Tissues and Cell Junctions

Tissues are a community of cells sharing common characteristics and embryonic origin.
This lecture covers various tissue types, their origins, cell adhesion, epithelial tissue, contrasting muscular and nervous tissues, membrane structure/function, and tissue repair with a focus on homeostasis.
There are four main tissue types: Epithelial, Muscular, Nervous, and Connective.

Epithelial Tissues:
- Cover the body, e.g., skin.
- Line internal body cavities (mucus membranes).
- Cover organs, providing a lining function for various structures.
Muscular Tissues:
- Enable muscle contraction for movement.
- Facilitate heartbeat and involuntary movements like vasoconstriction and peristalsis during digestion.
Nervous Tissues:
- Form the central and peripheral nervous systems.
- Composed of neurons and glial cells (support neurons).
Connective Tissues:
- Connect and support other tissues.
- Have different varieties and subdivisions.

Cell junctions create connections within cell communities, linking cells to each other or to the basement membrane.
Types include tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.

Seal adjacent plasma membranes, making the tissue waterproof.
Prevent water passage between cells.
Example: Intestinal lining uses tight junctions to control water absorption within the digestive system.
Also found in the lining of the atrium and ventricle and blood arteries to keep liquid inside of the structure.

Employ a protein belt (cadherin) to tie cells together, similar to Velcro.
Provide strong adhesion, preventing cells from separating.
Cadherins act like Velcro hooks and loops to connect cells.
Found in the intestinal wall (along with tight junctions) for controlled absorption and peristaltic movement.
Invention Inspired by nature.

Even stronger cell junctions, found in tissues under high stress.
Protein belt (cadherin) attached to intermediate filaments (cytoskeleton) for extreme strength.
Example: Skin; it's hard to tear due to these strong junctions.
Similar junctions called hemidesmosomes attach epithelial cells to the basement membrane.

Attach epithelial cells to the basement membrane.
Half desmosomes with the protein belt, filament, and Velcro protein attaching to the plasma membrane.

Pores (connexins) connecting cells, enabling communication, coordination, and nutrient sharing.
Allow passage of small materials between cells.
Example: Heart muscle cells use gap junctions for coordinated beating of atria and ventricles.
Enable rapid signal propagation for synchronized contraction.