The Sense of touch, Pain & Temperature:

Skin, Structure and Function

EXPERT VISION ACADEMY

Types of Skin

There are two major types of skin:

•Thin (hairy) skin covers all body regions except the palms, palmar surfaces of digits, and soles

•Thick (hairless) skin covers the palms, palmar surfaces of digits, and soles

Skin Our largest organ Its area is about 2 square meters and weighs

4.5-5kg (10-11 lb) Accounts for 16% of body weight Largest sense organ in the body

Accessory Structures

▫Sweat glands▫Sebaceous or oil glands▫Hair▫Nails

Skin Structure

Layers of Skin

Skin

Epidermis(the outer membrane

Layer)

Dermis

( the middle layer)

Subcutaneous

(the deepest layer)

EPIDERMIS

• Primarily made up of keratinized stratified

squamous epithelium

• The EPIDERMIS is the layer that gives strength to

the skin.

• Varies in thickness from a few to dozens of cells

thick (eyelids to palms)

• It does not have any vascularization, so it relies on

absorbing oxygen and nutrients from the blood

vessels in the connective tissues deep to it.

Layers and Cells of the Epidermis

Cells of Epidermis 1. Melanocyte1. Melanocyte produce MELANIN (dark brown produce MELANIN (dark brown

pigment) pigment) contribute color to the skin

• Everyone has the same number of melanocytesEveryone has the same number of melanocytes• Improper function causes light skinImproper function causes light skin• Regulated by DNA but can be altered by UV light,

prolonged exposure can increase the melanin secretion and darken the skin (Tanning)

• Function of Melanocytes- protection from UV light.

2. Keratinocyte2. Keratinocyte the most important cell in the epidermis become filled with a tough fibrous protien called keratin.

• They make up more than 90% of the epidermal cells

What is keratin?

• Keratin is a waxy protein substance only found in the epidermis.

• Keratin is waterproof and strong• It makes up the nails, hair, and is also in each

superficial skin cell.• It can absorb water, so keratin swells when

soaking wet. It makes the skin look wrinkled.

• Keratinization, the accumulation of more and more protective keratin, occurs as cells move from the deepest layer to the surface layer

Cells of Epidermis

3. Langerhans cell3. Langerhans cell : : it plays role in immunological reaction that effect the skin and may serve as defense mechanism for the body.

4. Merkel cellsMerkel cells - - combines with disc like sensory nerve endings to make Merkel’s discs

Layers of the Epidermis•Stratum basale (the deepest layer of

epidermis)•Stratum spinosum•Stratum granulosum•Stratum lucidum (only in thick skin)•Stratum corneum (most superficial layer of

epidermis)

Stratum Basale•Deepest layer•Columnar cells capable of continued cell

division.•Newly made cells get pushed to surface

where there is less blood supply and they begin to die.

Stratum spinosum•Multiple layered arrangement of cuboidal cells•Are spiny or prickly in appearance, due to

molecular bridges that connect them to other cells

Stratum spinosum

As new cells are made in the S. Basale, the older cells get pushed up and become the S. Spinosum

They no longer divide in this layer They provide the strength to the

epidermis

Stratum granulosum•3-5 rows of flattened cells•As more new cells are made in the S. basale,

the S. spinosum layer is pushed up to become the S. granulosum layer.

Stratum granulosum

• The cells in the S. granulosum begin to die

because they are now too far from nutrient

source (in dermis)

• After they die, they start to fill up with

KERATIN.

STRATUM LUCIDUM

This layer is only on the thick skin of palms of hands and soles of feet

It is just deep to the S. corneum and superficial to the S. granulosum

3-4 rows of flattened dead cells

This THIN layer provides protection from UV radiation.

Stratum corneum

•Most superficial•This is the layer you can see. •20-50 rows flattened dead cells•Cells are “sloughed off” by normal wear•Each cell contain keratin, protects skin

from water loss•Mainly responsible for waterproofing,

protection against infection, and wear and tear resistant.

Stratum corneum

As more new cells are made in the S. basale, the cells are all pushed up again, and the S. granulosum layer becomes the S. Corneum.

The main difference between thick skin and thin skin relates to the thickness of the Stratum corneum.

These are the dead cells, flaking off. In the stratum corneum the cells lose their nucleus

and fuse to squamous sheets, which are eventually shed from the surface (desquamation).

It takes about 2-4 weeks for a cell to move from the stratum basale to the distal edge of the stratum corneum and shed

We lose half a million cells per hour; 1.5 grams a day

DERMIS•Located deep to the epidermis•Sometimes called the true skin.•Contains a large amount of collagen• Contains

Skin glands Nerve sensors Blood vessels Connective tissue Arrector muscles to make hairs stand on end

Dermis 2 layers:

1)PAPILLARY LAYER

2)RETICULAR LAYER

PAPILLARY LAYER

• Named for finger like projections called papillae, that extend into the epidermis.

• Composed of loose connective tissue.• Papillae provide the dermis with a bumpy surface

that strengths the connection between the dermis and the epidermis and to increase surface area for contact with the epidermis

• In the palms, fingers, soles and toes they form contours in the skin called friction ridges.

• Friction ridges occur in patterns that are genetically determined. (Fingerprints)

RETICULAR LAYER

•Dense irregular Connective Tissue•Has lots of COLLAGEN and ELASTIN give

the dermis, strength, extensibility, and elasticity

•Stretch marks are caused from tiny tears in the collagen of the dermis.

•The epidermis is the strongest layer of the skin, but the reticular layer of the dermis is the strongest layer of the dermis. Gives the area strength.

•The accessory organs are located here.

HYPODERMIS:

•Subcutaneous layer (also called hypodermis) ) is deep to dermis

•Attaches the skin to the underlying tissues and organs.

•Varies tremendously in thickness.•Functions1) Stores fat2) Cushions 3) Insulation of heat from blood vessels in

this layer.

Accessory Structures of the Skin

HairHair• Most of the skin is haired although the hair in most areas is

short, fine and only lightly pigmented.

• Truly hairless are only the palms of hands and soles of feet

and sides of fingers and toes.

• In those parts of the skin which we perceive as "hairy" we

find terminal hairs. The free part of each hair is called the

shaft.

• The root of each hair is anchored in a tubular invagination of

the epidermis, the hair follicle, which extends down into

the dermis and, usually, a short distance into the

hypodermis.

The hair is actually dead keratinized cells.

Each hair follicle has an associated bundle of smooth muscle, the arrector pili muscle.

These muscles makes your hair stand up on its end.

•Hairs have a number of important functions:

▫protection▫reduction of heat

loss▫sensing light

touch

Hair Color and Texture

•Hair color is determined by the amount and type

of melanin present.

•Melanocytes become less active with age. Gray

hair is due to lack of melanin.

• Red hair results from a modified type of melanin.

• The thickness and texture of hair depends on the

size and shape of follicles. 

• Alopecia is the term for hair loss.

NAILS

• The EPIDERMIS gives rise to the nails.

• Plates of stratified squamous epithelial cells with hard keratin

• The nails are made of keratin

• At the nail matrix, there is rapid division of keratocytes and as

they die, the skin moves up and creates the nail. The matrix is

responsible for the producing cells that become the nail plate.

• Nail growth occurs in the lunula . The white half-moon visible

under the proximal part of a fingernail is the lunula.

• Cuticle is a fold of stratum corneum on the proximal end of

nail

Structure of a Nail

Exocrine Glands•Sebaceous glands

• Or oil glands• They secrete the sebum (seb = oil) an oily product.• Found in dermis at base of hairs • Sebum is secreted into a hair follicle• Produce sebum to condition, lubricate and waterproof

hair and skin• Prevents excessive evaporation of water from the skin• Keeps the skin soft and contains a bactericidal agent

that inhibits the growth of certain bacteria. • Sebaceous glands are scattered all over the surface of

the skin except in the palms, soles and the side of the feet.

•Sweat glands

Or sudoriferous glands are simple coiled tubular glands. They are divided into two principal types: eccrine and apocrine.

a. Apocrine glands are found mainly in the skin of the armpits, of the anogenital areas and of the areola of the breasts. b. Eccrine glands are the most common. Their secretory portion can be located in the dermis or in the hypodermis.

They produce sweat, a watery mixture of salts, antibodies and metabolic wastes. Sweat prevents overheating of the body and thus helps regulate body temperature.

Functions of the Skin

Functions of the Skin•The skin not just only gives us our

appearance and shape, it also serves other important functions:

•outermost covering•first line of defense against pathogens•protection • insulation •regulation of body temperature•sensations•excretion and absorption•synthesis of vitamin D

Protection

• A) from micro organism.

• B) from dehydration.

• C) from ultraviolet.

• D) mechanical trauma.

• E) pain

• F) heat and cold

Protection

• Keratin toughens cells, skin store fats cells which cushion blows and pressure receptors to measure possible damage so our skin is a shield that protects us from:

1. mechanical impact such as pressure and stroke.

2. thermal impact such as heat or cold.

3. environmental impact such as chemicals

4. the sun’s UV-radiation

First line of Defense

•It is the 1st line of defense from infection for our immune system

•It creates a barrier that keeps bacteria, viruses, fungi, and other things that can cause infection out of the body.

•The loss of large areas of skin due to injury makes a person extremely vulnerable to infection.

Protection from Bacteria •The acid mantle which has an acid pH

helps stop bacteria getting into the skin. •When sweat & sebum mix together on the

skin they make an acid barrier called the ACID MANTLE.

•Certain bacteria and fungi are able to exist on the outside of the skin and it is their action against the acid mantle that can create extreme body odour.

•If the acid mantle of the skin is removed, protection of the skin is lost.

•Waterproofing – contains lipids to prevent drying out

•Excretion of waste – urea and uric acid secreted in sweat

• Hair, fingernails and toenails for protection

• Hair provides protection against heat loss by adjustment of hair density through contraction of the arrector pili muscle attached to each hair follicle. By "fluffing up" the hair layer of air can be held adjacent to the skin to provide a heat trapping, invisible layer.

The 5th Sense • Besides the senses of smell, taste, sight and

hearing the sense of touch is one of our body's most important senses.

• Without it, we would not be able to feel the gentle touch of a dear person, the warmth of a hot cup of tea, or the wind blowing in our face.

• This sense is made possible by various cells and nerve endings in the skin, which send impulses to our central nervous system.

• Sensation of Pressure, touch, temp, pain, etc• Two specialized receptors:

Meissner corpuscle – detects light pressure(touch)

Pacinian corpuscle – detects deep pressure

Skin Sensor Receptors

Touch,pressure,heat,cold and pain

PRODUCTION

•Oils and sebum to condition.

•Sebum: oil, “natures skin cream”

The Skin Produces•Vitamin D

▫The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus.

▫By promoting calcium absorption, vitamin D helps to form and maintain strong bones.

▫Vitamin D also works in concert with a number of other vitamins, minerals, and hormones to promote bone mineralization.

▫Without vitamin D, bones can become thin, brittle, or misshapen.

▫Vitamin D sufficiency prevents rickets in children and osteomalacia in adults, two forms of skeletal diseases that weaken bones

▫UV rays combine with skin to make cholecalciferol▫Cholecalciferol is transported to the liver and kidneys

where it is changed to vit D

The Skin Produces

•Melanin▫ A dark brown to black

pigment found in the skin, hair, and parts of the eye.

▫ helps protect against the harmful effect of UV radiation.

▫ keeps uv rays from penetrating the body

The Skin Produces

•Keratin▫ Keratin is a tough,

fibrous, insoluble protein that makes up skin, hair, and nails.

▫ If pressure is put on some parts of the skin, more keratin is produced, forming thick calluses that protect the layers of skin beneath.

▫ Protects body from water loss

Temperature Regulation

•Too warm?▫Capillary sphincters in skin open to allow

more blood flow.▫Body heat radiated away.▫Sweat glands release sweat onto the skin

surface ▫Evaporation will remove heat from blood.▫Body releases most of heat through skin

Temperature Regulation

•Too cold?▫Vasoconstriction to decrease the flow of heat to

the skin. ▫Cessation of sweating. ▫Shivering to increase heat production in the

muscles ▫Secretion of norepinephrine, epinephrine, and

thyroxine to increase heat production ▫the erection of the hairs to increase insulation

and formation of goose bumps