The hypophyseal portal system is the system of blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s that link the hypothalamus

Hypothalamus

The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

 and the anterior pituitary

Anterior pituitary

A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland...

 in the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

.

It allows endocrine

Endocrine system

In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...

 communication between the two structures. It is part of the hypothalamic-pituitary-adrenal axis

Hypothalamic-pituitary-adrenal axis

The hypothalamic-pituitary-adrenal axis , also known as thelimbic-hypothalamic-pituitary-adrenal axis and, occasionally, as the hypothalamic-pituitary-adrenal-gonadotropic axis, is a complex set of direct influences and feedback interactions among the hypothalamus, the pituitary gland ,...

. The anterior pituitary

Anterior pituitary

A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland...

 receives releasing and inhibitory hormones in the blood. Using these, the anterior pituitary is able to fulfill its function of regulating the other endocrine glands.

It is one of three portal systems of circulation; that is, it involves two capillary beds

Capillary

Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...

 connected in series by venule

Venule

A venule is a very small blood vessel in the microcirculation that allows deoxygenated blood to return from the capillary beds to the larger blood vessels called veins. Venules range from 8 to 100μm in diameter and are formed when capillaries unite .Venules are blood vessels that drain blood...

s. The others are the hepatic portal system and that in the kidneys.

Hormone transport

Mechanism for hormone transport via hypothalamoportal vessels:

• cells regulated by different nuclei in hypothalamus, i.e., neurons that release neurotransmitters as hormones in the connective link between the pituitary and the brain. Hypothalamic hormones stimulate the release of the respective hormone from the anterior pituitary gland.
• ligands
  Ligand (biochemistry)
  In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...
  
  (in this case, hormones released by the hypothalamus to activate hormone release from the anterior pituitary) are picked up by blood vessels then taken to anterior pituitary where they are broken down and released back into blood vessels
• before they are broken down, hypothalamoportal vessel acts as local route for blood flow directly from hypothalamus to anterior pituitary.

External links

• http://www.llu.edu/llu/medicine/anatomy/glossary/ans102_109.html#Q103
• http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/anatomy.html