Case 1: Histology of the skin

Question 1

Functions of skin

Answer 1

1. protection from external influences (incl. dehydration, radiation, pathogens)
2. sensation
3. endocrine functions
4. heat regulation
5. immunity

Question 2

Three main layers of the skin

Answer 2

1. epidermis
2. dermis
3. hypodermis

Question 3

What is the epidermis comprised of

Answer 3

1. multiple layers of cells
2. glands
3. receptors
4. vessels and veins

Question 4

4 main cell types present in the epidermis

Answer 4

1. Keratinocytes
2. Melanocytes
3. Langerhans cells
4. Merkel cells

Question 5

List the layers of the epidermis

Answer 5

1. Stratum corneum (keratinised stratified squamous epithelium)
2. Stratum lucidum
3. Stratum granulosum
4. Stratum spinosum
5. Stratum basale

Question 6

Difference between thick and thin skin

Answer 6

• thin skin: covers majority of the body, contains hair
• thick skin: 6x thicker than thin skin & hairless. palms of hands, finger times and soles of feet.
• thick & thin refers to thickness of epidermal region alone

Question 7

Outline the structure of stratum corneum

Answer 7

• 10 to 20 cell layers
• comprises of layers of corneocytes (dead keratinocytes that lack nuclei and organelles)
• cells contain keratin and have a hard protein envelope

Question 8

Define Desquamation

Answer 8

shedding of dead cells from skin surface

Question 9

Outline the structure of stratum lucidum

Answer 9

• clear layer
• visible in thick skin
• 3 to 5 flattened layers of corneocytes, cells filled with eleidin (intermediate of keratin)

Question 10

Outline the structure of stratum granulosum

Answer 10

• granular layer
• cells contain keratohyalin granules (precursor to keratin)
• keratohyalin promotes hydration and cross linking of keratin

Question 11

Outline the structure of stratum spinosum

Answer 11

• 8 - 10 layers thick, polyhedral keratinocytes with large pale staining nuclei
• desmosomes
• langerhans cells mainly found here

Question 12

Outline the structure of stratum basale

Answer 12

• stratum germinativum
• one cell layer throughout body except hairless skin
• made of basal keratinocytes (stem cells of epidermis), melanocytes, merkel cells

Question 13

Outline the function of keratinocytes

Answer 13

• filled with keratin
• functions as waterproof barrier, protective against environment damage (UV, heat, waterloss, pathogen) and responsible for would healing (able to migrate)

Question 14

Outline the structure and function of melanocytes

Answer 14

• neural crest origin
• sits on basement membrane of stratum basale
• melanogenesis: production of melanin.
• Gives colour to skin, hair and eyes. Melanin is passed onto keratinocytes. Skin colour dependant on the amounts of melanin)

Question 15

Outline the morphology and function of Langerhans cells

Answer 15

• dendritic immune cells mainly found in stratum spinosum
• large granules (Birbeck granules)
• recognise and present antigens to the immune system, phagocytosis, play a role in allergy and chronic skin inflammation

Question 16

Outline the morphology and function of Merkel cells

Answer 16

• oval shaped receptor cells
• synaptic contact with somatosensory afferents
• detect light touch sensations
• found in stratum basale

Question 17

Outline the structure of the dermis

Answer 17

• flexible, supports the epidermis
• NB for thermoregulation
• rich vascular supply
• 2 layers:
  1) Papillary layer: loose areolar connective tissue, small blood vessels, lymph and nerves. Fine collagen fibres and elastic fibres

2) Reticular layer: denser irregular connective tissue, vascular plexus, lymph, nerves and appendages. Compact irregular collagen fibres and thick elastic fibres

Question 18

Structure of the dermo-epidermal junction

Answer 18

1. uneven boundary
2. Dermal papillae: projections from the dermis into the epidermis
3. Epidermal ridges/ epidermal peg: projections of epidermis into dermis
4. Provides mechanical strength due to the folds
5. give rise to fingerprints

Question 19

Outline the structure of the hypodermis

Answer 19

• subcutaneous, mainly for storage of fat (energy & insulation)
• consists of loose connective tissue and adipose tissue
• sweat glands
• hair follicles
• contains large blood vessels and nerves

Question 20

Sebaceous glands

Answer 20

• some can have ducts that lead into hair follicle, some open directly onto skin surface
• produces sebum for skin lubrication, prevents brittle hair, slightly acidic thus bactericidal
• holocrine secretion
• active at puberty

Question 21

Merocrine/eccrine glands

Answer 21

• most abundant
• open via duct to pore on skin
• stratified cuboidal epithelial cells
• myoepithelial cells assist with secretion
• produces sweat (water, vitC, salts, wastes) NB for thermoregulation
• associated odour from bacteria

Question 22

Apocrine glands

Answer 22

• found in the axillae, breast areolae, genital areas
• larger than merocrine sweat glands
• simple cuboidal to columnar shaped cells
• myoepithelial cells
• secretes fatty acids and proteins
• exact function unknown

Question 23

Skin nerve supply - outline the receptors found in the skin

Answer 23

1. thermoreceptors - senses heat and cold
2. meissner’s corpuscles - senses light touch
3. nociceptor & ruffini endings - senses pain
4. pacinian corpuscle - senses pressure and vibration