Question

1. Identify the organs and histology of the lymphatic system, and those associated with the immune system and their roles

Answer 1

**The lymphatic system consists of all lymphatic vessels and lymphoid organs.

**Primary Lymohoid organs - They have stem cells.
They produce Lymphocytes independent of antigen stimulus .eg Bone marrow and thymus.

**Function
Bone marrow produce B cells ----->Plasm cells and help in humoral immunity by producing antibody production .

**Function
Thymus -Produce T cells involved in Cell mediated immunity .eg Killing bacteriae and Protozaoe .

**Secondary Lymohoid organs produce immunity only after antigen exposure .
They dont have stem cells
Eg Lymph node ,Spleen ,MALT mucosa associated lymphoid tissue .,Tonsils etc.

**Also the lymphatic tissue found in the small intestine (Peyer's patches) and throat (adenoid tonsils, palatine and tubal tonsils) constitute lymphatic organs.

Histology
1) Lymph node
It is made up of Cortex ,paracortex and medulla ,capsule and Large subcapsular sinus filled with lymph .
Cortex contain lymphoid follicles .
Lymphocytes have large nucleus with peripheral thin cytoplasm .

**Function
Lymph nodes are reservoirs of B, T and other immune cells.
Lymph nodes act as filters or traps for foreign particles and are important in the proper functioning of the immune system. They are packed with white blood cells lymphocytes and macrophages.

2) Thymus there are 2 parts
Cortex and Medulla
Cortex is at periphery ,dark coloured and Medulla is at centre and Light coloured .
A).Cortex produces lymphocytes (95%) .Germinal centre appears in autoimmune disease .

B). Medulla -Contains Hassals Corpuscles ,epithelial cells which secrete Lymphopoeitin ( Competence inducing factor and form blood thymus barrier )

3) Spleen -White pulp and Red pulp
A) White pulp is 10-30 % with more anount of WBC. It contain Lymphoid follicles with germinal matrix in centre ( Light stained ) and periphery ( dark stained )
Centre had T lymphocytes and Periphery has B lymphocytes .

B)Red pulp is 70 -90 % with maximum of RBC's .
It is central arteriole present in lymphoid follicles .It is eccentric surrounded by T lymphocytes .

Stare cells ,stellate cells and malphigian bodies are present in sinusoids of spleen

Cords of Billroth are seen .which are reticulocytes with reticular fibres .

Function-

**The spleen is similar in structure to a large lymph node and it acts primarily as a blood filter.
It synthesizes antibodies in its white pulp and removes antibody-coated bacteria along with antibody-coated blood cells by way of blood and lymph node circulation.

4) Tonsils
*Palatine ,pharyngeal
Tonsils crypt lined by Non keratinised stratified squamous epithelium .
Function
**These immunocompetent tissues are the immune system’s first line of defense against ingested or inhaled foreign pathogens and form part of innate immunity .