BIOL 2457 1st Edition Lecture 10Outline of Last Lecture I. Glandular Epithelium Outline of Current LectureI. The Integumentary System II. The organs of the integumentary system include the cutaneous membrane (skin) and its accessory structures including hair, nails, and glands, as well as blood vessels, muscles and nervesIII. Dermatology is the medical specialty for the diagnosis and treatment of disorders of the integumentary system.IV. The epidermis develops from the ectoderm; nails, hair, and skin glands are epidermal derivatives - the epidermis of a fetus is protectedby a fatty substance calledvernixcaseosa(a special white sebum)V. The dermis develops from the mesoderm. It is connective tissue. VI. Types of SkinVII. Types of skina. Thin (hairy) skini. Covers all body regions except the palms, palmar surfaces of digits, and solesb. Thick (hairless) skini. Covers the palms, palmar surfaces of digits, and solesVIII. Functions of the SkinIX. Regulation of body temperature (insulation, evaporation, vasodilatation & vasoconstriction) X. Blood reservoirXI. Protection of underlying tissues & organsXII. Cutaneous sensations (touch, pressure, pain, & temperature)XIII. Excretion (salts, water, organic waists via glands) & absorptionXIV. Synthesis of vitamin DXV. Stores LipidsXVI. ConnectionsXVII. Connectionsa. Cardiovascular systemi. Blood vessels in the dermisb. Nervous systemi. Sensory receptors for pain, touch, pressure & temperatureXVIII. Structure of the SkinXIX. The skin (cutaneous membrane) covers the body and is the largest organ of the body by surface area and weightXX. Its area is about 2 square meters (22 square feet) and weighs 4.5-5kg (10-11 lb), about 16% of body weightXXI. It is 0.5 – 4 mm thick, thinnest on the eyelids, thickest on the heels; theaverage thickness is 1 – 2 mmXXII. Structure of the SkinXXIII. Major layersa. Outer, thinner layer called the epidermisi. Consists of epithelial tissueb. Inner, thicker layer called the dermisXXIV. Subcutaneous (subQ) layer a. Also called hypodermisb. Located underneath the dermisc. Attaches the skin to the underlying tissues and organs XXV. Epidermis characteristicsa. Avascular stratified squamous epitheliumi. Nutrients and oxygen diffuse from capillaries in the dermisb. Composed of keratinized stratified squamous epitheliumc. Contains four major types of cellsi. Keratinocytesii. Melanocytesiii. Langerhans cellsiv. Merkel cellsXXVI. Keratinocytes a. 90% of the cells (most abundant in epidermis)b. Produce keratin which is a tough fibrous protein that provides protectionXXVII. Melanocytesa. Produce the pigment melanin that protects against damage by ultraviolet radiationXXVIII.Langerhans cellsa. Involved in immune responses – fixed macrophageb. Arise from red bone marrowXXIX. Merkel cellsa. Function in the sensation of touch along with the adjacent tactile discsXXX. EpidermisXXXI. Epidermis layers a. Four layers in thin skinb. Five layers in thickskinXXXII. Layers a. Stratum basale or stratum germinativumi. Deepest layerii. Where continuous cell division occurs which produces all the other layersb. Stratum spinosumi. 8-10 layers of keratinocytesc. Stratum granulosumi. Includes keratohyalin and lamellar granulesd. Stratum lucidumi. Present only in thick skin (the skin of the fingertips, palms,and soles)e. Stratum corneumi. Composed of many sublayers of flat, dead keratinocytes called corneocytes or squames that are continuously shed and replaced by cells from deeper strataii. Constant friction can stimulate formation of a callus.XXXIII.Keratinizationa. Accumulation of more and more protective keratinb. Occurs as cells move from the deepest layer to the surface layerXXXIV. Dandruffa. An excess of keratinized cells shed from the scalpXXXV. Vitamin D3XXXVI. Vitamin D3a. Epidermal cells produce cholecalciferol (vitamin D3)i. In the presence of UV radiationb. Liver and kidneys convert vitamin D3 into calcitrioli. To aid absorption of calcium and phosphorusc. Insufficient vitamin D3i. Can cause ricketsXXXVII. DermisXXXVIII. Dermis characteristicsa. Composed of connective tissue containing collagen and elastic fibers & capillaries b. Contains two layers i. Papillary region 1. Outer layer2. Consists of areolar connective tissue containing thin collagen and elastic fibers, dermal papillae (including capillary loops),corpuscles of touch and free nerve endingsii. Reticular layer1. Consists of dense irregular connective tissue containing collagen and elastic fibers adipose cells, hair follicles, nerves, sebaceous (oil) glands, and sudoriferous (sweat) glands2. Striae or stretch markscan appear if the skin is stretched too