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Lymphatic Organs and Tissues

A lymph node is a small bean-shaped organ in the lymphatic system that lies along a lymph vessel, usually in a group.
Lymph nodes
A lymph node is a small bean-shaped organ in the lymphatic system that lies along a lymph vessel, usually in a group. There are 8 to 10 nodes in the lymphatic system that drain the lymph before returning to the veins. Depending on their size, these nodes range from very small to large: smaller nodes are the size of a pinhead, while larger nodes are the size of an almond.

The outer shell of lymph nodes is made up of fibers that dip into the tissue inside, forming partitions, also known as trabeculae. There are several lymphocytes and macrophages present in the reticular and lymphatic tissue of the lymph nodes. Four or five lymph vessels may carry lymph into a node, whereas only one efferent vessel transports the lymph out of the node. An artery enters each lymph node via its hilum, and a vein and efferent lymph vessels exit it via its vein. Throughout the body, there are large numbers of lymph nodes arranged in groups deep and superficial. A lymphatic fluid travels between the deep and superficial cervical nodes in the head and neck.

Lymph from the upper limb passes through nodes located in the elbow region, then through nodes located in the axillae and the deep lymph nodes. A group of lymph nodes is located close to the esophagus and the chest wall, so lymph from the thoracic cavity drains into it. A large proportion of breast lymph passes through axillary nodes.
Functions – phagocytosis and filtering, the proliferation of lymphocytes.

Spleen
The spleen is the largest of the lymph organs and contains reticular and lymphatic tissue. Within the abdominal cavity, the spleen is situated between the stomach fundus and the diaphragm on the left hypochondrium. A purplish-colored blood vessel usually measures 12 cm long by 7 cm wide by 2.5 cm thick and can vary in size from person to person. It weighs around 200 grams.

There is a hilum on the lower medial border of the spleen, giving it a slightly oval shape. There is a peritoneum covering the anterior surface. The organ is encased in a fibroelastic capsule, which dips into it, creating the trabeculae. Between the trabeculae lies the splenic pulp, a cellular material that consists of lymphocytes and macrophages. In a red pulp, blood is found in large amounts, while in a white pulp, lymphatic tissue consists of cells that surround blood vessels with lymphocytes and macrophages.

In the spleen, there are four structures: splenic artery, coeliac artery branch, splenic vein, lymphatic vessel (efferent only), and nerve. Splenic pulp is closely associated with splenic sinusoids, and blood traveling through them flows through pores between the endothelial cells.

Spleen-associated organs
From superior to posterior – diaphragm
Colic flexion of the left side of the large intestine is at inferior
In the anterior view, the stomach's fundus
Left kidney and pancreas medially
Located behind the diaphragm between the intercostal muscles and the nine, ten, and eleventh ribs
Functions – phagocytosis, storage of blood, immune response, erythropoiesis.

Thymus gland
Located in the upper part of the mediastinum, near the base of the neck, thymus glands are situated behind the sternum. During the puberty years, when it begins to atrophy, it weighs between 10 and 15 grams. Its maximum weight is between 30 and 40 g at puberty, and it returns to approximately its birth weight by middle age.

There are two lobes connected by the areolar tissue of the thymus. Fibrous caps surround the lobes, which are divided into lobules by a branching structure composed of epithelial and lymphocyte cells.

Thymus-associated organs
The sternum and the upper four costal cartilages are found anteriorly
Located posteriorly: Aortic arch and its branches, brachiocephalic veins, trachea
Then laterally, the lungs
A structure at the root of the neck is at superior
Inferiorly - the heart
Functions - In the bone marrow, lymphocytes are derived from stem cells- Activated T-lymphocytes from inside the thymus.

T-lymphocytes produced by thymic processing are mature and can differentiate self from foreign tissue, as well as being able to recognize only one specific antigen out of the millions it will come in contact with. T-lymphocytes enter the bloodstream after leaving the thymus. The lymphocytes enter lymphoid tissue, while the rest circulate in the bloodstream. T-lymphocytes are produced from thymic stem cells throughout life, although T-lymphocyte production is most abundant during youth. Thymosin, a hormone secreted by epithelial cells that comprise the structure of the thymus gland, stimulates the maturation of the thymus and other lymphoid tissues. In early adolescence, the glands shrink, and with age, the immune system becomes less effective at fighting off foreign pathogens.

Mucosa Associated Lymphoid Tissue (MALT)
In strategic locations throughout the body, there are collections of lymphoid tissue that are not encased within a capsule like a spleen and a thymus. As a result of migration from bone marrow and the thymus, they contain B and T lymphocytes, which are essential in detecting invaders early on. Nevertheless, since they do not have afferent lymphatic vessels, they are not affected by lymph-sponsored diseases. It is also found throughout the gastrointestinal system, in the respiratory system, and in the genitourinary system, which means it is found throughout the exteriors of the body. MALT consists primarily of tonsils and aggregated lymphatic follicles (Peyer's patches).

Tonsils
Antigens swallowed and inhaled will be destroyed by these in the mouth and throat.

Aggregated lymphatic follicles
The small intestine contains large collections of lymphoid tissue, which intercepts swallowed antigens.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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