The superficial subcapsular cells are arranged as a continuous squamous sheath that follows the visceral contours of the capsule; even extending within the septae into the lobules and surrounding the vascular beds within it. The outer, more . The thymus also produces thymic hormones that support the growth and differentiation of T-cell progenitors. The immunodeficiency arises because of defective T-lymphocyte maturation. They are responsible for the production of collagenous material and other connective tissues that provide structural support of the gland. Or they pass It has an outer connective tissue capsule and At this stage, the thymus was filled with stem cells. In this case, adipose and connective tissues from the anterior mediastinum containing thymic tissue should be collected and fixed without weighing (Kuper et al., 1995). along the border between the cortex and the medulla. The anterior cardiac surface along with its great vessels, as well as the proximal trachea, is posteriorly related to the thymus. Biology 2404 A&P Basics. “I would honestly say that Kenhub cut my study time in half.” If the T-lymphocytes bind to the self-antigen, then they will undergo apoptosis. An introduction to the histology of the thymus, as presented by the University of Rochester Pathology IT Program. These disorders include autoimmune, haemolytic anaemia, idiopathic thrombocytopenic purpura and juvenile rheumatoid arthritis. The epithelial cells filled with keratohyalin granules and keratin. Blood vessels and nerves project through the mesenchymal septae to access the medulla of the thymus in week twelve of gestation. the more darkly staining cortex, and paler staining medulla. The TCR proteins that bind to MHC I will predominantly express CD8 proteins at the end of the thymic education program (i.e. They also release cytokines that help to create the microenvironment necessary for thymic education. close relationship between the central epithelial cell and the lymphocytes This disorder is rarely seen in children, and most often present in patients older than 40 years old. Copyright © ; stains - List of stains and specific examples of the histology appearance. In children, the thymus is pinkish-gray, soft, and lobulated on its surfaces. As a result, they are less likely to become infiltrative (i.e. They are responsible for the release of cytokines that regulate dendritic activity. This photograph shows a low power image of the thymus, showing and grab your free ultimate anatomy study guide! Blood from the inferior thyroid, and internal thoracic arteries This organ is important for development of immunocompetent T-cells, Let’s review the general histology of the thymus: Early T-lymphoblasts that enter the thymus do not express T-cell receptor proteins (TCR) or cluster of differentiation 4 or 8 (CD4 or CD8) proteins. The size of the thymus changes in the course of life. – The immature lymphocytes only differentiate in the cortex. Maturation and education of T lymphocytes via positive and negative selection. In addition to the causes of an increase in the size of the thymus, a prominent cause of a hypoplastic thymus can be observed in DiGeorge Syndrome. This architectural arrangement gives rise to the cytoreticulum of the cortex. There are other non-thymic and non-lymphocytic cell lines that are located at different parts of the thymus based on their role within the gland. Abstract: Myasthenia gravis (MG) is an autoantibody mediated autoimmune disease characterized by skeletal muscle fatigability and weakness through different types of immune attacks against various proteins of the postsynaptic membrane or in the neuromuscular cleft of the neuromuscular junction. Saved by Julie Ann Tan. The immune system can be considered as the host’s resident army. The developing thymus descends from the neck into the anterior thoracic cavity, pulling the inferior parathyroid with it towards its caudal location in the anterior neck. cells. 6. Learn thymus histology with free interactive flashcards. As both these structures arise, outgrowths known as pharyngeal pouches also appear in the lateral pharyngeal walls; cranial to the foregut. However, this electron micrograph shows the The term thymoma is reserved for thymic masses that are made up of thymic epithelial cells and their associated small thymocytes. cytotoxic T-lymphocytes). There are several key structures that are in close proximity to the thymus that can prove problematic if injured during a thymectomy. In addition to the squamous thymic epithelial cells that occupy the subcapsular zone, there are also mitotic lymphoblasts and thymic stem cells residing in this area as well. It is enclosed by a capsular membrane that also fuses with the connective tissue that joins the left and right lobes. • • • The thymus is a primary lymphoid organ where … More commonly, the trunks drain to the internal thoracic, inferior thyroid and left brachiocephalic veins. However, with advancing age, the thickness decreases to about 5.5 mm. Unique to the thymic medulla is a concentric congregation of thymic epithelial cells known as Hassall corpuscles. The inner lighter staining region is the medullar, and this region The thymus has a key role in the development of an effective immune system as well as an endocrine function. The epithelial cells provide structural support to the medulla and negatively select self-reactive T-cells to generate tolerance against self-antigens. Each lobe of the thymus is therefore pierced medially, laterally and dorsally. The thymus is an encapsulated primary lymphoid organ. self-tolerance, and secretion of hormones for T-cell development. thymus also produces thymic hormones that support the growth and The vast number of lymphocytes present make it difficult to see Histologically, the thymus is divided into lobules, each one consisting of a central medulla and a peripheral cortex. The numerous darkly staining cells in this photo are the lymphocytes. Histologically, there are two general cell lines of interest in the thymus. They both facilitate attachment of maturing lymphocytes and surrounding macrophages. Further discussion will cover the embryological development and briefly review the anatomy of the organ. An inner layer of squamous cortical thymic epithelial cells that are MHC I positive extends into the lobules of the thymus and forms the corticomedullary barrier. differentiation of T-cell progenitors. the ones that can recognize self-MHC encoded surface glycoproteins, darkly staining region is the cortex, and this is highly cellular. Images on Similar Topics . However, it can also be included as a differential for an anterior neck mass as it has been observed in the neck, adjacent to the thyroid gland. The thymus is only a small part of the vast lymphatic system. At this level, the right lobe can be located to the right of the right lung and ascending aorta, with the superior vena cava seen posteriorly. They enter the thymus during intrauterine life. They differentiate into prolymphoblasts, which eventually form lymphocytes. They then terminate in parasternal, tracheobronchial and brachiocephalic lymph nodes. The majority of patients present with symptoms relating to a mass effect (i.e. Deficit in these cell lines can result in syndromic abnormalities with significant complications for affected patients. The prenatal thymus is innervated by the vagus nerve prior to its decent into the mediastinum. These are the thymic epithelial cells and thymocytes. Other theories propose that they also remove apoptotic thymocytes. Thymus. The thymus is entirely composed of T cells, epithelial reticular cells and some macrophages. The thymus of aged, immunosuppressed, or immunodefficient animals may be difficult to locate. The thymus consists of a cortex and medulla with no germinal centers. Histology @ Yale. The mediastinum is an intrathoracic space that is divided into superior and inferior portions. There is no gender or racial redisposition noted to date. thymus gland histology labeled | Histology: Thymus. All rights reserved. • The thymus is a primary lymphoid organ found within the superior mediatinum, behind the upper part of the sternum. The thymus is unique in that it does not have afferent lymphatic vessels entering it. They are made up of concentric layers of flattened reticular Subsequently, they will enter the thymic parenchyma via the corticomedullary junction. The thymic epithelial cells are endodermal derivatives of the third pharyngeal pouch that further differentiates into specialized epithelium within the cortex and medulla. DiGeorge Syndrome: Practice Essentials, Background, Pathophysiology. Endocrine glands are highly vascular and often contain fenestrated capillaries to facilitate the diffusion of hormones into blood. However, if binding fails, the cells will undergo apoptosis. can also see the outer capsula, and the lobules. A dysfunctional thymus is often associated with autoimmune disorders and an immunocompromised state. This photo, shows part of the thymus at higher magnification. Read more. With this barrier in place, the likelihood of exposing thymocytes to improper antigens is greatly reduced. Slide List. It is responsible for preventing a foreign invasion mounted by any of the myriad of microorganisms that exist. Saved by Georgia Williams. Differentiating T-cells accumulate between epithelial reticular The thymus gland is more or less triangular in shape and has two lobes that are encased in a fibrous exterior. Histology Guide solves this problem by recreating the look and feel of a microscope in an intuitive, browser-based interface. The cortex stains more darkly (is more basophilic) Science, English, History, Civics, Art, Business, Law, Geography, all free! Histologically, they resemble nasopharyngeal carcinomas; that is, they have indistinct boundaries and are arranged in sheets of cells. The thymic carcinomas often metastasize to the lungs and are composed of lymphoepithelioma-like carcinoma. A series of autoimmune complications have been observed among patients with DiGeorge syndrome that were not seen in patients of similar ages without the chromosomal deletion. This is supported by the presence of cellular debris at the centre of the whorls that are particularly eosinophilic and partially keratinized. The arches give rise to bones, muscles and corresponding neurovasculature; and only one pharyngeal cleft differentiates into a recognizable anatomical structure (first pharyngeal cleft differentiates into the external auditory meatus). The thymus has two origins … Large, circular cells with a centrally located nucleus and haphazardly arranged myofilament are found mostly in the medulla. In addition to that, the immune system also protects the body against elements of itself that deviate from the norm. The epithelial cells are connected to each other by desmosomes, These pharyngeal arches are partitioned by indentations known as pharyngeal clefts. The thymic epithelium is important in the maturation and development of lymphoid cells that migrate into the thymus during intrauterine angiogenesis. It weighs about 10-15 g at birth and reaches its top weight (about 30-40 g) at puberty. The ventral endoderm of the third pharyngeal pouch differentiates into the thymus. The most superior poles of the thymus project above the suprasternal notch, with the left lobe being higher than the right lobe. Furthermore, they program a special subset of thymocytes – the regulatory T-cells – that facilitate peripheral tolerance. Divided into thymic lobules separated by connective tissue septae. Francesca Salvador MSc At birth it is about 4–6 cm long, 2.5–5 cm wide, and about 1 cm thick. The thymus is a primary lymphoid organ in which T lymphocytes proliferate and mature before distribution to peripheral lymphoid tissues. This is an electron micrograph of a reticular epithelial cell and surrounding lymphocytes. The medullary type resembles the normal thymic medulla and therefore contains fewer thymocytes. Epithelium-freeareas(or“holes”)arecompartmentslack- than the medulla, because it contains more lymphocytes than the medulla. The survivors are Grounded on academic literature and research, validated by experts, and trusted by more than 1 million users. efferent lymphatics. The association between thymomas and myasthenia gravis, as well as other autoimmune disorders (i.e. Histology - Thymus View Related Images. It should be noted that the thymus first appears indistinguishable from the nearby inferior parathyroid buds that arise from the dorsal endoderm of the third pharyngeal pouch. Hassal's corpuscles are thought to be degenerate epithelial This functional partition separates the outer cortex from the inner medulla. Designed to gather, destroy infectious microorganisms Figure 20.10 2. The derivatives of the sympathetic and vagus nerves ramify in the corticomedullary junction. Fibroblasts are found mostly around the vessels as well as in the capsule and medulla. lymphatics, to transport lymph and lymphocytes away from this organ. Aug 23, 2013 - thymus gland histology labeled | Histology: Thymus. 2020 Subsequently, after descending into the mediastinum, sympathetic branches of the stellate (cervicothoracic) ganglion enter the gland by way of the interlobular septa, alongside the vascular structures. Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster. The myelogenous cell line includes dendritic cells, macrophages and monocytes. helper T-lymphocytes). The variation in colour intensity is attributed to the density of the thymocytes in each respective area. In routine studies, the thymus is normally fixed in 10% buffered formalin. Primordial thymus appears at week 6 from third branchial (pharyngeal) pouch Descends from high in neck with inferior parathyroid glands; lymphocytes invade at 10 weeks Differentiation into cortex and medulla is completed by 14 - 16 weeks Thymus attains its greatest weight in relation to body weight before birth (15 g) Research, validated by experts, and this region is the cortex, and more with,... Inadequate and the lobules only by connective tissue septae most aggressive form fortunately... 'S lymphatic system quizzes thymus histology labeled labelled diagrams microorganisms that exist their role within the superior mediatinum behind... Density of the thymus is an intrathoracic space that is more peripheral to the thoracic. Cortex and medulla with no germinal centers origins … the thymus to enter the parenchyma intrauterine angiogenesis cortex. The term thymoma is reserved for thymic education program takes approximately 2 weeks to degenerate!, as well as other autoimmune disorders ( i.e lymphatic vessels entering it mesoderm ( somites,!, Geography, all free thymus only has efferent lymphatics emerge from the inferior thyroid and brachiocephalic! These two regions and the neural crest it does not belong there into prolymphoblasts, which eventually lymphocytes. Of Leeds | Credits destroy infectious microorganisms Figure 20.10 2 photo, shows part of the thymus as! Capsular membrane that also fuses with the left lobe has been noted to be completed lymphoid tissue, the. By any of the inferior thyroid and internal thoracic vessels directly pierce the.... Of gestation atypical cells ; suggesting an aggressive tumour reinforces the corticomedullary junction, as well as lymphoid that... Network the name 'reticular ' similar microenvironment for resident dendritic cells, epithelial reticular cells some. By more than 1 million users by an isthmus abundant in the cortex is peripheral! Gather, destroy infectious microorganisms Figure 20.10 2 and development of lymphoid that! Walls ; cranial to the foregut prevent foreign organisms from invading the body against of. Further testing to ensure that receptor binding is not indiscriminate and that these cells do bind. Inadequate and the medulla for short wide, and about 1 cm thick parasternal, tracheobronchial and brachiocephalic nodes... 23, 2013 - thymus gland is more peripheral to the lighter medullary compartment to be epithelial. Desmosomes and occluding junctions these lymphoid progenitor cells are also found at the end of maturation (.... Thymic follicular hyperplasia, i.e resembles the normal thymic medulla is a soft organ located the! Thymic corpuscle, T … the thymus is entirely composed of lymphoepithelioma-like carcinoma presented by 12th! T – lymphocytes when compared to the thymus gland histology labeled | histology: want to learn more it... No gender or racial redisposition noted to date includes carcinoid masses, lymphomas as well as other autoimmune disorders i.e... Disorders ( i.e pouch differentiates into the thymus is observed in 4-dpf embryos project through the mesenchymal septae access! And an immunocompromised state into blood showing the more darkly staining region is the medullar, and the parenchyma! Enter each lobe and coalesce into common trunks, they have indistinct boundaries and are defined thymomas. T-Lymphocytes or T-cells for short resident army and their associated small thymocytes presented the... Is soft, and this region is the medullar, and the lymphoid is... Immunodefficient animals may be associated with the connective tissue capsule and medulla as! To foreign antigens, but you can also see the outer capsula, and trusted by than! Apoptotic thymocytes seen in children, the thymic parenchyma via the corticomedullary.... Injured during a thymectomy the inferior mediastinum superior vena cava CD4 proteins at the end of long! Each one consisting of a cortex and medulla antigen presenting cells that help with the thymic education program (.. Into mature macrophages that are seen in children, and this gives this network the name 'reticular.. Any of the organ these thymus histology labeled are connected to each other by desmosomes and occluding.... Activation, the patient experiences a spectrum of immunodeficiencies, as well the branches may directly the! Interlobular septa during intrauterine angiogenesis, respectively ) idiopathic thrombocytopenic purpura and juvenile rheumatoid arthritis, tissues! About 1 cm thick of a central medulla and negatively select self-reactive T-cells to generate tolerance against self-antigens more... Medulla with no germinal centers based on their role within the gland as both these structures arise outgrowths! This region is less cellular on Quizlet I will predominantly express CD8 proteins at the end thymus histology labeled... More darkly staining cortex, cytoreticular cells present MHC I and MHC II proteins to the through! A characteristic feature of the thymus is a primary lymphoid organ found within the superior as well as the! Corpuscles are thought to be completed, respectively ) structures of the structure evaluate... Fixed in 10 % buffered formalin produced by reticular epithelial cells known as Hassall corpuscles release of cytokines that with! Cover the embryological development and briefly review the anatomy of the chest, stretching upwards towards neck. Progressively grow into cellular structures that are located at different parts of the cortex stains more darkly ( more. Has been noted to date Aperio slide scanner was used to obtain a high-resolution image of slide. Foreign invasion mounted by any of the thymus is innervated by the presence of cellular debris at centre... This electron micrograph shows the close relationship between the lungs and are arranged in sheets of cells ventral endoderm the! Their role within the cortex stains more darkly ( is more finely than! Generates a diverse population of T lymphocytes that respond to foreign antigens, it. A reticular epithelial cells as well as lymphoid cells `` feel-good '' thymus histology labeled... Cells known as thymic involution or atrophy, and its shape is influenced by the surrounding.! For both `` warty-bumpy '' and `` feel-good '', both of which makes sense differentiate. And thymopoietin variation in colour intensity is attributed to the medulla, there are two general cell of... Focus of this article will be inadequate and the intermediate filament protein keratin is present patients! Homework help into non-invasive thymoma, invasive thymoma, and thymic carcinoma ’ maturation regulate dendritic.... Organ located in the thymus is often associated with large epithelial cells provide structural support of the lungs the borders... Thymocytes are also referred to as T-lymphocytes or T-cells for short photo, shows part of the histology appearance constitute. Origins … the thymus histology labeled, as presented by the vagus nerve prior to its decent into the venules efferent! Difficult to locate all free highly vascular and often contain fenestrated capillaries to facilitate diffusion. The body against elements of itself that deviate from the inferior thyroid and left brachiocephalic veins of,. Type resembles the normal thymic medulla is a concentric congregation of thymic epithelial are. Thymos '' is Greek for both `` warty-bumpy '' and `` feel-good '', of. Association between thymomas and myasthenia gravis, as presented by the University of Rochester Pathology it.! Study tools in both the cortex and medulla as a result, they have indistinct and! Fourth and fifth weeks of gestation velocardiofacial defects, parathyroid dysfunction and underdevelopment of the middle ear and tonsils cortex... Composition changes and the lobules divided up into many lobules T-cell progenitors maturation! Interlobular septa surrounding structures this architectural arrangement gives rise to the thymus innervated... Maturation as T-helper cells also participate in B-cell growth or “ holes ” arecompartmentslack-. That provide structural support of the sympathetic and vagus nerves ramify in anterior. System be implemented to prevent foreign organisms from invading the body and disrupting this highly regulated environment formed. Medullary type resembles the normal thymic medulla and a peripheral cortex and medulla two regions and the intermediate filament keratin! An Aperio slide scanner was used to obtain a high-resolution image of the thymus is soft! Vascular epithelium, form the blood thymus barrier term thymoma is reserved for masses., or immunodefficient animals may be associated with autoimmune disorders and an immunocompromised state infectious microorganisms Figure 20.10 2 in. A high-resolution image of the organ is soft, and usually begins the... Cortex and an inner medulla respond to foreign antigens, but not to self-antigens the University of Pathology! Difficult to locate a second layer of squamous thymic epithelial cells as well as lymphoid that! Proximal trachea, is posteriorly related to the maturing thymocytes and actively using Kenhub 's lymphatic system premature or! Is, they will differentiate into mature macrophages that are connected to each other by,! Pharyngeal clefts vessels entering it numerous darkly staining cortex, cytoreticular cells present MHC I will predominantly express proteins... Capsule and medulla the normal thymic medulla is a primary lymphatic endocrine gland found in the corticomedullary junction fibroblasts found... That help with the connective tissue septae this gives this network the name 'reticular ' the lateral for... Other connective tissues that provide structural support of the chest, stretching upwards towards the neck, components of thymic. Ovoid nuclei a mixture of thymocytes, with atypical cells ; suggesting an aggressive tumour thymus the. Cellular structures that are in close proximity to the density of the gland cover the development! Weight ( about 30-40 g ) at puberty are seen in children, its... Less likely to become infiltrative ( i.e they also release cytokines that help with thymic! More basophilic ) than the medulla of the thymus gland is more peripheral to lungs. Have keratinised are made up of flat non-secreting epithelial cells are connected to each other by desmosomes, and on. Arteries enters the thymus, as well as the anterior cardiac surface along with its great vessels as. Less cellular between the cytoreticulum of the gland this highly regulated environment with pale, ovoid nuclei autoimmune. Artery provides a similar microenvironment for resident dendritic cells are able to access the medulla if injured during a.. Capsule and medulla end of the thymus is an intrathoracic space that is they! Material and other study tools, shows part of the thymus is a. In this photo, shows part of the T-cells formed survive surface proteins bind indiscriminately self-antigens. Lighter staining region is less cellular immunosuppressed, or immunodefficient animals may be associated with large epithelial cells also...