Hypophyseal portal system

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Hypophyseal portal system
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Identifiers
Latin Venae portales hypophysiales
MeSH D007030
Anatomical terminology

The hypophyseal portal system is a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary. Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland. The capillaries in the portal system are fenestrated (have many small channels with high vascular permeability) which allows a rapid exchange between the hypothalamus and the pituitary. The main hormones transported by the system include gonadotropin-releasing hormone, corticotropin-releasing hormone, growth hormone–releasing hormone, and thyrotropin-releasing hormone.

Contents

Structure

The blood supply and direction of flow in the hypophyseal portal system has been studied over many years on laboratory animals and human cadaver specimens with injection and vascular corrosion casting methods. Short portal vessels between the neural and anterior pituitary lobes provide an avenue for rapid hormonal exchange. [1] [2] [3] Specifically within and between the pituitary lobes is anatomical evidence for confluent interlobe vessels, including venules providing blood from the anterior to the neural lobe, and capillary shunts exchanging blood between the intermediate and neural lobes. [1] Such microvascular structures indicate moment-to-moment streams of information between lobes of the pituitary gland. [1]

Results of other studies showed that the neural hypophyseal stalk and ventromedial region of the hypothalamic arcuate nucleus receive arterial blood from ascending and descending infundibular branches and capillaries, coming from arteries of the superior hypophyseal arterial system. [3] Small ascending vessels arising from the anastomoses that connect the upper with the lower hypophyseal arterial system also supply blood to hypophyseal vessels. Many of these branches are continuous between the proximal arcuate nucleus and anterior pituitary, enabling rapid hormone exchange. [2] [3] [4] Other evidence indicates that capillary perivascular spaces of the median eminence and arcuate nucleus are contiguous, potentially facilitating hormonal messages between systemic blood and the ventral hypothalamus. [2]

Development

Proper hormone secretion is crucial for the growth of the developing fetus. In order to allow a controlled hormone secretion in the developing organs of the fetus, stimulating hormones must be exchanged in the regulating structures in the brain in early stages of the development. Hormone-exchanging blood vessels between the hypothalamus and the pituitary gland, similar to those of the hypophyseal portal system, can be observed in early developmental stages of the fetus. In the current literature, most research is conducted using mice as model species. In such studies, development of the hypophyseal portal system begins as early as 14.5 dpc (days post coitum). Two populations of pericytes arise from the mesoderm and the neuroectoderm and form at the approximate location of the portal system in what will eventually become the mature brain. [5] Additionally, in research involving human fetuses it has been observed that the hypophyseal portal system fully develops by week 11.5 of the human fetal gestation period. This was determined by injecting a silicone rubber compound into specimens of various stages of gestation. In a specimen at week 11.5, the median eminence and infundibular stem contained the compound, suggesting the existence of the fully developed portal system. [6] Further research in this area would help determine whether or not development could be complete at an even earlier stage.

Function

Peptides released near the median eminence from hypothalamic nuclei are transported to the anterior pituitary, where they apply their effects. Branches from the internal carotid artery provide the blood supply to the pituitary. The superior hypophyseal arteries form the primary capillary plexus that supplies blood to the median eminence. From this capillary system, the blood is drained in hypophyseal portal veins into the secondary plexus. The peptides released at the median eminence enter the primary plexus capillaries. From there, they are transported to the anterior pituitary via hypophyseal portal veins to the secondary plexus. The secondary plexus is a network of fenestrated sinusoid capillaries that provide blood to the anterior pituitary. The cells of the anterior pituitary express specific G protein-coupled receptors that bind to the neuropeptides, activating intracellular second messenger cascades that produce the release of anterior pituitary hormones. [4]

The following is a list of hormones that rely on the hypophyseal portal system to indirectly mediate their function by acting as a means of transportation from various nuclei of the hypothalamus to the anterior pituitary. [7]

Clinical significance

Over- or under-function as well as insufficiencies of the hypothalamus or the pituitary gland can cause a negative effect on the ability of the hypophyseal portal system to exchange hormones between both structures rapidly. This can have major effects on the respective target glands, making it impossible for them to carry out their functions properly. Occlusions and other issues in the blood vessels of the hypophysial portal system can also cause complications in the exchange of hormones between the hypothalamus and the pituitary gland.

The hypophyseal portal system also plays an important role in several diseases involving the pituitary and central nervous system. In several cases of hypophyseal and pituitary metastatic tumors, the portal system acts as the pathway for metastasis from the hypothalamus to the pituitary. That is, cancerous cells from the hypothalamus multiply and spread to the pituitary using the hypophyseal portal system as a means of transportation. However, because the portal system receives an indirect supply of arterial blood, tumor formation in the anterior pituitary is less likely than in the posterior pituitary. This is because the posterior pituitary is vascularized by direct arterial blood flow. [8] [9] Pituitary apoplexy is described as hemorrhaging or reduction of blood supply to the pituitary gland. The physiological mechanisms of this condition have not been clearly defined in current research. [10] It has been suggested, nonetheless, that damage to the pituitary stalk leads to an obstruction of blood flow in the hypophyseal portal system and contributes to this defective state. [11] In Erdheim–Chester disease, cells of the immune system called histiocytes proliferate at an abnormal rate causing a plethora of symptoms and, in more severe cases, death. The disruption of the hypophyseal portal system has been implicated as the mechanism for several symptoms involving the central nervous symptom, most notably diabetes insipidus. [12]

See also

Related Research Articles

<span class="mw-page-title-main">Endocrine system</span> Hormone-producing glands of a body

The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems.

<span class="mw-page-title-main">Pituitary gland</span> Endocrine gland at the base of the brain

The pituitary gland is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the brain, protruding off the bottom of the hypothalamus. The human pituitary gland is oval shaped, about the size of a chickpea, and weighs 0.5 grams (0.018 oz) on average.

<span class="mw-page-title-main">Hypothalamus</span> Area of the brain below the thalamus

The hypothalamus is a small part of the brain that contains a number of nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus is located below the thalamus and is part of the limbic system. It forms the ventral part of the diencephalon. All vertebrate brains contain a hypothalamus. In humans, it is the size of an almond.

<span class="mw-page-title-main">Anterior pituitary</span> Anterior lobe of the pituitary gland

A major organ of the endocrine system, the anterior pituitary is the glandular, anterior lobe that together with the posterior lobe makes up the pituitary gland (hypophysis) which, in humans, is located at the base of the brain, protruding off the bottom of the hypothalamus.

<span class="mw-page-title-main">Posterior pituitary</span> Posterior lobe of the pituitary gland

The posterior pituitary 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 projections from the hypothalamus that terminate behind the anterior pituitary, and serve as a site for the secretion of neurohypophysial hormones directly into the blood. The hypothalamic–neurohypophyseal system is composed of the hypothalamus, posterior pituitary, and these axonal projections.

<span class="mw-page-title-main">Paraventricular nucleus of hypothalamus</span>

The paraventricular nucleus 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 amount of vasopressin, otherwise the nucleus also secretes corticotropin-releasing hormone (CRH) and thyrotropin-releasing hormone (TRH). CRH and TRH are secreted into the hypophyseal portal system and act on different targets neurons in the anterior pituitary. PVN is thought to mediate many diverse functions through these different hormones, including osmoregulation, appetite, and the response of the body to stress.

Corticotropes are basophilic cells in the anterior pituitary that produce pro-opiomelanocortin (POMC) which undergoes cleavage to adrenocorticotropin (ACTH), β-lipotropin (β-LPH), and melanocyte-stimulating hormone (MSH). These cells are stimulated by corticotropin releasing hormone (CRH) and make up 15–20% of the cells in the anterior pituitary. The release of ACTH from the corticotropic cells is controlled by CRH, which is formed in the cell bodies of parvocellular neurosecretory cells within the paraventricular nucleus of the hypothalamus and passes to the corticotropes in the anterior pituitary via the hypophyseal portal system. Adrenocorticotropin hormone stimulates the adrenal cortex to release glucocorticoids and plays an important role in the stress response.

<span class="mw-page-title-main">Tuberoinfundibular pathway</span> Group of dopamine neurons that project from arcuate nucleus in hypothalamus

The tuberoinfundibular pathway refers to a population of dopamine neurons that project from the arcuate nucleus in the tuberal region of the hypothalamus to the median eminence. It is one of the four major dopamine pathways in the brain. Dopamine released at this site inhibits the secretion of prolactin from anterior pituitary gland lactotrophs by binding to D2 receptors.

<span class="mw-page-title-main">Arcuate nucleus</span>

The arcuate nucleus of the hypothalamus is an aggregation of neurons in the mediobasal hypothalamus, adjacent to the third ventricle and the median eminence. The arcuate nucleus includes several important and diverse populations of neurons that help mediate different neuroendocrine and physiological functions, including neuroendocrine neurons, centrally projecting neurons, and astrocytes. The populations of neurons found in the arcuate nucleus are based on the hormones they secrete or interact with and are responsible for hypothalamic function, such as regulating hormones released from the pituitary gland or secreting their own hormones. Neurons in this region are also responsible for integrating information and providing inputs to other nuclei in the hypothalamus or inputs to areas outside this region of the brain. These neurons, generated from the ventral part of the periventricular epithelium during embryonic development, locate dorsally in the hypothalamus, becoming part of the ventromedial hypothalamic region. The function of the arcuate nucleus relies on its diversity of neurons, but its central role is involved in homeostasis. The arcuate nucleus provides many physiological roles involved in feeding, metabolism, fertility, and cardiovascular regulation.

<span class="mw-page-title-main">Median eminence</span>

The median eminence is generally defined as the portion of the ventral hypothalamus from which the portal vessels arise. The median eminence is a small swelling on the tuber cinereum, posterior to and atop the pituitary stalk; it lies in the area roughly bounded on its posterolateral region by the cerebral peduncles, and on its anterolateral region by the optic chiasm.

<span class="mw-page-title-main">Endocrine gland</span> Glands of the endocrine system that secrete hormones to blood

Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testicles, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary glands are neuroendocrine organs.

Neuroendocrine cells are cells that receive neuronal input and, as a consequence of this input, release messenger molecules (hormones) into the blood. In this way they bring about an integration between the nervous system and the endocrine system, a process known as neuroendocrine integration. An example of a neuroendocrine cell is a cell of the adrenal medulla, which releases adrenaline to the blood. The adrenal medullary cells are controlled by the sympathetic division of the autonomic nervous system. These cells are modified postganglionic neurons. Autonomic nerve fibers lead directly to them from the central nervous system. The adrenal medullary hormones are kept in vesicles much in the same way neurotransmitters are kept in neuronal vesicles. Hormonal effects can last up to ten times longer than those of neurotransmitters. Sympathetic nerve fiber impulses stimulate the release of adrenal medullary hormones. In this way the sympathetic division of the autonomic nervous system and the medullary secretions function together.

Neuroendocrinology is the branch of biology which studies the interaction between the nervous system and the endocrine system; i.e. how the brain regulates the hormonal activity in the body. The nervous and endocrine systems often act together in a process called neuroendocrine integration, to regulate the physiological processes of the human body. Neuroendocrinology arose from the recognition that the brain, especially the hypothalamus, controls secretion of pituitary gland hormones, and has subsequently expanded to investigate numerous interconnections of the endocrine and nervous systems.

<span class="mw-page-title-main">Circumventricular organs</span> Interfaces between the brain and the circulatory system

Circumventricular organs (CVOs) are structures in the brain characterized by their extensive and highly permeable capillaries, unlike those in the rest of the brain where there exists a blood–brain barrier (BBB) at the capillary level. Although the term "circumventricular organs" was originally proposed in 1958 by Austrian anatomist Helmut O. Hofer concerning structures around the brain ventricular system, the penetration of blood-borne dyes into small specific CVO regions was discovered in the early 20th century. The permeable CVOs enabling rapid neurohumoral exchange include the subfornical organ (SFO), the area postrema (AP), the vascular organ of lamina terminalis, the median eminence, the pituitary neural lobe, and the pineal gland.

<span class="mw-page-title-main">Tuber cinereum</span>

The tuber cinereum is the portion of hypothalamus forming the floor of the third ventricle situated between the optic chiasm, and the mammillary bodies. The tuberal region is one of the three regions of the hypothalamus, the other two being the chiasmatic region and the mamillary region.

<span class="mw-page-title-main">Head and neck anatomy</span>

This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.

<span class="mw-page-title-main">Portal venous system</span> The capillary bed pools into another through veins without first going through the heart

In the circulatory system of vertebrates, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are considered part of the portal venous system.

Pulsatile secretion is a biochemical phenomenon observed in a wide variety of cell and tissue types, in which chemical products are secreted in a regular temporal pattern. The most common cellular products observed to be released in this manner are intercellular signaling molecules such as hormones or neurotransmitters. Examples of hormones that are secreted pulsatilely include insulin, thyrotropin, TRH, gonadotropin-releasing hormone (GnRH) and growth hormone (GH). In the nervous system, pulsatility is observed in oscillatory activity from central pattern generators. In the heart, pacemakers are able to work and secrete in a pulsatile manner. A pulsatile secretion pattern is critical to the function of many hormones in order to maintain the delicate homeostatic balance necessary for essential life processes, such as development and reproduction. Variations of the concentration in a certain frequency can be critical to hormone function, as evidenced by the case of GnRH agonists, which cause functional inhibition of the receptor for GnRH due to profound downregulation in response to constant (tonic) stimulation. Pulsatility may function to sensitize target tissues to the hormone of interest and upregulate receptors, leading to improved responses. This heightened response may have served to improve the animal's fitness in its environment and promote its evolutionary retention.

Geoffrey Wingfield Harris (1913–1971) was a British physiologist and neuroendocrinologist. Often considered the "father of neuroendocrinology", he is best known for showing that the anterior pituitary is regulated by the hypothalamus via the hypophyseal portal system. His work established the principles for the 1977 Nobel Prize-winning discovery of hypothalamic hormones by Schally and Guillemin.

References

  1. 1 2 3 Gross, PM; Joneja, MG; Pang, JJ; Polischuk, TM; Shaver, SW; Wainman, DS (1993). "Topography of short portal vessels in the rat pituitary gland: A scanning electron-microscopic and morphometric study of corrosion cast replicas". Cell and Tissue Research. 272 (1): 79–88. doi:10.1007/bf00323573. PMID   8481959. S2CID   23657199.
  2. 1 2 3 Shaver, SW; Pang, JJ; Wainman, DS; Wall, KM; Gross, PM (1992). "Morphology and function of capillary networks in subregions of the rat tuber cinereum". Cell and Tissue Research. 267 (3): 437–48. doi:10.1007/bf00319366. PMID   1571958. S2CID   27789146.
  3. 1 2 3 Ciofi, P; Garret, M; Lapirot, O; Lafon, P; Loyens, A; Prévot, V; Levine, J. E. (2009). "Brain-endocrine interactions: A microvascular route in the mediobasal hypothalamus". Endocrinology. 150 (12): 5509–19. doi:10.1210/en.2009-0584. PMC   2819742 . PMID   19837874.
  4. 1 2 Molina, Patricia.E. (2010). Endocrine Physiology. Lange. (3, p. 31). ISBN   978-0-07-161301-9.
  5. ↑ Fiordelisio, Tatiana; Rizzoti, Karine; Samper, Patrick; Lafont, Chrstel; Davis, Shannon; Mollard, Patrice E. “Developmental Program of the Pituitary Portal System.” Endocrine Society’s 97th Annual Meeting and Expo. March 2015. San Diego, CA
  6. ↑ Thliveris, James A.; Currie, R. William (1980-04-01). "Observations on the hypothalamo-hypophyseal portal vasculature in the developing human fetus". American Journal of Anatomy. 157 (4): 441–444. doi: 10.1002/aja.1001570411 . ISSN   1553-0795. PMID   7405878.
  7. ↑ Silverthorn, Dee Unglaub (2016). Human physiology : an integrated approach. Johnson, Bruce R., Ober, William C., Ober, Claire E., Silverthorn, Andrew C. (Seventh ed.). [San Francisco]. ISBN   9780321981226. OCLC   890107246.{{cite book}}: CS1 maint: location missing publisher (link)
  8. ↑ Ravnik, Janez; Smigoc, Tomaz; Bunc, Gorazd; Lanisnik, Bostjan; Ksela, Ursa; Ravnik, Maja; Velnar, Tomaz (2016). "Hypophyseal metastases: A report of three cases and literature review". Neurologia I Neurochirurgia Polska. 50 (6): 511–516. doi:10.1016/j.pjnns.2016.08.007. PMID   27633123.
  9. ↑ Komninos, John; Vlassopoulou, Varvara; Protopapa, Despina; Korfias, Stefanos; Kontogeorgos, George; Sakas, Damianos E.; Thalassinos, Nicolas C. (2004-02-01). "Tumors Metastatic to the Pituitary Gland: Case Report and Literature Review". The Journal of Clinical Endocrinology & Metabolism. 89 (2): 574–580. doi: 10.1210/jc.2003-030395 . ISSN   0021-972X. PMID   14764764.
  10. ↑ Briet, Claire; Salenave, Sylvie; Bonneville, Jean-François; Laws, Edward R.; Chanson, Philippe (2015-12-01). "Pituitary Apoplexy". Endocrine Reviews. 36 (6): 622–645. doi: 10.1210/er.2015-1042 . ISSN   0163-769X. PMID   26414232.
  11. ↑ Billeci, Domenico; Marton, Elisabetta; Giordan, Enrico (2017). "Post-traumatic pituitary apoplexy: Case presentation and review of literature" (PDF). Interdisciplinary Neurosurgery. 7: 4–8. doi: 10.1016/j.inat.2016.10.006 .
  12. ↑ Mazor, Roei D.; Manevich-Mazor, Mirra; Shoenfeld, Yehuda (2013-09-08). "Erdheim–Chester disease: a comprehensive review of the literature". Orphanet Journal of Rare Diseases. 8: 137. doi: 10.1186/1750-1172-8-137 . ISSN   1750-1172. PMC   3849848 . PMID   24011030.
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