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# Functions of the Integument ## Learning Objectives - List and explain the varied functions of the integument. - Explain how the skin helps retain warmth or cool the body. The integumentary system has several functions: * Protection from the external environment * Preventing water loss and g...

# Functions of the Integument ## Learning Objectives - List and explain the varied functions of the integument. - Explain how the skin helps retain warmth or cool the body. The integumentary system has several functions: * Protection from the external environment * Preventing water loss and gain * Vitamin D synthesis * Secretion * Absorption * Temperature regulation * Assisting the immune system * Sensory perception ## Protection from the External Environment - The skin acts as a physical barrier that protects the body from harmful chemicals, toxins, microbes, and extreme temperatures. - The skin also protects deeper tissues from solar radiation, especially from ultraviolet (UV) rays. - An increase in UV ray exposure leads to increased melanin production, giving the skin a tanned look. ## Prevention of Water Loss and Water Gain - The skin is water resistant but not entirely waterproof. - Water loss occurs via sweat and transpiration, where fluids slowly penetrate the dermis and evaporate into the surrounding air. - Without the skin, much larger amounts of water would escape from body tissues. - The skin also helps prevent water gain. ## Vitamin D Synthesis - Keratinocytes convert a steroid molecule (7-dehydrocholesterol) to Vitamin D3, also called cholecalciferol in response to UV light. - Vitamin D3 is then released into the blood and transported to the liver, kidney, and to the small intestine. - Vitamin D3 is converted to calcitriol, the active form of vitamin D, and is considered a hormone. - Calcitriol increases absorption of calcium and phosphate from the small intestine into the blood and regulates the levels of calcium and phosphate in the blood. ## Secretion - Secretion is the production and release of physiological active substances by a cell or gland. - Sweat is excreted from sweat glands as a means of releasing excess heat. - Sweat contains the waste products of amino acid breakdown (water, salts, and urea). - Sebum, which is an oily mixture, also plays a role in electrolyte homeostasis. ## What do you think? - During the Industrial Revolution, many children in cities spent little time outdoors, which lead to an increase in rickets. - Rickets is a bone disorder caused by inadequate vitamin D. **Why do you think these children developed rickets?**