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Lesson 3 - Functions of Skin

Student Performance Objectives
1. Explain three ways in which the skin can help to regulate body temperature.
2. Explain two protective functions that come about through the metabolism of melanocytes.
3. Describe 5 ways that the skin can slow down or prevent the invasion of deeper tissues by
4. Explain the relationship of skin and vitamin D, and explain why D is not really a vitamin.
5. Explain how the skin prevents excessive loss of body fluids from its surface.

Lesson Outline - Taken as a totality, the skin functions in the following ways:
A.  It is the major organ of sexual attraction (combined with the contouring of the body
      surface by the adipose tissue of the hypodermis).
B.  Provides protection to the body from dehydration through its water-resistant surface coating
     of keratin-filled, dead keratinocytes.
C.  It helps to cool the body because it is not water-proof! Sweat glands secrete watery sweat
      (see lesson 4, below) continuously through ducts that penetrate through the epidermal layers
     and the majority of this sweat passes to the surface and evaporates without being noticed by
     you as accumulated moisture. This is referred to as insensible perspiration because you do
     not sense its presence. In addition, some water can penetrate upward right through the
     epidermal layers and evaporate from the skin surface without having passed through any
     sweat gland ducts. This is also part of insensible perspiration.
D.  Additional regulation body temperature occurs through the constriction or dilation of blood
     vessels thereby controlling heat radiation from the body surface, and through the presence
     adipose tissue acting as insulation to body heat loss.
E.  It prevents damage from sun exposure and prevents damage from excessive vitamin D
     formation, through melanocyte formation and distribution of the ultraviolet-absorbing
     pigment, melanin.
F.  It protects the body from microbial invasion through its surface that is dry (bacteria require
     water to thrive) and through the presence of Langerhan's cells that are part of the immune

G.  It further protects us from bacteria through sweat glandular secretion of iron-binding
     molecules (bacteria require iron for their survival), lysozyme (an enzyme that damages
     bacterial cell walls), and antibodies that coat bacterial surfaces.
H.  It converts a liver-produced cholesterol derivative (7-dehydrocholesterol) into vitamin D3
     with the assistance of absorbed ultraviolet radiation penetrating from sun exposure. This D3,
     an inactive form of vitamin D, leaves the skin and travels first to the liver and then to the
     kidneys where it is converted to calcitriol - active vitamin D (that helps the body to absorb
     and utilize calcium).