Study Guide The Integumentary System - Skin, Glands, Hairs, and Nails

Class Notes and Study Guide The Integumentary System Integument = Cutaneous Membrane = Skin and associated structures – 3 terms meaning the same thing (glands, hairs, nails) The integument is considered an organ because it has multiple tissue types that work together to do the functions of the integument. Functions of the Integument: • • • • • • • • Protection - physical barrier Metabolism of Vitamin D (UV)– epidermis helps make the active form of Vitamin D when UV light is absorbed Waterproofing – keratin keeping water both in and out Immune Function – immune cells in the skin perform immune and phagocytic actions Secretion/Absorption – sebum and sweat secreted, some chemicals and UV radiation absorbed Sensation – neural endings in the dermis detect stimuli like touch, vibration, temperature Temperature Regulation Communication Components of the Integument ● Epidermis – outer layer of integument • 4 or 5 distinct component layers • Keratinized stratified squamous epithelium ● Dermis – inner layer of integument • 2 component layers • Composed of connective tissue with nervous and smoothmuscle tissue within • Papillary layer (areolar) • Reticular layer (dense irregular connective tissue) • Subcutaneous layer (hypodermis) – not part of the integument, but its function is highly related • Areolar tissue • Adipose tissue Epidermis • • • Composed of 4-5 layers of keratinized stratified squamoustissue Deepest 3 layers are made of living cells; the most superficial one or two layers are made of dead cells that are full of keratin protein Keratin gives toughness and waterproofing qualities Some areas of our body surfaces experience a great deal more stress than others. In those areas (the palms of the hands and the soles of the feet), wehave an extra layer of keratinocytes to add stress resistance. Thick Skin – 5 layers of cells Thin Skin – 4 layers of cells Found in palms of hands, soles of feet Found everywhere else Layers: basale, spinosum, granulosum, lucidum, Layers: basale, spinosum, granulosum, corneum corneum The layers of epidermis represent the life-cycle of a keratinocyte. It’s born in the basale and the moves up through the layers as it matures, eventually dying and then sloughing off the body. How stem cells work: In integument, the specialized cell is keratinocytes. Layers (strata) of epidermis: DEEP SUPERFICIAL Stratum Basale – Deepest layer – cells look cuboidal or stumpy columnar in shape and are found in a single layer 3 cell types: ● Keratinocyte stem cells – divide to reproduce and make new skin cells (keratinocytes) ● Melanocyte (pigment cell) – produce & store melanin in response to UV light exposure; absorbs radiation to protect DNA ● Tactile cell (Merkel cell) – detects touch (compression of the cell stimulates underlying neuron) Stratum Spinosum – cells look spiny as they start to become more squamous-shaped • Made of daughter cells formed when stem cells in basale layer divide • 8-12 layers of daughter cells (polygonal keratinocytes)that are turning into keratinocytes (not making them) • Contains some immune cells - dendritic cells (aka langerhans cells) monitor for foreign invaders or other immune threats (i.e. cancerous cells) Stratum Granulosum – 3-5 layers of keratinocytes (cellsthat make keratin) look grainy • Begins keratinizaion to make keratin, fill up with it, and die (nucleus and organelles disintegrate) • Cells toward the superficial side of granulosum aremostly dead • Also contains some dendritic/langerhans cells Stratum Lucidum – Only in thick skin – 2-5 cell layers filled with a translucent keratin protein (eleidin) • Completely dead cells Stratum Corneum – Most superficial – 20-30 layers of dead, interlocked keratinized cells • Number of layers depends on the location - areas ofhigher stress have more layers • Dry, thickened surface for protection from abrasions, infection, etc. Skin Color is determined by the combination of color-producing molecules contained in skin. ● Hemoglobin looks red when bound to oxygen. It’s in the blood but can be seen through the epidermal layers. ● Melanin is brown. The amount in our skin varies based on exposure to UV and how rapidly we remove it. - Most people who can make melanin make about the same amount of it. How much remains in the skin is determined by how quickly it is removed/broken down. People with lighter skin remove melanin more rapidly than people with darker skin - Albinism is the inability to produce melanin ● Carotene is orange-yellow and is acquired from some vegetables we eat and moved to the skin as an antioxidant Skin Markings Nevus (mole) • Localized overgrowth/overdivision of melanocytes • Should be monitored for changes suggesting malignancy Freckles • Yellowish or brown spots • Localized areas of increased melanocyte activity Friction ridges • Large folds and valleys of dermis and epidermis • Found on both thin and thick skin, but more elaborate on thick skin • Form fingerprints and increase friction for gripping Dermis – two layers: Papillary Layer - Superficial • Named for the papillae (projections of the dermis) that interlock with epidermal papillae to create a strong bond between the dermis and epidermis • Prevents slipping and resists separation of the two tissues • Made of areolar connective tissue Reticular Layer - Deep • Has a lot of collagen and elastin arranged in parallel bundles (but in multiple directions) • Made of dense irregular connective tissue – able to resist stress in multiple directions • Arrangement of collagen and elastin creates “lines of cleavage” (tension lines) that hug body structures and resist stress – varies in directions in different areas of body • If the dermis is stretched too much collagen fibers can tear, creating “stretch marks” (striae) Subcutaneous Layer (hypodermis) (not part of integument) • Areolar and adipose connective tissue • Functions: protection, energy storage, insulation • Common drug injection site because of the extensive vascular network - promotes rapid absorption Fingernails (modified epidermis) Structure: Nail plate • Distal whitish free edge (no underlying capillaries) • Pinkish nail body (underlying capillaries) • Nail root (embedded in skin) Nail bed • Layer of living epidermis covered by nail body Nail matrix • Actively growing part of nail (stratum basale) at proximal end of nail body Lunula • Whitish semilunar area on proximal end of nail body Nail folds • Folds of skin overlapping nail Eponychium (cuticle) • Narrow band of epidermis from margin of nail wallonto nail body Hyponychium • Thickened stratum corneum over which free nail edge projects Hair (modified epidermis) Functions of hair: • • • • Protection Facial expression Heat retention Sensory reception • • Visual identification Chemical signals (spread and trap pheromones) Hair is everywhere except thick skin. 3 types of hair: Lanugo – fine, unpigmented hair on fetuses and newborns Vellus – fine hair found on upper and lower limbs Terminal – coarse, longer hair with pigment; found on eyebrows, scalp, eyelashes, beards, axillary and pubic regions Hair structures to know: Bulb • Base of the hair; composed of connective tissue; containsthe cells that make and maintain the hair Matrix • Epithelial stem cells divide and move up (like in epidermis) Papilla • Connective tissue that has blood vessels and nerves and the matrix surrounds it Cortex • Flattened cells closer in center part of hair; closer to outer hair surface Cuticle • Single layer of dead cells around cortex (forms superficial part of hair) Root • Runs from bulb to skin surface Shaft • Extends from epidermis Arrector pili muscle – smooth muscle that controls whether hair “stands up” or not. If the muscle contracts, hair stands up. If the muscle is relaxed,hair lies down. Hair Facts: Hair loss • Normally 10 to 100 hairs lost per day • Thinning of hair, alopecia is typically due to aging • Diffuse hair loss - Hair loss from all parts of scalp in clumps • Primarily in women • Due to stress, hormones, drugs, iron deficiency • Male pattern baldness - Loss of hair first from only crown region of scalp • Genetic and hormonal factors • Hirsutism • Excessive male-pattern hairiness Exocrine Glands Merocrine – produce and secrete sweat associated with thermoregulation • Secretions go onto skin and evaporate to remove heat • Sweat is mostly water (99%) plus some electrolytes and urea Apocrine – produce and secrete sweat associated with sexual communication • Don’t secrete until puberty • Secretions contain proteins and lipids and produce an odor • Located around the nipples, in pubic, anal, and axillary regions where they secrete into hair follicles • Apocrine sweat travels up the hair follicle to the skin surface Sebaceous – produce oily secretion called sebum • Sebum is secreted into a hair follicle and then moves up the hair to the skin surface • Sebum acts as a lubricant AND is bactericidal (kills bacteria) • These glands are also not active until puberty and are stimulated by hormones (especially sex hormones) Skin exocrine glands exhibit the 3 types of exocrinesecretion: