Week 6: Connective Tissues 3 - Cells

Question 1

What types of cells make up CT?

Answer 1

• Immature cells known as ‘blasts’ = builders
• Mature cells known as cytes
• Structural cells
• Defence cells

Question 2

What is the role of immature cells in CT?

Answer 2

Known as ‘blasts’ = builders
These synthesise and secrete ECM
They divide and differentiate into mature cells

Question 3

What is the role of mature cells in CT

Answer 3

Known as ‘cytes’
Referred to as caretaker cells i.e., they maintain and monitor the quality of ECM

Question 4

What is the role of structural cells in CT?

Answer 4

Synthesise (e.g., fibroblsats)
Store (e.g., adipocytes)

Question 5

What is the role of defence cells in CT?

Answer 5

Protect body against invasion
Main types seen are macrophages, mast cells, plasma cells and white blood cells (lymphocytes, neutrophils and eosinophils)

Question 6

Give examples of structural/ storage cells.

Answer 6

Fibroblasts and adipocytes/ fat cells

Question 7

Give examples of defence cells.

Answer 7

Macrophages, plasma cells, mast cells, leukocytes (migrate from bloodstream), pericytes (reserve/ stem cells), primate mesenchyme cells (reserve/ stem cells)

Question 8

Explain the difference between a fibroblast and fibrocyte.

Answer 8

Fibroblast is the younger cell, more active in protein production and in producing the intercellular components, i.e., fibres, AGS
Fibrocytes are the more mature cell; produces less protein and maintains intercellular components.
Fibrocytes can revert to active form in CT injury.
These are involved in repair; they respond to injury by dividing and producing large amounts of collagen, i.e., from scar tissue. During healing, fibroblasts can form myofibroblasts that are responsible for contraction of scar tissue at a wound.

Question 9

Describe the appearance of fibroblasts/ fibrocytes under H&E light microscopy.

Answer 9

Only nucleus seen, flattened, ovoid nucleus, cytoplasm is indistinguishable from collagen

Question 10

Describe the appearance of fibroblasts/ fibrocytes under EM.

Answer 10

Long cytoplasmic processes, features of protein producing and secreting cell.

Question 11

Describe the appearance of adipocytes/ fat cells under H&E light microscopy.

Answer 11

Huge cell with a thin rim of cytoplasm, surroundings a clear lipid droplet; peripheral nucleus.

Question 12

Describe the appearance of adipocytes/ fat cells under EM.

Answer 12

Lipid droplet is fixed and coloured grey-black by osmium tetroxide.

Question 13

Describe the appearance of a macrophage under H&E light microscopy.

Answer 13

Variable; when inactive, only nucleus seen, roundish, often indented. Cytoplasm of active macrophage often contains visible phagosomes and lysosomes.

Question 14

Describe the key features of a macrophage under EM.

Answer 14

Pseudopodia (1) with microfilaments for phagocytosis and cell mobility through tissue
Various phagosomes, lysosomes (2) and residual bodies (3) for intracellular digestion.
RER (4) and Golgi for production of lysosomes and secretory substances etc.

Question 15

Describe the appearance of plasma cells under LM.

Answer 15

Ovoid cell, basophilic cytoplasm, nucleus off centre, distinctive clock-face clumping of chromatin

Question 16

Describe the appearance of plasma cells under EM.

Answer 16

Abundant RER, extensive Golgi, no secretory granules.

Question 17

Describe the appearance of mast cells under H&E light microscopy.

Answer 17

Indistinguishable; special stains show large basophilic cytoplasmic granules filled with heparin sulphate.
Located near capillaries

Question 18

Describe the appearance of mast cells under EM.

Answer 18

Large electron dense granules, which appear black

Question 19

Describe the appearance of lymphocytes under H&E light microscopy.

Answer 19

Small round cell with dark, round nucleus; most common leukocyte in CT of a mucosa; principal cell in immune reactions.

Question 20

Describe the appearance of neutrophils under H&E light microscopy.

Answer 20

Lobulated nucleus; accumulate in inflammation, particularly if the cause is bacterial.

Question 21

Describe the appearance of eosinophils under H&E light microscopy.

Answer 21

Two lobes of nucleus; bright red granules in cytoplasm; accumulate in parasitic infections and allergy reactions.

Question 22

Where/ how are adipocytes/ fat cells found?

Answer 22

Occur as single cells or clumped together to form adipose tissue.

Question 23

What is the function of adipocytes/ fat cell?

Answer 23

Store fat as energy source, clumped together they act as insulation (hypodermis).
In some parts of body: act as shock absorbers (palms, soles), or protective padding (around kidneys).

Question 24

What surrounds adipocytes/ fat cels?

Answer 24

Thin basal lamina-type structure surrounds each cell.

Question 25

What do adipocytes/ fat cells arise from?

Answer 25

Fat cells arise from mesenchymal cells during period from late foetus to approximately 15 months. Though that fat cells only increase in size and not number in later life

Question 26

What is the origin of macrophages?

Answer 26

Monocytes (type of leukocyte) transform into macrophages when they cross a capillary wall

Question 27

What are macrophages?

Answer 27

Most important defence cell; a ‘scavenger cell’ that phagocytoses: cell debris, abnormal intercellular components, bacteria (invading organisms), inert particles (e.g., carbon), cancer cells.
Other functions include: antigen presenting cells (i.e., initiate immune response), produce cytokines that activate other defence cells, produce interferons that protect cells from viral infection.

Question 28

How do macrophages differ in different organs?

Answer 28

Have different functions and specific names.
e.g.,
spleen: macrophages phagocytose worn out RBCs
lungs: dust cells phagocytose particulate matter in the air
liver: kupffer cells phagocytose worn out RBCs

Question 29

What are plasma cells?

Answer 29

A plasma cell produces large quantities of only one specific antibody. Antibody combines with antigen and makes it harmless.

Question 30

What are mast cells?

Answer 30

Storage of chemical mediators of the inflammatory response.

Question 31

Explain mast cells role in allergy reactions.

Answer 31

First exposure: in some individuals, immune system identifies usually harmless substances (e.g., moulds, pollen, bee venom, penicillin and other drugs) as antigens. Antigens that cause allergic reactions are allergens. From the first exposure to these substances in hypersensitive individuals, plasma cells produce IgE that combines with receptors located on the surface of mast cells.
Second and subsequent exposures: allergen combines directly with IgE attached to mast cell and triggers a mass secretion (degranulation) from mast cell. All substances released from mast cells affect surroundings capillaries and cells. Hives (urticaria) result from allergy reactions in the skin. Asthma results from allergy reactions in the lungs.

Question 32

What is anaphylaxis? What occurs during this process?

Answer 32

Exaggerated reaction caused by a hypersensitive person being exposed to an allergen.
All mast cells in body degranulate. Blood volume drops as fluid accumulates in tissues. Tissue swelling impairs breathing, and constriction of bronchioles restricts breathing. Anaphylactic shock initiated within minutes of exposure to allergen. Fatal unless treated immediately with adrenalin.

Question 33

Give examples of substances released by mast cells. What are their role?

Answer 33

Heparin: contributes to AGS but has no major role when released from a mast cell
Histamine and other substances (e.g., prostaglandins, kinins, leukotrienes etc.) collectively: increase vasodilation (increase blood flow to site of tissue damage), increase capillary permeability (increase flow of plasma and blood-borne substances to site of tissue damage), facilitate defence (phagocytic) cell migration from blood to CT, increase contraction of smooth muscle in respiratory system, increase mucus production in respiratory system.

Question 34

Describe reserve (stem) cells in CT.

Answer 34

CT contains few reserves, undifferentiated mesenchymal cells. These give rise to several cell types that function in repair of CT and blood vessels. Pericytes = one type of undifferentiated mesenchymal cell, which are found located around capillaries. Some primitive mesenchyme cells are also present. Fibroblasts/ cytes can divide in response to tissue damage.