Lecture 1 - the skin

Question 1

What are the functions of the skin?

Answer 1

The skin act as a self-repairing barrier that prevents ingress of chemicals and microorganisms whilst regulating heat and water loss. The other functions are cutaneous sensation, metabolic functions such as synthesis of vitamin D from modified cholesterol molecules and a blood reservoir( 5% of entire blood volume)

Question 2

Describe the structure of the skin.

Answer 2

The skin is 3 parts, the epidermis, the dermis and the subcutaneous tissue. The epidermis consists of the stratum corneum, stratum granulosum, stratum spinosum and the stratum basale. The dermis consist of sweat duct, sebaceous gland, sweat gland, hair follicle and an arrector pilli muscle. The subcutaneous tissue consists of the blood vessels and the fat lobules.

Question 3

Give a brief explanation of the proliferation fo the stratum corneum.

Answer 3

The basal cells(stratum basale) divide, migrate outward, differentiate, flatten to form the stratum corneum. This takes about 14 days then another 14 days through the statum corneum. The skin replaces itself every 28 days.

Question 4

Give a brief summary of the keratinocyte.

Answer 4

The keratinocytes which produces keratin. Keratin is a fibrous protein which give the epidermis its protective properties. The keratinocytes arise from the basal layer, they undergo division until they reaches the surface where they are dead, keratin filled scale structures. The keratin production is increased on friction prone areas like hands and feets.

Question 5

What does a melanocyte does.

Answer 5

A melanocyte synthesises the pigment, melanin. The melanin is taken up by the keratinocytes to protect their nucleus from damaging effect of the uv radiation.

Question 6

What does a Merkel cell do.

Answer 6

A merkel cell act as a sensory receptor to touch. The merkel cells are low abundance cells linked to disk like sensory nerve ending..

Question 7

What does a Langerhan’s cell do?

Answer 7

Langerhan’s cell are dendritic cells that arise from the bone marrow and migrate to the epidermis. They process microbial antigens to become antigen presenting cells.

Question 8

Describe the structure of the dermis.

Answer 8

The dermis makes up the bulk of the skin and it is made of fibrous connective tissue. It is richly supplied with nerve fibres, blood vessels and lymphatic vessels.
It is normally divided into 2 layers know as the reticular and the papillary layer. The papillary layer normally form the dermal papillae to produce structures such as nipple and ridges( fingerprint) The reticular layer accounts for 80% of the dermis. The collagen fibres in the reticular layer provide it with its strength and resiliency.

Question 9

Name the different appendages of the skin.

Answer 9

1. Sebaceous glands
2. Hair
3. Sweat glands
4. Hair follicles
5. Nail

Question 10

Give a brief summary of the role of sweat glands and their structure.

Answer 10

Every individual has over 2.5 million of sweat glands. There are two types of sweat glands; eccrine and apocrine. Eccrine sweat glands are simple, coiled tubular glands. They secrete sweat which is composed of 99% water, some salt, vitamin c, some antibodies, metabolic wastes and lactic acid. The sweat is secreted into the duct which lead to the surface of the skin. This is regulated by the autonomous nervous system and it regulates the temperature of the body by preventing over heating.

The apocrine sweat glands are larger than the eccrine glands and ducts. They are emptied into hair follicles. They produce sweat plus some fatty substances and proteins. These apocrine glands are present in certain areas of the body such as the areolas, armpits, ear canal, eyelids, perianal region and some parts of the external genitalia. Modified apocrine glands can produce different substances such as ear was or breast milk

Question 11

What are sebaceous glands for?

Answer 11

They are found all over the body except palm of hands and soles of feet. They secrete sebum which softens and lubricates the hair and skin. It also has an antibacterial activity. The secretion is controlled by hormonal changes (androgen).

Question 12

Difference between stratum corneum and nails.

Answer 12

Nails are tough keratinised layer with lower levels of lipids than the stratum corneum.

Question 13

List the advantages of topical delivery.

Answer 13

Large surface area available so potential numerous sites
Good patient compliance
Easy cessation.
Avoidance of the first pass metabolism

Question 14

Name the 3 potential route through the skin.

Answer 14

1. Shunt route (Follicle and sweat ducts, only 0.1% area of skin)
2. Transcellular (through the cells)
3. Intercullular (Between the cells and the major route)

Question 15

Define these 4 terms.

1. Permeant
2. Flux(J)
3. Permeability coefficient (Kp)
4. Diffusion coefficient (D)

Answer 15

1. Permeant is defined as the molecule moving through or into the skin.
2. Flux is defined as the rate of permeant crossing the skin
3. Permeability coefficient is defined as the speed of the permeant transport.
4. Diffusion coefficient is known as the fundamental property of the permeant in a particular membrane.