The document summarizes the structure and function of the integumentary system in 3 paragraphs: The integumentary system has two main divisions - the skin and accessory structures. The skin is the largest organ and has two layers, the epidermis and dermis. Accessory structures include sweat and sebaceous glands, hair follicles, and nails, which are derived from the epidermis. The epidermis has several strata with different cell types and densities. The dermis lies below with two layers - a papillary layer interdigitated with the epidermis and a deeper reticular layer. Various sensory receptors are located within the skin layers. The skin has

1. Lecture 5 Integumentary System

2. 2 Divisions of the Integumentary system 1. Skin = integument = Cutaneous membrane Skin is the largest organ of the body Composed of the superficial EPIDERMIS and the deeper DERMIS 2. Accessory skin structures = Appendages of the skin: i) Sweat (sudoriferous) glands ii) Sebaceous ( oil) glands iii) Hair/hair follicles iv) Nails

3. Figure 5.1: Skin structure, p. 153. Epidermis Dermis Hypodermis (superficial fascia) Hair root Hair shaft Pore Dermal papillae (papillary layer of dermis) Meissner's corpuscle Free nerve ending Reticular layer of dermis Sebaceous (oil) gland Arrector pili muscle Sensory nerve fiber Eccrine sweat gland Pacinian corpuscle Artery Vein Adipose tissue Hair follicle receptor (root hair plexus) Hair follicle Eccrine sweat gland

4. Strata of the Epidermis Stratum Basale – deepest stratum Stratum Spinosum – contains tonofilaments Stratum Granulosum – contains granules Stratum Lucidum – present only in thick skin Stratum Corneum - superficial stratum

5. Figure 5.2: The main structural features in skin epidermis, p. 154. Sensory nerve ending Melanocytes Melanin granules Merkel cell Langerhans’ cell Stratum corneum Stratum granulosum Stratum spinosum Stratum basale Dermis Dermis Cells are dead; represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Cells are flattened; organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules. Cells contain thick bundles of intermediate filaments made of pre-keratin. Cells are actively mitotic stem cells; some newly formed cells become part of the more superficial layers. Keratinocytes Desmosomes (b) (a)

6. Stratum Basale The deepest stratum. A single layer of cells including Keratinocytes, Melanocytes, Merkel cells: Keratinocytes are mitotically active producing cells for the superficial layers hence, the stratum basale is also known as the stratum Germinativum Melanocvtes produce the pigment MELANIN contained in granules called melanosomes – melanosomes accumulate on the superficial surface of the keratinocvtes in the stratum basale. Melanin acts as a chemical shield to protect the nuclei of the keratinocytes from the harmful effects of UV radiation in sunlight. Melanin gives skin its color. When you go out into the sun , these cells make extra melanin to protect you from getting burned by the sun's ultraviolet, or UV, rays = tanning Merkel cells at the epidermal-dermal junction associate with free nerve endings to form Merkel Discs which act as Touch receptors

7. Stratum Spinosum Several layers of cells Cells are connected by desmosomes – hold cells together which cause the cells to appear “spiny” during histological preparation Cells contain intermediate filaments called Tonofilaments Epidermal dendritic cells – Langerhans’ cells in the stratum spinosum act as macrophages to engulf and digest pathogens

8. Stratum Granulosum Composed of 3-5 layers of cells Cells contain 2 types of granules: Lamellated granules – contain Glycolipids – the lipids make the epidermis water-proof. keratohyaline granules – contain the tough, insoluble protein, Keratin , which makes the epidermis tough and abrasive- resistant

9. Stratum Lucidum Thin, translucent layer of dead cells Present only in thick skin – palms, soles

10. Stratum Corneum Superficial layer of the epidermis Composed of 20-30 layers of dead, flat cells Dead cells are impregnated with glycolipids and keratin to provide a tough, durable, water-proof “coat”. Replaced every three to four weeks

11. The Dermis Consists of the superficial PAPILLARY layer and the deep RETICULAR layer The papillary Layer Composed of areolar CT In thick skin, the surface of the papillary layer forms Dermal Ridges which form impressions on the epidermal surface called the EPIDERMAL RIDGES (= friction ridges) – increase friction and enhance gripping Pattern of epidermal ridges is genetically determined and therefore unique to an individual – acts as the basis for finger-printing Contains the Meissner’s Corpuscles – act as touch receptors

12. Figure 5.1: Skin structure, p. 153. Epidermis Dermis Hypodermis (superficial fascia) Hair root Hair shaft Pore Dermal papillae (papillary layer of dermis) Meissner's corpuscle Free nerve ending Reticular layer of dermis Sebaceous (oil) gland Arrector pili muscle Sensory nerve fiber Eccrine sweat gland Pacinian corpuscle Artery Vein Adipose tissue Hair follicle receptor (root hair plexus) Hair follicle Eccrine sweat gland

13. Reticular Layer of the Dermis Deeper layer accounting for 80% of the dermis Composed of dense irregular CT Contains the touch receptors for deep pressure called Pacinian corpuscles Cleavage (tension) lines – areas of the reticular layer with less collagen bundles Incisions made parallel to the cleavage lines gape less and therefore heal faster. Striae ( stretch marks) – indicate dermal tearing replaced by slivery white scars

14. Location of the Nervous Structures in the Skin Merkel discs : epidermal-dermal junctions Meissner’s Corpuscles : Papillary layer of the dermis Root hair plexus : wrapped around the base of a hair follicle called the hair bulb and it’s stimulated when the hair bend Pacinian Corpuscles : located in the reticular layer of the dermis and they respond to deep pressure placed on the skin

15. Accessory Structures of the Skin Sweat glands Sebaceous glands Hairs/hair follicles Nails

16. Accessory structures of the skin All derived from the epidermis but reside in the dermis: Sweat ( Sudoriferous) glands Sebaceous ( oil ) glands Hairs/hair follicles Nail

17. Figure 5.3: Cutaneous glands, p. 159. Sebaceous gland duct Sebaceous gland Sweat pore Eccrine g land (a) Sectioned sebaceous gland (b) Sectioned eccrine gland

18. Sweat Glands Also known as suderiferous glands Simple coiled tubular multicellular exocrine glands 2 types: Eccrine and Apocrine Eccrine Sweat Glands: 3 million per person Abundant in the palms, soles and forehead Secrete SWEAT Use the MEROCRINE mode of secretion Hence, the eccrine sweat glands are also known as merocrine sweat glands

19. Composition of Sweat Hypotonic filtrate of blood 99% water Antibodies Vitamin C Salts – NaCl Metabolic wastes Dermicidin – antimicrobial protein pH between 4-6 = Acidic ACIDIC MANTLE – acidic pH of sweat prevents microbial growth on the surface of the skin

20. Apocrine Sweat glands 2000 of them located in the anogenital and axillary (armpits) areas Become active after puberty when they are stimulated by the sex steroid hormones Secrete a viscous, yellowish fluid onto hair follicles Secrete their product via MEROCRINE mode of secretion Secretion is associated with body odor hence, the apocrine sweat glands are also known as “ODORIFEROUS” glands

21. 2 Specialized Sweat Glands Ceruminous glands : specialized sweat glands located in the lining of the external ear canal; they secrete a bitter substance called CERUMEN (earwax) which prevents entry of foreign objects such as, insects and water, into the ear Mammary glands : specialized sweat glands located in breasts; secrete milk to feed the young

22. Figure 5.3a

23. Sebaceous Glands Also known as Oil glands Simple alveolar glands Found all over the body except the palms/soles Secrete an oily substance called SEBUM into hair follicles and via pores to the surface of the skin Sebum softens and lubricates hair and skin Secrete via the HOLOCRINE mode of secretion Whiteheads: sebum accumulated in the ducts of the sebaceous glands Blackheads : popped whiteheads that result in oxidation and darkening Acne : inflammation of sebaceous glands caused by bacteria

24. Figure 5.4 Hairs = Pili Produced by cells in the MATRIX inside hair follicles Each hair has 2 regions – shaft and root SHAFT – region exposed above the skin ROOT – region below the skin enclosed by the hair follicle

25. Hairs = Pili Produced by cells in the MATRIX inside hair follicles Each hair has 2 regions – the shaft and the root SHAFT – region exposed above the skin ROOT – region below the skin enclosed by the hair follicle Matrix

26. Figure 5.5c-d: Structure of a hair and hair follicle , p. 161. Hair shaft Arrector pili Sebaceous gland Hair root Hair bulb in follicle Hair root (cuticle, cortex, medulla) Internal epithelial root sheath External epithelial root sheath Connective tissue root sheath Hair matrix e Hair papilla Subcutaneous adipose tissue Medulla Cortex Glassy membrane (d) (c)

27. Figure 5.5a-b: Structure of a hair and hair follicle, p. 161. Hair shaft Arrector pili Sebaceous gland Hair root Hair bulb in follicle Connective tissue root sheath Follicle wall Cuticle Cortex Medulla Internal epithelial root sheath External epithelial root sheath Glassy membrane (a) (b) 2 regions – shaft and root SHAFT – region above the skin ROOT – region below the skin enclosed by the hair follicles

28. 3 Concentric Layers of hair Hair is composed of 3 concentric layers of keratinized cells: Inner medulla – the core Middle cortex – the largest layer Outer cuticle – a single layer of overlapping cells that protects the underlying layers and to prevent hair from matting Conditioners keep the cuticle smooth to prevent matting of the hair and split ends Alopecia – rate of hair loss outpaces rate of hair growth

29. Function of Hairs For protection; hair on scalp, eyelashes To provide insulation: in cold weather, bands of smooth muscle attached to the hair follicles called the arrector pili muscles , contract pulling the hair follicles and hairs from an oblique position to an upright position resulting in dimpling of the skin referred to as “goose bumps”; in this position a layer of air can be trapped on the surface of skin to act as an insulator to prevent heat loss from the body

30. Figure 5.6: Structure of a nail , p. 163. Free edge of nail Body of nail Lateral nail fold Lunula Eponychium (cuticle) Nail matrix Root of nail Proximal nail fold Eponychium (cuticle) Body of nail Nail bed Free edge of nail Hyponychium Phalanx (bone of fingertip) (a) (b)

31. Figure 5.7 Basal cell carcinoma Squamous cell carcinoma Melanoma

32. Skin Cancer Basal Cell Carcinoma : involves the proliferation of stratum basale cells. The least malignant and most common type of skin cancer ( 80% ); grows slowly Squamous Cell Carcinoma : involves the cells in the stratum spinosum. Second most common type of skin cancer; grows rapidly Melanoma : proliferation of the melanocytes; most aggressive type of skin cancer, highly metastatic and resistant to chemotherapy; least common Further reading: www.mayoclinic.com/health/skin-cancer/DS00190

33. Figure 5.8: Estimating the extent and severity of burns, p. 167. Totals Anterior and posterior head and neck, 9% Anterior and posterior upper limbs, 18% Anterior and posterior trunk, 36% Anterior and posterior lower limbs, 36% (Perineum, 1%) 100% 4 1 / 2 % Anterior trunk, 18% 9% 9% (a) (b) (c) (d) 4 1 / 2 % 4 1 / 2 % First-degree burn Second-degree burn Third-degree burn blisters

34. Burns Tissue damage by intense heat, radiation, electricity and chemicals such as acids Classified based on severity: First-degree burns – damage is confined to only the epidermis; associated with redness, swelling and pain; heal in 3day without medical intervention. Ex. Sunburn Second-degree burns – damage to the entire epidermis and the papillary layer of the dermis; associated with blisters ( fluid collection at the epidermal-dermal junction), swelling, redness and pain; heal in 3-4 weeks if infection is prevented Third-degree burns – damage to the entire skin= damage to the entire epidermis and dermis including all nerve endings hence, the burn site is not painful; subjected to infections and fluid loss; medical intervention involving grafting, fluid, protein and ion replacement are required for healing

35. Wrinkles How Do Wrinkles Form? loss of elasticity - thinning skin - lack of moisture When skin is young, thick, and full of elasticity it can resist muscle tension and does not develop a grove or crease when a facial muscle is contracted - such as a frown, squint, or a smile. However as we age and our skin becomes thinner, drier, less resilient, it starts to adhere itself to the underlying muscle tissue. So now when we frown the skin gets pulled along with the muscle creating a valley, a line, or a deep wrinkle over time. Botox blocks the transmission of signals from nerves to the muscles, by hindering the production of the neurotransmitter (the chemical which relays the signals). When used for cosmetic purposes this causes the muscle to relax giving it a smoother appearance and greatly reducing the appearance of lines and wrinkles Source: botoxguidance.com

36. Figure UN 5.1