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IHO: Week 1 - WLB > Lymphatic Tissue - Downing > Flashcards

Lymphatic Tissue - Downing Flashcards

1
Q

What are the two central (primary) locations of lymphatic tissue?

A
  1. Bone marrow - source of B-cells
  2. Thymus - source of T-cells

central = where lymphocytes originate

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2
Q

What are the peripheral (secondary) locations of lymphatic tissue?

A
  • Mucosa-associated lymphatic tissue (MALT) or nodular non-encapsulated lymphatic tissue
    • lymphatic nodues, tonsils, Peyer’s patches, appendix, respiratory system
  • Lymph nodes
  • Spleen

peripheral = where lymphocytes respond to antigens

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3
Q

Lymphatic tissue is populated mostly with what kind of lymphocytes?

A
  • Small lymphocytes
    • B-cells
    • T-cells
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4
Q

What constitute the large lymphocytes in lymphatic tissue?

A
  • Activated lymphocytes
  • NK (natural killer) lymphocytes
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5
Q

What are the functions of lymphatic tissue?

A
  • Lymphocyte production
  • Immune responses: small lymphocytes
    • recirculate between blood & lymph
    • immunocompetent cells - capable of responding to antigen
      • B-cells: differentiate into plasma cells (and produce humoral antibodies) or remain as memory cells
      • T-cells: cell-mediated immune responses or remain in tissues as memory cells
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6
Q

What are the cellular components (4) of lymphoid tissue stroma?

A
  • Reticular cells
    • fibroblast-like, produce reticular fibers (Type III collagen)
  • Macrophages (APCs)
    • process and present antigens
    • phagocytosis of foreign particulate matter
  • Dendritic cells
    • very efficient APCs (professionals)
  • Follicular dendritic cells
    • bind antibody-antigen complexes on surface of processes
    • do not process/endocytose antigen
    • not APC
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7
Q

How do lymphocytes respond to antigen exposure?

A

Enlargement & Proliferation

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8
Q

What are the two classifications of non-encapsulated tissue that are based on gross histological arrangement?

A
  • Diffuse lymphatic tissue
    • loose
    • dense
    • GI tract, respiratory tract, & others
  • Nodular lymphatic tissue
    • solitary lymphatic nodules (follicles)
    • represent local immune responses to antigens
    • GI, respiratory, urinary tract, & others
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9
Q

What is a primary lymphatic nodule?

A
  • Dark staining spherical ball of lymphocytes
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10
Q

What is a secondary lymphatic nodule?

A
  • Contains a reaction (germinal) center
  • Antigen dependent (antigen insult required)
  • Cells include:
    • Large and medium sized mitotic lymphocytes (primarily B-cells, lymphoblasts)
    • Small lymphocytes (both B- & T-cells)
    • Macrophages (APCs)
    • Follicular dendritic cells (FDCs)
    • Developing plasma cells (periphery of germinal center
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11
Q

When do secondary lymphatic nodules appear, occur, and decline?

A
  • Do not appear until after birth
  • Disappear in absence of antigen, and reappear with re-exposure to antigen
  • Numerous during childhood, but decline in number with age
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12
Q

Where do lymphatic nodules (follicles) occur in the body?

A
  • Solitary (isolated)
  • Lymph nodes
  • Spleen
  • NOT IN THE THYMUS
    • if present → pathological condition
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13
Q

What are three examples of nodular non-encapsulated lymphatic tissue?

A
  • Tonsils
    • Palatine (on each side of uvula)
    • Lingual (behind tongue)
    • Pharyngeal and tubal tonsils (nasopharynx)
  • Peyer’s patches (ileum of small intestine)
  • Appendix
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14
Q

What are the three functions of non-encapsulated lymphatic tissues?

A
  1. Trapping/processing of antigen
  2. Lymphocyte production in response to antigen (B-cell proliferation)
  3. Destruction of antigen
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15
Q

What are the three encapsulated lymphatic tissues discussed in class?

A
  1. Lymph Node
  2. Thymus
  3. Spleen
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16
Q

What is the only lymphatic organ located in course of lymphatic vessels, the only lymphatic organ that has lymphatic sinuses, and the only lymphatic organ that filters lymph?

A

Lymph Node

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17
Q

What are the four main morphological features of a lymph node?

A
  1. Capsule
  2. Trabeculae
  3. Stroma (with cells & fibers)
  4. Endothelial cells lining sinusoids
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18
Q

What are the two major divisions of a lymph node?

A
  • Cortex
    • superficial
    • mid-cortex (germinal centers)
    • deep cortex (paracortex)
  • Medulla
    • medullary cords
    • medullary sinuses
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19
Q

Describe the lymph flow through a lymph node.

(hint: 6 steps)

A
  1. Afferent lymphatic vessels
  2. Subcapsular (marginal) sinus
  3. Trabecular (peritrabecular) sinus
  4. Paracortical (subcortical) sinus
  5. Medullary sinus
  6. Efferent lymphatic vessel
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20
Q

Describe the blood flow through a lymph node.

(hint: 5 steps)

A
  1. Arterial vessels (hilum)
  2. Trabecular vessels
  3. Arterioles & capillaries
  4. Post-capillary venules (outer cortex: superficial/mid & deep: paracortex/HEV’s)
  5. Venous vessels (hilum)
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21
Q

What unique process happens in the deep cortex post-capillary venules?

A
  • Passage of lymphocytes (T- & B-) from the blood vessels (venules) into the lymphatic tissue for recirculation via the efferent lymphatics back to the blood vascular system
    • venules lined by simple cuboidal endothelium: HEV’s (high endothelial venules)
22
Q

What happens if a thymectomy (removal of the thymus) is performed at birth?

A
  • Depletion of lymphocytes from deep & mid-cortex
  • HEV endothelium reverts to simple squamous
23
Q

What is the source of lymphocytes in lymph nodes?

A
  • Mitotic division of lymphocytes in lymphatic nodules
  • Circulating lymphocytes
    • Post-capillary venules (95%)
  • Afferent lymphatics
24
Q

What is the pathway of recirculating T-lymphocytes?

(hint: 7 steps)

A
  1. Afferent arterioles
  2. Pre-capillary arterioles
  3. Capillaries
  4. Post-capillary venules (HEV’s)
  5. Lymphatic tissue
  6. Lymphatic sinuses
  7. Efferent lymphatic vessels
25
What are the three functions of lymph nodes?
1. Lymph filter (macrophages) 2. Lymphocyte production 3. Antibody production (plasma cells)
26
When is the thymus largest?
* Size (proportionally) largest during fetal & first 2 years of postnatal life * increases in size up to puberty * Regresses in size as we subsequently age
27
Where are the afferent & efferent lymphatic vessels of the thymus?
* No afferent lymphatic vessels * Efferent lymphatic vessels are limited to capsule and connetive tissue
28
What embryologic tissue is the thymus derived from?
* Endoderm of 3rd branchial pouch * endodermal epithelial cells proliferate & migrate → reticular stroma of thymus (cytoreticulum) & Hassall's (thymic) corpuscles
29
What are the morphological features of the thymus?
* Two lobes * beneath upper anterior thoracic wall * enclosed by connective tissue capsule * divided into incomplete lobules by connective tissue trabeculae or septae * Cortex (stains darker) * Medulla (stains lighter)
30
What is the most important cell of the thymus cortex? Why?
* Epithelial reticular cells * form a loose cellular network that supports the differentiating T-lymphocytes * Produces thymic hormones * promote differentiation of stem cells into T-cells and induce formation of T-cell surface markers * Helps form the blood-thymus barrier * prevents antigens from entering the thymic cortex
31
What cells in the cortex of the thymus destroy or weed out dying or abnormally developing T-lymphocytes?
Macrophages
32
What are the three distinguished regions of lymphocytes in the cortex of the thymus? What differentiates each region?
* Outer region * stem cells enter from vascular system * proliferate & give rise to lymphoblasts * largest cells * Middle region * proliferation & differentiation continue * cells getting smaller * Inner region * smallest lymphocytes * no mitoses * mature T-cells enter circulation @ corticomedullary junction
33
What is in the medulla of the thymus?
* Epithelial reticular cells * Some lymphocytes * Some connective tissue cells & fibers * Characteristic feature = Hassall's (thymic) corpuscles * degenerate/dying cells (medulla is not involved in the education process)
34
What major branches give vascular supply to the thymus?
Internal thoracic Artery & Inferior Thyroid Artery
35
Where do newly formed T-lymphocytes enter the vascular system?
Through the post-capillary venules at the corticomedullary junction.
36
What is the purpose of the blood-thymus barrier?
Prevent antigens in the blood stream from entering the cortex of the thymus.
37
What are the five components of the Blood-Thymus Barrier?
1. Endothelial cells (with tight junction) 2. Basal lamina of endothelial cell 3. Perivascular space (contains connective tissue fibers, macrophages, & tissue fluid) 4. Basal lamina of reticulo-epithelial cells 5. Epithelial reticular cells (with desmosomes)
38
What happens if a person is born without a thymus?
Congenital absence of the thymus * patient lacks T-lymphocytes * no cellular immunity
39
Thymomas are neoplasms of what cells?
Thymus reticular cells
40
What are four unique characteristics of the spleen?
* Largest lymphatic organ * No afferent lymphatic vessels * Efferent lymphatic vessels are present * No lymph sinuses * Filters blood
41
What are the five gross features of the spleen?
* Hilus * Thick capsule with some smooth muscle * Thick connective tissue trabeculae * Splenic pulp (white & red) * NO CORTEX OR MEDULLA
42
What four things are located in the hilus of the spleen?
1. Artery 2. Vein 3. Efferent lymphatic vessels 4. Sympathetic nerve fibers
43
What does the splenic pulp consist of?
Blood cells embedded in and supported by a reticular fiber stromal network.
44
What does white pulp consist of?
* Periarterial lymphatic sheaths * sheath of T-cells surrounding a central artery (white pulp artery) * Splenic (lymphatic) nodules * lymphatic nodules along periarterial sheaths * have germinal center * contain primarily B-cells
45
What does red pulp consist of?
* Splenic sinuses (sinusoids) * leaky vascular passageways (whiskey barrel like) * Splenic cords (Billroth cords) * area of various cells (RBCs, granulocytes, lymphocytes, macrophages, platelets, plasma cells, reticular cells & fibers) * located between sinuses * Marginal zone * transitional zone b/t red & white pulp
46
What important event happens in the marginal zone of the red pulp in the spleen?
* Small blood vessels dump their blood into this area * Recirculating lymphocytes return to enter either the periarterial lymphoid sheaths or the splenic nodules
47
Describe the splenic vascular circulation. (Hint: 8 steps)
1. Splenic artery 2. Trabecular artery 3. White pulp/central artery 4. Penicillus OR Follicular artery 5. Venous sinusoids/Red pulp 6. Pulp veins 7. Trabecular veins 8. Splenic veins
48
What are the three parts of the Penicillus?
1. Red pulp artery 2. Sheathed artery (capillaries) 3. Terminal arterial capillaries
49
What is the difference between closed and open circulation in the red pulp? Which is more prevalent?
* Closed circulation * terminal arterial capillaries open directly into sinusoids * Open circulation * terminal arterial capillaries open into an area of red pulp * Electron microscopy has shown that open circulation is most prevalent.
50
What immune functions are performed by the spleen?
* Forms antibodies in response to blood-borne pathogens * main source of circulating antibody * Antibody presentation by APCs * Activation and proliferation of B- & T- lymphocytes * Removal of macromolecular antigens from the blood
51
What hemopoietic functions are performed by the spleen?
* Removal and destruction of senescent, damaged, and abnormal erythrocytes & platelets. * Retrieval of iron from erythrocyte hemoglobin. * Formation of erythrocytes during early fetal life. * Storage of blood, especially RBCs.

IHO: Week 1 - WLB (8 decks)

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