skin directed reading

Question 1

What is the structure of the skin?

Answer 1

The skin is the largest organ of the body. It covers an area of about 1.8m2 and accounts for 16% of body weight. The skin has 3 layers – the epidermis, dermis and hypodermis (subcutis).

Question 2

What is the epidermis’ main function?

Answer 2

• To replace damaged cells to maintain the skins protective properties. It does this by continually producing keratinocytes and pushing these cells up through the four layers of the epidermis until finally the cells are shed. (takes 28 days)
• Also produces melanin to product the body from UV radiation

Question 3

What does the epidermis consist of?

Answer 3

Keratinocytes with some Melanocytes (which produce the skins pigment, melanin) and Langerhans cells (involved in immune response

Question 4

What are the 4 layers of the epidermis?

Answer 4

1. Stratum Basale
2. Stratum Spinosum
3. Stratum Granulosum
4. Stratum Corneum

Question 5

What happens in the stratum basale?

Answer 5

Contains a single layer of keratinocytes cells. These cells are constantly undergoing cell division and push older cells up into the stratum spinosum. Melanocytes are found in the stratum basale and contain the pigment melanin. Melanin is a pigment that is produced when skin is exposed to sunlight. It absorbs the UV radiation found in sunlight to help protect the skin. Melanin is distributed to adjacent keratinocytes for skin coverage

Question 6

What happens in the stratum spinosum?

Answer 6

This layer anchors cells together by interlocking cytoplasmic processes. The cells are called prickle cells because of their appearance

Question 7

What happens in the stratum granulosum?

Answer 7

In this layer, cells undergo enzyme induced destruction loosing their nuclei and cytoplasmic organelles . This contains a lipidrich secretion which acts as the skins water sealant. Keratin is laid down further meshing of structures together.

Question 8

What happens in the stratum corneum?

Answer 8

This layer contains dead cells which are flattened cells filled with densely packed keratin (corneocytes). Corneocytes are shed from the skin.

Question 9

What is the dermis?

Answer 9

The dermis is located below the epidermis. Its function is to provide strength to the skin (by containing collagen and fibroblasts) but provide elasticity (contains elastin) to make the skin strong. In the dermis are specialised structures including sweat glands, hairs, sebaceous glands, smooth muscle (goose bumps), cuteaneous lymphatics and nerves.

Question 10

What is the hypodermis?

Answer 10

Contains nerves, blood supplies and fat. This layer cushions and insulates the tissue beneath the hypodermis

Question 11

What are the 4 functions of the skin?

Answer 11

1. Production of vitamin D
2. Acts as a sensory organ for touch, pain and temperature
3. Controls body temperature
4. The skin functions as a barrier to protect the tissue and organs

Question 12

How is vitamin D produced?

Answer 12

7-dehydrocholesterol in the skin produces vitamin D3 (cholecalciferol) in the presence of ultraviolet radiation in sunlight

Question 13

How else can vitamin D be obtained other than from sunlight?

Answer 13

Can be obtained in the GI tract from food like oily fish or eggs

Question 14

How is vitamin D3 converted into an active form of vitamin D?

Answer 14

Vitamin D3 is converted in calcidol in the liver and then hydroxylated to calcitriol in the kidney to produce an active form of vitamin D. Vitamin D raises plasma calcium levels by stimulating the intestinal epithelium to produce more carrier protein molecules for calcium transport.

Question 15

What can a lack of vitamin D lead to?

Answer 15

Lack of vitamin D can lead to inadequate calcium absorption and lack of deposition in bone, causing bone deformity in children (rickets) and bone pain and tenderness in adults (osteomalacia).

Question 16

What does the skin contain that detect information?

Answer 16

Sensory receptors - detect info from the skin surface and send information to the CNS via sensory neurones

Question 17

What are the different types of sensory receptors?

Answer 17

Sensory receptors called machanoreceptors which can detect light touch / deep pressure on the skin surface. Sensory receptors called thermoreceptors to detect warmth and cold; nociceptors respond to pain stimuli.

Question 18

What makes fingertips more sensitive?

Answer 18

Different parts of the skin have different numbers of sensory neurones. Large numbers of sensory neurones and overlapping sensory neurones make fingertips more sensitive.

Question 19

How does the skin control temperature?

Answer 19

• The skin contains special blood vessels (capillaries) to control body temperature by altering blood circulation. In hot weather the capillaries fully open, increasing blood flow (vasodilation) and heat loss occurs at the skin surface. In cold weather the capillaries close (vasoconstriction) reducing skin blood circulation and minimising heat loss.
• Sweat glands in the skin actively secrete water and salt when the internal body temperature increases above 37°C., this cools the body.

Question 20

What feature of the skin in newborns helps protect against the cold?

Answer 20

The skin is a weak insulator. Under the skin in newborns is brown fat. The mitochrondria oxidise brown fat to produce more heat than ATP, protecting against the cold.

Question 21

What does the skin protect the tissue and organs from?

Answer 21

• Bacteria and toxins
• Dehydration
• UV radiation
• Mechanical damage and trauma

Question 22

What produces a corny hard waterproof protective outer layer of the skin?

Answer 22

The outer epidermal layer consists mainly of keratinocytes, which are constantly being formed in the stratum basale and push up older dying cells. This produces a corny hard waterproof out protective layer

Question 23

How does the body create an immune response ?

Answer 23

• Once the epidermis is damaged, the skin contains mechanisms to start an immune response by recognising foreign matter and initiate inflammatory response.
• For the body to make an immune response to a foreign particle, the particle must be processed by an ‘antigen presenting cell’ to active T and B cells. The Langerhans Cells in the epidermis ingests the foreign particle and presents it to the immune system to active an immune response.

Question 24

What are the 4 stages in the skin healing process?

Answer 24

1. Clot formation (haemostatis)
2. Inflammatory process (inflammatory phase)
3. Dermal repair with epidermal regeneration (proliferative phase)
4. Scar formation (maturation phase)

Question 25

How does the skin heal if the injury only affects the epidermis?

Answer 25

If the injury affects only the epidermis (e.g. burn or graze), the keratinocytes in the stratum basale, break from the basement membrane . The cells enlarge and move across the wound until they meet another cell. This process stops due to contact inhibition – growth stops once the cell touches another cell.

Question 26

What is Haemostasis?

Answer 26

In this phase the priority is to stop bleeding . Platelets in the blood recognise the exposed collagen from the exposed dermis and the platelets become sticky and release Thromboxane A2 (activated platelets). This causes platelets to group together (aggregate) with the collagen in the vessel wall, forming a temporary plug. The activated platelets release serotonin which reduces the blood supply around the wound. The plug and vasoconstriction minimises blood loss from the injury.

Question 27

In haemeostasis, what do the damaged tissue release?

Answer 27

Thromboplastin. This combines with calcium to produce insoluble fibrin at the end of the clotting cascade. The fibrin combines with the platelet aggregate, trapping red blood cells to produce a clot. If this clot is left uncovered it dries out and forms a scab

Question 28

Describe what happens in the inflammatory phase

Answer 28

This stage cleans the wound to prepare for healing. The inflammatory response is triggered by physical injury but is progressed by immune and chemical processes

Question 29

What happens upon injury in the inflammatory phase?

Answer 29

On injury, Langerhans cells in tissues are activated and release inflammatory mediators. The inflammatory mediator bradykinin increases pain at the site. Leukotrines increase blood flow at the wound which causes the skin to become warm. There is an increase in vascular permeability at the capillaries (giving the wound a red appearance), allowing white blood cells to move into the wound from the blood. The movement of plasma from the capillaries gives the wound a swollen appearance. The white blood cells produce neutrophils which digest bacteria and particles in the wound. Monocytes then move to the wound maturing into macrophages which continue the wound cleaning process throughout healing

Question 30

What happens in the proliferative stage?

Answer 30

Healing stage, the dermis is repaired and the epidermis is regenerated. The macrophages present in the wound commence the proliferative phase. If the wound has low oxygen levels, macrophages release angiogenic growth factors to develop new blood vessels. These blood vessels bring oxygen and nutrients to the cells in the wound. The macrophage releases chemicals to attract granulation tissue to the wound to produce new connective tissue. Platelet derived growth factors and macrophages activate fibroblasts which grow and divide to produce a collagen network to strengthen the wound. Specialised fibroblasts (myofibroblasts) act like a muscle and can contract the edges of the wound, closing the wound. Epithelial cells move over the top of moist granulation tissue. Once the cells meet at the top of the wound they stop due to contact inhibition.

Question 31

What happens in the maturation stage?

Answer 31

This phase forms a scar. It can take up to 2 years to form a scar. Collagen is re-aligned to improve strength. Collagen strands pull the wound inwards. Extra blood vessels close.

Question 32

What intrinsic factors affect the healing process?

Answer 32

1. patient nutrition
2. skin perfusion
3. age
4. weight
5. co-morbidity including medication
6. smoking

Question 33

What extrinsic factors affect the healing process?

Answer 33

1. moist wound
2. wound temperature at 37 degrees
3. tissue oxygenation
4. pH
5. infection delays wound healing
6. clean wound surface