The term hypophyseal portal system sounds complicated and, at a glance, seems difficult to understand. If you're into some form of anatomy, physiology, and psychology, you have probably come across the term and tried to figure out what the hypophyseal portal system is.
The hypothalamic-hypophyseal portal system links the hypothalamus and anterior pituitary gland through a system of veins that start and end in capillaries to quickly transport and exchange hormones. It is also located at the base of the brain and is one of two portal systems in humans.
There are two portal systems in the human body, each consisting of blood vessels to transport and exchange hormones. The hypophyseal portal system is responsible for several vital hormones. This article discusses the HPS in detail and how it distinguishes it from the hepatic portal system.
The Hypophyseal Portal System
The hypophyseal portal system also called the hypothalamic-hypophyseal portal system, is a hormone transportation and exchange system that runs through a capillary bed connected by blood vessels. The hormones are transported between the hypothalamus and the anterior pituitary.
Understanding it is not as complicated as it seems. There are some keywords and terms that the Hypophyseal Portal System consists of and is necessary to understand first. They are listed and explained below:
The hypothalamus is a structure based deep in the base of the brain, is the body's intelligent coordinating center, and works to keep the body in homeostasis. It produces and manages hormones to control the body's temperature, hunger, heart rate, and mood. The hypothalamus directly influences your autonomic nervous system.
The anterior pituitary is a pea-sized frontal lobe of the pituitary gland located below the hypothalamus, at the base of your brain. It is part of your endocrine system to control the function of other endocrine glands and is connected to the brain by blood vessels carrying hormones.
Endocrine glands produce hormones, and endocrine communication signals these chemicals being transported directly into the bloodstream. The hormones then move towards distant body regions and extract a response from their target cells.
Inhibitory hormones are produced in the hypothalamus to stop and start the production of other hormones in the body. The inhibitory hormones inhibit the release of other hormones through the anterior pituitary lobe.
Capillary beds are a network of small blood vessels. In the hypophyseal portal system, the capillary beds are located at the top and bottom of the anterior pituitary lobe and connected by veins in the middle. They transport the hormones released and inhibited between the hypothalamus and anterior pituitary and then to necessary parts of the tissue cells in the body.
The hypothalamus and anterior pituitary gland functions with the hypophyseal portal system are detailed below.
Hypothalamus Function In The Hypophyseal Portal System
The hypothalamus is directly connected to and involved in the hypophyseal portal system. It produces, releases, and inhibits hormones responsible for the following:
- Maintaining daily physiological cycles
- Controlling appetite
- Managing sexual behavior
- Regulating emotional responses
- Regulating body temperature
There are three main regions in the hypothalamus; anterior, middle, and posterior. Each one is responsible for specific hormones transmitted through the hypophyseal portal system to the anterior pituitary lobe.
Anterior Pituitary Function In The Hypophyseal Portal System
The anterior pituitary is one of two lobes from the pituitary gland. It is the frontal lobe and located below the hypothalamus. It is responsible for creating and releasing six different hormones. Those hormones regulate a variety of cellular processes such as:
- Stress and trauma responses
It is directly linked to the hypothalamus through the hypophyseal portal system's blood vessels. It gets signals from the hypothalamus, which tells it which hormones to release. The pituitary gland produces several different hormones at alternating periods of activity and inactivity.
Importance Of The Hypophyseal Portal System
The hypophyseal portal system is vital in transporting hormones between the two brain structures. It is called a portal because it's an access link between the hypothalamus and anterior pituitary.
The hypophyseal portal system consists of a system of blood vessels. The blood vessels are tiny and make two sets of capillary beds; one connected to the hypothalamus and the other to the anterior pituitary lobe. Veins connect the two capillary beds.
The anterior pituitary gland contains fewer hypothalamic hormones. The blood vessels from the hypothalamus have more. Because of the hypophyseal portal system, the hormones can diffuse out of the pituitary capillary bed into the anterior pituitary lobe. That is how the hormones can find their targets.
An essential point to remember is that, unlike the posterior pituitary lobe, the anterior pituitary does not have a direct tissue connection with the hypothalamus. The posterior pituitary can receive hormones through the infundibulum, whereas the anterior pituitary requires the portal system to transport and exchange hormones.
The system is also called the hypothalamic-hypophyseal portal system because it links the two parts of the hormone-producing brain structures.
If the hypophyseal portal system did not exist, the chemicals generated would get dispersed directly into the bloodstream and become diluted before it reaches their target. The HPS allows the hormones to remain concentrated instead of becoming diluted due to the immense dispersion. Dispersion could lead to hyposecretion of hormones, leading to specific health conditions.
Endocrine System And Hypophyseal Portal System
Earlier, we mildly discussed the endocrine communications, which signal the chemicals being transported into the bloodstream to their target cells. The endocrine system creates and releases hormones that control nearly all the processes in your body.
The chemicals help coordinate body functions, such as metabolism, development and growth, emotions and mood, sexual function, and sleep. There are glands all over the body that make up the endocrine system, and they release hormones.
The hormones are referred to as the chemical that coordinate the functions in your body. It carries messages through the bloodstream to target regions like your organs, skin, muscles, and other tissue cells. These signals tell your body what and when to do something, i.e., endocrine communications.
So how is the endocrine system connected to the hypophyseal portal system? The pituitary gland is included in the endocrine system. The endocrine system from around the body sends communication signals for what chemicals are needed when needed and what they need to do.
The hypothalamus and pituitary gland receive these signals, then create and either release or inhibit the necessary hormones. They are then transported and exchanged through the hypophyseal portal system. It is all connected through blood vessels in the body and brain.
Additionally, you may want to note that the importance also arises from the anterior pituitary lobe being a true endocrine gland. No neurons extend from the hypothalamus, unlike the posterior pituitary. That is why the communication between the hypothalamus and anterior-posterior needs to happen through blood vessels.
Hormones Transported Through The Hypophyseal Portal System
The hypophyseal portal system is a hormone transport system between the hypothalamus and anterior pituitary. Below are the primary hormones that pass through the portal system:
Hypothalamic releasing hormones (stimulates secretion)
- Gonadotrophin-releasing hormone
- Corticotropin-releasing hormone
- Growth hormone-releasing hormone
- Thyrotropin-releasing hormone
- Prolactin-releasing hormone
Hypothalamic inhibiting hormones (suppresses secretion)
- Growth hormone-inhibiting hormone
- Prolactin-inhibiting hormone – dopamine
Anterior Pituitary Hormones
- Human growth hormone – somatotropin (the most plentiful hormone in the anterior pituitary)
- Thyroid-stimulating hormone – thyrotropin
- Luteinizing hormone
- Prolactin (primary function during pregnancy)
- Adrenocorticotropic hormone – corticotropin
- Melanocyte-stimulating hormone (skin pigmentation)
Problems In The Hypophyseal Portal System
The hypophyseal portal system is a set of blood vessels containing veins that connect two series of capillary beds. What happens when a problem occurs, such as a blood clot in the hypophyseal portal system?
Suppose there is an over or under function of the hypothalamus or pituitary gland. In that case, it can negatively affect the hypophyseal portal system in exchanging hormones between the two structures. When that happens, they can't carry out their functions efficiently.
Occlusion in the blood vessels of the portal system can cause complications during hormone exchange between the hypothalamus and the anterior pituitary gland.
Posterior Pituitary And The Hypophyseal Portal System
The posterior pituitary is connected to the anterior pituitary and the hypothalamus. But is not part of the hypophyseal portal system. The posterior pituitary lobe does not make any hormones. It is a storage base for hormones it receives from the hypothalamus and is an extension of the hypothalamus. They communicate through nerves.
The hormones from the hypothalamus pass through the infundibulum to the posterior pituitary. The capillary bed on the posterior pituitary transports the hormone to the heart. Unlike the anterior, the posterior pituitary does not require the hypophyseal portal system. The anterior pituitary requires the system because there is no direct connection to the hypothalamus without it.
Understanding that the posterior pituitary gland does not synthesize or create any hormones is essential. Two hormones are secreted into the posterior pituitary through the hypothalamus. They travel down the infundibulum and then get stored in the posterior pituitary. Those two hormones are oxytocin and ADH.
The Hypophyseal Portal System And Diseases
Problems with the hypophyseal portal system play a role in specific diseases that involve the pituitary and central nervous system. In cases of metastatic tumors, the portal system is the pathway for metastasis from the hypothalamus to the pituitary.
Cancerous cells multiply and spread from the hypothalamus to the pituitary gland through the portal system and use the portal as a means of transportation. Tumor formation is unlikely in the anterior pituitary compared to the posterior pituitary because the portal system receives an indirect blood supply.
Another disease called pituitary apoplexy is hemorrhaging or reduction of the blood supply to the pituitary gland. The damage to the pituitary stalk is obstruction of the blood flow in the hypophyseal portal system, which then contributes to the defective state.
There are other diseases connected to the hypophyseal portal state. A health professional should address any concern with the central nervous system and refer to a neurologist.
How Many Portal Systems Do Humans Have?
The human body has two portal systems, namely, the hypophyseal portal system and the hepatic portal system. In non-mammals, there is also a renal portal system. We have already discussed the hypophyseal portal system in detail. But what is the hepatic portal system, and are the two human portal systems related?
Like the hypophyseal, the hepatic portal system is a system of veins. In the hepatic portal system, the veins transport blood from the digestive tract to the liver. The portal system includes the hepatic portal vein and other veins that drain into it. The other veins are the superior mesenteric vein, inferior mesenteric vein, and splenic vein.
Blood rich in nutrients and toxins is processed in the liver and carried through the hepatic portal and hepatic vein, regulating it with the heart through systemic circulation. The hepatic portal system is significant in the digestive process and works with the intestines, gallbladder, pancreas, spleen, and liver.
The hepatic portal venous system involves draining the GI tract. It also transports blood from organ to organ instead of directly returning it to the heart. The hypothalamic-pituitary portal system deals with the brain and heart when receiving endocrine communications.
Is The Hepatic And Hypophyseal Portal Systems Related?
The two portal systems do not directly connect, and the hypophyseal system is not as well-known as the hepatic system. The hypophyseal system controls the central nervous system and runs significant hormones from the brain to target cells in the body. If the central nervous system and hormones are not functioning efficiently, it can negatively affect the hepatic system.
So, while the two portal systems are not directly connected, it is relatively related, as is the entire human body. If one is not working, it cannot communicate and effectively send signals to the brain, which stimulates responses to help the body function properly.
The hypophyseal portal system is a transport system made up of blood vessels. It contains capillary beds connected by veins to transport and exchange hormones created in the hypothalamus and anterior pituitary gland.