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Lymphatic Tissue Flashcards

0
Q

What are the primary lymphatic organs?

A

Bone marrow and thymus

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1
Q

Lymphatic tissue can be organized into what three categories?

A
  1. Lymphatic tissue
  2. Lymphatic nodules
  3. Lymphatic organs
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2
Q

What are the secondary lymphatic organs?

A

Lymphatic nodules, tonsils, appendix, lymph nodes, and spleen

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3
Q

Where do the lymphocytes develop?

A

In primary lymphatic organs - bone marrow or thymus

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4
Q

Where do lymphocytes function?

A

In secondary lymphatic organs - lymphatic nodules, tonsils, appendix, lymph nodes, and spleen

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5
Q

What is the function of cells in lymphatic tissues?

A

Recognize and destroy antigens - B lymphocytes, plasma cells, T lymphocytes, macrophages, and antigen presenting cells

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6
Q

What is an antigen?

A

Any substance that can induce an immune response - soluble substances, infectious microorganisms, foreign tissue, or transformed/cancerous cells.

Most antigens must be processed by cells of the immune system before other cells can initiate an immune response

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7
Q

What is an antibody?

A

An immunoglobulin synthesized and secreted by the plasma cells, they create an antigen-antibody complex that gets eliminated in one of several ways

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8
Q

Describe the innate immune response:

A

It is non-specific, functions as the first line of defense against antigens - the mechanisms include physical barriers like skin and internal epithelial linings (mucous membranes), and chemical (low pH) and secretory substances (lysozyme, proteins in saliva). If the antigen gets past the non-specific barrier, it is attack by the adaptive immune system.

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9
Q

Describe the adaptive immune response:

A

It is acquired, specific, and occurs when the body is exposed to various antigens and builds a defense that is specific to that antigen. Lymphocytes are a part of adaptive immune responses

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10
Q

Humoral and cellular immunity are a part of what immune response?

A

Acquired or adaptive immune response

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11
Q

What happens in the humoral immune response?

A

B lymphocytes (B cells) differentiate into plasma cells that synthesize and secrete antibodies to destroy antigens and prevent the spread of infection

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12
Q

What happens in the cellular immune response?

A

In cellular immunity, T lymphocytes (T cells) destroy transformed and virus-infected cells. ***Antibodies do not function in cellular immune responses

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13
Q

Cells of the immune system include lymphocytes, as well as:

A

Supporting cells - monocytes, macrophages, neutrophils, basophils, eosinophils, reticular cells, dendritic cells, follicular dendritic cells, Langerhan’s cells, and epithelioreticular cells

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14
Q

In what ways are different types of cells in lymphatic tissue identified by?

A

By proteins expressed on their cell surface - cluster of differentiation (CD) markers, major of histocompatibility (MHC) proteins, T cell receptors (TCR), and B cell receptors (BCR)

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15
Q

What are CD proteins and what are they useful for?

A

CD proteins are transmembrane proteins that have a cell-type and differentiation-type specific expression pattern. They are used to distinguish between different types of T CELLS - CD4 and CD8

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16
Q

What are MHCs?

A

Group of transmembrane proteins that act in the regulation of the immune system through recognition of “self” and “non-self.” MHCs are an absolute requirement for an individual to successfully respond against and to subsequently eliminate foreign agents. (A lack of these would mean a lack of immune response –> severe immunodeficiency)

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17
Q

Where is MHC I expressed?

A

On all nucleated cells and on platelets. They act as a target to allow elimination of abnormal host cells - virus-infected or transformed cancerous cells

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18
Q

Where do MHC I present peptide fragments?

A

To cytotoxic CD8+ lymphocytes

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19
Q

Where are MHC II expressed?

A

On the surface of antigen presenting cells (APCs), such as dendritic cells and macrophages

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20
Q

What do MHC II present foreign peptides to?

A

Helper CD4+ lymphocytes

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21
Q

What are TCRs?

A

Expressed by T lymphocytes - recognize a single antigen, and are used along with other proteins in T cell recognition of antigens

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22
Q

What are BCRs?

A

BCRs are expressed on the surface of B cells and also recognize only ONE antigen. BCR recognition of an antigen leads to the differentiation of a B cell to a plasma cell

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23
Q

What is the main cellular component of lymphatic tissue and organs?

A

Lymphocytes - B or T. Circulating lymphocytes are IMMUNOCOMPETENT - they are capable of developing an immune response following exposure to antigen

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24
Describe the basics of T lymphocytes:
They undergo ANTIGEN-INDEPENDENT differentiation in the thymus (primary lymphatic organ for T cell maturation) to become immunocompetent cells. They have a long lifespan and are involved in CELL-MEDIATED IMMUNITY. They enter the bloodstream or lymphatic systems and account for the majority (60-80%) of circulating lymphocytes. They become incorporated into lymphatic tissue and secondary lymphatic organs
25
What are the two classes of T lymphocytes?
Helper T lymphocytes and Cytotoxic T lymphocytes
26
What are the Helper T lymphocytes?
CD4+ T cells because they express CD4 protein,
27
What is the function of helper T lymphocytes?
Help with humoral and cellular immunity - promote activation and proliferation of B cells and CD8+ T cells that have encountered their specific antigens
28
What are cytotoxic T lymphocytes and what is their function?
CD8+ T lymphocytes because they express CD8 protein. They kill cells infected with intracellular pathogens or destroy transformed cells or cancerous cells.
29
What are B lymphocytes? What time of differentiation do they undergo?
Undergo antigen-independent differentiation in the bone marrow, become plasma cells, 20-30% of the cells circulating in blood, become part of lymphatic tissues and secondary lymphatic organs. They participate in humoral immunity by differentiating into plasma cells in the presence of an antigen --> secrete antibodies (immunoglobulins)
30
What are antigen presenting cells?
They are required by lymphocytes to recognize and destroy antigens. B and T cells cannot function on their own, they need the APCs. They are part of the mononuclear phagocytic system and include: Macrophages in CT and lymphatic organs, Kupffer cells of the liver, Langerhan's cells in epidermis, and dendritic cells in the spleen, and lymph nodes, and epithelioreticular cells in the thymus
31
What is the function of APCs?
Recognize molecules or antigens --> endocytose them --> process (digest) them --> bind and display them on their cell surface complexed to MHC II --> present them to lymphocytes
32
What are some of the other functions of APCs in the immune response? (3)
1. They secrete proteins necessary for immune and inflammatory reactions 2. Activated macrophages destroy phagocytosed bacteria and foreign antigens 3. Macrophages can fuse to form multinucleate foreign body giant cells to isolate certain pathogens from the body
33
Describe the lymphatic vessel system:
It is a separate circulatory system from the blood vascular system, begins as networks of blind-ended capillaries in loose CT, especially in skin and mucous membranes. Lymphatic capillaries merge to form lymphatic vessels
34
Function of lymphatic vessels:
Primarily to carry lymph (tissue fluid, a filtrate of blood plasma) - lymph returns proteins and lymphocytes back to the blood, transposts antigens to lymph nodes, and transports lipids (chylomicrons) and lipid-soluble vitamins absorbed in the GI tract to the blood (central lacteal in small intestine).
35
Describe lymphatic vessels:
Resemble blood vessels - have very thin walls that consist essentially of endothelium
36
There is no pump in the lymphatic system so how does the lymph move throughout the system?
By skeletal muscle action and respiratory movement. Lymph enters lymph nodes via afferent lymphatic vessels and exits via efferent lymphatic vessels.
37
Lymphatic vessels eventually lead to:
Right lymphatic duct or the thoracic duct (left lymphatic duct)
38
Where does the lymph become a part of the blood vascular system?
Where the right lymphatic and thoracic duct empty into venous circulation at the base of the neck
39
What is diffuse lymphatic tissue?
- Consists of T and B cells, plasma cells, and APCs - Not enclosed by a CT capsule - Recognizes antigens that have broken through the nonspecific epithelial barriers - immune cells positioned to recognize antigens and initiate immune responses
40
Where is diffuse lymphatic tissue found?
In loose CT lamina propria of the GI tract, respiratory passages, and genitourinary tract. GALT - gut-associated lymphatic tissue, MALT (mucosa), and BALT (bronchial)
41
Describe lymphatic nodules:
- Aka lymphatic follicles - Localized concentrations of lymphocytes - Found singly or in groups in the GI, respiratory, and genitourinary tracts - NOT ENCAPSULATED by CT - Primary and secondary lymphatic nodules are identified based on histological func/char
42
Describe primary lymphatic nodules histologically:
Consist of mainly small, inactive B lymphocytes, are round or oval in shape, have defined edges but no CT capsule, and are uniformly and densely basophilic
43
Describe secondary lymphatic nodules histologically:
Have an inner germinal center and an outer mantle zone or corona
44
Which zone of the secondary lymphatic nodule develops in response to an antigen?
Germinal centers
45
Describe the central germinal center:
Paler staining because of increased numbers of large maturing B lymphocytes
46
Describe the mantle zone or corona:
Outer ring of small B cells that encircles the germinal center. It is typically densely basophilic
47
Secondary lymphatic nodules are mostly found where?
Locations in the outer cortex of lymph nodes, the appendix, the ileum of the small intestine as Peyer's patches, spleen white pulp, and tonsils (although they can form anywhere in the body)
48
Describe what tonsils are:
Aggregates of primary and secondary lymphatic nodules with a surface covering of epithelium and a CT base.
49
What is Waldeyer's ring?
Tonsils form a ring of lymphatic tissue at the entrance of the oropharynx known as tonsillar or Waldeyer's ring
50
What type of epithelium do pharyngeal (adenoids) and tubal tonsils have?
Respiratory epithelium - pseudostratified columnar with Goblet cells
51
What type of epithelium do palatine and lingual tonsils have?
Stratified squamous nonkeratinized epithelium
52
Do tonsils have afferent lymphatic vessels? Efferent lymphatic vessels?
NO!; yes to efferent
53
What is special about the appendix?
The CT lamina propria of the appendix is heavily infiltrated with lymphocytes and contains many lymphatic nodules
54
What are lymph nodes?
Encapsulated secondary lymphatic organs located along the pathway of lymphatic vessels, where B and T cells live and carry out their functions
55
Functions of lymph nodes: (5)
1. Filtration of lymph 2. Removal of bacteria and other particulate matter from lymph 3. Production of antibodies from plasma cells 4. Storage of T and B cells 5. All lymph will pass thru at least one lymph node on its way to the right lymphatic or thoracic duct (L)
56
Connective tissue elements of the lymph node includes: (3)
1. Capsule - each lymph node is surrounded by a dense irregular CT capsule (encapsulated lymphatic organ) 2. Trabeculae - CT extends into lymph nodes as trabeculae, stains eosinophilic 3. Reticular connective tissue stroma - collagen type III - provides a fine meshwork that surrounds and organizes the lymph node parenchyma
57
The cellular elements of the lymph nodes include:
(Called parenchyma) 1. Outer (superficial) cortex 2. Paracortex 3. Medulla
58
What is the outer (superficial) cortex of the lymph node?
- Parenchyma just underneath the capsule - Contains primary and secondary lymphatic nodules with B cells, reticular cells, plasma cells, and macrophages - Follicular dendritic cells (type of APC) will be located in the germinal centers of the secondary lymphatic nodules - B-cell-dependent region of lymph node
59
What is the paracortex (deep cortex) of the lymph node?
- Parenchyma that lies between the superficial cortex and the medulla - Lacks lymphatic nodules - Zone of densely packed cells, mainly T cells - Dendritic cells (another APC) are localized here - Contains specialized bv - high endothelial venule (HEV) - T cell-dependent region of the lymph node
60
What is the medulla of the lymph node?
- Consists of a network of medullary cords (dark staining basophilic) and medullary sinuses (pale-staining)
61
Medullary cords consist of:
Plasma cells, macrophages, T cells, dendritic cells (APC), and reticular cells
62
Where is there a high concentration of antibodies in the lymph node?
In the medulla because of the plasma cells
63
What is the function of the medullary sinus?
Channel lined with endothelium, function in draining lymph out of the lymph node
64
Which side are the sinuses lined with a continuous endothelium?
Next to the connective tissue
65
Which side are the sinuses lined with a discontinuous endothelium?
Next to the parenchyma
66
What spans the lumens of the sinuses?
Macrophages and reticular cell processes and by reticular fibers. This causes the lypmh to slow down as it flows through the sinuses so particulate matter and degenerating cells can be removed
67
Describe the flow of lymph through a lymph node:
Afferent lymphatic vessels (with valves) --> pierce the capsule and bring lymph into the lymph node --> subcapsular sinuses (located underneath the capsule) --> trabecular sinuses (located along the CT trabeculae) --> medullary sinuses (between medullary cords) --> efferent lymphatic vessels exiting the lymph node at the HILUS
68
What are HEVs?
Type of postcapillary venule located in the paracortex of lymph nodes, lined with cuboidal or columnar endothelial cells (instead of squamous). HEVs are the entry site of T and B cells from the blood into the lymph node
69
What is diapedesis?
Lymphocytes cross HEV endothelium by squeezing through the endothelial cells and crossing thru the basal lamina
70
Once lymphocytes have left the blood, where do T cells remain? Where do B cells migrate to?
T cells remain in the deep cortex; B cells migrate to the lymphatic nodules in the outer cortex
71
How do lymphocytes leave the lymph node?
By entering into the lymphatic sinuses and then getting into the efferent lymphatic vessel. They CANNOT leave a lymph node by entering the blood vascular system
72
What is a reactive lymph node?
Enlarged lymph node, described as a swollen gland, caused by injury or an infection
73
What is the thymus?
Bilobed, encapsulated lymphatic organ in the superior mediastinum, primary lymphatic organ because it is the site of T cell differentiation
74
Connective tissue elements of the thymus include: (3)
1. Capsule 2. Trabeculae 3. Stroma of epithelioreticular cells - the thymus does NOT contain reticular cells and fibers - lymphocytes are organized and supported by epithelioreticular cells held together in a network throughout the thymus by desmosomes - 6 different types of epithelioreticular cells that function to provide physical and metabolic support to lymphocytes
75
Describe the thymic cortex:
- Peripheral location and is strongly basophilic | - Contains developing T cells (thymocytes) within a meshwork of epithelioreticular cells
76
Describe the thymic medulla:
- More central location with a paler staining with H/E - Contains epithelioreticular cells and immunocompetent T cells - Continuous through all of the lobules - NO lymphatic nodules in thymus
77
Where are Hassell's corpuscles?
Unique feature of the thymic medulla - composed of concentric layers of flattened epithelioreticular cells (role in dendritic cell-mediated secondary positive selection of self-reactive T cells?)
78
The thymus is the site of:
Immature thymocytes differentiating into immunocompetent T cells. This process is promoted by substances secreted by epithelioreticular cells During development of thymus, multipotent lymphoid stem cells invade epithelial rudiment --> as immature thymocytes develop in cortex --> express correct CD, TCR, and recognize self-antigens --> or die by apoptosis (98%) --> phagocytosed by macrophages
79
What happens to T cells that have developed correctly?
They migrate to the medulla where they enter the bloodstream through post-capillary venules or enter the lymph thru efferent lymphatic vessels at the corticomedullary junction --> populate secondary lymphatic organs
80
How does the thymus prevent antigens from interacting with the developing thymocytes?
1. Thymus only has efferent lymphatic vessels (no afferent lymphatic vessels) 2. Capillaries in the cortex of the thymus are part of the blood-thymus barrier
81
The blood-thymus barrier consists of:
- Continuous endothelium with tight junctions - Endothelial cell basal lamina - Perivascular CT that may contain macrophages - Epithelioreticular cell basal lamina - Epithelioreticular cells
82
When does the thymus reach its greatest relative weight?
At birth
83
When does the thymus reach its greatest absolute weight?
At puberty - the thymus then begins to involute and becomes infiltrated with adipose and CT
84
Describe the spleen:
Encapsulated secondary lymphatic organ - the largest
85
What are the functions of the spleen? (6)
- Filtration of blood by macrophages and dendritic cells to remove antigens and cellular debris - Destruction of aged or abnormal erythrocytes - Ab production - Platelet and erythrocyte storage - Participates in hemopoiesis during fetal development - Despite variety of functions, spleen is NOT essential for life
86
Connective tissue elements of spleen include:
Capsule, trabeculae, and stroma of reticular cells and reticular fibers
87
What is the parenchyma of the spleen?
It is splenic pulp and is organized into white pulp and red pulp
88
Describe the white pulp of the spleen:
It is organized around an arteriole called the central artery - splenic artery branches into trabecular arteries, then into central arteries and these enter into the white pulp
89
What is each central artery surrounded by?
A sleeve of T lymphocytes - this is the periarterial lymphatic sheath (PALS). It has a high concentration of T cells so it is T cell-dependent region of the spleen
90
In addition to the central artery and PALS, what else does the white pulp contain?
Primary and secondary lymphatic nodules that are continuous with PALS. They consist of mainly B cells, macrophages, and APCs - this region is B-cell dependent
91
How does the white pulp appear in H/E staining?
As circular basophilic regions with an eosinophilic profile of the central artery
92
Describe the red pulp of the spleen - what does it consist of? Where is it located?
Consists of splenic cords (red pulp cords, cords of Bilroth) and splenic sinuses (venous sinuses). It stains eosinophilic and is located between and around the areas of white pulp
93
What are splenic cords?
Loose meshwork of reticular cells and reticular fibers that contain large numbers of erythrocytes, macrophages, lymphocyte, and other white blood cells, dendritic cells, and plasma cells
94
What are splenic sinuses?
Special sinusoidal vessels, the endothelial cells lining the sinusoids are long, rod-shaped, and are oriented along the longitudinal axis of the vessel. There are large intercellular spaces and perisinusoidal loops of basal lamina. This permits blood cells to pass in and out of the sinusoids easily.
95
What extends into the lumen of sinuses and what is the purpose?
Processes of macrophages, to monitor passing blood for antigens
96
What is the flow of blood in the open circulation of the spleen?
Splenic artery --> trabecular artery --> central artery --> penicillar arterioles --> sheathed capillaries --> terminal arterial capillaries --> reticular meshwork of the splenic cords --> splenic sinus --> trabecular vein --> splenic vein
97
What happens in the open circulation?
Capillaries open directly into the red pulp and blood percolates thru the red pulp until it reachs a splenic sinus.
98
It is thought that most of the circulation in the human spleen is open. What is the purpose?
To expose blood more efficiently to the macrophages of the red pulp
99
What is the blood flow of the closed circulation system?
Splenic artery --> trabecular artery --> central artery --> penicillar arterioles --> ensheathed capillaries --> splenic sinus --> trabecular vein --> splenic vein
100
What happens in closed circulation?
Blood is always enclosed in a vessel although it freely leaves and enters the splenic sinus

Histology (24 decks)

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