Human Skin

What is the largest organ in the human body?

Skin

Why is skin an organ?

It is an organ because it consists of different tissues that are joined to perform a specific function

What does the skin do?

Guards the underlying muscles, bones, ligaments and internal organs

What percentage does the skin consist of body weight?

Skin makes up of 12-15% of the body weight

pH of skin

4 - 5.6

how does skin play an important role?

Because it interfaces with the environment, skin plays a key role in protecting the body against pathogens and excessive water loss

Function of Skin

1. protection

2. sensory function

3. excretion

4. regulation of body temperature

5. formation of vitamin D

6. absorption

7. water resistance

epidermis

The outermost layer of skin, provides a waterproof barrier and

creates our skin tone

dermis

Beneath the epidermis, contains tough connective tissue, hair

follicles, and sweat glands

hypodermis

The deeper subcutaneous tissue is made of fat and connective tissue

renewal of epidermis

approx 28 days

layers of epdiermis

5 layers

stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum

stratum basale

The stratum basale is in the deepest layer of epidermis. New skin cells develop in this layer. It also contains the keratinocyte stem cells, which produce the protein keratin. Keratin helps form hair, nails and your skin's outer layer

stratum spinosum

This layer mostly consists of keratinocytes held together by sticky proteins called desmosomes. The stratum spinosum helps to make skin flexible and strong

stratum granulosum

Third layer of epidermis composed of 3-5 layers of flattened keratin. Cells die in this region as they remain far from the dermis to receive nutrients

stratum lucidum

It's a thin, transparent layer of keratinocytes that are becoming less round and have a flatter shape. Present only in finger tips, palms feet

stratum corneum

The stratum corneum is the top layer of the epidermis. This is the layer we see. Here, keratinocytes become corneocytes. Corneocytes are strong, dead keratinocytes that protect us from harm, including abrasions, light, heat and pathogens

Major Cells of Epidermis

1. Keratinocytes: Keratinocytes produce the protein keratin,

which is the main component of the epidermis

2. Melanocytes: Melanocytes make our skin pigment, known as

melanin

3. Langerhans cells: Langerhans cells prevent things from

getting into our skin

melanin and pigments

Melanin is the body's natural coloring whereas pigment refers to natural or artificial coloring

things that impacts a person's skin color

3 things impact a person's skin color

• The amount of melanin

• The type of melanin (eumelanin and pheomelanin)

• The distribution of melanin

pigmentation of the skin

Pigmentation of the skin can be ascribed to the accumulation of melanin containing melanosomes in the basal layer of the epidermis

nerve of skin

The skin is predominantly innervated by sensory nerve

fibers that detect and respond to physical and chemical stimuli in the environment

Function of Epidermis

1. hydration

2. producing new skin cells

3. protection

4. skin color

what is dermis

Dermis

is located between epidermis and subcutaneous layer

layers of dermis

two layers

• Reticular dermis: The reticular layer is the bottom layer of dermis. It's thick, and it contains blood vessels, glands, hair follicles, lymphatics, nerves and fat cells. A netlike structure of elastin fibers and collagen fibers surrounds the reticular dermis. These fibers support skin's overall structure, as well as

allow it to move and stretch

• Papillary dermis: The papillary layer is the top layer of dermis. It's much thinner than the reticular dermis. It consists of collagen fibers, fibroblast cells, fat cells, blood vessels (capillary loops), nerve fibers, touch receptors (Meissner corpuscles) and cells that fight bacteria ( The papillary dermis extends to the basement layer of the epidermis layer. They form a strong bond that connects like interlocking fingers

Functions of Dermis

1. supporting epidermis

2. feeling different sensations

3. producing sweat

4. keeping skin moist

5. producing hair

what is hypodermis?

The hypodermis is the deepest section of the skin

the hypodermis layer includes:

adipose tissue

blood vessels

bursa

connective tissue

fibroblasts

hair follicles

lymphatic vessels

macrophages

nerves

sweat glands

Functions of Hypodermis

1. connection

2. insulation

3. protecting body

4. storing energy

Skin Appendages

Skin Appendages (specialized derivatives of skin)

• Hairs

• Nails

• Sebaceous glands

• Sweat glands

Hair is mainly composed of

keratin

how do hairs form

Dead keratinocytes fuse together to form the hair

What happens at the base of the follicle?

At the base of the follicle is the bulb, which contains cells that give rise to the keratinocytes that make up the hair, as well as blood vessels that nourish the growing hair

what does each hair follicle contain?

Each hair follicle also contains arrector pili, a muscle that

contracts in response to cold, fright, and other emotions. When the muscle contracts, it pulls the hair in the follicle into a vertical position, in humans, because of our sparse coat of body hair, it merely produces 'goose bumps'

Structure of hair

• Hair Follicle: Hair follicles are the organs that form the hairs.

Located deep in dermis

• Arrector pili: Involuntary smooth muscle. Causes hairs to

stand up. Produces 'goose bumps'

• Sebaceous glands: Lubricate the hair

Regions of Hair

• Hair root: Lower part of the hair. Attached to the integument

• Hair shaft: Upper part of the hair

• Medulla: Core, dead cells contain soft keratin and air to provide flexibility

• Cortex: Middle layer, dead cells contain hard keratin to provide stiffness

• Cuticle: Outermost, overlapping dead keratinized cells form shiny surface

Functions of Hair

• Hair on Head

• Nostrils, Ear canals, Eyelashes

• Body Hair

• Root Hair Plexus

• Arrector Pili Muscle

nail is produced by

epithelial cells

nail formation

• The nail root, closest to the nail matrix, is living

• The outer part, like the hair and skin, consists of dead

keratinized cells

• Protect fingers and toes

• Metabolic disorders can change nail structure

nail production

Occurs in a deep epidermal fold near the bone called the nail root

nail structure

• Nail body: The visible portion of the nail. Covers the nail bed

• Lunula: The pale crescent at the base of the nail

• Nails Sides: Lie in lateral nail grooves. Surrounded by lateral nail folds

Sebaceous Glands

• Sebaceous or Oil glands are found all over the body

except on the palms, the soles, and the top of the feet

• These are most numerous on the face and scalp

• Most sebaceous glands open into hair follicles

• But the glands also occur in some hairless areas, such as the lips and inside the mouth

what do the sebaceous glands do?

It produces an oily substance called Sebum, which keeps the skin and hair from drying out and inhibits the growth of certain harmful bacteria

Sweat Glands

• Most common type called Eccrine Sweat glands which are

found almost all over the surface of the body and are most

numerous on the palms and soles

• These glands begin deep in the dermis and connect to the

surface of the skin by a coiled duct

• In addition, nerve fibers that encircle the sweat glands stimulate the glands in response to fear, excitement, or anxiety

• Other sweat glands, known as Apocrine Sweat glands are

much less numerous than eccrine sweat glands. They are also

anchored deep in the dermis, but open into hair follicles rather

than onto the surface of the skin

• Apocrine sweat glands are located mainly in the armpit, genital area, and around the nipples of the breasts

Acne

• It is commonly located on face, neck, shoulders, chest upper back

• Breakout of acne on the skin composed of blackheads, whiteheads, pimples or deep, painful cysts nodules

• It may leave scars or darken the skin if untreated

Cold Sore

• Red painful fluid-filled blister appears in the mouth or lips

• Affected area will often tingle or burn before the sore is visible

• Outbreaks may also be accompanied by mild flue like symptoms such as low fever, body aches swollen lymph nodes

blister

• Characterized by watery, clear, fluid filled areas on skin.

• May be smaller than 1 cm(vesicle) or larger than 1 cm(bulla) & occur alone or in groups.

• It can be found anywhere on the body.

Hives

• Itchy, raised welts that occurs after exposure to an allergen.

• Red, warm & mildly painful to the touch.

Actinic Keratosis

• Thick, scaly, or crusty skin patch.

• Appears on parts of the body that receive a lot of sun exposure (hands, feet, scalp & neck).

• It is usually pink in color but can have a brown tan or grey base.

Psoriasis

1. Scaly, silvery, sharply defined skin patches

2. Commonly located on the scalp, elbows, knees lower

back

3. May be itchy or asymptomatic

skin cancer

Uncontrolled growth of abnormal skin cells

alopecia areata

losing your hair in small patches

eczema

dry, itchy skin that leads to swelling, cracking or scaliness

Management & Treatment of Skin Diseases

• Antibiotics

• Antihistamines

• Laser skin resurfacing

• Medicated creams, ointments or gels

• Moisturizers

• Steroid pills, creams or injections

• Surgical procedures

We may also reduce symptoms of skin conditions by making

lifestyle changes

Layers of Skin

Skin has three layers

epidermis, dermis, hypodermis