Cell Junctions and Inflammation Concepts

Study Notes

Epithelial tissue is characterized by cellularity, meaning cells are tightly bound with minimal space between them
Cell junctions form bonds with other cells or extracellular material
- Gap junctions allow rapid communication between cells
  - Composed of connexons that allow small molecules and ions to pass
  - Coordinate contractions in heart muscle
- Tight junctions prevent the passage of water and solutes
  - Found between two plasma membranes with an adhesion belt attached to the terminal web
  - Keep enzymes, wastes, and acids within the lumen of the digestive tract
- Desmosomes connect opposing plasma membranes using cell adhesion molecules (CAMs) and proteoglycans
  - Spot desmosomes tie cells together, allowing bending and twisting
  - Hemidesmosomes attach cells to the basement membrane

Tissues respond to injury in two stages: inflammation and regeneration
Inflammation, also known as the inflammatory response, can be triggered by trauma (physical injury) or infection (presence of pathogens)
Damaged cells release prostaglandins, proteins, and potassium ions
Damaged connective tissue activates mast cells
During the inflammatory response, lysosomes release enzymes that destroy injured cells and surrounding tissues, which is called necrosis
- Necrosis begins several hours after injury
- Necrotic tissues and cellular debris (pus) accumulate in the wound
- An abscess is pus trapped in an enclosed area
The ability of tissues to regenerate varies
- Epithelia, connective tissues (excluding cartilage), and smooth muscle regenerate well
- Skeletal muscle, cardiac muscle, and nervous tissues regenerate poorly or not at all
- Damaged cardiac muscle cells are replaced by fibrous tissue through fibrosis

Epithelial tissues are characterized by cellularity, meaning cells are tightly bound with minimal space between them.
Cell junctions are intercellular connections that form bonds with other cells or extracellular material
- Gap junctions allow rapid communication between cells through connexons, facilitating the passage of small molecules and ions.
  - Examples include coordination of contractions in heart muscle.
- Tight junctions form between plasma membranes, with an adhesion belt attaching to the terminal web.
  - They prevent the passage of water and solutes, helping to maintain the integrity of barriers like the digestive tract lumen, keeping enzymes, wastes, and acids contained.
- Desmosomes provide strong adhesion between cells, allowing for bending and twisting.
  - Spot desmosomes connect cells together, while hemidesmosomes attach cells to the basement membrane.

Tissue response to injury involves two stages: inflammation and regeneration.
Inflammation, also known as the inflammatory response, can be triggered by trauma (physical injury) or infection (presence of pathogens).
- Damaged cells release prostaglandins, proteins, and potassium ions, which activate mast cells.
During the inflammatory response, lysosomes release enzymes that destroy injured cells and surrounding tissues - necrosis.
- Necrosis begins several hours after injury, and pus (necrotic tissues and cellular debris) accumulates in the wound. An abscess is pus trapped in an enclosed area.
Regeneration capabilities vary among tissues:
- Epithelia, connective tissues (excluding cartilage), and smooth muscle regenerate effectively.
- Skeletal muscle, cardiac muscle, and nervous tissues regenerate poorly, if at all.
- Damaged cardiac muscle cells are replaced by fibrous tissue through fibrosis.