Upload
adin
View
136
Download
2
Embed Size (px)
DESCRIPTION
Chapter 6: Skin and Its Appendages. INTRODUCTION. Skin (integument) is the body’s largest organ Approximately 1.6 to 1.9 m 2 in average-sized adult Integumentary system describes the skin and its appendages: hair, nails, and skin glands. STRUCTURE OF THE SKIN. - PowerPoint PPT Presentation
Citation preview
04/21/23 1
Chapter 6: Skin and Its Appendages
04/21/23 2
INTRODUCTION
Skin (integument) is the body’s largest organ Approximately 1.6 to 1.9 m2 in average-sized
adult Integumentary system describes the skin
and its appendages: hair, nails, and skin glands
04/21/23 3
STRUCTURE OF THE SKIN
Skin classified as a cutaneous membrane Two primary layers: epidermis and dermis;
joined by dermoepidermal junction (Figures 6-1 and 6-2)
Hypodermis lies beneath dermis Thin and thick skin (Figure 6-3)
Thin skin covers most of the body’s surface (1 to 3 mm thick)
Thick skin covers soles and palms (4 to 5 mm thick)
04/21/23 4
04/21/23 5
04/21/23 6
04/21/23 7
STRUCTURE OF THE SKIN: EPIDERMIS Epidermis
Cell types (Figure 6-4) Keratinocytes: constitute more than 90% of cells present;
principal structural element of the outer skin; sometimes called corneocytes after they are fully keratinized
Melanocytes: pigment-producing cells (5% of the total); contribute to skin color and filter ultraviolet (UV) light
Epidermal dendritic cells: branched antigen-presenting cells; play a role in immune response; also called Langerhans cells
Tactile epithelial cells (Merkel cells): attach to sensory nerve endings to form “light touch” receptors
04/21/23 8
04/21/23 9
STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
Cell layers Stratum basale (base layer): single layer of columnar
cells; only these cells undergo mitosis and then migrate through the other layers until they are shed
Stratum spinosum (spiny layer): cells arranged in eight to 10 layers with desmosomes that pull cells into spiny shapes; cells rich in RNA
Stratum germinativum (growth layer): another name for stratum basale or stratum spinosum and stratum basale together
04/21/23 10
STRUCTURE OF THE SKIN: EPIDERMIS (cont.)
Stratum granulosum (granular layer): cells arranged in two to four layers and filled with keratohyalin granules; contains high levels of lysosomal enzymes
Stratum lucidum (clear layer): cells filled with keratin precursor called eleidin; absent in thin skin
Stratum corneum (horny layer): most superficial layer; thin squamous cells, dead cells filled with keratin (barrier area – to environment and water loss)
04/21/23 11
Epidermal growth and repair Turnover or regeneration time refers to time required for
epidermal cells to form in the stratum basale and migrate to the skin surface—approximately 35 days
Epidermal growth factor regulates epidermal growth and repair
Shortened turnover time due to abrasion will increase the thickness of the stratum corneum and result in callus formation
Normally 10% to 12% of all cells in stratum basale enter mitosis daily
STRUCTURE OF THE SKIN:
EPIDERMIS (cont.)
04/21/23 12
STRUCTURE OF THE SKIN: EPIDERMIS (cont.) Dermoepidermal junction
A basement membrane with unique fibrous elements and a polysaccharide gel “glue” the epidermis to the dermis below
The junction is a partial barrier to the passage of some cells and large molecules
Separation of the epidermis from the DEJ result in blisters
04/21/23 13
STRUCTURE OF THE SKIN: DERMIS Dermis
Sometimes called “true skin”—much thicker than the epidermis and lies beneath it
Gives strength to the skin Serves as a reservoir storage area for water and
electrolytes Contains various structures
Arrector pili muscles and hair follicles (Figure 6-5) Sensory receptors (Figure 6-6) Sweat and sebaceous glands Blood vessels
Rich vascular supply plays a critical role in temperature regulation
04/21/23 14
04/21/23 15
04/21/23 16
STRUCTURE OF THE SKIN: DERMIS (cont.)
Layers of dermis Papillary layer: composed of dermal papillae that
project into the epidermis; contains fine collagenous and elastic fibers and the dermoepidermal junction; forms a unique pattern that gives individual fingerprints
Reticular layer: contains dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable; when processed from animal skin, produces leather
04/21/23 17
STRUCTURE OF THE SKIN: DERMIS (cont.)
Dermal growth and repair The dermis does not continually shed and regenerate
itself as does the epidermis During wound healing, fibroblasts begin forming an
unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar
Cleavage lines: patterns formed by the collagenous fibers of the reticular layer of the dermis; also called Langer’s lines (Figure 6-7)
04/21/23 18
04/21/23 19
STRUCTURE OF THE SKIN: HYPODERMIS Hypodermis
Also called the subcutaneous layer or superficial fascia Located deep to the dermis; forms connection between
skin and other structures Not part of the skin Rich blood supply makes it a perfect site for fast a
relatively pain free absorption of injected material – insulin
04/21/23 20
SKIN COLOR
Melanin Basic determinant 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
Melanin formed from tyrosine by melanocytes (Figure 6-8) Melanocytes release melanin in packets called melanosomes Melanosomes are ingested by surrounding keratinocytes and
form a cap over the nucleus
04/21/23 21
04/21/23 22
SKIN COLOR (cont.)
Albinism: congenital absence of melanin Expression of melanin genes regulated by tyrosinase,
exposure to sunlight (UV radiation), and certain hormones, including melanocortins (adrenocorticotropic hormone, alpha melanocyte stimulating hormone) and endothelin-1 (Figures 6-9 and 6-10)
Cumulative effects of UV ray exposure may produce age spots (Figure 6-11)
04/21/23 23
04/21/23 24
04/21/23 25
SKIN COLOR: OTHER PIGMENTS 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 (Figure 6-12) Bruising can cause a rainbow of different colors to appear in
the skin (Figure 6-13) Other pigments: from cosmetics, tattoos, and bile pigments
in jaundice (Box 6-4)
04/21/23 26
04/21/23 27
04/21/23 28
FUNCTIONS OF THE SKIN
Protection (Table 6-2) Physical barrier to microorganisms Barrier to chemical hazards Reduces potential for mechanical trauma Prevents dehydration Protects from excess UV ray exposure (melanin function)
04/21/23 29
FUNCTIONS OF THE SKIN (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 Antibacterial, antifungal activity Lubrication Hydration of skin surface Buffer of caustic irritants Blockade of toxic agents
04/21/23 30
FUNCTIONS OF THE SKIN (cont.)
Chemical composition From epithelial elements: amino acids, sterols,
and complex phospholipids From sebum: fatty acids, triglycerides, and
waxes From sweat: water, ammonia, urea, and lactic
and uric acid
04/21/23 31
FUNCTIONS OF THE SKIN (cont.) Sensation
Skin acts as a sophisticated sense organ Somatic sensory receptors detect stimuli that
detection of pressure, touch, temperature, pain, and other general senses
Flexibility Skin is supple and elastic, thus permitting change
in body contours without injury
04/21/23 32
FUNCTIONS OF THE SKIN (cont.) Excretion
Water Urea/ammonia/uric acid
Hormone (vitamin D) production (Figure 6-14) Exposure of skin to UV light converts 7-dehydrocholesterol
to cholecalciferol, a precursor to vitamin D Blood transports precursor to liver and kidneys, where
vitamin D is produced Process and end result fulfill the necessary steps required
for vitamin D to be classified as a hormone
04/21/23 33
04/21/23 34
FUNCTIONS OF THE SKIN (cont.) Immunity
Phagocytic cells destroy bacteria Epidermal dendritic cells trigger helpful immune reaction
working with helper T cells Homeostasis of body temperature
To maintain homeostasis of body temperature, heat production must equal heat loss; skin plays a critical role in this process
Heat production By metabolism of foods in skeletal muscles and liver Chief determinant of heat production is the amount of
muscular work being performed
04/21/23 35
FUNCTIONS OF THE SKIN (cont.)
Homeostasis of body temperature Heat loss: approximately 80% of heat loss occurs through the
skin; remaining 20% occurs through the mucosa of the respiratory, digestive, and urinary tracts (Figure 6-15) 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 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 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
04/21/23 36
04/21/23 37
FUNCTIONS OF THE SKIN (cont.)
Homeostatic regulation of heat loss (Figure 6-16) Heat loss by the skin is controlled by a negative
feedback loop Receptors in the hypothalamus monitor the body’s
internal temperature If 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
04/21/23 38
04/21/23 39
APPENDAGES OF THE SKIN
Hair (Figure 6-17) Development of hair
Distribution is over entire body except palms of hands and soles of feet and a few other small areas
Fine and soft hair coat present before birth called lanugo Coarse pubic and axillary hair that develops at puberty called
terminal hair Papilla: cluster of capillaries under germinal matrix Root: part of hair embedded in follicle in dermis Shaft: visible part of hair Medulla: inner core of hair Cortex: outer portion
04/21/23 40
04/21/23 41
APPENDAGES OF THE SKIN: HAIR (cont.)
Appearance of hair Color: result of different amounts, distribution, types of
melanin in cortex of hair (Figure 6-18) Growth: growth and rest periods alternate; hair on head
averages 5 inches of growth per year Sebaceous glands attach to and secrete sebum (skin
oil) into follicle Male pattern baldness (androgenic alopecia) results
from combination of genetic tendency and male sex hormones (Figure 6-19)
04/21/23 42
04/21/23 43
APPENDAGES OF THE SKIN (cont.) Nails (Figure 6-20)
Consist of epidermal cells converted to hard keratin Nail body: visible part of each nail Root: part of nail in groove hidden by fold of skin, the cuticle Lunula: moon-shaped white area nearest root Nail bed: layer of epithelium under nail body; contains abundant
blood vessels Appears pink under translucent nails Nails may have pigmented streaks (Figure 6-21) Separation of a nail from the nail bed is called onycholysis
(Figure 6-22) Growth: nails grow by mitosis of cells in stratum basale beneath
the lunula; average growth about 0.5 mm/week, or slightly over 1 inch per year
04/21/23 44
04/21/23 45
04/21/23 46
04/21/23 47
APPENDAGES OF THE SKIN (cont.) Skin glands (Figure 6-23)
Two types of sweat glands Eccrine glands
Most numerous sweat glands; quite small Distributed over total body surface with exception of a few small areas Simple, coiled, tubular glands Function throughout life Secrete perspiration or sweat; eliminate wastes and help maintain a
constant core temperature Apocrine glands
Located deep in subcutaneous layer Limited distribution: axilla, areola of breast, and around anus Large (often more than 5 mm in diameter) Simple, branched, tubular glands Begin to function at puberty Secretion shows cyclic changes in female with menstrual cycle Odor is from bacteria feeding off gland production
04/21/23 48
04/21/23 49
APPENDAGES OF THE SKIN: SKIN GLANDS (cont.)
Skin glands (cont.) Sebaceous glands
Secrete sebum: oily substance that keeps hair and skin soft and pliant; prevents excessive water loss from skin
Lipid components have antifungal activity From hair follicles Found in dermis except in palms and soles Secretion increases in adolescence; may lead to formation of
pimples and blackheads Ceruminous glands
Modified apocrine sweat glands Empty contents into external ear canal alone or with sebaceous
glands Mixed secretions of sebaceous and ceruminous glands called
cerumen (wax) Function of cerumen to protect area from dehydration; excess
secretion can cause blockage of ear canal and loss of hearing
04/21/23 50
CYCLE OF LIFE: SKIN
Children Skin is smooth, unwrinkled, and characterized by elasticity and
flexibility Few sweat glands Rapid healing
Adults Development and activation of sebaceous and sweat glands Increased sweat production
Body odor Increased sebum production
Acne Old age
Decreased sebaceous and sweat gland activity Wrinkling (Figure 6-24) Decrease in body’s ability to cool itself
04/21/23 51
04/21/23 52
THE BIG PICTURE: SKIN AND THE WHOLE BODY Skin is a major component of the body’s
structural framework Skin defines the internal environment of the
body Primary functions are support and protection
04/21/23 53
Severity of Burns First-degree burns
Only epidermis is damaged Skin is red and swollen
Second-degree burns AKA partial thickness burns Epidermis and upper dermis are damaged Skin is red with blisters
Third-degree burns Destroys entire skin layer Burn is gray-white or black
04/21/23 54