Transcript Chapter_6_Notes_Part_3

Skin Color
• Melanin
– Basic determinant of skin color is quantity, type, and
distribution of melanin
– Types of melanin
• Eumelanin—group of dark brown (almost black) melanins
• Pheomelanin—group of reddish and orange melanins
Skin Color
• Melanin (cont.)
– Melanin formed from tyrosine by melanocytes
• Regulated by the enzyme tyrosinase
• Albinism—congenital absence of tyrosinase
– Other factors
• Genetics (4-6 pairs of genes control the amount of melanin
produced)
• Sunlight
• Adrenocorticotropic hormone (ACTH)
• Melanocyte-stimulating hormone (MSH)
• Increasing age…decreasing tyrosinase activity
• Other pigments
Skin Color
• Other pigments
– Beta carotene (group of yellowish pigments from food)
can also contribute to skin color
– Hemoglobin—color changes also occur as a result of changes in
blood flow
• Redder skin color when blood flow to skin increases
• Cyanosis—bluish color caused by darkening of hemoglobin
when it loses oxygen and gains carbon dioxide
• Bruising can cause a rainbow of different colors to appear in
the skin
– Other pigments—from cosmetics, tattoos, and bile pigments in
jaundice
Functions of the Skin
(Table 6-1)
• Protection
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Physical barrier to microorganisms
Barrier to chemical hazards
Reduces potential for mechanical trauma
Prevents dehydration
Protects (via melanin) excess UV exposure
Functions of the Skin
• Protection (cont.)
– Surface film
• Emulsified protective barrier
• Formed by mixing of residue and secretions of
sweat and sebaceous glands with sloughed
epithelial cells from skin surface
• Shedding of epithelial elements is called
desquamation
Functions of the Skin
– Surface film (cont.)
• Functions
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Antibacterial, antifungal activity
Lubrication
Hydration of skin surface
Buffer of caustic irritants
Blockade of toxic agents
Functions of the Skin
• Surface film (cont.)
– Chemical composition
• From epithelial elements
– Amino acids
– Sterols
– Complex
phospholipids
• From sebum
– Fatty acids
– Triglycerides
– Waxes
• From sweat
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Water
Ammonia
Urea
Lactic acid
Uric acid
Functions of the Skin
• Sensation
– Skin acts as a sophisticated sense organ
– Somatic sensory receptors detect stimuli that permit
us to detect pressure, touch, temperature, pain, and
other general sensations
– When activated, the receptors make it possible for the
body to respond to changes occurring in both the
external and internal environments.
Functions of the Skin
• Movement Without Injury
– Skin is supple and elastic
• Permitting change in body contours without injury
– It grows as we grow
– Exhibits stretch and recoil characteristics
Functions of the Skin
• Excretion
– Regulation of volume and chemical content of sweat
influences the body’s total fluid volume and the
amounts of certain waste products
– Water
– Waste Products
• Urea
• Ammonia
• Uric acid
– Overall, the skin plays a minor role in excretion of
body wastes
Functions of the Skin
• Vitamin D Production (Endocrine Function)
– Skin is exposed to UV light
– 7-dehydrocholesterol is converted to cholecalciferol
• Vitamin D precursor
– Blood transports precursor to liver and kidneys
– Vitamin D is produced
– Process and end result fulfill the necessary steps
required for vitamin D to be classified as a hormone
Functions of the Skin
• Immunity
– Phagocytic cells destroy bacteria
– Langerhans cells trigger helpful immune reaction
working with “helper T cells”
Functions of the Skin
• Homeostasis of body temperatures
– Body temperature changes very little in the course of
a day
• Set point is ~37° C
– Healthy survival depends on biochemical reactions
taking place at certain rates…requires normal
enzyme functioning
– To maintain homeostasis of body temperature, heat
production must equal heat loss
– Heat production
• By metabolism of foods in skeletal muscles and liver
• Chief determinant of heat production is the amount of
muscular work being performed
Functions of the Skin
– Heat production
• By metabolism of foods in skeletal muscles and liver
• Chief determinant of heat production is the amount of
muscular work being performed
• During exercise and shivering, metabolism and heat
production increase greatly
• During sleep, very little muscular work results in decreasing
metabolism and heat production
Functions of the Skin
– Heat loss
• Approximately 80% of heat loss occurs through the skin
• Remaining 20% occurs through the mucosa of the
respiratory, digestive, and urinary tracts
• Vasoconstriction
– Dermal vessels constrict
– Warm blood circulates deeper in the body
• Vasodilation
– Dermal vessels widen
– Warm blood is moved from deeper tissues to the skin
– Heat can then be lost to external environment
» Evaportation
» Radiation
» Conduction
» Convection
Functions of the Skin
– Heat loss
• Evaporation
– To evaporate any fluid, heat energy must be expended
– This method of heat loss is especially important at high environmental
temperatures, when it is the only method by which heat can be lost
from the skin
• Radiation
– Transfer of heat from one object to another without actual contact
– Important method of heat loss in cool environmental temperatures
• Conduction
– Transfer of heat to any substance actually in contact with the body
– Accounts for relatively small amounts of heat loss
• Convection
– Transfer of heat away from a surface by movement of air
– Usually accounts for a small amount of heat loss
Functions of the Skin
– Homeostatic regulation of heat loss (Figure 6-7)
• Heat loss by the skin is controlled by a negative feedback
loop
• Receptors in the hypothalamus monitor the body’s internal
temperature
• If the body temperature is increased, the hypothalamus
sends a nervous signal to the sweat glands and blood
vessels of the skin
• The hypothalamus continues to act until the body’s
temperature returns to normal