File Name: structure and function of hypothalamus .zip
The hypothalamus is a small region of the brain. The hypothalamus has three main regions. Each one contains different nuclei.
One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus is located below the thalamus and is part of the limbic system. All vertebrate brains contain a hypothalamus.
The hypothalamus is a small but important area of the brain formed by various nucleus and nervous fibers. Through its neuronal connections, it is involved in many complex functions of the organism such as vegetative system control, homeostasis of the organism, thermoregulation, and also in adjusting the emotional behavior.
It also modulates the endocrine system through its connections with the pituitary gland. Precise anatomical description along with a correct characterization of the component structures is essential for understanding its functions.
Hypothalamus in Health and Diseases. At the end of the fourth week of embryological development, the neural tube is organized in primary vesicles: the forebrain vesicle or prosencephalon, the midbrain vesicle or mesencephalon, and the hindbrain vesicle, also called rhombencephalon. Prosencephalon further divides into two secondary vesicles, the telencephalon that will form the cerebral hemispheres and the diencephalon which gives rise to the diencephalon. Mesencephalon forms the midbrain, structure involved in the processes of vision and hearing.
The hindbrain vesicle or rhombencephalon divides in metencephalon, which further forms the pons and the cerebellum and the myelencephalon that forms the medulla. Since Herrick [ 1 ] first proposed the columnar model of the forebrain organization, the anatomical description was accepted per se and very few research papers have questioned its validity.
The columnar morphologic model is based on the division of the forebrain in functional longitudinal units, placing the telencephalon in the most rostral region and the diencephalon caudally, in between the telencephalon and the midbrain, while the hypothalamus if formed from the ventral most part of the diencephalic vesicle [ 2 ].
In the last decades, mapping of the genes involved in hypothalamic development allowed the identification of a disparity between the morphological, classic boundaries of this region and the molecular ones. This condition puts the diencephalon rostrally between the telencephalon cranially and the midbrain caudally and sets the hypothalamus independent from the diencephalon as a distinct posterior part of the forebrain [ 2 , 3 ].
An important role in hypothalamic development is assigned also to the presence of specific signaling centers Wingless-Int protein family—Wnt, Hedgehogs family—Hh, and Bone morphogenetic family—FgF that modulates cell proliferation and neurulation [ 4 ]. The hypothalamus is a small, central region of the human brain formed by nervous fibers and a conglomerate of nuclear bodies with various functions. The hypothalamus is considered to be a link structure between the nervous and the endocrine system, its main function being to maintain the homeostasis of the body.
The hypothalamus is located under the thalamus from which it is separated by the hypothalamic sulcus of Monro. The sulcus is located at the lateral wall of the third ventricle and extends anteroposteriorly from the interventricular foramen of Monro that assures the communication between the third, diencephalic ventricle and the frontal horn of each lateral ventricle up to the level of Sylvius cerebral aqueduct.
The hypothalamus is limited anteriorly by the lamina terminalis , a gray matter layer of triangular aspect extended above the chiasma optique, in between the two anterior horns of the fornix. Lamina terminalis also forms the anterior wall of the third ventricle and contains the organum vasculosum, a circumventricular structure characterized by the absence of blood—brain barrier and thus highly sensitive to osmotic variations of the blood [ 5 ].
The superior wall of the hypothalamic region participates in the formation of the inferolateral wall of the third ventricle of the brain and has close relations with the white matter structure that surrounds it, called the fornix. Posteriorly, the hypothalamus extends up to the periaqueductal gray substance and the tegmentum of the superior part of the brainstem. The mammillary bodies are small, round white-matter structures that belong to the limbic system.
They are involved in memory due to their connections with the hippocampal region and also in maintaining the sense of direction [ 7 ]. The hypothalamus is limited laterally by the optic tracts in their direction toward the lateral geniculate bodies, an important relay of the optical pathway.
Inside the delimited area on the exterior surface of the brain, a small prominence, called tuber cinereum or infundibulum connects the hypothalamus with the posterior lobe of the underneath pituitary gland.
The pituitary or the hypophyseal gland is located at the base of the brain, in a depression of the sphenoid bone called the sella turcica. The pituitary gland is a three-lobe structure: anterior, posterior and intermediate lobe, with different embryological origin. The anterior gland contains a heterogeneous cellularity that synthesized and secreted hormones in the blood stream: the majority of the cells are somatotrope cells that produced the human growth hormone hGH or somatotropin hormone STH , a peptide that promotes growth in childhood.
The production of the somatotropic hormone is under the control of the hypothalamic growth-releasing hormone GRH produced by the arcuate nucleus. The next hormones produced in high quantity by the anterior gland of the hypophysis are the corticotrope ones adrenocorticotropic hormone—ACTH, melanocyte-stimulating hormone—MSH, and beta-endorphins.
This group of hormones is under the control of the hypothalamic corticotropin-relasing hormones CRHs derived from the paraventricular nuclei.
In smaller percentages, the adenohypophysis has population of cells that produced 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-releasing hormone TRH and inhibited by the dopamine [ 9 ].
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 venous system of the body. It is absent or of small size in adults. 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 presence of uterine contractions.
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 two structures.
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. 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. 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. 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 ]. 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 ]. The hypothalamus is a small region of the brain connected with numerous, various cerebral structures that allows it to intervene in many regulatory processes of the organism.
More, the hypothalamus is involved in the homeostasis of the organism in terms of body temperature, blood pressure, fluid balance, and body weight. The ascending reticular activating system represents a structure composed by neural fibers passing from the reticular formation of the midbrain, through the thalamus, reaching the cerebral cortex [ 15 ].
The system is responsible for concentration, attention, and for maintaining the awakening state. Through it, the reticular formation is connected with the hypothalamic nuclei: the lateral mammillary bodies [ 12 ], the tuberomammillar nuclei, and the periventricular ones.
The periventricular nuclei receive information about the general visceral sensibility [ 16 ] while the two others mediate behavior and are involved in consciousness [ 17 ]. Information from the solitary tract nucleus passing from the reticular substance of the midbrain can also reach the hypothalamus.
The nucleus of the solitary tract is connected with the hypothalamus through either the solitarohypothalamic tract or through colaterales from the solitariothalamic tract. The anterior hypothalamus has connections with the intralaminar nucleus and the nucleus of the median line.
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 ]. Direct connections of amygdala with the hypothalamus are either through the ventral amygdalofugal pathway or through the stria terminalis.
The hippocampus is a curved-shaped cerebral structure located in the temporal lobe. CA1 and CA3 are connected with the infundibular and the ventromedial nuclei of the hypothalamus [ 22 ]. 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 its connections with the supramammillary nuclei of the hypothalamus. 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 accumbens nucleus [ 12 ].
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 suprachiasmatic nuclei. The connections are involved in the circadian rhythm. 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 gyrus, fibers project into the paraventricular and ventromedial nuclei. Axons from the spinal cord can project in the hypothalamic region using the path of the spinohypothalamic tract.
They carry out pain and temperature information. The hypothalamus exerts its effects within two projections: the spinothalamic tract reaching the lateral horn of the spinal cord of T1-L2 segments regulates the sympathetic autonomic response; the mammillotegmental tract and the dorsal longitudinal fasciculus carry out information from the posterior region of the hypothalamus while the anterior one connects with the thalamus mammillothalamic tract and the above fornix.
In case of high body temperature, the hypothalamus responds through thermoregulatory heat loss behavior either sweating or vasodilatation.
Hypothalamus , region of the brain lying below the thalamus and making up the floor of the third cerebral ventricle. The hypothalamus is an integral part of the brain. It is a small cone-shaped structure that projects downward from the brain, ending in the pituitary infundibular stalk, a tubular connection to the pituitary gland. The hypothalamus contains a control centre for many functions of the autonomic nervous system , and it has effects on the endocrine system because of its complex interaction with the pituitary gland. The hypothalamus and pituitary gland are connected by both nervous and chemical pathways. The posterior portion of the hypothalamus, called the median eminence, contains the nerve endings of many neurosecretory cells , which run down through the infundibular stalk into the pituitary gland. Important structures adjacent to the median eminence of the hypothalamus include the mammillary bodies, the third ventricle, and the optic chiasm a part of the visual system.
There is only sparse and ambiguous information about circadian and pulsatile secretion features of the hypothalamus-pituitary-adrenocortical system in depression. We studied 15 severely depressed Hamilton Depression Scale Twenty-four-hour blood sampling from — h with min sampling intervals was performed; from — h, blood was drawn every 10 min. Multivariate analysis of covariance, with the covariate being age, revealed mean h cortisol The frequency of cortisol 2. We conclude that increased hypothalamus-pituitary-adrenocortical activity in depression is related to a greater frequency of episodic hormone release, and we hypothesize that the observed circadian changes might be partly due to altered mineralocorticoid and glucocorticoid receptor capacity and function. In contrast to the huge literature about function tests, only little information about the circadian activity and features of pulsatile secretion of ACTH and cortisol at baseline in depressed patients has been communicated.
The hypothalamus is a small but important area of the brain formed by various nucleus and nervous fibers. Through its neuronal connections, it is involved in many complex functions of the organism such as vegetative system control, homeostasis of the organism, thermoregulation, and also in adjusting the emotional behavior. It also modulates the endocrine system through its connections with the pituitary gland. Precise anatomical description along with a correct characterization of the component structures is essential for understanding its functions. Hypothalamus in Health and Diseases.
Structure and Function. The Hypothalamus. a. Hypothalamic Nuclei and Neurosecretory Cells. The pituitary gland in all groups of vertebrates.
Brain Made Simple. In a continuation of the journey through the human brain , we arrive at the hypothalamus. The hypothalamus is an organ central to many autonomous functions of the human body, the most notable of which is the regulation of homeostasis.
Computer artwork of a person's head showing the left side of the brain with the hypothalamus highlighted. The hypothalamus is located on the undersurface of the brain. It lies just below the thalamus and above the pituitary gland , to which it is attached by a stalk.
The hypothalamus plays a significant role in the endocrine system. Hypothalamic Disease A disease or disorder of the hypothalamus is known as a hypothalamic disease. A physical injury to the head that impacts the hypothalamus is one of the most common causes of hypothalamic disease. Hypothalamic diseases can include appetite and sleep disorders, but because the hypothalamus affects so many different parts of the endocrine system , it can be hard to pinpoint whether the root cause of the disorder is actually related to another gland.
Are you hot right now? Maybe you're like Goldilocks and are just right. What about your height? Are you tall? Maybe your metabolism is lightning fast and you're always hungry, or maybe it's a bit slow and you stay full longer. All of these—regardless of which one you identify with—are regulated by the endocrine system. What is the endocrine system?
structure of the hypothalamus, and outline what we hypothalamus, and the pituitary stalk. (infundibulum) the extensive variations in function. The differences.
Fundamentals of Comparative Vertebrate Endocrinology pp Cite as.Vignette M. 19.12.2020 at 04:36
Brain Structure & Function. ;(1) DOI: /s [.Saymedingtag 20.12.2020 at 17:22
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