Cells and Tissues

This article is part II of a Anatomy & Physiology Series for healthcare professionals

Every movement, injury, and recovery process depends on the behavior of cells and tissues. Before learning individual muscles, joints, and movement patterns, it is important to understand the basic building blocks of the body: cells, tissues, and the healing process.

Cells: The Basic Unit of Life

Cells are the smallest living units in the human body. Every tissue, organ, and body system is made of specialized cells that perform specific functions. Cells contain several important structures that allow them to survive, produce energy, communicate, and create proteins needed for growth, repair, and adaptation.

• The cell membrane controls what enters and leaves the cell.
  The cell membrane is a thin, flexible structure made primarily of phospholipids and proteins. It surrounds the cell and acts as a selective gatekeeper, controlling the movement of substances in and out. Some small molecules, such as oxygen, can pass directly through the membrane, while larger molecules and charged particles, including glucose and many electrolytes, require specialized protein channels or transporters. This selective control helps maintain the cell’s internal environment and allows it to function properly. The structure and chemical properties of the cell membrane will be discussed in more detail in the Chemistry Foundations.

• The nucleus stores genetic information and regulates cell activities.
  The nucleus contains the cell’s genetic material, primarily DNA. DNA provides instructions for making proteins needed for cell structure, repair, and function. RNA molecules, including messenger RNA (mRNA), help use this genetic information. mRNA carries instructions from DNA to ribosomes, where proteins are produced.

• The mitochondria‍ ‍generate ATP to power cellular activities.
  The mitochondria produce ATP, the primary energy source used by cells. ATP provides energy for essential processes such as maintaining cell function, transporting substances, and supporting tissue repair.

Four Types of Body Tissues

The human body is organized into four major types of tissues: epithelial, connective, muscle, and nervous tissue. Each tissue type contains specialized cells that work together to perform specific functions. Understanding these tissues provides the foundation for understanding movement, injury, and rehabilitation.

• Epithelial tissue covers body surfaces and protects underlying structures.

  Epithelial tissue forms the outer layer of the skin and lines many internal structures, including organs and blood vessels. It functions as a protective barrier and also plays roles in absorption and secretion. In physical therapy, epithelial tissue is especially relevant in areas such as wound healing, scar management, and maintaining skin integrity.

• Connective tissue supports, connects, and provides structure to the body.

  Connective tissue contains specialized cells surrounded by an extracellular matrix that provides strength, flexibility, and support. It includes structures such as bone, tendons, ligaments, cartilage, fascia, and fat tissue. Connective tissue is especially important in physical therapy because many common injuries involve these structures. Examples include tendon injuries, ligament sprains, cartilage degeneration, and fractures. Understanding how connective tissue responds to stress and heals is essential for rehabilitation.

• Muscle tissue produces force and creates movement through contraction.

  There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscle is responsible for voluntary movements such as walking, lifting, and maintaining posture. Cardiac muscle produces contractions of the heart, while smooth muscle controls movement within organs and blood vessels. Physical therapists primarily focus on skeletal muscle because it plays a major role in strength, mobility, balance, and functional movement.

• Nervous tissue communicates information and controls movement throughout the body.

  Nervous tissue is made of specialized cells that transmit electrical signals between the brain, spinal cord, and other parts of the body. It allows us to sense our environment, coordinate movement, and control body functions. Nervous tissue is highly relevant in physical therapy because conditions affecting the nervous system, such as stroke, spinal cord injury, or nerve damage, can influence strength, sensation, coordination, and mobility.