What Is the Function of Lymphatics?
Immunity is the defense mechanism of the body, that is the ability of the body to resist damage from foreign substances such as microorganisms and harmful toxins. The defense mechanism of the body includes phagocytosis (nonspecific engulfing process), and immune response (specific reaction to microorganisms and antigens).
The cell type involved in the immune response is lymphocytes. The lymphocytes are smaller than monocytes and have large nuclei. The lymphocytes circulate in the blood and are present in large numbers in lymphatic organs and tissues. They develop from pluripotent stem cells in the red bone marrow and then travel in the blood to lymphoid tissues elsewhere in the body where they are activated, which means they are able to respond to antigens (for example- bacteria, viruses, etc.). The two distinct types of lymphocytes include the T-lymphocytes that are produced in the thymus gland (providing cell-mediated immunity) and the B-lymphocytes that are processed in bone marrow (these cells provide antibody-mediated immunity).
Cell-Mediated Immunity: When the antigen comes in contact with these T-lymphocytes, it stimulates the division and proliferation of the T-lymphocytes, leading to the production of three main types of specialized T-lymphocytes:
- Cytotoxic T-lymphocytes bind to the antigen and destroy it.
- Helper T-lymphocytes release cytokines to support cytotoxic T-lymphocytes.
- Memory T-lymphocytes are long-lived and provide immunity against the antigen
Antibody-Mediated (Humoral) Immunity: The B-lymphocytes, unlike T-lymphocytes, which are free to circulate around the body are fixed with lymphoid tissue. When B-lymphocytes come in contact with an antigen, they enlarge and begin to divide. It produces two functionally distinct types of cells:
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Plasma cells produce and release antibodies (immunoglobulins - IgG, IgA, IgM, IgE, and IgD) that bind to the antigen and destroy it.
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Memory B-lymphocytes function the same as memory T-lymphocytes.
How Is the Lymphatic Drainage of the Head and Neck?
Lymph nodes in the head and neck are arranged in two horizontal rings and two vertical chains on either side. The outer (superficial) ring consists of the occipital, preauricular (parotid), submandibular and submental nodes. The inner (deep) ring is contributed by MALT (mucosa-associated lymphoid tissue) located primarily in the nasopharynx and oropharynx (Waldeyer's ring).
The vertical chain consists of superior and inferior groups of nodes related to the carotid sheath. All lymph vessels of the head and neck drain into the deep cervical nodes, either directly from the tissues or indirectly via nodes in outlying groups. Lymph reaches the systemic venous circulation via the right lymphatic duct or the thoracic duct.
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Superficial Cervical Lymph Nodes lie along the external jugular vein in the posterior triangle and along the anterior jugular vein in the anterior triangle. Lymphatics from the face, scalp, and ear drain into the occipital, retro auricular, parotid, buccal, submandibular, submental, and superficial cervical nodes, which themselves drain into the deep cervical nodes (including the jugulodigastric and jugulo-omohyoid nodes). They drain into the deep cervical nodes.
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Deep Cervical Lymph Nodes are divided into two groups: Superior and inferior. Superior deep cervical nodes lie along the internal jugular vein in the carotid triangle of the neck. They receive afferent lymphatics from the back of the head and neck, tongue, palate, nasal cavity, larynx, pharynx, trachea, thyroid gland, and esophagus. The efferent vessels join those of the inferior deep cervical nodes to form the jugular trunk, which empties into the thoracic duct on the left and into the junction of the internal jugular and subclavian veins on the right. Inferior deep cervical nodes lie on the internal jugular vein near the subclavian vein. They receive afferent lymphatics from the anterior jugular, transverse cervical, and apical axillary nodes.
What Is the Epithelio Lymphoid System of the Head and Neck?
It consists of mucosa walls of alimentary, respiratory, and genitourinary tracts. It consists of a large amount of unencapsulated lymphatic tissue that exists collectively and it is termed mucosa-associated lymphoid tissue (MALT). The mucosa-associated lymphoid tissue is generally subdivided into two types:
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Gut-associated lymphoid tissue (GALT).
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Bronchus-associated lymphoid tissue (BALT).
The important collections or aggregations of mucosa-associated lymphoid tissue in the pharyngeal region are as follows:
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Pharyngeal Tonsil is the aggregation of lymphoid tissue underneath the mucous lining of the roof and posterior wall of the pharynx. When enlarged due to infection, it is termed an adenoid that obstructs nasal respiration and makes breathing through the mouth obligatory.
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Tubal Tonsil is the aggregation of lymphoid tissue around the upper and posterior margin of the opening of the pharyngotympanic tube in the nasopharynx.
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Palatine Tonsil is a large aggregation of lymphoid tissue, one on each side, in the lateral wall of the oropharynx in the triangular fossa called the tonsillar fossa. They are commonly infected in children causing tonsillitis.
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Lingual Tonsil - The dorsal surface of the posterior one-third of the tongue (pharyngeal part) contains numerous lymphoid follicles underneath the mucosa, which together form the lingual tonsil.
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Peyer's Patches are aggregated lymphoid follicles varying from 2 to 10 cm in length, underneath the mucous membrane of the small intestine, being the largest and most numerous in the ilium and placed lengthwise along the anti mesenteric border. The Peyer's patches are ulcerated in typhoid fever forming ulcers (typhoid ulcers) having the long axis perpendicular to the long axis of the bowel.
Conclusion:
To conclude thus the human lymphatic and epithelio lymphoid systems are major contributors to the overall immunity of the individual, especially in the head and neck regions both through cell-mediated and humoral defense mechanisms. Apart from their innate cell ability, they also filter lymph and protect the immune system from the spread of potential microorganisms and interstitial fluid toxins.
