8/13/2019 skin 2012

1/21

Gerry Lennon

8/13/2019 skin 2012

2/21

Learning Outcomes

1. Describe the layers of the skin

2. Describe the organisation of the cutaneous

circulation

3. Identify the structures found within the skin and

describe their function

4. Describe the role of the skin in protection, fluidbalance, thermoregulation and sensation

8/13/2019 skin 2012

3/21

Skin

Also called the Integumentary System which meanscovering,

Includes the skin, sweat and oil glands, hair and nails

The skin is the largest organ in the body

Made up of 3 layers;

Epidermis (outer surface)

Dermis (just below epidermis)

Subcutaneous Layer (FAT)

8/13/2019 skin 2012

4/21

Functions

1. Regulates body temperature more detail later.....

2. Protection physical barrier against infection, drying

out , plus has melanin protection from UV rays

3. Sensation lots of receptors in skin and merkel cells

for touch4. Excretion water, salts & urea

5. Immunity provides non-specific immunity, lots of

white blood cells and immune system cells

6. Blood reservoir can divert to internal organs when

needed

7. Synthesis of Vitamin D sunlight converts cholesterol

Vit D

8/13/2019 skin 2012

5/21

8/13/2019 skin 2012

6/21

Skin Structure with Fibres

8/13/2019 skin 2012

7/21

B:

C:

L1:

L2:

L3:

A:

Figure 1. The skin

Skin Structure

Indicate where you think the arteries, veins and nerves are situatedWhich layer is are the melanocyte cells situated?Point to the papillary layer and explain the relevance of its wave appearance

8/13/2019 skin 2012

8/21

B:

C:

L1:

L2:

L3:

A:

Figure 1. The skin

Skin Structure

Hair Shaft

Sebacous Oil Gland

Sweat Gland

Epidermis

Dermis

SubcutaneousTissue

Errector pillimuscle

8/13/2019 skin 2012

9/21

The Epidermis

The outermost layer The epidermis is composed

of stratified squamousepitheliumwhich begins

at the deepest germinativelayer and gradually movestowards the surfaceundergoing change as it

does so This area has no nerve

endings or blood vesselsbut deeper layers are

bathed in interstitial fluid

8/13/2019 skin 2012

10/21

This picture

is toillustratethe detail ofthe simpleeptiheliumthis detailis notrequired forHAPmoduleoutcomes

Epidermis-

Is 4 or 5 layersthick dependingon location

8/13/2019 skin 2012

11/21

Maintenance of the epidermis isthrough three processes:

1. Continual cell division in thedeeper layers with cells beingpushed to the surface

2. Effective keratinisationof the

cells approaching the surface3. Then shedding of the

keratinised cells from thesurface (desquamation!)

The renewal process is mostefficient during childhood anddeclines as we get older. - thishas obvious implications forwound healing in different age

groups;

Epidermis

The outermost layer of

the epidermis isknown as the StratumCorneum because itprovides the toughouter coating of the

skin.

8/13/2019 skin 2012

12/21

As epidermal cells become exfoliated, they maycontinue around us in the form of dust;

The surface of the epidermis is also uneven, with

ridges that create an individuals fingerprint; These ridges are created by cells within the dermis

called papillae.

The purpose of these ridges is thought to aid nutrition

of epidermal cells and prevent the dermis andepidermis shearing apart.

Epidermis

8/13/2019 skin 2012

13/21

Dermis

The dermis is the inner layer of the skin, oftenreferred to as true skin;

This is essentially a connective tissue containing:

COLLAGEN, ELASTINANDRETICULARFIBRES* Fibroblasts - which make the CT fibres

Blood vessels, lymph vessels and nerve endings;

*The arrangement of these fibres gives rise to Cleavage lines(also known as Langar lines), which are the natural foldsand creases of the skin.

8/13/2019 skin 2012

14/21

Sebaceous glands Abundant on the face, neck, scalp, and back.

Secrete SEBUM - a fatty substance containingcholesterol and lipids

Secreted onto hair follicles or directly on skin

sruface Sebum keeps hair and skin supple and acts as an

anti bacterial and anti fungal waterproofingbarrier.

The activity of sebaceous glands increases duringpuberty and is low at the extremes of age.

8/13/2019 skin 2012

15/21

Sweat Glands

SWEAT = water , salts and waste products eg. urea anduric acid

Acidic to prevents bacterial growth.

Lots found on palms, soles of feet and the forehead

MAJOR

TEMPERATURE

REGULATION

ROLE

Controlled by the autonomic nervous system (ANS)

and therefore NOT CONSCIOUS CONTROL

Sweat glands in axillary and genital areas producessweat with proteins and fatty acids these are notinvolved in temperature control

Ceruminous glands of external ear canal andincludes mammary glands

8/13/2019 skin 2012

16/21

Hair follicles and Temperature Regulation

A down growth of

epidermal cells into thedermis.

The bulb is a cluster of cellsat the base of follicle

The hair is formed by thecell division at the bulb andthen cells move upwards

where they die and then

become keratinised; The area of the hair above

the skin is known as theshaftand the remainder isthe root.

Associated with the hair follicles aresmall bundles of involuntarymuscles.

Contraction of these muscles makesthe hair erect and raises the skinaround the hair to form goosebumps.Hair TRAPS WARM AIR and

important in thermoregulation

8/13/2019 skin 2012

17/21

Blood supply

The epidermis has no blood supply and obtainsoxygen and nutrients from interstitial fluid in the

papillae of the dermis. (look at diagram!) Sweat glands, sebaceous glands, hair follicles and

the dermis are supplied by a fine network ofarterioles and capillary branches within the

dermis.(look at colour diagram in your book andcheck you have these labelled in your diagram)

8/13/2019 skin 2012

18/21

Sensory nerve endings

Skin contains the different sensory receptors that areable to differentiate between the touch of a feather toextremes of temperature.

Within the dermis are nerve endings which are

sensitive to touch, temperature, pain and pressure. Merkel cells are important touch sensation find

these on your diagram

The information gathered from these nerve endings is

relayed via the spinal cord to the brain where thesesensations are perceived and responded to as needed.

8/13/2019 skin 2012

19/21

Skin pigmentation

This is due to the presence or absence of three factors:1. Haemoglobin creates pink colour of caucasian skin

2. Melanin brown / black pigment produced byepidermal melanocytes creates differences in skin

colour, including freckles and changes associatedwith a tan. Melanin also provides some protectionfrom the suns ultra violet rays.

3. Carotene yellow orange pigments which combine

with melanin to create an oriental appearance.

8/13/2019 skin 2012

20/21

Waterproofing

The skin forms a waterproof layer which preventsexcessive water loss or entry. The sebum acts like awaxed jacket. If this barrier is breached as in the caseof severe burns - the resulting fluid loss results in

hypovolaemic shock. The fluid replacement therapy ofburns patients is calculated according to percentage ofbody area affected.

8/13/2019 skin 2012

21/21

Hair and Nails

Function is protection - eyelashes, nasal, ears.Hair is not so important for insulation as in otheranimals. Hair colour is determined by theamounts of different types of melanin

Nails - saclike modification of the epidermis.Normally appears pink due to the rich bed ofcapillaries in the underlying dermis. Like hair,nails contain hard keratin.