Chapter 4

Chapter 4 – The Skin and Its Parts

Applied Learning Outcomes

Use the terminology associated with the integumentary system

Learn about skin structure, function, appendages, glands, and care

Understand the aging and pathology of the integumentary system

The integumentary system is a dynamic continuous body covering composed of:

• Blood vessels• Connective tissue structures• Glands• Hair• Nails• Skin

It is the largest organ system of the human body.

Overview

Chapter 4 – The Skin and Its Parts

OverviewThe skin has inherent or inborn features.An example would be-nails only grow in the upper tips of fingers and toes.-under genetic control.Skin also has adaptive features-this refers to the ability of an organism’s genes to respond to the environment. Calluses on feet to protect underlying tissue and bone.Blister on skinSkin will darken when exposed to light Skin will stretch as we growSkin can also shrink back as a person loses weight and after a woman has a baby.

The Integumentary System

Develops from two embryological germ layers: the ectoderm and mesoderm.Ectoderm forms outermost layer of skin from a simple squamous tissue-it becomes stratified as embryo develops.In some areas-the ectoderm forms nervous system which later becomes integrated into the skin.

Development of Integumentary System

Dynamic continuous body covering that includes the skin and mucous membranes.4 to 5 weeks after the egg is fertilized the integumentary system begins to develop.

6 to 7 weeks Deeper part of skin forms from mesoderm.

8 to 9 weeks stem cells called mesenchyme (embryonic connective tissue) develop.Fibroblasts develop from certain mesenchyme cells. Fibroblasts are cells that secrete proteins that form collagen and elastin fibers)

10 weeks small ridges start to form between inner and outer layers of skin.They ensure a large surface area of contact between these layers. -prevents separation of layers when skin is stretched or rubbed.

11 weeks small nails at tips of fingers and toes start forming.

20 weeks glandular structures start forming -produce oil and sweat glands.

25 weeks embryo is able to produce skin coloration (pigmentation) Melanoblasts differentiate in the mesenchyme. Few more weeks mature into melanocytes.Also forming are the nervous tissue structures that help skin perceive pain, temp, and touch.

What are the major characteristics of the

skin?• Waterproof, stretchable,washable, and permanent-press, that automatically repairs small cuts, rips and burns and is guaranteed to last a lifetime.

• Surface area of up to 2.2 square meters

• 11 pounds• 7% of total body weight• Pliable yet tough

What are the 3 major layers of the skin?

• Epidermis (epi-upon)– Composed of epithelial tissue (stratified squamous)

– Non-vascularized

• Dermis – underlies the epidermis– Tough leathery layer composed of fibrous connective tissue

– Good supply of blood

• Hypodermis (Subcutaneous layer)– Made of adipose and areolar tissue– Stores fat, anchors skin, protects against blows

Epidermis

DermisBasement membrane

At birth:

The integument (skin) has three distinct layers: the epidermis, the dermis, and the hypodermis.

The Integumentary System

Chapter 4 – The Skin and Its Parts

Epidermis

Dermis

Hypodermis (Subcutaneous layer)

Skin StructureEpidermis – Outermost layer, where new skin cells are continually produced

Composed of stratified squamous epithelium.

--Older cells on the outside

--Innermost layer (Stratum basale or Stratum germinativium) is made of metabolically active cells undergoing mitosis.

It takes 60-75 days for these cells to reach outermost surface.

Cells of this layer are bound tight to the ridged layer of the dermis

(dermal papillae)

Malpighian layer is the layer of epidermis containing melanocytes.

It is found in and above the stratum germinativium.

Melanocytes- are cells that secrete black to brown colored chemical

called melanin.

--Stratum spinosum (prickly layer)-second innermost layer of the epidermis.

In this layer Langerhans cells (immune cells) important in fighting skin

infections and healing injured skin.

--Stratum granulosum- has granules in cytoplasm that reflect an accumulation of yellowish sulfur rich

protein called keratin. Keratin is a tough protein that gives skin its strength.

Keratocytes also produce a substance that acts as waterproofing material.-prevents free flow of water

into and out of skin.

--Stratum compactum -layer of dying cells that are filled with keratin.

--Stratum corneum- uppermost layer of the skin. It is composed of flattened dead cells that regularly shed

What are the layers of the epidermis?

• Stratum basale or stratum germinativum: deepest layer of the epidermis, undergoes rapid cell division.

• Stratum spinosum: intermediate layer, contain spiny shaped keratinocytes, Langerhans cells (immune cells)

• Stratum corneum: outermost layer 20-30 cells thick of dead keratinized cells.– Dandruff– Average person shed 40 pounds of these cells in their lifetime.

What are the different types of cells in the

epidermis?• Keratocytes

– Produce a fibrous protein called keratin

– Are formed in the lowest levels of the epidermis.

– Pushed upward by the production of new cells beneath them.

– Become dead and scale-like

-- Gives skin strength and

waterproofing.– Millions rub off

everyday

What are the different types of cells in the

epidermis?• Melanocytes

– Synthesizes the pigment melanin

– Melan-black– Protects skin from ultraviolet light.

melanocyte

Melanin in keratinocytes

What are the different types of cells in the

epidermis?• Langerhans’ cells– Formed in bone marrow.

– Move to the skin

– Found in stratum

spinosum – Macrophages

Langerhans’cell

What are the characteristics of the

dermis?• Made up of connective tissue• Richly supplied with blood vessels and lymph vessels

• Has hair follicles, oil and sweat glands and sensory receptors

What causes the color of skin?

• 3 pigments contribute to skin color– Melanin- protein pigment (natural sunscreen)

• Can range in color from yellow to reddish-brown to black

• Everyone has the same number of melanocytes but make varying amounts and colors (differences in skin color)

• Increased melanin production can caused by sunlight.

– Carotene-yellow to orange pigment found in carrots.• Most commonly found in the palms or soles. Most intense when large amounts of carotene-rich foods are eaten.

– Hemoglobin- Red blood gives a pinkish hue to fair skin

Dermis – middle layer, composed mostly of connective tissue

attached to the stratum germinativum by hemidesmosomes

(specialized junctions between an epithelial cell and the basement

membrane) along the dermal papilla.

Dense, irregular connective tissue makes up the bulk of the dermis.

It also contains loose connective tissue called areolar connective

tissue.

Areolar connective tissue is found throughout the body. It binds

blood vessels, membranes, muscles, nerves, and skin to other

structures.

Hypodermis (or Subcutaneous layer) – innermost layer

It is absent or very thin in the eyelids, penis, scrotum, and nipples.

After puberty- it is responsible for increase in size of female breasts

and hips.

--Composition- loosely arranged elastic fibers that anchor the skin to

underlying fascia (fibrous connective tissue covering muscle, the skull,

and some organs).

Also has a large amount of adipose tissue

Has a lot of blood and lymphatic vessels.

Has deep nerves

Sometimes microbes enter this layer and cause fasciitis. It can also be caused by injury that leaves fragments of bone or other material in the skin.

What are the major appendages of the

skin?• Sweat glands• Sebaceous glands• Nerves• Hairs• NailsThey are any complex structure that assists the skin with its functions.

• What are the types of glands found in the skin?

• Sweat glands-sudoriferous– Apocrine- produce sweat plus a milky or yellowish substance composed of fat and protein.• Found in the arm pits and genitalia• Thought to be scent glands.• Inactive until puberty• Secrete chemicals called pheromones• Secretions readily broken down by bacteria-causes body odor

– Eccrine-found mostly on skin of armpits, forehead, palms, soles• Eccrine sweat composed mainly of water, many chemicals causing food odor leak out of body by eccrine sweat.(Most numerous)

• These secretions also cause body odor due to bacterial breakdown

– Ceruminous- produce cerumen (ear wax)• Apocrine gland• Large glands found in skin lining the ear canal

Types of Glands (cont’d)

• Sebaceous glands- oil glands (sebum) - Holocrine-means they secret whole dead cells – Softens and lubricates hair and skin– Produce and store a lot of fat– Once secreted in the gland ducts they burst open and die

– Releases fats on the surface of skin as an oily secretion.

– Slows water loss and kills bacteria– Secrete sebum into hair follicles

Nerves in the Integumentary system

Sensory receptors- nerve cells found in all skin layers

are critical for the skin’s ability to communicate information from the

environment to the body.

Types of Sensory ReceptorsFree nerve endings-numerous pain-sensing

structures found in the lower part of the

epidermis. detect chemicals associated with

tissue damage and bleeding.

Merkel cells- nerves sensitive to gentle physical

sensations found in small numbers in the

stratum germinativum.-most numerous in

fingertipsMeissner’s corpuscles-(tactile) nerves found

in upper region of dermis (in dermal papilla).

Responds to pressure. They are nerve receptors surrounded

by club-shaped pile of connective tissues.

Nerves continued

Pacinian corpuscles (Lamellated)-look like onions, located in deeper parts

of the hypodermis, respond to hard pressureRuffini receptors-nerves that respond to pressure or constant touch

Krause end bulbs-nerves found in the mucous membrane of the mouth

sensitive to touchFree nerve

Pacinian

Krause

Meissner

Ruffini

receptor endings function location

Different types respond Various types found

to mechanical, thermal,throughout the skin

or noxious stimulation

Free nerve endings

Messiner’s

Responds to vibrationsand pressure

Dermis of Skin(Dermal Papilla)

Pacinian

Responds to hard pressureDeeper part of hypodermisin both hairy and glabrous skin

receptor endings function location

Responds to pressure Dermis of both or touchhairy or glabrous

(smooth) skin.

Ruffini

Krause

Responds to pressure or touch

Lips, tongue, and genitals

Merkel

In the stratumgerminativum Touch receptors

What are the parts of nails?• A nail is a scale like modification of the

epidermis• Made of tightly compressed keratinized cells• Useful tools to pick up small objects or scratch an itch.

Nails will grow back if removed as long as the nail root and skin-nail folds are not damaged.

Parts of the nail-- Nail root-the area of nail where growth takes place. Skin-nail folds-a fold of hardened overlapping the base of a

fingernail or toenail. Nail body or matrix- is the fingernail or toenail. Lunula-the white half moon shape at the base of the nail body. Cuticle- an outgrowth of the skin-nail fold.

Why is hair useful?

• Senses insects that land on the skin.

• Hair on the head protects the head from a blow, sunlight and heat loss.

• Eyelashes shield the eye• Nose hairs filter the air

What are hairs?

• Modified stratum corneum formed by inward protrusion of epidermis called the hair follicle.

• Made of dead keratinized skin cells• Two parts shaft and root• Shaft has 3 layers of cells

– Medulla (central core)– Cortex (bulky layer)– Cuticle (heavily keratinized; protects hair)

Parts of the hair

• Hair follicle- buried in the hypodermis. Each hair grows from a follicle

• Hair papilla-the base of the hair follicle. Associated small blood vessels and a nerve.

• Hair shaft-the main part of the hair structure. • Most hair shafts are composed of two regions

– Outer hair cortex made dead, densely packed keratinized cells

– Hair cuticle-dried surface found on large hairs– Hair medulla-found inside the hair cortex--composed of

loosely arranged cells.• Keratin-gives a yellow color to hair• Melanocytes at base of the hair secrete the red, brown, and

black pigmentation• Differences in hair color are due to the amount and location of

melanin deposited in the cortex and medulla.

Accessory structures to the hair

• Arrector pili muscle• Sebaceous gland• Types of body hair• Vellus hair-fine body hair-chest, face, stomach• Terminal hair- hair on the head• Pubic hair- around the genitals • Lanugo- temporary fine body hair found on

fetuses and new born babies

Functions of the Integumentary System

• Protection• Acts as a barrier against three types of environmental

damage: • Chemical-any chemical including water that breaks down cells

or connections between cells Sweat, cerumen, and sebum help protect the skin from chemicals

• Mechanical- damage caused by any force that compresses, erodes, or stretches the skin. -shedding of stratum corneum reduces skin erosion, adipose helps absorb shocks, callus minimize compression damage.

• Microbial- damage caused by microorganisms on the skin. Microbes can produce destructive secretions in sebum and sweat. These secretions are kept in check by chemicals in sweat that assist beneficial bacteria-commensals.

• Commensal bacteria and yeast reduce the chance that harmful microorganisms will survive on your skin.

Functions of the Integumentary System

• Heat Regulation --Body’s ability to maintain a constant temperature.

• Special network of blood vessels expands and contracts to control body temperature.

• Evaporation of sweat lowers the body’s temperature

• Adipose tissue in the subcutaneous (hypodermis) keeps body from lsing too much heat.

Functions of the Integumentary System

• Sensations-Received stimuli from the environment.

• Sensory receptors permit the skin to detect cold, heat, injury, pressure, stretching, and touch.

• Waste Excretion-handled primarily by eccrine sweat glands.

• Eccrine waste products are urea, organic chemicals, and excess salt.

• Other functions-• Production of Vitamin D when exposed to

sunlight.

Burns to the Skin• Burns cause skin to lose its ability to maintain homeostasis.

• Burns can be caused by sunlight, cooking accidents, acids, bases, corrosive chemicals, electricity, and fires.

• First degree burns-involve superficial damage causing reddening and swelling of the skin. Usually only upper layers of the epidermis involved

• Second degree burns-damage to lower layers of epidermis and top layer of dermis. Blisters, reddening, swelling, fluid build up are indicators.

• Third degree burns-entire epidermis is charred or missing. Usually damage to dermis that can cause permanent nerve cell loss. Glands can be damaged. Adipose cells, muscle, and bone may be affected. Person is susceptible to dehydration, loss of body heat, and infection.

Aging is due to:• intrinsic factors• extrinsic factors

One’s lifestyle can accelerate aging.

Pathology can be categorized as:• degenerative• genetic• infectious

Wellness and Illness over the Life Span

Chapter 4 – The Skin and Its Parts

Pathology of the Integumentary SystemDegenerative skin disorders- due to progressive deterioration of tissue caused by continous injury from environmental and or physical stresses.

Solar lentigenes-freckles in people over 30 who overexpose their skin to sunlight or tanning beds.Dermatitis- an inflammation of the skin caused by an allergic reaction or

contact with an irritant.Skin cancer- has an underlying genetic component- called precancerous

genes. If these genes are damaged by sunlight or certain chemicals they can begin to divide abnormally.

Tumors not associated with cancerMoles- flat squamous -cell tumors containing melanocytesSkin tags- soft, colored, knob-shaped tumors that grow out of skinSeborrhoeic keratosis- black or brown growth on the face or body.Sebaceous hyperplasia- overgrowth of oil glands appear as small yellow bumps with an opening in the center.Syringomas- tumors of sweat gland ducts- appear as small lumps on the cheek or eyelids. Lipoma- fatty tumor under the skin.

Pathology of the Integumentary SystemGenetic Skin Disorders -result of mutations that diminish skin function and

structureAcne-believed to be stimulated by hormonal changes that cause overproduction sebum.Furuncle- (boil) inflammation of hair follicles that results in build up of cells and blood components.

Psoriasis- inflammation of the skin accompanied by an increase in skin cell production. Causes a build up of thick scales on the skin that appear red, swollen and warm. The affected skin is dry and itchy.

Vitiligo- (hypopigmentation) Micheal Jackson. Found in 1% of the population cause is unknown. Thought to be caused by an immune system attack on the melanocytes. Treated with vitamins and drugs that are activated by U-V light.Albinism- genetic disease in which there is no melanin production in the eyes, hair, or skin.Melasma- brown patches on both sides of the face. Distribution usually symmetrical. See on some pregnant women.

Types of Birthmarks

Port wine stains-looks like a spot of red wine spilled on the skin. It is due to abnormality of skin blood vessels

Affects less than 1% of populationSpider veins- describes another type of enlarged blood vessel condition of the skin.

Tend to see them in legs of older peopleStrawberrry hemangiomas

Summary

The skin is composed of three distinct layers: the epidermis, the dermis, and the hypodermis (subcutaneous)

It contains many appendages, including several kinds of glands, nerves, nails, and hair

The functions of the skin are: to protect the body from damage, help regulate body temperature, detect sensory cues, and assist in waste removal

Chapter 4 – The Skin and Its Parts