The
posterior pituitary (or
neurohypophysis) comprises the posterior lobe of the
pituitary glandThe pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g . It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
and is part of the
endocrine systemThe endocrine system is a system of glands that involve the release of extracellular signaling molecules known as hormones.The endocrine system is instrumental in regulating metabolism, growth, development, puberty, tissue function, internal environment and also plays a part in determining...
. Despite its name, the posterior pituitary gland is not a gland,
per se; rather, it is largely a collection of
axonAn axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts electrical impulsesaway from the neuron's cell body or soma....
al projections from the
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
that terminate behind the anterior pituitary gland.
The posterior pituitary consists mainly of
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
al projections (
axonAn axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts electrical impulsesaway from the neuron's cell body or soma....
s) extending from the
supraopticThe supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, it contains about 3,000 neurons....
and
paraventricular nucleiThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
of the
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
.
The
posterior pituitary (or
neurohypophysis) comprises the posterior lobe of the
pituitary glandThe pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g . It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
and is part of the
endocrine systemThe endocrine system is a system of glands that involve the release of extracellular signaling molecules known as hormones.The endocrine system is instrumental in regulating metabolism, growth, development, puberty, tissue function, internal environment and also plays a part in determining...
. Despite its name, the posterior pituitary gland is not a gland,
per se; rather, it is largely a collection of
axonAn axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts electrical impulsesaway from the neuron's cell body or soma....
al projections from the
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
that terminate behind the anterior pituitary gland.
Anatomy
The posterior pituitary consists mainly of
neuronA neuron is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, the vertebrate spinal cord, the invertebrate ventral nerve cord, and the peripheral nerves...
al projections (
axonAn axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts electrical impulsesaway from the neuron's cell body or soma....
s) extending from the
supraopticThe supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, it contains about 3,000 neurons....
and
paraventricular nucleiThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
of the
hypothalamusThe hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland ....
. These axons release
peptide hormonePeptide hormones are a class of peptides that are secreted into the blood stream and have endocrine functions in living animals. Peptide hormones are increasingly being identified in plants with important roles in cell-to-cell communication and plant defence...
s into the capillaries of the hypophyseal circulation. In addition to axons, the posterior pituitary also contains
pituicyteA pituicyte is a glial cell of the posterior pituitary. They generally stain dark purple, and are among the easiest structures to identify in the region . They are similar to the astrocytes/glial cells of the CNS....
s, specialized
glial cellGlial cells, commonly called neuroglia or simply glia , are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system...
s resembling
astrocyteAstrocytes are characteristic star-shaped glial cells in the brain and spinal cord. They perform many functions, including biochemical support of endothelial cells which form the blood-brain barrier, provision of nutrients to the nervous tissue, maintenance of extracellular ion balance, and a...
s.
Classification of the posterior pituitary varies, but most sources include the three regions below:
Pars nervosa: Also called the neural lobe or posterior lobe, this region constitutes the majority of the posterior pituitary, and is sometimes (incorrectly) considered synonymous with it. Notable features include
Herring bodiesHerring bodies are structures found in the posterior pituitary. They represent the terminal end of the axons from the hypothalamus, and hormones are temporarily stored in these locations....
and
pituicyteA pituicyte is a glial cell of the posterior pituitary. They generally stain dark purple, and are among the easiest structures to identify in the region . They are similar to the astrocytes/glial cells of the CNS....
s.
Infundibular stalk: Also known as the infundibulum or pituitary stalk, the infundibular stalk bridges the hypothalamic and hypophyseal systems.
Median eminence: This is only occasionally included as part of the posterior pituitary. Other sources specifically exclude it from the pituitary.
A few sources include the
pars intermediaPars intermedia is the boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells - basophils, chromophobes, and colloid-filled cysts. The cysts are the remainder of Rathke’s pouch....
as part of the posterior lobe, but this is a minority view. It is based upon the gross anatomical separation of the posterior and anterior pituitary along the cystic remnants of Rathke's pouch, causing the pars intermedia to remain attached to the neurohypophysis.
Hormones secreted
Hormones known classically as posterior pituitary hormones are synthesized by the hypothalamus. They are then stored and secreted by the posterior pituitary into the bloodstream.
| Hormone |
Other names |
Symbol(s) |
Target |
Effect |
Source |
OxytocinOxytocin is a mammalian hormone that also acts as a neurotransmitter in the brain.It is best known for its roles in female reproduction: it is released in large amounts after distension of the cervix and vagina during labor, and after stimulation of the nipples, facilitating birth and...
|
- |
OT |
UterusThe uterus is a major female hormone-responsive reproductive sex organ of most mammals, including humans. It is within the uterus that the fetus develops during gestation. The term uterus is used consistently within the medical and related professions; the Germanic term, womb is more common in...
, mammary glandMammary glands are the organs that, in mammals, produce milk for the sustenance of the young. These exocrine glands are enlarged and modified sweat glands and give mammals their name...
s |
Uterine contractions; lactation Lactation describes the secretion of milk from the mammary glands, the process of providing that milk to the young, and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, and in humans it is commonly referred to as breastfeeding or nursing...
|
supraoptic The supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, it contains about 3,000 neurons....
and paraventricular nucleiThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
|
| Vasopressin Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a hormone found in most mammals, including humans. Vasopressin is a peptide hormone. It is derived from a preprohormone precursor that is synthesized in the hypothalamus and stored in vesicles at the...
(antidiuretic hormone) |
Arginine vasopressin, argipressin, antidiuretic hormone |
VP, AVP, ADH |
KidneyThe kidneys are paired organs, which have the production of urine as their primary function. Kidneys are seen in many types of animals, including vertebrates and some invertebrates. They are part of the urinary system, but have several secondary functions concerned with homeostatic functions. ...
s or ArterioleAn arteriole is a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have thin muscular walls and are the primary site of vascular resistance...
s |
Stimulates water retention; raises blood pressure by contracting arterioles, induces male aggression |
supraoptic The supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, it contains about 3,000 neurons....
and paraventricular nucleiThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
|
Role in disease
Insufficient secretion of
vasopressinArginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a hormone found in most mammals, including humans. Vasopressin is a peptide hormone. It is derived from a preprohormone precursor that is synthesized in the hypothalamus and stored in vesicles at the...
underlies
diabetes insipidusDiabetes insipidus is a condition characterized by excessive thirst and excretion of large amounts of severely diluted urine, with reduction of fluid intake having no effect on the latter. There are several different types of DI, each with a different cause...
, a condition in which the body loses the capacity to concentrate urine. Affected individuals excrete as much as 20 liters of dilute urine per day. Oversecretion of vasopressin causes the
syndrome of inappropriate antidiuretic hormoneThe syndrome of inappropriate antidiuretic hormone hypersecretion is a condition commonly found in the hospital population, especially in patients being hospitalized for central nervous system injury. This is a syndrome characterized by excessive release of antidiuretic hormone from the...
(SIADH).