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Flashcards in Histology Week 2 Deck (30):

What are the fiber types in connective tissue?

Connective tissue fibers:
- collagen
- reticular
- elastic


What are the different cell types in connective tissue?

Resident Cells: Relatively stable, permanent residents of connective tissue. These cells remain in the connective tissue and include:
Fibroblasts and myofibroblasts (primary cells involved in collagen and ground substance secretion).
Macrophages (arise from migrating monocytes).
Adipose cells.
Mast cells (arise from stem cells in the bone marrow). Mesenchymal cells.

Transient Cells Wandering cells that have migrated into the connective tissue from the blood in response to specific stimuli (usually during inflammation). This population is not normally found in connective tissue and is composed of cells involved in the immune response: Lymphocytes
Plasma cells


Connective tissue cells can be put in two categories:

Structural: fibroblast, chondrocytes, osteoblasts, tendon, adipocytes
Migratory: (blood stream) produce bone marrow, part of the blood stream


Describe fibroblasts

Fibroblasts: large, flat, branching cells which appear spindle-shaped in a side view. In mature tissue they are quiescent. After injury, they begin to form new fibers. Under the electron microscope, the activated fibroblast shows the extensive rough ER needed for the synthesis of collagen and elastin fibgers. Proteoglycans, a chief component of the ground substances of connective tissues are also synthesized by these cells. Fibroblasts have large, oval and faint staining nuclei with one or two conspicuous nucleoli.


Describe Macrophage (histiocyte)

next in abundance to the fibroblasts in loose connective tissue, these cells are initially non-motile. During inflammation, they become very actively amoeboid and phagocytic ("angry macrophages"). They readily engulf blood cells, bacteria, dead cells and debris digesting this material with powerful enzymes. The nucleus of this cell type is often indented and dark staining. Nucleoli are not conspicuous. These cells are an important component of the reticuloendothelial system (RES) located in the spleen, liver, lymph nodes and other organs.


Describe Adipose cells

These cells are commonly seen in loose connective tissue (areolar). They are often found arranged around small blood vessels. Initially they resemble fibroblasts but with numerous vacuoles of fat droplets. In adult cells, the droplets coalesce bloating the fat cells with a huge fat vacuole.


Describe Leukocytes

are white blood cells which wander into the connective tissues surrounding blood vessels. Eosinophiles are very common throughout the respiratory and digestive tracts, as well as in active mammary tissue. Neutrophiles are found at sites of inflammation. Plasma cells, derived from B lymphocytes, are common in areas of chronic inflammation.


Describe Mast cells

Mast cells - are large cells (20 to 30 um) filled with deeply basophilic granules which often obscure the nucleus. They are usually adjacent to blood vessels. Like the blood


Describe Melanocytes

are pigment cells found in the connective tissues of the skin and choroid coat of the eye. The melanin produced by these cells is known to absorb ultra violet light.


List the major classes of extracellular molecules that comprise the ground substance of connective tissue and relate how the molecular structures support the functions of these molecules.

Ground substance is a viscous, clear substance that occupies the space between the cells and fibers within connective tissue. Ground substance contains three main types of macromolecules:
- Proteogylcans
- Glycoproteins
- Fibrous proteins

The fibrous proteins and glycoproteins are embedded in a proteoglycan gel, where they form an extensive ECM that serves both structural and adhesive functions.


What is the core molecule of a proteoglycan aggregate? Describe its function:

hylauronic acid

These macromolecules consist of a core protein that is covalently attached to approximately 100 glycosaminoglycan (GAG) molecules and a linker protein, which binds hyaluronic acid (HA) and strengthens its interaction with the proteoglycan molecule. Proteoglycans are very large, highly negatively charged macromolecules that attract water into the ground substance, giving it a gel-like consistency. This highly hydrated gel is able to resist compressive forces while allowing diffusion of O2 and nutrients between the blood and tissue cells.


Describe how the combination of cells, fibers and ground substance combine to produce the different varieties of connective tissue.

Ground substance may be highly modified in the special forms of connective tissue:
- blood: lacks stabilizing macromolecules, free-flowing ground substance plasma.
- skeletal tissue: mineralized by deposition of calcium salts = bone = rigid ground substance
- cartilage: more solid than in ordinary connective tissue but still retains more resiliency than bone.


Distinguish between nucleated and non-nucleated blood cells and describe how morphology and cell structures support the cell function.

Red blood cells are non-nucleated:
WBC = leukocytes: nucleated
Only the red blood cells, like trolley cars, are confined to the highways (i.e., blood vessels). All other cell types in blood, and most plasma constituents as well, can circulate rather freely from blood to connective tissue and back again. Thus, most of the mobile cellular components of ordinary connective tissue are interchangeable with those in blood.


Distinguish between granulocytes and agranulocytes and what the functions are for each cell type

Granulocytes (innate immune system) are a category of white blood cells characterized by the presence of granules in their cytoplasm.[1] They are also called polymorphonuclear leukocytes (PMN, PML, or PMNL) because of the varying shapes of the nucleus, which is usually lobed into three segments. This distinguishes them from the mononuclear agranulocytes.
- Basophil granulocytes: the circulating equivalent of tissue mast cells. Prevent blood from clotting too quickly. Contain vasodilator histamine.
- Eosinophil granulocytes: involved in responses to allergy and parasites.
- Neutrophil granulocytes: phagocytic cells travel in blood until called out into peripheral tissues. An inflammatory response (triggered in part by mast cells) summons neutrophils to the affected area. Neutrophils have the ability to approach, engulf, and kill most bacteria. bone marrow derived
Mast cells: bone marrow derived
Mnemonic: "BEN”

Agranulocytes, (adaptive immune system) also known as mononuclear leukocytes, are white blood cells with a one-lobednucleus. They are characterised by the absence of granules in their cytoplasm, which distinguishes them from granulocytes.
- Lymphocytes: ability to recognize and bind to foreign substances
- Monocytes: circulating precursors of macrophages.
- Macrophage: remove and digest the by-products of both bacterial warfare and normal growth and degeneration. Enter connective tissue from the blood as monocyte, also recycles iron, involved phagocytosis


Introduce the role that blood cells play in the host defense

Connective tissue forms the principal battleground for invasions: Bacteria do not easily proliferate within epithelia --cell membranes block entry into cells, and there is little extracellular food for bacteria within epithelia. On the other hand, connective tissue offers a potential paradise. The abundant extracellular material provides all the necessary nutrients as well as an ideal warm, humid, oxygenated environment. Without vigorous immunological defenses within the connective tissue, any small break in the epithelium would convert the body into an excellent bacterial culture.

Inflammation is a specific function of connective tissue.


Draw a connection between peripheral blood cells and cells in loose CT:

various WBC’s are delivered to the loose CT and become active: basophil = mast cell, monocyte = macrophage


Types of collagen: major types

Type I: bone (typical/most abundant collagen) (one = bone)
Type II: Hyaline cartilage (two = cartwolage)
Type III: granulation tissue and reticular fibers.
Type IV: Basal Laminae (epithelial cells) (Four = floor)


Identify the physical barriers that play a role in innate immunity

- skin, unless lesion(s) present (tight junctions (Zonula Occludins)
- mucosae (specialized epithelial lining) of GI tract and respiratory tract
- cilia in respiratory tract (movement of mucus)
- turbinate bones of nasal passage (trap microbes as air passes over)
- regular “flushing” of urinary system


Identify the physical and chemical barriers that play a role in innate immunity

- lysozymes (degradative enzymes) in tears and saliva
- stomach acid, GI enzymes (ex. pepsin in stomach - breaks down protein)
- fatty acids on skin
- normal microbiota (aka normal flora, aka commensals, aka “good microbes”)


What are the cell types involved with inflammation (innate immune cells)?

- Phagocytes: Neutrophils (polymorphonuclear leukocytes), immature dendritic cells, macrophages
- Also mentioned: Compliment proteins, Natural Killer (NK) cells


What are the steps of inflammation?

Step 1) Host molecules called pattern recognition receptors (“PRRs”) bind microbial molecules (aka antigens)
- PRRs are found on the cell membranes of the phagocytes mentioned above.
(Note: PRRs do in fact recognize microbial “patterns”, so are not specific to particular microbes. This is in contrast to B- & T-cells, which are very specific (will be discussed in the future). (examples: TLR, Mannose receptor, scavenger receptor)

Step 2) PRRs bind to conserved microbial molecules (antigens) called Pathogen-associated molecular patterns (“PAMPs”)
Characteristics of PAMPs: little variation for a given class, essential for survival of microbe, expressed by microbes but not host cells [this expression may be a unique way that it is expressed as is the case for mannose]

Step 3) The interaction of PRRs with PAMPs induces intracellular signal transduction cascades (in the phagocytes)

Step 4) These signal transduction cascades result in gene expression of cellular products that are responsible for the inflammatory response and elimination of the pathogen

Steps 5) Expression of inflammatory cytokines (TNF, IL-1, IL-12), Chemokines (IL-8, MCP-1, rantes), Endothelial adhesion molecules (E-secretin), Costimulatory molecules (CD80, CD86), antiviral cytokines

Step 6) inflammation


What are defensins? Describe Alpha and Beta Defensins:

Defensins: antimicrobial peptides released in acute inflammation:
• Alpha defensins: Neutrophils, Paneth cells, Constituitive,
T cell chemoattractant (naïve T cells), Attract immature dendritic cells, Activate complement

•Beta defensins: Epithelial cells
Inducible, Upregulated by LPS or TNF-α, T cell chemoattractant (memory cells)


Describe the complement system:

Complement: proinflammatory serum proteins, circulate as inactive precursors, “complement inflammation”
• Definition: a set of 9 plasma proteins (C1-9) that act together to eliminate extracellular forms of pathogens
• Major functions: Opsonization (the process by which a pathogen is marked for ingestion and destruction by a phagocyte) and Chemotaxis (movement of an organism in response to a chemical stimulus)
• Tip: Also involved in adaptive immune mechanisms (classic pathway)
• All roads (3 pathways) lead to Rome or in this case the synthesis of C3 convertase

•Classical pathway: C1 binds to IgG or IgM that is bound to antigen [pneumonic:“GM makes classic cars”]
• Alternative pathway: microbial products directly activate complement
• Mannose binding lectin pathway - MBL binds mannose on microorganisms and activates complement

• C3 convertase => C5 convertase => formation of MAC (creates hole in organism)
• C3a and C5a - trigger mast cell degranulation
• C5a - chemotactic for neutrophils; helps activates neutrophils
•C3b - opsonin for phagocytosis
• MAC - lyses microbes by creating holes in cell membrane


Compare and contrast the mechanisms of killing pathogens by NK cells and macrophages; be able to explain the importance in the differences in the types of immune responses generated

- Macrophages: phagocytose, release mediators as well (indirect killing); widespread immune response can be generated by macrophages
- NK cells: release lytic granules that kill some virus-infected cell; cytokines also released, effects depend on pathogen type


What uses the same pathway as TLR to activate transcription and the production of inflammatory mediators?



What are the two important functions of innate immunity ?

1.) Initial response to microbes that prevents controls or eliminates infection of the host
2.) Stimulates adaptive immune responses to be optimally effective against different types of microbes.


What does scurvy result from and what are some of typical complications?

Scurvy is caused by vitamin C deficiency resulting in the inability to hydroxylate proline and lysine residues in α-chain polypeptides of collagen molecules (see step 5 above). This results in weakening of the capillaries and the following complications:

- Ulceration of gums and gingival bleeding.
- Loose teeth (due to loss of periodontal ligaments, which are collagen rich).
- Tissue hemorrhage.
- Anemia.
- Poor wound healing.
- Impaired bone formation (in infants).


What would cause a defect in collagen synthesis?

Collagen has three polypeptide chains that form a triple helix. Chains are made up of glycine-X-Y repeats. Point mutation in glycine prevents the formation of a triple helix.


What does Tay-Sachs disease result from:

lysomal dysfunction


Chediak-Higashi disease results from what?

Chédiak-Higashi disease, resulting from abnormal microtubular assembly, leads to decreased polymorphonucleocyte (PMN or neutrophil) phagocytosis and frequent infections.

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