Skin

Question 1

Integument

Answer 1

term used to describe skin and its associated structures; hair, nails, glands. The integument is considered an organ because of its important and complex role.

Question 2

How much does skin weigh?

Answer 2

typically 4 - 5 kg (9-11 lbs.)

the largest organ of the body

Question 3

major roles of the skin

Answer 3

1. Protection
2. Temperature regulation
3. Sensory perception
4. Metabolism
5. Blood reservoir
6. Waste disposal

Question 4

what are the three protective barriers of the skin?

Answer 4

Physical barrier– cells on the surface of skin are wear resistant, and waterproof. Skin connective tissue is durable and flexible (leather is skin).

Chemical barrier - skin secretions are acidic and retard bacterial growth. Skin pigment (melanin) shields the body from ultra-violet radiation.

Biological barrier – cells of the immune system live in skin identifying and destroying microrganisms (antigens) that try to invade the skin. These cells are effective against; viruses, bacteria, fungi and protozoa.

Question 5

What happens when the body is too hot?

Answer 5

blood flow to the skin increases so heat is lost by radiation

sweat is produced and cooling occurs by evaporation

Up to 12L of body fluid can be lost per day in sweat.

Question 6

What happens when the body is too cold?

Answer 6

blood flow to the skin is decreased and heat is retained

sweat glands are inactivated

muscles shiver to generate heat

Question 7

Blood Reservoir

Answer 7

The skin has an extensive blood supply. It can hold about 5% of the body’s entire blood volume.

This volume can decrease e.g diverted to other body organs if required - to working muscles

Or it can increase, e.g. when the body is hot to cool it down (“red faced”).

Question 8

excretions

Answer 8

Small amounts of nitrogen containing wastes (ammonia, urea, and uric acid) are removed from the body in sweat (most is lost in the urine).

Sweating also loses water and salts that have to be replaced by dietary intake.

Question 9

3 main layers of the skin

Answer 9

The outer Epidermis, inner Dermis and hypodermis

Question 10

hypodermis

Answer 10

Anchors the skin to underlying structures and has fat stores that act as shock absorber and insulator.

Question 11

how thick is skin?

Answer 11

1-2 mm thick, though can be thicker, e.g. on the back where it can be up to 6mm.

Question 12

epidermis

Answer 12

the smaller component of skin. It is an epithelial layer made solely of cells

Question 13

4 layers of cells

Answer 13

Stratum Corneum

Stratum Granulosum

Stratum Spinosum

Stratum Basale

On the fingertips, palms and soles of the feet (high wear areas) there is an extra layer (“thick skin”), this layer is the Stratum lucidum.

Question 14

Non-keratinized Skin

Answer 14

the layers are less clear, the cells do not accumulate keratin and importantly the cells at the surface are still alive when they are lost.

This type of skin is found where there is a need for movement of molecules across the skin.

Question 15

Keratinocytes

Answer 15

The main cell of the epidermis.

Millions of stratum corneum cells are lost from the skin surface every day and have to be replaced.

New cells are made constantly by cell division (mitosis) of the stratum basale

Question 16

how often are cells of the epidermis replaced?

Answer 16

every 25-45 days.

Question 17

what happens when new cells move to the surface?

Answer 17

they produce keratin and glycoproteins that give the cells wear resistance and waterproofing.

By the time the cells reach the surface they are; flat, full of keratin and dead.

Question 18

Langerhans Cells

Answer 18

Bone marrow derived cells that migrate to the epidermis.

These cells are macrophages and form part of the immune system that protects the skin from bacterial and viral infection.

Question 19

Merkel Cells

Answer 19

These cells are few in number and found at the epidermal /dermal junction.

Each cell is associated with a disc like sensory nerve ending.

The combination of cell and nerve forms a light touch receptor called a Merkel Disc.

Question 20

The Dermis

Answer 20

the major component of skin. It is strong and flexible

Question 21

What is the dermis made of?

Answer 21

Cells (not many)

Fibres (lots) – collagen and elastin

Matrix - a gel like material that fills in the spaces.

Collagen fibres are long protein molecules that are incredibly strong.

A rich system of blood vessels

Nerves

Sensory – touch and temperature detectors etc.

Motor – sending instructions to the structures within the dermis.

e.g. to smooth muscle cells around blood vessels that adjust blood flow

Question 22

Sweat glands (sudiferous)

Answer 22

Found all over the body except at the nipples and parts of the external genitalia.

Question 23

2 major types of sweat glands

Answer 23

Eccrine sweat glands

Apocrine sweat glands

Question 24

Eccrine sweat glands

Answer 24

Most numerous, particularly on the palms, soles of the feet, and forehead.

Question 25

Apocrine sweat glands

Answer 25

Found mainly in the axillary (arm pit) and anogenital areas. These glands empty into hair follicles. Do not begin secreting until puberty (thought to secrete your pheramones). Bacteria on skin decompose these substances to produce B.O.

Question 26

Sebaceous (oil) Glands

Answer 26

found all over the body except on the palms and soles of the feet and secrete an oil called sebum

Question 27

Sebum

Answer 27

is bactericidal and helps reduce the number of bacteria living on the surface of the skin.

Question 28

what are the glands are regulated by?

Answer 28

hormones and while relatively inactive in childhood become activate in both sexes during puberty (acne).

Question 29

When are the Sebaceous glands very active?

Answer 29

during the last few months of foetal development. Their secretion mixed with shed epidermal cells form a protective superficial layer – the vernix caseosa. Coats the skin surface. But stops After a birth.

Question 30

Hair

Answer 30

produced by follicles that run from the skin surface.

Question 31

what is found in hair?

Answer 31

Hard keratin - is tougher and more durable than that found in epidermal layers and does not flake.

Question 32

what is also found in hair?

Answer 32

a tough keratin protein

Question 33

hair follicle

Answer 33

anchors each hair into the skin.

Question 34

hair bulb

Answer 34

forms the base of the hair follicle. Blood vessels nourish the cells in the hair bulb, and deliver hormones that modify hair growth and structure at different times of life.

Question 35

Nails

Answer 35

scalelike modification of the epidermis made of hard keratin in the matrix deep in the lunula region deep into the dermis. Useful to tools to pick up small objects. They have hard keratin. Deepest portion of the nail roots lies very close to the bone of the fingertip. Underlying blood vessels give the nail is characteristic pink colour. Changes in nail appearance can help diagnose certain condition. For example, Spoon nail might indicate iron deficiency.