**3. Structure of the hypothalamus**

The hypothalamus is divided by the anterior horns of the fornix in a lateral, medial, and periventricular (median) region and by a coronal plane passing through the infundibulum in an anterior and posterior region. The anterior region is also referred to as the prechiasmatic region, due to its location above the chiasma optic, while the posterior region is called the mammillary region. The infundibular region is situated between the previous two regions.

thyrotropes, gonadotropes, and lactotropes. Thyrotropes respond to signals from the hypothalamic thyrotropin-releasing hormone (TRH) produced in the paraventricular nuclei and further synthesize the hormone responsible for thyroid hormones production—thyroid stimulating hormone (TSH). Luteinizing hormones (LHs) and follicle stimulating hormones (FSHs) are secreted by gonadotrope cells of the gland under the influence of pulsatile secretion of gonadotropin-releasing hormone (GRH) produced in hypothalamus preoptic area. The secretion of prolactine (PRL) from the lactotropes is stimulated by hypothalamic thyrotropin-

Hypothalamic hormones reach the adenohypophysis through a vascular system. Hypothalamus exerts its effects over the anterior part of the gland through the hypothalamo-hypophyseal portal system, a special vascular system formed by fenestrated capillaries. The proximal vascular structure of the portal system is the anterior hypophyseal artery, branch from the ophthalmic segment of the internal carotid artery [9]. Through it, hypothalamic hormones are transported to the primary plexus, located near the infundibulum of the hypothalamus. From this region, hormones are drained into the second vascular venous plexus of the hypothalamo-hypophyseal portal system that surrounds the adenohypophysis [9]. This vascular system allows hormones to diffuse through the wall, inside of the gland. The hypophyseal vein further drains the blood into the venous sinuses of the dura mater and from here in the

The posterior wall of Rathke's pouch forms the intermediate lobe of the gland [8]. It is absent or of small size in adults. In children, it is the part of the gland responsible for skin pigmentation through the secretion of the melanocyte stimulating hormone (MSH) or "intermedins" [9]. Pars intermedia also produces corticotrophin-like intermediate lobe peptide (CLIP) and adrenocor-

The posterior lobe of the gland, pars distalis or neurohypophysis derives from the neuroectoderm [9]. It is an inferior extension of the hypothalamus and is mainly from its neural fibers. The connection between the hypothalamus and the posterior lobe of the gland forms the infundibular stalk. Through this complex, hormones synthetized in the hypothalamus nuclei are transported and deposited in the posterior gland where they are stored in presynaptic vesicles and then released into the blood stream. The supraoptic nuclei of the hypothalamus are responsible for the secretion of antiduretic hormone (ADH) or vasopressin, the hormone involved in maintaining the water balance in organism and thus in preventing dehydration. The paraventricular nuclei produce oxytocin, a hormone released during labor, in the pres-

The hypothalamus intervenes along with the pituitary gland the majority of the endocrine and metabolic functions of the body through a double-sense transport of hormones between

The hypothalamus is divided by the anterior horns of the fornix in a lateral, medial, and periventricular (median) region and by a coronal plane passing through the infundibulum in

releasing hormone (TRH) and inhibited by the dopamine [9].

venous system of the body.

6 Hypothalamus in Health and Diseases

ticotrophic hormone (ACTH) [9].

ence of uterine contractions.

**3. Structure of the hypothalamus**

the two structures.

From a structural point of view, the hypothalamus is formed by gray matter conglomeration of neurons that organize in nuclei and also by white-matter substance formed by myelinated nervous fibers.

The anterior region of the hypothalamus is located above the optic chiasm and is referred to as the supraoptic area. It contains the following nucleus: supraoptic, preoptic and medial preoptic, the suprachiasmatic and the anterior hypothalamic nucleus, alongside with the paraventricular one (**Figure 2**). The supraoptic nucleus produces vasopressin or the antidiuretic hormone (ADH) that is stored in the posterior lobe of the pituitary gland and is responsible for blood pressure control and water balance of the organism. The preoptic region alongside with the anterior hypothalamic nucleus is involved in cooling (thermoregulation) of the body through the sweating process. The preoptic nucleus is also involved in the habit of eating and in reproduction while the medial preoptic region is involved in cardiovascular control as a response to stress [10]. The suprachiasmatic nucleus is situated above the optic chiasm and is involved in the circadian rhythm. The paraventricular nucleus (named after its location near the third diencephalic ventricle) represents an important autonomic center of the brain involved in stress and metabolism control [11].

The central part as the hypothalamus is located above tuber cinereum and is named the tuberal area. It is composed of two parts, anterior and lateral, and contains the following nucleus: dorsomedial, ventromedial, paraventricular, supraoptic, and arcuate (**Figure 2**). The ventromedial area is involved in controlling the habits of eating and the feeling of satiety [12]. The arcuate or infundibular nucleus is responsible for orexigenic peptides secretion: ghrelin, orexin, or neuropeptide Y [11].

**Figure 2.** Schematic representation of hypothalamic nuclei (sagittal section).

The posterior region is formed by a medial and, respectively, lateral area. The medial region contains the mammillary nucleus alongside with the posterior hypothalamic nucleus, the supramammillary and the tuberomammillary ones. The nucleus of the lateral region contains the hypocretins (orexin) peptides that control feeding behavior, thermoregulation, gastrointestinal motility [13], and cardiovascular regulation and are also involved in sleep regulation [14]. Lesions of the lateral region lead to the refusal to feed or aphagia. The posterior part of the hypothalamus is involved overall in energy balance, blood pressure, memory, and learning. The posterior hypothalamic nucleus has a major role in controlling the body temperature [12]. The tuberomammillar nucleus is involved in memory due to their connection with the hippocampus and Papez memory circuit [9].

**4.3. The amygdala**

terminalis.

**4.4. The hippocampal region**

nuclei of the hypothalamus [22].

**4.5. The olfactory bulb**

accumbens nucleus [12].

**4.6. The retina**

**4.7. Cerebral cortex**

The amygdala represents a conglomerate of perykarions located in the temporal lobe. Efferent fibers from this region project directly to hypothalamus or neural fibers can detach from the amygdala-thalamic fascicle and reach the anterior hypothalamus [12]. It is involved in body's response to fear and rewards but also in memory [21]. Direct connections of amygdala with the hypothalamus are either through the ventral amygdalofugal pathway or through the stria

Anatomy and Function of the Hypothalamus http://dx.doi.org/10.5772/intechopen.80728 9

The hippocampus is a curved-shaped cerebral structure located in the temporal lobe. It is formed by the dentate gyrus and different regions called Cornus Ammonis (CA): CA1, CA2, CA3, and CA4 [22]. CA1 and CA3 are connected with the infundibular and the ventromedial

According to a recent study [23] CA2 area lighted that also CA2 area, a small region in the hippocampus composed from pyramidal neurons, is involved in memory and learning through

Fibers from the olfactory bulb reach the periamigdalian region (the entorhinal and periamygdaloid cortex) and then the lateral hypothalamus through either the amigdalian or the

Visual information from the retinal neuroepithelium through the lateral geniculate body of the mesencephalon and then the superior colliculus reach the suprachiasmatic and supraoptic nuclei of the hypothalamus and are involved in circadian rhythm [12]. The hypothalamus can receive direct fibers from the retina through a retinohypothalamic tract that reach the

There is a double sense connection between the cerebral cortex and the hypothalamus. The hypothalamus projects on the surface of the cortex diffuse, in a poorly defined area over the cortex and transmits information that maintain the cortical tonus while from the gray matter of the cerebral cortex, neural fibers projects over the hypothalamus and triggers visceral response according to the affective state (sweating in case of fear, intestinal manifestations in case of stress). Neural fibers from the lateral hypothalamus project in the prefrontal cortex while the frontal lobe also has efferent for all the hypothalamic regions [24]. Through these connections, the autonomic control is assured in the organism. More, from the paraorbital

suprachiasmatic nuclei. The connections are involved in the circadian rhythm.

gyrus, fibers project into the paraventricular and ventromedial nuclei.

its connections with the supramammillary nuclei of the hypothalamus.
