body systems

Chapter 25: The Human Body

1. Levels of Organization in the Human Body

• Cells: The basic unit of life, each specialized for specific functions.​
  
  

• Tissues: Groups of similar cells performing a common function.​
  
  

• Organs: Structures composed of different tissues working together to perform specific tasks.​
  
  

• Organ Systems: Groups of organs that collaborate to carry out complex functions essential for survival.​
  
  

2. Four Types of Tissue

• Epithelial Tissue: Covers body surfaces and lines internal cavities, providing protection and facilitating absorption and secretion.​
  
  

• Connective Tissue: Supports and binds other tissues; includes bone, blood, cartilage, and adipose tissue.​
  
  

• Muscle Tissue: Responsible for movement; includes:​
  
  

  • Skeletal Muscle: Voluntary muscles attached to bones.​
    
    

  • Cardiac Muscle: Involuntary muscle found in the heart.​
    
    

  • Smooth Muscle: Involuntary muscle found in walls of internal organs.​
    
    

• Nervous Tissue: Composed of neurons and supporting cells; transmits electrical impulses throughout the body.​
  
  

3. Major Organ Systems and Their Functions

• Nervous System: Coordinates body activities by transmitting electrical signals; includes the brain, spinal cord, and nerves.​
  
  

• Endocrine System: Regulates bodily functions through hormones; includes glands such as the pituitary, thyroid, and adrenal glands.​
  
  

• Skeletal System: Provides structural support, protects internal organs, and facilitates movement; composed of bones and joints.​
  
  

• Muscular System: Enables movement, maintains posture, and produces heat; consists of skeletal, cardiac, and smooth muscles.​
  
  

• Digestive System: Breaks down food into nutrients for absorption; includes the mouth, esophagus, stomach, intestines, liver, and pancreas.​
  
  

• Circulatory System: Transports oxygen, nutrients, hormones, and wastes; includes the heart, blood, and blood vessels.​
  
  

• Respiratory System: Facilitates gas exchange (oxygen and carbon dioxide); includes the lungs, trachea, and nasal passages.​
  
  

• Urinary System: Eliminates waste products and maintains fluid balance; includes the kidneys, ureters, bladder, and urethra.​
  
  

• Integumentary System: Protects the body; includes skin, hair, nails, and associated glands.​
  
  

• Immune and Lymphatic Systems: Defend against pathogens and maintain fluid balance; include lymph nodes, lymph vessels, and white blood cells.​
  
  

• Reproductive System: Enables reproduction; includes male and female reproductive organs.​
  
  

4. Homeostasis

• Definition: The maintenance of a stable internal environment despite external changes.​
  
  

• Negative Feedback: A mechanism that counteracts deviations from a set point to maintain balance (e.g., regulation of body temperature).​
  
  

• Positive Feedback: A mechanism that amplifies responses; less common but occurs in processes like childbirth and blood clotting.​
  
  

5. Integumentary System and Skin Function

• Skin Layers:
  
  

  • Epidermis: The outermost layer; provides a barrier and creates skin tone.​
    
    

  • Dermis: Beneath the epidermis; contains tough connective tissue, hair follicles, and sweat glands.​
    
    

• Functions:
  
  

  • Protects against environmental hazards.​
    
    

  • Regulates body temperature through sweating and blood flow.​
    
    

  • Prevents water loss.​
    
    

  • Synthesizes vitamin D when exposed to sunlight.