3.6.1 The neuroendocrine system
The Neuroendocrine System
The basic definition of the neuroendocrine system is a coordinated group of cells with a neural determination that secrete hormones or neuropeptides. To ensure an effective response to physical and psychological stimuli, including infections, the hypothalamic-pituitary-adrenal (HPA) axis is regarded as the primary neuroendocrine system (Toni, 2004).
Pituitary Gland
The pituitary gland, a pea-sized organ, is known as the master gland of the body. The pituitary gland is located in two lobes anterior and posterior lobes. It is situated beneath the hypothalamus at the base of the brain. The pituitary gland is a major component of the endocrine system and is in charge of producing a wide range of crucial hormones. Additionally, the pituitary gland directs the release of hormones from other endocrine system glands. As a result, it regulates essential processes in the brain, skin, and reproductive system, and the pituitary gland is connected to the hypothalamus through a stalk of nerves and blood vessels. This stalk is known as the pituitary stalk.
Hypothalamus instructs the pituitary gland to release particular hormones. The function of the hypothalamus is for controlling processes including heart rate, blood pressure, digestion and body temperature.
Hypothalamic Regulation of the Pituitary Secretions
Most of the pituitary’s release is regulated by a hormonal or neurological signal received from the hypothalamus. Hypothalamus receive a signal from different parts of the body in the nervous system. Nerve impulses that start in the hypothalamus and end in the posterior pituitary regulate the secretion of hormones from this gland. Contrarily, hormones known as hypothalamic releasing and hypothalamic inhibitory hormones (or factors) are secreted within the hypothalamus itself and then transported to the anterior pituitary through tiny blood vessels known as hypothalamic-hypophysial porta vessels. These hormones regulate anterior pituitary secretion. These releasing and inhibitory hormones work on the glandular cells in the anterior pituitary to regulate their release.
Anterior pituitary release:
- Thyrotropin-releasing hormone (TRH), induces the secretion of thyroid-stimulating hormone.
- Corticotrophin-releasing hormone (CRH), activates the release of adrenocorticotropic.
- Prolactin inhibitory hormone (PIH), stimulates the inhibition of prolactin release (Jakoi, 2004).
Feedback control:
An illustration of negative feedback is when the body starts to heat up and a reaction counteracts and stops the increase in body temperature. A good example of unfavourable feedback is sweating.
The Function of the Posterior Pituitary Gland
The posterior pituitary is primarily responsible for producing and releasing two hormones oxytocin and antidiuretic (ADH, or vasopressin) hormones.
ADH is crucial for keeping the body’s electrolyte and fluid balance. The brain contains specific osmoreceptors that help to maintain water balance.
Oxytocin plays a vital role in childbirth since it stimulates the contraction of the smooth muscles of the uterus. Oxytocin also causes the smooth muscle of the breast to contract, causing the milk to let down during breastfeeding (Brown, 2011).
References:
(1) Toni, R. (2004). The neuroendocrine system: organization and homeostatic role. Journal of endocrinological investigation, 27(6 Suppl), 35-47.
(2) Jakoi, E. R. (2004). Hypothalamus and pituitary gland.
(3) Brown, C. H. (2011). Magnocellular neurons and posterior pituitary function. Comprehensive physiology, 6(4), 1701-1741.