Connective Tissue

Epithelial to Mesenchymal Transition (EMT)

Cells leave the epithelium and dive into the underlying mesenchyme (CT) occurring during embryogensis (tissue regeneration and cancer)

Connective Tissue

A few cells with a lot of extracellular matrix are vital for cell functioning and the generation of fibrillar networks.

Mesenchymal Stem Cell (MSC)

Give rise to connective tissue of the body, producing a variety of different cells. Capable of regeneration, and highly prevalent in embryos, and decreases with age.

Fibroblasts

Maintain ECM by producing collagen and other components, essentially everywhere, but they are molecularly different in different tissues (proliferate). Has a large amount of rER, producing many proteins for ECM maintenance.

Fibrocyte

Structural support and do not proliferate

Adipocytes

Derived from fibroblasts and act as fat storage for energy metabolism and heat generation

White Fat Cells (Unilocular)

Energy storage

Brown Fat Cells (Multilocular)

Thermogenesis

Macrophages

Remove damaged material, remodel ECM and tissue, stimulate angiogenesis, recruit and regulate other immune cells. Diversity of forms depending on organ type, involved in the innate immune system, and phagocytosis.

Fibrillar Collagen

Long, thick fibers, moving from “left to right”.

Fibril-associated Collagens

Attach to fibrillar collagens through proteins or covalent linkages, “up to down”

Networking Collagens

Form dense sheets, which is the core structural component of basal lamina

Procollagen

Smallest unit of collagen

Tropocollagens

Made from helix of procollagen

Collagen Fibrils

Multiple tropocollagens

Collagen FIber

Multiple collagen fibrils

Collagen Control in ECM

Assembled extracellularly by secretion of pro-collagen, which is cleaved by peptidase to form tropocollagen, which attaches to pre-existing collagen fibrils.

Dense Regular Connective Tissue

Unidirectional resistance (tendons, ligaments)

Dense Irregular Connective Tissue

Multi-directional resisting strength from all directions (submucosa, skin)

Loose Connective Tissue

Provides support having elastic and collagen fibers

Collagen Types

Molecularly different forms correspond to structural differences between tissues.

Type I Collagen

Skin, tendon, bones, and CT, providing strength and elasticity

Type II Collagen

Cartilage, offering joing support and flexibility

Type IV Collagen

Forms basement membrane and layers of skin

Reticular Fibers

Thin, mesh-like network for support, anchoring cells (SM, bone marrow, liver, lymphoid structures)

Elastic Fibers

Collagen fibers are linked with elastin, and when stretched, create force for recoil (skin, lungs, walls of blood vessels)

Ground Substance

Gel-like fluid outside of cells w/in the extracellular matrix of CT. A mixture of water, carbs, proteins allow for nutrients to move from blood to cells.

Proteoglycans

Core protein w/ GAG side chains, hydrophilic. Bind cells, other proteins, and/or ECM components, providing structural support, controlling molecule movement, and involved in cell signaling.

Glycosaminoglycans (GAGs)

Linear polysaccharides, hydrophilic (-) due to negative charges. Bind water, support tissue hydration, lubrication, and regulate cell behavior.

Hyaluronic Acid

Bound covalently to the protein core as part of a proteoglycan (hydrophobic GAG)

Wound Repair

Blood clot, inflammation, angiogenesis, fibroblasts, tissue remodeling

Clot formation

Signals platelets to cause clotting, which signals for migration of leukocytes

Inflammation

WBCs (macrophages) move toward the damaged area (signaling and recruiting more immune cells and removing damaged tissue), encouraging angiogenesis.

Angiogensis

Forming new blood vessels from pre-existing ones near wound area

Cell Migration & Proliferation

Fibroblasts and WBCs recruited, increasing ECM, with cells moving under wound and proliferating basally,

Remodeling and Resolution

Cells inflammation decreases and cells have grown basally and covered up the wound.