The Pineal & Thymus Glands

Brigitte Azzi, Alexandra Chevalier, & Melissa Cinquina

Pineal Gland: Physical

Characteristics•Small, pine-cone-shaped gland (hence its name)

•Reddish-gray in color

•It is larger in children, but shrinks with the onset of puberty

•In adults, it weighs a bit more than 0.1 grams and is about 0.8 cm long

•Situated between 2 cerebral hemispheres ; Attached to the posterior wall of the 3rd cerebral ventricle

•Suspended in a cavity of cerebrospinal fluid

•Lacks a blood-brain barrier, therefore, receives blood, oxygen, & nutrients through a rich vascular network

•Contains a large supply of adrenergic nerve fibers

•Composed of pinealocytes (endocrine cells with extensions that interact with the extensions of nearby cells) and supporting cells that resemble astrocytes

Pineal Gland: Chemical

Characteristics

Structural Formula of melatonin

•It contains a number of neuropeptides & neurotransmitters such as somatostatin,

norepinephrine, serotonin, and histamine.

•Somatostatin is a hormone that inhibits the secretion of several hormones, including growth hormone, insulin,

and gastrin.

•Norepinephrine is the main neurotransmitter that regulates its melatonin secreting activity.

•Serotonin is a neurotransmitter that helps maintain a "happy feeling," and seems to help keep our moods under control by helping with sleep, calming anxiety,

and relieving depression.

•Histamine is neurotransmitter that causes inflammation and several allergic symptoms.

•However, melatonin, a derivative of tryptophan, is the only hormone secreted by the gland.

•The chemical formula of melatonin is C13H16N2O2.

Pineal Gland: Molecular

Characteristics•It is developed from epithelial

tissue

•The soft tissue of the adult pineal gland contains more fluoride than

any other soft tissue in the body - a level of fluoride capable of

inhibiting enzymes.

•The pineal gland also contains hard tissue(hyroxyapatite crystals), which accumulates more fluoride than any other hard tissue in the

body (ex. teeth and bone)

•Studies show that fluoride reduces the levels of melatonin in the blood

Functions of the Pineal Gland The major function of the pineal gland is producing melatonin, a

hormone that has several important effects on the body.

Melatonin regulates daily body rhythms, most importantly circadian rhythm, the wake/sleep cycle. We feel sleepy at night because darkness stimulates the pineal gland to produce melatonin and we feel alert during the day because light inhibits the pineal gland from producing melatonin. Since the activity of the pineal gland depends on the amount of available energy, it is a photosensitive organ.

The abundant levels of melatonin in children inhibit the secretion of gonadotropins, hormones that regulate normal growth, sexual development, and reproductive functions, before puberty. Therefore, they prevent the onset of puberty before the appropriate age. 

Functions of the Pineal Gland cont’d

Melatonin levels are low in children with autism, and as a result, about 70% of them suffer from sleeping problems.

Studies show that low doses of melatonin can help children with autism sleep better without giving them any noticeable side effects.

Studies show that melatonin levels may be related to the risk of certain types of cancer.

Melatonin levels tend to be lower in women with breast cancer than in those without the disease.

Laboratory experiments show that low levels of melatonin stimulate the growth of certain types of breast cancer cells. However, adding melatonin to these cells slows their growth.

New research also suggests that melatonin may strengthen the effects of some chemotherapy drugs used to treat breast cancer.

In one study, several women with breast cancer were given melatonin 7 days before beginning chemotherapy. The melatonin prevented the lowering of platelets in the blood, a common complication that can cause bleeding.

Functions of the Pineal Gland cont’d In another study, several women with breast cancer were taking tamoxifen, but were not

improving. However, once melatonin was added, the tumors in over 28% of the women modestly shrank.

Studies also show that melatonin levels are lower in men with prostate cancer than in those without the disease.

In test tube studies, melatonin blocks the growth of prostate cancer cells.

In one small-scale study, melatonin, along with improved regular medical treatment, improved survival rates in 9 out of 14 men with metastatic prostate cancer.  

Melatonin has been found to be able to slow the aging process.

It is a powerful antioxidant that can easily pass through cell membranes and the blood-brain barrier.

It is a highly effective and direct scavenger of the very reactive and toxic free radicals.

Unlike other antioxidants, melatonin does not undergo redox cycling. Once it is oxidized it can never be reduced to its former state. Therefore, it never promotes free radical formation.

By terminally disarming the free radicals, melatonin protects the cells’ DNA from oxidation damage.

Pineal Gland: Interactions with Other Organs

Secretion of melatonin by the pineal gland inhibits the secretion of

the Gonadotropin-releasing hormone (GnRH) by the

hypothalamus.

Secretion of melatonin also indirectly inhibits the pituitary from

secreting gonadotropins, Leutenizing Hormone (LH) and Follicle

Stimulating Hormone (FSH), because the secretion of GnRH is

necessary for this to occur.

Because its secretion reduces the levels of LH in the blood,

melatonin may inhibit ovulation in women and can decrease

sperm mobility and sex drive in men.

The pineal gland also interacts with the hypothalamus in

regulating the circadian rhythm. 

Pineal Gland: Diseases & Disorders

One sleep disorder is Delayed Circadian Rhythm Disorder. DCR constitutes a mismatch between you external and internal clocks. Your internal clock runs slower than a normal circadian rhythm which is a 24-hour period so your body doesn't 'wake up' until later in the morning or day.

When this occurs in the body, the pineal gland releases the nighttime hormone, melatonin, too late, often causing you to fall asleep later. When its time to wake up, your body clock believes it’s only midnight and is still producing the nighttime hormones.

As a result of this disorder a person may experience the following symptoms:

Difficulty falling and staying asleep, and or late night insomnia.

A general lack of energy in the morning.

An increase of energy/mood in the evening or late at night.

Difficulty concentrating, being alert, or accomplishing tasks

Some DCR sufferers oversleep and have trouble getting up

Treatment:

Dawn Simulation helps people maintain a steady circadian rhythm by exposing their internal body clocks to a properly timed signal of light through their retina. The light gradually becomes brighter, simulating a sunrise, to reset the body clock while not to bright to cause premature awakening.

Diseases & Disorders cont’d

Advanced Circadian Rhythm Disorder (ACR) is the opposite of DCR. With ACR, your internal body clock is running faster than a normal circadian rhythm. You tend to run out of energy before their day is up. ACR compresses the sleep portion of your daily cycle, causing you to lose valuable sleep. ACR sufferers often sleep less than 8 hours per night, and awaken early.

Because your circadian rhythm is running fast, your pineal gland releases melatonin too soon, causing lethargy earlier in the day. Then, because melatonin is released prematurely, you are unable to maintain a complete sleep cycle, and you wake up too early.

As a result of this disorder a person may experience the following symptoms:

Early morning awakening and/or early morning Insomnia

Inconsistent sleep with one or more awake periods during the night

Lack of energy during the day, feeling tired in the early afternoon and/or evening

Alertness and ability to function may also be diminished

Some ACR sufferers may not notice a sleep problem but lose energy and feel tired or down in the afternoon or evening time.

Treatment:

Specialized bright light is the only effective treatment for ACR. Bright light will inhibit the release of melatonin for about 3 hours. Use bright light in the late afternoon and evening and avoid bright morning light before 9:00 am. Where sunglasses if you need to be exposed to bright light early in the morning and make your night time as dark as possible.

Diseases & Disorders cont’d

Precocious Puberty: An unusually early onset of puberty beginning before age 8 for girls and before age 9 for boys.

If left untreated, children will become able to reproduce and will stop growing too soon.

One of the causes for precocious puberty is having lower than normal levels of melatonin. This is a problem because melatonin is responsible for inhibiting the actions of the gonadotropins.

Symptoms for girls are breast growth and a first menstruation

Symptoms for boys enlarged testicles and penis, facial hair, and a deepening of the voice

Symptoms for boys AND girls are pubic or underarm hair, rapid growth, acne, and adult body odor

If the children’s precocious puberty is caused by abnormally low melatonin levels, melatonin supplements can be a very successful form of treatment.

Treatment is very important because precocious puberty will prevent children from reaching their full height because they stop growing too early.

Going through puberty before anyone their age can also have negative psychological effects on children, including low self-esteem and depression.

Thymus Gland: Physical Characteristics

•Pinkish-gray color in children and yellow in adults

•Soft

•About 5 cm long at birth

•Continuously grows during childhood

•Begins to steadily atrophy after puberty until it is ultimately replaced by adipose tissue

•Largest and most active in children

•Weighs between 20 and 37 grams, its maximum weight, by puberty

•Made up of two identical lateral lobes

•Each lobe is composed of lobules that are held together by delicate areolar tissue, and the thymus as a whole is

enclosed in a protective capsule

•The two lobes are slightly different in size and can be joined together or separated

•Located in the thoracic cavity, just below the neck and behind the sternum

•Divided into two parts, the outer cortex and inner medulla.

Thymus Gland: Molecular

Characteristics

Made up of mucosa-associated lymphoid tissue

Lymphoid tissue mostly consists of lymphocytes, but it is also rich in macrophages and reticular cells

The thymus is enclosed by a thin connective tissue capsule

Each lobule consists of medullary tissue with numerous lateral extensions, each of which is covered by a layer of cortical tissue

Between lobules are connective tissue septa, extensions of the capsule containing arterioles and veins.

With age, there is a heavy accumulation of fat associated with the connective tissue

Functions of the Thymus Gland

The thymus produces and processes a white blood cell called a T-lymphocyte. These T cells help cells recognize and destroy invading bacteria, viruses, abnormal cell growth, and foreign tissue.

The T cells travel from the bone marrow to the thymus gland where they remain until they are activated. After they mature, the T cells enter the blood stream and travel to other lymphatic organs to act as a defense mechanism against diseases.

The thymus gland produces thymosin, a hormone that stimulates T cells in other lymphatic organs to mature. It also produces thymopoietin, another hormone which is protein present in the mRNA and is encoded by the TMPO gene.

The thymus gland has a reputation for becoming underactive which may lead to the development of immunodeficiency diseases.

Thymosin also plays a role in the initiation of the aging process.

Thymus Gland: Interactions with Other Organs

This gland is responsible for development of the lymphatic system, which plays a major role in the immune and waste removal systems.

If the thymus’s development is hindered in any way in the fetus, the whole of the immune system cannot develop.

The thymus also contributes to the immune system by producing and processing T Lymphocytes (see functions for T Cells’ duty)

Thymus Gland: Diseases & Disorders Thymus Cancer

Thymus cancer develops when malignant cancer cells form on the outer surface of the thymus gland. There are primarily two kinds of cancer that can arise in the thymus.

The first type involves a thymoma, a tumor whose cancerous cells look like normal thymus tissue. Thymomas are linked to autoimmune

diseases which cause the immune system to attack healthy tissue.

The second sort of thymus cancer includes thymic carcinomas, tumors which contain cells that do not look like thymus cells. Thymic carcinomas are exceptionally

dangerous because they grow more quickly and will more probably extend to other tissues.

Both thymomas and thymic carcinomas can be present in an individual without triggering any symptoms and may only be found in a routine chest x-ray. But when symptoms do occur, it is most commonly in the form of a continuing cough, chest pain, and trouble breathing.

Diseases & Disorders cont’d

DiGeorge Syndrome (Thymic Dysplasia)

DiGeorge syndrome is a rare congenital defect that causes dysfunction of a number of different tissues.

Patients with DiGeorge syndrome have a small deletion on their 22nd chromosome, known as 22q11.2, which contains between 20 and 30 genes responsible for the development of different parts of the body.

Often, in DiGeorge syndrome, a symptom is having a very small or absent thymus gland.

As a result of having DiGeorge syndrome, patients will have very weak immune systems and are extremely prone to infections.

Patients may need to receive a thymus transplant or receive infusions of immune cells to help prevent dangerous infections.

Diseases & Disorders cont’d

Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal muscles

Myasthenia gravis is caused by a transmission malfunction of nerve impulses to the muscles.

In myasthenia gravis, antibodies produced by the body’s own immune system obstruct, change, or destroy the receptors for acetylcholine at the neuromuscular junction, which inhibits the muscle from contracting.

In adults with myasthenia gravis, the thymus gland remains large and is abnormal. It contains certain clusters of immune cells indicative of lymphoid hyperplasia—a condition usually found only in the spleen and lymph nodes during an active immune response. Some may develop thymomas which are generally benign, but can become malignant.

The relationship between the thymus gland and myasthenia gravis is not yet fully understood. Scientists believe the thymus gland may give incorrect instructions to developing immune cells, ultimately resulting in autoimmunity and the production of the acetylcholine receptor antibodies, thereby setting the stage for the attack on neuromuscular transmission.

Thymectomy, the surgical removal of the thymus gland, reduces symptoms in some individuals without thymoma and may cure some people, possibly by re-balancing the immune system.

Most common in women under 40 and men over 60.

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