Pierce College Putman/Biol 241 Lecture Unit 05 Notes: The Integumentary System INTRODUCTION 1. 2. 3.

Cutaneous membrane (= skin) + structures derived from the cutaneous membrane. Largest organ in body; ~ 16% of body weight. Dermatology: study of the skin

COMPONENTS 1.

Cutaneous membrane (= skin) is composed of the a. Epidermis: thin, exposed layer; keratinized, stratified squamous epithelium; basement membrane attaches to dermis b. Dermis: anchors to hypodermis by collagen fibers.

2.

Hypodermis: Not part of the cutaneous membrane—not part of the skin. Consists of a. Areolar connective tissue, which is made of collagen and elastin b. Adipose tissue c. Connects to muscles & organs beneath d. Pacinian corpuscles found on border between hypodermis & dermis; are nerve endings sensitive to pressure e. Functions: Fat storage, insulation & cushioning

EPIDERMIS Cell Types 1.

2.

3.

4.

Keratinocytes. a. In various stages of development from basal layer to apical layer. b. Form bulk of epidermis. c. Produce keratin, which accumulates as cells mature. Keratin prevents/inhibits water loss from underlying tissues, and protects underlying tissues from microbes and chemicals, although lipid-soluble chemicals may enter through skin. They also help protect the body from heat. Melanocytes. a. Found among keratincytes in stratum basale. b. Synthesize melanin and transfer melanin granules to keratinocytes. 1) Melanin granules moved by keratinocytes to position over nucleus, providing UV shield! 2) Note that UV stimulates melanin production. Merkel Cells. a. Found in stratum basale. b. Work with Merkel Disks in fine touch reception. Langerhans Cells. a. Stratum spinosum. b. Macrophages.

Forms Epidermal Ridges 1. 2. 3.

Epidermis interlocks directly with dermal papillae, thereby stabilizing & strengthening connection between epidermis and dermis. Epidermal ridges are skin ridges on palmar & plantar surfaces; they increase friction & grip. Epidermal ridge patterns genetically determined & unique

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Layers of Epidermis 1.

Stratum Basale. a. Attaches to basement membrane. b. Single layer of cells, mainly cuboidal keratinocytes. c. Stem cells here 1) Highly mitotic 2) Divide & differentiate into new keratinocytes 3) Old cells push toward apical surface. d. Melanocytes & Merkel Cells also found here. e. UV radiation stimulates synthesis of cholecalciferol here and in stratum spinosum 1) Liver & kidney modify into calciferol (vitamin D) that activates calcium receptors in gut so calcium can be absorbed.

2.

Stratum Spinosum a. Thick b. Keratinocytes mainly 1) Polyhedral 2) Mitotic. c. Langerhans Cells found here too.

3.

Stratum Granulosum a. Thin (3-5 cells). b. Flattened (squamous) keratinocytes. c. Apoptosis occurs here. d. Lamellar granules secrete lipid interstitially.

4.

Stratum Lucidum a. Thin (3-5 cells) b. In thick skin (skin of palms and soles of feet) only c. Squamous, mortibund keratinocytes. d. Keratin in columns, making tissue look transparent. e. Lamellar granules present, secrete lipid interstitially.

5.

Stratum Corneum a. Thick (15 to 30 cell layers) b. Keratinocytes; squamous; mortibund c. Cytoplasm mostly keratin d. Lipid in interstitial spaces e. Constantly sloughed off, replaced by cells from deeper in the tissue.

DERMIS 1.

General Structure a. Connective tissue (areolar & dense irrecular) rich in collagen and elastin b. Vascular—vessels service overlying epidermis, which is not vascular. c. Innervated d. Host epidermal modifications (glands, hair follicles) that extend down into dermis from epidermis.

2.

Layers of Dermis a.

Papillary Layer (thin) 1) Dermal papillae interlock with overlying epidermal ridges. 2) Areolar connective tissue. 3) Highly vascularized 4) Many sensory nerve endings, including

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a) Free Nerve Endings, which project into dermal papillae and sense pain & temperature b) Meissner Corpuscles, which also project into dermal papillae, and serve as touch receptors. b.

Reticular Layer (thick) 1) Attached to underlying hypodermis. 2) Dense irregular connective tissue, which is rich in collagen and elastin, thus has the characteristics of being strong, stretchable yet elastic. 3) Striae (stretch marks) formed here, caused by extreme stretching resulting in tissue damage. Such stretching may occur around joints, in obesity and during pregnancy.

SKIN COLOR 1.

Pigments a. Melanin—black/brown/yellow/red 1) Genetic 2) Highest concentration of melanocytes in forehead & cheeks, arms, nipples/areolae, genitals. 3) Racial differences in skin tone due to variation in melanin production as all races normally have the same number of melanocytes. Melanin hues in the yellows and reds due to expression of various levels of iron and/or sulfur in melanin.

2.

Carotene—yellow/orange a. Dietary b. Accumulates in lipids: keratinocytes, dermis, hypodermis c. Obtained by eating egg yolks and yellow/orange vegetables/fruits. d. Converted into retinol (vitamin A), necessary for vision.

3.

Dermal Capillaries a. Transient color effects b. Includes 1) Vasodilation (red flush), 2) Vasoconstriction (white flush) 3) c) Low blood oxygen (cyanosis)

EPIDERMAL DERIVATIVES Hair 1.

Hair Papillus, in bulb of hair follicle. a. composed of connective tissue extensions of dermis 1) Vascularized & innervated. a) Root Hair Plexus, responds to touching hair. 2) Note: Matrix cells (st. basale of epidermis) cover the hair papillus; these cells are mitotic and form a) Medulla of the hair (innermost layer), b) Cortex of the hair (middle layer) and c) Cuticle of the hair (outermost layer) composed of shingle-shaped cells rich in carotene. d) Internal root sheath

2.

Hair Shaft. This is the hair above the dermis and extending into the outside world.

3.

Hair Root. The part of the hair sheathed in the follicle at the level of the dermis.

4.

Hair Follicle. The sheath enclosing hair. a. Bulb: Wide base area of follicle.

5.

Follicle structure: a. Dermal Root Sheath, from dermis.

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b. c. 6.

External Root Sheath, from epidermis. Internal Root Sheath, formed by matrix (from epidermis).

Arrector Pili Muscle. Contracts during sympathetic responses.

Glands 1.

Glands are invaginations of epidermis into dermis.

2.

Types: a.

Sebaceous Glands. 1) Connected to hair follicles by ducts. 2) Secrete sebum. a) Contraction of arrector pili muscle causes gland to secrete. b) Oily substance, coats hair & skin c) Inhibits desiccation of hair & skin, inhibits skin from cracking d) Bacteriocide. 3) Increase activity at puberty. 4) Acne vulgaris: Blocked ducts w/ subsequent bacterial infection of gland secretions.

b.

Sudoriferous Glands 1) Eccrine Sweat Glands. a) Release sweat via ducts directly onto skin. b) Function from birth. c) Found all over skin; concentrated in forehead, and palmar and plantar surfaces. d) Evaporative cooling e) Minor role in excretion. 2) Apocrine Sweat Glands. a) Release sweat via duct into hair follicles. b) Begin functioning at puberty. c) Found in axilla, groin, areola, facial hair. d) Sweat composition is odorless, BUT contains proteins & lipids that bacteria can act on, producing musty smell.

c.

Ceruminous Glands 1) External ear 2) Secrete via ducts into external auditory canal or into ducts of sebaceous glands. 3) Cerumen (= earwax) composed of ceruminous gland secretion + sebum.

Nails 1. 2. 3.

Location: Ends of fingers & toes Structure: Stratified epithelial cells, heavily keratinized & densely packed. Function: Protects ends of digits, allows fine manipulation of object and lets you scratch!

WOUND HEALING AND TISSUE REPAIR Epidermal Wound Healing 1. 2.

Trauma: Epidermis only Process a. Stratum basale cells adjacent to wound migrate across wound until they contact other basal cells and stop b. Stem cells replace migrating basal cells. c. Basal cells form new overlying strata and secrete new basement membrane.

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Deep Wound Healing 1. 2.

Trauma: Involves dermis & subcutaneous tissue Process a.

Inflammatory Phase. 1) Blood clot forms, stops bleeding 2) Histamine released from damaged cells initiates inflammation a) Histamine (1) Increases permeability of vessels (2) Causes vasodilation. (a) Edema results, which results in pressure & stimulation of free nerve endings (pain) and causes tissue to flush red and become hot (feverish). (b) With the increase flow of blood to the region, phagocytes enter and begin eating pathogens. Phagocytes include neutrophils and monocytes; monocytes differentiate into macrophages. (c) Mesenchymal cells enter. These are stem cells. They differentiate into fibroblasts.

b.

Migratory Phase 1) Scab forms from clot; scab is protective. 2) Basal cells migrate across the wound under the scab. 3) Fibroblasts begin secreting matrix fibers (collagen & glycoproteins) in dermis. 4) Endothelium proliferates

c.

Proliferative Phase 1) Basal cells form new epithelium 2) Fibroblasts proliferate, form new areolar & dense irregular connective tissues. 3) Endothelium continues to repair itself.

d.

Maturation Phase 1) Scab sloughs off. 2) Epithelium restored to normal thickness. 3) Fibrosis occurs (= scar formation). a) Granulation tissue develops into scar by fibroblasts. Scars are made of thick collagen fibers with less elasticity. b) Lack of melanocytes & melanin makes scars lighter in color than surrounding tissue.

PATHOLOGIES 1.

Burns. a. Caused by various factors including sun, heat, electricity, radiation, chemicals. b. Severity 1) First Degree. a) Only epidermis is damaged. b) No blisters. c) Heals in 3-6 days. d) Some pain. e) Example includes mild sunburns. 2) Second Degree. a) Epidermis & some of dermis involved. b) Blistering occurs; blistering is edema that separates epithelium from dermis. c) Epidermally-derived structures usually not involved. d) Very painful. e) Heals in 3-4 weeks if infection is not involved. f) Scarring may result. 3) Third Degree.

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a) Epidermis, dermis & subcutaneous layer involved. b) Marked edema. c) Nerve endings destroyed, thus no pain (surrounding, unaffected tissues may have intact nerve endings that would send intense pain signals). d) Healing slow, scarring results, skin grafts may be needed. 2.

Cancers of Skin. a. Skin cancers usually triggered by too much sun exposure. b. Types 1) Basal Cell Carcinoma. a) Most skin cancers. b) Involves basal cells. c) Benign, rarely malignant. 2) Squamous Cell Carcinoma. a) ~ 20% of all skin cancers. b) Squamous cells. c) Can become malignant & metastasize d) Death in 1% of cases. 4) Melanomas. a) ~ 2% of all skin cancers. b) Melanocytes. c) Malignant & deadly! Early detection is key—use following to diagnose melanomas: (1) Assymetric, border irregular, (2) Color uneven, (3) Diameter > 6 mm.

2.

Decubitus Ulcers a. Constant pressure over bony area stops blood to tissues & tissue necrosis results b. Seen in bed-ridden patients, prisoners.

3.

Vitiligo a. Loss of melanocytes, thus patients have little protection from UV exposure & skin is very light/white. b. Autoimmune

4.

Rickets/Osteomalacea a. Insufficient cholecalciferol production by skin (lack of UV light) leads to 1) Weak, bent bones in children (rickets) and 2) Poorly-calcified bones in adults that break easily (osteomalacea).

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