Essentials of Human Anatomy & Physiology PDF

Essentials of Human Anatomy & Physiology Thirteenth Edition...

Essentials of Human Anatomy & Physiology Thirteenth Edition Global Edition Unit 3 Chapter 4 INTEGUMENTARY AND Skin and Body BODY MEMBRANES Membranes Lecture Presentation by Student's Copy Patty Bostwick-Taylor Florence-Darlington Technical College Modified by Anna Michel Owatan Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. LEARNING LEARNING OBJECTIVES OBJECTIVES When provided List the Compare the List several with a model or Name the layers of Name the factors that Describe the Differentiate general structure important diagram of the skin, the epidermis, and determine skin color, distribution and among first-, functions of functions of the recognize and name and describe the function of the (tissue the following skin describe the epidermal second-, third-, each integumentary function of melanin. makeup) of the system, and structures: characteristics of appendages-sebace and fourth-degree membrane epidermis, dermis major explain how each. ous glands, sweat type (papillary and burns. cutaneous, membrane these functions reticular layers), glands, hair, and types. are hair and hair nails. mucous, follicle, sebaceous accomplished. serous, and gland, and sweat synovial-and gland. give its location in the body.  LEARNING OBJECTIVES Explain the Summarize the importance of the characteristics of basal cell carcinoma, squamous cell "rule of nines." carcinoma, and malignant melanoma. Body Membranes (1 of 2) Functions of body membranes ⚬ Cover body surfaces ⚬ Line body cavities ⚬ Form protective sheets around organs Classified according to tissue types Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Body Membranes (2 of 2) Epithelial Membranes (1 of 5) Two major categories Epithelial membranes are simple organs ⚬ Epithelial membranes Also called covering and lining ￭ Cutaneous membranes membranes ￭ Mucous membranes These membranes contain both: ￭ Serous membranes ⚬ Epithelial tissue layer ⚬ Connective tissue layer ⚬ Connective tissue membranes ￭ Synovial membranes Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Epithelial Membranes (2 of 5) Figure 4.1a Classes of Epithelial Membranes Cutaneous membrane = skin ⚬ Dry membrane ⚬ Outermost protective boundary ⚬ Consists of two layers ￭ Epidermis is composed of keratinized stratified squamous epithelium ￭ Dermis is mostly dense (fibrous) connective tissue Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Epithelial Membranes (3 of 5) Figure 4.1b Classes of Epithelial Mucous membranes (mucosae) Membranes ⚬ Moist membranes ⚬ Some mucosae secrete protective, lubricating mucus ⚬ Line all body cavities that open to the exterior body surface ⚬ Adapted for absorption or secretion ⚬ Consists of two layers ￭ Epithelium type depends on site Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. ￭ Loose connective tissue (lamina propria) Epithelial Membranes (4 of 5) Figure 4.1c Classes of Epithelial Membranes Serous membranes (serosae) ⚬Line compartments in the ventral body cavity that are closed to the exterior of the body ⚬Occur in pairs, separated by serous fluid, with a visceral and parietal layer ⚬Consists of two layers ￭ Simple squamous epithelium ￭ Areolar connective tissue Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.  Figure 4.1d Classes of Epithelial Epithelial Membranes (5 of 5) Membranes Specific serous membranes ⚬ Peritoneum ￭ Cover organs in the abdominal cavity ⚬ Pleurae ￭ Surround the lungs ⚬ Pericardia ￭ Surround the heart Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Connective Tissue Membranes Figure 4.2 A Typical Synovial Joint Synovial membranes ⚬ Loose areolar connective tissue only (no epithelial tissue) ⚬ Line fibrous capsules surrounding joints ￭ Line bursae ￭ Line tendon sheaths ⚬ Secrete a lubricating fluid to cushion organs Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. moving against each Integumentary System Functions of the Integumentary System (1 of 2) Integumentary system consists of Insulates and cushion deeper body the: organs ⚬Skin (cutaneous membrane) Protects the entire body from: ⚬Skin appendages ⚬ Mechanical damage (bumps and cuts) ￭ Sweat glands ⚬ Chemical damage (acids and bases) ￭ Oil glands ⚬ Thermal damage (heat or cold) ￭ Hair ⚬ Ultraviolet (U V) radiation (sunlight) ￭ Nails ⚬ Microbes (bacteria) ⚬ Water loss Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Functions of the Integumentary Table 4.1 Functions of the System (2 of 2) Integumentary System (1 of 2) Regulates heat loss as controlled by the Functions How accomplished Physical barrier contains keratin, which nervous system Protects deeper tissues from toughens cells; fat cells to cushion blows; and Acts as a mini-excretory system; sweat Mechanical damage (bumps) both pressure and pain receptors, which alert the nervous system to possible damage. aids in the loss of Has relatively impermeable keratinized cells; ⚬ Urea Chemical damage (acids and contains pain receptors, which alert the nervous bases) ⚬ Salts system to possible damage. Has an unbroken surface and “acid mantle” ⚬ Water (skin secretions are acidic and thus inhibit Synthesizes vitamin D Microbe damage microbes, such as bacteria). Phagocytes ingest foreign substances and pathogens, preventing Secretions create a protective acid them from penetrating into deeper body tissues. mantle Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Table 4.1 Functions of the Table 4.1 Functions of the Integumentary System (1 of 2) Integumentary System (2 of 2) Functions How accomplished Functions How accomplished Heat loss: By activating sweat glands Ultraviolet (U V) radiation Melanin produced by and by allowing blood to flush into Aids in body heat loss or heat (damaging effects of melanocytes offers protection skin capillary beds so that heat can retention (controlled by the sunlight or tanning beds) from U V damage. radiate from the skin surface. nervous system) Heat retention: By not allowing blood Thermal (heat or cold) Contains heat/cold/pain to flush into skin capillary beds. damage receptors. Aids in excretion of urea and Contained in perspiration produced by Contains a water-resistant uric acid sweat glands. Desiccation (drying out) glycolipid and keratin. Modified cholesterol molecules in skin Synthesizes vitamin D converted to vitamin D in the presence of sunlight. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (1 of 11) Figure 4.3 Skin Structure (1 of 2) Two kinds of tissue compose the skin ⚬ Epidermis ⚬ Dermis Subcutaneous tissue (hypodermis) ⚬ Anchors the skin to underlying organs ⚬ Not technically part of the integumentary system ⚬ Composed mostly of adipose tissue ⚬ Serves as a shock absorber and insulates deeper tissues Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (2 of 11) Epidermis—outer layer ⚬ Composed of stratified squamous epithelium ⚬ Most cells are keratinocytes which produce a fibrous protein called keratin ￭ Keratinization makes the epidermis tough ￭ Desmosomes connect keratinocytes together ⚬ Avascular ⚬ Composed of five layers (strata) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (3 of 11) Summary of strata (layers) of the epidermis from deepest to most superficial ⚬ Stratum basale ⚬ Stratum spinosum ⚬ Stratum granulosum ⚬ Stratum lucidum (thick, hairless skin only) ⚬ Stratum corneum Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (4 of 11) Stratum basale (stratum germinativum) ⚬ Deepest layer of epidermis ⚬ Lies next to dermis ⚬ Wavy borderline with the dermis anchors the two together ⚬ Cells undergoing mitosis ⚬ Daughter cells are pushed upward to become the more superficial layers Stratum spinosum ⚬ Cells become increasingly flatter and more keratinized Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (5 of 11) Stratum granulosum Stratum lucidum ⚬ Formed from dead cells of the deeper strata ⚬ Occurs only in thick, hairless skin of the palms of hands and soles of feet Stratum corneum ⚬ Outermost layer of epidermis ⚬ Shingle-like dead cells are filled with keratin (protective protein prevents water loss from skin) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.  Figure 4.4 The Main Structural Features of the Epidermis Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (6 of 11) Structure of the Skin (7 of 11) Melanin ⚬ Melanin is a pigment Epidermal dendritic cells produced by ⚬ Alert and activate immune cells to a melanocytes threat (bacterial or viral invasion) ⚬ Melanocytes are Merkel cells mostly in the stratum ⚬ Associated with sensory nerve endings basale of the ⚬ Serve as touch receptors called epidermis Merkel discs ⚬ Color is yellow to brown to black Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (8 of 11) Dermis ⚬ Connective tissue ⚬ Underlies the epidermis ⚬ Two regions ￭ Papillary ￭ Reticular Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (9 of 11) Structure of the Skin (10 of 11) Two regions of the dermis Two regions of the dermis ⚬ Papillary layer (upper dermal region) ⚬ Reticular layer (deepest skin layer) contain projections called dermal papillae ￭ Dense irregular connective tissue ￭ Areolar connective tissue ￭ Blood vessels ￭ Indent the epidermis above ￭ Sweat and oil glands ￭ Many projections contain capillary ￭ Deep pressure receptors (lamellar loops, and others house pain and touch corpuscles) receptors ￭ On palm and sole surfaces, papillae increase friction and gripping ability ￭ Fingerprints are identifying films of Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. sweat Figure 4.5 Light Micrograph of the Two Structure of the Skin Layers of the Dermis 100 times Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Structure of the Skin (11 of 11) Skin Color (1 of 2) Other dermal features Three pigments involved/ contribute to skin color ⚬Cutaneous sensory receptors 1. Melanin ⚬Phagocytes ￭ Yellow, reddish brown, or black pigments ⚬Collagen and elastic fibers ⚬Blood vessels ⚬Nerve supply Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Skin Color (1 of 2) Skin Color (1 of 2) Three pigments contribute to skin colon 2. Carotene Three pigments contribute to skin color ￭ Orange-yellow pigment (also found in some vegetables) 3. Hemoglobin ￭ Red coloring from blood cells in dermal capillaries ￭ Oxygen content determines the extent of red coloring Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Skin Color (2 of 2) Skin Color (2 of 2) Redness (erythema)—due to embarrassment, Pallor (blanching)—due to emotional stress inflammation, hypertension, fever, or allergy (such as fear), anemia, low blood pressure, impaired blood flow to an area Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Skin Color (2 of 2) Skin Color (2 of 2) Jaundice (yellow cast)—indicates a liver Bruises (black and blue marks)—hematomas disorder Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Appendages of the Skin (1 of 10) Figure 4.3 Skin Structure (2 of 2) Cutaneous glands are all exocrine glands ⚬ Sebaceous glands ⚬ Sweat glands Hair and hair follicles Nails Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Appendages of the Skin (2 of 10) Figure 4.6a Cutaneous Glands Sebaceous (oil) glands ⚬ Located all over the skin except for palms and soles ⚬ Produce sebum (oil) ￭ Makes skin soft and moist ￭ Prevents hair from becoming brittle ￭ Kills bacteria ⚬ Most have ducts that empty into hair follicles; others open directly onto skin surface ⚬ Glands are activated at puberty with increased androgens Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Appendages of the Skin (3 of 10) Appendages of the Skin (4 of 10) Sweat (sudoriferous) glands Eccrine glands ⚬ Produce sweat ⚬ More numerous, located all over the body ⚬ Widely distributed in skin ⚬ Open via duct to sweat pores on the skin’s Two types of sudoriferous glands surface 1. Eccrine glands ⚬ Produce acidic sweat 2. Apocrine glands ￭ Water, salts, vitamin C, traces of metabolic waste ⚬ Function in body temperature regulation Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 4.6b Cutaneous Glands Appendages of the Skin (5 of 10) Apocrine glands ⚬ Ducts empty into hair follicles in the armpit and genitals ⚬ Begin to function at puberty ⚬ Release sweat that also contains fatty acids and proteins (milky or yellowish color) ⚬ Play a minimal role in body temperature regulation Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Appendages of the Skin (6 of 10) Hair ⚬ Located body-wide except for palms, soles, nipples, lips ⚬ Produced by hair follicle ⚬ Root is enclosed in the follicle ⚬ Shaft projects from the surface of the scalp or skin ⚬ Consists of hard keratinized epithelial cells ⚬ Melanocytes provide pigment for hair color ⚬ Hair grows in the matrix of the hair bulb in stratum basale Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 4.7a Structure of a Hair Root and Appendages of the Skin (7 of 10) Follicle Hair anatomy ⚬ Central medulla ⚬ Cortex surrounds medulla ⚬ Cuticle on outside of cortex ￭ Most heavily keratinized region of the hair ⚬ Melanin provides color Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 4.7b Structure of a Hair Root and Figure 4.7c Structure of a Hair Root and Follicle Follicle Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.  Figure 4.7d Structure of a Hair Root and Follicle Appendages of the Skin (8 of 10) Associated hair structures ⚬Hair follicle ￭ Composed of an inner epithelial root sheath and an outer fibrous sheath ￭ Dermal region provides a blood supply to the hair bulb (deepest part of the follicle) ￭ Arrector pili muscle connects to the hair follicle to pull hairs upright when we are cold or frightened Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Appendages of the Skin (9 of 10) Nails ⚬ Heavily keratinized, scalelike modifications of the epidermis ⚬ Stratum basale extends beneath the nail bed, which is responsible for growth ⚬ Lack of pigment makes nails colorless Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Appendages of the Skin (10 of 10) Figure 4.8 Structure of a Nail Parts of a nail ⚬ Free edge ⚬ Body is the visible attached portion ⚬ Nail folds are skin folds that overlap the edges of the nail; the cuticle is the proximal edge ⚬ Root of nail is embedded in skin ⚬ Growth of the nail occurs from nail matrix of nail bed Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (1 of 13) Infections and allergies ⚬ Athlete’s foot ￭ Caused by fungal infection (Tinea pedis) ￭ Itchy, red peeling skin between the toes ⚬ Boils (furuncles) and carbuncles ￭ Caused by inflammation of hair follicles ￭ Carbuncles are clusters of boils caused by bacteria ⚬ Cold sores (fever blisters) ￭ Caused by human herpesvirus 1 Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. ￭ Blisters itch and sting Homeostatic Imbalances of Skin (2 of 13) Infections and allergies ⚬ Contact dermatitis ￭ Caused by exposure to chemicals that provoke allergic responses ￭ Itching, redness, and swelling of the skin ⚬ Impetigo ￭ Caused by bacterial infection ￭ Pink, fluid-filled raised lesions around mouth/nose ⚬ Psoriasis ￭ Triggered by trauma, infection, hormonal changes, or stress ￭ Red, epidermal lesions covered with dry, silvery scales that itch,Copyright burn,© 2022 crack, Pearsonor sometimes Education, Ltd. All Rights Reserved. bleed Figure 4.9 Cutaneous Lesions Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (3 of Homeostatic Imbalances of Skin (4 of 13) 13) Burns Extent of a burn is estimated using the rule of ⚬ Tissue damage and cell death caused by nines heat, electricity, U V radiation, or chemicals ⚬ Body is divided into 11 areas for quick ⚬ Associated dangers estimation ￭ Protein denaturation and cell death ⚬ Each area represents about 9 percent of total ￭ Dehydration and electrolyte imbalance body surface area ￭ Circulatory shock ￭ The area surrounding the genitals (the ⚬ Result in loss of body fluids and infection perineum) represents 1 percent of body from the invasion of bacteria surface area Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 4.10a Burns Diagram of Rule of Nines Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (5 of 13) First-degree burn (superficial burn) ⚬ Only epidermis is damaged ⚬ Skin is red and swollen Second-degree burn (superficial partial-thickness burn) ⚬ Epidermis and superficial part of dermis are damaged ⚬ Skin is red, painful, and blistered ⚬ Regrowth of the epithelium can occur Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (6 of 13) Third-degree burn (full-thickness burn) ⚬ Destroys epidermis and dermis; burned area is painless ⚬ Requires skin grafts, as regeneration is not possible ⚬ Burned area is blanched (gray-white) or black Fourth-degree burn (full-thickness burn) ⚬ Extends into deeper tissues (bone, muscle, tendons) ⚬ Appears dry and leathery ⚬ Requires surgery and grafting ⚬ May require amputation Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 4.10b Examples of Burns Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.  Homeostatic Imbalances of Skin (7 of 13) Criteria for deeming burns critical (if any one is met): ⚬ Over 30 percent of body has second-degree burns ⚬ Over 10 percent of the body has third- or fourth-degree burns ⚬ Third- or fourth-degree burns of the face, hands, feet, or genitals ⚬ Burns affect the airways ⚬ Circumferential (around the body or limb) burns have occurred Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (8 of Concept Link 13) Skin cancer Recall that mitosis gone wild is the basis for cancer ⚬ Most common form of cancer in humans (Chapter 3, pp. 104–105). These cells lack normal ⚬ Most important risk factor is overexposure to control of cell division and divide quickly, resulting in ultraviolet (U V) radiation in sunlight and errors during D N A replication, mitosis, or both. Cells tanning beds experiencing rapid, uncontrolled growth become cancerous and can metastasize (spread) to other parts Cancer can be classified two ways of the body. 1. Benign means the neoplasm (tumor) has not spread 2. Malignant means the neoplasm has invaded other body areas Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (9 of Homeostatic Imbalances of Skin (10 of 13) 13) Most common types of skin cancer Basal cell carcinoma ⚬ Basal cell carcinoma ⚬ Least malignant and most common type of ⚬ Squamous cell carcinoma skin cancer ⚬ Malignant melanoma ⚬ Arises from cells in stratum basale that are altered so that they can no longer make keratin ⚬ Lesions appear as shiny, dome-shaped nodules that develop a central ulcer Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 4.11a Photographs of Skin Homeostatic Imbalances of Skin (11 of Cancers 13) Squamous cell carcinoma ⚬ Believed to be induced by U V exposure ⚬ Arises from cells of stratum spinosum ⚬ Lesions appear as scaly, reddened papules that gradually form shallow ulcers ⚬ Early removal allows a good chance of cure ⚬ Metastasizes to lymph nodes if not removed Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.  Figure 4.11b Photographs of Skin Homeostatic Imbalances of Skin (12 of Cancers 13) Malignant melanoma ⚬ Most deadly of skin cancers, but accounts for only 5 percent of skin cancers ⚬ Cancer of melanocytes ⚬ Metastasizes rapidly to lymph and blood vessels ⚬ Detection uses A B C D E rule for recognizing melanoma Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Homeostatic Imbalances of Skin (13 of 13) Figure 4.11c Photographs of Skin Malignant melanoma ⚬ A = Asymmetry Cancers ￭ Two sides of pigmented mole do not match ⚬ B = Border irregularity ￭ Borders of mole are not smooth ⚬ C = Color ￭ Different colors in pigmented area ⚬ D = Diameter ￭ Spot is larger than 6 mm in diameter ⚬ E = Evolution ￭ One or more of the ABCD characteristics is evolving Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Developmental Aspects of Skin and Developmental Aspects of Skin and Body Membranes (1 of 2) Body Membranes (1 of 2) Vernix caseosa, an oily covering, is apparent Lanugo, a at birth downy hair, covers the body by the fifth or sixth month of fetal development but disappears by birth Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Developmental Aspects of Skin and Developmental Aspects of Skin and Body Membranes (1 of 2) Body Membranes (1 of 2) Milia, small Acne may appear during adolescence white spots, are common at birth and disappear by the third week Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Developmental Aspects of Skin and Developmental Aspects of Skin and Body Membranes (1 of 2) Body Membranes (2 of 2) In youth, skin is thick, resilient, and well hydrated Pimples, With aging, skin loses elasticity and thins scales, and Skin cancer is a major threat to skin exposed dermatitis are more to excessive sunlight common with Balding (alopecia) and/or graying occurs with aging skin aging; both are genetically determined; other factors that may contribute include drugs and emotional stress Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.