CHAPTER 6: SKIN AND THE INTEGUMENTARY SYSTEM
OBJECTIVES:
1.
Explain why the skin is called the cutaneous membrane.
2.
Name the layers of the skin, describe the structure (tissues) of each, and name a general
function of each.
3.
Discuss the four cell types present in the epidermis.
4.
List the four/five layers of the epidermis and explain the process of keratinization.
5.
Explain the protective role of keratin, and in turn, the epidermis.
6.
Name the pigment responsible for skin and hair color, and explain how people of
different races (i.e. and skin color) differ in regards to it, and the cell that produces it.
7.
List some factors that promote the production of melanin (besides DNA).
8.
Distinguish between the papillary layer and reticular layer of the dermis, and locate the
appropriate sensory receptor in each of these layers.
9.
Compare and contrast Meissner's and Pacinian Corpuscles in terms of their structure,
function, and location.
10.
Describe the structure and function of the subcutaneous layer.
11.
Explain what is meant by the term epidermal derivative, and list four examples.
12.
Describe the general structure of a hair follicle and identify two other structures that are
usually associated with them.
13.
Distinguish between merocrine (eccrine) and apocrine sweat glands in terms of structure,
secretion content and odor, activation, and major body locations.
14.
Name two modified apocrine glands of the skin.
15.
Describe the structure, function, secretion, and location of sebaceous glands.
16.
Discuss the many functions of skin.
17.
Describe some major homeostatic imbalances of the skin.
18.
Sketch a typical layer of skin and label each layer and all structures. Then in complete
sentences, discuss the function of each layer and structure.
I.
INTRODUCTION
The integumentary system is the first body system studied. Before we begin any study of
a body system, we will first think about the organs/tissues that work together to perform
the function(s) of that system.
The integumentary system consists of a major organ, skin, and many epidermal
derivatives (accessory organs), which include hair follicles, sebaceous glands, sweat
glands, and nails.
In addition, the organs of the integumentary system are composed of many different
tissues that perform common functions. Look at Figure 6.1, page 159 and Figure 6.2,
page 160, and name as many different tissues as you can. These tissues include stratified
squamous epithelium, glandular epithelium, dense irregular CT, smooth muscle tissue,
adipose tissue, and nervous tissue. The functions that these tissues collectively perform
are many. Functions of the skin include protection, excretion, regulation of body
temperature, sensory reception, immunity, synthesis of Vitamin D, and blood reservoir.
II.
SKIN AND ITS TISSUES (Cutaneous Membrane)
A.
General Structure: See Fig 6.2, page 160.
1.
b.
Two distinct regions or layers compose the skin:
a.
Epidermis = outermost layer;
o
keratinized stratified squamous ET.
Dermis = inner layer;
o
keratinized epithelium (hair follicles),
o
glandular epithelium (sweat, sebaceous glands),
o
dense irregular CT (collagen),
o
smooth muscle tissue (arrector pili muscles),
o
nervous tissue (Meissner's & Pacinian Corpuscles), and
o
blood vessels.
2.
Subcutaneous layer = adipose tissue;
distinct layer beneath skin
also called hypodermis
II.
SKIN AND ITS TISSUES (Cutaneous Membrane)
B.
Skin Functions
1.
Protection:
o
Physical barrier
a.
from water loss;
b.
from injury;
c.
from chemicals and microorganisms.
o
Chemical barrier
a.
pH or 5-6
b.
prevents microorganism growth
o
Biological barrier
a.
Langerhan’s cells (epidermis)
b.
Macrophages and mast cells (dermis)
2.
Excretion (minimal, most through kidneys!):
o
urea;
o
uric acid.
3.
Regulation of body temperature:
Review negative-feedback mechanisms from Ch. 1 and see Figure 6.11, page 170.
4.
Cutaneous Sensation:
o
Light touch detection = Meissner's Corpuscle's;
a.
egg-shaped;
b.
located in dermal papillae;
c.
populate areas in the fingertips, palms, soles, eyelids, tip of
tongue, nipples, clitoris, tip of penis.
o
Pressure detection = Pacinian Corpuscle's;
a.
onion-shaped;
b.
located in deep
subcutaneous regions;
dermis
5.
Vitamin D Synthesis:
o
UV rays in sunlight activate its synthesis;
o
Vitamin D is required for bone homeostasis.
6.
Blood Reservoir:
o
The dermis houses about 10% of the body's blood vessels.
o
Skin only requires 1-2% of the body’s blood
7.
Immunity:
o
Langerhan’s cells (macrophages);
o
interact with T-helper cells in immune responses.
and
II.
SKIN AND ITS TISSUES (Cutaneous Membrane)
C.
Epidermis:
1.
Structure = keratinized stratified squamous epithelium;
See Fig 6.3, page 161 and Table 6.1, page 161.
a.
Four distinct layers determined by the extent of keratinization in
the epithelial cells:
1.
Stratum corneum = outermost layer.
o
***
Stratum lucidum = translucent layer cells separating
s. corneum from s. granulosum.
o
extra layer only in thick skin of soles & palms;
2.
Stratum granulosum is composed of 3-5 layers of
flattened granular cells (filled with keratin granules);
3.
Stratum spinosum is composed of many layers of spiky
cells with large nuclei;
4.
Stratum basale (germinativum)= innermost layer;
o
o
o
2.
II.
composed of dead epithelial cells filled with the
protein keratin;
directly above basement membrane;
composed of a single row mitosing cuboidal
epithelial cells and
composed of melanocytes.
a.
specialized cells that produce the pigment
melanin.
b.
See Figure 6.4, page 162, which illustrates
the pigmentation in melanocytes.
Main Function = Protection (keratin):
a.
prevents moisture loss (waterproof);
b.
prevents injury by penetration;
c.
prevents microorganisms/chemicals entry
SKIN AND ITS TISSUES (Cutaneous Membrane)
C.
Epidermis:
3.
Pigment = Melanin: See Fig 6.4, page 162.
a.
determines skin color:
b.
is produced by melanocytes in stratum
basale (germinativum);
D.
Dermis:
1.
a.
E.
III.
Structure:
See Fig 6.2, page 160.
two distinct layers:
1.
papillary layer (20%) is below epidermis:
o
composed of loose areolar CT;
o
surface forms dermal papillae (finger-like
projections into the epidermis) that form
fingerprints in thick skin
o
Meissner's Corpuscles (sensory receptor for light
touch).
2.
b.
inner layer of skin;
binds epidermis to underlying tissues.
reticular layer (80%) = dense irregular CT;
o
bundles of collagen fibers,
o
elastic fibers, and
o
reticular fibers which give skin its
o
strength and resiliency.
o
Pacinian corpuscles –sensory receptors for deep
pressure
The dermis houses epidermal derivatives or accessory organs (see
below).
2.
Main Function = nourishment of epidermis.
Subcutaneous Layer (hypodermis) = beneath skin.
1.
Structure = adipose tissue & blood vessels;
2.
Function = insulation.
ACCESSORY ORGANS OF THE SKIN (Epidermal Derivatives)
A.
1.
Hair Follicles:
See Fig 6.5 and 6.6, page 165.
Structure:
a.
root or base in deep dermis;
b.
follicle throughout dermis;
c.
hair shaft in epidermis.
2.
Keratinization
a.
cells are epithelium;
b.
cells in root = active mitosis;
c.
cells in follicle = maturing & accumulating
keratin;
d.
cells in epidermis = dead epithelial cells;
full of keratin = exposed hair or hair shaft.
3.
Pigment = Melanin
4.
Arrector Pili Muscle = a bundle of smooth muscle
associated with every hair follicle. See Fig 6.5a, page 165.
a.
causes hair to stand on end ("goose bumps") when frightened or
cold.
B.
1.
Nails: See Fig 6.7, page 167.
Epithelium undergoing keratinization (active mitosis in lunula).
2.
Functions:
a.
manipulation;
b.
protection of digit ends.
C.
Sebaceous Glands: See Fig 6.8, page 167.
a.
b.
4.
1.
holocrine gland (simple cuboidal epithelium);
2.
associated with every hair follicle;
3.
Secretion (holocrine) = sebum (i.e. oil).
fat
cellular material
Sebum is secreted into hair follicle;
5.
Function: Sebum keeps skin & hair soft, pliable and
virtually waterproof!
6.
Disorders:
a.
acne (hypersecretion of sebum; ducts clog &
inflame); See Clinical Application 6.3, page 169.
b.
seborrhea (hyperproduction of sebum; oily
scales)
ACCESSORY
Derivatives)
III.
D.
ORGANS
OF
THE
SKIN
(Epidermal
Skin Glands (Sweat Glands or Sudoriferous Glands)
1.
types
(based
on
glandular
secretion):
See Fig 6.9 &
6.10, page 168.
Merocrine
(Eccrine)
Glands:
Structure:
a.
1.
2.
3.
Two
coil in deep dermis
duct in dermis
pore at surface
Characteristics:
1.
respond
to
elevated temperature / exercise
2.
no odor in
secretion
3.
function
throughout life
4.
not associated
with hair follicles
5.
Location:
forehead
neck
back
Secretion (merocrine) = water plus
1.
salts and
2.
wastes (urea and uric acid)
b.
Apocrine glands:
Structure:
ducts terminate into hair follicles
Characteristics:
1.
respond
to
2.
odor
in
stress / emotions
secretion
3.
begin
function at puberty & continue through life
4.
associated
with hair follicles
5.
to
Location:
armpits
groin
Secretion (apocrine) = sweat
above plus
1.
oil and
2.
cellular debris.
2.
Modified Apocrine Glands
1.
Ceruminous
glands = external ear; secretion = earwax;
Mammary glands = breasts; milk.
***Note that the above structures under III. ACCESSORY ORGANS OF THE SKIN
(Epidermal Derivatives) are epithelial in nature and are actually specialized parts of the
epidermis, even though their location is within the dermis.
IV.
REGULATION OF BODY TEMPERATURE – normally near 98.6 F set point
A.
Heat production and loss.
1.
Heat production is mostly a by-product of cellular metabolism.
2.
Heat loss is controlled by regulating dermal blood flow.
a.
Vasodilation – increases dermal blood flow, which also increases
heat loss
b.
Vasoconstriction – decreases derma blood flow which decreases
heat loss
3.
Heat loss is by four methods
a.
Radiation
o
most heat loss by this mode
o
infrared heat rays move from area of high heat (i.e. the
blood) to areas of low heat (i.e. the environment)
b.
Conduction
o
less heat loss
o
heat moves by physical contact
o
the reason the seat you sit in is warm when you stand up
c.
Convection
o
heat loss to surrounding air
o
increases as air movement increases, that is why turning on
a fan cools your body
d.
Evaporation
o
heat loss varies
o
if heat increases our sweating increases, so we lose more
heat by evaporating the sweat on the surface of our skin
4.
Low body temperatures require heat loss to be minimized
a.
The Hypothalamus signals for sweating to
decrease (decreasing heat loss by evaporation) and dermal
vasoconstriction (decreasing heat loss by radiation)
b.
Usually this brings the body temperature back to
normal
5.
If the body temperature remains low after the above
action
a.
Heat must be produced
b.
Shivering occurs and the tiny muscle contractions
involved produce heat
c.
See Figure 6.11 page 170
IV.
REGULATION OF BODY TEMPERATURE
B.
Problems in Temperature Regulation
1.
Hyperthermia – elevated body temperature
a.
Two common causes
o
humid air decreases evaporation
o
air temperature exceeds body temperature, thus heat is
gained not lost
o
See Clinical Application 6.4 page 171.
2.
Hypothermia – low body temperature
a.
very dangerous if core body temperature drops below 94 F
b.
limbs can withstand about 65 F because they contain no vital
organs
c.
cause is intentional during some surgical procedures, see
box on the bottom of page 171.
V.
SKIN COLOR
A.
Genetic Factors
1.
People of different races have essentially the same # of
melanocytes, but the amount of melanin produced varies (determined by
DNA);
B.
Environmental Factors affect melanin production: by
affecting gene expression
1.
2.
3.
C.
UV rays,
chemicals,
drugs (antihistamines & antibiotics);
Physiologic Factors may affect skin color (but not melanin production):
1.
4.
Carotene may accumulate in s. corneum = orange;
2.
Hemoglobin (Hb) in dermal blood vessels =
pink;
3.
Lack of Hb in dermal blood vessels = blue
(cyanosis.)
Inability to breakdown Hb (liver problems) = yellow (jaundice)
VI.
HEALING OF WOUNDS AND BURNS
Inflammation – process that involves blood flow changes and chemical signaling leading to
healing.
A.
Cuts
1.
Epidermal cuts are closed by increased cell division in the stratum basale
2.
Deep cuts involve blood vessel damage resulting in:
a.
b.
c.
d.
e.
f.
g.
B.
Inflammation
Blood clotting (See Hemostasis Chapter 14, pages 526-531)
Scab formation
Fibroblast infiltration and repair
Scab falls off
Scar may or may not remain
See Figure 6.13 page 174
Burns
1.
Superficial partial-thickness burns (1st degree)
a.
b.
c.
d.
e.
2.
Deep partial-thickness burns (2nd degree)
a.
b.
c.
d.
e.
3.
Epidermis only
Reddening due to increased blood flow
Mild pain
Common in sunburn
Heals in a few days-2 weeks
Epidermis and some dermal damage
Reddening and blistering caused by blood vessel damage
Moderate pain
Common to physical contact with hot objects
Heals in 2-6 weeks without scars unless infected
Full-thickness burns (3rd degree)
a.
b.
c.
d.
Epidermis, entire dermis, and potentially subcutaneal damage
Dry, leathery tissue with red or black color
Severe pain
Caused by prolonged heat or chemical contact
VI.
e.
Healing rarely occurs due to lack of surviving
skin cells, skin replacements (grafts) are usually needed, usually
extensive scarring
o
Autograft – transplant from undamaged area of yourself
o
Homograft – temporary transplant from cadaver
o
Skin substitutes – From Science to Technology 5.2 page 153
HEALING OF WOUNDS AND BURNS
B.
Burns
4.
Body Surface affected
a.
b.
c.
VII.
VIII.
Estimated by “rule of nines”
Important for determining treatment and prognosis
See Figure 6.14 page 175.
LIFE SPAN CHANGES
A.
Aging skin exhibits:
1.
wrinkling
2.
sagging
3.
age spots or liver spots
a.
See Fig 6.15, page 176.
B.
Efficient regulation of body temperature declines with age.
1.
The number of sweat glands changes.
2.
Capillary beds in the skin shrink.
C.
Synthesis of vitamin D declines as skin ages, which affects skeletal health.
HOMEOSTATIC IMBALANCES OF THE SKIN
Throughout the text of each chapter, your authors present selected imbalances, disorders,
and diseases of each system. Although you may only discuss some major disorder in
class, these disorders and diseases are very interesting to learn about. You are strongly
encouraged to study them.
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
Epidermolysis bullosa. See blue box on page 158.
Psoriasis. See blue box on page 160.
Contact dermatitis. See blue box on page 164.
Rashes. See Table 6.2, page 161.
Skin Cancer = carcinoma. See Clinical Application 6.1, pages 163.
Folliculitis. See blue box on page 166.
Hair loss. See Clinical Application, page 166.
Acne. See Clinical Application, page 169.
Hypothermia. See blue box on page 171.
Albinism. See Fig 4.26, page 127, Fig 6.12, page 172, and blue box on page 172.
Elevated body temperature. See Clinical Application 6.4, page 171.
L.
Jaundice. See blue box on page 172.
IX.
COMMON SKIN DISORDERS – See pages 176 and 178.
X.
Innerconnections between the Integumentary System and other organ systems: Page
177.
Chapter 6: Skin and the Integumentary System
I. Skin and Its Tissues
A. Introduction
1. The skin is composed of several kinds of tissues.
2. Skin is a protective covering that prevents many harmful substances from
entering the body.
3. Skin also retards water loss and helps regulate body temperature.
4. Skin houses sensory receptors and contains immune system cells.
5. Skin synthesizes vitamin D and excretes a small amount of waste products.
6. The two distinct layers of skin are epidermis and dermis.
7. The outer layer is called the epidermis and is composed of stratified squamous
epithelium.
8. The inner layer is called dermis and is made up of connective tissues, epithelial
tissue, muscle tissue, nervous tissue, and blood.
9. A basement membrane separates the two skin layers.
10. The subcutaneous layer is beneath the dermis.
11. The subcutaneous layer is composed of loose connective tissues and adipose.
B. Epidermis
1. The epidermis lacks blood vessels.
2. The deepest layer of the epidermis is called the stratum basale.
3. The stratum basale is nourished by blood vessels in the dermis.
4. Cells of the stratum basale can divide and grow because they are nourished so
well.
5. When new cells enlarge they push old epidermal cells away from the dermis
toward the surface of skin.
6. The farther the cells travel, the poorer their nutrient supply becomes and
eventually they die.
7. Older skin cells are called keratinocytes and are held together with
desmosomes.
8. Keratinization is the accumulation of keratin in epidermal cells which hardens
the epidermis.
9. As a result of keratinization many layers of tough, tightly packed cells
accumulate in the epidermis.
10. The outermost layer of the epidermis is called the stratum corneum.
11. The epidermis is thickest on palms of the hand and the soles of the feet.
12. Most areas of epidermis have 4 layers.
13. The four layers starting with the deepest are stratum basale, stratum
spinosum, stratum germinativum, and stratum corneum.
14. An additional layer called stratum lucidum is in thickened skin.
15. In healthy skin, production of epidermal cells
is balanced with loss of dead cells from the stratum corneum.
16. The rate of cell division increases where the skin is frequently rubbed or
pressed.
17. Calluses are a thickening of the stratum corneum.
18. Corns are keratinized conical masses on the toes.
19. Specialized cells in the epidermis called melanocytes.
produce melanin.
20. Melanin provides skin color and absorbs UV radiation.
21. Melanocytes lie in the stratum basale and
in the underlying connective tissues of the dermis.
22. The extensions of melanocytes transfer melanin granules to epidermal cells
by a process called cytocrine secretion.
C. Dermis
1. The boundary between the dermis and epidermis is uneven because
the
epidermis projects inward and the dermis has papillae between the ridges of the
epidermis.
2. Fingerprints form from the undulations of the dermis and epidermis.
3. The dermis binds the epidermis to the subcutaneous layer.
4. The dermis is largely composed of irregular dense connective tissue that
includes tough collagenous fibers and elastic fibers in a gel-like ground substance.
5. The dermis also contains smooth muscles that can wrinkle the skin of the
scrotum.
6. Some smooth muscle of the skin is associated with hair follicles.
7. In the face, skeletal muscles are anchored to the dermis.
8. Nerve cell processes are scattered throughout the dermis.
9. Pacinian corpuscles are stimulated by heavy pressure.
10. Meissner’s corpuscles are stimulated by light touch.
D. Subcutaneous Layer
1. The subcutaneous layer consists of loose connective tissue and adipose tissue.
2. No sharp boundary separates the dermis and subcutaneous layer because the
fibers of the dermis are continuous with the fibers of the subcutaneous layer.
3. The adipose tissue of the subcutaneous layer insulates the body.
4. The subcutaneous layer contains major blood vessels that supply the skin.
II. Accessory Organs of the Skin
A. Hair Follicles
1. Hair is present on all skin surfaces except the palms, soles, lips, nipples, and parts of
external reproductive organs.
2. A hair follicle is a group of epidermal cell at the base of a tubelike depression
in the dermis of skin.
3. A follicle extends from the surface of skin into the dermis.
4. The hair root is the portion of hair embedded in skin.
5. The hair papilla is a projection of connective tissue at the end of the hair
follicle. It contains blood vessels.
6. The hair shaft is the portion of hair that extends from the surface of skin.
7. A hair is composed of dead keratinocytes.
8. Baldness results when hairs fall out and are not replaced.
9. Genes determine hair color by directing the type and amount of pigment that
epidermal melanocytes produce.
10. Dark hair has more melanin than blond hair.
11. White hair of albinos lack melanin.
12. Red hair contains an iron pigment called trichosiderin.
13. Hairs appear gray from a mix of pigmentation and unpigmentation.
14. An arrector pili muscle is a band of smooth muscle and attaches to hair
follicles.
15. Goose bumps are produced when arrector pili muscles contract.
B. Nails
1. Nails are protective coverings on the ends of fingers and toes.
2. Each nail consists of a nail plate that overlies a surface of skin called the nail
bed.
3. The lunula of a nail is the whitish, thickened, half-moon shaped region at the
base of a nail plate.
C. Skin Glands
1. Sebaceous glands contain groups of specialized epithelial cells and are
associated with hair follicles.
2. Sebaceous glands are holocrine glands and their cells produce sebum.
3. Sebum is a mixture of fatty material and cellular debris.
4. Sebum is secreted into hair follicles and helps keep hair and skin soft and
pliable.
5. Sebaceous glands are not found on palms and soles.
6. Sebaceous glands open directly onto skin in some regions, such as, the lips,
corners of the mouth, and parts of the external reproductive organs.
7. Sweat glands are also called sudoriferous glands.
8. Each sweat gland consists of a tiny tube in the dermis or superficial
subcutaneous layer.
9. The most numerous sweat glands are eccrine.
10. Eccrine glands respond to heat.
11. Eccrine glands are common on the forehead, neck, and back.
12. A pore is the opening of a sweat gland duct.
13. Sweat contains water, wastes, and salts.
14. Apocrine glands become active at puberty.
15. They can wet certain areas of skin when a person is nervous or stressed.
16. Apocrine glands are most numerous in the axilla, groin, and around the
nipples.
17. Ceruminous glands of the external ear canal and secrete cerumen.
18. Mammary glands secrete milk.
III. Regulation of Body Temperature
A. Introduction
1. Regulation of body temperature is important because even slight shifts can
disrupt the rates of metabolic reactions.
2. A normal temperature of deeper body parts remains close to 37oC.
B. Heat Production and Loss
1. Heat is a product of cellular metabolism.
2. When body temperature rises above the set point, nerve impulses stimulate
structures in the skin and other organs to release heat.
3. During physical activity, active muscles release heat, which the blood carries
away.
4. When warmed blood reaches the hypothalamus, muscles in the walls of dermal blood
vessels relax.
5. As dermal blood vessels dilate, heat escapes to the outside world.
6. Skin reddens because dermal blood vessels are dilated.
7. The primary means of body heat loss is radiation.
8. Radiation is the spread of heat from warm areas to cooler areas.
9. Conduction is the movement of heat into molecules of cooler objects.
10. Convection is the continuous circulation of air over a warm surface.
11. Evaporation is the change of a liquid to a gas.
12. When sweat evaporates, it carries heat away from the skin surface.
13. When body temperature falls below the set point, muscles of dermal blood
vessels constrict which decreases the flow of blood through the skin.
14. When body temperature falls, sweat glands become inactive.
15. When body temperature continues to fall, small groups of muscles to contract
slightly to produce shivering.
C. Problems in Temperature Regulation
1. Hyperthermia is a rise in body temperature.
2. If air temperature is high, heat loss by radiation is less effective.
3. Hypothermia is a low body temperature.
4. Hypothermia can result from prolonged exposure to cold or an illness.
5. Hypothermia can lead to mental confusion, lethargy, and loss of
consciousness.
6. Children and the elderly are at a higher risk for developing hypothermia.
IV. Skin Color
A. Genetic Factors
1. Regardless of racial origin, all people have about the same number of
melanocytes in their skin.
2. Differences in skin color result from the differences in the amount of melanin
melanocytes produce.
3. The more melanin produced, the darker the skin.
4. The distribution and size of pigment granules within melanocytes also
influence skin color.
B. Environmental Factors
1. Environmental factors such as sunlight and X rays affect skin color.
2. These factors stimulate melanocytes to produce more pigment.
3. Tans fade as pigmented epidermal cells become keratinized and wear away.
C. Physiological Factors
1. When blood is well oxygenated, the blood pigment hemoglobin is bright red
and the skin of light-complexioned people appears pink.
2. When blood oxygen concentration is low, hemoglobin is dark red and the skin
appears bluish.
3. If dermal blood vessels are dilated, more blood enters skin and skin appears
pinkish or reddish.
4. If dermal blood vessels are constricted, less blood enters skin and skin appears
pale.
5. Carotene is a yellow-orange pigment found in certain vegetables.
6. Carotene can give skin a yellowish color.
V. Healing of Wounds and Burns
A. Introduction
1. Inflammation is a normal response to injury or stress.
2. During inflammation, blood vessels dilate and become more permeable.
3. Inflamed skin may become reddened, swollen, warm, and painful to the touch.
4. The dilated blood vessels provide the tissues with more nutrients,
which aids healing.
5. The specific events of healing depend on the nature and extent of the injury.
B. Cuts
1. If a break in the skin is shallow, epithelial cells are stimulated to divide more
rapidly than normal.
2. If a cut extends into the dermis or subcutaneous layer, blood vessels break and
the escaping blood forms a clot.
3. A clot consists mainly of fibrin, plasma, blood cells, and platelets.
4. A scab is a blood clot and dried fluids.
5. Fibroblasts migrate into the injured area and begin forming new fibers that
bind the edges of the wound together.
6. Connective tissue matrix secretes growth factors that stimulate certain cells to
divide and regenerate damaged tissues.
7. As healing continues, blood vessels extend into the area beneath the scab.
8. Phagocytic cells remove dead cells and other debris.
9. A scar results when the wound is extensive.
10. A granulation consists of a branch of a blood vessel, and a cluster of
collagen-secreting fibroblasts.
C. Burns
1. A first degree burn is one that only affects the epidermis.
2. A second degree burn is that affects a part of the dermis and epidermis.
3. Blisters appear in second degree burns.
4. The healing of second degree burns depends on accessory organs of the skin
that survive the burn.
5. A third degree burn is one that affects the entire thickness of skin.
6. In a third degree burn, the skin becomes dry and leathery.
7. If a third degree burn is extensive, treatment may involve removing a thin
layer of skin from an unburned region of the body and transplanting it to the
injured area.
8. An autograft is a graft from the same person.
9. A homograft is a graft from a cadaver.
10. Skin substitutes include amniotic membranes, membranes of silicon,
polyurethane or nylon.
11. The treatment of a burn patient requires estimating the extent fo the body’s
surface that is affected.
12. To estimate, physicians use the rule of nines.
13. This rule divides the skin’s surface into 11 areas of 9% each.
VI. Life-Span Changes
A. Aging skin affects appearance, temperature regulation and vitamin D
production.
B. Age spots or liver spots are patches of pigments.
C. The dermis becomes reduced as synthesis of the connective tissue proteins
collagen and elastin slows.
D. Wrinkling and sagging skin result from the shrinking of the dermis and loss of
fat from the subcutaneous layer.
E. Skin becomes drier because sebaceous glands produce less oil.
F. Slowed melanin production causes gray or white hair.
G. Nail growth is impaired because the blood supply to the nails is diminished.
H. Sensitivity to pain and pressure diminishes with age.
I. An older person is less able to tolerate heat because the sweat glands and hair
follicle shrink, and the number of dermal blood vessels decrease.
J. Vitamin D is necessary for calcium absorption.