Lymphoid Tissue Flashcards
Innate immune system
Monocytes/ macrophages, neutrophils
Lack immunological memory
Invertebrates
Adaptive immune system
Added form of defense
High specificity and memory
Trillions of lymphocytes
Slow reaction
Major role = destruction
Lymphocytes must not react to self antigens - immune tolerance
When tolerance breaks down -immune system fails to distinguish self - ‘non- self’
= Autoimmune disease
Autoimmune disease
When immune system fails to distinguish ‘self’ from ‘non self’ and attacks body
Primary lymphoid organs
Site of lymphocytes production and maturation
Bone marrow and thymus
Secondary lymphoid organs
Site to which lymphocytes migrate and aggregate
Spleen, lymph nodes and lymph nodules
3 principal forms of lymphocytes
B lymphocytes (B cells)
T lymphocytes (T cells)
Natural killer cells
B lymphocytes
Produce antibodies
T lymphocytes (T cells)
Participate in cellular immunity
Found in 3 forms
- helper T cells
- cytotoxic T cells
- suppressor T cells
Natural killer cells
Kill virus infected cells and some tumor cells
How is identifying cells of the immune system done?
using immunohistochemistry for cell surface markers called cluster designation (CD) molecules
thymus
Is located in the mediastinum
increases in size from birth to puberty, regresses and becomes more fatty
Two lobes subdivided by septa
The lobules have a higher cellular outer cortex and a less cellular inner medulla
Cortex of thymus contains
large number of T cells - sometimes called thymocytes
as well as epithelioreticular cells and macrophages
Medulla of thymus contains
mainly T cells- larger and less tightly packed
and also epithelioreticular cells
Where do T cells enter first in thymus
cortex then if survive the medulla
What happens to T cells that don’t survive the cortex
undergo apoptosis
what are Hassall’s corpuscles
whorls of epithelial cells with keratin at the core , accumulate in medulla of thymus
In the cortex the T cells must express the correct surface antigens and recognise self and foreign antigens to survive, this is called ?
Positive selection
In the medulla maturing T cells that recognise self antigens are eliminated, this is called?
negative selection
The system of lymphatic vessels and associated lymph nodes provide for:
Drainage of lymph into the vascular system
Surveillance of tissues for signs of antigens from foreign invaders such as bacteria
Delivery of absorbed fats from the small intestine into the vascular system via lymphatic vessels in the villi of small intestines.
lymph vessels are
thin walled and lined by endothelium and anchored to tissue by filaments
Lymphocytes enter the lymph node via
incoming lymph or from the blood stream
lymph node structures
connective tissue capsule, subcapsular sinus, cortex, paracortex, medulla, follicles and connective tissue trabecular
Follicles beneath capsule contain
mainly B cells
Primary follicle in lymph node
uniformly and densely packed
unstimulated
