Skin

Question 1

Functions of skin

Answer 1

• acts as a protective physical barrier
• moisture control
• thermoregulation
• sensation
• UV protection
• production of vitamin D

Question 2

3 layers of skin

Answer 2

• epidermis; keratinised stratified squamous epithelium
• dermis; collagenous dense connective tissue
• hypodermis; loose connective tissue (mainly adipose tissue)

Question 3

Epidermis

Answer 3

• top layer of skin
• keratinised stratified squamous epithelium
• composed mostly of keratinocytes (90%)
• four or five discrete layers
• cuboidal cells at the stratum basale

Question 4

Layers of the epidermis

Answer 4

• stratum basale
• stratum spinosum
• stratum granulosum
• stratum lucidum (only in thick skin)
• stratum corneum

British and Spanish Grannies Love Cornflakes

Question 5

Melanocytes

Answer 5

• synthesise and store melanin
• found in the stratum basale and stratum spinosum of the epidermis
• involved in the pigmentation of skin and UV protection.

Question 6

Keratinocytes

Answer 6

• contain keratin
• comprise 90% of the epidermis
• provide protection against mechanical forces
• superficial layer of dead cells is constantly shed

Question 7

Merkel cells

Answer 7

• associate with free nerve endings to form sensory mechanoreceptors
• found in the stratum basale

Question 8

Langerhans cells

Answer 8

• serve as antigen presenting cells

- distributed throughout the stratum spinosum and basale

Question 9

Dermis

Answer 9

• mainly composed of dense collagenous connective tissue, with elastin present throughout
• comprised of reticular and papillary layers
• blood vessels important for thermoregulation (vasoconstriction/vasodilation)
• nerve supply from the subpapillary and cutaneous plexus controlled by the ANS
• nerve endings may be free or encapsulated

Question 10

Papillary layer

Answer 10

• thin superficial layer of the dermis
• composed of loosely arranged elastic fibres and thin collagen fibres
• rich in blood vessels

Question 11

Reticular layer

Answer 11

• thick deep layer of the dermis
• composed of dense irregularly arranged collagen fibres and a small number of elastic fibres
• fewer blood vessels

Question 12

Pilosebaceous unit

Answer 12

Comprised of a hair follicle, sebaceous glands and an erector pili muscle. Sebaceous glands secrete an oily substance called sebum, which forms a protective layer over the skin. The erector pili is a smooth muscle controlled by the sympathetic division of the ANS.

Question 13

Hairy skin

Answer 13

Covers most of the body, only on thin skin (not the thick skin of the palmar/plantar surfaces). Hair follicles extend into the dermis, or the hypodermis on the scalp.

Question 14

Eccrine sweat glands

Answer 14

• present all over the body in large numbers
• secrete watery sweat directly onto the skin surface
• important for thermoregulation

Question 15

Apocrine sweat glands

Answer 15

• found only in the armpits and genital region

- secrete viscous sweat, which may produce odour

Question 16

Innervation of the skin

Answer 16

• free nerve endings
• Meissner’s corpuscles
• Pacinian corpuscles
• Ruffini’s corpuscles

Question 17

Meissner’s corpuscles

Answer 17

Rapidly-adapting, encapsulated neurons that sense touch and vibration. They are prominent in the papillary dermis of the fingers, toes, palms and soles.

Question 18

Pacinian corpuscles

Answer 18

Rapidly adapting, deep receptors that sense deep pressure and vibration. Usually found deep in the hypodermis.

Pacinian= Pressure

Question 19

Ruffini’s corpuscles

Answer 19

Slow-adapting, encapsulated neurons that sense temperature, mechanical stimuli and respond to skin stretch.

Question 20

Merkel’s discs

Answer 20

Slow-adapting receptors associated with free nerve endings that respond to light touch.

Question 21

Free nerve endings

Answer 21

Unencapsulated neurons found in the upper layers of skin, that sense pain, itch, temperature etc. May associate with Merkel cells or surround hair follicles.

Question 22

Skin disorders

Answer 22

• psoriasis
• malignant melanoma
• benign skin naexus (mole)
• vitiligo
• allergic contact dermatitis

Question 23

Dermatitis

Answer 23

Inflammation of the skin, triggered by environmental, chemical or seborrheic factors.

Question 24

Burns

Answer 24

Injuries to the skin caused by heat, chemicals, radiation, friction or electricity. Classified as superficial, partial thickness or full thickness. Full thickness burns may be painless due to the destruction of nerve endings.