Lymphoid Tissue Flashcards
1
Q
What are specific defenses?
A
- Humoral response
- Cellular response
2
Q
What are nonspecific defenses?
A
- Physical barriers (ex. skin)
- Chemical defenses (ex. low pH)
- Secretory substances (ex. interferons, lysozymes)
- Phagocytic cells
- NK cells
3
Q
What are the primary lymphatic organs?
A
- Bone marrow and thymus
- Function to develop immunocompetence
- Antigen-independent production of lymphocytes
4
Q
What are the secondary lymphatic organs?
A
- Spleen, lymph tissue, nodes, vessels
- Surveillance, detection, and response to the presence of antigen
- Antigen-dependent production of lymphocytes
5
Q
What is the function of the thymus gland?
A
To harbour T cells, where they undergo positive and negative selection
6
Q
What is the structure of the thymus gland?
A
- Irregular left and right lobes
- Surrounded by a CT capsule
- Septae divide the parenchyma into lobules
- Efferent lymphatics run in the capsule and septae to reach the parenchyma
- There are no afferent lymphatics - not involved in initiating the immune response
- Each lobule has a cortex and medulla
- The cortex has numerous thymocytes, epithelioreticular cells and macrophages
- The medulla is lighter-staining, has fewer lymphocytes, and epithelioreticular cells
- Nascent T cells from the bone marrow develop in the cortex
7
Q
All lymphocytes, including T cells, B cells, and NK cells, develop in the ____.
A
Bone marrow
8
Q
Lymphocytes that are selected to live migrate to ____ where they undergo self-renewal through cell division and monitor body fluid for antigen.
A
Secondary lymphatic tissues
9
Q
What is the thymic stroma composed of?
A
- Cytoreticulum - composed of epithelioreticular cells joined by desmosomes
- Provide support to the parenchyma
10
Q
The majority of the cells of the thymic cortex are…
A
T-cells/thymocytes
11
Q
How can we histologically differentiate between macrophages and epithelioreticulocytes?
A
- Epithelioreticular cells - pale, eosinophilic cytoplasm, oval, euchromatic nuclei, and cell processes
- Macrophages - large size, presence of T cell nuclei in their cytoplasm
12
Q
Corticial epitheliorecticular cells secrete hormones that…
A
Regulate T cell differentiation and proliferation
13
Q
What is the blood-thymus barrier?
A
- Prevents premature stimulation of developing T cells
- Vessels in the cortex are sheathed by flattended ER cells joined by tight junctions
- Endothelial cells lining BVs are also joined by tight junctions
- CT between these layers have macrophages capable of phagocytosing any antigen that tries to enter the cortex from the blood
14
Q
The thymic medulla is supported by…
A
A cytoreticulum of epithelioreticular cells
15
Q
What types of T cells reside in the medulla?
A
Mature, immunocompetent T cells that will leave the thymus via post-capillary venules and efferent lymphatic capillaries to colonize secondary lymph organs
16
Q
What are thymic corpuscles?
A
- Characteristic of the medulla
- Consist of concentrically arranged epithelioreticular cells packed with keratin
- Appear as whirls of stratum corneum
- Unknown function
17
Q
What are diffuse lymphoid tissues?
A
- Loose CT dominated by lymphocytes (similar to adipose tissues being dominated by adipocytes)
- No CT capsule and no afferent lymphatics
- Forms lymphoid nodules in the lamina propria, called mucous-associated lymphoid tissue (MALT)
18
Q
What are mucous membranes?
A
- Line all passageways that open to the exterior
- Composed of an epithelium and an underlying lamina propria, consisting of loose aerolar CT
- MALT is located in the lamina propria
19
Q
A lymphoid nodule not actively responding to an antigen is called a…
A
Primary lymphoid nodule
20
Q
What is a secondary lymphoid nodule?
A
- A nodule that has become activated by antigen
- Has a paler germinal centre due to increased voume of cytoplasm in activated lymphocytes
21
Q
What is MALT?
A
- Mucosa associated lymphoid tissue
- Different names depending on the area
- There is GALT in the gut, and BALT in the bronchi
22
Q
The tonsils, Peyer’s patch, and the vermiform appendix are examples of…
A
GALT
23
Q
Lymphatic capillaries originate in the peripheral tissues as…
A
Blind-ended tubes
24
Q
What is the function of anchoring filaments in lymphatic vessels?
A
Connect to vessels from the collagen fibres of adjacent CT and function to keep vessels open
25
Lymph contains...
ISF, lymphocytes, macrophages, and other APCs, pathogens, and transformed cells
26
Overlapping endothelial cells in lymphatic vessels function as...
Valves to ensure one-way movement of lymph
27
What are lymph nodes?
* Function as in-line filters that detect and clear antigen from lymph
* Normally 2-10 mm in diameter, but become enlarged with activity
28
What are the two major lymphatic vessels?
Thoracic duct and right lymphatic duct, which join the venous system at the left and right venous angles
29
What is the general structure of lymph nodes?
* Dense fibrous CT capsule
* Trabeculae that extend into the node to subdivide its parenchyma
* Parenchyma is organized into cortex, paracortex, and medulla and is arrnaged around reticular fibre stroma
* Bean-shaped, with a hlium in the concave area containing arteries, veins, nerves and efferent lymphatics
* Afferent lymphatics enter the node on the convex surface
30
Lymph percolates through which spaces in the node before leaving the efferent lymph vessel?
Subcapsular, trabecular, and medullary sinuses
31
Lymph nodes contain which cell types?
Lymphocytes, macrophages, dendritic cells, reticular cells, and plasma cells
32
What structures of the lymph node faciliate interaction between antigen and lymphocytes?
1. Reticular fibres criss crossing the sinuses to slow antigen migration
2. Discontinuous epithelium lining the sinuses to faciliate interaction between antigen and resident cells
33
Describe the function of the cortex in lymph nodes.
* Afferent lymph passes through subcapsular and trabecular sinuses
* Macrophages detect and process antigen for presentation to T cells of the paracortex
* B cells form lymphoid nodules
* B cells proliferate and differentiate into plasma cells to form the germinal centres
* Plasma cells then migrate to the medulla to release antibodies into efferent lymph
34
Describe the function of the paracortex in lymph nodes.
* T cells dominate and are activated when resident APCs present antigen from afferent lymph
* Activated T cells leave via the efferent lymph
* There are no lymph nodules
* High endothelial venules (HEVs) are the point of entry into the paracortex for T cells from the circulation
35
Describe the function of the medulla in lymph nodes.
* Medullary cords, separated by sinuses, contain B cells, plasma cells, and macrophages
* Antibodies produced by plasma cells of the medulla leave via efferent lymph for systemic distribution
36
# True or False:
The spleen contains afferent lymph vessels.
False
37
What are the two functions of the spleen?
1. Functions similar to lymph nodes but for blood, releasing activated T cells and antibodies into the circulation in response to blood borne antigens
2. Removes aged/damaged RBCs from circulation via phagocytosis
38
Describe the general structure of the spleen.
* Surrounded by fibreoelastic CT capsule rich with afferent pain fibres
* Again, CT septae/trabeculae extend into the parenchyma to subdivide it
* The spleen is supported by reticular fibre stroma
* The parenchyma contains reticulocytes, lymphocytes, other blood cells, macrophages, and other APCs
* The parenchyma is organized into white pulp and red pulp
39
What is the white pulp of the spleen?
* Mostly lymphocytes and APCs
* Where immune responses to blood borne antigens occur
* Antigen is presented to T cells, which leave the spleen via efferent blood
* B cells form peripheral white pulp, comparable to the cortex of lymph nodes
* Marginal zone sinueses is where B and T cells interact with antigen/APCs
40
How does blood flow into white pulp of the spleen?
* Blood from splenic artery flows into trabecular arteries, then into central arterioles
* Central arterioles are surrounded by T cells and macrophages forming the periarteriolar lymphoid sheaths (PALS)
41
What is the red pulp of the spleen?
* Where old RBCs are removed
* Consists of blood-filled spaces called the splenic sinusoids, which exist between splenic cords
* Central arterioles of white pulp become the penicillar arterioles of the red pulp
* Some pencillar arterioles are surrounded by macrophages ("sheathed") in case antigens escape white pulp
* Sheathed capillaries open into the splenic cords, where blood leaves the vascular system
* Red pulp veins flow into trabecular veins, coalescing as the splenic vein
42
What is open circulation in red pulp?
* Blood leaving sheathed capillaries and entering the splenic cords must pass through "slits" in the walls of splenic sinusoids to re-enter circulation
* These slits are created by stave cells, which are arranged parallel to the flow of blood and are stabilized by reticular fibres
* The stave cells are separated by spaces smaller than RBCs
* This does not present a barrier to young, flexible RBCs, WBCs, and platelets
* Older platelets cannot pass through and are phagocytosed by macrophages of the splenic cord
43
Contrast the histology of the red pulp vs the white pulp.
* White pulp: densely-packed nuclei give white pulp a basophilic appearance, and germinal centers in splenic nodules are paler staining
* Red pulp: appears eosiniphilic due to predominance of RBCs; consists of sinusoids and splenic cords
