Biology Chapter: Tissues Overview

Tissues

• Tissues are groups of specialized cells and their surrounding extracellular substances.
• Histology is the study of tissues under a microscope.
• Tissues are classified by their cell structure, extracellular matrix composition, and cell function.

Four Primary Tissue Types

• Epithelial tissue: Covers and lines body surfaces.
• Connective tissue: Supports, connects, and protects other tissues.
• Nervous tissue: Specialized for communication through electrical signaling.
• Muscle tissue: Specialized for contraction.

Embryonic Germ Layers

• Endoderm: Forms the lining of the digestive tract.
• Mesoderm: Develops into organs, muscles, bones, and blood vessels.
• Ectoderm: Gives rise to skin and the nervous system.

Characteristics of Epithelial Tissue

• Primarily composed of cells.
• Covers or lines body surfaces.
• Has an exposed (apical) surface.
• Attaches at the basal surface.
• Connected by cellular junctions.
• Avascular (lacks blood vessels).
• Capable of regeneration.

Classification of Epithelial Tissue

• Number of layers: Simple (single layer), stratified (multiple layers), pseudostratified (appears layered but all cells touch the basement membrane).
• Shape of cells: Squamous (flat), cuboidal (cube-shaped), columnar (tall and column-shaped).
• Cell modifications: Keratinization (presence of keratin protein), cilia (hair-like projections).

Functions of Epithelial Tissue

• Protection of underlying structures.
• Acts as a barrier.
• Permits the passage of substances.
• Secretes substances.
• Absorbs substances.

Glands: Endocrine vs. Exocrine

• Endocrine glands: Ductless, release hormones into the bloodstream (e.g., growth hormone, testosterone, insulin).
• Exocrine glands: Have ducts, release products into a body cavity or onto the skin (e.g., sweat, digestive enzymes, sebum).

Types of Exocrine Glands

• Unicellular glands: Single-celled glands (e.g., goblet cells).
• Multicellular glands: Composed of multiple cells (e.g., sweat glands).

Functions of Connective Tissue

• Support.
• Enclosing and separating other tissues.
• Connecting tissues to each other.
• Storage.
• Cushioning and insulating.
• Transporting.
• Protection.

Connective Tissue Origins

• All connective tissue originates from mesenchyme, an embryonic connective tissue derived from mesoderm.

Components of Connective Tissue

• Specialized Cells: Vary depending on the specific type of connective tissue.
• Extracellular Matrix: Composed of protein fibers and ground substance.
  • Protein fibers: Collagen (strength), reticular (fine network), elastic (flexibility).
  • Ground substance: Varies from liquid to solid, providing support and medium for diffusion.

Types of Muscle Tissue

• Skeletal muscle: Striated, voluntary.
• Cardiac muscle: Striated, involuntary.
• Smooth muscle: Unstriated, involuntary.

Nervous Tissue

• Specialized for communication via electrical signals.
• Found within the nervous system.
• Composed of neurons and glial cells.

Inflammation Response

• Release of chemical mediators.
• Increased blood flow to damaged tissue.
• Decreased blood flow out of tissue.
• Increased vascular permeability.
• Increased presence of immune cells and antibodies.

Signs of Inflammation

• Redness (rubor).
• Heat (calor).
• Swelling (tumor).
• Pain (dolor).
• Loss of function.

Tissue Repair

• Regeneration: Damaged tissue is replaced by the same tissue type.
• Fibrosis: Damaged tissue is replaced by scar tissue.

Cell Types and Tissue Repair

• Labile cells: Continue to divide throughout life (e.g., bone marrow).
• Stable cells: Don't usually divide but have the ability to do so (e.g., liver cells).
• Permanent cells: No ability to replicate and divide (e.g., cardiac muscle, nerve cells).

The Process of Healing

• Inflammation: Initiates the healing process.
• Organization: Damaged tissue fragments are removed and new blood vessels form.
• Regeneration or Fibrosis: Depending on the tissue type, regeneration or fibrosis takes place.

This quiz covers essential concepts related to tissues, including their types and characteristics. It explores epithelial, connective, nervous, and muscle tissues, as well as the embryonic germ layers that give rise to these tissues. Test your knowledge of histology and tissue functions.