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Histology > Lymph organs/tissue > Flashcards

Lymph organs/tissue Flashcards

1
Q

What are the components of the lymphatic system (7)

A
  1. bone marrow
  2. thymus
  3. spleen
  4. lymph nodes
  5. tonsils
  6. general lymphatic tissue
  7. peyer’s patches
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2
Q

What is the main diff between lymphoid organs and tissue

A

organs are delimited by a capsule of CT whereas lymphoid tissue is made of groups of lymphoid cells (forming follicles) that do NOT have a CT capsule

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3
Q

2 types of lymphoid organs

A

PRIMARY: BM & Thymus

  • site of B and T cell production
    -BM produces B cells and pre T cells
    -Thymus produces T cells from pre-T cells

SECONDARY: lymph nodes/spleen/lymph nodules

-site of most immune responses
-site of antigen contact with lymphocytes
-mainly made of B and T cells

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4
Q

concentration of lymphocytes within diff organs of lymph system

A
  1. BM: 90% B cells
  2. Thymus: 100% T cells
  3. Blood: 70% T cells
  4. Spleen: 55% B cells
  5. Lymph nodes: 60% T cells
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5
Q

route of travel between lymph organs of the B and T cells

A
  1. PRIMARY ORGANS: maturation of lymphocyte progenitors to produce B cells in BM and T cells in thymus
  2. Migration of B cells and T cells into secondary organs
  3. B cells proliferate and differentiate to form plasma cells and aid in humoural response
  4. T cells mature and help in cell mediated response
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6
Q

Thymus functions (3) and location

A

LOCATION: above heart, posterior to sternum

FUNCTIONS:
1. site of T cell maturation via negative and positive selection (which then migrate to blood)
2. secrete hormone THYMOSIN which stimulates T cell maturation
3. destructure of incorrect T cells by macrophages

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7
Q

general structure of the thymus

A

-CT capsule with extending trabeculae (contains bood vessels)
-Trabeculae split thymus into lobules
-each lobule has a cortex and an inner medulla
-100% T lymphocytes that give it a basophilic affinity

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8
Q

what is the relative staining intensity of thymus cortex vs medulla and why

A

basophilic extent of cortex is greater than that of medulla

REASON: medulla has cells that are less densely packaged

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9
Q

Cells present in the cortex of the thymus (3)

A
  1. Epithelioreticular cells (ERs) type 1 to 6
  2. thymocytes (T cells)
  3. macrophages – allow digestion of incorrect T cells
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10
Q

Cells present in the medulla (5)

A
  1. Epithelioreticular (ER)
  2. Thymocytes
  3. Macrophages
  4. dendritic cells
  5. Hassal corpuscles (made of ER type 6)
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11
Q

Role of all the types of epithelioreticular cells in the thymus

A

1 - make the thymus blood barrier within cortex (blocks antigens from coming into contact with T cells during maturation)

2 - act with T cells for positive selection

3/4 - form barrier between cortex and medulla

5- contact with T cells in medulla that stimulate T cell differentiation

6- form medullar hassal corpuscle that releases cytokines to help T cell differentiation

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12
Q

what are the three elements of the thymus blood barrier

A

ER type 1
macrophages
capillary endothelium and basal lamina

!! no lymphatic vessels are present so that antigens do not come into contact with the maturing t cells

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13
Q

how are T cells determined to be correct or incorrect?

A

LOCATION: THYMUS

+ve selection: in cortex, T cells that can recognise antigens mature

-ve selection: in medulla, T cells that CANT recognise SELF antigens move into capillaries (others are phagocytosed by macrophages)

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14
Q

How does the thymus age over time

A

-peak during childhood and undergoes regression past puberty
-reduced in size
-parenchyma replaced by adipose tissue

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15
Q

lymph nodules location and function

A

LOCATIONS: neck, inguinal area, abdomen –> positioned along lymphatic vessels

FUNCTIONS:
-filters lymph before it returns to blood
-contains defense cells and has B/T cells that respond to antigens

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16
Q

General morphology of the lymph nodes

A
  • CT capsule + trabeculae
    -subcapsullar sinus (lymph brought in by lymph vessels)
    -lymphocytes are the main cell of the parenchyma
    -superficial cortex containing follicles with an outer mantle and a germinal center
    -paracortex (deep) containing high endothelium vessels (HEVs)
    -medulla made of lymphatic sinuses
    -hilum = place of concentration of ducts/blood and lymph vessels leaving node
17
Q

Cells of the lymph nodules (7)

A
  1. B cells (unstimulated in mantle and stimulated in germinal center of follicles)
  2. T cells in deep cortex
  3. Macrophages in medulla
  4. dendritic cells
  5. reticular fibroblasts (produce reticular fibers)
  6. follicular dendritic cells (FDC) that bind antigens to B cells and aid B cell differentiation
  7. Plasma cells in medulla
18
Q

what is the role of HEVs in the lymph node?

A

-entrance of lymphocytes into nodules
-circulation of lymph
-migration of T/B cells to underlying lymphatic tissues mediated by certain adhesion molecules and chemokines

19
Q

Spleen functions () and location

A

LOCATION: left side of stomach and the biggest lymph organ

FUNCTIONS:

IN FETUS: haematopoietic, forming RBC (but this is lost post birth)

IN ADULT:
-immunological filter of blood (removes antigens)
-removes Ag
-acts as blood reservoir
-hemocatheresis: destruction of aged arythrocytes

20
Q

General morphology of spleen

A

-CT capsule containing myofibroblasts + septa
-splenic artery enters at hilum
-branching of splenic artery to form the CENTRAL artery and wrapping of these branches in layers of lymphocytes –> PALS (peri-arterial lymphatic sheath)
-PALS enlarge and become rounded (accummulating B cells aggregates) –> Malphghian corpuscles
-branching of artery past the MCs forms penicilalr arterioles
-sheath capillaries surrounded by macrophages
-connection of sheath capillaries with sinusoids, then connected with splenic vein

21
Q

2 types of pulp in the spleen and the components of each type

A

20% WHITE PULP: central artery, periarterial sheath and malpighian corpuscle
IMMUNE RESPONSES

80% RED PULP: sinusoids, blood cells and macrophages
ERYTHROCATHERESIS

!! these are mixed throughout the spleen

22
Q

similarities difference between lymph node follicle and cross section of PALS

A

similarity: both have a germinal center

difference: PALS contains the central artery that is covered by the lymphocyte sheath whereas follicles are not vascularised internally

23
Q

cells of the spleen

A

-B and T cells
-Red pulp macrophages
-APCs
-STAVE CELLS: endothelial cells lining the splenic sinuses

24
Q

2 mechanisms by which blood flows from the penicillar arterioles into the sinusoids and then to capillaries

A
  1. NOT IN HUMANS: through closed circulation where the capillaries and sinusoids are connected (hence direct blood flow)
  2. METHOD IN HUMANS:
    open circulation with no connection between sheath capillaries and sinusoid. Blood exits into open space, aged erythrocytes have trouble move through fenestrations. Macrophages ready to engulf the exposed (old) RBCs
25
Q

structure of the splenic sinuses

A

CONTAIN CAPILLARIES AND SINUSOIDS: dilated capillaries with discontinuous wall

-STAVE CELLS: long endothelial cells arranged with spaces between them which favours exposure to macrophages

BASAL MEMBRANE: fragmented and wrapped in rings around stave cells to form the openings

-SHEATH CAPILLARIES: surrounded by macrophages devoted to phagocytosis of aged erythrocytes

-CHORDS OF BILLROTH: cords of cells filling space between sinusoids and capillaries (macrophages, RBCs, WBCs) - reservoir

-sinusoids connected to the SPLENIC VEINS

26
Q

How is hemocatheresis possible in the spleen?

A

new vs old erythrocytes distinguished via modification on the surface which makes old cells move less rapidly

!! causes tendendency to agglutinate, and hence are exposed due to open circulation for macrophages to engulf

27
Q

Classifications of lymphoid tissue

A

-formed by lymphoid nodules that are aggregated and immersed in the walls of certain orgains

MALT - tunica mucosa
GALT- digestive (gut)
BALT- bronchial

2 special tissues:
-tonsils (oral cavity)
-peyer patches (ilium)

28
Q

types of tonsils and the diff characteristics/ locations of each

A
  1. LINGUAL: stratified squamous non keratinised epithelium
  2. PHARYNGEAL: pseudostratified ciliated epithelium
  3. TUBARIC
  4. PALATINE

!! WALDEYER RING: the ring formed by all of the tonsils

CRYPTS: openings (seen as white spaces) where antigens can enter and come into contact with lymphocytes

FOLLICLES: contained in the CT

29
Q

Payer Patches location and function

A

LOCATION:
-marker of the ilium
-found in the tunica mucosa (but can be large enough to penetrate into the sub-mucosa)
!!! only present on one side of the ilium

FUNCTION: traps and destroys bacteria

30
Q

What occurs in the wall of organs that posess lymph nodules?

A

DOME: area containing B cells, macrphages and plasma cells at the tip of the nodule

M (microfold) CELLS: intercalated between lining epithelia of the wall
-stimulate immune response by having microfolds for entrance of lymphocytes (favours antigenic contact)

HEVs: allow entrance of lymphocytes into nodule. Also allows exit of lymphocytes into efferent lymph vessels

Histology (12 decks)

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