Dermatology: Anatomy - The integumentary system

Question 1

List 5 functions of the skin

Answer 1

1. Protection of the body from harmful environmental effects
2. Containment for the body’s structures
3. Thermal regulation through sweat evaporation and/or dilation or construction of superficial blood vessels
4. Sensation by way of superficial nerves and their sensory endings
5. Synthesis and storage of vitamin D

Question 2

What are the three layers of the skin, from most to least superficial?

Answer 2

1. Epidermis
2. Dermis
3. Hypodermis

Question 3

Compare and contrast the composition of the three layers of the skin

Answer 3

Epidermis: avascular, keratinised squamous superficial layer with regenerative and pigmented deep basal layer (various skin appendages are all derivatives of the epidermis)
Dermis: deeper layer, mesodermal in origin, consisting of bundles of collagen fibres, elastic tissue, blood vessels, lymphatics and nerve fibres - provides skin tone and strength
Hypodermis: subcutaneous tissue, also mesodermal in origin, consisting primarily of loose connective tissue, and containing larger blood vessels and nerves than those found in the dermis - also a major site of fat storage

Question 4

What determines skin pigmentation?

Answer 4

Main factor determining the color of skin is the degree of pigmentation produced by melanocytes, mainly found in the basal layer of the epidermis
In darker skins, melanocytes are more active and produce more pigment rather than being more numerous

Question 5

Describe the typical pattern of tension lines

Answer 5

Tend to spiral longitudinally in the limbs, and transversely in the neck and trunk
Tension lines at the elbows, knees, ankles, and wrists are parallel to the transverse creases that appear when the limbs are flexed

Question 6

What are the three main skin appendages?

Answer 6

Sweat glands (including apocrine glands)
Sebaceous glands
Hair and nails

Question 7

Describe the distribution of sweat glands on the body

Answer 7

Distributed all over the skin except on TM, lip margins, nipples, inner surface of prepuce, glans penis, and labia minora
Greatest concentration is on palms, soles and face

Question 8

Describe the distribution of apocrine glands on the body

Answer 8

Large, modified sweat glands that are confined to the axillae, areolae, periumbilical, genital and perianal regions

Question 9

Describe in brief the structure and location of a sweat gland

Answer 9

Coiled tubular structures that extend into the dermis and subcutaneous tissue

Question 10

Where do apocrine ducts open onto?

Answer 10

Hair follicles

Question 11

Do secretions from apocrine glands smell?

Answer 11

No - their odourless secretion acquires a smell through bacterial action

Question 12

What is the effect of puberty on apocrine glands?

Answer 12

Causes them to enlarge

Question 13

Describe in brief the structure and location of a sebaceous gland

Answer 13

Small saccular structures in the dermis, where they open on to the side of hair follicles

Question 14

Describe the distribution of sebaceous glands on the body

Answer 14

None on sole or palms
Particularly large on the face

Question 15

Are sebaceous glands innervated?

Answer 15

No - androgens act locally on these glands

Question 16

What kind of fibres do the cutaneous nerves carry, and what are their respective roles?

Answer 16

Afferent somatic fibres, mediating general sensation
Efferent autonomic (sympathetic) fibres supplying smooth muscle of blood vessels, arrector pili, muscles and sweat glands

Question 17

Explain the rule of 9’s

Answer 17

Used to estimate the proportionate surface area of the skin over different regions:
Head = 9%
Upper limb = 9%
Lower limb = 18%
Front of thorax and abdomen =18%
Back of thorax and abdomen = 18%

Question 18

What are hair and nails composed of?

Answer 18

Hard type of keratin

Question 19

Describe hair development

Answer 19

Each hair is formed from the hair matrix, a region of epidermal cells at the base of the hair follicle, which extends deeply into the dermis and subcutaneous tissue
As the cell moves up inside the tubular epidermal sheath of the follicle they lose their nuclei and become converted into the hard keratin hair shaft

Question 20

Describe nail development

Answer 20

Compacted keratin-filled squames form the nail plate, which develops from the epidermal cells of the nail matrix deep to its proximal part

Question 21

What are the arrector pili?

Answer 21

Most hair follicles have an arrector pili muscle attached to the connective tissue of the base, which contracts with sympathetic innervation to make the hair stand on end

Question 22

Where are the arteries of the skin derived from?

Answer 22

Derived from a tangential plexus at the boundary between the dermis and the subcutaneous connective tissue

Question 23

Where in the skin do lymphatics pass?

Answer 23

Lymphatics pass to a network between the dermis and hypodermis, running centrally with the blood vessels

Question 24

What is the role of arteriovenous anastamoses in the skin?

Answer 24

Play a role in conserving body heat