Lymphoid Organs Flashcards
What does the immune system of humans lack
An immunological memory
What are the components of the innate immune system
Barriers against invasion, phagocytes, a cascade of plasma proteins that form an enzyme system and defends against bacteria and extracellular killers
Examples of extracellular killers
Lymphocytes and eosinophils
What is the major role high specificity adaptive immune system
Destruction
What must the immune system have the ability to do
Distinguish from self and non-self
What occurs when the immune system fails to distinguish between self and non-self
An autoimmune disease occurs
Characteristics of the adaptive immune system
Slower to react, highly flexible, very specific, based on lymphocytes and a vast array of genetically determined cell surface receptors
What is the major role of the adaptive immune system
Destruction
What happens when the tolerance of lymphocytes breaks down
The immune system fails to distinguish between self and non-self
What are organs of the immune system known as
Lymphoid organs
How are lymph organs linked
By the blood vascular and lymphatic vascular systems
What are the primary lymphoid organs
Bone marrow and thymus
What do the primary lymphoid organs do
Sites of lymphocyte production and maturation
What are the secondary lymph organs
Spleen, lymph nodes and lymph nodules
What occurs within the secondary lymph organs
The lymphocytes migrate to these organs and aggregate in large numbers
What are the three types of lymphocytes
B cells, T cells and natural killer cells
What do B cells produce
Antibodies
What do T cells participate in
Cellular immunity
What are the three forms of T cells
Helper T cells, cytotoxic T cells and suppressor T cells
Function of natural killer cells
Kill virus infected cells and some tumour cells
How are cells of the immune system identified
Using immunohistochemistry
Where are B and T cells produced
In the bone marrow
Where is the thymus located
In the mediastinum
What subdivides the thymus
Septa
Structure of the lobules of the thymus
Highly cellular outer cortex and a less cellular inner medulla
What is contained within the cortex of the thymus
Large number of T cells, epithelioreticular cells and macrophages
What does the medulla of the thymus contain
Fewer T cells that are less tightly packed and larger and epithelioreticular cells
What part of the thymus are the immature T cells found
Cortex
What process do the immature T cells go through
Proliferation, maturation and a selection process
What occurs to the T cells that fail the processes
They undergo apoptosis and are phagocytosed by macrophages
What happens to T cells that survive
They enter the medulla and interact with the epithelioreticular cells and present self antigens
What are the whorls of epithelial cells found in the medulla of the thymus called and what else do they contain
Hassall’s corpsucles and keratin
What does the system of lymphatic vessels and accociated lymph nodes allow
The drainage of lymph into the vascular system, surveillance of tissue for signs of antigens and the delivery of absorbed fats from the small intestine
Structure of lymphatic vessels
Thin walled, lined by endothelium and anchored to the tissue by filaments
Areas of clusters of lymph nodes
Neck, axilla and groin
How do lymphocytes enter the lymph node
Via the incoming lymph or the blood stream
What are the circular aggregations with the lymph node known as and what do they contain
Follicles and B cells
What are the densely pack follicles of the lymph node called
Primary follicles
What is the centre of active lymph node follicles called
The germinal centre
What does the germinal centre of lymph follicles contain
Actively dividing B calls
What surrounds the germinal centre of the lymph follicle
Mantle zone
What is within the mantle zone
Resting B cells
What is within the paracortical region of the lymph node
T cells and high endothelial venules
What lines the high endothelial venules
Cuboidal epithelium
What is within the medulla of the lymph node
Medullary sinuses and medullary cords that contain plasma cells and macrophages
What areas do the developing B cells go through in the lymph node
Form a follicle in the superficial cortex, to the paracortex and finally into the medulla
What are aggregations of lymph in the gut known as
GALT
What is aggregations of lymph in the respiratory tract and gastrointestinal tract known as
MALT
Examples of aggregations of lymphoid tissue
Waldeyer’s ring and payer’s patches
Functions of the spleen
Immune response against blood-borne antigens, removes particulate matter and aged blood cells and produces blood cells during foetal life
Structure of the spleen
Composed of white pulp nodules surrounded by red pulp
What makes up the white pulp
Either T or B cells
What is contained within the red pulp
Blood filled capillaries with discontinuous endothelium and sinuses
What happens to old RBCs within the spleen
They lyse and become phagocytosed by macrophages associated with the sinuses
