Skin & Appendages PDF

# SKIN & APPENDAGES ## Prof. Dr. Burak BİLECENOĞLU, DDS, PhD Ankara Medipol University, Faculty of Medicine Dept. of Anatomy [email protected] ## SKIN - Integumentary system (L. integumentum: a covering) - One of the best indicators of general health, careful observation of i...

# SKIN & APPENDAGES ## Prof. Dr. Burak BİLECENOĞLU, DDS, PhD Ankara Medipol University, Faculty of Medicine Dept. of Anatomy [email protected] ## SKIN - Integumentary system (L. integumentum: a covering) - One of the best indicators of general health, careful observation of it is important in physical examinations - Largest organ of the body - Approximately 16% of body weight - Surface area ~2 m², weight 5 kg, thickness between 0.5-5 mm - The thinnest part of the skin is the eyelids (0.5 mm), the thickest part is the palmar surface of the hand and the plantar surface of the foot (4-5 mm) - The skin provides: - Protection of the body from environmental effects - Abrasions, fluid loss, harmful substances, UV radiation, microorganisms... - Containment for the body's structures and vital substances - Preventing dehydration - Thermal regulation - Sweat and/or the dilation or constriction of superficial blood vessels - Sensation - Superficial nerves and sensory endings - Synthesis and storage of vitamin D - 2 different types of skin: - Thin and hairy skin - covering most of the body - Thick, hairless skin - Glabrous skin - Palmar surface of the hand - Plantar surface of the foot - Flexor surfaces of the fingers - The skin has ridges and indentations arranged in different ways on the hand's palmar surface, the foot's sole, and the fingertips' flexor surface. Dermatoglyphic (fingerprints): Unique - Skin has a two-layered structure ## EPIDERMIS - Keratinized epithelium derived from ectoderm - Consists of stratified squamous epithelium made up of cells called keratinocytes - It is an avascular, waterproof barrier, supplied by arteries of the dermis - Thin > cuts in the skin immediately penetrate the dermis and cause bleeding - Renews every 20-30 days - Sweat glands, sebaceous glands, nails, and hair are derivations of the epidermis - The epidermis has a five-layered structure (from superficial to deep): - Cornified layer (stratum corneum) - Clear layer (stratum lucidum) - Protects from UV - Thicker at palms & soles, therefore these areas do not tan in the sun - Granular layer (stratum granulosum) - Spinous layer (stratum spinosum) - Thickest layer - Basal (germinal) layer (stratum basale) - Layer where new cells are produced, Merkel cells & melanocytes are found ### IMPORTANT NOTE - MERKEL (MERKEL-RANVIER) CELLS (tactile epithelial cells) - Mechanoreceptors essential for light touch senses - Abundant in areas of touch-sensitive skin, such as the fingertips, and make synaptic contacts with general somatic afferent (GSA) nerve fibers ## DERMIS (CORIUM) - Connective tissue that supports the epidermis - Formed by collagen & elastic fibers - Originates from mesoderm - Rich in blood vessels (superficial capillary beds) and nerves - Has two layers: - Papillary layer - Contains type III collagen - Meissner & Krause's corpuscles are in this layer - Reticular layer - Rich in type I collagen - Sweat and sebaceous glands, blood and lymph vessels, nerve terminals, hair follicles, and arrector pili muscles are in this layer - Pacinian corpuscles & Ruffini's end organ are in the deep parts of the dermis ### IMPORTANT NOTE - **TYPE I COLLAGEN** - Most abundant (80%) collagen in the dermis - Provides tensile strength to the skin - **TYPE III COLLAGEN** - 2nd most abundant (20%) type of collagen in soft tissues - Active in the wound healing ## RECEPTORS - Meissner's (tactile) corpuscles: Responsible for sensitivity to light touch. Most concentrated in thick hairless skin, especially at the finger pads. Tactile corpuscles are rapidly adapting mechanoreceptors. They are sensitive to shape and textural changes in exploratory and discriminatory touch (Braille text) - Krause corpuscles: Thermoreceptors (?) - Ruffini ending; sensitive to skin stretch and contributes to the kinesthetic sense of and control of finger position and movement. They are at the highest density around the fingernails where they act in monitoring slippage of objects along the surface of the skin, allowing modulation of grip on an object (+thermoreceptors) - Pacinian corpuscle; is found in both types of skin, viscera, joints, and attached to the periosteum of bone, primarily responsible for sensitivity to vibration & pressure ## CLINICAL CORELATION - Orientation of collagen fibers within the reticular dermis > creates lines of tension called Langer's lines (distraction/cleavage lines) - Relevant in surgery and wound healing - Provide the tension of the skin - Surgical incisions made parallel to these lines result in less bleeding, and small scars & healing will be faster. Incisions made perpendicular to these lines create larger keloidal scars after healing - During puberty/pregnancy elastic & collagen fibers of the dermis could tear apart as a result of extreme stretch. On the skin of the abdomen, gluteal region, breast, and thighs, initially red, then pink and then white lines remain (stretch marks) and do not completely disappear ## HYPODERMIS (SUPERFICIAL FASCIA) - Superficial fascia, subcutaneous tissue - Loose connective tissue layer deep to the dermis - Facilitates the movement of the skin & acts as a heat insulator - Composed of two layers and muscles of facial expression, superficial vessels & nerves, and breasts (mammary glands) are found btw. these two layers - The outer layer contains varying proportions of fat cells in some areas. Especially in the lower part of the anterior abdominal wall, it is very rich in fat cells and is known as panniculus adiposus. The outer layer of the hypodermis is the body's fat storage. The inner layer consists of fibrous tissue. - It is absent in the external ear (auricle & external acoustic meatus) ## DEEP FASCIA - Tight connective tissue layer deep to the superficial fascia - It's rich in nerves and it's all about the muscles - It wraps around the muscles, allows the muscles to move together, and creates the origin for the muscles. It forms intermuscular septums, retinaculums, fibrous sheaths, tendinous arches, and aponeuroses - It is expressed by the name of the region (deep fascia of the arm/forearm/leg or pectoral fascia...) - Like the superficial fascia, it is found throughout the body. It is absent only in the face region ## SKIN GLANDS ### SWEAT (SUDORIFEROUS) GLANDS - **ECRINE SWEAT GLANDS** - Opens to the skin surface - Plays an important role in the regulation of body temperature - Sympathetic (cholinergic) - Abundant on palms & soles - Absent in glans of penis (clitoris), inner surface of foreskin of penis (prepuce), eardrum, nail beds, margins of lips, nipples & labia minora of the vagina - **APOCRINE SWEAT GLANDS** - Opens into the hair canal or skin surface - Sympathetic (cholinergic) - Abundant in the axilla, areola of the breasts, periumbilical region, prepuce, inner lips of vagina, scrotum, mons of pubis & perianal skin - Larger & deeper - Examples: Ceruminous glands of the external acoustic meatus & Moll glands of the eyelids ## SEBACEOUS GLANDS - They secrete an oily/waxy matter, called sebum - The main function of sebum is lubrication & protection - (+ protective effect against bacteria and fungi) - Generally connected to a hair follicle - Absent in palms of the hands and soles of the feet, abundant at back, face & scalp - Controlled by androgens - Examples; - Inner surface of prepuce: Tyson's glands - Margin of eyelids; Tarsal glands (Meibomian glands) - Eyelids Wolff's glands ### CLINICAL NOTE - Increased production of sebum can lead to a blockage of the sebaceous gland duct. This can cause an inflamation (comedo). Comedo is the primary lesion of acne ## CLINICAL CORELATION - CYANOSIS - Blood flow through the superficial capillary beds of the dermis affects the color of skin - When the blood is not carrying enough O₂ the skin can appear bluish (Cyanotic) - Cyanosis occurs because the O₂-carrying hemoglobin of blood appears bright red when carrying O₂ & appears deep, purplish blue when lack of O2. - Cyanosis is especially evident where the skin is thin, such as the lips, eyelids and deep to the transparent nails ## CLINICAL CORELATION - ERYTHEMA - Skin injury, exposure to excess heat, infection, inflammation, or allergic reactions may cause the superficial capillary beds to become engorged, making the skin look abnormally red, a sign called erythema ## CLINICAL CORELATION - JAUNDICE - In certain liver disorders, a yellow pigment called bilirubin builds up in the blood, giving a yellow appearance to the whites of the eyes and skin, a condition called jaundice ## HAIR - Develops from cells in hair follicles formed by the invagination of the epidermis - The enlargement in the lowest part of the follicle is called the hair bulb - Arrector pili muscle (smooth muscle_Symp.), which is attached to the middle part of the follicle, pulls the follicle and straightens the hair when it contracts (goosebumps) - This muscle is absent at the; eyebrows, eyelashes, hairs of the nose & ear, face, axilla & mons of pubis - Each strand of hair is made up of by three layers formed by keratin; the medulla, cortex, and cuticle (from deep to superficial) - The cortex, which contains melanin, which gives hair its color, is the thickest layer - Hair turns white as the pigment in the cortex decreases and the medulla fills with air (as seen by aging) - There are no hair follicles at the: Palms, soles, belly button, glans of penis (clitoris), lips, prepuce, labia minora of the vagina, inner surface of the labia majora of the vagina & nipples ## NAIL - Is a keratinized epithelial cell plate - Hyponchium: Epidermis section under the free (distal) edge of the nail - Eponychium (cuticle): Fold on nails lateral edges and the proximal edge - Lunula (L. small moon): Visible part of the matrix, the whitish crescent-shaped base of the visible nail - Nail bed - Nail matrix: The skin around the root of the nail, which plays a role in nail growth and repair, is where new nail cells are formed ## MAMMARY GLANDS (BREASTS) - Originates from ectoderm - They are specialized accessory glands of the skin (mammary glands) - Modified sweat glands - Btw. the levels of 2nd-6th ribs, and btw. the layers of the superficial fascia (before puberty & in males) - They are rudimentary & functionless in males - Weight and dimensions vary among individuals - The size of the nonlactating breasts depends on the fat surrounding - Upper lateral quadrant of the breasts reaches out to the axilla (armpit), this part is called the axillary (lateral) process (Spence's tail) - Nipples, are located at the 4th intercostal space in females before puberty & in males - Nipples are rich in melanocytes and contain smooth muscle cells - Nipples are surrounded by a pigmented area called the areola. The bumps formed on the skin by glands called areolar glands located here are called areolar tubercles (Montgomery tubercles). These glands secrete an oily fluid during breastfeeding, making the nipple slippery - Each breast consists of 15-20 lobules separated by fibrous partitions (lobules of the mammary gland) - Each lobule contains glands that produce and secrete milk & has one main lactiferous duct - These ducts make expansions called lactiferous sinus deep to the areola. During lactation (breastfeeding), these sinuses, where milk is stored, open to the nipple. There are 15-20 holes in the nipple. - The breast lobules are separated from each other by fibrous (not elastic) partitions extending from the ducts to the dermis - These extensions, called the suspensory ligaments of breasts (Cooper's ligaments), hold the breasts in position - Lateral thoracic artery - Lateral mammary branches - Superior thoracic artery - Thoracoacromial artery - Subscapular artery - Anterior intercostal arteries 2-4 - Medial mammary branches - Posterior intercostal arteries 2-4 - Lateral mammary branches ## QUADRANTS of BREAST ## LYMPH of the BREASTS - Originate from the subareolar lymphatic plexus around the nipple - Lateral quadrants (75%) > axillary lymph nodes (mainly to the pectoral) - Medial quadrants (25%) > parasternal (internal mammary) lymph nodes - Inferior quadrants > to the abdominal lymph node or to the opposite side - Interpectoral nodes (Rotter's nodes) drain the lymph from breasts, but it is not a member of the axillary lymph node group ## CLINICAL NOTE - BREAST CANCER - Most common type of cancer in females (%25) - 2 million cases/year - 627000 deaths/year - Symptoms; - Lump on breast - Shape change & asymmetry of the breasts - Skin dimpling - Clear/bloody fluid from the nipple - Change in the shape of the nipple - Red scaly lesions on the breast skin - Risc factors; - Females (x100 compared to males) - Obesity - Inactive lifestyle - Alcoholism - Radiation - Early onset of the menstrual cycle - Familial factors & genetics