulses into humoral signals, uniting The Nervous system and Endocrine glands into a single neuroendocrine regulatory system (Fig. 343).

The hypothalamus incorporates the following structures of the Diencephalon: the tuber cinereum, infundibulum, neurohypophysis, median eminence (eminentia medialis), lamina terminalis, optic chiasm (chiasma opticum), and mammillary bodies (corpora mаmillаrіа).

The hypothalamus is not only the principal center for regulating vital endocrine Functions; it also controls and integrates all visceral Functions of the Organism by housing higher autonomic centers. Consequently, the hypothalamus bridges endocrine regulatory mechanisms with neural ones.

Within the Gray matter of the hypothalamus, 32 pairs of nuclei are distinguished, some of which consist of neurosecretory Neurons (neuronum secretorium) that produce neurohormones.

The anterior region contains the supraoptic nuclei (nuclei supraoptici) and paraventricular nuclei (nuclei paraventriculares). Large neurosecretory Cells of the supraoptic Nucleus primarily produce a neurohormone known as antidiuretic hormone (ADH), or vasopressin, which stimulates Water reabsorption from the renal collecting ducts and affects smooth myocytes in the vascular wall, leading to an increase in Blood pressure. Similarly, neurons of the paraventricular nucleus predominantly produce the hormone oxytocin, which induces the contraction of uterine smooth myocytes.

The small neurosecretory cells of the hypothalamus secrete 10 adenohypophysiotropic neurohormones, through which the hypothalamus exerts control over the hormone-producing activity of the adenohypophysis. Adenohypophysiotropic Hormones are divided into two groups: liberins and statins.

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Fig. 343. Diagram of the reciprocal interactions within the hypothalamo-hypophysial system (according to B. V. Aleshin):

1 - optic chiasm; 2 - median eminence; 3 - cavity of the Third ventricle; 4-7 - projection of hypothalamic nuclei onto the wall of the third ventricle (4 - supraoptic nucleus; 5 - anterior hypothalamic nucleus; 6 - paraventricular nucleus; 7 - arcuatoventromedial complex of the mediobasal hypothalamus); 8 - neurosecretory peptidergic-adrenergic cells; 9 - adrenergic neurons of the mediobasal hypothalamus; 10 - thalamus; 11 - infundibular recess; 12 - posterior lobe of the hypophysis; 13 - Herring bodies; 14 - intermediate lobe of the hypophysis; 15 - anterior lobe of the hypophysis; 16 - portal vein; 17 - pars tuberalis of the adenohypophysis;

Arrows indicate the direction of hormones and their action on target Organs

Liberins act directly on the endocrinocytes of the anterior lobe of the hypophysis, stimulating their hormone secretion; they are also collectively referred to as releasing hormones (from the English "release").

Hypothalamic releasing hormones reach the adenohypophysis via the portal blood vessel system, prompting its endocrinocytes to synthesize and release hypophysial hormones. By acting on the anterior lobe of the hypophysis (adenohypophysis), they stimulate the release of specific tropic hormones, for example: somatoliberin stimulates the secretion of Growth Hormone (somatotropin); thyroliberin stimulates the secretion of thyroid-stimulating hormone; corticoliberin stimulates the secretion of adrenocorticotropic hormone; folliberin stimulates the secretion of follicle-stimulating hormone; luliberin stimulates the secretion of luteinizing hormone (testosterone); prolactoliberin stimulates the secretion of prolactin (lactotropin).

Statins, conversely, suppress the function of endocrinocytes in the anterior lobe of the adenohypophysis by inhibiting the release of its tropic hormones.

The production of liberins and statins is carried out primarily by small neurosecretory cells in the arcuate nucleus (nuсl. arcuatus / infundibularis) and the ventromedial nucleus (nuсl. ventromedialis) of the hypothalamus.

The neurosecretory activity of the thalamus is modulated by higher centers of the Brain (the limbic system, Pineal Gland, hippocampus, and mamillary nuclei). For the General structural layout of the hypothalamus, its connections with the hypophysis, and other PARTS OF THE CNS, see Fig. 343.