Tissues of the Body: Structure, Function, and Classification

Tissues of the Body

Introduction to Tissues

Tissues are collections of specialized cells and cell products that perform a limited number of functions. The study of tissues is known as histology.

• Tissue: A group of similar cells working together to carry out specific activities.

• Histology: The scientific study of tissues.

Types of Tissues

Four Basic Types of Tissues

The human body contains four primary types of tissues, each with distinct functions and characteristics.

• Epithelial tissue: Covers surfaces, lines cavities, and forms glands.

• Connective tissue: Provides support, fills spaces, and stores energy.

• Muscle tissue: Specialized for contraction and movement.

• Nervous tissue: Transmits electrical impulses and processes information.

Figure 4-1 (described): Diagram showing the relationship between cells, tissues, organs, and organ systems, with examples of each tissue type and their functions.

Epithelial Tissue

Epithelial Tissue Overview

Epithelial tissue covers both internal and external body surfaces and composes most glands. It serves several essential functions in the body.

• Covers surfaces (skin, lining of digestive tract, etc.)

• Forms glands (e.g., sweat glands, salivary glands)

• Serves essential protective and regulatory functions

Characteristics of Epithelial Tissue

Epithelial tissue is defined by several key structural and functional characteristics.

• Cells are bound closely together, forming continuous sheets.

• Has an exposed (apical) surface facing the environment or internal space.

• Attached to underlying connective tissue by a basement membrane.

• Avascular: Lacks blood vessels; nutrients diffuse from underlying tissues.

• Cells undergo continual replacement or regeneration.

Locations of Epithelial Tissue

Epithelial tissue is found covering and lining various body surfaces and cavities.

• Covers external surfaces (e.g., skin)

• Lines internal passageways (digestive, urinary, respiratory, reproductive tracts)

• Lines internal cavities (e.g., cavities around lungs and heart)

• Forms selective barriers and prevents friction

Functions of Epithelia

Epithelial tissues perform four essential functions:

• Physical protection: Shields underlying tissues from abrasion, dehydration, and chemical damage.

• Control permeability: Regulates movement of substances into and out of the body.

• Provide sensation: Contains sensory receptors for detecting stimuli.

• Produce specialized secretions: Forms glands that secrete substances (glandular epithelium).

Glandular Epithelium

Glandular epithelium consists of epithelial cells specialized to produce and secrete substances.

• Exocrine glands: Discharge secretions onto the surface of the epithelium (e.g., sweat, saliva).

• Endocrine glands: Release hormones into surrounding tissue fluid and blood (e.g., thyroid, pituitary).

The Epithelial Surface

The apical surface of epithelial cells is exposed to an internal or external environment and may have specialized structures.

• Microvilli: Increase surface area for absorption (e.g., small intestine).

• Cilia: Move materials along the surface (e.g., ciliated epithelium in respiratory tract moves mucus; in uterine tube moves egg).

• Note: Cilia do not move the cell itself in humans.

The Basement Membrane

The basement membrane is a thin, noncellular layer that anchors the epithelium to underlying connective tissue.

• Composed of a network of protein fibers (mainly collagen).

• Provides strength and resists distortion.

• Acts as a barrier to proteins and large molecules.

Figure 4-3 (described): Diagram showing cilia, microvilli, apical and basal surfaces, and the basement membrane in epithelial cells.

*Additional info: The basement membrane is essential for tissue integrity and selective filtration between epithelial and connective tissues.*