The neurohypophysial hormones form a
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
of structurally and functionally related
peptide hormones
Peptide hormones or protein hormones are hormones whose molecules are peptide, or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine system of animals, including h ...
. Their representatives in humans are
oxytocin
Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytocin ...
and
vasopressin
Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travel ...
. They are named after the location of their release into the blood, the
neurohypophysis
The posterior pituitary (or neurohypophysis) is the posterior lobe of the pituitary gland which is part of the endocrine system. The posterior pituitary is not glandular as is the anterior pituitary. Instead, it is largely a collection of axonal ...
(another name for the posterior pituitary).
Most of the circulating oxytocin and vasopressin hormones are synthesized in
magnocellular neurosecretory cell
Magnocellular neurosecretory cells are large neuroendocrine cells within the supraoptic nucleus and paraventricular nucleus of the hypothalamus. They are also found in smaller numbers in accessory cell groups between these two nuclei, the larges ...
s of the
supraoptic nucleus
The supraoptic nucleus (SON) 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, the SON contains about 3,000 ne ...
and
paraventricular nucleus
The paraventricular nucleus (PVN, PVA, or PVH) is a nucleus in the hypothalamus. Anatomically, it is adjacent to the third ventricle and many of its neurons project to the posterior pituitary. These projecting neurons secrete oxytocin and a smaller ...
of the hypothalamus. They are then transported in neurosecretory granules along axons within the
hypothalamo-neurohypophysial tract by
axoplasmic flow to
axon terminal
Axon terminals (also called synaptic boutons, terminal boutons, or end-feet) are distal terminations of the telodendria (branches) of an axon. An axon, also called a nerve fiber, is a long, slender projection of a nerve cell, or neuron, that condu ...
s forming the pars nervosa of the posterior pituitary. There, they are stored in
Herring bodies
Herring bodies or neurosecretory 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. They are neurosecretory terminals.
...
and can be released into the circulation on the basis of hormonal and synaptic signals with assistance from
pituicyte
Pituicytes are glial cells of the posterior pituitary. Their main role is to assist in the storage and release of neurohypophysial hormones.
Structure
Pituicytes are located in the pars nervosa of the posterior pituitary and interspersed with un ...
s.
Oxytocin mediates contraction of the
smooth muscle
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
of the uterus and mammary gland, while vasopressin has
antidiuretic
An antidiuretic is a substance that helps to control fluid balance in an animal's body by reducing urination, opposing diuresis. Its effects are opposite that of a diuretic. The major endogenous antidiuretics are antidiuretic hormone (ADH; also ca ...
action on the kidney, and mediates vasoconstriction of the peripheral vessels.
Due to the similarity of the two hormones, there is cross-reaction: oxytocin has a slight antidiuretic function, and high levels of
AVP can cause uterine contractions.
In common with most active peptides, both hormones are synthesised as larger protein precursors that are enzymatically converted to their mature forms.
Members of this family are found in birds, fish, reptiles and amphibians (
mesotocin,
isotocin, valitocin, glumitocin, aspargtocin, vasotocin, seritocin, asvatocin, phasvatocin), in worms (annetocin, nematocin), octopuses (cephalotocin, octopressin), insects (locupressin, inotocin) and in molluscs (conopressins G and S).
Animals that ''lack'' a hormone from this family include fruit flies, and at least some mosquitos, silkworms, and honeybees.
References
{{InterPro content, IPR000981
Protein families
Hormones
Peptides