Integumentary System

• Removes excess body heat; synthesizes vitamin D₃ for calcium and phosphate absorption; protects underlying muscles
  
• Skeletal muscles pulling on skin of face produce facial expressions

Skeletal System

• Maintains normal calcium and phophate levels in body fluids; supports skeletal muscles; provides sites of attachment
  
• Provides movement and support; stresses exerted by tendons maintain bone mass; stabilizes bones and joints

Nervous System

• Controls skeletal muscle contractions; adjusts activites of respiratory and cardiovascular systems during periods of muscular activity
  
• Muscle spindles monitor body position; facial muscles express emotion; intrinsic laryngeal muscles make speech possible

Endocrine System

• Hormones adjust muscle metabolism and growth; parathyroid hormone and calcitonin regulate calcium and phosphate ion concentrations; hormones release glucose and lipids from storage sites
  
• Skeletal muscles provide protection for some endocrine organs

Cardiovascular System

• Delivers oxygen and nutrients; removes carbon dioxide, lactic acid, and heat
  
• Skeletal muscle contractions assist in moving blood through veins; protects deep blood vessels

Lymphoid System

• Defends skeletal muscles against infection and assists in tissue repairs after injury
  
• Protects superficial lymph nodes and the lymphatic vessels in the abdominopelvic cavity

Respiratory System

• Provides oxygen and eliminates carbon dioxide
  
• Muscles generate carbon dioxide; muscles control entrances to respiratory tracts, fill and empty lungs, control airflow through larynx, and produce sounds

Digestive System

• Provides nutrients; liver regulates blood glucose and fatty acid levels and removes lactic acid from circulation
  
• Protects and supports soft tissues in abdominal cavity; controls entrances to and exits from digestive tract

Urinary System

• Removes waste products of protein metabolism; assists in regulation of calcium and phosphate concentrations
  
• External sphincter controls urination by constricting urethra

Reproductive System

• Reproductive hormones accelerate skeletal muscle growth
  
• Contracts of skeletal muscles eject semen from male reproductive tract; muscle contractions during sex produce pleasurable sensation