Transcript Dermis
Chapter 2 The Integumentary System Integumentary System The body’s covering Includes: skin, nails, and hairs Skin: cutaneous membrane The skin (integument), is the largest organ of the body covering over 7600 cm2 (3000 in2) Structure Two main parts Epidermis - surface epithelial layer Dermis - deeper connective tissue layer Subcutaneous (subQ) layer or hypodermis lies deep to dermis; is not part of the skin Integumentary System Epidermis Keratinized stratified squamous epithelium Cell types (4): Keratinocytes Melanocytes Langerhans cells Merkel cells Epidermal Cells Keratinocytes 90% of epidermal cells 4-5 layers Produce keratin Protects skin Waterproofs skin Epidermal Cells Melanocytes Produce melanin that gives color to skin, hairs Transfer pigment to keratinocytes Make up 8% of epidermal cells Epidermal Cells Langerhans cells Immune response Merkel cells Sense of touch Consist of tactile disc and neuron for touch sensation Epidermal Layers Four Layers (strata) Stratum basale Stratum spinosum: 8-10 cell layer Cells beginning to look flattened Stratum granulosum makes keratin Includes stem cells; new cells arise here Losing cell organelles and nuclei Have waterproofing lipid Stratum corneum: flattened dead cells Cells here consist mostly of keratin. Cells here are shed and replaced from below. Layers of the Epidermis Dermis The dermis has several important characteristics: is composed of connective tissue containing collagen and elastic fibers contains two layers the outer papillary region consists of areolar connective tissue containing thin collagen and elastic fibers, dermal papillae (including capillary loops), corpuscles of touch and free nerve endings Dermis The deeper reticular region consists of dense irregular connective tissue containing collagen and elastic fibers adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands Striae or stretch marks can appear if the skin is stretched too much Dermis Lines of cleavage - “tension lines” in the skin indicate the predominant direction of underlying collagen fibers Epidermal ridges reflect contours of the underlying dermal papillae and form the basis for fingerprints (and footprints); their function is to increase firmness of grip by increasing friction. Dermatoglyphics - the study of the pattern of epidermal ridges Skin Color Normal skin color is caused by the expression of a combination of i) melanin, ii) carotene & iii) hemoglobin. Melanin – brown-black pigment produced in the melanocytes of the stratum basale All races have virtually same # of melanocytes, but the amount of melanin produced + degree of granular aggregation of the melanin determine whether an individual’s skin color is black, brown, tan or white Melanin – protective device against UV damage Gradual exposure to sunlight promotes the increased production of melanin within the melanocytes – tanning Albino – normal melanocytes but lacks the enzyme tyrosinase (tyrosine melanin) Vitiligo – lacks of melanocytes in localized area – white spot Albino vitiligo Coloration of the Skin Carotene – yellowish pigment found in epidermal cells and fatty parts of the dermis Carotene is abundant is the skin of Asians + melanin – yellow-tan skin Hemoglobin – not a pigment, oxygen-binding pigment found in RBC Oxygenated blood flowing through the dermis gives the skin its pinkish tones Accessory Structures Hair Skin glands Nails Hair Found on most skin surfaces Made of fused keratinized cells Consists of shaft and root Surrounded by hair follicle Not on palmar surfaces of hand and fingers or plantar surfaces of feet Base is bulb which includes growing matrix producing cells Nerves in hair root plexuses Muscle that pulls on hair: arrector pili Causes hair to stand on end Hair Humans have three distinct kinds of hair Lanugo is a fine, silky fetal hair that appears during the last trimester of development. Not evident on a baby at birth unless it has been born prematurely. Angora hair grows continuously in length, as on the scalp of males and females and on the face of males. Definitive hair grows to a certain length and then ceases to grow. It is the most common type of hair. Eg. eyelashes, eyebrows, pubic & axillary hair. Glands Sebaceous gland: secrete oily sebum Sudoriferous (sweat) gland Connected to hair follicles; keeps hair from drying out Eccrine sweat gland Wide distribution – thermoregulation Apocrine sweat gland Axilla, groin, areolae, beard Contain other cell material Ceruminous (wax) gland Wax combines with sebum to produce earwax Nails Plates of packed hard dead keratinized cells Nail body: major visible portion Free edge: part extending past finger or toe Root: cells deep to here (in nail matrix) form new nail cells Nails Functions of Skin Temperature regulation Protection Sensory reception Excretion and absorption: small amounts Vitamin D synthesis Thermoregulation Body temperature tends to increase as a result of exercise, fever, or an increase in environmental temperature. Homeostasis is maintained by the loss of excess heat. The blood vessels (arterioles) in the dermis dilate and allow more blood to flow through the skin, thus transferring heat from deeper tissues to the skin. To counteract environmental heat gain or to get rid of excess heat produced by the body, sweat is produced. The sweat spreads over the surface of the skin, and as it evaporates, heat is lost from the body. Thermoregulation If body temperature drops below normal, heat can be conserved by a decrease in the diameter of dermal blood vessels, thus reducing blood flow to the skin. With less warm blood flowing through the skin, however, the skin temperature decreases. If the skin temperature drops below approximately 15 degrees Celsius, blood vessels constrict, which helps to prevent tissue damage from the cold. Contraction of the arrector pili muscles causes hair to stand on end, but with the sparse amount of hair covering the body, this does not significantly reduce heat loss in humans. Hair on the head, however, is an effective insulator. Aging Adolescence: can develop acne Most effects in dermis, with visible signs of aging by about age 40. These include: Loss of collagen fibers Loss of elasticity Loss of immune responses Decreased melanocyte functions: gray hair, skin blotches Thinning of skin and hairs Anti-aging treatments Conditions of the skin & associated structures indicating nutritional deficiencies or body dysfunctions Condition Deficiency Comments General dermatitis Zinc Redness & itching Scrotal or vulva dermatitis Riboflavin Inflammation in genital region Hyperpigmentation B12, folic acid, or starvation Dark pigmentation on backs of hands & feet Dry, stiff, brittle hair Protein, kcal, & other nutrients Usually occurs in young children or infants Follicular hyperkeratosis Vit A, unsaturated fatty acids Rough skin due to keratotic plugs from hair follicles Pellagrous dermatitis Niacin & tryptophan Lesions on areas exposed to sun Thickened skin at pressure point Niacin Noted at belt area at the hips Spoon nails Iron Thin nails that are concave of spoonshaped Dry skin H20 or thyroid hormone Dehydration, hypothyroidism, rough skin Oily skin (acne) Hyperactivity of sebaceous glands Spoon nail Additional Info: Sun Safety Tips Watch the clock Sunblock SPF 15 or 30 if at high risk Avoid exposure from 10AM – 4PM UVA/UVB Apply 30min before exposure Reapply every 2hrs Wear sunglasses & protective clothing Do not prolong sun exposure just because you are wearing sunscreen! Copyright 2010, John Wiley & Sons, Inc.