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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 preadolescent 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
• http://en.wikipedia.org/wiki/Tonsil
• http://en.wikipedia.org/wiki/Lymph_node
• http://www.webmd.com/digestivedisorders/picture-of-the-spleen
• http://en.wikipedia.org/wiki/Thymus