Skeletal System

• Provides structural support
  
• Synthesizes vitamin D₃, essential for calcium and phosphorus absorption (bone maintenance and growth)

Muscular System

• Contractions of skeletal muscles pull against skin of face, producing facial expressions important in communication
• Synthesizes vitamin D₃, essential for normal calcium absorption (calcium ions play an essential role in muscle contraction)

Nervous System

• Controls blood flow and sweat gland activity for thermoregulation; stimulates contraction of arrector pili muscles to elevate hairs
• Receptors in dermis and deep epidermis provide sensations of touch, pressure, vibration, temperature, and pain

Endocrine System

• Sex hormones stimulate sebaceous gland activity; male and female sex hormones influence growth, distribution of subcutaneous fat, and apocrine sweat gland activity; suprarenal hormones alter dermal blood flow and help mobilize lipids from adipocytes
• Synthesizes vitamin D₃, precursor of calcitrol

Cardiovascular System

• Provides oxygen and nutrients; delivers hormones and cells of immune system; carries away carbon dioxide, waste products and toxins; provides heat to maintain normal skin temperature
  
• Stimulation of mast cells produces localized changes in blood flow and capillary permeability.

Lymphoid System

• Assists in defending the Integument by providing additional macrophages and mobilizing lymphocytes
• Provides physical barriers that prevent entry of pathogens; dendritic cells and macrophages resis infection; mast cells trigger inflammation and initiate the immune response

Respiratory System

• Provides oxygen and eliminates carbon dioxide
• Hairs guard entrance to nasal cavity

Digestive System

• Provides nutrients for all cells and lipids for storage by adipocytes
• Synthesizes vitamin D₃, needed for absorption of calcium and phosphorus

Urinary System

• Excretes waste products; maintains normal pH and ion composition of body fluids
  
• Assists in excretion of water and solutes; keratinized epidermis limits fluid loss through skin

Reproductive System

• Sex hormones affect hair distribution, adipose tissue distribution in subcutaneous layer, and mammary gland development
• Covers external genitalia; provides sensations that stimulate sexual behaviors; mammary gland secretions provide nourishment for the newborn infant