Lecture 4

The Integumentary System

The Skin and Subcutaneous Tissue

  • ______ is the largest organ of the body
  • It covers an area of 1.5 to 2.0 m2and accounts for 15% of the body weight
  • Functions of the Skin
  • Resistance to trauma and ______
  • Epidermal cells are packed with tough protein called keratin
  • It resists and recovers from injury better than other organs
  • Bacteria and fungi may live on the skin surface, but the relative dryness and slight acidity of the skin keeps the numbers down
  • Water retention
  • It prevents the body from absorbing excess water when ______
  • It prevents the body from losing excess water
  • Vitamin D synthesis
  • Vitamin D is necessary for bone development and maintenance
  • The ______ step in synthesis occurs in the skin
  • Sensation
  • The skin is equipped with nerve endings that react to heat, cold, touch, texture, ______, vibration, and tissue injury
  • Thermoregulation
  • In response to chilling, the skin helps to retain heat through vasoconstriction
  • Vasoconstriction is the ______ of blood vessels to the skin
  • In response to overheating, the skin helps to cool the body through vasodilation
  • Vasodilation is the widening of dermal blood vessels to ______cutaneous blood flow and increase heat loss
  • Nonverbal communication
  • Complex skeletal muscle insert on dermal collagen fibers and pull on the skin to create subtle and varied facial expressions
  • The Epidermis
  • Cells of the Epidermis
  • Stems cells – undifferentiated cells that undergo mitosis and give rise to kerotinocytes. They are only found in the stratum basale
  • Keratinocytes – cells that make up most of the epidermal cells and that are named for their role in synthesizing ______
  • Melanocytes – cells that synthesize melanin. They are found in the stratum ______
  • Tactile cells – cells that are receptors for the sense of touch. They are found in the stratum basale
  • Dendritic cells – cells that are macrophages that “stand guard” against pathogens that penetrate the skin and alert the ______system if such invaders are detected. They are found in the stratum spinosum and in the stratum granulosum.
  • Layers of the Epidermis
  • Stratum basale – bottom layer of the epidermis
  • Mainly single layer of cuboidal to low columnar stem cells and keratinocytes on the ______membrane
  • Some melanocytes and tactile cells are scattered here
  • Stem cells here undergo mitosis and give rise to keratinocytes that migrate toward the skin surface
  • Stratum spinosum – many layers of keratinocytes above the stratum basale
  • Deepest cells are capable of mitosis, but cells closer to the surface stop dividing and produce more keratin which causes the cells to flatten
  • Dendritic cells may be found here
  • Cells here have a ______appearance, but only after preservation techniques
  • Stratum granulosum–three to five layers of flat keratinocytes and some dendritic cells
  • The kerotinocytes in this layer produce keratyhyalin granules
  • Stratum lucidum – a thin transparent layer seen only in ______skin
  • Cells here have no organelles, so the zone appears featureless
  • Stratum corneum – up to 30 layers of dead, scaly, keratinized cells
  • Forms a durable, water-resistant surface layer
  • The Dermis
  • Layers of the Dermis
  • Papillary layer – thin zone of areolar tissue in and near the dermal papillae
  • Loosely organized tissue allows for mobility of leukocytes and other defenses against organisms introduced through breaks in the dermis
  • Reticular layer – deeper and ______layer of the dermis consisting of dense irregular connective tissue
  • Stretching of the skin in obesity or pregnancy can tear the collagen fibers producing striae (stretch marks)
  • The Hypodermis
  • The layer below the reticular layer of the dermis has more areolar and adipose tissue
  • It binds the skin to the underlying muscle and ______the body
  • This layer is highly vascular (so drugs are often injected here)
  • This layer contains subcutaneous fat
  • Fat serves as an ______reservoir and thermal insulator
  • Skin Color
  • Melanin – pigment produced by the melanocytes which accumulates in keratinocytes of the stratum basale and stratum spinosum
  • ______– brownish black pigment
  • Pheomelanin- reddish yellow pigment
  • Hemoglobin- red pigment of blood, which makes the skin look reddish or pink
  • Skin is ______in places like the lips, where blood comes closer to the surface
  • Carotene – yellow pigment acquired from egg yolks and yellow and orange vegetables
  • It can become concentrated in the stratum corneum and subcutaneous fat
  • Abnormal coloration
  • ______– blueness of the skin resulting from deficiency of oxygen
  • Erythema – abnormal redness of the skin, caused by increased blood flow in dilated cutaneous blood vessels
  • ______– pale or ashen color when there is so little blood flow through the skin that the white color of the of the dermal collagen shows through
  • Albinism – genetic lack of melanin, resulting in white hair, pale skin, and pink eyes.
  • ______– yellowing of the skin and whites of the eyes
  • Bronzing – golden-brown skin color that results from Addison disease
  • Skin Markings
  • ______ridges – marking on the fingertips that leave distinctive oily fingerprints on the surfaces we touch
  • Remain essentially unchanged for life
  • Not even identical twin have identical fingerprints
  • Flexion lines –lines on the flexor surfaces of the digits, palms, wrists, elbows, etc. where the skin folds during flexion of the joints
  • Freckles – flat melanized patches that vary with heredity and exposure to the sun
  • ______– Elevated patches of melanized skin, often with hair

Hair and Nails

  • Hair – slender filament of keratinized cells that grown from an oblique tube in the skin called a hair follicle
  • Distribution of hair
  • Found almost everywhere except the lips, nipples, palms & soles, parts of genitals, and parts of fingers (glabrous skin is hairless)
  • Extremities and trunk have about 55-70 hairs per square cm
  • There are about 30,000 hairs in a man’s beard and 100,000 on the scalp
  • There are few differences in numbers from person to person, but texture and pigmentation influence appearance
  • Types of hair
  • ______– fine downy, unpigmented fetal hair
  • Vellus – fine, unpigmented hair that replaces lanugo
  • Terminal hair – longer, courser, pigment hair that forms the eyebrows, eyelashes, scalp hair, facial hair, axillary hair, pubic hair
  • Structure of the Hair and Follicle
  • Hair
  • Zones of hair along the length
  • ______– portion of the hair below the skin
  • Shaft – portion of the hair above the skin
  • Bulb – rounded portion at the lower end of the root
  • Dermal papilla – bud of vascular connective tissue surrounding the bulb, and providing the hair with its nutrition
  • Hair ______– the hair’s growth center, above the papilla, where the cells are mitotically active
  • Hair in cross section
  • Medulla – a core of loosely arranged cells and air spaces found in thick hairs, but absent from thin ones
  • ______– a layer of keratinized cuboidal cells
  • Cuticle – a surface layer of scaly cells that overlap each other like roof shingles
  • Follicle structures
  • Epithelial root sheath – an extension of the epidermis
  • It lies immediately adjacent to the hair root
  • Connective tissue root – derived from the dermis
  • It surrounds the epithelial sheath
  • Hair ______– nerve fibers that entwine each follicle and respond to hair movements
  • Piloerector muscle (arrector pili) – bundle of smooth muscle cells extending from dermal collagen fibers to the connective tissue root sheath of the follicle
  • When these muscles______, the hair stands on end
  • Hair Texture and Color
  • Texture – due to differences in cross-sectional shape
  • Straight hair – round in cross-section
  • Wavy hair – ______in cross-section
  • Tightly curly hair – relatively flat in cross-section
  • Color – due to pigment granules in the cells of the cortex
  • Brown and black hair- rich in eumelanin
  • ______hair – less eumelanin, high in pheomelanin
  • Blond hair - intermediate pheomelanin, very little eumelanin
  • Grey and white hair – little or no ______, air in the medulla
  • Nails – clear, hard derivatives of the stratum corneum
  • Nail Matrix – growth zone beneath the skin at the proximal edge of the nail
  • Nail Plate – the visible portion of the nail, covering the tip of the finger or toe
  • Nail bed – the skin on which the nail ______rests
  • Eponychium – the dead epidermis which covers the proximal end of the nail
  • Hyponychium – the epithelium of the nail bed

Cutaneous Glands

  • Sweat Glands – also known as sudoriferous glands
  • Merocrine sweat glands – the most numerous type, which produce ______perspiration to cool the body
  • Widely distributed throughout the body
  • Apocrine sweat glands – occur in the groin, anal region, axilla, areola, and beard area in mature males
  • Ducts lead into hair follicles rather than directly to the skin
  • Apocrine sweat is thicker and more ______than merocrine sweat
  • Apocrine sweat glands are scent glands that secrete pheromones
  • With poor hygiene, apocrine sweat acquires a rancid odor
  • Sebaceous Glands – produce oily secretions
  • These are holocrine glands
  • Their secretion consists of broken down cells that are replaced by ______
  • The secretion, called sebum, keeps the skin and hair from becoming dry, brittle, and cracked.
  • Ceruminous Glands – produce cerumin, which is ______
  • Found only in the external ear canal
  • Keep the eardrum pliable, waterproofs the canal, kills bacteria
  • Mammary Glands
  • Milk-producing glands that develop within the breasts under conditions of pregnancy and ______

Developmental and Clinical Perspectives

  • The Aging Integumentary System
  • By the late 40s hair turns grayer and thinner as melanocytes die out and dead hairs are not replaced
  • Atrophy of sebaceous glands leaves the skin and hair more dry
  • Aged skin has less elasticity due to loss of ______fibers
  • Aged skin has fewer blood vessels and those that remain are more fragile
  • Thermoregulation can be a problem because of atrophy of blood vessels, sweat glands, and subcutaneous fat
  • Skin Disorders
  • Skin Cancer
  • Basal cell carcinoma
  • Most common type, but least dangerous
  • Arises from cells of stratum ______
  • Lesion first appears as a small, shiny bump, then develops a depression as it enlarges
  • Squamous cell carcinoma
  • Arises from keratinocytes in stratum basale
  • Can be treated with surgical removal
  • Recovery is good if treated ______
  • Malignant melanoma
  • Arises from melanocytes of a preexisting mole
  • Metastasizes quickly
  • Often ______if not treated immediately
  • Burns
  • First degree burn
  • Involves only the epidermis
  • Redness and pain
  • Second degree burn
  • Involves epidermis and part of the dermis
  • Blisters and ______
  • Third degree burn
  • Involves complete destruction of epidermis and dermis
  • Skin is blacked or charred, and ______damage may occur
  • Often requires skin grafts