20.2 Lymphoid cells and tissues are found in lymphoid organs and in connective tissue of other organs

What are the two major components of lymphoid tissue?

•lymphoid cells

•supporting (stromal) cells

What are the main warriors of the immune system?

lymphotcytes

What are the two major types of lymphocytes?

•T lymphocytes (T cells)

•B lymphocytes (B cells)

What is an antigen?

anything that triggers and immune response

Examples of antigens

bacteria, viruses, cancer cells, toxins, and mismatched RBCs

What do T cells do?

•manage immune responses

•directly attack infected cells

What do B cells do?

differentiate into plasma cells that produce antibodies

Which lymphocyte produces antibodies?

B lymphocyte (through plasma cells)

What do antibodies do?

mark antigens for destruction

T cells vs B cells?

attack infected cells; make antibodies

Function of macrophages?

•phagocytize foreign material

•activate T cells

What does phagocytize mean?

engulf and digest foreign substances

Function of dendritic cells?

capture antigens and transport them to lymph nodes

Which cells are considered antigen-presenting cells?

•macrophages

•dendritic cells

What do reticular cells produce?

reticular fiber stroma

What is stroma?

supporting framework (scaffolding) of lymphoid tissue

What type of cells are reticular cells?

fibroblast-like supporting cells

Reticular cells function?

they build the framework

What type of connective tissue make up most lymphoid tissue?

reticular connective tissue

Which lymphoid organ is NOT dominated by reticular connective tissue

thymus

Two major functions of lymphoid tissue?

•house lymphocytes

•provide a site for activation and proliferation

Why is lymphoid tissue considered a surveillance site?

lymphocytes and macrophages monitor for pathogens

Where do macrophages live in lymphoid tissue?

on reticular fibers

How do lymphocytes enter lymphoid tissues?

through postcapillary venules

After leaving lymphoid tissue, how do lymphocytes return to the bloodstream?

through lymphatic vessels

Why do lymphocytes constantly circulate?

to rapidly reach infection or injury sites

Lymphocyte travel pathway?

•lymphoid tissue

•lymphatics

•blood

What is diffuse lymphoid tissue?

loose arrangement of lymphoid cells and reticular fibers

Where is diffuse lymphoid tissue found?

virtually every organ

Where are large collections of diffuse lymphoid tissue commonly found?

mucous membranes

Which body system contains abundant diffuse lymphoid tissue?

digestive system

Why is lymphoid follicle (lymphoid nodule)?

solid spherical collection of tightly packed lymphoid cells

What is another name for lymphoid follicle?

lymphoid nodule

What is the germinal center?

lighter central regions where B cells rapidly divide

Which cells dominate germinal centers?

B lymphocytes

Why do germinal centers enlarge?

rapid B-cell proliferation and plasma cell production

Diffuse vs Follicle?

diffuse = scattered

follicle = organized ball

What are peyer’s patches?

aggregated lymphoid nodules in the small intestine

Where are Peyer’s patches located?

small intestine

Which organ contains abundant lymphoid follicles?

appendix

What are primary lymphoid organs?

sites where lymphocytes mature

Name the primary lymphoid organs?

•red bone marrow

•thymus

Where do B cells mature?

red bone marrow

Where do T cells mature?

thymus

What are secondary lymphoid organs?

sites where lymphocytes encounter antigens and become activated

Name the major secondary lymphoid organs

•lymph nodes

•spleen

•tones

•Peyer’s patches

•appendix

Which lymphoid organs filter lymph?

lymph nodes

Which lymphoid organ actually cleanses lymph?

lymph nodes

What makes lymph nodes unique among lymphoid organs?

they are the only organs that filter lymph