Pineal Gland

What is the Pineal gland?

The pineal gland is an endocrine gland located in the epithalamus, near the center of the human brain. As it is one of the endocrine glands it secretes its product, the hormone called melatonin, directly into the blood. Sleep patterns are considered to be modulated by this hormone as its production is stimulated by the absence of light. The pineal gland has also other functions in the central nervous system but these will be discussed more about later in this text.

Its name, the pineal gland owes to the shape it has. It is the shape which resembles a pine cone and some other names that are used to refer to this part of the human anatomy are the pineal body, conarium and the epiphysis cerebri.

The pineal gland is a shared feature between most vertebrates with the exception of few and it has been a subject of both scientific and pseudoscientific research for a long time. As a subject of the scientific research, the pineal gland, remains not completely understood even in the twenty first century. In pseudoscience it has been a subject of great interest for many centuries. Supernatural characteristics have been attributed to the pineal gland in many cultures. It has been considered to be a type of a “third eye” or a sort of a connection between the physical and the spiritual domain. The central position it takes inside the brain has, before its physical functions have been discovered, always been a cause for the pineal gland to be considered a mystical part of the body connected with psychic and supernatural powers.

pineal gland

Picture 1: Pineal gland diagram

Where is Pineal gland located?

The pineal gland is located in the thalamus, at the central part of the brain, between the two hemispheres. More specifically, the pineal gland is located behind the third ventricle and the habenular commissure (Nerve fiber bands which connect the diencephalon sides with the habenular nuclei. The principal regulator of the neurotransmitter of the central nervous system). It is inserted deep into the brain and inside a trench located between the two halves of the thalamus.

Structure of Pineal gland

The characteristic shape of the pineal gland has already been mentioned previously in this text and it was said that it resembles a pine cone in appearance. This pine cone-like structure is approximately five to eight millimeters in diameter which, size wise, makes it a small endocrine gland. This glandular tissue structure is coated with cerebrospinal fluid which is provided by the third ventricle through the pineal recess.

structure of pineal gland

Picture 2: Structure and Location of Pineal gland

The structure of the pineal gland is very similar to the structure of the rest of the nervous system. Its body is mostly formed by a type of soft tissue called parenchyma containing pinealocytes, the pineal gland cells, embedded in its structure. On all sides, it is covered by the connective tissue and the pia mater layer which is encapsulating the body of the pineal gland5. The pinocyte or the pineal parenchymal cell is categorized as a specialized neuron and it is surrounded by four other different cells in this small structure:

  • Peptidergic neuron-like cells
  • Perivascular phagocyte
  • Interstitial cells
  • Pinealocytes

The pinealocytes are the most common of all the cells found in the structure of the pineal gland. The scientists involved in doing research in this field, believe that this type of cells might have been formed or derived from photoreceptor cells due to their characteristic behavior in the process of the production of melatonin as well as this action being highly dependent of the circadian rhythm.

The pineal gland has a profuse and very developed blood flow which is supplied by choroidal branches of the posterior cerebral artery.

This endocrine gland is innervated by both the sympathetic and parasympathetic nervous systems. The sympathetic innervation is supplied by the superior cervical ganglion and the parasympathetic innervation is supplied through the otic and pterygopalatine ganglia. Nerve fibers which contain Pituitary adenylate cyclase-activating polypeptide, most commonly known as PACAP, are stretching from the trigeminal ganglion and are also innervating the pineal gland.

Function

The pineal gland’s main function is the production of its hormone called melatonin. The production of this hormone is stimulated by changes in the illumination levels, more specifically, it is inhibited by low light levels or darkness. This role of the pineal gland is very important for establishing the so called day-night cycle which is one of the most important cycles when it comes to the functioning of the human brain and body as a whole. This function of melatonin production is by far the most significant function of the pineal gland although the complete influence of this hormone, on the processes developing inside the human body, has not yet been fully understood.

Some studies performed on rodents have given results implying that the pineal gland can affect the secretion of the sex hormones (Follicle-stimulating hormone (FSH) and the Luteinizing hormone (LH)) and that it can affect the actions of drugs such as antidepressants and cocaine through the protective role its hormone melatonin has in reversing the neurodegeneration process.

The complete range of functions which can be attributed to the pineal gland is still very much a matter of more scientific research and debate and it will probably remain like that for some time in the future.

Clinical significance

A condition which is typically affecting the pineal gland is the calcification. This is a process which is thought to be very much connected with the so called “brain sand” or the corpora arenacea collecting inside the pineal gland, and it can easily be observed through the brain X-ray10. It is a condition which develops progressively with aging but it can also affect children as young as two years.

Some studies have also shown a connection between the calcification and Alzheimer’s disease, with the higher level of calcification of the pineal gland being present in patients suffering from Alzheimer’s than in those affected by other types of dementia. High levels of calcification in children have been connected with a more rapid development of bones and reproductive organs. Migraines have also been associated with the pineal gland calcification.

Another relatively common imagenological finding related with the pineal gland are the cysts, as they can be present in up to 10% of patients that need an MRI or the CT scan examination for another cause. The presence of cysts in the pineal gland can be completely asymptomatic, in rare cases there are some symptoms that can be explained by the effect of the mass or the size of the cyst and this is the reason why the symptoms vary depending on the severity of the condition. These symptoms usually are:

  • Headache
  • Migraine
  • Parinaud syndrome (impossibility of moving the eyes in the up direction)
  • Problem with the movement of the eyes.
  • Vertigo
  • Difficulties for moving
  • Disrupted sleep pattern
  • Secondary parkinsonism
  • Epilepsy

The eye related symptoms that might be present concomitant with cysts in the pineal gland appear due to the compression of the optical nerve which passes by just underneath the pineal gland. If the cysts press or move an active area of the brain or interrupt the appropriate hormonal secretion, the presentation of the symptoms will be in accordance with the function of the affected brain area.

The presence of cysts in the pineal gland does not entirely depend of age or gender but scientists consider that the cysts are most commonly found in adults around their forties. As it was mentioned before, the cysts may be an “accidental finding” but it is important to consider the possibility of this condition being present when faced with some of the symptoms mentioned above. The treatment of patients with the progressive enlargement of the cysts, hydrocephalus and severe neurological symptoms is usually surgical. The procedure can be performed by using a method of neuroendoscopy (guided video surgery), open surgery or stereotaxy (minimally invasive surgery).

The abnormality in the production or secretion of melatonin is related with different disorders in the human body. Lifestyle, diet and stress may lead to an insufficiency in the production of hormones as melatonin and serotonin. Decreased levels of melatonin have been associated with psychotic depression and peptic ulcers.

Another disorder related with the pineal gland is the alteration in the sleeping pattern known as insomnia. The treatment is basically the identification of the underlying precursor of the condition.

Anxiety is not a completely understood condition. Scientists have identified a variety of risk factors related with anxiety such as lifestyle, stress, diet, environmental conditions as well as some anatomical and/or functional changes in the brain. The treatment of anxiety is multidisciplinary, anxiolytics (anti-anxiety medication) and antidepressant are very important parts of the therapy for this condition but also a complete approach with psychotherapy sessions included is of a great importance. Some studies have shown the persistence of decreased levels of melatonin in patients with anxiety. This is the reason why treatments including lifestyle change as well as a diet rich in tryptophan (amino acid needed for the production of melatonin) is required in these patients. Some foods rich in tryptophan are:

  • Chicken
  • Turkey
  • Almond
  • Sweetcorn
  • Peanuts

Some other conditions related with low levels of melatonin are: Schizophrenia, Bipolar syndrome, dementia, Alzheimer’s and breast cancer.

Although the function of the pineal gland is not completely understood yet, its relevance and the role it has in different conditions and processes developing inside the human body is well noted.