What percentage of T cells which enter thymus survive?
2%
Thymus: Embryological origin
Epithelium of 3rd branchial pouches
How can the spleen be distinguished from a lymph node on histologic section?
Spleens have no subscapsular sinus and no cortex or medulla. They have white pulp and red pulp.
Innate immunity vs adaptive immunity: How are receptors that recognize pathogens encoded?
Innate: Germline encoded
Adaptive: Undergo VDJ recombination during development
Where is the red pulp of the spleen located?
Around and between the lymphatic nodules of the white pulp
Innate immunity vs adaptive immunity: How fast is response to pathogens?
Innate: Always fast, no memory response.
Adaptive: Slow on 1st exposure but memory response is faster and more robust.
Splenic cords: What are they?
Structures containing macrophages, plasma cells, lymphocytes, and few RBCs. Separated from each other by splenic sinusoids.
Thymus: What does the cortex contain and what does it look like?
The lobules resemble lymphatic nodules except they are angular, not round.
Contains:
1. Densely packed (dark) immature T cells.
2. Large epithelial reticular cells which appear as holes within the cortical cells.
Thymus: What does the medulla contain and what does it look like?
Pale Contains: Thymic (Hassall's) corpuscles which have a lamellated or whorled appearance due to degenerating epithelial reticular cells.
What does the white pulp of the spleen contain?
1. Lymphoid follicles with germinal centers (mostly B cells). Can see aggregation of dark basophilic lymphocytic nuclei.
2. Characteristic central arterioles. Surrounded by a Periarterial lymphatic sheath (PALS) which is a collection of T-lymphocytes
