THE INTEGUMENTARY SYSTEM
• The organs of the integumentary system include the
◦ skin, hair, nails, glands, blood vessels, muscles and nerves.
‣ Note that all 4 of the basic tissue types are well-represented in this organ system: Epithelium in
the hair, nails, and the epidermis of the skin; the dermis contains C.T.; muscle is found attached to
the hair follicles, and in the substance of arteries and veins; nerves provide an abundance of
sensation.
• Dermatology is the medical specialty for the diagnosis and treatment of disorders of the integumentary
system
• The integument can also be thought of as a cutaneous membrane that covers the outer surface of the
body.
◦ It is the largest organ by surface area and weight.
◦ Its area is about 2 square meters (22 square feet) and weighs 4.5–5kg (10–11 lb), about 16% of
body weight.
◦ It is 0.5–4 mm thick, thinnest on the eyelids, thickest on the heels.
◦ We lose almost a kg of skin epithelium a year that becomes a major part of household “dust”.
• Besides protection, the skin functions in:
◦ Regulation of body temperature
◦ Sensory perceptions
◦ Synthesis of vitamin D.
◦ Emotional expression
◦ It also serves as an important reservoir of blood.
The 5 major functions of the skin:
1. Body temperature regulation.
a. The skin contributes to the homeostatic regulation of body temperature by liberating sweat at its
surface and by adjusting the ow of blood in the dermis.
2. Protection.
a. Keratin in the skin protects underlying tissues from microbes, abrasion, heat, and chemicals.
Lipids released by lamellar granules inhibit evaporation of water from the skin surface.
3. Cutaneous sensations.
a. These include tactile sensations (touch, pressure, vibration, and tickling), thermal sensations
(warmth and coolness) and pain.
4. Excretion and absorption.
5. Synthesis of vitamin D.
STRUCTURE OF THE SKIN
The skin has 2 major layers:
1. The outer, thinner layer is called the Epidermis and
consists of epithelial tissue.
2. The inner, thicker layer is called the dermis and
consists of Connective tissue
3. The subcutaneous (subQ) layer (also called the
hypodermis) is located underneath the dermis.
4. It is a loose areolar/adipose C.T. that attaches the skin
to the underlying tissues and organs.
THE EPIDERMIS
• The epidermis is composed of keratinized strati ed squamous epithelium which contains four major
types of cells and is Avascular:
1. Keratinocytes
a. make up 90% of the cells. They produce keratin - a
tough brous protein that provides protection.
2. Melanocytes
a. produce the pigment Melanin that protects against
damage by ultraviolet radiation.
3. Langerhans cells
a. are macrophages that originated in the red bone
marrow. They are involved in the immune responses.
4. Merkel cells
a. function in the sensation of touch along with the other
adjacent tactile discs (receptors).
• Present in the keratinocytes are granules which release a lipidrich secretion that;
◦ acts as a water-repellent sealant
◦ retarding loss of body uids
◦ Blocks entry of foreign materials
• Newly formed cells in the stratum basale are slowly pushed to the surface.
◦ As the cells move from one epidermal layer to the next, they accumulate more and more keratin, a
process called keratinization
◦ Eventually the keratinized cells slough o and are replaced by underlying cells
Epidermis is 4 or 5 Layers
• Deepest layer (Stratum Basale/Germinativum)
◦ Basal cells-continuous cell division produces all the other layers above it
◦ Form ridges that extend into deeper dermis
◦ Melanocytes
◦ keratinocytes
• Intermediate Layers
◦ Tightly tting, dying keratinocytes
◦ Langerhans cells
◦ Projections of melanocytes
• Super cial layers (Stratum Corneum)
◦ Dominated by dead, attened keratinocytes,
containing mainly keratin
The epidermis has 4 strata or layers:
1. Stratum basale – deepest layer
2. Stratum spinosum – provides strength &
exibility
3. Stratum granulosum – keratinocytes undergo
apoptosis here (genetic programmed cell death)
4. Stratum corneum – most super cial layer
The palms and soles (thick skin), have 5 layers:
• Stratum lucidum (only found in thick skin and is located between the granulosum and corneum)
The Epidermis and Skin Color
Skin Pigments
Melanin
◦ is produced by melanocytes in the stratum basal
◦ secreted in granules and taken up by the more super cial keratinocytes where the pigment
protects the nuclei from UV damage
◦ contribute to skin colour
Carotene
• Yellow-orange pigment
• Found in the stratum corneum, dermis, and subcutaneous layer
Hemoglobin
• Produce “red” tones in the skin
• Located in erythrocytes owing through dermal capillaries
The Dermis
• The deeper part of the skin and is composed mainly of connective tissue containing collagen & elastic
bers.
• The super cial part of the dermis makes up about one- fth of the thickness of the total layer It consists
◦ areolar connective tissue containing ne elastic bers.
• Its surface area is increased by dermal papillae, touch receptors (Meissner corpuscles) and free nerve
endings.
• The deeper part of the dermis, which is attached to the subcutaneous layer, consists of dense irregular
connective tissue containing bundles of collagen and some coarse elastic bers.
‣ Adipose cells, hair follicles, nerves, oil glands, and sweat glands are found between the bers
The dermis is composed of connective tissue containing collagen and elastic bers and It
contains two regions:
◦ The papillary region lies just below the epidermis and consists of areolar connective tissue
containing thin collagen and elastic bers, dermal papillae (including capillary loops), corpuscles of
touch and free nerve endings..
◦ The reticular region consists of dense irregular connective tissue containing collagen and elastic
bers, adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands.
‣ Tears or excessive stretching in this region cause stretch marks (also called striae).
Lines of cleavage are “tension lines”
• They are in the skin that indicate the predominant direction of underlying collagen bers.
◦ Plastic surgeons make their incisions parallel to the normal cleavage lines in order to minimize scarring.
• Epidermal ridges re ect contours of the underlying dermal papillae and form the basis for ngerprints (and
footprints)
• Function to increase rmness of grip by increasing friction
The Subcutaneous Layer (hypodermis)
• attaches the skin to underlying tissues and organs.
◦ It contains blood vessels and nerves in transit to the more super cial layers.
◦ It also contains lamellated (pacinian) corpuscles that detect deep external pressure applied to the
skin.
Sensory Receptors
• The skin contains di erent types of sensory receptors to
di erentiate between the di erent tactile (“touch”) sensations.
◦ Light touch, pressure, vibration, itch and tickle
• These sensory receptors are found in di erent layers:
◦ Super cially
‣ Merkel discs, free nerve endings (detect many stimuli),
Miessner corpuscles, and hair root plexuses
◦ Deep
‣ Pacinian corpuscles
Accessory structures of the skin
Hair (“pili”)
◦ It is present on most surfaces except the palms, anterior
surfaces of ngers, and the soles of the feet.
◦ It is composed of dead, keratinized epidermal cells.
◦ genes determines thickness and distribution.
• Hair helps with touch sensations and protects the body against the
harmful e ects of the sun and against heat loss.
Skin Glands
• Recall that glands are epithelial cells that secrete a substance.
• Sebaceous (oil) glands are connected to hair follicles.
◦ They secrete an oily substance sebum into the follicle which does 2
important things:
‣ Prevents dehydration of hair and skin
‣ Inhibits growth of certain bacteria
2 types of skin sweat glands (sudoriferous glands).
• Both are simple, coiled tubular glands
1. Eccrine sweat glands
A. are located all over the body and secrete a watery solution that helps to cool the body, eliminates
small amounts of waste and responds to stress
2. Apocrine sweat glands
A. are located mainly in the skin of the axilla, groin, areolae, and bearded facial regions of adult males.
They secrete a slightly viscous sweat and contribute to body odor
Nails
• Nails are composed of hard, keratinized epidermal cells located over the
dorsal surfaces of the ends of ngers and toes.
• Nail structures include:
◦ Free edge
◦ Transparent nail body (plate) with a whitish lunula at its base
◦ Nail root embedded in a fold of skin
Aging
• The integumentary system changes with age:
◦ Wrinkles develop.
◦ Dehydration and cracking occurs.
◦ Sweat production decreases.
◦ A decrease in the numbers of functional melanocytes results in gray hair and atypical skin
pigmentation.
◦ Subcutaneous fat is lost, and there is a general decrease in skin thickness.
◦ Nails may also become more brittle.
Most of the age-related changes begin at about age 40 and occur in the proteins in the dermis.
1. Collagen bres in the dermis begin to decrease in number, sti en, break apart, and disorganize into a
shapeless, matted tangle.
2. Elastic bres lose some of their elasticity, thicken into clumps, and fray, an e ect that is greatly
accelerated in the skin of smokers.
3. Fibroblasts, which produce both collagen and elastic bers, decrease in number, the result, the skin forms
crevices known as wrinkles
With age = increased susceptibility to pathological conditions (bed sores)