W1 Anatomy of the Skin

Question 1

Characteristics of the Epidermis

Answer 1

• Stratified, squamous epithelium and keratinocytes - 0.4-0.6mm thick - Avascular - Receives nutrients from dermal layer - 4-5 layers (from deepest to most superficial): stratum germinativum, stratum spinosum, stratum granulosum, stratum lucidum (sometimes) and stratum corneum.

Question 2

Characteristics of Stratum Germinativum

Answer 2

• Deepest layer - Single layer of basal cells - Keratinocytes - Melanocytes (synthesise melanin for skin tone) - Merkel cells (touch receptors)

Question 3

Characteristics of Stratum Spinosum

Answer 3

• Several layers of polyhedral shaped cells (w large oval nuclei) - Beginning of keratinisation (keratin filaments, keratohyaline and lamellar granules form in cytoplasm) - Langerhan’s cells (reactivate lymphocytes in response to antigen– skin graft rejection)

Question 4

Characteristics of Stratum Lucidum

Answer 4

• Only in thicker layers of epidermis (palms, soles of feet) - Transparent, no nuclei - Enzymatic activity

Question 5

Characteristics of Stratum Corneum

Answer 5

• Most superficial layer (horny layer) - Thick, flat, keratinised layer

Question 6

Characteristics of Basement Membrane Zone

Answer 6

• Membrane separating stratum germinativum and dermis - Avascular and non-innervated - Regulates transfer of proteins and other materials (eg. O2) across dermis-epidermis junction - Mechanical support for epidermis

Question 7

Characteristics of Dermis

Answer 7

• Approx. 2-4mm thick - Two layers (from deepest to most superficial): Reticular layer, papillary layer. - Vascular - 2 types of nerve endings for: Vasomotor and pilomotor control; eccrine sweat production - 2 dermal proteins (synthesised by fibroblasts): Collagen (for tensile strength) and elastin - Lymphatics - Mast cells with granules of heparin, protease and histamine (for capillary permeability and vasodilation). Granules synthesise leukotrienes and prostaglandins, stimulate inflammatory responses. - Sensory receptors: Messiner’s corpuscles (texture and anatomical site), Krause’s end bulbs ( cold), Ruffini terminals (heat), Pacinian corpuscles (vibration, deep pressure; st cold, heat, pain, pressure, itch, tickle)

Question 8

Characteristics of Papillary Layer

Answer 8

• Most superficial layer (under basement membrane zone) - Reti ridges (upward projections) - Dermal papillae (downward projections): have papillary loops for O2 and nutrients

Question 9

Characteristics of Reticular layer

Answer 9

• Attached to hypodermis - Thicker collagen - Tough and flexible layer which can stretch for more weight

Question 10

Characteristics of the Hypodermis

Answer 10

• AKA subcutaneous layer - Thickest skin layer - Support framework for skin - Attachment and protective layer for organs etc. - Thermoregulation - Lipid storage - Adipose tissue - Connective tissue - Blood vessels

Question 11

Appendages of the skin

Answer 11

• Eccrine sweat glands - Apocrine sweat glands - Ceruminous glands - Sebaceous glands - Nails - Hair

Question 12

Eccrine sweat glands

Answer 12

• Open onto skin - Thermoregulation - Increased core temp stimulates hypothalamus to activate glands and produce hypotonic sweat

Question 13

Apocrine sweat glands

Answer 13

• Activated at prepubescence - Open into hair follicles - Odour results when drainage reacts with skin bacteria - Located in axilla, anogenital region, external auditory canal and mammary areola

Question 14

Ceruminous glands

Answer 14

• Modified sweat glands - External auditory canal - Secrete cerumen to keep tympanum moist

Question 15

Sebaceous glands

Answer 15

• Empty into hair follicle duct - All skin except palms and soles of feet - Sebum: moisturiser and helps w vitamin D synthesis - Most active in adolescence, decrease with age

Question 16

Nails

Answer 16

• Keratin - Constant regeneration - Growth depends on nutrient and O2 supply - Nail plate, lunula and paronychium - Angle 160 degrees - 0.3- 0.65mm thick

Question 17

Hair

Answer 17

• Keratin - Bulb, root and shaft - Growth at bulb - Lanugo (forehead, buttocks, pinnacle of ears, and back of infants) - Vellus (short, fine hair found on face of women) - Terminal (thick, long, pigmented found on scalp, legs, pubis, chest and face of men)

Question 18

Characteristics of the Extracellular Matrix

Answer 18

• Structure surrounding cells in all tissues - Composition varies between tissues - Largest component of dermis - Gel-like - Molecules secreted by fibroblasts and epidermal cells - Fibrous structural proteins: collagen, elastin and laminin (strength and resilience) - Proteoglycans and glycosaminoglycans (polysaccharides): dermatan sulfate, hyaluronan, chondroitin sulfate, heparin, heparan sulfate, keratan sulfate (water-heavy molecules to cushion cells) - Functions: Support cells and tissues, Integrate cells into tissues, Influence cell shape and movement, Influence cell movement and differentiation, Reservoir for extracellular signalling molecules, regulate/direct wound healing processes

Question 19

Functions of the Skin

Answer 19

• Protection of underlying structures from: mechanical, chemical and thermal trauma; invading pathogens; dehydration - Sensation - Communication - Thermoregulation: radiation from blood vessels, excretion and evaporation of sweat, convection and conduction of heat, insulation by hair and subcutaneous tissue - Metabolic synthesis: melanin, keratin, vitamin D - Cosmesis