Chapter 4: Tissue—The Living Fabric (Study Guide)

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Tissues are groups of cells that are similar in structure and perform a common or related function.
Histology is the study of tissues, essential for understanding how organs function.
There are four basic tissue types in the human body: epithelial, connective, muscle, and nervous tissue.

Polarity: Epithelial cells have an apical (top, exposed) surface and a basal (bottom, attached) surface, each with different structures and functions.
Specialized contacts: Cells are tightly joined by junctions (e.g., tight junctions, desmosomes) to form continuous sheets.
Supported by connective tissue: The basal surface is attached to a basement membrane, which reinforces the epithelium and helps resist stretching and tearing.
Avascular: Epithelial tissues lack blood vessels but are innervated (supplied by nerve fibers); nutrients diffuse from underlying connective tissues.
Regeneration: Epithelial cells have a high regenerative capacity, rapidly replacing lost or damaged cells.

Disruption of epithelial tissue structure or function can lead to diseases, including cancer.

Cancer often arises from epithelial cells (carcinomas), which can lose their polarity and specialized contacts, leading to uncontrolled growth and invasion.

All epithelial tissues have two-part names:
- First name: Indicates the number of cell layers
- Second name: Indicates the shape of the cells
Number of layers:
- Simple: One layer of cells
- Stratified: Two or more layers of cells
Cell shapes:
- Squamous: Flat and scale-like
- Cuboidal: Box-like, as tall as they are wide
- Columnar: Tall and column-shaped

Example: Simple squamous epithelium is a single layer of flat cells found in areas of filtration or exchange, such as the air sacs of lungs.

Simple squamous: Diffusion and filtration; found in alveoli, lining of blood vessels.
Simple cuboidal: Secretion and absorption; found in kidney tubules, ducts of small glands.
Simple columnar: Absorption, secretion of mucus; found in digestive tract lining.
Stratified squamous: Protects underlying tissues; found in skin, mouth, esophagus.
Transitional: Stretches; found in urinary bladder.

Endocrine glands: Ductless glands that secrete hormones directly into the bloodstream (e.g., thyroid gland).
Exocrine glands: Secrete products into ducts that open onto body surfaces or cavities (e.g., sweat glands, salivary glands).
Goblet cells: Unicellular exocrine glands that secrete mucus; found in the lining of the intestines and respiratory tract.
Mucous cells: Also secrete mucus; found in various epithelial linings.

Merocrine: Secrete products by exocytosis (e.g., sweat glands).
Holocrine: Accumulate products until the cell ruptures (e.g., sebaceous glands).
Apocrine: Accumulate products just beneath the surface, then the apex pinches off (controversial in humans).

Tissue Class and Example: Four main classes—connective tissue proper (e.g., adipose), cartilage (e.g., hyaline cartilage), bone (e.g., compact bone), blood.
Subclasses Name: Each class has subclasses (e.g., loose and dense connective tissue proper).
Description/Structure: Consists of cells (fibroblasts, chondrocytes, osteocytes, etc.) and extracellular matrix (protein fibers—collagen, elastic, reticular—and ground substance).
Location: Widely distributed; found in tendons, ligaments, fat, bone, cartilage, and blood.
Function: Supports and binds tissues, stores energy, insulates, transports substances.

Three types of membranes:
- Cutaneous membrane: The skin; covers the body surface.
- Mucous membrane: Lines body cavities open to the exterior (e.g., digestive, respiratory tracts).
- Serous membrane: Lines closed ventral body cavities (e.g., peritoneum, pleura, pericardium).
Function: Protection, secretion, absorption, and lubrication.
Location: Depends on membrane type; skin, internal passageways, body cavities.

Not on Exam 1, but important for final exam.
Involves inflammation, organization (restoration of blood supply), and regeneration/fibrosis (replacement of destroyed tissue).

Not on Exam 1, but important for final exam.
Tissues develop from three primary germ layers: ectoderm, mesoderm, and endoderm.
With aging, tissues lose regenerative capacity and function may decline.

Additional info: Academic context and examples have been added to supplement the outline and provide a self-contained study guide.