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CVS & IBL - Histology 🔬 > L3: Lymphatic tissue > Flashcards

L3: Lymphatic tissue Flashcards

1
Q

What is the lymphatic system comprised of?

A
  • lymphatic vessels, which transport interstitial fluid (lymph) back to the blood circulation
  • The lymphoid tissue which house lymphocytes and other cells of the body’s immune defense system
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2
Q

What are the types of organs in the Lymphatic system?

A

1ry lymphatic organs: Sites where lymphocytes mature and become immunocompetent “has function” (B cells in bone marrow and T cells in the thymus).

2ry lymphatic organs: Mature lymphocytes are distributed via blood Or lymph to secondary lymphoid organs (e.g., lymph nodes, spleen) where they await activation.

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3
Q

What is a description of the thymus?

A

A flattened bilobed organ lying behind the sternum.

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4
Q

What are the Steps of development of the thymus?

A

It continues to enlarge up to puberty but then undergoes a slow involution becoming replaced by adipose tissue.

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5
Q

What is the Thymus formed of?

A

Formed of:

1) Stroma
2) Parenchyma

“Any parenchymal organ (those with no lumen)”

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6
Q

What is the structure of the stroma of the thymus?

A
  • Capsule: thin loose C.T.
  • Trabeculae: thin, divide gland into 2 lobes then, subdivided into incomplete lobules.

” + reticular fiber network that forms the floor of cells”

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7
Q

What is the structure of the parenchyma of the thymus?

A

Each lobule is formed of:
- Cortex: outer dark part (high content of lymphocytes). “As it is the site of development”

  • Medulla: central pale part of the thymus lobule (due to low content of lymphocytes).
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8
Q

What are the cells found in the cortex of the thymus?

A
  1. Lymphoblasts (thymocytes): In the outer cortex.
    - Have dark nuclei “inactive” and are derived from the CFUs (Colony forming units) in the bone marrow.
  2. T- lymphocytes:
    - Deep in of the cortex.
    - Numerous, derived from the lymphoblasts.
    - Migrate to the medulla.
  3. Few macrophages:
  4. Reticular “has processes” epithelial cells “endothelial characters” : Branched cells with a pale nucleus. “Secrete thymic hormones”
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9
Q

What are the cells found in the medulla of the thymus?

A
  1. T- lymphocytes:
    - Less numerous
    - They have completed their development in the cortex, then migrate to the medulla.
  2. Reticular epithelial cells. “Less numerous”
  3. Few macrophages “less numerous”
  4. Hassall’s corpuscles: A central hyaline acidophilic mass “Remaining of the cytoplasm and cell membrane of T-sales” surrounded by concentric layers of reticular epithelial cells.
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10
Q

What is the function of the thymus gland?

A
  • Production of T- lymphocytes: In the cortex, then migrate to the medulla post capillary venule blood circulation the lymph node and the spleen where they settle to produce T- lymphocytes
    throughout life.
  • It is essential for the normal development of the lymphoid tissue “t-cells” in early life
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11
Q

What is the histological structure of the lymphoid follicles or lymphoid nodule “Structural and functional unit of lymphatic system”?

A
  • Spherical basophilic mass of small lymphocytes mainly B lymphocytes and few T lymphocytes with a rich network of reticular fibers supporting the cells.
  • It is not encapsulated with connective tissue. “Unlike the thymus”
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12
Q

What is the size of lymphoid follicles?

A

Lymphoid nodules vary widely in size, measuring a few hundred micrometers to one mm in diameter.

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13
Q

What are the sites of lymphoid nodules?

A
  • They are found free in many connective tissues in the body.
  • They are also present within lymph nodes, spleen, and tonsils, but not in the thymus which contains only T cells.
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14
Q

What are the types of lymphoid follicles?

A

Primary and secondary

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15
Q

What is the shape of primary follicles?

A

Primary follicle without germinal center

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16
Q

What is the shape of secondary follicles?

A
  • Has germinal center: Which is a pale central area formed as a result of exposure to infection or antigen, so the small B- lymphocytes (have dark nuclei) develop into activated medium sized lymphocytes (have pale nuclei) which aggregate in the center of the primary follicle forming a pale area called germinal center.
17
Q

What is the definition of the lymph node?

A

Lymph nodes are bean-shaped, encapsulated structures, generally 2–10 mm in diameter “ Unlike lymphoid follicles which are 1 mm at max” , distributed throughout the body along the course of the lymph

18
Q

What is a lymph node formed of?

A
  • Stroma.

- Parenchyma.

19
Q

Mention the structure of the stroma of lymph nodes

A
  • Capsule:
    ✓ Dense fibrous “C.T Like most capsules”
    ✓ Penetrated by afferent lymphatics at the convex surface of the lymph node.
    ✓ Thickened at the hilum through which arteries and nerves enter and veins and efferent lymphatics leave the node
  • Trabeculae:
    ✓ They arise from the capsule.
    ✓ They divide the cortex into cortical compartments and the medulla into irregular areas.
  • Reticular fibers:
    ✓ They form network holding the parenchymal cells in its
    meshes.
    ✓ They appear only with silver stain.
    ✓ The network is more condensed at the site of lymphoid follicles and the medullary cords.
20
Q

Mention the structure of the parenchyma of lymph nodes

A
  • The cortex:
    ✓ It is formed of lymphatic follicles (primary or secondary)
    surrounded by lymph sinuses.
  • Lymph sinuses:
    ✓ They are spaces surrounding the cortical lymphatic follicles and the medullary cords.
    ✓ They contain lymph, lymphocytes and macrophages.
  • The medulla:
    ✓ It is formed of irregular medullary cords (as follicles but
    arranged in the form of cords) surrounded by lymph sinuses.
21
Q

What is the function of lymph nodes?

A
  • Filtration of lymph by the macrophages of lymph sinuses.
  • Humoral immunity by B-lymphocytes which produce antibodies.
  • Cell mediated immunity by T-lymphocytes which when activated form killer cells to destroy the antigens.
22
Q

What is the structure of MALT?

A

Large and diffuse collections of lymphocytes, plasma cells, and lymphoid nodules present in the mucosa of the digestive, respiratory, and genitourinary tracts

23
Q

Give examples for MALT.

A

As the tonsils, the Peyer patches in the ileum and aggregates of lymphoid follicles in the appendix

24
Q

What is the definition of tonsils?

A

Masses of lymphatic tissue “Lymphatic follicles + diffuse lymphatic tissue” present in the lamina propria “epithelium + C.T” of a mucous membrane.

25
Q

What are types of tonsils?

A

According to their location
• Palatine tonsil. “اللوز”
• Pharyngeal tonsil. “اللحمية”
• Lingual tonsil.

26
Q

What is the function of tonsils?

A

Quick defense mechanism through formation of antibodies against infective agents taken with food or air

27
Q

What is the definition of palatine tonsil?

A

Two masses of lymphatic tissue embedded in the C.T. under the mucous membrane of oro-pharynx

28
Q

What is the structure of palatine tonsil?

A

1- Non-keratinized stratified squamous: Cover its surface & dips into the underlying lymphatic tissue forming primary and secondary tonsillar crypts.

2- Lymphatic tissue: types:

  • Lymphatic nodules → Primary or secondary.
  • Diffuse lymphatic tissue: formed of lymphocytes and plasma cells. It occupies the areas between the lymphatic nodules.

3- Capsule: Dense C.T. separates the tonsils from the muscular wall of the pharynx.

29
Q

What’s the definition of pharyngeal tonsil?

A

Single mass of lymphatic tissue present in nasopharynx.

30
Q

What is the structure of pharyngeal tonsils?

A

Covered by pseudo-stratified columnar ciliated epithelium which forms folds. “Small folds not crypts”

31
Q

What does hypertrophied pharyngeal tonsil result from and what is it called?

A

Hypertrophied pharyngeal tonsils resulting from chronic inflammation are called adenoids.

32
Q

What is the definition of lingual tonsils?

A

They are small collections of lymphatic tissue in the C.T

33
Q

What is the definition of the spleen?

A

The spleen is the largest single accumulation of lymphoid tissue in the body.

34
Q

What is the structure of the spleen?

A

Stroma:

Capsule:
✓ Thick dense fibrous connective tissue capsule, containing smooth muscle fibers “To push blood in case of emergency” and penetrated by afferent lymphatics.

Trabeculae:
✓ Divide the spleen into lobules, containing smooth muscle fibers

Reticular network→ similar to that of lymph node.

Parenchyma: It is formed of splenic lobules.

Each splenic lobule includes:
- White pulp:
• White pulp is a lymphatic follicle with central artery which is eccentric in position.
• The white pulp may contain germinal center.
• They are scattered all over the spleen.

  • Red pulp:
    • It occupies the areas between the white pulps.
    • The red pulp is formed of splenic cords and blood sinusoids.
  • Blood sinusoids: Irregular blood channels surrounded by macrophages. “For filtration”
  • Splenic cords (Billroth cords): Irregular masses of lymphatic tissue mixed with blood cells (RBCs & WBC), fill spaces between the blood sinusoids.
35
Q

What is the function of the spleen?

A

 Humoral and cell mediated immunity.
 The only lymphoid organ involved in filtration of blood.
 It is also the main site of destruction of aged erythrocytes.
 Storage of blood

36
Q

Compare between the lymph node and spleen according to:

Number
Capsules
parenchyma
Sinuses
Function
A

Number: Numerous, widely distributed in the body - Single organ, in the abdomen.

Capsule: Dense C.T. - Dense C.T. with smooth muscles

Parenchyma:
Cortex → lymph follicles (no central artery).
Medulla → medullary cords

-

White pulp →lymph follicles (with central artery)
Red Pulp →blood & diffuse lymph tissue

Sinuses: Lymph sinuses (contain lymph) - Blood sinusoids (contain blood)

Function:
Filtration of lymph
Production of small

-

lymphocyte → humoral & cell mediated immunity
Filtration & storage of blood
Destruction of old RBCs

CVS & IBL - Histology 🔬 (5 decks)

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