Hypothalamus

Hypothalamus

Question 1. Describe the hypothalamus under the following headings:

1. Introduction,
2. Boundaries,
3. Regions/parts and nuclei,
4. Functions and
5. Applied anatomy.
   

Answer.

Hypothalamus  Introduction The hypothalamus is a small part of the diencephalon that lies below the thalamus. It forms the floor and lower part of the lateral walls of 3rd ventricle.

The hypothalamus controls the various autonomic activities of the body. The sympathetic activities are controlled by its posterior part, while parasympathetic activities are controlled by its anterior part. Hence, it is also called the head ganglion of the autonomic nervous system.

Hypothalamus Boundaries The hypothalamus is bounded:

• Anteriorly by the lamina terminalis
• Posteriorly by the subthalamus
• Laterally by the internal capsule
• Medially by the cavity of 3rd ventricle
• Superiorly by the thalamus
• Inferiorly by the structures in the floor of the 3rd ventricle, i.e. tuber cinereum, a stalk of the infundibulum and mammillary bodies (these are parts of the hypothalamus)

Regions/parts and nuclei. The various regions of the hypothalamus and the nuclei present in them are as follows:

• Preoptic region adjoining the lamina terminalis: It contains a preoptic nucleus.
• Supraoptic region (above the optic chiasm). It contains:
  • Supraoptic nucleus
  • Anterior nucleus
  • Paraventricular nucleus
• The tuberal region includes the tuber cinereum, the infundibulum and the area around it. It contains:
  • Arcuate (infundibular) nucleus
  • Ventromedial nucleus
  • Dorsomedial nucleus
• Mammillary region (includes mammillary bodies and the area around it). It contains:
  • Posterior nucleus
  • Mammillary nuclei

Pineal Gland Functions

• Autonomic control: The anterior part controls the parasympathetic nervous system, while the posterior part controls the sympathetic nervous system.
• Endocrine control: By producing and releasing hormones or release-inhibiting hormones, it controls the functions of the endocrine glands of the body.
• Neurosecretion: The oxytocin and antidiuretic hormone (ADH)/vasopressin are synthesized in the supraoptic and paraventricular nuclei, respectively, and are transported to the posterior pituitary via the hypothalamo-hypophyseal tract.
• Regulation of food and water intake: The medial zone is responsible for hunger, thirst and drinking, while the lateral zone acts as a ‘satiety centre’.
• Temperature regulation: The anterior portion prevents the temperature rise, while the posterior portion promotes heat production and conservation.
• Control of sexual behaviour and reproduction: By influencing the secretion of gonadotrophin (Gnrh) by the pituitary gland.
• Control of emotional behaviour like laughing, crying, sweating and flushing.
• Acts as a biological clock, i.e. regulates the cyclic activities of the body (sleep and wake cycle called circadian rhythm).

Pineal Gland Applied Anatomy The impaired secretion of ADH/vasopressin leads to diabetes insipidus characterized by polyuria and polydipsia. The absence of glycosuria differentiates it from diabetes mellitus.