THE INTEGUMENTARY SYSTEM
What is an organ?
A group of two or more tissues that performs a specific function is called an
organ.
What is a system?
A group of two or more organs that work together towards a common goal is a
system.
A.
SKIN
What are the components of the integumentary system?
The skin and organs that are embryonic epidermal derivatives comprise
the integumentary system. These include hair, nails, glands, and enamel
of teeth.
1.
ANATOMY
Describe each of the following:
Epidermis – The epidermis is the outer, thinner, waterproof portion
of the skin. It is composed of keratinized stratified epithelium divided into four (thin skin) or five (thick) distinct layers
or strata.
Dermis -- The epidermis is attached to the dermis, the inner,
thicker portion of skin. It is composed of elastic and
collagenous connective tissues and bears a vascular supply.
The dermis is very thick on the palms and soles, and tends
to be thicker on the dorsal body surfaces than on the ventral
surfaces.
Hypodermis - Deep to the dermis is the hypodermis
(subcutaneous layer or superficial fascia). The hypodermis is
not a true part of the skin. It is formed from areolar and
adipose tissues and serves to attach the dermis to underlying tissues, give protection from mechanical blows, and
store energy.
29
2.
PHYSIOLOGY
List and give a brief description of the seven functions of the skin.
Regulation of body temperature -- In response to strenuous
exercise or high environmental temperature, evaporation of
sweat from the skin surface lowers body temperature to
normal. Sweating ceases when temperatures are low.
Increased blood flow to the skin also participates in
regulation of temperature.
Protection -- Skin covers the body and provides a physical barrier
that protects underlying tissues from physical abrasion,
microbial invasion, dehydration, and ultraviolet (UV)
irradiation.
Sensation -- Skin contains abundant nerve endings and receptors
that detect stimuli related to temperature, touch, pressure,
and pain.
Excretion -- In addition to thermoregulation, sweat also is the vehicle for excretion of a small amount of salts and several
organic compounds.
Immunity -- Certain cells of the epidermis are important components of the immune system, working to fend off foreign
invaders.
Blood reservoir -- Blood vessels in the dermis carry 8-10% of total
blood volume in a resting adult. This blood can be moved
quickly to skeletal muscles to facilitate exercise.
Synthesis of vitamin D -- One step in the activation of vitamin D
requires UV light. This occurs as blood passes through the
skin.
3.
EPIDERMIS
List the four cell types of the epidermis, give the percent of the total
population of epidermal cells, and give a brief description of each.
Keratinocytes -- (90%) produce the keratin that waterproofs and
protects the skin and underlying tissues. Anchoring
junctions between cells called desmosomes “weld” cells
together to form a formidable membrane.
30
Melanocytes -- (8%) produce the brown-black pigment melanin that
absorbs ultraviolet light. The cells produce melanin then
transfer it to the keratinocytes in the stratum spinosum for
distribution throughout the layers of the epidermis. Once
inside a keratinocyte, melanin clusters over the apical side of
the nucleus, giving it protection from the UV irradiation that
penetrates it.
Langerhans cells -- (1%) involved in immune function, working with
lymphocytes called helper T cells.
Merkel cells -- (1%) make contact with the flattened portion of a
sensory nerve ending called a tactile (Merkel) disc and are
thought to function in the sense of touch.
Describe each of the following strata of the epidermis:
Stratum basale -- single layer of cells, mostly mitotic keratinocytes,
resting on basement membrane; gives rise to new cells of
the epidermis; also contains the melanocytes and Merkel
cells.
Stratum spinosum -- 8-10 rows (sheets) of spiny-shaped cells
derived from the keratinocytes below; receive melanin from
melanocytes; no longer mitotic.
Stratum granulosum -- 3-5 rows of cells that begin producing and
accumulating the molecule keratohyalin, a precursor of
keratin.
Stratum lucidum -- 3-5 rows of clear, flattened, dead cells packed
with eleidin, the intermediate molecule in the formation of
keratin; only present in thick skin.
Stratum corneum -- 25-30 rows of flattened dead cells, completely
filled with keratin; gives the skin a water-proof, anti-microbial,
and abrasion-resistant barrier.
4.
DERMIS
Describe the papillary dermis.
The outermost portion (top one-fifth) of the dermis is the papillary
dermis. It consists of areolar connective tissue rich in fine elastin
fibers. Its surface area is greatly increased by small, hill-like
projections called dermal papillae. Each papilla contains loops of
blood capillaries.
31
Describe the reticular dermis.
The deeper layer is the reticular dermis. It consists of dense
irregular connective tissue rich in interlacing bundles of collagen
and coarse elastin fibers.
What is the function of the dermis?
The combination of elastin and collagen, particularly in the reticular
dermis, gives the skin strength, elasticity (the ability to return to
shape after stretching), and extensibility (the ability to stretch). The
dermis has a large blood supply, especially in areas of skin used for
temperature regulation. This is the blood supply for the epidermis
as well.
B.
GLANDS
1.
SEBACEOUS (OIL) GLANDS
2.
SUDORIFEROUS (SWEAT) GLANDS
a.
ECCRINE
b.
APOCRINE
Describe each of the following exocrine glands of the skin.
Sebaceous glands -- secrete sebum, a mixture of lipids, proteins, and
salts onto the surface of the epidermis. It forms a protective film, in
combination with sweat, called the acid mantle, that lubricates the
skin and hair, prevents evaporation of water through the epidermis,
and is anti-microbial.
Eccrine sweat glands -- are most common, being found over most of the
skin. Secretion is copious and about 90% water. It is used as the
body’s principal means of losing body heat via evaporation. The
glands are poorly functional prior to the age of two; therefore,
young children are poor thermoregulators in the heat.
Apocrine sweat glands -- found mainly in the skin of the axillary region,
pubic region, areolar regions of the breasts, and the beard area of
men. Beginning at about puberty, they produce only a very small
amount of a viscous milky fluid. The role of this secretion is
unknown, but it is released in response to emotional stress and
sexual excitement. The glands apparently correspond to the scent
glands of other mammals. The secretion does not have a
disagreeable odor.
32
C.
THERMOREGULATION: HOMEOSTASIS OF BODY TEMPEATURE
Describe the role of thermoregulation.
Homeotherms (warm-blooded animal) maintain a constant body
temperature regardless of the environment.
In the skin of homeotherms, particularly in the scalp, palms, and soles of
humans, there is a large blood supply in the form of arterio-venous
plexuses that can deliver a huge amount of blood to the dermis of that
area.
The control of body temperature is dependent upon a negative feedback
system to ensure that there is little fluctuation in the internal body
temperature.
Suppose you are in a place where environmental temperature is 101
degrees Fahrenheit, so that heat is continually flowing to your body,
raising core temperature from the outside.
Thermoreceptors in the skin and probably internally as well become
stimulated by the increase in body temperature and create nerve impulses
which serve as input to the control center.
The control center, located in the hypothalamus of the brain, receives the
input, integrates and interprets the information and then initiates two
changes in the body.
In response to output from the hypothalamus, there is increased eccrine
sweat secretion and increased blood flow to the skin.
Increased blood flow brings heat from the body core to the surface where
it is lost by radiation and by evaporation of water; the net result is a
decrease in body temperature.
Return to homeostasis occurs when core body temperature is back within
normal range, and the sweating-increased skin blood mechanism is turned
off.
33