L E A R N I N G O U T C O M E A 4

The Skin

A4 – The Skin

Student Achievement Indicators:

Describe the make-up, function and location of epithelial tissues.

Identify the structure of skin and identify accessory structures

Epithelial Tissue

Forms large continuous sheets.

Helps form skin and covers the entire outer surface of the body.

Sheets of epithelium also line most inner cavities such as the mouth, respiratory tract and reproductive tract.

The function of this tissue to protect, absorb, filter and secrete.

Examples of Epithelial Tissue

Example – skin protects tissue from UV light and from disease-causing bacterial.

Example – epithelial tissue in the digestive system absorbs nutrients and water into the cells, and secretes wastes from the cells.

Example – glands secrete enzymes and hormones.

Epithelial Tissue in the Small Intestine

Types of Epithelial Tissue

Epithelial tissue is divided into two groups:

simple

stratified

Simple Epithelial Tissue

Simple Squamous

Present in the walls of blood vessels, kidneys, and in the alveoli (air sacs of the lungs).

Permits the exchange of nutrients and wastes.

Allows the diffusion of oxygen and carbon dioxide.

Filtration of water and electrolytes.

Simple Squamous Epithelium

Simple Epithelial Tissue

Simple Cuboidal

Present in the lining of the kidney tubes, and in various glands.

Example – pancreas, thyroid, salivary glands

Allows absorption of water and electrolytes.

Secretes enzymes and hormones.

Simple Cuboidal

Simple Epithelial Tissue

Simple Columnar

Present in the digestive tract.

Function in protection, absorption and secretion of digestive enzymes.

Often contain goblet cells which secrete mucus.

Simple Columnar Cells

Goblet Cells

Arrows – secrete mucus

Pseudostratified Columnar

Line respiratory tract and reproductive tubes (fallopian tubes).

Function in protection and secretion.

Cleans respiratory system

Sweeps egg to uterus

Pseudostratified Columnar

Stratified Epithelial Tissue

Stratified Squamous

Outer layer of skin

Also found lining the mouth, esophagus and female reproductive organs.

Function to protect the body from invading microorganisms, and helps prevent friction.

Stratified Squamous

Stratified Epithelial Tissue

Transitional

Found in the urinary bladder.

Allows the expansion of an organ without tearing.

Transitional

Characteristics of Epithelial Tissue

Forms continuous sheets; cells fit together like tiles.

Has two surfaces:

Unattached/free – like the surface of outer skin or the inner lining of the mouth

Under surface – attached to basement membrane; which is a thin layer that anchors the epithelium to underlying structures.

Characteristics of Epithelial Tissue

Does not have own blood supply; depends on blood from underlying connective tissue.

Epithelial tissue is so well nourished from the connective tissue.

Classified based on shape and number of layers.

Cells the make-up Epithelial Tissue

Squamous epithelial cells - are think and flat and look like fish scales

Cells the make-up Epithelial Tissue

Cuboidal cells – are cube-liked and look like dice.

Cells the make-up Epithelial Tissue

Columnar cells – are tall and narrow cells that look like columns.

Epithelial Tissue

Epithelial cells are arranged in either a single layer or multiple layers.

Simple epithelium – is a single layer

Stratified epithelium – is two or more layers

Shape and number of layers is used to describe epithelial tissue.

Example – simple squamous epithelium is a single layer of thin flat cells.

Simple Epithelia

Thin and function in the movement, or transport of various substances across the membrane from one body compartment to others.

Simple squamous epithelium is a single layer of squamous cells with an underlying basement membrane.

Found where substances need to diffuse or filtrate quickly.

Example – walls of capillaries diffuse oxygen to tissues and collect wastes.

Example – walls of alveoli (air sacs in lungs)

Simple Cuboidal Epithelium

Is a single layer of cuboidal cells resting on a basement membrane.

Most often found in glands, and in kidney tubules.

Function to transport and secrete various substances.

Simple Cuboidal Epithelium

Simple Columnar Epithelium

Single layer of columnar cells resting on a basement membrane.

These tall tightly packed cells line the digestive tract and play a major role in the absorption of food.

A lubricating mucus is produced by goblet cells; that are present in columnar epithelium.

Simple Columnar Epithelium

Pseudostratified Columnar Epithelium

Single layer of columnar cells.

Cells are irregularly shaped; so they appear multi-layered.

Also function in absorption and secretion.

Stratified Epithlia

Multi-layered and are stronger than simple epithelial tissue.

Function in protection.

Protect tissues that are exposed everyday.

Example – mouth, esophagus, skin

Transitional Epithelium

Found primarily in organs that need to stretch.

Example – the bladder

Cells can slide past one another when stretched.

The tissue appears stratified when the urinary bladder is empty, and as the bladder stretched the tissue appears simple.

Glandular Epithelial

Gland – is made up of one or more cells that secrete a particular substance.

Most glandular tissue is composed of simple cuboidal cells.

There are two types of glands:

Exocrine

Endocrine

Exocrine Glands

Have ducts or tiny tubes into which exocrine secretions are released before reaching body surfaces and/or cavities.

Examples of exocrine secretions are mucus, sweat, saliva and digestive enzymes.

Ducts carry exocrine secretions outside the body.

Example - sweat

Exocrine Glands

Endocrine Glands

Secrete hormones; such as thyroid hormones.

Do not have ducts; so these glands are often known as ductless glands.

Hormones are secreted directly into the blood.

Blood carries hormones.

Endocrine Glands

Functions of the Skin

Keeps harmful substances of the body and helps retain water and electrolytes.

Protects the internal structures and organs from injury. The skin acts as a physical barrier and its acidic secretions

discourage the growth of pathogens on the surface.

Performs the excretory function, and secretes water salts and small amount of waste such as urea.

Functions of the Skin

Acts as a gland by synthesizing and secreting Vitamin D. Skins cells contain a molecules that is converted to vitamin D

when exposed to sunlight

Vitamin D plays a role in the utilization of calcium by bone tissue.

Performs a sensory role by housing the sensory recept0rs for touch, pressure, pain and temperature.

Helps regulate body temperature.

Structures of the Skin

The skin is composed of two layers:

Epidermis (outer layer)

Dermis (inner layer)

Epidermis

Is the thin outer layer of the skin.

Composed of stratified squamous epithelium.

Is avascular, which means it has no blood supply of its own.

Oxygen and nutrients diffuse into the lower epidermis from the rich blood supply of the underlying dermis.

The epidermis can be divided into five layers.

The two deeper layers are known as the stratum germinativum and the other more superficial layers are known as the stratum corneum.

Epidermis

Stratum germinativum

Lies close to the dermis and has a rich supply of blood.

The cells in this layer are continuously dividing.

As the cells divide, they push the older cells up toward the surface of the epithelium.

As cells move away from the dermis two changes take place: Move away from their source of nourishment

Undergo the process of keratinization

Epidermis

Keratinization – is the process where the tough protein keratin is deposited within in the cell.

Keratin also waterproofs the cells

Epidermis

Stratum corneum

Is the surface layer of the epidermis

Composed of about 30 layers of dead, flattened, keratinized cells.

Dead cells are continuously sloughed off through wear and tear.

These cells are replaced by other cells that are constantly moving up from deeper layers.

Dermis

Dermis

Dermis

AKA true skin

Located under the epidermis and is thicker than the epidermis.

The dermis is composed of dense, fibrous connective tissue and contains numbers collagenous and elastic fibers which are surrounded by a gel like substance

Fibers make the dermis strong and stretchable.

The thickness of the epidermis and dermis varies according to location in the body.

Dermis

Example – soles of your feet vs. inner arm

Dermis also contains blood vessels, nervous tissue and some muscle tissue.

Many of the nerves have specialized endings called sensory receptors which detect pain, temperature, pressure and touch.

Accessory Structures

Structures such as hair, nails and certain glands are embedded in the dermis, alth0ugh they are formed initially at the epidermis.

Subcutaneous Layer

Dermis lies above the subcutaneous layer.

The layer is not considered part of the skin, because it lies beneath the skin.

Composed primarily of loose connective and adipose tissue.

Has two function:

Helps insulate the body from extreme temperature changes in the external environment.

Anchors the skin to underlying structures.

Few areas in the body do not have a subcutaneous area and the skin anchors directly the bone.

Example – skin on knuckles

Hair

Has specific functions:

Eyelashes and eyebrows function to protect he eyes from dust and perspiration.

Nasal hairs trap dust and prevent it from being inhaled into the lungs

Scalp hair helps keep us warm

Hair growth is influenced by estrogen and testosterone (sex hormones)

Puberty increase hair growth due to increase testosterone level.

Hair

Can be divided into the above skin portion which is know as the shaft and the root which is embedded in the dermis.

Each hair arises from a group of epidermal cells that penetrate or project down into the dermis.

Downward extension of epithelial cells form the hair follicle.

Hair

Epidermal cells at he base of the hair follicle receive a rich supply of blood from the dermal blood vessels.

As these cells divide and grow, the older cells are pushed toward the surface o the skin.

As they move away form their source of nourishment, the cells divide.

Hair becomes keratinized.

Hair that we brush is composed of keratinized cells.

Hair Follicle

Hair

Color is controlled be genetics and is determined by the type and amount of melanin.

Melanin – is pigment released by melanocytes (melanin cells) in the skin

An abundance of melanin produces dark hair, whereas less melanin produced light hair.

With age the melanocytes become less active, and the absence of melanin produced white hair.

Gray hair is due to a mixture of pigmented and non-pigmented hair.

Red hair is due to a modified type of melanin that contains iron

Melanocyte

Hair

A round hair shaft produced straight hair.

An oval hair shaft produce wavy hair.

Curly hair is a result of a flat hair shaft.

A perm flattens the hair shaft so hair will appear curly.

Round Hair Shaft

Oval Hair Shaft

How does hair stand on end?

Attached to hair follicle is a bundle of smooth mucle cells called the errector pilli muscles.

Contractions of this muscle causes the hair to stand on end.

When frightened or cold the brain sends a signal along the nerves to these muscles causing this muscle to contract.

When cold hair also stand on end in an attempt to trap heat.

Contraction of errector pilli muscles helps generate heat within the body.

Errector Pilli Muscles

Nails

Are think plates of stratified squamous epithelial cells that contain a very hard form of keratin.

Nails are found on the distal ends of the fingers and toes and protect these areas from injury.

Each nail is composed of a free edge and nail body and a nail root.

The cells of the nail body develop and are keratinized in the nail root.

Nails

Glands

There are two major exocrine glands associated with skin:

Sebaceous gland

Sweat glands

Sebaceous Glands

Aka oil glands

Are associated with hair follicles are found in all areas of the body that have hair.

Secrete and oily substance called sebum that flows in the hair follicle and then out onto the surface of the skin.

A small number of sebaceous glands open directly onto the surface of the skin

Sebaceous Glands

Sebum lubricates and helps waterproof the hair and skin.

Sebum also inhibits the growth of bacteria on the surface of the skin.

With aging sebum production gradually decreases, this accounts for dry skin and brittle hair in older persons.

If a gland becomes blocked with sebum or other debris and is exposed to air, it forms a black head.

When a blocked gland become infected it is known as a pimple.

Sebaceous Gland

Sebaceous Gland

Formation of a Pimple

Sweat Glands

AKA sudoriferous glands

Located in the dermis and subcutaneous layers.

Found in all regions of skin and are particularly abundant on the palms and soles.

Secrete sweat.

There are two types of sweat glands:

Apocrine

Eccrine

Apocrine Glands

Are associated with hair follicles found in the armpits and genital area.

Respond to emotional stress and become active when a person is frightened upset or in pain.

Development of this glands is stimulated by sex hormone they are more active during puberty.

Sweat produced by these glands does not have a strong odour.

If sweat accumulated on the skin broken down by bacterial and strong odour is formed

Apocrine Glands

Eccrine Glands

Eccrine glands are more numerous and widely distributed on the body.

Especially abundant on the forehead, upper lip palms and soles.

Not associated with hair follicles.

Function in temperature regulation.

When sweat evaporates form the skin surface heat is lost.

Eccrine Glands

These glands cause you to sweat during warm weather and exercise.

Function entire life

Eccrine secretions is composed of water and salt.

Modified Sweat Glands

Mammary glands – secrete milk

Ceruminous glands - are found in the external auditory canal of the ear secret cerumen or ear wax.

Functions to repel insect and trap foreign materials.

What Happens when Skin is Burned?

Burns are classified according to the depth of the burn and the extend of the surface area burned.

On the basis of depth, burns are classified ad either partial-thickness burns or full-thickness burns.

Partial thickness burns are further divided into first, second and third degree burns.

A first degree burn is red, painful and slightly swollen.

Only the epidermis is involved

Example - sunburn

A second degree burn involve damage to both the epidermis and dermis.

What Happens when Skin is Burned?

Symptoms include redness pain, edema and blister formation if the burn in limited in the dermis area.

If there is greater damage to the dermis the skin may appear red tan or white.

Full-thickness burns are called third degree burns. Burn is severe to both the epidermis and dermis which are

destroyed often with additional destruction to the deeper underlying layer.

What Happens when Skin is Burned?

Third degree burns are painless because sensory receptors have been destroyed.

Burns may appear white than brown black or deep cherry red.

The body surface is divided into 9 regions the extent of the burn injury is based on this. Head and neck = 9% of total body surface

Each upper limb = 9%

Each lower limb = 18%.

First Degree Burn

Second Degree Burn

Third Degree Burn