How does the thalamus bring bout this control?
The hypothalamic nuclei synthesize releasing factors or hormones, which are transported and stored in the median eminence or posterior pituitary via neuronal axons and are released in response to stimulating signals from the brain and brainstem. The releasing factors are carried to the anterior pituitary to regulate the secretion of adenohypophyseal hormones and thus enter the hypothalamo-pituitary portal circulation. In the pituitary gland, these hormones bind to specific receptors on the surface of the pituitary cells for activating them. Based on the activation, the gland either starts or stops the secretion of the concerned hormone into the bloodstream.
The following are the major hormones secreted by the hypothalamus:
o Thyrotropin-releasing hormone
o (Prolactin-releasing hormone)
o Corticotropin-releasing hormone
o (Prolactin-inhibiting hormone)
o Growth-hormone-releasing hormone
o Gonadotropin-releasing hormone
o (growth-hormone inhibiting hormone)
Hypothalamus is stimulated by the below-mentioned conditions, which are connected to a specific function:
• Length of the day, duration, and intensity of light controls the regulation of circadian and seasonal rhythms
• Olfactory stimuli like pheromones have roles in the behavioral, sexual and attachment patterns
• Steroids, including gonadal steroids and corticosteroids, which takes care of the features associated with growth, development, and reproduction
• Information transmitted through the neural network from organs like the heart, stomach and reproductive system.
• Autonomic inputs, associated with the functioning of the autonomous nervous system
• Other stimuli originating from blood such as insulin, pituitary hormones, cytokines, angiotensin, leptin, ghrelin, levels of glucose, osmolarity etc. Change in glucose levels sends appropriate signals related to appetite in the hypothalamus.
• Stress and psychological pressure
• Pyrogenetic response caused by the invasion of foreign agents such as microorganisms, antigens, allergens etc