Posterior Pituitary Hormones
What Are They, Their Function, and More
Editors:Alyssa Haag,Ahaana Singh,Ian Mannarino, MD, MBA
Copyeditor:David G. Walker
What are posterior pituitary hormones?
Posterior pituitary hormones are released from the posterior lobe of the pituitary gland found at the base of the brain and include two hormones: vasopressin (i.e., antidiuretic hormone) and oxytocin. The pituitary gland is a pea-sized organ that is referred to as the master gland of the body as it secretes hormones that direct other glands and organs to release hormones throughout the body. Therefore, it controls vital functions of the skin, brain, reproductive organs, and vision.The pituitary gland is divided into two lobes, the anterior and the posterior lobe. The anterior pituitary makes up 80% of the pituitary gland and regulates growth, metabolism, and reproduction through the production of various hormones, including human growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ATCH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. The pituitary gland is connected to the hypothalamus via a stalk of blood vessels and nerves. The hypothalamus is a part of the brain that plays a vital role in connecting the endocrine system and nervous system by communicating with the pituitary gland in order to produce and secrete specific hormones for specific bodily functions. It communicates with the anterior pituitary by releasing hormones, whereas it communicates with the posterior pituitary using nerve impulses. This intimate connection is known as the hypothalamic-pituitary axis. Ultimately, the hypothalamus controls several bodily functions, including body temperature, thirst, appetite and weight control, sleep cycles, blood pressure and heart rate, and emotions.
How many hormones are produced by the posterior pituitary gland?
What hormones are produced by the posterior pituitary gland?
The hormones produced by the posterior pituitary gland include vasopressin and oxytocin. Vasopressin is also referred to as antidiuretic hormone (ADH) and acts on the kidney to conserve water. It is also important for maintaining fluid and electrolyte balance in the body. There are specialized osmoreceptors in the hypothalamus that assist with water homeostasis. Osmoreceptors are nerve cells that have the inherent ability to detect the amount of solute, such as sodium or potassium, in the blood. When the body loses water (i.e., through sweating during exercise, vomiting, diarrhea), dehydration may occur and the plasma solute concentration increases. The hypothalamic osmoreceptors then initiate the release of ADH from the posterior pituitary gland. ADH primarily acts on the kidneys to increase the amount of water reabsorbed from the kidney filtrate back into the blood. The amount of urine produced thereby decreases and, consequently, the urine filtrate becomes more concentrated and darker in color. Increased reabsorption of water helps counter the increased solute concentration of the blood.
A decrease in blood volume or blood pressure, such as during hypovolemic shock, can also prompt ADH release. By promoting greater water reabsorption in the kidney, blood volume increases, thereby maintaining blood pressure in times of volume loss. ADH can also function as a vasopressor, or an agent that constricts the blood vessels, further increasing and normalizing blood pressure. This action of ADH is especially prevalent in the peripheral, small arteries.
Reduced secretion of ADH by the posterior pituitary can lead to diabetes insipidus (DI), a condition associated with polyuria, or frequent urination. This is because those with DI cannot concentrate their urine and large volumes of urine are subsequently produced daily, potentially leading to severe dehydration.
The other hormone released by the posterior pituitary gland is oxytocin. Oxytocin is mainly produced in the hypothalamus, where it is either sent to the pituitary gland for storage and subsequent release into the blood or is sent to other parts of the brain and spinal cord, where it binds to oxytocin receptors to influence behavior and physiology. Oxytocin is important in childbirth since it stimulates the contraction of the smooth muscles of the uterus. Because of this effect, synthetic oxytocin (pitocin) is sometimes used to induce labor or increase the force of contractions. Oxytocin also contracts the smooth muscle of the breast to allow the milk to flow during breastfeeding, referred to as the milk letdown reflex. More recently, oxytocin has been found to have roles in facilitating orgasm, social recognition, bonding, and maternal behaviors. Oxytocin has also been shown to play a role in sperm movement in those assigned male at birth. It also appears to affect testosterone levels in the testes.
Individuals assigned male at birth who have high levels of oxytocin sometimes develop benign prostatic hyperplasia, or the enlarging of the prostate gland. A lack of oxytocin in those assigned female at birth can prevent the milk letdown reflex and make breastfeeding difficult.
What are the most important facts to know about the posterior pituitary hormones?
The posterior pituitary gland plays a critical role in hormone production. The two hormones produced by the posterior pituitary gland are oxytocin and vasopressin, also known as antidiuretic hormone. The purposes of oxytocin include facilitating uterine contractions during labor, allowing for milk let down during breastfeeding, promoting social bonding, and moderating testosterone levels. Vasopressin regulates blood pressure by increasing the amount of water retained by the kidneys in times of dehydration or loss of blood. Dysfunctions in the posterior pituitary gland can result in diabetes insipidus and benign prostatic hyperplasia, among several other disorders. The functions of the pituitary gland are highly regulated by the hypothalamus, an area of the brain whose primary function is to maintain homeostasis in the body. In addition to regulating the posterior pituitary gland, the hypothalamus also sends hormone signals to the anterior lobe of the pituitary to promote the secretion of other hormones throughout the body.
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Resources for research and reference
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Magon, N., & Kalra, S. (2011). The orgasmic history of oxytocin: Love, lust, and labor. Indian Journal of Endocrinology and Metabolism, 15 Suppl 3(Suppl3), S156–S161. DOI: 10.4103/2230-8210.84851
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