The Skin and Subcutaneous Tissue

Lecture 4

The Integumentary System

______ 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