Thymus, spleen, tonsils Dora Malić Medical English, 2013/14 Mentor: A. Žmegač Horvat

Thymus Anterior superior mediastinum Two asymmetrical lobes Each lobe composed of lobules Lobule – outer cortex and inner medulla

Two types of cells 1.stromal cells - cortical epithelial cells, thymic medullary epithelial cells, dendritic cells - selection of functional and self-tolerant T-cell receptors 2.cells of hematopoietic origin – derived from bone marrow hematopoietic stem cells

Function of thymus Maturation of T-cells Migration of hematpoietic progenitor cells from bone marrow Thymocytes undergo: 1.positive selection – those with no affinity for self-MHC on stromal cells are destroyed 2.negative selection – those with high affinity for thymic antigens are destroyed – central tolerance

Involution of thymus largest and most active during the neonatal and pre- adolescent periods

Spleen Upper left quadrant of the abdomen Not a vital organ Surrounded by a fibrous capsule Composed of red and white pulp

Structure of spleen Red pulp 1.sinuses – vessel-like spaces filled with blood 2.splenic cords – reticular fibers 3.marginal zone bordering on white pulp White pulp - nodules - Malpighian corpuscles 1.follicles - rich in B-lymphocytes 2.periarteriolar lymphoid sheath - T-lymphocytes

Functions of spleen Removes old red blood cells from circulation Reserve of blood Storage of red blood cells, platelets, and lymphocytes Metabolizes hemoglobin Recycles iron Part of mononuclear phagocyte system Active immune response to antigens

Tonsils Collections of lymphoid tissue in aerodigestive tract Waldayer’s tonsillar ring - adenoid tonsil, two tubal tonsils, two palatine tonsils, lingual tonsil First line of defense against ingested or inhaled foreign pathogens

Palatine tonsil Non-keratinized stratified squamous Incompletely encapsulated Long, branched crypts Sides of oropharynx - between palatoglossal and palatopharyngeal arches Tonsillectomy

References disorders/picture-of-the-spleen disorders/picture-of-the-spleen