Thymus, spleen, tonsils

Dora MalićMedical 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 destroyed2.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 afibrous capsule• Composed of red and white pulp

Structure of spleen

• Red pulp 1. sinuses – vessel-like spaces filled with blood2. splenic cords – reticular fibers3. marginal zone bordering on white pulp

• White pulp - nodules - Malpighian corpuscles1. follicles - rich in B-lymphocytes2. 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

• http://en.wikipedia.org/wiki/Tonsil• http://en.wikipedia.org/wiki/Lymph_node• http://www.webmd.com/digestive-disorders/

picture-of-the-spleen• http://en.wikipedia.org/wiki/Thymus