Throughout the body, the skin's characteristics vary (i.e., thickness, color, texture). For instance, the head contains more hair follicles than anywhere else, while the soles of the feet contain none. In addition, the soles of the feet and the palms of the hands are much thicker.

The skin is made up of the following layers, with each layer performing specific functions:

HOW often have I been asked the question, 'Is our skin different'? The answer is yes, our skin -- that of men and women -- is different.

* The skin of a man tends to be more deeply pigmented than the skin of a woman, therefore women are known as the fairer sex.

* The skin of a man is thicker than the skin of a woman and has more collagen, therefore women tend to age faster than men.

*Women have more subcutaneous fat -- that is fat below the skin -- than men. Therefore women suffer from cellulite. When last did you hear a man complain about cellulite?

* Men tend to show signs of ageing less than women because of the presence of facial hair.

* The skin of the face is more alkaline in females than the skin of the males. The skin is also thinner in women.

* Men secrete more sebum (oil) and they secrete it throughout life. Women stop secreting sebum after menopause, therefore the skin looks coarser and drier as the woman ages. On the other hand, men suffer more from seborrhoeic eczema as they age.

* Men sweat more than women and the sweat stays on the body longer. Men also have more body hair and therefore more surface area for bacteria to colonise .

* We also find that the skin is drier in women than in men. The female skin is also more functionally responsive than the skin of men Therefore female skin has a greater tendency to redness and to irritation to skin care products and so women are said to have tender skin.

* The skin of women is slightly cooler than the skin of men especially at the fingertips.

It is important for us to realise these important differences between the skin of a man and the skin of woman. These differences are important in developing skin care products, for example odour control is more difficult in males than in females, because of the presence of body hair and the increased production of sweat and of sebum.

Facial stinging is also more prevalent in women and therefore we must test facial products and cosmetics more rigorously for sensitive skin in women.

Less collagen in female skin combined with thinner skin means a larger anti-ageing market for women.

Lastly, the increased subcutaneous fat in women means that the market for the development of cellulite treatment is almost completely confined to this group.

There are profound differences between the sexes and these differences start with the skin.

Integumentary Male

Epidermis	The epidermis is the thin outer layer of the skin which consists of the following three parts: Stratum corneum (horny layer) This layer consists of fully mature keratinocytes which contain fibrous proteins (keratins). The outermost layer is continuously shed. The stratum corneum prevents the entry of most foreign substances as well as the loss of fluid from the body. Keratinocytes (squamous cells) This layer, just beneath the stratum corneum, contains living keratinocytes (squamous cells), which mature and form the stratum corneum. Basal layer The basal layer is the deepest layer of the epidermis, containing basal cells. Basal cells continually divide, forming new keratinocytes, replacing the old ones that are shed from the skin's surface. The epidermis also contains melanocytes, which are cells that produce melanin (skin pigment).
Dermis	The dermis is the middle layer of the skin. The dermis contains the following: Blood vessels Lymph vessels Hair follicles Sweat glands Collagen bundles Fibroblasts Nerves The dermis is held together by a protein called collagen, made by fibroblasts. This layer gives skin flexibility and strength. It also contains pain and touch receptors.
Subcutis (also known as the subcutaneous layer)	The subcutis is the deepest layer of skin. The subcutis, consisting of a network of collagen and fat cells, helps conserve the body's heat and protects the body from injury by acting as a "shock absorber."

Your integumentary system is a multifaceted system protecting you from the environment and creating a balance with your surroundings. The skin is the main component of the system interfacing with the environment. Hair and nails are also part of the system, protecting you from environment attacks.

Parts Include: Skin, Hair, Nails, Sweat Glands, Oil Glands

Skin
Made of several layers designed to protect the body from the environment. The skin is a major detoxifying organ, an important factor in vitamin D creation.

Hair
A combination of protein and minerals; the texture and quality of hair are impacted by stress, diet and hormonal function. The color of hair is also impacted by diet and stress.

Nails
Nails are made of connective tissue, proteins and minerals. The integrity of one’s nails is dependent on proper digestion, diet, adrenal health and blood flow.

Sweat Glands
Glands in the body designed to release and absorb water, controlling body temperature.

Oil Glands
Glands in the body used to secrete oil when needed for protection from the environment and lubrication in cases of friction.

Man's Skin Summary:

The skin on a man versus that on a woman is significantly different. The ability to grow a beard is just one obvious distinction among many others that are not so evident. From a structural point of view, some of the differences include skin thickness, collagen density, loss of collagen as we age, texture and hydration. These differences in the skin may in fact create differences in the treatment room. Let’s look at each of these aspects in more detail.

Skin Thickness
We know that the thickness of the skin varies with the location, age and sex of the individual. Additionally, androgens (i.e. testosterone), which cause an increase in skin thickness, accounts for why a man’s skin is about 25 percent thicker than that of a woman’s. A man’s skin also thins gradually with age, whereas the thickness of a woman’s skin remains constant until about the age of fifty. After menopause, her skin will thin significantly, which will continue as she ages.

Collagen Density
Regardless of age, men have a higher collagen density than women; this is the ratio of collagen to the thickness of the skin. Researchers believe that the higher collagen density accounts for why women appear to age faster than men of the same age. When considering intrinsic (genetically-programmed) aging of the skin, it has been said that women are about 15 years older than men of the same age. Of course, the role of daylight exposure in skin aging, combined with the fact that men do not use sunscreen as often as women, may account for why we do not readily notice. Extrinsic aging from UV radiation can add years to a man’s skin and negate the benefit of slower intrinsic aging.

Loss of Collagen
The physical signs of aging in adults, such as wrinkles and laxity to the tissue, are closely related to the collagen content of the skin. Both men and women lose about one percent of their collagen per year after their 30th birthday. For women, however, this escalates significantly in the first five years after menopause then slows down to a loss of two percent per year.

Texture
From a superficial perspective, the texture of a man’s skin is very different than a woman’s. The texture (on a man) is rougher, and the Stratum Corneum is thicker. There is also a difference in the composition of sebum and its production. After puberty, sebum production is greater in males than in females, which is attributed to androgen secretions and accounts for why men have longer lasting acne. The cells in a man’s sebaceous glands have more positive receptors for androgens, which explains why they produce more sebum. Interestingly, redness, proliferation of the sebaceous glands and swelling of the skin on the nose, (a condition known as rhinophyma that is found in extreme cases of rosacea) is only seen in males. It is unknown if this condition is controlled by androgens in a similar capacity as sebum production.

Hydration
Puberty also stimulates the appearance of facial hair in men and gives rise to sweat secretions. Males have more Lactic Acid in their sweat, which accounts for a lower pH (.05 lower) when compared to female sweat. Men also sweat more than twice as much as women and are more prone to sweating, which is stimulated by an increase in body temperature. However, male skin appears to be better hydrated than women’s, which is fortunate, as men are less likely to apply a hydrating moisturizer to their body or face. Perhaps the excess sweating and production of Lactic Acid, a known natural humectant for the skin, is responsible for the level of tissue hydration.

Treating a Man’s Skin
The health of a man’s skin is, of course, just as important as that of a woman. But while treatment for a man sometimes differs from a woman, remember that the same amount of care must be taken regardless of the sex of the client. Even if the man appears to have tough, resilient skin, he may still have internal issues or surround himself in environments that sensitize him.

Integumentary Female

Parts Include: Skin, Hair, Nails, Sweat Glands, Oil Glands

Skin
Made of several layers designed to protect the body from the environment. The skin is a major detoxifying organ, an important factor in vitamin D creation.

Hair
A combination of protein and minerals; the texture and quality of hair are impacted by stress, diet and hormonal function. The color of hair is also impacted by diet and stress.

Nails
Nails are made of connective tissue, proteins and minerals. The integrity of one’s nails is dependent on proper digestion, diet, adrenal health and blood flow.

Sweat Glands
Glands in the body designed to release and absorb water, controlling body temperature.

Oil Glands
Glands in the body used to secrete oil when needed for protection from the environment and lubrication in cases of friction.

Integumentary System

The skin and its associated structures (hair, nails, sweat glands, and oil glands) make up a complex body system called the integumentary system.

Functions of the Integumentary System

The integumentary system has many functions:

Protects Against

invasion of microorganisms

UV damage

mechanical damage

It also contains macrophages, lymph nodes and other structures which identify pathogens and provide first line of defense against the

Prevents Water Loss

The epidermis is water resistant and prevents unnecessary water loss.

Regulates Body Temperature

By diverting blood into or away from the skin the body can release or conserve heat.

The skin can also release sweat which releases heat when the water in the sweat evaporates off of the skin

Regulates Calcium and Phosphate Levels

Certain cells in the skin use the UV rays that penetrate the skin to synthesize (make) cholecalciferol

The cholecalciferol goes to the kidneys where it is converted to calcitriol, which is a hormone that is the active form of Vitamin D3. Vitamin D3 helps the body absorb calcium and phosphate from the food we eat (this is done in the small intestine). All you need is 15 minutes of sun a day to get your vitamin D requirement.

Defends Against Pathogens

The skin contains cells called epidermal dendritic cells or Langerhan cells that can phagocytize pathogens that have penetrated the skin and also epidermal cancer cells.

Allows Sensations

The skin contains sense organs for light touch, pressure, temperature, and pain.

Excretes Substances

Skin excretes sweat and sebum (which contain substances including water, urea and salts).

In females, the skin also produces milk

Structure of the Skin

The skin consists of two parts:

1. Epidermis (outer layer)

2. Dermis (inner layer)

Beneath the dermis lies the subcutaneous layer also known as the hypodermis or superficial fascia.

Epidermis

Is avascular

Is made of stratified squamous epithelium divided into 5 sublayers:

Stratum Basale - basal layer, single row of cells

When a basal layer cell divides, one daughter cell migrates through the different layers to the surface where its nucleus degenerates and the cytoplasm fills with a tough waterproof protein called keratin.

The cell then dies, becomes flat, and eventually shed.

Stratum Spinosum - spiny layer, 8 to 10 rows

Stratum Granulosum - granular layer, 3-5 rows, keratin visible

Stratum Lucidum - clear layer, transparent keratin called eleiden, absent on hairy skin, found on palms, soles

Stratum Corneum - horny skin, 25 to 30 rows, keratinized, flat, dead.

Epidermal Cells

The epidermis is made up of several different types of cells

Keratinocytes

90% of epidermal cells are keratinocytes

Produce keratin

Have anchoring junctions called desmosomes that act as spot welds

Melanocytes

8% of epidermal cells are melanocytes

Produce the pigment melanin which absorbs UV light thereby protecting cell nuclei (DNA)

Melanin varies in color from yellow to reddish to brown to black.

Differences in skin color occur because of variations in :

Melanin color

Number of melanin granules in a person's skin

Amount of pigment in each melanocyte

Langerhans Cells

Migrate from bone marrow involved in immunity by assisting helper T cells

Merkel Cells

Make contact with flattened sensory nerve endings (merkel discs), function in touch sensation.

Dermis

Made of connective tissues
Cells include fibroblasts, macrophages, and adipocytes (fat cells)
Has nerve endings, capillaries, muscles, glands, and hair follicles
It assists in the production of the active form of vitamin D (calcitriol) using UV light. Vitamin D helps in the absorption of calcium from foods
Made of 2 sublayers:

Papillary Layer
- made of areolar connective tissue
- it is folded into numerous dermal papillae, which increase surface area and prevent the skin from sliding and shifting
- The epidermis conforms to the papillae creating epidermal ridges (fingerprints)
Reticular layer
- Is the deeper layer
- Is made of of dense irregular connective tissue which provides strength, elasticity and extensibility

Hypodermis (also called Subcutaneous Layer or Superficial Fascia)

Is the layer deep to the skin
Is made of adipose and areolar connective tissue
Is not considered part of the skin

Skin Color

Three pigments contribute to skin color:
1. Melanin

Uellow to reddish-brown to black pigment

Responsible for dark skin color

Rreckles and pigmented moles result from local accumulations of melanin

2. Carotene

Yellow to orange pigment that the body obtains from vegetable sources such as carrots and tomatoes

most obvious in the palms and soles of the feet

3. Hemoglobin
Blood with lots of oxygen is bright red, so the blood vessels in the dermis give the skin a reddish tint

This is easy to see in lightly pigmented individuals

Because Caucasian skin contains little melanin, the epidermis is nearly transparent and allows the color of blood to show through

Accessory Structures of the Skin

The skin holds many structures and derivatives:

Nerve receptors for cold, heat, and pain, lamellated corpuscles (pressure) and corpuscles of touch
Sebaceous (Oil) Glands
Sudoriferous (Sweat) Glands
Mammary Glands
Ceruminous Glands
Hair
Nails

All of the above glands are made of specialized glandular (secretory) epithlelium

Sebaceous Glands

Secrete lipid-rich sebum (oil) for waterproofing and softening of skin and hair.

Sudoriferous Glands - sweat glands

2 Types of Sweat Glands:

Eccrine Glands
- for evaporative cooling distributed throughout the skin except margin of lips, nail beds and, genitalia
- The duct of the eccrine gland empties out on the skin surface (pores)
Apocrine Glands
- are found in the axilla (armpit), pubic region, and areolae
- The excretory ducts empty into the hair follicle.
- Become active at puberty
- Apocrine secretion contains the same basic components as eccrine sweat, but it also contains fatty acids and proteins, giving the sweat a milky or yellowish color; the secretion is odorless, but bacteria on the skin decompose the fatty acids and proteins, giving it its characteristic musky odor.

Mammary Glands

Are specialized sudoriferous glands that secrete milk in females

Ceruminous Glands

secrete cerumen, a waxy substance, combined with sebum provides a sticky barrier in the external auditory meatus (ear canal) for protection against foreign bodies.

Skin Injury and Repair

Four Stages in Skin Healing:

Inflammation

Blood flow increases

Phagocytes attracted

Scab Formation

Cell Division and Migration

Scar Formation

Nails

Each nail has 3 parts; free edge, body, and nail root
The nail does not grow from the root, but from the underlying portion of the epidermis called the nail matrix
The cells from this area become keratinized, harden, and move forward and over the stratum germinativum (basale)
Growth rate is approx. 1mm per week

Hair

Is a column of dead epidermal cells covered with a layer of flattened, scale-like cells called the cuticle
The cuticle surrounds the cortex and the central medulla which contains pigment granules and air spaces
The part of the hair that extends from the skin surface is called the shaft
The root is embedded in the hair follicle which is an extension of the epidermis, part of which extends into the dermis called the external root sheath
At the base of the internal root sheath is the bulb into which a papilla protrudes
A layer of epidermal cells called the germinal layer covers the hair papilla and gives rise to the hair itself
Attached to the connective tissue sheath around the hair follicle is a small smooth muscle called the arrector pili

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Thermoregulation

The integumentary system also functions in thermoregulation, the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. This process is one aspect of homeostasis: a dynamic state of stability between an animal's internal and external environment.

The skin assists in homeostasis (keeping different aspects of the body constant, e.g. temperature). It does this by reacting differently to hot and cold conditions so that the inner body temperature remains more or less constant. Vasodilation and sweating are the primary modes by which humans attempt to lose excess body heat.

The brain generates much heat through the countless reactions that occur, even the process of thought creates heat. The head has a complex system of blood vessels which keeps the brain from overheating by bringing blood to the thin skin on the head, allowing heat to escape.

There are four avenues of heat loss:

convection
conduction
radiation
evaporation

If skin temperature is greater than that of the surroundings, the body can lose heat by radiation and conduction. But if the temperature of the surroundings is greater than that of the skin, the body actually gains heat by radiation and conduction. In such conditions, the only means by which the body can rid itself of heat is by evaporation. So when the surrounding temperature is higher than the skin temperature, anything that prevents adequate evaporation will cause the internal body temperature to rise. Humidity affects thermoregulation by limiting sweat evaporation and thus, heat loss.

In hot conditions, endocrine sweat glands under the skin secrete sweat (a fluid containing mostly water with some dissolved ions) which travels up the sweat duct, through the sweat pore and onto the surface of the skin. This causes heat loss via evaporative cooling; however, a lot of essential water is lost.

The hairs on the skin lie flat, preventing heat from being trapped by the layer of still air between the hairs. This is caused by tiny muscles under the surface of the skin, called arrector pili muscles, relaxing so that their attached hair folliclesare not erect. These flat hairs increase the flow of air next to the skin, increasing heat loss by convection.

When environmental temperature is above core body temperature, sweating is the only physiological way for humans to lose heat.

By contrast, in cold conditions sweat stops being produced. The arrector pili muscles contract (piloerection), lifting the hair follicles upright. This makes the hairs stand on end which acts as an insulating layer, trapping heat. This is also how "goose bumps" are caused, since humans don't have very much hair and the contracted muscles can easily be seen.

The Protective Functions of the Integumentary System

The integumentary system is the organ system that protects the body from damage. It comprises the skin and its appendages. It is an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense. The integumentary system has a variety of functions; it may serve to waterproof, cushion, and protect the deeper tissues, excrete wastes, and regulate temperature, and is the attachment site for sensory receptors to detect pain, sensation, pressure, and temperature. In most terrestrial vertebrates with significant exposure to sunlight, the integumentary system also provides for vitamin D synthesis.

The Epidermis

The epidermis is the top layer of the skin made up of epithelial cells. It does not contain blood vessels. Its main function is protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized stratified squamous epithelium that is made up of four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans' cells. The major cell of the epidermis is the keratinocyte, which produces keratin. Keratin is a fibrous protein that aids in protection. Keratin is also a water-proofing protein. Millions of dead keratinocytes rub off daily. The majority of the skin on the body is keratinized, meaning that it is waterproofed. The only skin on the body that is non-keratinized is the lining of skin on the inside of the mouth. Non-keratinized cells allow water to "stay" atop the structure.

The Dermis

The dermis is the middle layer of skin, composed of dense irregular connective tissue and areolar connective tissue such as collagen with elastin arranged in a diffusely bundled and woven pattern. The dermis has two layers. The Papillary layer which is the superficial layer and consists of the areolar connective tissue and the Reticular layer which is the deep layer of the dermis and consists of the dense irregular connective tissue. These layers serve to give elasticity to the integument, allowing stretching and conferring flexibility, while also resisting distortions, wrinkling, and sagging. The dermal layer provides a site for the endings of blood vessels and nerves. Many chromatophores are also stored in this layer, as are the bases of integumental structures such as hair, feathers, and glands.

The Hypodermis

The hypodermis is the bottom layer of the integumentary system in vertebrates. Types of cells that are found in the hypodermis are fibroblasts, adipose cells, and macrophages. It is derived from the mesoderm, but unlike the dermis, it is not derived from the dermatome region of the mesoderm. In arthropods, the hypodermis is an epidermal layer of cells that secretes the chitinous cuticle.

Langerhans cells in the skin also contribute to protection as they are part of the adaptive immune system.

Homeostatic function

The integumentary system has multiple roles in homeostasis. All body systems work in an interconnected manner to maintain the internal conditions essential to the function of the body. The skin has an important job of protecting the body and acts as the body’s first line of defense against infection, temperature change, and other challenges to homeostasis. The integumentary system protects the body's internal living tissues and organs, protects against invasion by infectious organisms, protects the body from dehydration, to name a few.

The Physiological Effects of Massage

Benefits & Effects of Massage

In order to understand the benefits and effects of massage, it is important to consider how the body responds physiologically.

Massage involves two types of responses:

• mechanical responses as a result of pressure and movement as the soft tissues are manipulated
• reflex responses in which the nerves respond to stimulation

Effects on the Skeletal System

• Massage can help increase joint mobility by reducing any thickening of the connective tissue and helping to release restrictions in the fascia.
• It helps to free adhesions, break down scar tissue and decrease inflammation. As a result, it can help to restore range of motion to stiff joints.
• Massage improves muscle tone and balance, reducing the physical stress placed on bones and joints.

Effects on the Muscular System

• Massage relieves muscular tightness, stiffness, spasms and restrictions in the muscle tissue.
• It increases flexibility in the muscles due to muscular relaxation.
• It increases blood circulation bringing more oxygen and nutrients into the muscle. This reduces muscle fatigue and soreness.
• It promotes rapid removal of toxins and waste products from the muscle.

Effects on the Cardiovascular System - Massage can:

• improve circulation by mechanically assisting the venous flow of blood back to the heart
• dilate blood vessels helping them to work more efficiently
• produce an enhanced blood flow; delivery of fresh oxygen and nutrients to the tissues is improved and the removal of waste products, toxins and carbon dioxide is hastened via the venous system
• help temporarily to decrease blood pressure, due to dilation of capillaries
• decrease the heart rate due to relaxation

Effects on the Lymphatic System - Massage helps to:

• reduce oedema (excess fluid in the tissue) by increasing lymphatic drainage and the removal of waste from the system
• regular massage may help to strengthen the immune system, due to the increase in white blood cells

Effects on the Nervous System

• Massage stimulates sensory receptors: this can either stimulate or soothe nerves depending on the techniques used.
• It also stimulates the parasympathetic nervous system, helping promote relaxation and the reduction of stress.
• Massage helps to reduce pain by the release of endorphins (endorphins are also known to elevate the mood).

Effects on the Skin - Massage can bring about:

• improved circulation to the skin, increased nutrition to the cells and encouraging cell regeneration
• increased production of sweat from the sweat glands, helping to excrete urea and waste products through the skin
• vaso-dilation of the surface capillaries helping to improve the skin's colour
• improved elasticity of the skin
• increased sebum production, helping to improve the skin's suppleness and resistance to infection.

Effects On The Respiratory System

• Massage deepens respiration and improves lung capacity by relaxing any tightness in the respiratory muscles.
• It also slows down the rate of respiration due to the reduced stimulation of the sympathetic nervous system.

Effects on the Digestive System - Massage can:

• Increase peristalsis in the large intestine, helping to relieve constipation, colic and gas.
• Promote the activity of the parasympathetic nervous system, which stimulates digestion.

Effects on the Urinary System

• Massage increases urinary output due to the increased circulation and lymph drainage from the tissues.

The Psychological Effects of Massage -

• Massage can help to: reduce stress and anxiety by relaxing both mind and body
• create a feeling of well-being and enhanced self-esteem
• promote positive body awareness and an improved body image through relaxation
• ease emotional trauma through relaxation

Benefits & Effects of Sports Massage

Benefits & Effects
There are three areas where sports massage is used to benefit athletes.

Maintenance Massage:
A regular massage treatment programme based on the therapist’s understanding of anatomy and of the muscles used in a given sport and which are likely candidates for trouble. By concentrating on particular muscle groups, the therapist can help the athlete maintain or improve range of motion and muscle flexibility.

Event Massage:
Pre-event and post-event massage therapies are tailored for distinct purposes. Pre-event treatment is used as a supplement to an athlete’s warm-up to enhance circulation and reduce excess muscle and mental tension prior to competition. It is tailored to the needs of the athlete and his/her event and can be relaxing or stimulating as appropriate. Post-event massage, on the other hand, is geared towards reducing the muscle spasms and metabolic build-up that occur with rigorous exercise. Various sports massage techniques enhance the body’s own recovery process improving the athlete’s ability to return to training and competition, and reducing the risk of injury.

Rehabilitation:
Even with preventative maintenance, muscles cramp, tear, bruise, and ache. Sports massage can speed healing and reduce discomfort during the rehabilitation process.

• Soft tissue techniques employed by sports massage therapists are effective in the management of both acute and chronic injuries.
• Trigger point techniques reduce the spasm and pain that occur both in the injured and "compensation" muscles.
• Cross-fibre friction techniques can help with healing by improved formation of strong and flexible repair tissue, which is vital in maintaining full pain-free range of motion during rehabilitation.

In all cases, such massage techniques are employed in collaboration with other appropriate medical care.

Detailed Integumentary System Interactive Review.

This review will take over 8 hours approximately and you should be ready for the exam after this

CLASS SUMMARY/OUTLINE

The integumentary system provides the first example of a system to be studied by students. The anatomy of skin, the heaviest organ in the body, is thoroughly examined; in addition, the physiology of the skin is also described. The structural and functional characteristics of accessory structures of the skin, namely hair, sebaceous glands, sudoriferous glands, ceruminous glands, and nails are described as well. A concise comparison of thin skin and thick skin is provided. The blood supply of the integumentary system is portrayed. The development of the integumentary system and the effects of aging on the integumentary system are concisely examined. A glossary of key medical terms associated with the integumentary system is provided.

STUDENT OBJECTIVES

1. Describe the various layers of the epidermis and dermis, and the cells that compose them.

2. Explain the basis for skin color.

3. Compare the structure, distribution, and functions of hair, skin glands, and nails.

4. Compare structural and functional differences in thin and thick skin.

5. Describe how the skin contributes to body temperature regulation, protection, sensation, excretion and absorption, and synthesis of vitamin D.

6. Describe the blood supply of the integumentary system.

7. Describe the development of the epidermis, its accessory structures, and the dermis.

8. Describe the effects of aging on the integumentary system.

LECTURE OUTLINE

A. Introduction

1. Tissues are organized to form an organ, and organs are organized to form systems.

2. The organs of the integumentary system include the skin and its accessory structures including hair, nails, and glands, as well as muscles and nerves.

B. Structure of the Skin (p. 122)

1. The skin (cutaneous membrane) covers the body and is the largest organ of the body.

2. It consists of two major layers:

i. outer, thinner layer called the epidermis

ii. inner, thicker layer called the dermis

3. Beneath the dermis is a subcutaneous (subQ) layer (also called hypodermis) which attaches the skin to the underlying tissues and organs; the subcutaneous layer contains lamellated (Pacinian) corpuscles that detect pressure.

4. The epidermis has a number of important characteristics:

i. the epidermis is composed of keratinized stratified squamous epithelium

ii. it contains four major types of cells:

a. 90% of the cells are keratinocytes, which produce keratin

b. melanocytes, which produce the pigment melanin

c. Langerhans cells, which are involved in immune responses

d. Merkel cells, which function in the sensation of touch

iii. the epidermis contains four or five major layers :

a. stratum basale (deepest layer) or stratum germinativum, where continuous cell division occurs which produces all the other layers

b. stratum spinosum

c. stratum granulosum

d. stratum lucidum is present only in the skin of the fingertips, palms, and soles

e. stratum corneum (surface layer), composed of many sublayers of flat, dead keratinocytes that are continuously shed and replaced by cells from deeper strata

iv. keratinization, the accumulation of more and more protective keratin, occurs as cells move from the deepest layer to the surface layer

5. The dermis has several important characteristics:

i. the dermis is composed of connective tissue containing collagen and elastic fibers

ii. the dermis contains two layers :

a. the outer papillary region consists of areolar connective tissue containing fine elastic fibers, dermal papillae, corpuscles of touch (Meissner’s corpuscles), and free nerve endings

b. the deeper reticular region consists of dense, irregular connective tissue containing collagen and elastic fibers (which provide strength, extensibility, and elasticity to the skin), adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands

6. Epidermal ridges reflect contours of the underlying dermal papillae and form the basis for fingerprints; their function is to increase firmness of grip by increasing friction.

7. Variations in skin color arise from variations in the amounts of three pigments:

i. melanin (located mostly in the epidermis, where it absorbs UV radiation)

- albinism is an inherited inability to produce melanin

ii. carotene (found in the stratum corneum, dermis, and subcutaneous layer)

iii. hemoglobin (located in erythrocytes flowing through dermal capillaries)

C. Accessory Structures of the Skin

1. Accessory structures of the skin are organs that develop from the embryonic epidermis.

2. These organs include hair, skin glands, and nails.

3. Hair (pili) have a number of important characteristics:

i. hair is composed of dead, keratinized epidermal cells

ii. each hair consists of:

a. shaft which projects above the surface of the skin

b. root which penetrates into the dermis

c. hair follicle which surrounds the root

iii. hair grows due to cell division occurring in the matrix of the bulb, located at the base of a hair follicle; there is a growth cycle that includes a growth stage and resting stage

iv. associated with hairs are sebaceous (oil) glands, arrector pili muscles, and hair root plexuses

v. the color of hair is determined primarily by the amount and type of melanin

vi. the primary functions of hair are protection, reduction of heat loss, and sensing light touch

4. Sebaceous (oil) glands have several important characteristics:

i. they are typically connected to hair follicles

ii. they secrete an oily substance called sebum which prevents dehydration of hair and skin, and inhibits growth of certain bacteria

5. Sudoriferous (sweat) glands produce sweat (perspiration) which helps to cool the body by evaporating, and also eliminates small amounts of wastes; there are two types of sweat glands :

i. numerous eccrine sweat glands which have an excretory duct that opens at a pore at the surface of the epidermis

ii. apocrine sweat glands which are located mainly in the skin of the axilla, groin, areolae, and bearded facial regions of adult males; their excretory ducts open into hair follicles

6. Ceruminous glands are modified sweat glands located in the ear canal; they are involved in producing a waxy secretion called cerumen (earwax) which provides a sticky barrier that prevents entry of foreign bodies into the ear canal.

7. Nails are composed of hard, keratinized epidermal cells located over the dorsal surfaces of the ends of fingers and toes.

i. Each nail consists of:

a. free edge

b. transparent nail body with a whitish lunula at its base

c. nail root embedded in a fold of skin

ii. Associated with a nail are:

a. hyponychium (located under the free edge) attaches the nail to the fingertip

b. eponychium (cuticle) attaches the margin of nail wall to neighboring epidermis

c. nail matrix in which cell division occurs resulting in growth of the nail

iii. The functions of nails include helping to grasp and manipulate objects, providing protection against trauma to the ends of the digits, and scratching various body parts.

D. Types of Skin

1. There are two major types of skin:

i. thin skin covers all body regions except the palms, palmar surfaces of digits, and soles

ii. thick skin covers the palms, palmar surfaces of digits, and soles

E. Functions of the Skin

i. regulation of body temperature

ii. blood reservoir

iii. protection

iv. cutaneous sensations

v. excretion and absorption

vi. synthesis of vitamin D. Vitamin D3 is made in the skin when 7-dehydrocholesterol reacts with ultraviolet light of UVB type at wavelengths between 280 and 315 nm, with peak synthesis occurring between 295 and 297 nm. Depending on the intensity of UVB rays and the minutes of exposure, an equilibrium can develop in the skin, and vitamin D degrades as fast as it is generated. Cholecalciferol (D3) is produced photochemically in the skin from 7-dehydrocholesterol; 7-dehydrocholesterol is produced in relatively large quantities in the skin of most vertebrate animals, including humans.

F. Blood Supply of the Integumentary System

Points

· The blood vessels in the deepest layers provide nourishment to the upper layers.

· The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis.

· The papillary region is composed of loose areolar connective tissue. This is named for its fingerlike projections called papillae, that extend toward the epidermis and contain terminal networks of blood capillaries.

1. The epidermis is avascular, i.e. it contains no blood vessels.

2. The dermis receives blood from:

i. branches of arteries supplying skeletal muscles

ii. arteries that supply the skin directly, including:

a. cutaneous plexus

b. papillary plexus

3. Venous plexuses drain blood from the dermis into larger subcutaneous veins.

G. Development of the Integumentary System

1. The epidermis develops from the ectoderm; nails, hair, and skin glands are epidermal derivatives.

2. The dermis develops from the mesoderm.

H. Aging and the Integumentary System

1. The skin of a fetus is protected by a fatty substance called vernix caseosa.

2. Adolescents may develop acne.

3. Pronounced aging effects do not typically occur until people reach their late forties.

4. The effects of aging include wrinkling, decrease of skin’s immune responsiveness, dehydration and cracking of the skin, decreased sweat production, decreased numbers of functional melanocytes resulting in gray hair and atypical skin pigmentation, loss of subcutaneous fat, a general decrease in skin thickness, and an increased susceptibility to pathological conditions.

5. Growth of hair and nails decreases during the second and third decades of life; nails may also become more brittle with age.

6. Intrinsic aging is caused by internal factors alone such as diminished collagen synthesis and is sometimes known as chronological aging.

7. Extrinsic aging is caused by external factors such as exposure to ultraviolet radiation which can result in photodamage and may lead to skin cancer formation.

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