lec3 anatomy

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Anatomy Dr.Israa H. Mohsen
Lecture 3
INTEGUMENTARY SYSTEM
skin is crucial for human survival. Perhaps its most obvious task is to define the body’s structure:
1. joining forces with the muscular and skeletal systems to build the body’s framework. But that’s just one small part of the skin’s role.
2. This thin, self-regenerating tissue also separates the internal from the external environment,
3. protects the body from invasion by harmful substances,
4. and helps maintain homeostasis.
5. In addition, sensory nerve receptors in the skin gather information about the outside world
6. while its flexibility and ability to stretch permit freedom of movement. Last but not least,
7. changes in the skin can signal diseases or disorders in other body systems.
For these reasons and more, the skin and its appendages (hair, nails, and skin glands)—collectively known as the integumentary system.
Structure of the Skin
The skin, also called the cutaneous membrane, consists of :
1.The epidermis—the outermost layer— consists of stratified squamous epithelial tissue. It contains no blood vessels; instead, it obtains oxygen and nutrients by diffusion from the dermal layer beneath it.
2.The dermis—is composed of connective tissue. It contains collagen fibers (which strengthen the tissue), elastin fibers (which provide elasticity) and reticular fibers (which bind the collagen and elastin fibers together). The dermis contains an abundance of blood vessels , sweat glands, sebaceous glands, and nerve endings. Hair follicles are also embedded in the dermis. Finger-like projections, called papillae, extend upward from the dermis. These projections interlock with downward waves on the bottom of the epidermis, effectively binding the two structures together.
3.the hypodermis. Made of loose connective(areolar) tissue and adipose tissue, the hypodermis binds the skin to the underlying tissue. Hypodermis that’s composed mostly of adipose tissue is called subcutaneous fat. This layer of fat helps insulate the body from outside temperature changes; it also acts as an energy reservoir
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Skin Color
Scattered throughout the basal layer of the epidermis are cells called melanocytes.
These special cells produce a substance called melanin, which accumulates in the
cells of the epidermis. There are two types of melanin: a reddish pheomelanin and a
brown-black eumelanin.
A person’s skin color is determined by the amount, and type, of melanin—not the
number of melanocytes. (Infact, persons of all races have about the same number of
melanocytes. The cells in dark-skinned people produce more melanin, and the
melanin is broken down more slowly.)
hypodermis
epidermis
dermis
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Melanocytes, which have long projections reaching between cells, release melanin.
• The keratinocytes then bring the melanin into their cells.
• The melanin forms a cap over the top of the cell nucleus to protect it from exposure
to the harmful ultraviolet rays of the sun.
• Prolonged exposure to sunlight stimulates the cells to secrete more melanin. This
protects the cell’s nucleus and also darkens the skin.
Note :When ultraviolet radiation reaches the nucleus of the cell, it
damages the cell’s DNA and can lead to skin cancer.
A yellow pigment called carotene is also stored in skin tissue. Eating large quantities
of foods containing carotene (such as carrots) can give the skin a yellow tint.
Appendages of the Skin
The appendages of the skin are hair, nails, and glands.
Hair
Hair occurs everywhere on the body except for a few locations: the palms and soles,
lips, nipples, and some areas of the genitals. In some locations, hair has a protective
role: the eyelashes and eyebrows keep perspiration out of the eyes; hair in the nostrils
filters out dust; and the hair on the head provides insulation against heat and cold.
Nails
Nails consist of densely packed, heavily keratinized epithelial cells.
Attached to each hair follicle is a
small bundle of smooth muscle
called the arrector pili muscle.
Cold temperatures, or emotions
such as fear, cause the muscle to
contract. When it does, the hair
becomes more upright,
sometimes called “standing on
end
The shaft is the part of the hair that
extends above the skin’s surface.
Each hair lies within a sheath of
epidermis called a hair follicle.
Hair follicles have a rich nerve
and blood supply.
Buried in the dermis is the hair
bulb or root; this is the lowest
part of the hair and is where
growth occurs.
At the base of the hair is a
cluster ofconnective tissue
and blood vessels called the
papilla that nourishes each
hair.
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Glands
The glands associated with the skin include sweat glands, sebaceous glands, and
ceruminous glands.
Sweat Glands
These are the most numerous of the skin glands.
Eccrine glands
• Contain a duct that leads from a secretory portion (consisting of a twisted coil in the dermis),
through the dermis and epidermis, and onto the skin’s surface.These glands are widespread
throughout the body, but are especially abundant on the palms, soles, forehead, and upper
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Torso .Produce a transparent, watery fluid called sweat, which contains potassium, ammonia,
lactic acid, uric acid, and other wastes. Sweat plays a chief role in helping the body maintain a
constant core temperature and also helps the body eliminate wastes.
Apocrine glands
• Contain a duct that leads to a hair follicle (as opposed to opening onto the skin’s
surface).Are located mainly in the axillary and anogenital (groin) regions. Are scent glands
that respond to stress and sexual stimulation. Begin to function at puberty
Sebaceous glands, which open into a hair follicle, secrete an oily substance called sebum.
Sebum helps keep the skin and hair from drying out and becoming brittle.
Ceruminous Glands
Ceruminous glands, which exist in the external ear canal, secrete a waxy substance
called cerumen, or ear wax. Cerumen helps keep the ear canal from drying out.
However, excess cerumen can accumulate in the ear canal and harden, diminishing
hearing.
Life lesson: Burns
Burns can be caused by fire, hot water, steam, electricity, chemicals, and sunlight.
Considering the skin’s crucial role in protecting against infection, controlling fluid
loss, and thermoregulation, it’s easy to understand the seriousness of severe or
extensive burns. In fact, following a serious burn, a patient may lose as much as 75%
of his circulating fluid volume in the first few hours, placing that person at risk for
circulatory collapse and cardiac arrest. Another complication of burns is the
development of eschar—the dead tissue resulting from a burn. Besides secreting
toxins and promoting bacterial growth, eschar can restrict circulation. Burns are
classified according to their depth: in other words, the number of tissue layers affected
by the burn.
Classification of burns
Apocrine glands
Eccrine glands
Sebaceous glands
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• Involves only the
epidermis
• Causes redness, slight
swelling, and pain
• Often results from
sunlight (sunburn)
• Involves the epidermis as
well as part of the dermis
• Results in blisters, severe
pain, and swelling
• May result in scarring
• May appear red, white, or
tan
• Extends through the
epidermis and dermis and
into the subcutaneous layer
• May not be painful initially
because of the destruction
of nerve endings
• May appear white or
black and leathery
• Often requires skin grafts