Connective Tissues 1

Question 1

1. Describe the structural relationships among connective tissue and epithelia, blood vessels, and muscles.

Answer 1

CT–> secretes ECM

Question 2

2. Describe connective tissue cellular and extracellular components and their functions: State the types, origins, and functions of the different cell types found within connective tissues. Describe the components of the extracellular matrix, their functions, and how they are organized in different connective tissues.

Answer 2

-CT, found under the basal lamina of epithelia, around muscles and nerves, connects/regulates other tissue types.
-Different CT from tissue to tissue, but all have an ECM (though these are very varied in their components).
-Near body surface = continuous, loose tissue = superficial fascia.
-Under that is tougher, dense tissue = deep fascia (includes epimysium covering muscles).
-All bones/cartilage structures made of CT.
CT functions =
-mechanical strength
-exchange of nutrients and signals between cells and organs
-control behaviors/functions of cells that contact ECM.

Regulatory functions =
-polarization/cell shape,
-cell migration,
-cell proliferation/differentiation/metabolism,
- defense,
tissue formation/organization/modification, and
-inflammation/repair.

• Core residents of CT family produce/secrete components of ECM, and produce new CT.
• Mesenchymal cells = precursors to all other CT cells.
• Function in embryogenesis, but function as stem cells in adult hood.
• fibroblasts = precursor to many cells
• myofibroblasts = smooth muscle-like contractile function
• adipocytes = store fat.
• Brown fat in babies/children that make heat
• osteoblasts and osteocytes make bone
• chondrocytes make cartilage
• some smooth muscle cells, which contribute to ECM
• Immigrant blood-derived cells = WBCs produced from hematopoietic cells and are important for defense.
• Respond to tissue damage.
• lymphocytes = immunity
• macrophages = phagocytic.
• Also involved in angiogenesis, remodeling damaged tissues, and remodeling normal tissues
• neutrophils and eosinophils important for defense
• mast cells = vasodilators that promote swelling; release histamine
• osteoclasts = phagocytes that function in bone resorption and remodeling.
• Macrophages and osteoclasts derive from blood monocytes.
• Mast cells derive from basophils.
• Lymphocytes, neutrophils, and eosinophils come from cells in the blood of the same type.
• Fibroblasts are central CT cell type, makes most of the material of CT.
• Secretory machines, can divide to produce new fibroblasts, and are highly regulated.
• Tissue injury increases fibroblast production; can differentiate into other tissue cell types.

Question 3

3. For the proteins that form extracellular fibers, describe their types, their properties, and how they are made and assembled in the extracellular matrix.

Answer 3

ECM has:

• structural fibers,
• hydrated gelatinous material (ground substance),
• extracellular macromolecules embedded within.

1) Structural fibers =
- collagen, for the most part.
- 3 intertwined alpha helices make 1 collagen.
- They can cross link with other collagen molecules to form higher order fibers.
- fibrillar collagen = large collagen bundles, long and thick to resist tensile stresses.
- Generally made by type I.
- fibril-associated collagen = on surface of fibrils, probably link them.
- network-forming collagen = thin fibers that form porous sheets in the basal lamina (anchor fibers that attach BL).
- Can also form filtration barriers; type IV most common.
- Collagen can arrange into loose connective tissues (thin fibrils that are sparse, with many cells and ground substance components; lots of capillaries and nerves).
- Dense connective tissues have thick collagen fibrils that are abundant as opposed to low number of cells.
- Ligaments are parallel-organized sheets of DCT; resist strong shear forces and have great strength.
- Collagen synthesized intracellularly, secreted and modified extracellularly.
- Intracellularly = synthesized in ER, glycosylated and hydroxylated, form a triple helix.
- Extracellularly = N and C-termini cleaved by proteases; N-terminal fragments = N-telo peptides (can be used to diagnose CT/bone disease).
- Can form bundles, cross-link, and increase tensile strength.

2) Elastic fibers in tissues that need distensibility and resiliency.
- Elastic fibers = elastin + fibrillin.
- Elastin is unstructured and can be stretched upon exertion of force.
- Secreted by fibroblasts.
- Fibrillin helps organize elastin.

3) Ground substance composed of:
- proteoglycans = proteins + GAGs.
- Hyaluronic acid not attached to protein.
- GAGs are negatively charged (hold on to water = hydrated structure) and are rigid (can form gels).
- This allows them to form a gel that allows diffusion of small things but inhibits movement of large structures (like bacteria).
- Provide turgor pressure to resist compression forces. -Can also bind to activate/inactivate other proteins.
- inorganic/small organic solutes.
- other proteins and glycoproteins (proteases, enzymes, signaling proteins)

Question 4

4. Describe the basis and functional consequences of connective tissue diversity.

Answer 4

-While connective tissues are heavily related they are highly diverse due to cell type diversity (different precursors can differentiate into many cells) but also variations in ECM components vary from organ to organ.

Question 5

5. Describe how connective tissues are regulated upon tissue injury. Describe the events that occur following wounding and inflammation.

Answer 5

-CT aids in inflammation and wound repair by using a network of secreted ligands, cell receptors, and intracellular signaling.

1) Inflammation/clotting = tissue injury releases blood platelets = blood clots.
- CT components release signaling compounds that increase water permeability of capillaries (cause swelling), increase cellular permeability of endothelia (to cause migration of monocytes, lymphocytes, and other immune cells), attract migration of WBCs (via chemotaxis), stimulate proliferation of fibroblasts and macrophages. Mast cells secrete histamine and WBCs secrete cytokines.

2) New tissue formation: fibroblasts divide and secrete ECM components. Epithelial stem cells start to divide and differentiate. New tissue undergoes angiogenesis, repair, and remodeling.

3) Tissue remodeling = density of cells is reduced and ECM becomes thinner. Extensive damage = scar tissues.
Dysfunction of inflammation control = diseases like chronic inflammation (IBD, arthritis), cancers.