The Endocrine System. Endocrine Glands and Hormones.

Hypothalamus

The hypothalamus is a small region of the brain near the pituitary gland that functions as a gland also. Saper and Lowell (2014) of Current Biology say that the hypothalamus is the earliest parts of the brain to form. It is also the smallest, weighing in at about 4 gm of the average 1400 gm of the adult human brain (Saper & Lowell, 2014, p. 1111). Despite its small size, the hypothalamus has several important functions including releasing hormones, regulating body temperature, maintaining biological functions, controlling appetite, managing sexual behavior and controlling emotional responses. According to Han (2018) of Healthline, the hypothalamus is divided into three regions each with its own nuclei, which is a cluster of neurons that perform the vital functions listed above (Han, 2018). Each section of the hypothalamus secretes hormones that have specific functions.

Many of the hormones that the hypothalamus produces function to stimulate the pituitary gland to produce hormones that are involved in the functioning of the body. The nuclei of the anterior or supraoptic region of the hypothalamus secretes a called corticotropin-releasing hormone (CRH). This hormone is secreted when physical and emotional stress trigger it. CRH signals the pituitary gland to secrete adrenocorticotropic hormone (ACTH). ACTH then triggers the production of cortisol, an important stress hormone that is also credited with causing weight gain, sleep disturbances and other stress-related issues. The hypothalamus also secretes thyrotropin-releasing hormone (TRH). TRH stimulates the pituitary gland to produce thyroid-stimulating hormone (TSH). TSH is involved with the functioning of the heart, gastrointestinal tract, and muscles (Han, 2018). Gonadotropin-releasing hormone (GnRH) is another hormone secreted by the supraoptic region of the hypothalamus. GnRH causes the pituitary gland to produce reproductive hormones, such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (Han, 2018). Other hormones associated with this region of the hypothalamus include oxytocin which controls behaviors and emotions such as sexual arousal, trust, recognition, childbirth, lactation and maternal behavior. Vasopressin, or antidiuretic hormone (ADH), regulates hydration levels in the body. It signals the kidneys to absorb water. The supraoptic region of the hypothalamus also releases Somatostatin, or Growth hormone–inhibiting hormone (GHIH), which stops the pituitary gland from releasing certain hormones, including growth hormones and thyroid-stimulating hormones (Han, 2018). The supraoptic region of the hypothalamus also helps to regulate body temperature through sweat and maintains circadian rhythms (Han, 2018).

The middle area of the hypothalamus is known as the tuberal region. The nuclei in this region help to control appetite and are involved in stimulating growth by releasing growth hormone-releasing hormone (GHRH). GHRH stimulates the pituitary gland to produce growth hormone and then GHIH from the supraoptic region of the hypothalamus stops the growth at the appropriate time. The posterior region, or the mammillary region, helps to regulate body temperature by causing shivering and blocking sweat production. While its function is not entirely clear, the mammillary portion of the hypothalamus may also be involved in memory functions (Han, 2018).

Other hormones associated with the hypothalamus include prolactin-releasing hormone (PRH), which stimulates the pituitary gland to begin milk production and prolactin-inhibiting hormone (PIH) or dopamine. PRH causes the pituitary to release prolactin and that stimulates milk production. Dopamine inhibits prolactin, and stops milk production. Prolactin also prepares the body during pregnancy to produce breast milk. Prolactin function also depends upon estrogens, progesterone, and other hormones. Dopamine also prevents milk production in non-pregnant women. Melanocyte-inhibiting hormone (MIH) functions to stimulate the pituitary gland to produce melanin which provides the bodies response to UV light exposure.

Disorders of the hypothalamus can result in appetite, temperature and sleep disorders. Hypothalamic obesity is an example of an appetite disorder caused by a major hypothalamic injury. Comorbidities include diabetes, dyslipidemia, obstructive sleep apnea and mood disorder. Wisse (2019) says that disorders of the gland are often referred to as hypothalamic syndrome. Hypothalamic syndrome can affect physical function in many areas including childbirth, emotions, behavior, memory, growth, production of breast milk, salt and water balance and sex drive (Wisse, 2019). Hypothalamic syndrome is diagnosed through blood and urine tests, hormone injections along with timed blood samples, MRI or CT scans, and possibly a visual field eye exam to see if it is