Date: 22. November 2017
Introduction to Hypothalamus
In this lecture educator explains the Hypothalamus starting with the introduction of Hypothalamus in the first section of the lecture. The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis).
Location and Structure: It is a part of Diencephalon, it Extend from Optic Chiasm to caudal border of Mammillary Bodies, it is superiorly Thalamus. Forms floor and inferior part of lateral walls of third ventricle. Pre-optic area is also included in Hypothalamus. Caudally it merges with tegmentum of Midbrain. Lateral boundary is formed by Internal Capsule.
The hypothalamus is responsible for the regulation of certain metabolic processes and other activities of the autonomic nervous system. It synthesizes and secretes certain neurohormones, called releasing hormones or hypothalamic hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones.
Nuclei of Hypothalamus
Hypothalamus is composed of small nerve cells, arranged in groups or nuclei. The Nuclei are divided by imaginary parasagittal plane into medial and lateral zones. Lying within planes are columns of fornix and mammilothalamic tract, which serves as markers.
Medial Zone: The following Hypothalamic Nuclei are recognized from anterior to posterior: Preoptic Nucleus (Regulates the release of gonadotropic hormones, Contains the sexually dimorphic nucleus, which releases GnRH, Thermoregulation). Anterior Nuclear Thermoregulation (Panting Sweating thyrotropin inhibition). Suprachiasmatic Nucleus (Circadian rhythms). Paraventricular Nucleus (Thyrotropin-releasing hormone release, corticotropin-releasing hormone release oxytocin release vasopressin release somatostatin release). Dorsomedial Nucleus (Blood Pressure Heart Rate GI stimulation). Ventromedial Nucleus (Satiety neuroendocrine control). Infundibular or Arcuate Nucleus (Growth hormone-releasing hormone (GHRH) Feeding Dopamine-mediated prolactin inhibition).
Lateral Zone: Following hypothalamic nuclei are recognized from anterior to posterior, as follows: Preoptic Nucleus (Regulates the release of gonadotropic hormones, contains the sexually dimorphic nucleus, which releases GnRH, Thermoregulation), Suprachiasmatic Nucleus, Supraoptic Nucleus (Vasopressin release Oxytocin release), Lateral Nucleus (Primary source of orexin neurons that project throughout the brain and spinal cord), Tuberomammilary Nucleus (Memory) and Lateral Tuberal Nuclei.
Hypothalamic Lines of Communications
In the third section of this lecture educator explains the Hypothalamic Lines of Communication. The hypothalamus receives information from the rest of the body through (1) nervous connections, (2) the bloodstream, and (3) cerebrospinal fluid. The neurons of the hypothalamic nuclei respond and exert their control via the same routes. Nervous Connections of Hypothalamus lies in the centre of Limbic system, It r eceive afferents from Viscera, Olfactory mucous membrane, Cerebral cortex and Limbic system- It sends efferent fibers to Limbic system, Reticular formation of midbrain and Thalamus craniosacral and thoracolumbar outflow. Later on, in this section educator explained the Afferent Nervous Connections and Efferent Nervous Connections with their Pathway origin and insertion in table.
Functions of Hypothalamus
Autonomic Control preserve body homeostasis. Anterior hypothalamic area and preoptic area influence the parasympathetic responses, lowering blood pressure, lowering heart rate, Contraction of bladder, and Increase motility of GI tract, salivation and pupillary constriction. Posterior and lateral nuclei cause sympathetic responses, Elevation of BP, Acceleration of heart rate, Cessation of peristalsis in GI tract and Pupillary dilation and hyperglycemia.
Effect of Hypothalamic Releasing and Inhibitory Hormones on Pituitary Explained well
Hypothalamus Functions: The hormones from the hypothalamus govern physiologic functions such as temperature regulation, thirst, hunger, sleep, mood, sex drive, and the release of other hormones within the body. This area of the brain houses the pituitary gland and other glands in the body.
Regulation of Temperature, Food, and Water Intake is undertaken by Anterior portion of hypothalamus. It causes dilation of blood vessels, sweating, heat loss. Stimulation of posterior portion of hypothalamus – Vasoconstriction – inhibit sweating, (shivering start) – Heat production, Normal temperature 37 Degree. Lateral Region – Hunger Center – Thirst Center - Increase Hunger/ Thirst – increase food/ water intake. Destruction cause Anorexia (body weight loss), Medial Region –Satiety Center – inhibits eating – reduce food intake.
General Considerations: Activities are modified by information received by different parts of CNS and by plasma levels of circulating hormones. Hypothalamus Influences body by ANS and Endocrine System. It is the chief centre of brain for maintaining internal milieu of body. Hypothalamus may be site of inflammation, neoplasm or vascular disorder. Because of its deep seated central position. Compressed by surrounding tissue tumors, Or by development of internal hydrocephalus. Lesion of hypothalamus may cause different syndromes. Acute lesion is more likely to produce sign and symptoms than in a slow growing tumor.
Obesity and Wasting: Hypothalamic lesion causes severe obesity associated with Genital hypoplasia or atrophy, Wasting is less common than obesity, Severe Cachexia is suggestive of damage of hypophysis (Pituitary gland).
Hyperthermia Hypothermia: Hyperthermia occur because of head injury following surgical operations in the region of hypothalamus. Patient is normal, no signs of malaise, which occur with pyrexia secondary to infections.