8.1: Tissues

Tissues are a group of cells that share a common embryonic origin. Microscopic observation reveals that the cells in a tissue share morphological features and are arranged in an orderly pattern to perform specific functions. From an evolutionary perspective, tissues appear in more complex organisms. Although there are many types of cells in the human body, they are organized into four broad categories of tissues: epithelial, connective, muscle, and nervous. Each of these categories is characterized by specific functions that contribute to the overall maintenance of the body.

Epithelial tissue refers to the sheets of cells that cover exterior surfaces of the body, line internal cavities/passageways, and form certain glands. Connective tissue, as its name implies, binds the cells and organs of the body together and protects, supports, and integrates all parts of the body. Muscle tissue is excitable, responding to stimulation and contracting to provide movement. Muscle tissue has three major types: skeletal, smooth, and cardiac. Nervous tissue is also excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body.

Different tissue types are organized into organs. Each organ has a specific arrangement of these tissues that helps perform their functions. A disruption of the structure in any of these tissue types is a sign of injury or disease. Such changes can be detected through histology, the microscopic study of tissue appearance, organization, and function.

This text is adapted from Openstax, Anatomy and Physiology 2e, Section 4.1: Types of Tissues

Tissues are groups of structurally similar cells that work together as functional units.

Based on their structure and function, tissues can be of four types.

Epithelial tissues are composed of single or multiple cell layers that cover external body parts, line internal body surfaces and form different glands.

Muscle tissues consist of specialized contractile cells that facilitate body movements.

Connective  tissues contain cells in a viscous matrix of extracellular fibers. They provide structural support, transport nutrients, and serve as fat reservoirs.

Nervous tissues consist of neurons that respond to stimuli by generating electrical signals, which help coordinate various body activities.

Different tissue types organize to form organs and carry out specialized functions.

For instance, food ingestion activates the nervous tissue, stimulating the stomach's epithelial lining to secrete digestive juices. Smooth contractile muscles and the adjoining connective tissues on the stomach wall then churn the food to release nutrients to be absorbed throughout the body.