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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
Q

What are the three functions of lymph nodes?

A
  1. Lymph filter (macrophages)
  2. Lymphocyte production
  3. Antibody production (plasma cells)
26
Q

When is the thymus largest?

A
  • 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
Q

Where are the afferent & efferent lymphatic vessels of the thymus?

A
  • No afferent lymphatic vessels
  • Efferent lymphatic vessels are limited to capsule and connetive tissue
28
Q

What embryologic tissue is the thymus derived from?

A
  • Endoderm of 3rd branchial pouch
    • endodermal epithelial cells proliferate & migrate → reticular stroma of thymus (cytoreticulum) & Hassall’s (thymic) corpuscles
29
Q

What are the morphological features of the thymus?

A
  • 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
Q

What is the most important cell of the thymus cortex? Why?

A
  • 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
Q

What cells in the cortex of the thymus destroy or weed out dying or abnormally developing T-lymphocytes?

A

Macrophages

32
Q

What are the three distinguished regions of lymphocytes in the cortex of the thymus? What differentiates each region?

A
  • 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
Q

What is in the medulla of the thymus?

A
  • 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
Q

What major branches give vascular supply to the thymus?

A

Internal thoracic Artery

&

Inferior Thyroid Artery

35
Q

Where do newly formed T-lymphocytes enter the vascular system?

A

Through the post-capillary venules at the corticomedullary junction.

36
Q

What is the purpose of the blood-thymus barrier?

A

Prevent antigens in the blood stream from entering the cortex of the thymus.

37
Q

What are the five components of the Blood-Thymus Barrier?

A
  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
Q

What happens if a person is born without a thymus?

A

Congenital absence of the thymus

  • patient lacks T-lymphocytes
  • no cellular immunity
39
Q

Thymomas are neoplasms of what cells?

A

Thymus reticular cells

40
Q

What are four unique characteristics of the spleen?

A
  • Largest lymphatic organ
  • No afferent lymphatic vessels
  • Efferent lymphatic vessels are present
  • No lymph sinuses
  • Filters blood
41
Q

What are the five gross features of the spleen?

A
  • Hilus
  • Thick capsule with some smooth muscle
  • Thick connective tissue trabeculae
  • Splenic pulp (white & red)
  • NO CORTEX OR MEDULLA
42
Q

What four things are located in the hilus of the spleen?

A
  1. Artery
  2. Vein
  3. Efferent lymphatic vessels
  4. Sympathetic nerve fibers
43
Q

What does the splenic pulp consist of?

A

Blood cells embedded in and supported by a reticular fiber stromal network.

44
Q

What does white pulp consist of?

A
  • 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
Q

What does red pulp consist of?

A
  • 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
Q

What important event happens in the marginal zone of the red pulp in the spleen?

A
  • Small blood vessels dump their blood into this area
  • Recirculating lymphocytes return to enter either the periarterial lymphoid sheaths or the splenic nodules
47
Q

Describe the splenic vascular circulation.

(Hint: 8 steps)

A
  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
Q

What are the three parts of the Penicillus?

A
  1. Red pulp artery
  2. Sheathed artery (capillaries)
  3. Terminal arterial capillaries
49
Q

What is the difference between closed and open circulation in the red pulp? Which is more prevalent?

A
  • 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
Q

What immune functions are performed by the spleen?

A
  • 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
Q

What hemopoietic functions are performed by the spleen?

A
  • 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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