Thymus secretes which hormones

In some people, though, this organ is found in the neck or upper chest. While that may seem odd, it's part of the organ's mystery that has baffled scientists for centuries.

Researchers only began to understand some of the gland's function about 50 years ago. They still aren't sure where it got its name. Some experts say the ancient Greeks, who discovered the organ, named it thymus because its shape looks like the leaves of thyme, a cooking herb. Others say the name came from the Greek word for the soul because the organ is near the heart.

Either way, the thymus gland is considered an immune system organ. Like your tonsils and adenoids, it helps fight infections. Unlike your heart or lungs, what the thymus gland does isn't apparent. Its job involves a lot of tiny chemical processes. Inside the thymus gland, there are many different cells. These include:. This list hints at how complex the thymus gland's job is. Its role also changes throughout your life. The famous Greek philosopher-surgeon, Galen, was the first to notice that the thymus gland changes with age.

Galen wrote that it's large in newborn animals and becomes smaller when they're adults. Your thymus gland reaches its maximum size when you're a teenager. Then, it starts to shrink slowly.

By the time you turn 75 years old, your thymus gland turns to fat. The term scientists use to describe this organ shrinking process is called involution. Doctors also know that severe stress can cause the thymus to shrink. In fact, during the early part of the 20th century, researchers didn't believe the thymus was larger in infants. When they did autopsies on babies who had died from conditions like diphtheria, it had shrunk. From the time you're conceived until you reach puberty, your thymus gland is very active.

It serves both the immune and endocrine systems. That's the system that makes hormones, the body's chemical messengers. To understand the thymus' immune system role, you need to know the difference between two kinds of white blood cells. They are the T lymphocytes T-cells and B lymphocytes B-cells.

These cells are like the immune system's "special ops" forces. T-cells are also known as thymus-derived lymphocytes. They help fight off the body's foreign invaders, such as bacteria, viruses, and toxins. They can also identify and attack cancer cells.

B lymphocytes, or B-cells, have a different role. They produce proteins called antibodies and use them to destroy specific invaders.

When the immune system's first responders and defenders need extra help, they call in the T-cells. They're made in the bone marrow, the spongy tissue within your bones. When T-cells are young or immature, they travel through the bloodstream and into the thymus gland. The thymus has two lobes. One houses a sort of "boot camp" training ground for T-cells. That's where they mature and turn into specialty disease-fighting cells with different jobs. T-cells in the thymus turn into three main immune system disease fighters:.

The part of the thymus called the cortex is where the T-cell boot camp training is held. Here, young T-cells learn to identify antigens or toxins linked to foreign cells and matter. This process is called "positive selection. Once the T-cells recognize specific pathogens, they travel to another part of the thymus gland called the medulla.

Here, they get a different kind of training, "negative selection. This prevents autoimmune disorders. These are medical conditions where things go wrong, and your cells attack your body tissues and cells instead of foreign invaders. Not all T-cells make it through this selection process. Next, the survivors get exposed to hormones produced by the thymus gland to complete their training.

Then they are released to do their job. These highly trained cells circulate in the bloodstream or wait in the lymph nodes until the immune system sounds an alarm.

Mature T-cells play some vital roles. T-cells are part of the body's adaptive immunity system. That's immunity your body develops after your immune system has been exposed to an infection, vaccine, or foreign substance. T-cells are trained to recognize and take out foreign threats that get past the body's first line of defense.

When killer cytotoxic T-cells recognize a foreign invader, they lock onto the cell and destroy it with the aid of helper and regulatory T-cells. This is what's known as cell-mediated immunity, or using immune cells to fight infections.

The process of negative selection occurs in the thymus. It is used to get rid of T-cells that have become overly reactive and have bound too strongly to other molecules.

The weed-out process clears T-cells that might attack the body's own tissues and cells. This prevents the development of autoimmune disorders. Scientists used to believe that aging was just the body wearing out. They now realize that aging is an active chemical process. Some scientists believe the shrinking of the thymus may be what triggers the aging process. As the thymus shrinks, your immunity decreases. That's why older people are more likely to get sick or get diseases like cancer.

They're also less likely to respond to vaccines. Studies are now looking at ways to delay the thymus shrinking, boost immunity, and slow the aging process. This line of research is very new. In one small study of nine healthy men, researchers used a growth hormone, steroids, and a diabetes drug to reboot the thymus. For over two years, they did blood and imaging tests of the men. They also measured their epigenetic ages. That's how old the body is based on biology.

The men were between 51 and 65 years old,. The researchers say after one year, the men had more T-cells and stronger immune systems. Based on biology, their bodies were also about 2. The thymus gland produces several hormones, including:. The thymus gland also makes small amounts of hormones produced in other areas of the body. These include melatonin, which helps you sleep, and insulin, which helps control your blood sugar.

Many conditions can affect the thymus gland, ranging from genetic disorders to cancers in older adults. It is located medially between the two cerebral hemispheres Fig 1 and is attached to the rear of the third ventricle by a small pineal stalk. However, there is much variation in shape, with many human pineal glands being pea-shaped or fusiform tapering at both ends Afroz et al, The average adult pineal gland is a tiny brown structure, typically mm long, that weighs around mg.

Unlike most other brain components, the pineal gland is found outside of the neuroprotective blood brain barrier Chlubek and Sikora, It increases in size throughout early childhood and becomes fully developed at around age 5 to 7 years Patel et al, Structurally, pinealocytes are believed to be related to the photosensitive rods and cones of the retina; although, in humans, they only have an indirect response to light, as detected at the retina, through a series of complex neural pathways Zhao et al, Pinealocytes take up the essential amino acid tryptophan, which is enzymatically converted into the neurotransmitter serotonin and then into melatonin Fig 2.

Melatonin secretion is governed by light levels perceived by the retina. Action potentials nerve impulses generated from retinal rods and cones are relayed to the visual cortex of the brain via the optic nerves. These cross over each other at the optic chiasm Fig 3 , above which is a specialised collection of around 10, neurons called the suprachiasmatic nucleus SCN. Neurons in the SCN have an inherent hour rhythm synchronised to cues in light intensity detected by the retina Challet, The major trigger for melatonin release is reduced light, with neural output from the SCN stimulating the pineal gland via sympathetic nerves originating in the superior cervical ganglion in the neck Fig 3.

This usually corresponds to the period of deepest sleep. As light gradually returns, levels decrease again, with secretion usually ceasing around 8am. Initially, melatonin is released into the densely arranged local blood vessels of the pineal gland and the cerebrospinal fluid of the third ventricle; it then enters the general circulation and is distributed systemically around the body Zisapel, It is also synthesised and released from a wide range of other human organs, tissues and cells, including the retina, bone marrow, lymphocytes, platelets, skin and gastrointestinal tract Tordjman et al, Melatonin circulates in the plasma and, like most hormones, exerts its effects by binding to specific receptors.

These are widespread throughout the human body; few tissues are thought to be devoid of melatonin receptors Emet et al, ; Omar and Saba, It has long been established that melatonin is an important regulator of sleep in diurnal species such as humans. Sleep, which accounts for around a third of our lives, is recognised as a highly orchestrated neurochemical process, involving both arousal and sleep-promoting regions of the brain that are influenced by a variety of chemical signals and cues Zisapel, It is essential to both physical and psychological health, and facilitates a significant reduction in external sensory input while simultaneously allowing unconscious:.

The exact mechanisms by which melatonin influences sleep remain unclear, but it is recognised that it reduces sleep latency time taken to fall asleep , while improving sleep quality and duration, and reducing fragmented sleep Grima et al, Insomnia , defined as a difficulty in falling or staying asleep, is estimated to affect around one in three people in the UK.

Melatonin has been shown to be a non-addictive substance of therapeutic value in treating patients experiencing insomnia. Exogenous melatonin prolongs sleep, improves sleep efficiency, enhances sleep quality and subsequently, when awake, improves functional performance and mental acuity Grima et al The blue light emitted from the screens of electronic devices such as TVs, computers and mobile phones is known to suppress melatonin biosynthesis and secretion.

Exposure to such displays for at least 30 minutes before sleep is associated with increased sleep latency, poor sleep quality, sleep disruption and increased daytime sleepiness Rafique et al, Reducing blue-light exposure, particularly in the evening before going to bed, has been demonstrated to improve sleep quality Shechter et al, and some devices have settings or apps to restrict the amount of blue light emitted.

Spectacles with blue-light filters are also available, which can effectively block the amount of blue light reaching the retina, thereby enhancing melatonin release Pateras, Melatonin is a powerful antioxidant, acting as an efficient scavenger of free radicals for example, superoxide anions that could, otherwise, inflict significant cellular damage and denature proteins and nucleic acids. This is of particular importance in the mitochondria, where cellular respiration can generate large quantities of free radicals capable of damaging mitochondrial DNA and potentially causing genetic mutation Cipolla-Neto and Amaral, The absence of a blood—brain barrier allows the pineal gland to freely accumulate minerals, such as calcium, and trace elements, including zinc, cobalt, fluoride and selenium Chlubek and Sikora, Eventually, these mineral aggregates enlarge to form pineal concretions up to 1mm in size; this usually leads to a gradual hardening as the pineal gland progressively becomes calcified with age Sergina et al Pineal calcification is readily visible on X-ray and is of use clinically as an anatomical landmark during various forms of brain imaging.

As calcification progresses, the volume of active pineal tissue decreases and the secretion of melatonin is reduced. This is thought to, at least partially, explain age-associated changes to sleep patterns such as poor-quality sleep and insomnia Song, Most are small and asymptomatic, and usually only discovered during brain imaging.

Cysts that reach larger sizes of between 7mm and 4cm may become symptomatic but, fortunately, are rare. Occasionally, large pineal cysts can weaken blood vessels, potentially resulting in sudden death through intracystic haemorrhage Gheban et al, The thymus is a small, delicate bilobed gland located below the manubrium upper portion of the sternum. It is usually pinkish grey and resides in the mediastinum space between the lungs resting on the superior portion of the heart Fig 4.

The gland is protected by a thin outer capsule and each lobe is composed of multiple lobules of around mm held together by loose connective tissue Nigam and Knight, The thymus is a primary lymphoid organ recognised as having both immune and endocrine functions. Its major immune role is to act as the site where T lymphocytes T cells mature before being released into the general circulation.

T cells play many diverse immune roles in specific immunity. Other populations of T cells include suppressor T cells, which dampen down immune responses, and cytoxic T cells, which target and destroy malignant and virally infected cells. Internally, each lobule of the thymus consists of multiple follicles, composed of a framework of epithelial cells and a population of T cells in varying states of maturation.

The thymus gland secretes a range of peptide hormones synthesised by the thymic epithelial cells, including thymulin, thymopoietin, thymic humoral factor and thymosin Rezzani et al, The exact mechanisms by which thymic hormones exert their effects remain poorly understood, but they are known to be essential to normal immune function because they facilitate development and maturation of T cells in the thymic follicles.

This ensures competent, functional T cells are released into the circulation where they can participate in effective immune responses. If you need to talk, we'll listen. Share experiences, ask questions and talk to people who understand.

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