The Integumentary system is
an organ that consist of the skin, its derivatives (sweat and oil glands), nails
and hair. The basic function of the skin is protection. The skin consists of epidermis
and dermis.
I.
EPIDERMIS
A. Cells of the
Epidermis
Cells: consists of
keratinocytes, melanocytes, Merkel cells and Langerhans
cells.
·
Keratinocytes: tightly
packed and connected to desmosomes; originate from stratum basale; produce
keratin
·
Melanocytes: spider-like
cells that produce melanin (forms a pigment shield that protects the nucleus
from the UV rays).
·
Langerhans cells:
star-shaped cells from bone marrow. Function to activate the immune system as
macrophages.
·
Merkel cells: function as
sensory receptors
B. Layers of the
Epidermis
·
Stratum
basale:
consist of predominantly single row of keratinocytes; some melanocytes (10-25%)
and Merkel cells;
·
Stratum
spinosum: several layers thick;
Contains flattened irregularly-shaped keratinocytes, pre-keratin intermediate
filaments.
·
Stratum
granulasum:
consist of flattened keratinocytes which accumulate keratohyaline granules
(granules form keratin) and lamellated granules (produce water-resistant
chemical).
·
Stratum
lucidum:
present only in thick skin and made up
of a few rows of clear,
flat, dead keratinocytes.
·
Stratum
corneum:
outermost layer, conts many layers of cells (cornified or horny cells). Dead
skins slough off.
II.
DERMIS
Richly supplied with nerves
(sensory receptors), blood vessels, lymphatic vessels, sweat and sebaceous
glands derived from the epidermis.
Contains two layers: papillary and reticular
·
Papillary
layer:
Consists of areolar connective tissue made up of loose collagen and
elastic fibers, projections called papillae which contain
touch and pain receptors (Messsner’s corpusles). The papillae also form epidermal
ridges found on the surfaces of palms, fingers and feet. On the palm and fingers
they form the fingerprints (genetic markers of
individualilty).
·
Reticular
layer:
account for about 80% of thickness of dermis; consist of dense irregular
connective tissue. The ECM of this layer consist of bundles of
collagenous fibers which run in parallel and opposite directions. The
fibers give strength and resilience (toughness) and recoil, while collagen
absorbs water and keep the skin hydrated. Stretch marks found on the buttocks,
thighs, abdomen and breast are due to these fibers.
·
Disturbances of the
skin
Stretch and tear;
blisters
Skin
Coloration
Skin color is due to a
combination of three pigments: melanin, carotene and
hemoglobin.
·
Melanin is a brown-black
pigmentation formed in cells called melanocytes. Cells are found in the stratum
basale and spinosum. The amount of melanin produced by an individuals is based
on inheritance. Freckles are small patches of Melanin on the skin due to uneven
distribution.
·
Hemoglobin is the molecules found in
RBC that gives blood its red coloration. It is made of non-protein (heme which
contains iron) and the protein (globin).
·
Carotene is the yellowish pigment
found in the corneum and the dermis.
·
Skin color of human races
occur as a result of the relative abundance of melanin and carotene. Dark-skin
coloration is due to melanin. Caucacians produce more carotene than melanin.
·
Melanin protects the skin
and cells of the skin by shielding the UV light of the sun against the
nucleus.
III. ACCESSORY
STRUCTURES
Accessory structures include
hair, nail, and glands.
·
Hair: formed of keratinized
cells and consist of two parts: a shaft and root. The shaft is above the skin and root
embedded in the dermis, in a hair follicle connected to blood supplies and
arrector muscle.
·
Nail: they are formed of
keratinized epidermal cells and occur on the finger and toes. Consist of a
visible area (body) and the root (embedded in the dermis).
·
Glands: There are there exocrine (conts ducts)
glands: sebaceous,
sudoriferous and ceruminous glands. These glands secrete their contents to the
exterior unlike endocrine which secrete their contents directly into
blood.
a.
Sebaceous
glands:
produce oil (sebaum) which keeps the skin oily. The glands are branched and
attached to the hair follicle. Blockage of the gland causes
acne.
b.
Sudoriferous(sweat)
gland:
produce sweat or perspiration composed of water, salt, urea and uric acid. They
are coiled and tubular shaped and of two types: Eccrine (found on forehead, back of palm
and soles), and Apocrine (larger that eccrine, found in pubic regions and
secrete into hair follicles).
Mammary glands: are specialized form of sudoriferous gland secrete
milk.
c.
Ceruminous
glands:
found only in the external auditory canal where they secrete cerumen (earwax).
Cerumen is an insect repellant and also keep the eardrum (tympanic membrane)
from drying out. Excess amount may block.
Skin
Cancers
·
Basal cell
carcinoma:
originate from the stratum basel (about 70% of skin cancers). Treated by
excision.
·
Squamous
carcinoma:
originate from cells immediately above the basale layer. Treatment consist of X-ray and
excision.
·
Malignant
melanoma:
most life-threatening arises from melanocytes in the basale. Most often begins
as a mole-like growth and enlarges. May change and metastatize. Often removed by
excision, x-ray.
Temperature
Regulation
·
The regulation of body
temperature is carried out by the hypothalamus in conjunction with the
skeletal muscle. The system works similar to the thermostat in
buildings.
·
Normal body temperature is
37 C(98.6F). This temperature is produced as a result of metabolic activities
which produce heat in the body.
·
During the cold when heat
loss is excessive, the blood vessel constrict (therefore less blood to the
surface) the muscle contract frequently (shivering) to produce
heat.
·
In the summer, the vessels
dilate (more blood to the skin surface, more heat loss), sweat pores open and
produce perspiration that cool the surface as heat is
lost.
Skin Aging
·
After 50 years, wrinkles and
sagging of the skin become more noticeable.
·
Effects of aging are a
result of deterioration of collagen, elastic fibers; decrease in sebaum
production, decrease in melanin production, decrease in content and
decomposition of cutaneous fat.
Disorders of the
skin
·
There are several types of
skin disorders associated with the skin. Some of them are infectious
(contagious) or non-infectious.
·
These disorders include
acne, athletes foot, boils, fever blisters, impetigo, warts, alopecia, burns,
calluses (corns), cancers, dandruff, eczema, moles psoriasis and others.
Contagious skin
disorders
A.
Contagious disorders are
caused by bacteria or virus or fungus
·
Acne: characterized by plugged
hair follicles that form pimples. Caused by bacteria, prevalent in teenage
years.
·
Boils: painful infection of
hair follicles and sebaceous glands by Staphylococcus
bacteria.
·
Fever
blisters:
cold sores…fluid filled blisters on the lips or oral membrane caused by Herpes
simplex virus and transmitted by oral and respiratory exposure. Genital Herpes
are painful blisters on the genitals and transmitted by sexual
contact.
·
Impetigo: highly contagious skin infection caused
by bacteria, occurs in children and characterized by fluid-filled pustules
forming yellow crust over infected area.
·
Warts: small skin tumors caused
by viral infection that stimulate excessive growth of epithelial
cells
B.
Non-contagious skin disorders
·
Alopecia: loss of hair (pattern
baldness) is most prevalent in males and inherited. May also be caused by factors such as
poor nutrition, sensitivity to drugs, and eczema.
·
Eczema: inflammation producing
redness, itching, scalding and cracking of skin. Seborrheic eczema is produced
by hyperactivity of the sebaceous glands.
·
Psoriasis: a chronic dermatitis characterized by
reddish raised patches of skin covered with whitish scales. Result from
excessive cell production caused by emotional stress or poor health. Occurs often on the buttocks, elbows,
scalp and knees. Others conditions
are: dandruff, cancers, calluses, hives,
burnes.