Lecture 4
The Integumentary System
The Skin and Subcutaneous Tissue
 ________________________ is the largest organ of the body
o It covers an area of 1.5 to 2.0 m2 and accounts for 15% of the body weight
 Functions of the Skin
o 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
o Water retention
 It prevents the body from absorbing excess water when
________________
 It prevents the body from losing excess water
o Vitamin D synthesis
 Vitamin D is necessary for bone development and maintenance
 The ______________ step in synthesis occurs in the skin
o Sensation
 The skin is equipped with nerve endings that react to heat, cold,
touch, texture, ___________________, vibration, and tissue injury
o 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
o Nonverbal communication
 Complex skeletal muscle insert on dermal collagen fibers and pull
on the skin to create subtle and varied facial expressions
 The Epidermis
o 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.
o 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
o 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
o The layer below the reticular layer of the dermis has more areolar and
adipose tissue
o It binds the skin to the underlying muscle and ___________ the body
o This layer is highly vascular (so drugs are often injected here)
o This layer contains subcutaneous fat



Fat serves as an _________________ reservoir and thermal
insulator
Skin Color
o Melanin – pigment produced by the melanocytes which accumulates in
keratinocytes of the stratum basale and stratum spinosum
 ____________________ – brownish black pigment
 Pheomelanin- reddish yellow pigment
o 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
o Carotene – yellow pigment acquired from egg yolks and yellow and
orange vegetables
 It can become concentrated in the stratum corneum and
subcutaneous fat
o 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
o _____________________ 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
o Flexion lines –lines on the flexor surfaces of the digits, palms, wrists,
elbows, etc. where the skin folds during flexion of the joints
o Freckles – flat melanized patches that vary with heredity and exposure to
the sun
o __________________ – 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
o 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
o 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
o Structure of the Hair and Follicle
 Hair
 Zones of hair along the length
o _____________ – portion of the hair below the skin
o Shaft – portion of the hair above the skin
o Bulb – rounded portion at the lower end of the root
o Dermal papilla – bud of vascular connective tissue
surrounding the bulb, and providing the hair with its
nutrition
o Hair _______________ – the hair’s growth center,
above the papilla, where the cells are mitotically
active
 Hair in cross section
o Medulla – a core of loosely arranged cells and air
spaces found in thick hairs, but absent from thin
ones
o _______________ – a layer of keratinized cuboidal
cells
o Cuticle – a surface layer of scaly cells that overlap
each other like roof shingles
 Follicle structures
 Epithelial root sheath – an extension of the epidermis
o It lies immediately adjacent to the hair root
 Connective tissue root – derived from the dermis
o 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
o When these muscles ________________, the hair
stands on end
o 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
o Nail Matrix – growth zone beneath the skin at the proximal edge of the
nail
o Nail Plate – the visible portion of the nail, covering the tip of the finger or
toe
o Nail bed – the skin on which the nail ______________ rests
o Eponychium – the dead epidermis which covers the proximal end of the
nail
o Hyponychium – the epithelium of the nail bed
Cutaneous Glands
 Sweat Glands – also known as sudoriferous glands
o Merocrine sweat glands – the most numerous type, which produce
__________________ perspiration to cool the body
 Widely distributed throughout the body
o 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
o 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 _________________
o Found only in the external ear canal
o Keep the eardrum pliable, waterproofs the canal, kills bacteria
 Mammary Glands
o Milk-producing glands that develop within the breasts under conditions of
pregnancy and ______________________
Developmental and Clinical Perspectives


The Aging Integumentary System
o By the late 40s hair turns grayer and thinner as melanocytes die out and
dead hairs are not replaced
o Atrophy of sebaceous glands leaves the skin and hair more dry
o Aged skin has less elasticity due to loss of ______________ fibers
o Aged skin has fewer blood vessels and those that remain are more fragile
o Thermoregulation can be a problem because of atrophy of blood vessels,
sweat glands, and subcutaneous fat
Skin Disorders
o 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
o 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