Integumentary System
Part 2 Appendages of the skin
Goals:
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Compare the structure, location and secretions of sweat and oil glands
Compare and contrast the eccrine and Apocrine glands
List the parts of the hair follicle and explain their function
Describe the purpose of the arrector pili muscle
Describe the structure of nails
Vocabulary
Skin appendages
Sweat glands (sudoriferous glands)
Eccrine (merocrine) sweat glands
Apocrine sweat glands
Ceruminous glands
Mammary glands
Sebaceous (oil) glands
Sebum
Hair (pili)
Cuticle
Hair follicles
Hair bulb
Root hair plexus
Connective tissue root sheath
Epithelial root sheet
Hair matrix
Arrector pili
Vellus hair
Terminal hair
Hirsurtism
Alopecia
Nail matrix
Nail folds
Cuticle (eponychium)
A) Sweat (Sudoriferous) Glands
These are found over the entire body. There are approximately 3 million per person
There are 2 types:
o Eccrine
o Apocrine
Both are associated with myoepithelial cells which contract when stimulated by the
nervous system leading to sweat secretion onto the surface.
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1) Eccrine Sweat Glands (Merocrine)
o Found on the palms, soles and forehead
o Secretory portion lies in the dermis and the duct extends up through the epidermis
o Consists of a simple, coiled tubular gland
o Their secretions are known as sweat and consists of:
 Hypotonic, 99% water
 An antimicrobial protein called dermcidin
 Urea and salts
 Composition can vary with diet
In the diagram above, note that the gland in a simple coiled tubular arrangement with the
duct going through the epidermis.
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2) Apocrine Sweat Glands
o There are approximately 2000 and they are confined to the anogential and axillary
regions
o These are merocrine glands releasing products by exocytosis
o Lie deep in the dermis and the ducts empty out onto the hair follicle
o Composition is similar to Eccrine glands but also contain fatty compounds and
proteins making it milky white to yellow in color
o Decomposition of these secretions by bacteria leads to the creation of body order
o They begin to function at puberty and are influenced by hormonal cycles
Note how the duct opens into the hair duct in contrast to the sweat glands. They also
have a simple coiled tubular arrangement.
3) Ceruminous Glands
o Modified Apocrine glands that are found in the external ear canal
o Secretions consist of sebum from the sebaceous glands and a sticky substance
secreted from the ceruminous glands, together the product is ear wax.
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4) Mammary Glands
o Glands which have been modified to secrete milk
B) Sebaceous (Oil) Glands
o Oil glands are simple branched alveolar glands
o Found over entire body except the soles and palms of feet and hands
o More concentrated on face, neck and upper chest
o Central cells of the alveoli accumulate oil and burst releasing cell fragments and
lipids in a holocrine type of secretion.
o Sebum is the secretory material formed from the lipids and cell fragments
o The sebum is secreted onto the hair follicle
o Sebum serves to lubricate the hair and skin and has a antibacterial effect
o Its formation is influenced by sex hormones
o Arrector pili muscles contract to secrete the sebum
Homeostatic imbalance
If the sebaceous glands become blocked by accumulated sebum and white head (zit)
appears. As this material dries it becomes a blackhead. Acne is an inflammation of the
sebaceous gland.
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C) Hair and Hair Follicles
Hair is distributed over the entire body except the soles, palms, lips and portion of the
gentitalia. In the human, it serves to protect the head against trauma and heat loss.
1) Structure of the hair
Hair consists largely of dead keratinized cells that are tougher than those found on the
skin. Hair consists of several regions:
a) Shaft – a region where keratinization is complete.
b) Root- a region where keratinization is on going.
The shape of the shaft determines the type of hair.
o If the shaft is flat and ribbon like in cross section, the hair is kinky
o If the shaft is oval, the hair is wavy
o If the shaft is round, the hair is straight and course
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Hair is made of 3 concentric levels:
a) Medulla- central core and is filled with large cells and air spaces
b) Cortex- surrounds the medulla and is made of flatten cells
c) Cuticle- outermost layer, one cell layer thick and helps keep hair from matting as it
wears out it forms the so called split ends
d) Hair color is produced by the different types of melanin, gray or white hair is brought
about by decreased melanin production in the hair follicle. This is brought about by
“delayed action genes”
2) Hair Follicles
o Extend from the dermis down through the dermis and into the hypodermis
o The base of the follicle is the hair bulb. It is surrounded by nerve endings (root
plexus) and makes hair sensitive to touch
o The hair papilla protrudes into the hair bulb and contains capillaries
o The hair follicle is made of a connective tissue root sheath and an inner epidermal
root sheath.
o The hair matrix is an area of active mitosis located just above the hair bulb and is
responsible for producing hair
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o The arrector pili is smooth muscle that raises hair and is responsible for “goose
bumps”
In the diagram above the dermal papilla and bulb are seen. This is the region where new
hair is produced. The diagram below shows the arrector pili muscle and is relationship to
the sebaceous gland the hair follicle.
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3) Types and Growth of Hair
Hair shape and size can vary but there are two types, vellus hair and course hair.
o Vellus hair is body hair found on children and adult females
o Terminal hair is found on the eye brows and scalp, face (beard) and pubic regions
o Hirsutism is excessive hairiness and is seen with certain hormonal tumors
(bearded lady)
4) Hair Growth
Hair growth varies from one body region to another and varies with age and sex. On
average hair grows about 2.5 mm per week. Hair follicles go through a growth cycle
which can range from weeks to years.
Hair thinning, alopecia, is most evident in males as male pattern baldness. This is
influenced by genetics where the hair follicles sensitivity to DHT (dihydrotestosterone)
occurs.
D) Finger Nails
Nails correspond to hooves and claws of other animals. They are a modification of the
epidermis and are made of hard keratin. Each nail is made of a free edge, a body and a
root. The nail matrix is responsible for the growth of the nail. Outwardly this appears as
the white crescent seen at the base of a nail and is called the lunule.
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E) Functions of the skin
Protection
The skin makes up three different types of barriers:
1. Chemical barrier: The skin has secretions, melanin and low pH which help retard
bacterial growth. In addition natural antibiotics such as defensins and
cathelicidins aid in preventing group A strep infections.
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2. Physical/ Mechanical barriers made up by the thickness of the epidermis and the
water resistant glycolipids block the diffusion of water and water soluble
materials into the skin cells. Organic or lipid soluble material can pass through.
3. Biological barriers include the dendritic cells of the epidermis and the
macrophages in the dermis.
Body Temperature Regulation
Sweat glands release water onto the surface of the skin where evaporation cools the skin.
Capillaries can dilate or contract and control the flow of blood to the skin retaining or
loosing heat.
Cutaneous Sensation
Skin is covered with different types of receptors which are part of the nervous system.
Metabolic Functions
Skin can produce vitamin D through exposure to the sun light
Blood Reservoir
About 5% of the body’s blood is found in the dermis.
Excretion
Sweating eliminates urea and salts similar to the urine.
F) Diseases and Trauma
Skin cancer and burns can have a profound impact on a person. 1 in 5 will have some
form of skin cancer at some point in their life.
Types:
o Basal Cell Carcinoma is the most common and least malignant and is about 80%
of skin cancers. Seen most often in sun exposed areas.
o Squamous Cell Carcinoma is the second most common and arises from the
keratinocytes.
o Melanoma is a cancer of the melanocytes and is most dangerous.
Burns can be life threatening due to loss of body fluids leading to renal shut down.
Damage to the skin leads then to infection.
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