Lymphoid System in Histology

Questions and Answers

What is the primary function of secondary lymphoid organs?

To filter antigens and expose them to lymphocytes (correct)

To store macrophages

To produce lymphocytes

To destroy old red cells

Which of the following is a component of the lymph node medulla?

Cords containing B cells and macrophages (correct)

High endothelial venules

Reticulin fibers

Lymphoid follicles

What is the function of the germinal center in a secondary lymph node follicle?

To contain small, dark lymphocytes

To produce macrophages

To contain larger lymphocytes (correct)

To filter antigens that try to cross mucosal surfaces

Which of the following vessels carries lymph from the lymph node and returns it to the blood?

Efferent lymphatic vessels Signup and view all the answers

What is the function of the spleen?

To filter blood Signup and view all the answers

What is the composition of the lymph node stroma?

Reticulin fibers Signup and view all the answers

Which of the following is a characteristic of primary lymphoid follicles?

Composed of small, dark lymphocytes Signup and view all the answers

Which of the following vessels penetrates the capsule of the lymph node on the convex side?

Afferent lymphatic vessels Signup and view all the answers

What are the primary lymphoid organs?

Bone marrow and thymus Signup and view all the answers

What is the main function of the spleen in the immune system?

To filter blood and trap antigens Signup and view all the answers

What is the name given to the parenchyma of the spleen?

Splenic pulp Signup and view all the answers

Which of the following components is NOT found in the white pulp of the spleen?

Splenic sinuses (sinusoids) Signup and view all the answers

What is the function of the splenic sinuses (sinusoids) in the red pulp?

To filter and remove old or damaged red blood cells Signup and view all the answers

What is the function of MALT (Mucosa-Associated Lymphoid Tissue)?

To protect the body from pathogens that enter through mucosal surfaces Signup and view all the answers

Which of these is a secondary lymphoid organ?

Lymph node Signup and view all the answers

What is the primary function of splenic cords?

To contain macrophages that remove old or damaged red blood cells Signup and view all the answers

Study Notes

Lymphoid System Outline

The lymphoid system consists of primary and secondary lymphoid organs
Primary lymphoid organs: bone marrow and thymus
Secondary lymphoid organs: lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT)

Secondary Lymphoid Organs

Act as filters that trap antigens and expose them to lymphocytes
Lymph nodes filter lymph, spleen filters blood, and MALT filters antigens that try to cross mucosal surfaces

Lymph Node Components

Cortex contains lymphoid follicles composed of B cells
Paracortex contains T cells and high endothelial venules
Medulla composed of cords containing B cells and macrophages, and sinuses containing reticular fibers, lymph, and circulating cells and antigens
Stroma composed of reticulin (type III collagen) fibers

Lymph Node Follicles

Primary follicles consist of small, dark, mature lymphocytes
Secondary follicles consist of:
- Germinal center: a lighter-staining central area containing larger lymphocytes
- Mantle zone: around germinal center; contains small, dark lymphocytes

Afferent and Efferent Lymphatic Vessels

Afferent lymphatic vessels penetrate the capsule of the lymph node on the convex side and carry lymph with antigen and cells from sites of infection back to the lymph node
Efferent lymphatic vessels leave through the hilum and carry lymph with lymphocytes from the lymph node and return it to the blood

Functions of the Spleen

Filters blood (traps antigens)
Provides a place for lymphocytes to encounter antigens and become activated
Removes old red cells and platelets

Structure of the Spleen

Parenchyma of spleen is called splenic pulp and consists of white pulp and red pulp
No cortex or medulla are present
Stroma consists of capsule, trabeculae, and reticular connective tissue
Hilum contains nerves, arteries, and veins

White Pulp of the Spleen

Consists of:
- Periarteriolar lymphatic sheaths (PALS): tubule-shaped collections of T cells around arterioles
- Splenic follicles (nodules): similar to secondary follicles in lymph nodes, with an additional marginal zone composed of B cells

Red Pulp of the Spleen

Consists of:
- Splenic sinuses (sinusoids): leaky vessels lined by specialized endothelial cells and surrounded by rings of reticular fibers
- Splenic cords (cords of Billroth): contain lots of macrophages that eat old or damaged red cells

Mucosa-Associated Lymphoid Tissue (MALT)

Unencapsulated lymphoid tissue in mucosa and submucosa of digestive, respiratory, reproductive, and urinary systems
Catches antigens as they try to cross the mucosa and get into the body
Found in lung and other systems