Histo Quiz 1

Question 1

Vocabulary

1. Molecules that bind to antibodies or the T cell receptor (bacteria, parasites and viruses)
2. Bind small regions (epitomes) of large molecules e.g
   - proteins, complex carbohydrates, lipids, nuclei acids (linear or conformational)
   - small molecules like steroid hormones
3. Where antigen bind. B lymphocytes have membrane bound antibodies while T lymphocytes have its own T cell receptors that recognize small peptides on SURFACE of antigen presenting cells or infected cells.
4. Network of RETICULAR FIBERS and spherical Non encapsulated aggregates of lymphocytes that make up cortex of lymph node
5. Lighter staining central areas of lymphoid nodules
6. Peyer’s patch’s are what loose CT of part of small intestine? Mucosa-associated lymphoid tissue are found here
7. Secondary lymphoid organ associates with ?
8. Located underneath the mucosa

Answer 1

1. Antigen
2. Antibody
   - structure composed of 2 heavy chains and 2 light chains
3. Antigen receptor
4. Lymphoid nodule
5. Germinal center
6. Lamina propria
7. Mucosa (innermost layer of digestive tube)
   - consist of a lining epithelium and glands that extend into the underlying loose CT called lamina propria
8. Submucosa

Question 2

Compare primary and secondary lymphoid tissues?

**what processes occur in each

Answer 2

1. PRIMARY lymphoid tissues
   - BONE MARROW (B cell) and THYMUS (T cell)
   - generative organs where lymphocytes are born and mature
   - mature but NAIVE B CELLS migrate to secondary lymphoid tissue
   - immature T cells migrate to the thymus for further maturation
2. SECONDARY lymphoid tissues
   - LYMPH NODES (filter for the lymph, initiate adaptive immune responses to lymph-borne antigens)
   - SPLEEN, (filter for the blood), remove aged RBCs
   - TONSILS,
   - MALT (mucosa associated lymphoid tissue)

Question 3

Compare Innate immunity, adaptive, humoral and cell-mediated immunity

**what cell types are associated with each

Answer 3

1. Innate immunity - neutrophi, macrophages
   -first line of defense to prevent spread of infection
   - RAPID and mobilize neutrophils, mast cells, macrophages, NK cells
   -FAST and NONSPECIFIC, NO MEMORY cells
   E.G dendritic cells in langerhan’s cells.
2. Adaptive immunity - lymphocytes, plasma cells
   - slower, more specific with memory cells
   - have rapid, stringer and longer lasting defense on second antigen attack
   - T cells and B cells
   - 2 types humoral or cell mediated
3. Humoral Immunity
   - B cells, plasma cells and antibodies in the blood and lymph
   - B cells first encounter antigen and then proliferate and turn to plasma cells
   - need help of T cell too
4. Cell-mediated immunity
   - Specific T cells stimulated by antigen on surface of APCs
   - T cell secrete cytokines that activate other T cells, B cells and cytotoxic T cells (apoptosis - programmed cell death of target cells)
   - activated T cells destroy by direct contact
   - T cells can also attach indirectly by activating B cells or stimulating macrophages

Question 4

Compare antigens and antigen receptors on B cells and T cells

**Describe the structure of antibody and what constitutes its binding site

Answer 4

1. B-cell antigen receptor
   - B lymphocytes have MEMBRANE BOUND ANTIBODIES which recognized epitomes on a various EXTRACELLULAR MACROMOLECULES
2. T-cell antigen receptor
   - T lymphocytes have TCR which recognizes small peptides on the SURFACE of antigen presenting cells or infected cells

Structure of antibody

• 2 heavy chains and 2 light Chadian
• N terminal highly variable
• antigen binding domain has variable regions of light and heavy chains (specific, diverse, 2 binding sites per antibody molecule)
• membrane bound antibodies also have a transmembrane domain at C-terminal

Antigen binding site
-In TCR (t cell antigen receptor), a single antigen binding site is formed by variable regions

Question 5

1. What is lymphoid nodule
   - what immune process occurs here
   - what cell types are involved
   - where are lymphoid nodules found
2. What is a germinal center

Answer 5

1. Lymphoid nodule
   - B cells congregate here (cortex of lymph nodes). T cells in deep cortical region
2. Germinal center
   - central region o lymphatic nodule (lighter stained)

• Lymph nodes are the sites of antigen recognition and activation of B cells which give rise to plasma cells and memory B cells
• B cells are activated by APCs and the proliferate in the germinal centers

Question 6

Describe the organization of the thymus

• cell types in each region
• histology feature that is a defining character for thymus
• blood-thymus barrier?

Answer 6

1. Organization of thymus (lobule, cortex, medulla)
   - main function is to produce mature T cells that respond to antigens (also collect undifferentiated lymphocytes from bone marrow via bloodstream)
2. Cell types
   - epithelial reticular cells (thymus nurse cells); surround and promote proliferation and maturation of lymphocytes (mature to immunocompetent T cells, helper T cells, cytotoxic T cells)
3. Histology
   - THYMIC (HASSAL) corpuscle ; present in the center of the medulla in one of the lobes
4. BTB (blood-thymus barrier)
   - formed by endothelial cells, epithelial reticular cells and macrophages
   - prevents exposure of IMMATURE T cells to foreign antigens (macrophages)
   - no afferent lymph vessels
   - capillaries have thick basal lamina (non fenestrated and have tight junctions btw adjacent endothelial cells)
   - epithelial reticular cells have tight junctions and thick basal lamina

**PEAK activity of thymus is from birth to puberty.

Question 7

1. Organization of lymph node (encapsulated lymphoid organ along with spleen)
2. describe blood and lymph flow in lymph node
3. cell types in each region of lymph node
4. How lymphocytes circulate form lymph node to the blood
5. How lymphocytes return to the lymph node

Answer 7

1. ORGANIZATION (trabeculae - anterior, outer cortex, inner medulla, capsule)
   - located throughout body along lymph vessels (inguinal and AXILLARY regions of body)
   - FILTER for the LYMPH
   (Monitors for foreign antigens in tissues, adaptive immune responses to lymph-borne antigens initiated)
2. BLOOD and LYMPH FLOW
   - movement of lymphocytes btw lymph nodes where they can be ACTIVATED and sites of infection where they can ELIMINATE PATHOGENS
   - takes place in the lymph nodes, tonsils, Peter patches and spleen
3. CELL TYPES
   * *B cells made (also has T cells)
4. Lymphocytes leave lymph nodes via efferent lymphatic vessels
   - they enter blood circulation through lymphatic ducts
   * *lymph nodes - efferent lymphatic vessels - lymphatic ducts - blood - (HEV - back to lymph nodes)
5. Return to lymph node
   - lymphocytes B and T cells enter lymph nodes from blood through HEV (high endothelial venules) ; called HOMING
   * found in secondary lymphoid tissue except spleen
   * specialized endothelium with tall cuboidal cells
   * *HEV are present in Peter patches, tonsils appendix and cortex of thymus
   * *HEV are absent from the spleen

Question 8

1. Organization of spleen
2. Function
3. Compare cords and sinuses
4. Cell types in each region of spleen
5. How do cell types help function of spleen

Answer 8

1. ORGANIZATION
   A. Capsule - surround spleen and divides incomplete parts into splenic pulp (white and red)
   B. Trabeculae
   C. White pulp (B and T lymphocytes
   D. Red pulp (red blood cells, macrophages and other blood cells)
   **NO CORTEX OR MEDULLA
2. FUNCTION
   A. Filter for the BLOOD
   - monitors for foreign antigens in the blood
   - activates lymphocytes (production of antibodies)
   B. Removes aged red blood cells (recycle iron)
   C. Reservoir for blood
3. CELL TYPES
   A. Red pulp; dense reticular fibers; erythrocytes, lymphocytes, plasma cells, macrophages, granulocytes (filter blood)
   B. White pulp (immune part); lymphocytes in nodule that surround central artery
   * mainly T cells that form PALS - around central artery
   *B cells in lymphoid nodule
4. CELL TYPES FUNCTION
   - T and B cells detect trapped bacteria and antigen and initiate immune responses against them

Question 9

1. Where are mucosal associated lymphoid tissues found
2. How can they be distinguished
3. What lymphoid cell types are associated with MALT

Answer 9

1. MALT are collections of lymphoid tissue in the lamina propria underlying the mucosal epithelium of tissues with opening to external environments
   - GI tract
   - respiratory tract
   - reproductive tract
2. Distinguished by the associated epithelium
3. Large amounts of IgA (secreted dimer for mucosal immunity) are secreted by plasma cells (mature B cells?) and transported across mucosal epithelium to lumen of tissue

Question 10

1. Compare thymus, lymph node, spleen and MALT with respect :
   * to the presence of germinal centers/lymphoid nodules
   * location of B and T lymphocytes

Answer 10

1. THYMUS
   - T cells mature here (helper T cells, cytotoxic, memory and suppressor T cells)
   - no B cells (Helper T cells secrete cytokines or interleukins that stimulate B cells to become plasma cells and secrete antibodies)
2. LYMPH NODE
   - has lymphoid nodules (B cells) that form the outer cortex, activated B cells form germinal layer
   - produce, store and recirculate B cells and T cells
3. SPLEEN
   B and T cells in the white pulp (lymphoid nodules has Germinal center around central artery)
   - T cells form PALS around central arteries
   -B cells found in lymphatic nodules
4. MALT (mucosa associated lymphoid tissue)
   - large amounts of IgA (secreted dimer for mucosal immunity) secreted by plasma cells and go across epithelium into lumen of tissue

Question 11

Categorize the immunoglobulin isotopes into

• isotype
• *form
• selected function

Answer 11

1. IgM
   - form; MEMBRANE and SECRETED PENTAMER
   - function; B CELL type antigen receptor
2. IgD
   * form - MEMBRANE
   * function - B CELL antigen receptor
3. IgG
   * form - SECRETED (major immunoglobulin found in SERUM)
   * function - phagocytosis, neonatal immunity
4. IgE
   * form - SECRETED (binds to receptors on MAST CELLS)
   * function - Allergic reactions, parasites
5. IgA
   * form - SECRETED, DIMER
   * function - Mucosal immunity

Question 12

WHAT are the 3 types of tonsils ?

• location
• cell type
• crypts of no crypts

Answer 12

1. Pharyngeal
   - superior portion of the pharynx
   - ciliated pseudostratified columnar epithelium and stratified squamous nonkeratinizing epithelium
   - NO CRYPTS
2. Palatine
   - lateral walls of the oral pharynx
   - stratified squamous nonkeratinizing epithelium
   - MULTIPLE CRYPTS
3. lingual
   - base of tongue
   - stratified squamous epithelium
   - SINGLE CRYPT