The posterior pituitary secretes two important endocrine hormones—oxytocin and antidiuretic hormone. The posterior pituitary or neurohypophysis comprises the posterior lobe of the pituitary gland and is part of the endocrine system.
Despite its name, the posterior pituitary gland is not a gland; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary gland. The posterior pituitary consists mainly of neuronal projections axons extending from the supraoptic and paraventricular nuclei of the hypothalamus.
These axons release peptide hormones into the capillaries of the hypophyseal circulation. These are then stored in neurosecretory vesicles Herring bodies before being secreted by the posterior pituitary into the systemic bloodstream. The posterior pituitary is derived from the hypothalamus and is distinct from the more fleshy, vascularized anterior lobe.
The posterior pituitary is composed of two parts:. Privacy Policy. Skip to main content. Endocrine System. Search for:. The Pituitary Gland. Overview of the Pituitary Gland The pituitary gland is connected to the hypothalamus and secretes nine hormones that regulate body homeostasis. Learning Objectives Summarize the structure and function of the pituitary gland.
Key Takeaways Key Points The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea. Although located at the base of the brain and often considered to be part of the brain, the pituitary gland is in fact a separate organ, and is not part of the brain. For example, the pituitary gland produces prolactin , which acts on the breasts to induce milk production. Through secretion of its hormones, the pituitary gland controls metabolism , growth, sexual maturation, reproduction, blood pressure and many other vital physical functions and processes.
The anterior pituitary gland produces the following hormones and releases them into the bloodstream:. Each of these hormones is made by a separate type of cell within the pituitary gland, except for follicle stimulating hormone and luteinising hormone , which are made together by the same cell. Two hormones are produced by the hypothalamus and then stored in the posterior pituitary gland before being secreted into the bloodstream.
These are:. Between the anterior pituitary and the posterior pituitary lies the intermediate pituitary gland. Cells here produce:. The pituitary gland is an important gland in the body and the hormones it produces carry out varied tasks and regulate the function of many other organs. Secretion of the posterior pituitary hormones is directly from magnocellular neurons of the paraventricular and supraoptic nuclei into the circulation. These neurons project axons into the posterior pituitary via the hypothalamo-neurohypophyseal tract and terminate on a capillary bed of the inferior hypophyseal artery.
Control of release in this system is under neural control and so this represents a reflex system with neural input and hormonal output. Secretion of anterior pituitary hormones is driven by the influence of releasing, or release-inhibiting hormones factors that are synthesized in parvocellular neurons of the supraoptic, paraventricular, arcuate and periventricular hypothalamic nuclei. These neurons project axons in the tuberoinfundibular tract onto a capillary bed of the superior hypophyseal artery at the base of the median eminence.
These capillaries coalesce into the hypophyseal portal veins, which descend to the anterior pituitary and form a second capillary bed where the anterior pituitary hormones are released. The anterior pituitary hormones diffuse to peripheral targets to provoke release of endocrine hormones that induced tissue effects. Control of release in this system is via feedback of releasing-hormones, anterior pituitary hormones, and peripheral endocrine hormones onto hypothalamic and pituitary cells in a series of feedback loops.
This system thus represents a hormone-and neural-evoked and hormone-output reflex. The immune system is also influenced by neural activity. Inhibition of ACTH secretion by cortisol is an example of what type of neuroendocrine feedback loop? Neurons in the paraventricular and the supraoptic nuclei project to the posterior pituitary via the hypothalamo-neurohypophyseal tract. Inputs to the hypothalamus regulating the release of vasopressin include neurons with cell bodies in sensory ganglia of the peripheral nervous system.
The blood supply to the posterior pituitary is provided by the inferior hypophyseal artery. Prolactin is secreted with neurophysin II. This system is characterized by reflexes with neural input and hormonal output.
Hormones of the anterior pituitary are synthesized in the arcuate, periventricular and supraoptic nuclei of the hypothalamus. Single parvocellular neurons of the supraoptic nucleus can control the synthesis and release of more than one type of anterior pituitary hormone.
Parvocellular neurons in the arcuate nucleus project to hypophyseal portal veins via the tuberoinfundibular tract. The secretion of releasing hormones is controlled by multiple neurotransmitter systems of the brain. Anterior pituitary hormones are secreted in circadian patterns.
Which of the following is the intracellular second messenger that initiates the acuate phase response within neurons in the hypothalamus? Which of the following is a possible pathway for CRF to reach the pituitary? Hormones from the hypothalamus are rapidly degraded in the anterior pituitary, which prevents them from entering the circulatory system. The posterior lobe of the pituitary gland develops as an extension of the hypothalamus.
As such, it is not capable of producing its own hormones; instead, it stores hypothalamic hormones for later release into the systemic circulation.
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