Human Body Structure and Function: Cells, Tissues, and Organ Systems

The Organization of the Human Body

Cellular and Tissue Hierarchy

A Cell is the basic structural and functional unit of living things.

• All human cells originate from a single initial cell called the Zygote.
• Although we originate from one cell, we develop several types of specialized cells.
• A group of specialized cells results in a Tissue.

From Tissue to Organism

A Tissue is a set of cells of the same type performing a specific function.

• The combination of various tissues forms an Organ.
• A combination of organs results in an Organ System or Apparatus.

We use the term System when there is only one predominant tissue type (e.g., Nervous System).

The union of all systems and apparatuses results in a Multicellular Organism.

Specific Roles of Human Tissues

Tissues perform distinct roles within the body. We can distinguish the following types:

• Protection (Epithelial Tissue):
  • Integumentary: Covers the body (e.g., skin).
  • Mucous Membranes: Protects internal cavities.
• Storage (Adipose Tissue): Fat cells accumulate, serving as a food reserve.
• Support (Bone Tissue): Provides structure; it is hard due to its mineral content.
• Secretion (Glandular Tissue): Produces and releases substances (e.g., hormones) with various functions.
• Connection (Connective Tissue): Provides cohesion between tissues and surrounds organs.
• Movement (Muscular Tissue): Cells contract and relax, causing the body's movements.
• Communication (Nervous Tissue): Coordinates the functioning of all organs.

Major Organ Systems and Their Functions

The body relies on several major systems to maintain homeostasis:

• Digestive System: Prepares food so that cells can absorb and utilize nutrients.
• Respiratory System: Introduces the necessary oxygen into the blood for all cells.
• Cardiovascular System: Collects nutrients and oxygen and distributes them throughout the cells of the body.
• Urinary System: Filters waste substances from the blood and facilitates their excretion into the environment.

Coordination and Interaction Systems

• Nervous System: Receives external information, develops appropriate responses, and coordinates and links all bodily functions.
• Sensory Organs: Specialized organs that capture vital information from the environment for the body.
• Endocrine System: Made up of organs (glands) that secrete chemical substances (hormones), which have varying regulatory effects on the body.
• Locomotor System: Responsible for the movement of the individual. It consists of the muscles and bones.