L7 - Organs of the Lymphatic System Flashcards
precocious development
advanced development (of an organ, such as the thymus)
parenchymal structural cell type of the thymus
epithelio-reticular cells
thymic cortex
outer, dark-staining region of thymus comprised of large thymocytes and PAS cells
PAS cells
macrophages in the thymic cortex that protect thymocytes from being exposed to antigen
thymic medulla
inner, lighter-staining region of thymus that contains Hassall’s corpuscles
Hassall’s corpuscles
akin to keratin pearls, these are the identifying feature of the thymic medulla; comprised of keratohyalin granules, intermediate filaments, and lipid droplets
blood/thymic barrier
- Capillary Endothelium with Basal Lamina
- Perivascular CT with macrophages
- Epithelio-Reticular Cells (Type I) with basal lamina and tight junctions
lymphatic nodule (follicle)
sites where B and T cells encounter antigen
pharyngeal tonsils (adenoids)
tonsils marked by pseudostratified columnar epithelium with goblet cells and cilia; found in the superior and posterior portion of pharynx
palatine tonsils
marked by stratified squamous epithelium and crypts
lingual tonsils
tonsils marked by stratified squamous epithelium and located at base of tongue
lymph node structure
CT capsule > sinus (containing macrophages) > nodular cortex (B-cells) > paracortex (T-cells) > Hilar region
advanced development (of an organ, such as the thymus)
precocious development
epithelio-reticular cells
parenchymal structural cell type of the thymus
outer, dark-staining region of thymus comprised of large thymocytes and PAS cells
thymic cortex
macrophages in the thymic cortex that protect thymocytes from being exposed to antigen
PAS cells
inner, lighter-staining region of thymus that contains Hassall’s corpuscles
thymic medulla
akin to keratin pearls, these are the identifying feature of the thymic medulla; comprised of keratohyalin granules, intermediate filaments, and lipid droplets
Hassall’s corpuscles
sites where B and T cells encounter antigen
lymphatic nodule (follicle)
tonsils marked by pseudostratified columnar epithelium with goblet cells and cilia; found in the superior and posterior portion of pharynx
pharyngeal tonsils (adenoids)
marked by stratified squamous epithelium and crypts
palatine tonsils
tonsils marked by stratified squamous epithelium and located at base of tongue
lingual tonsils
thymus
The thymus is surrounded by a dense CT capsule from which trabeculae extend penetrating through the gland, organizing it into a dense cortex and lighter medulla. The cortex contains small T lymphocytes (also called thymocytes) which occupy spaces surrounded by epithelioreticular cells (stromal or supporting cells). Macrophages are also present and are responsible for phagocytosis of T cells that do not become thymic educated. Hence they are programed to die prior to leaving the thymus. The medulla is the lighter, inner portion of the thymus gland. It also contains epithelioreticular cells and larger lymphocytes with paler-staining nuclei and more abundant cytoplasm. There are multiple types of epithelioreticular cells but one of importance – Type VI – form Hassall’s corpuscles, which is the characteristic histological feature of the thymus gland. These acidophilic staining structures are isolated masses of cells that exhibit flat nuclei, keratohyalin granules and intermediate filaments. The core of the corpuscle often appears keratinized. Their function is unknown and they increase in number with age.
