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Immune System pt.1 (Primary Lymphoid Tissue) Flashcards

1
Q

What type of organ is the thymus?

A

primary lymphoid organ

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2
Q

Where is the thymus located?

A
  • in the neck
  • extends into the thorax
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3
Q

What forms the framework of the thymus?

A

epithelial cells (instead of connective tissue!)

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4
Q

What forms the thymus?

A

epithelial cells seeded with developing lymphocytes from the bone marrow

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5
Q

What type of organ is the thymus?

A

lobed (comprised of lobes)

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6
Q

What in the thymus is covered by what? What do they form?

A
  • lobes are covered by connective tissue capsule
  • capsule extends into the lobes (septa) -> divides the parenchyma into lobules
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7
Q

What are the primary lymphoid organs?

A
  • thymus
  • bone marrow
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8
Q

What do primary lymphoid organs have in common?

A

the organs produce and mature immune system cells.

produces new cells (nothing else)

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9
Q

Where are new immune system cells produced?

A

bone marrow

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10
Q

What occurs in the thymus?

A

T-lymphocytes undergo maturation

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11
Q

What do secondary lymphoid organs have in common?

A

location in which immune responses occur

response against invadors occur

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12
Q

State examples of secondary lymphoid organs.

A
  • lymph nodes
  • spleen
  • Bayer’s patches
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13
Q

What is the thymus surrounded by?

A

capsule of dense connective tissue

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14
Q

What regions do each thymus lobe have?

A

cortical region and medullary region

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15
Q

What surrounds the thymus lobules? Through what?

A
  • blood vessels
  • transverse the fine reticular connective tissue surrounding the lobules
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16
Q

What connective tissue surrounds the thymus lobules?

A

fine reticular connective tissue

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17
Q

Explain the ‘life span’ of the thymus.

A
  • most prominent in young animals
  • regresses later in life
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18
Q

What happens to the parenchyma of the involuted thymus?

A

it is replaced by adipose and connective tissue

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19
Q

State the two parts of the thymus lobules and where they are located.

A

outer= cortex
inner= medulla

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20
Q

State the difference in cell composition of the cortex and medulla.

A
  • composition is the same!

cortex is darker as it is more concentrated in cells.

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21
Q

What cells are named after the thymus?

A

T-lymphocytes

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22
Q

What cells form the framework of the cortex of the thymus?

A

stellate epithelial reticular cells

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23
Q

State the composition of the thymus cortex.

A
  • stellate epithelial reticular cells form the framework
  • large, light-staining nucleus
  • several long processes
  • cells flatten at the periphery of the lobule
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24
Q

What do the processes of stellate epithelial reticular cells in the thymus do?

A

branch and connect to cell processes extending from other epithelial reticular cells

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25
Describe what occurs at the periphery of the thymus lobules. What do these cells produce?
- epitheial reticular cells flatten - form a sheet around the margin of the lobule - produce thymosin, thymulin, thymic humoral factor and thymopoetin - proteins influencing immunity and the maturation of lymphocytes
26
What proteins influence immunity and the maturation of lymphocytes? What produces them?
- thymosin, thymulin, thymic humoral factor and thymopoetin - hormones! - produced by flattened stellate epithelial reticular cells
27
What do epithelial cells typically do at the basement membrane? How does this compare to the thymus?
- typically line the basement membrane by layers - reticular cells do not have a basement membrane - do not have layers - go by a 3-dimentional network
28
State the maturation process of T-lymphocytes.
- T-lymphocytes produced in the bone marrow - travel through blood vessels - mature in the thymus
29
What happens if there are no reticular cells?
no reticular cells --> no chemicals --> no development for t-lymphocytes --> serve no function
30
What occupies the space between the epithelial reticular cells (in the thymus)?
thymocytes (maturing T-lymphocytes)
31
Where do blast thymocytes migrate to? What do they do?
- migrate from bone marrow - via blood vessels - to cortex periphery - undergo mitotic division
32
What happens as thymocytes continue to mature?
- they move from the outer thymic cortex towards the medulla
33
What happens to most thymic lymphocytes?
undergo apoptosis in the cortex
34
What percentage of thymic lymphocytes are actually released into the circulation? Where are they released? What happens with the rest?
- 1-3% - released into the lumen of medullary blood vessels - rest= apoptosis
35
What is interspersed among lymphocytes? What is their function?
- macrophages - remove spent lymphocytes - have remnants of aptotic cells in their cytoplasm
36
What is the name of the not-yet mature T-lymphocyte?
thymocyte
37
What direction do maturing lymphocytes travel in?
towards the medulla
38
How do medullary epithelial reticular cells compare to the cortical epithelial cells?
- larger - form the framework in the medulla of the thymus
39
What is lighter staining and why?
- **medulla** is lighter staining than the cortex - **fewer** small **lymphocytes** and **macrophages** fill the space of the framework
40
What is also found in the medulla? What is its function?
- unique thymic corpuscles (Hassall's corpuscles) - unknown function
41
State the composition of the Hassall's corpuscles.
- degenerated central wall - surrounded by layers of keratinized cells - can be calcified
42
Why is the medulla less dense than the cortex?
- most T-lymphocytes are killed when migrating (apoptosis)
43
What are the different types of bone marrow?
**red** bone marrow **yellow** bone marrow
44
What is red bone marrow? What does it do?
- highly cellular - specialized to produce blood cells and platalets
45
State the 'life span' of the red bone marrow.
birth: - principal source of blood cells - found throughout the entire animal skeleton adult: - mostly limited to the sternum, ribs, vertebrae, skull, ilia and the ends of long bones
46
State the composition of yellow marrow.
- rich in adipose tissue - occupies the remainted of the adult skeleton
47
What does bone marrow produce?
- erythrocytes - immune system cells
48
What direction does bone marrow change with aging?
red --> yellow
49
Compare red and yellow bone marrow.
red bone marrow: - lots of immune system cells - erythrocytes in different development stages yellow bone marrow: - same composition yet much less concentrates - high concentration of adipose tissue
50
State the composition of red bone marrow.
- extravascular **hematopoietic tissue** - vascular sinusoids - rich in blood cells in various stages of formation - white blood cells in various development stages - connective tissue cells - supported by a **reticular meshwork**
51
What cells are present in red bone marrow?
- hematopoietic cells - adipocytes (lipocytes) - megakaryocytes (platalet production)
52
What is hematopoietic tissue composed of?
- many different blood cells in many different development stages - reticular connective tissue
53
What type of capillaries does red bone marrow contain? What are they?
- vascular sinusoids - type of capillary with holes in the wall - allowing new bone marrow cells into the circulation
54
What type of cell series (Cell line) do cells undertake to turn from a morphologically indistinct stem cell to a specific mature blood cell.
erythroid (red blood cell) series or granulocytic (myeloid; white blood cell) series
55
What cell series do red blood cells undergo?
erythroid
56
What cell series do white blood cells undergo?
granulocytic (myeloid)
57
What is a proerythrocyte? Other name?
- large, round cell with a basophylic cytoplasm - rubiblast
58
What does the proerythrocyte give rise to? How? Other name?
- multiple divisions - basophyllic erythrocytes (prorubicytes)
59
What does the basophylic erythrocyte give rise to? How do they compare? Other name?
- polychromatophillic erythroblasts - rubicytes - smaller cells - more condensed chromatin
60
What are the characteristics of orthochromatophilic erythroblasts (normoblasts, metarubricytes)?
nucleus: - round - highly condensed - deeply stained cytoplasm: - eosinophylic - shows slight blue tinges
61
What is the final step of erythrocyte maturation?
- nucleus is extruded - anucleate reticulocyte is left
62
State the maturing erythrocyte names of cells in order.
proerythrocyte (rubriblast) basophylic eyrthroblast (prorubricyte) polychromatophillic erythroblast (rubricytes) orthochromatiphillic erythrocyte (normoblast, metarubicyte) anucleate reticulocyte erythrocyte
63
How do the cells compare when an erythrocyte is maturing?
size: precursor cells are much **larger**! nucleus: precursor cells have a much **more highly concentrated nucleus** nucleus: **nucleoli is lost** during erythythrocyte development
64
What happens to the nucleus when the erythrocyte matures?
decreases in concentration
65
How do immature cells of the bone marrow look?
- large - eurochromatic nucleus - nucleoli
66
What form of cell predominates?
older cells > immature forms

Histology (22 decks)

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