Integument Flashcards
Skin
largest organ and accounts for 7% of body weight
varies in thickness from 1.5-4.4 mm
divided into two distinct layers: epidermis and dermis
Hypodermis
lies deep to dermis
also called superficial fascia
contains areolar and adipose connective tissue
anchors skin to underlying structures
helps insulate the body
hypodermis is area that can thicken dramatically with development of increased adipose tissue in people with obesity (e.g., adipose deposits in the abdominal wall)
Functions of Skin and Hypodermis
protection: cushions organs and protects from bumps, chemicals, water loss, UV radiation
regulation of body temperature
excretion: urea, salts, and water lost through sweat
production of vitamin D in deep epidermis
sensory reception: keeps us aware of conditions at the body’s surface
Embryologic Origin of Skin
epidermis: develops from embryonic ectoderm
dermis and hypodermis: develop from mesoderm
melanocytes: develop from neural crest cells which are of ectoderm origin
Epidermis (layers)
stratum of corneum stratum of lucidum (only in thick skin) stratum granulosum stratum spinosum stratum basale (straum germinativum) vitamin D3 (cholecalciferol) is synthesized from 7-dehydrocholesterol in the deep epidermis (stratum basale & stratum spinosum)
Epidermis (cell types)
epidermis is deratinized stratified squamous epithelium with four distinct cells types:
keratinocytes: most common cell type in epidermis
melanocytes: location - basal layer; manufacture and secrete pigment
tactile epithelial cells: location - basal layer; attached to sensory nerve endings
dendritic cells: location - stratum spinosum; part of immune system; macrophage-like
Keratinocytes vs. Keratocytes
keratinocytes: predominant cell type in skin epidermis
keratocytes: specialized fibroblasts in the cornea
Keratinocytes in Epidermis (1)
most abundant cell type in epidermis
present in all epidermis layers
cells are tightly connected by a large number of desmosomes
produce antibodies and enzymes that detoxify chemicals that are exposed to our skin
produce keratin, a tough fibrous protein that gives skin epidermis its protective properties
Keratinocytes in Epidermis (2)
arise from deepest layer of epidermis (stratum basale) from cells that undergo continuous mitosis
as these cells are pushed up by the production of new cells beneath them, they make keratin that fills their cytoplasm
Keratinocytes in Epidermis (3)
by the time they reach the surface of the skin they are dead flat cells full of keratin
millions of these dead cells rub off from our skin every day
35-45 days is average time from the birth of a keratinocyte until it sloughs off of the exterior skin
we form an entirely new skin epidermis every 35-45 days
the average person sheds 40 pounds of skin flakes in a lifetime
Keratinocytes in Epidermis (4)
where the skin experiences friction, both the cell production and keratin production are accelerated and the epidermis can become thick in this area
persistent friction can cause a significant thickening of the epidermis called a callus
short term severe friction can result in a blister of the skin which is the separation of the epidermis from the dermis by a fluid-filled pocket
Stratum Basale (1)
deepest layer of epidermis
consists of the single row of cells, most of which are stem cells representing the youngest keratinocytes
cells actively divide
attached to underlying dermis
relies on capillaries in the underlying dermis for nutrients
Stratum Basale (2)
tactile epithelial cells (Merkel cells) associated with sensory nerve endings are sparsely distributed among the keratinocytes in the stratum basale
melanocytes: spider-shaped melanocytes make up 10-25% of the cells in stratum basale
melanocytes make melanin and transport it through its spider-shaped cells process to nearby keratinocytes
Stratum Basale (3)
melanin shields the cell nuclei from incoming UV radiation
darker skinned people have darker melanin and more pigment in each melanocyte
melanocytes respond to ultraviolet radiation by increasing production of melanin and increasing its transfer to keratinocytes, the protective response which results in a suntan
Stratum Basale (4)
vitamin D3 (cholcalciferol) is a fat-soluble secosteroid formed from 7-dehydrocholesterol in deep epidermis (stratum basale and stratum spinosum) after exposure to ultraviolet B light vitamin D is essential for uptake of calcium from the diet and formation of healthy bones as well as providing other health benefits
Stratum Basale (5)
inverse relationship between level of melanin in keratinocytes and ability to produce vitamin D given the same UV exposure
humans with high levels of melanin tend to have originated from regions of the world (e.g., equatorial latitudes) where they have been exposed to large amounts of UV light, whereas humans with low levels of melanin tend to have originated from regions of the world exposed to lower levels of UV light
Stratum Spinosum (1)
several cell layers of keratinocytes united by desmosomes
mitosis can occur in keratinocytes in this layer, however, less often that in the basal layer
relies on capillaries in the underlying dermis for nutrients
Stratum Spinosum (2)
contains thick bundles of intermediate filaments (tonofilaments) which consist of the tension-resisting protein pre-keratin
contains star-shaped dendritic cells scattered among the keratinocytes
dendritic cells are part of the immune system and engulf foreign antigens that have invaded the epidermis and generate an immune response
Stratum Graunulosum
consists of 1-5 layers of flattened keratinocytes
relieson capillaries in teh underlying dermis for nutrients
contains intermediate filaments (tonofilaments) which consists of the tension-resisting protein pre-keratin
contain keratohyaline granules which help form keratin
contain lamellated granules which contain a waterproofing glycolipid which is secreted into the extracellular space
Stratum Lucidum
clear layer
occurs only in thick skin e.g., palms and soles
composed of a few rows of flat, dead keratinocytes which are like cells in the stratum corneum
Stratum Corneum
horny layer
thick layer (multiple layers of cells) of dead keratinocytes
keratinocytes with thickened plasma membranes
dead keratinocytes are flat sacs filled with keratin
protects skin against abrasion and penetration
intercellular glycolipid keeps layer water proof
humans shed millions of dead keratinocytes off the outer surface of teh stratum corneum each day
Skin Color
pigments which contribute to skin color:
melanin: most important pigment - made from tyrosine, differences both in the amount and type of melanin in humans
carotene: yellowish pigment from carrots and tomatoes can accumulate in stratum corneum and in the hypodermis
hemoglobin: skin with low amounts of melanin allows crimson color of blood to show through skin
Albinism
people with albinism lack the enzyme necessary to make melanin
Freckles
both freckles and moles are localized accumulations of melanin in the skin
freckles can develop as a result of repeated exposure to sunlight
with freckles, the increase in melanin is restricted to the basal layer of the epidermis
people with light complexions are more prone to freckle formation
Moles
both freckles and moles are localized accumulations of melanin in the skin
moles form when clusters of melanocytes are transformed into melanin-containing cells (nevus cells)
these clusters of cells are both in the lower layer of the epidermis and in the top layers of the dermis
many people are born with moles which are birth marks
large moles (especially moles that are increasing in size) need to be followed by a dermatologist to rule out possibility of development of a melanoma
Skin Cancer
basal cell carcinoma: lease malignant and most common
squamous cell carcinoma: arises from keratinocytes of stratum spinosum
melanoma: a cancer of melanocytes, the most dangerous type of skin cancer, melignant are asymmetrical with irregular borders and variable color
Dermis (1)
second major layer of the skin
strong, flexible connective tissue
binds the entire body together like a body stocking
corresponds to animal hides used to make leather
the connective tissue proper contains fibroblasts, macrophages, mast cells, and white blood cells as well as collagen, elastic, and reticular fibers
Dermis (2)
richly supplied with nerves
richly supplied with blood vessels configured in two vascular plexuses
the more superficial subpapillary vascular plexus is located just below the dermal papillae and supplies superficial dermal tissue, the dermal papillae, and the epidermis
the deep dermal vascular plexus is configured between the hypodermis and the dermis and it nourishes the hypodermis and deep dermis
blood running through the hands plays a role in temperature regulation
Dermis (Layers) (3)
papillary layer
reticular layer
flexure lines
Papillary Layer (Dermis) (1)
made up of areolar connective tissue proper
dermal papillae are finger-like projections that interface with the overlying epidermis and increase surface area for exchange of gases, nutrients, and waste products
Papillary Layer (Dermis) (2)
on the palms of the hands and the soles of the feet, dermal papillae lie atop larger mounds called dermal ridges which elevate overlying epidermis into epidermal ridges (friction ridges) which create finger prints
Reticular Layer (Dermis)
makes up 80% of thickness in dermis
dense irregular connective tissue
thick bundles of interlacing collagen and elastic fibers give skin its stretch and recoil properties
Reticular Layer - Cleavage Lines (Dermis)
separations or less dense regions between the collagen bundles form the cleavage lines or tension lines in the reticular dermis of the skin over the entire body
the cleavage lines run longitudinally in the skin of the limbs and head and in circular patterns around the neck and trunk
knowledge of cleavage lines is important to surgeons; when possible it is best of cut parallel cleavage lines
Reticular Layer - Striae (Dermis)
stria are stretch marks
extreme sustained stretching of the skin which can occur with obesit and pregnancy can tear the collagen in the reticular dermis resulting in linear patches on the skin called striae which are also known as stretch marks
Flexure Lines (Dermis)
arise from the deep part of the dermis and result from the repeated folding of the skin such as in the palms of your hands and around joints e.g., at the wrist, fingers, and toes
Skin Burns (Types)
first-degree burn: only epidermis is damaged
second-degree burn: epidermis and upper part of dermis are damaged resulting in blister formation from separation of the epidermis from the dermis; typically heals with no scar formation
third-degree burn: damages entire thickness of skin and produces permanent scar
Tissue Response to Injury
inflammatory response: nonspecific, local response; limits damage to injury site
immune response: takes longer to develop and very specific; destroys particular microorganisms at infection site
Acute Inflammation (Tissue Response to Skin Injury)
heat redness swelling pain chemicals signal nearby blood vessels to dilate and histamine increases permeability of capillaries producing edema in region
Edema (Tissue Response to Skin Injury)
accumulation of fluid in tissue as local blood vessels become more permeable
helps dilute toxins secreted by pathogen
brings white blood cells and antibodies from blood to fight infection
brings nutrients from blood
brings clotting factors from blood
Repair (Skin)
inflammation: with blood clot in incised wound
organization: clot is replaced by granulation tissue which restores blood supply
fibrosis: proliferation of underlying scar tissue
regeneration: fibrosed area matures and contracts and scar tissue is covered by a fully regenerated epithelium
Sebaceous Glands
skin glands occur over entire body except palms and soles secrete sebum (an oily substance): simple branched alveolar glands, holocrine secretion (entire cell breaks up to form secretion), most are associated with a hair follicle functions of sebum: softens and lubricates hair and skin
Sweat (Sudoiferous) Glands
widely distributed on body
sweat is a blood filtrate
99% water with some salts
contains traces of metabolic wastes including urea and ammonia
humans typically produce 500 ml of sweat a day, however with heat exposure and intensive exercise the production can increase dramatically
Eccrine Gland (Merocrine)
sweat gland
most numerous type of sweat gland, these produce true sweat and are present on palms, soles, and forehead
Apocrine Gland (1)
large sweat glands confined to axillary, anal, and genital areas and their ducts open into hair follicles
produce a special kind of odorless sweat which contain fats and proteins mixed in with sweat
organic compounds in the sweat are broken down by bacteria on the skin resulting in a musky odor (body odor)
Apocrine Gland (2)
secretions function as a pheromone and can contribute to mate attraction
activity of these glands increases with sexual foreplay and around the time of ovulation in women
signal information about a person’s immune system, MHC (major histocompatibility complex)
women tend to be more attracted to body odor scents of males with immune systems different than their own
Other Specialized Sweat Glands
ceruminous glands: modified apocrine glands in external ear canal that produce cerumen (wax)
mammary glands: specialized glands modified to secrete milk
Nails
scale-like modification of epidermis made of hard, dead keratinized cells which do not flake off
corresponds to the hoof or claw of other mammals
nail rests on nail bed of deep epithelium
nail matrix: actively growing part of a nail in thickened bed at proximal end of nail
lunule: visible white crescent of proximal nail which represents the thickened nail matrix
Hair (1)
flexible strand of dead, keratinized cells
hard keratin - tough and durable
hair roots are associated with sebaceous oil glands and arrector pili muscles
cheif parts of a hair:
root (imbedded in the skin)
shaft (projects above skin’s surface)
Hair (2)
round cross-section of hair shaft is associated with straight hair
oval cross-section of hair shaft is associated with wavy hair
flattened cross-section of hair shaft is associated with kinky hair
head lice has more difficulty attaching to hair with flattened cross-section compared to round cross-section
Hair Color
hair pigment is made by melanocytes at the base of the hair follicle and is transferred into cells of the hair root
different proportions of two types of melanin (black-brown and yellow-rust in color) combine to produce the common hair colors - black, brown, red, and blonde
