Lymphoid System

Question 1

What are the two major types of lymphocytes and their associated immunological responses?

Answer 1

T-Lymphocytes- Cell-mediated immunity

B-Lymphocytes- humoral immunity (B-cells differentiate into plasma cells and secrete antibodies)

Question 2

Lymphocytes are “recirculating, Immunocompetent” cells. What does this mean?

Answer 2

Recirculating- travel through blood/lymphatic vessels and lymphoid tissue.
Immunocompetent- Ability to recognize a single foreign antigen

Recirculation ensures that the “correct” immunocompetent lymphocytes will detect an antigen, regardless of location of infection.

Question 3

What’s the difference in Primary and secondary lymphoid tissue?

Answer 3

Primary- lymphocytes differentiate into T&B cells

Secondary- Foreign antigens are captured/controlled here. (Positioned near common sites of foreign antigen presence)

Question 4

Where do T-cells mature?

Answer 4

Thymus

Question 5

Where do B-cells mature?

Answer 5

Bone Marrow

Question 6

Areas of loose connective tissue where large members of lymphocytes and plasma cells are present are called?

Answer 6

Diffuse Lymphatic Tissue

Question 7

What are some common locations of diffuse lymphatic tissue?

Answer 7

Digestive, Respiratory, Urogenital tracts

Question 8

If a foreign antigen gets past the epithelium of the digestive system, where will lymphocytes intercept it?

Answer 8

Lamina Propria immediately deep to the epithelium

Question 9

A discrete concentration of lymphocytes contained in a meshwork of reticular cells is called?

Answer 9

An Isolated lymphatic nodule/follice

Question 10

Where are isolated lymphatic nodules generally located?

Answer 10

Digestive, Respiratory, Urogenital tracts

Question 11

What are the 2 types of isolated lymphatic nodules?

Answer 11

Primary lymphatic nodule- oval accumulations of small lymphocytes beneath the epithelium.

Secondary lymphatic nodule- Lighter central region with large lymphocytes (mostly Bcells) and dark outer region of small lymphocytes

Question 12

When do secondary lymphatic nodules form?

Answer 12

After antigen exposure - location of immune response (high B-cell concentration = more antibody secretion)

Question 13

What are PERMANENT aggregates of lymphoid nodules called?

Answer 13

Aggregated lymphoid nodules.

Examples: Peyer’s Patches/Appendix, tonsils,

Question 14

Where are Peyer’s Patches located?

Answer 14

Ileum, on ONE SIDE of intestinal wall.

Question 15

What does MALT stand for?

Answer 15

Mucosal Associated Lymphoid Tissue. Constitutes 85% of lymphoid tissue in the body, because mucosa are the most common site of entry for microorganisms.

Question 16

What permanent aggregated lymphoid structures capture and mount immune responses to antigens entering through the mouth and nose?

Answer 16

Tonsils

Question 17

Name the 3 kinds of tonsils.

Answer 17

1) Pharyngeal- roof of pharynx
2) Palatine (“the tonsils”) - either side of pharynx
3) Lingual- base of tongue

Question 18

What type of epithelium lines the tonsils? (think mucosa)

Answer 18

Non-keratinized stratified squamous epithelium

Question 19

Why do tonsils become infected easily?

Answer 19

Deep crypts- no clear border between epithelium and parenchyma

Question 20

What is the stroma and parenchyma of a lymphoid organ?

Answer 20

Stroma- supporting framework (generally CT/reticular fibers)

Parenchyma - functional part of an organ

Question 21

Lymphoid nodules generally contain which 3 types of cells?

Answer 21

B-cells, Plasma Cells, and Macrophages

Question 22

In lymph nodes, where are B-cells located?

Answer 22

Outer cortex in nodules

Question 23

In lymph nodes, where are T-cells located?

Answer 23

Paracortex

Question 24

How do lymphocytes get into the lymph nodes?

Answer 24

Postcapillary venules inside lymph node are lined with HIGH CUBOIDAL CELLS which have surface receptors that specifically recognize lymphocytes.

These venules are more specifically called HEVs (high endothelial venules)

Question 25

The spleen parenchyma contains white and red pulp. What is the difference?

Answer 25

White pulp: lymphatic tissue

Red pulp: RBCs

Question 26

Splenic lymphatic nodules are also called:

Answer 26

Malpighian corpuscles

Question 27

Explain the open circulation of the spleen.

Answer 27

The splenic artery enters the spleen and sends branches out into the trabeculae (dense irregular CT from stroma). Once in the parenchyma, the artery is called the central artery. Central artery is surrounded by white pulp - periarterial lymphatic sheath, and splenic lymph nodules. Central artery runs into red pulp, etc etc… and they end blindly in the red pulp, dumping the blood into the spleen.

Question 28

How does blood exit the spleen?

Answer 28

Blood contents are dumped into splenic tissue, and RBCs re-enter circulation through VENOUS SINSUSES by squeezing through the elongated epithelial cells. Only healthy RBCs can get through, and macrophages pick out impurities.

Question 29

In the spleen, where are the T-cells? B cells?

Answer 29

T-cells are in the periarterial lymphatic sheath surrounding the central artery.

B-cells are in the splenic lymphoid nodules

Question 30

WTF is a cord of Billroth?

Answer 30

Strands of lymphatic tissue in the red pulp.

Question 31

What are the functions of the spleen?

Answer 31

1- Trap and mount immune responses against blood antigens.

2- Remove and phagocytose old RBCs and platelets

3- Remove iron from Hemoglobin and store it.

4- Hematopoeisis of FETUS

Question 32

If the spleen is removed, what takes over its role of removing damaged RBCS from the bloodstream?

Answer 32

Bone Marrow

Question 33

Where to T-cells develop?

Answer 33

Thymus

Question 34

What does the Thymus have instead of nodules?

Answer 34

Lobules

Question 35

What provides the structural framework for the Thymus?

Answer 35

Epithloireticular cells - form a continuous epithelium but are pushed aside as thymus develops. Retain their desmosomal junctions and their processes support the structure of the Thymus.

Question 36

Do epithelioreticular cells secrete reticular fibers?

Answer 36

No.

Question 37

What DO ecpithelioreticular cells secrete?

Answer 37

Soluble factors that promote T -cell differentiation.

Question 38

Differentiated T-cells are located in what part of the Thymus?

Answer 38

medulla