Lecture 5

Integumentary System

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

Figure 5.1: Skin structure, p. 153.

Epidermis

Dermis

Hypodermis(superficialfascia)

Hair root

Hair shaft

Pore

Dermal papillae (papillary layer of dermis)

Meissner's corpuscle

Free nerve endingReticular layer of dermis

Sebaceous (oil) gland

Arrector pili muscle

Sensory nerve fiberEccrine sweat gland

Pacinian corpuscle

Artery

Vein

Adipose tissue

Hair follicle receptor(root hair plexus)

Hair follicle

Eccrine sweatgland

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

Figure 5.2: The main structural features in skin epidermis, p. 154.

Sensorynerveending

MelanocytesMelanin granules

Merkelcell

Langerhans’ cell

Stratumcorneum

Stratum

granulosum

Stratumspinosum

Stratumbasale

Dermis

Dermis

Cells are dead; representedonly by flat membranous sacsfilled with keratin. Glycolipidsin extracellular space.

Cells are flattened; organellesdeteriorating; cytoplasm full oflamellated granules (releaselipids) and keratohyalinegranules.

Cells contain thick bundles ofintermediate filaments madeof pre-keratin.

Cells are actively mitotic stemcells; some newly formedcells become part of the moresuperficial layers.

KeratinocytesDesmosomes

(b)(a)

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

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

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

Stratum Lucidum

• Thin, translucent layer of dead cells

• Present only in thick skin – palms, soles

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

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

Figure 5.1: Skin structure, p. 153.

Epidermis

Dermis

Hypodermis(superficialfascia)

Hair root

Hair shaft

Pore

Dermal papillae (papillary layer of dermis)

Meissner's corpuscle

Free nerve endingReticular layer of dermis

Sebaceous (oil) gland

Arrector pili muscle

Sensory nerve fiberEccrine sweat gland

Pacinian corpuscle

Artery

Vein

Adipose tissue

Hair follicle receptor(root hair plexus)

Hair follicle

Eccrine sweatgland

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

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

Accessory Structures of the Skin

Sweat glands

Sebaceous glands

Hairs/hair follicles

Nails

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

Figure 5.3: Cutaneous glands, p. 159.

Sebaceousgland duct

Sebaceousgland

Sweatpore

Eccrinegland

(a) Sectioned sebaceous gland (b) Sectioned eccrine gland

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

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

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

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

Figure 5.3a

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 secretionWhiteheads: 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

Figure 5.4

Hairs = Pili

Produced by cells in the MATRIX inside hair follicles

Each hair has 2 regions – shaft and rootSHAFT – region exposed above the skinROOT – region below the skin enclosed by the hair follicle

Hairs = Pili

Produced by cells in the MATRIX inside hair follicles

Each hair has 2 regions – the shaft and the rootSHAFT – region exposed above the skinROOT – region below the skin enclosed by the hair follicle

Matrix

Figure 5.5c-d: Structure of a hair and hair follicle, p. 161.Hair

shaft

ArrectorpiliSebaceousglandHair root

Hair bulbin follicle

Hair root(cuticle, cortex, medulla)Internal epithelialroot sheath

External epithelialroot sheath

Connectivetissue root sheath

Hair matrixe

Hair papilla

Subcutaneousadipose tissue

Medulla

Cortex

Glassy membrane

(d)(c)

Figure 5.5a-b: Structure of a hair and hair follicle, p. 161.

Hairshaft

Arrectorpili

Sebaceousgland

Hair root Hair bulbin follicle

Connective tissueroot sheath

Follicle wall

Cuticle

CortexMedulla

Internal epithelialroot sheath

External epithelialroot sheath

Glassy membrane(a)(b)

2 regions – shaft and rootSHAFT – region above the skin

ROOT – region below the skin enclosed by the hair follicles

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

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

Figure 5.6: Structure of a nail, p. 163.

Free edgeof nailBody ofnailLateralnail fold

Lunula

Eponychium(cuticle)

Nailmatrix

Root ofnail

Proximalnail fold

Eponychium(cuticle) Body of nail

Nail bed

Free edgeof nail

HyponychiumPhalanx(bone offingertip)

(a) (b)

Figure 5.7

Basal cell carcinoma

Squamous cell carcinoma

Melanoma

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

Figure 5.8: Estimating the extent and severity of burns, p. 167.

Totals

Anterior and posteriorhead and neck, 9%

Anterior and posteriorupper limbs, 18%

Anterior and posteriortrunk, 36%

Anterior and posteriorlower limbs, 36%

(Perineum, 1%)

100%

41/2%

Anteriortrunk, 18%

9% 9%

(a)

(b)

(c)

(d)

41/2% 41/2%First-degree burn

Second-degree burn

Third-degree burn

blisters

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

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

Figure UN 5.1