Human Anatomy - Kotsan I. Y. 2009

Organs of Hematopoiesis and the Immune System
Lymphoid tissue in the walls of the digestive and respiratory systems
Tonsils

Tonsils (tonsillae) are accumulations of diffuse lymphoid tissue containing smaller, denser cellular masses known as lymphoid nodules (follicles). They are arranged in a circular formation around the initial sections of the respiratory and digestive tracts. This is the primary site where The Immune System encounters foreign substances and Cells entering the body via food, Water, and air. Due to the anatomist who first described it, this lymphoid ring is commonly referred to as Waldeyer's ring (or the Pirogov-Waldeyer ring).

There are two paired tonsils (palatine and tubal) and two unpaired tonsils (lingual and pharyngeal).

The palatine tonsil (tonsilla palatina) is a paired, almond-shaped Structure that is oval and slightly flattened laterally. It is located within the tonsillar fossa (fossa tonsillaris) between the palatoglossal and palatopharyngeal arches. The dimensions of the tonsil are: vertical 1.5–3.0 cm, sagittal 1.5–2.0 cm, and frontal 1.2–2.0 cm. A layer of loose Connective Tissue lies between the lateral surface of the tonsil and the superior pharyngeal constrictor Muscle, to which the tonsil is adjacent. The lateral surface of the tonsil is covered by a thin tonsillar capsule (capsula tonsillaris), which is part of the buccopharyngeal fascia. Trabeculae (connective tissue septa) extend medially from the capsule into the lymphoid tissue of the organ, dividing the tonsil into lobules when well-developed. Dense, rounded accumulations of lymphoid tissue—the lymphoid nodules of the tonsil—are located within the organ. They are most numerous in children and adolescents (aged 2 to 16 years). The lymphoid nodules are rounded and vary in size from 0.1 mm to 1.2 mm. The largest lymphoid nodules feature germinal centers. Diffuse lymphoid tissue surrounds the nodules. The reticular stroma of the organ consists of reticular cells and fibers forming a meshwork that houses lymphocytes (up to 90–95%), plasma cells, immature lymphoid cells, macrophages, and granulocytes.

On the medial free surface of the palatine tonsil, 10–20 shallow tonsillar pits (fossulae tonsillae) are visible, into which the tonsillar crypts (cryptae tonsillares)—invaginations of the mucous membrane—open. Some crypts take the form of simple tubules, while others branch deep within the tonsil. The lumen width of individual crypts ranges from 0.8 to 1.0 mm. The mucous membrane is covered with non-keratinized stratified squamous epithelium infiltrated by lymphocytes. During swallowing, the tonsils are slightly compressed, clearing the crypts of desquamated epithelium, foreign particles, Bacteria, lymphocytes, and macrophages. If the body's immune defenses are weakened and a sufficiently virulent strain of microorganisms enters the crypts, a local infection develops, leading to the accumulation of pus within the crypts, their blockage, and inflammation of the tonsils (tonsillitis).

The palatine tonsil receives its Blood supply from Branches of the ascending pharyngeal, facial, and lingual Arteries. Venous blood drains via 3–4 tonsillar Veins into the VEINS OF THE pterygoid plexus. Lymphatic vessels, originating from intra-organ capillaries (including those surrounding the lymphoid nodules), drain into the lateral deep cervical Lymph Nodes.

Innervation of the palatine tonsil is provided by fibers of the greater palatine nerve (from the pterygopalatine ganglion), the tonsillar branch of the Glossopharyngeal nerve, and sympathetic fibers from the internal carotid plexus.

The tubal tonsil (tonsilla tubaria) is a paired structure located in the area of the torus tubarius, which bounds the pharyngeal opening of the auditory tube posteriorly. The tonsil is an accumulation of lymphoid tissue within the thickness of the mucous membrane, containing Solitary lymphoid nodules. The mucous membrane is covered with non-keratinized stratified squamous epithelium.

The tubal tonsil begins to develop during the 7th to 8th month of fetal life within the mucous membrane surrounding the pharyngeal opening of the auditory tube. Initially, discrete clusters of future lymphoid tissue appear, from which the tubal tonsil subsequently forms. In newborns, the tonsil is already quite well-developed (measuring 7–7.5 mm in length). Lymphoid nodules and their germinal centers emerge during the child's first year of life. The tubal tonsil reaches its peak development between 4 and 7 years of age. Age-related involution of the tonsils begins during adolescence and youth.

The tubal tonsil is supplied with blood from branches of the ascending pharyngeal artery. Venous blood from the tonsil drains into the veins of the pharyngeal plexus. Nerve fibers reach the tonsil as part of the branches of the facial, glossopharyngeal, and vagus nerves, as well as from periarterial sympathetic plexuses.

The lingual tonsil (tonsilla lingualis) is an unpaired structure lying beneath the stratified squamous epithelium of the mucous membrane at the ROOT of the Tongue, typically forming two accumulations of lymphoid tissue. The boundary between these clusters On the surface of the tongue is the sagittally oriented median sulcus of the tongue, and deep within the organ, it is the septum of the tongue. The lingual tonsil consists of lymphoid nodules, numbering 80–90, which are most numerous in children, adolescents, and young adults. The nodules protrude slightly above The surface of the tongue as rounded elevations. Small depressions, or crypts, are located between these elevations. The excretory ducts of mucous glands open into the crypts. The walls of the crypts are formed by stratified squamous epithelium infiltrated by lymphocytes.

The lingual tonsil begins to form in the fetus during the 6th to 7th month of development as scattered diffuse accumulations of lymphoid tissue in the lateral PARTS OF THE root of the tongue. By the 8th to 9th month of prenatal life, this lymphoid tissue forms denser clusters known as lymphoid nodules. By birth, the number of lymphoid nodules in the developing tonsil increases markedly. Germinal centers within the nodules appear immediately after birth. In children and adolescents, virtually all lymphoid nodules possess germinal centers. As the child ages, the size of the nodules increases to 2–4 mm, while germinal centers become progressively less frequent. In old age, The amount of lymphoid tissue in the lingual tonsil is minimal, being largely replaced by connective tissue.

The lingual tonsil is supplied with blood by branches of the right and left lingual arteries, and occasionally by branches of the facial artery. Venous blood drains from the tonsil into the lingual vein. Lymph from the lingual tonsil flows through lymphatic vessels to the regional lymph nodes—the lateral deep cervical nodes.

Innervation of the tonsil is supplied by fibers of the glossopharyngeal and vagus nerves, along with sympathetic fibers from the external carotid plexus.

The pharyngeal (adenoid) tonsil (tonsilla pharyngealis (adenoidea)) is an unpaired structure located in the region of the roof and partially the posterior wall of the Pharynx, situated between the pharyngeal openings of the right and left auditory tubes. This area features 4–6 arcuate, thick folds of the mucous membrane containing the lymphoid tissue of the pharyngeal tonsil. Between the folds lie downward-opening grooves of varying depth, into the lumens of which open the ducts of glands located within the folds. The free surface of the folds is covered with non-keratinized stratified squamous epithelium, whereas areas of pseudostratified ciliated epithelium are found deep within the grooves. Beneath the epithelium, within the lamina propria of the mucous membrane and the diffuse lymphoid tissue, lie the lymphoid nodules of the pharyngeal tonsil, measuring up to 0.8 mm in diameter. The connective tissue stroma of the tonsil is fused with the pharyngobasilar Fascia of the pharynx.

The pharyngeal tonsil develops during the 3rd to 4th month of prenatal life within the forming mucous membrane of the nasal part of the pharynx. In the newborn, the tonsil is already well-developed, measuring 5–7 mm in length and 5–6 mm in width. Lymphoid nodules appear in the pharyngeal tonsil During the first year of life. Starting from the first year, the relative size of the pharyngeal tonsil begins to increase. Hypertrophy of the tonsil can lead to narrowing or even complete blockage of the choanae by the mucosal folds, a condition that requires surgical intervention. By 6–7 years of age, the pharyngeal tonsil reaches its maximum relative size, with absolute dimensions of approximately 2.5 cm in length and 1.5 cm in width. Between 12 and 14 years of age, the growth phase of the tonsil is succeeded by regression and involution. In adults, complete Atrophy of the tonsil is sometimes observed.

The pharyngeal tonsil receives its blood supply from branches of the ascending pharyngeal artery. Venous blood drains into the veins of the pharyngeal plexus. The tonsil receives nerve fibers from branches of the facial, glossopharyngeal, and vagus nerves.