T1L12/13: The Outer Body Covering

Question 1

Neoplasia

Answer 1

Autonomous ‘new growth’ – abnormal, uncoordinated and excessive cell growth.
Persists following withdrawal of stimulus and associated with genetic alterations
Classified according to behaviour and histogenesis (recognising the cell of origin)
May be benign, borderline or malignant

Question 2

Dysplasia

Answer 2

Abnormal cell morphology (malignant)

Question 3

Histogenesis of neoplasms

Answer 3

• Classification by cell of origin
• Determined by examining tissue under the microscope
Resemblance to parent tissue correlates with clinical behaviour

Question 4

Skin

Answer 4

• Largest organ of body (15% body weight)
• Cover entire surface - continuity at mucocutaneous junctions
Forms interface between body/person and environment

Question 5

Properties and function

Answer 5

• Maintenance of body integrity
	• Waterproofing
	• Protection from injury
	• Protection from infection
	• Sensory functions
	• Immune functions
	• Absorption / excretion
	• Control of body temperature
	• Vitamin D metabolism
Personal, social and sexual significance

Question 6

Structure of the skin

Answer 6

• Epidermis (epithelium of ectodermal origin)
• Dermis (CT of mesodermal origin)
• Subcutaneous adipose tissue
Variability according to site: Thick, hairless or thin, hairy

Question 7

Epidermis

Answer 7

• Stratified squamous epithelium composed of keratinocytes undergoing terminal differentiation (approx. 4 weeks)
• Basement membrane at the junction with the dermis
• Four important layers:
○ Horn cell layer (stratum corneum)
○ Granular cell layer (str. granulosum)
○ Prickle cell layer (str. spinosum)
Basal cell layer (stratum basale)

Question 8

Melanocytes

Answer 8

• Origin from the neural crest
• Stuck to the basement membrane
• Melanin, formed in melanosomes
• One melanocytes delivers melanin to 36 keratinocytes
Keratinocytes phagocytose the tips of melanocyte dendrites

Question 9

Langerhans cells

Answer 9

• Originate from the bone marrow
• Also dendritic
Antigen presenting cells

Question 10

Merkel cell

Answer 10

• Mediate tactile sensation
• Not recognizable in normal sections
• Originate from the neural crest
Associated with sensory nerve endings

Question 11

Basement membrane

Answer 11

• Collagen type IV
	• Highlighted by PAS stain
	• Resistance to shearing forces
	• Structural significance
Control of epithelial – mesenchymal interactions (e.g. invasion)

Question 12

BM disease

Answer 12

• Increased fragility and impaired wound healing
• Control of invasion in SCC and melanoma
• Blistering diseases of the skin
• Autoimmune diseases
○ Bullous pemphigoid
○ Dermatitis herpetiformis
Genetic diseases Epidermolysis bullosa

Question 13

Dermis

Answer 13

• Dense connective tissue (collagen, elastin, extracellular matrix)
	• Nerves, blood vessels, lymphatics, histiocytes, mast cells, plasma cells, lymphocytes
	• Mechanoreceptors, thermoreceptors
	• Subcutaneous fat
	• Epidermal appendages            
		○ Pilosebaceous units
		○ Sweat glands
	• Papillary dermis
Reticular dermis

Question 14

Skin appendage

Answer 14

• Hairs and sebaceous glands = pilosebaceous unit

Sweat glands

Question 15

Temperature regulation

Answer 15

• Vasodilatation causes increased bloodflow, hence loss of heat = cooling.
Evaporation of sweat lowers surface temperature.