Lecture Notes: Tissues and Cell Junctions

Introduction to Tissues

• Cell Junctions: Ways that cells connect to each other to form tissues.
• Extracellular Matrix: A fluid, gel-like substance containing carbohydrates and proteins.
  • Regulates cell growth, movement, and differentiation.
  • Contains macromolecules like collagen, elastin, and fibronectin.
  • Includes proteoglycans and hyaluronic acid.
  • Fibroblasts are crucial for tissue repair.

Cell to Cell Adhesions

• Points where cells are held together to form tissues and organs.
• Surface Types in Tissues:
  • Basal surface: Base of the tissue.
  • Apical surface: Open surface (in epithelial tissues).
  • Lateral surface: Where cells join together.
• Basement Membrane: Connects epithelial tissues to connective tissues.

Cell Adhesion Molecules (CAMs)

• Proteins on the cell surface.
  • Examples: Integrin, cadherin, selectins, immunoglobulin superfamily.
• Embedded in the lipid bilayer, they connect cells to each other and to the extracellular matrix.

Specialized Cell Junctions

• Adherens Junctions: Resemble a belt, found in epithelial tissues.
• Desmosomes: Button-like structures, strong connections, found in skin, cardiac muscle, bladder, and GI tract.
• Hemidesmosomes: Half desmosomes, connect epithelial tissue to basement membrane.
• Tight Junctions: Prevent movement of substances between cells, found in kidney, GI tract, and skin.
• Gap Junctions: Allow ion passage between cells, facilitating electrical impulse transmission, important in cardiac muscles.

Cell Communication

• Important for maintaining homeostasis and coordinating body functions.
• Types of Signaling:
  • Paracrine: Local hormone signaling affecting nearby cells.
  • Autocrine: Hormone signaling affecting the secreting cell.
  • Endocrine: Hormones traveling through the bloodstream affecting distant cells.
  • Neurotransmitters: Local signaling between neurons across synapses.

Signal Transduction

• Process of transmitting signals into cells.
• First Messengers: Bind to receptors on the cell surface.
• Second Messengers: Transmit signals inside the cell (e.g., calcium, cyclic AMP).
  • Activation of protein kinases, which add phosphates to proteins, altering their function (on/off).

Overview of Four Main Tissue Types

• Epithelial Tissue: Lines surfaces like skin, blood vessels, and GI tract.
• Connective Tissue: Diverse, connects various tissues, cells spaced apart.
• Muscle Tissue: Responsible for movement.
• Nervous Tissue: Conducts nerve impulses.