1.2 Structural Organization of the Human Body

Levels of Organization

• Chemical Level

  • Basic building blocks: subatomic particles, atoms, molecules
  • Examples: hydrogen atoms, water molecules

• Cellular Level

  • Smallest independently functioning unit
  • Examples: bacteria (single-cell organisms), human cells with organelles

• Tissue Level

  • Group of similar cells working together
  • Example: smooth muscle tissue

• Organ Level

  • Composed of two or more tissue types
  • Example: bladder and urethra

• Organ System Level

  • Group of organs working together
  • Example: urinary system

• Organismal Level

  • The whole human body functioning as an independent organism

Organ Systems of the Human Body

• Integumentary System

  • Encloses body structures, sensory receptors
  • Includes: skin, hair, nails

• Skeletal System

  • Supports movement
  • Includes: bones, cartilage

• Muscular System

  • Enables movement, maintains body temperature
  • Includes: skeletal muscles, tendons

• Nervous System

  • Processes sensory information, activates responses
  • Includes: brain, spinal cord, peripheral nerves

• Endocrine System

  • Secretes hormones, regulates processes
  • Includes: glands like pituitary, thyroid

• Cardiovascular System

  • Delivers oxygen and nutrients
  • Includes: heart, blood vessels

• Lymphatic System

  • Returns fluid to blood, defends against pathogens
  • Includes: lymph nodes, spleen

• Respiratory System

  • Removes carbon dioxide, delivers oxygen
  • Includes: lungs, trachea

• Digestive System

  • Processes food, removes waste
  • Includes: stomach, intestines

• Urinary System

  • Controls water balance, removes waste
  • Includes: kidneys, bladder

• Reproductive System

  • Produces sex hormones and gametes
  • Male: testes, Female: ovaries, uterus

Key Points

• Human body is organized from simple to complex
• Organ systems work interdependently to maintain life
• Biological differences relate to sex, not gender identity
• All systems contribute to the organism's overall function

Figures

• Figure 1.3: Pyramid illustrating levels of biological organization
• Figure 1.4 & 1.5: Illustrations of human body organ systems

Additional Resources

• Full Textbook available online
• License: Creative Commons Attribution License
• Attribution: OpenStax, Rice University

For more detailed exploration, refer to the full textbook on OpenStax's website.