Anatomy & Physiology: Tissues (Chapter 4) Study Notes

Body Tissues

Overview of Tissues

Tissues are groups of cells with similar structure and function, forming the basic building blocks of organs and body systems. There are four primary tissue types in the human body:

• Epithelial tissue (epithelium)

• Connective tissue

• Muscle tissue

• Nervous tissue

Epithelial Tissue

General Characteristics

Epithelial tissue covers body surfaces, lines internal cavities and passageways, and forms certain glands. It serves as a protective barrier and is involved in absorption, filtration, and secretion.

• Locations:

  • Body coverings (e.g., skin)

  • Body linings (e.g., lining of digestive tract)

  • Glandular tissue (e.g., sweat glands)

• Functions:

  • Protection (e.g., skin protects underlying tissues)

  • Absorption (e.g., intestinal lining absorbs nutrients)

  • Filtration (e.g., kidney tubules filter blood)

  • Secretion (e.g., glands secrete sweat, sebum, hormones)

Structural Features

• Sheet-like arrangement: Epithelial cells are closely packed in continuous sheets.

• Polarity: Each sheet has an apical surface (free, exposed to the body exterior or cavity) and a basement membrane (anchored, attached to underlying connective tissue).

• Avascular: Epithelial tissues lack blood vessels and receive nutrients by diffusion from underlying tissues.

• Regeneration: Epithelial cells divide rapidly to replace lost or damaged cells, especially if well-nourished.

Example: The outer layer of skin (epidermis) is epithelial tissue that protects against pathogens and dehydration.

Classification of Epithelial Tissue

Epithelia are classified by the number of cell layers and the shape of the cells at the apical surface.

• Number of Layers:

  • Simple epithelium: Single cell layer (specialized for absorption, secretion, filtration)

  • Stratified epithelium: Multiple cell layers (specialized for protection)

• Cell Shape:

  • Squamous: Flattened, scale-like cells (e.g., lining of blood vessels)

  • Cuboidal: Cube-shaped cells (e.g., kidney tubules, glands)

  • Columnar: Tall, column-like cells (e.g., lining of digestive tract)

Additional info: The combination of layers and shapes gives rise to specific types such as simple squamous, stratified cuboidal, etc.

Key Properties of Epithelial Tissue

• Apical surface: Exposed to the body exterior or internal cavity

• Basement membrane: Thin, non-cellular layer anchoring epithelium to connective tissue

• Avascular: No direct blood supply

• High regenerative capacity: Rapid cell division for repair

Summary Table: Epithelial Tissue Types

Type	Layers	Shape	Main Locations	Main Functions
Simple squamous	1	Flat	Air sacs of lungs, capillaries, serous membranes	Filtration, diffusion
Simple cuboidal	1	Cube	Kidney tubules, glands, ovary surface	Secretion, absorption
Simple columnar	1	Column	Digestive tract lining, mucous membranes	Absorption, secretion (mucus)
Pseudostratified columnar	1 (appears multi-layered)	Column	Respiratory tract (ciliated)	Secretion, movement of mucus
Stratified squamous	Multiple	Flat (apical)	Skin, mouth, esophagus	Protection
Stratified cuboidal/columnar	2 or more	Cube/Column	Ducts of large glands	Protection (rare)
Transitional	Multiple	Varies (can stretch)	Urinary bladder, ureters	Stretching, distension

Additional info: Glandular epithelium forms glands that secrete hormones (endocrine) or other substances (exocrine).