Introduction
Pineal gland (or conarium. epiphysis cerebri, pineal organ, or pineal body) is found in vertebrates and releases melatonin. It is a tryptophan-derived hormone that regulates the circadian rhythm (the 24-hour cycle of biological activities associated with natural cerebrospinal fluid periods of light and darkness).
Structure
Pineal gland is located in a small (8mm long), pinecone-shaped mass of glandular tissue. It is found attached to the brain along the body's midline at the union of the superior colliculi of the midbrain and then replaced by fat thalamus lobes. The base of pineal gland tapers to a point on extending posteriorly from the brain.
Histologically, pineal gland resembles the nervous tissue and is made up of astrocytes and pinacocytes surrounded by pia mater (inner layer of the meninges covering the brain and spinal cord). Pia mater is a thin layer of fibrous connective tissue and is richly supplied with blood vessels which support the underlying tissues.
Astrocytes, a type of neuroglial cells found in the CNS, usually support and protect the I neurons; but in pineal gland they support the pinacocytes. Melatonin is synthesized and released by pinacocytes (unique secretory cells) which occur only in the pineal gland.
Hormone
Melatonin is a tryptophan-derived hormone which plays a very important role in the regulation of a 24-hour (diurnal) rhythm or circadian rhythm of the body. For example, it helps in maintaining the normal rhythms of sleep-wake cycle and body temperature. In addition, melatonin also influences metabolism, skin pigmentation, menstrual cycle, as well as the defined ability of an individual.
Functions
1) Melatonin controls melanin development and concentration in melanocytes of the skin, thus lightening the skin color.
2) Circadian rhythm is a 24-hour biological cycle characterized by sleep-wake patterns. Daylight and darkness help direct the circadian rhythm. Melanin is not released on exposure to light; thus, the circadian rhythms are controlled. During the daytime, melatonin is released in low levels; while it is released in high amounts during the night. This has some influence over the reaction of photoperiod (the length of day versus night).
3) It inhibits the anterior pituitary gland to release gonadotropins (LH and FSH).
Functions
The most essential functions of pineal gland are:
1) It secretes melatonin, which causes sleepiness and regulates certain endocrine functions.
2) It also allows the body to convert the signals from the nervous system to signals in the endocrine system.
3) It regulates the levels of female hormones, and affects their fertility and menstrual cycle.
Introduction
Thymus gland is a small, pinkish-grey coloured, lobular structure located in the mediastinum of the thoracic cavity. It is responsible for maturation of lymphocytes, thus plays a major role in the development of the immune system. The activity of thymus is highest during puberty and decreases as age increases, thus resulting in a decreased production of hormones. This is the reason why the immune responses of older individuals become weak.
Structure
Thymus is a two-lobed gland lying on top of the heart and extending up along the trachea. This triangular-shaped gland has two opaque and pink-coloured lobes enclosed within a fibrous exterior. The outer layer of thymus is the cortex, and the layer within is the medulla.
Thymus gland is made up of lymphocytes (WBCs) and reticular cells. The latter form a loose meshwork (as in a lymph node) and the spaces between them are packed with the former cells. The cortex having large concentrations of lymphocytes forms the site of lymphocytic proliferation occurring throughout the cortex, instead of in germinal centers (as in other lymphoid tissue). T (thymus-derived) cells are the daughter produced in the cortex. These cells reach the medulla and enter the blood circulation medullary veins, adding to the lymphocytes seen in the peripheral blood and lymphoid organs.
Hormone
This gland secretes the peptide hormones called thymosin.
Functions
Thymosin’s play a major role in the differentiation and maturation of T-lymphocytes, which provide cell-mediated immunity. Thymosin also promotes the production of antibodies to provide humoral immunity, and participate in immune reactions.
Functions
Thymus gland mainly produces cells that migrate to the organs and defend them by producing antibodies. Some other functions of thymus gland are:
1) Produce and Process T-Cells: It produces T-cells or lymphocytes to boost up the immune system. These cells after maturity move to the lymph nodes and They produce antibodies that fight against bacteria, viruses, and other pathogens.
2) Secrete Thymopoietin: It also produces thymopoietin hormone, which is a protein found in messenger RNA (mRNA). Simultaneously, it produces thymosin hormone which stimulates the lymphocytes and other lymphatic organs.
3) Prevent Anomalous Cell growth: It prevents irregular cell growth that may form tumors, and cause malignancy and cancer. The T-cells from the bone marrow migrate to the thymus gland for becoming active. After they mature, they enter the bloodstream and then the lymphatic organs to strengthen the Défense mechanisms.
Classification of Hormones
On the basis of chemical composition, hormones are categorised into lipid-soluble and water-soluble hormones. This classification also describes the hormone function since both the classes exert their effects differently:
1) Lipid-Soluble Hormones: These include:
i) Steroid Hormones: These hormones are synthesized from cholesterol. They are unique individually as different chemical groups are attached at different sites on the four rings present in the core of their structure. Such minor differences result in varied functions.
ii) Thyroid Hormones: The TB and T4 are the seat of the soul the two thyroid hormones with iodine linked to location deep tyrosine amino acid. The benzene ring of tyrosine along with the iodine’s attached increases the lipid solubility of T3 and T4 hormones.
iii) Nitric Oxide (NO): Nitric oxide synthase enzyme aids in the synthesis of NO. This gas behaves like a hormone as well as a neurotransmitter.
2) Water-Soluble Hormones: These include:
i) Amine Hormones: These hormones are produced upon decarboxylation
(removal of C02 molecule) or modification of certain amino acids. The term amine is associated with these hormones because they carry an amino group (—NHO. For example, some catecholamines (e.g., epinephelinae, norepinephrine, and dopamine) sleep disorders are obtained through modification of tyrosine amino acid; histamine hormone melatonin results from mast cells and platelets by the action of histidine amino acid; serotonin and melatonin are obtained from tryptophan amino acid.
ii) Peptide Hormones: These hormones are amino acid polyenes. The smaller peptide hormones are made up of 3-49 amino acid chains, whereas the larger ones contain 50-200 amino acid chains. Antidiuretic hormone and oxytocin are the examples of peptide hormones.
iii) Protein Hormones: These hormones are termed glycoprotein hormones since thyroid stimulating hormone of melatonin secretion this category contains carbohydrate groups. small gland Other examples of protein hormones are human growth hormone and insulin.
iv) Eicosanoid Hormones: Arachidonic acid (a 2()-carbon fatty acid) acts as a precursor for these hormones. They act as circulating and local hormones. Prostaglandins and small endocrine gland leukotrienes are the two major types of eicosanoids
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