Integumentary System PDF

Course Instructor: Tarek Nasr Required readings: Hole’s Essentials of Human Anatomy and Physiology. Chapter 6  Learning Outcomes By the end of this lecture, students should be able to: – List the components of the integumentary system. – Describe the layers of the skin and as...

Course Instructor: Tarek Nasr Required readings: Hole’s Essentials of Human Anatomy and Physiology. Chapter 6  Learning Outcomes By the end of this lecture, students should be able to: – List the components of the integumentary system. – Describe the layers of the skin and associated structures – List the functions of the skin. – Describe & compare accessory organs of the skin. – Describe common skin disorders.  Introduction - An organ is body structures composed of two or more different tissues. - Integumentary system consists of skin (the largest organ in the body), and the various accessory structures associated to it (hair, fingernails, glands, etc.)  Skin Functions: - Protective covering - Regulate body temperature - Retard water loss from deeper tissue - Houses sensory receptors - Excrete small quantity of waste - Production of vit.D - Play a role in immunity  Skin Layers: The skin includes 2 distinct layers: - Epidermis - Dermis Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed. Skin Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Skin Epidermis: - The epidermis is made up of stratified squamous epithelium and lacks blood vessels. - The layer of reproducing cells (the stratum basale) which lies at the base of the epidermis, is well- nourished by dermal blood vessels.  Skin Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Skin Epidermis: - Cells are pushed outward as new cells are formed, and become keratinized (filled with tough fibrous, waterproof protein called keratin) as they die. Four or five layers may be may accumulate forming a layer called stratum corneum. Dead cells will eventually shed. - The production of epidermal cells is in balance with the shedding of dead cells from S. corneum so, the skin does not wear - The thickness of epidermis differ from an area to another.  Skin Epidermis: - Thickest on the palms of the hands and the soles of the feet (0.8–1.4 mm). In other body regions, it is thin (0.07–0.12 mm). - In most areas, four layers are distinguishable (in order inward to outward). 1) Stratum basale (stratum germinativum)  Deepest layer 2) Stratum spinosum 3) Stratum granulosum 4) Stratum lucidum (only in thickened skin of palms & soles) 5) Stratum corneum (fully keratinized outermost layer) Skin Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Skin Epidermis: - Protects against water loss, mechanical injury, chemicals, and microorganisms. - Melanocytes, lie deep in the epidermis and underlying dermis, produce melanin that protects deeper cells from the sun's UV rays. - Skin color depends on the amount of melatonin produced. Other factors may include O2 in blood, diet (beta carotene), and disease states (e.g., Jaundice)  Skin Melanocyte Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Skin Dermis: - Binds the epidermis to underlying tissues. - Consists of connective tissue with collagen and elastic fibers within a gel-like matrix. - Contains blood vessels that carry nutrients to upper layers of skin and help regulate temperature. - Also contains nerve fibers, sensory fibers, hair follicles, sebaceous glands, and sweat glands.  Skin Hypodermis (subcutaneous): - Lies beneath the dermis and composed of loose connective tissue (mainly adipose tissue). - Hypodermis is not a true layer as there is no sharp boundary exists between the dermis and subcutaneous layer. - The hypodermis binds the skin to underlying organs and contains the blood vessels that supply the skin. In addition, the adipose tissue works as insulator.  Accessory Organs of the Skin Nails: Are protective coverings over the ends of fingers and toes. Consist of stratified squamous epithelial cells overlying the nail bed, with the lunula as the most actively growing region of the nail root. As new cells are produced, older ones are pushed outward and become Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed. keratinized.  Nails Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Accessory Organs of the Skin Hair follicle:  Hair can be found in nearly all regions of the skin.  Individual hairs develop from cells at the base of the hair follicle, an invagination of the lower epidermis that dips down into the dermis.  As new cells are formed, old cells are pushed outward and become keratinized, and die forming the hair shaft. Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Accessory Organs of the Skin Hair follicle:  A bundle of smooth muscle cells, called the arrector pili muscle, attaches to each hair follicle. These muscles cause goose bumps when cold or frightened.  Hair color is determined by genetics; melanin from melanocytes is responsible for most hair colors. Dark hair has eumelanin while blonde and red hair have pheomelanin Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed. Accessory Organs of the Skin Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Accessory Organs of the Skin Sebaceous gland: Sebaceous glands (holocrine glands) are associated with hair follicles and secrete sebum that waterproofs and moisturizes the hair shafts and keep the skin moist and soft. Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Accessory Organs of the Skin Sweat gland: Formed from a tiny coiled tube in the deeper dermis. The coil is lined with sweat secreting epithelium There are three types of sweat glands:  Eccrine (merocrine) glands  Apocrine glands  Modified glands Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Accessory Organs of the Skin Sweat glands: - Eccrine glands (merocrine) - Abundant in forehead, neck, and back. - Secrete sweat in response to heat and physical activities. - Secrete into duct that opens at the surface of the skin as a pore. - The secretion is mainly water + salt, uric acid, and urea (excretory functions).  Accessory Organs of the Skin Sweat glands: - Apocrine glands: - Abundant in axilla and groin. - Become active in puberty and secrete sweat in response to fear, pain, or sexual arousal. - Secrete into hair follicle and cause an odor. - Modified: - E.g., glands secreting ear wax and the female mammary glands secreting milk.  Regulation of body temperature - Why important? Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Skin Glands Source: Hole's Essentials of Human Anatomy & Physiology, 10th ed.  Common Skin Disorders - Acne - Photosensitivity - Sunburn - Eczema - Psoriasis - Infections skin conditions (Athlete’s foot, wart, pediculosis, scabies)  Acne  Acne vulgaris: increased sebaceous glandular activity at puberty.  Common, multi-factorial, self limiting skin condition.  Affects 80% of people between age 11 – 30.  4 factors are involved in the development of acne:  Follicular keratinization,  excess sebum,  P. acnes proliferation, and  inflammation. Acne  Photosensitivity Def. excessive response of the skin to sun in the presence of a sensitizing agent (under normal conditions, neither the light nor the compound cause tissue damage but the combination) It results from direct damage to tissue caused by a photo-activated compounds Perfumes, cosmetics, drugs and even sunscreen may cause photosensitivity. Patients should avoid sun exposure when taking these medications  Photosensitivity Many drugs can cause photosensitivity:  ACE Inhibitors  Chemotherapeutic agents  Antibiotics  Diuretics  Antidepressants  Hypoglycemics  Antihistamines  NSAIDs  Antipsychotics  Psoriasis Background: - A persistent chronic skin disease characterized by the production of patches of red, scaly skin. - It has no cure. - Appears commonly on elbow and knee but may affect any part of the body. - Genetics play an important role.  Sun and the Skin Sunburns: A burn of the skin produced by overexposure to UV (both A and B) radiation (sun or artificial sources) Sunburn cause tissue damage. Symptoms: Usually mild (reddish skin that is hot to the touch, general fatigue, and mild dizziness). It can be severe and life-threatening.  Sun and the Skin Skin type Tan/burn Skin hair and eye color Type I Never tan white skin, freckles, blond or always burn red hair, blue or green eyes Type II Sometimes tan white skin, blond hair, blue or usually burn green eyes Type III Usually, tan white skin, usually dark hair, seldomly burn and brown eyes Type IV & V Always tan brown to dark skin/ brown or never burn black hair/ brown eyes Sun and the Skin  Skin Burn Burns are classified by the extent of tissue damage: – 1st degree burn: A burn injuring only the epidermis. Healing  few days to 2 weeks + No scarring. – 2nd degree burn: A burn that destroys some epidermis as well as some of the dermis  forming blisters. – 3rd degree burn: A burn that destroys the epidermis + dermis + accessory structures of the skin  Eczema Eczema (referred to as Dermatitis): - An allergic skin disorder characterized by hot, itchy, red, oozing skin/skin lesions - Classified to - Atopic dermatitis. - Contact dermatitis.  Eczema Atopic Dermatitis: - Chronic pruritic eruption. - Allergic, hereditary, and psychogenic factors appear to be involved. - Treatment: – Topical corticosteroids and antihistamines are used. Absorption may occur if applied to large surface are. – TCA with strong antihistaminic effect. – Doxepin – Avoid Sunlight and alcohol.  Eczema Contact Dermatitis: - Contact dermatitis – inflammatory reaction in response to contact with an irritating agent. - Example: Poison ivy. - Treatment: Antihistamines, topical corticosteroids, and doxepin.