anatomy and physiology chapter 5

integumentary system

the skin, hair, nails, and cutaneous glands

dermatology

branch of medicine that treats the integumentary system

integument

the skin

how much percent of the body weight does skin account for?

8%

what are the 2 layers of the skin? 

• epidermis which is a stratified squamous epithelium

• dermis which is a deeper connective tissue 

hypodermis

connective tissue just underneath skin

examples of variation in skin thickness

• 0.5 mm of thick skin on palms, soles, and corresponding surfaces of fingers and toes

• 0.1 mm of thin skin on most of the body

characteristics of thick skin

• adaptive for high friction

• hairless

• no sebaceous glands

• capable of sweating

characteristics of thin skin 

contains hair, sebaceous glands, and sweat glands 

stratum corneum

a thick surface layer of dead cells

functions of skin 

• resistance to trauma and infection

• prevents penetration of water

• protects from UV rays and some chemicals

• carries out first step for vitamin d synthesis which is then completed by livers and kidney

• sweat glands excrete urea, metabolites, and some chemicals in perspiration

• sensation 

• thermoregulation for regulating body temperature through vasodilation or vasoconstriction

• nonverbal communication

keratin

a tough protein formed by keratinocytes that constitutes the hair, nails, and stratum corneum of the epidermis

thermoreceptor 

neuron specialized to respond to heat or cold, found in the skin and mucous membranes, for example

epidermis

a stratified squamous epithelium that constitutes the superficial layer of the skin, overlying the dermis

characteristics of epidermis 

• surface has dead cells packed with keratin

• lacks blood vessels and needs diffusion of nutrients from underlying connective tissue 

• nerve sensations due to dermis location

list the epidermis cells

• keratinocytes

• stem cells

• melanocytes

• tactile cells

• dendritic cells

keratinocyte

a cell of the epidermis that synthesizes keratin, then dies; most cells of the epidermis are keratinocytes, with dead ones constituting the stratum corneum

stem cell 

any undifferentiated cell that can divide and differentiate into more functionally specific cell types such as blood cells and germ cells

melanocyte

a cell of the stratum basale of the epidermis that synthesizes melanin and transfers it to the keratinocytes

tactile cells

receptors found in the basal layer of the epidermis and associated with an underlying dermal nerve fiber

dendritic cell 

an antigen-presenting cell of the epidermis, vaginal mucosa, and some other epithelia

where are keratinocytes located? 

majority of epidermal cells 

where are stem cells located?

deepest layer of the epidermis called stratum basale

where are melanocytes found? 

stratum basale amid the stem cells and deepest keratinocytes 

what are functions melanocytes do in the body? 

• brown and black pigment melanin are synthesized 

• the cells have long branching processes that spread among keratinocytes and keep shedding melanin-containing fragments from their tips 

• the keratinocytes phagocytize the fragments and accumulate melanin granules on the sunny side of the nucleus 

• the pigment shields DNA from UV radiation

tactile disc 

tactile cell and its nerve fiber 

where are dendritic cells found?

stratum spinosum and granulosum which are two layers in the epidermis

where do dendritic cells originate from?

bone marrow

how many dendritic cells in the epidermis? 

1800 per square millimeter 

what functions do dendritic cells carry out in the body?

• guarding against toxins, microbes, and disease agents that penetrate into the skin

• foreign matter fragments get taken to the lymph nodes and alert immune system for defense

what are the epidermis layers?

• stratum basale

• stratum spinosum

• stratum granulosum

• stratum lucidum

• stratum corneum

stratum basale

mainly a single layer of cuboidal to low columnar karatinocytes resting on the basement membrane

what’s scattered among the stratum basale? 

• melanocytes

• tactile cells

• stem cells

what happens to stem cells that divide in stratum basale?

it gives rise to keratinocytes that migrate toward the skin surface and replace lost epidermal cells

stratum spinosum

consists of several layers of keratinocytes; in most places this is the thickest stratum but, on the palms and soles it is thinner than stratum corneum

what happens to the deepest cells of the stratum spinosum when they keep dividing?

when they’re pushed further up, they stop dividing and instead make more keratin filaments which flatten the cell

what keeps keratinocytes firmly attached to each other? 

• desmosomes which partly contribute to epidermis toughness 

• desmosomes create bridges from cell to cell 

stratum granulosum

3-5 layers of flat keratinocytes (more common in thick skin) and has dendritic cells

where does stratum granulosum get its name from? 

the coarse dark staining keratohyalin which is in the layer

stratum lucidum 

a thin translucent zone seen only in thick skin where keratinocytes are densely packed with a clear protein named eleidin 

what’s the structure of the stratum lucidum?

anucleate without organelles making it look pale and featureless without distinct cell boundaries

how many layers of dead keratinized cells are there for stratum corneum?

30

most superficial to deep skin layers 

• corneum

• lucidum

• granulosum

• spinosum

• basale 

how are keratinocytes produced?

• mitosis of the stem cells in the stratum basale

• oxygen and nutrients acquired for mitosis from blood vessels in nearby dermis

• when epidermal cells migrate 2-3 cells away from the dermis, mitosis stops

why is mitosis rarely seen in the skin slides?

it occurs at night while most histological sections are taken during the day

how long does it take for a keratinocyte to flake off? 

30-40 days 

what slows down the speed of flaking keratinocytes and what speeds it up?

• old age and injured skin

• manual labor or tight shoes

calluses or corns

thick accumulations of dead keratinocytes on the hands or feet

lamellar granules 

found in keratinocytes, these granules release a lipid mixture that coats the cell surface, preventing water loss

in the stratum granulosum, what 4 developments occur for keratinocytes?

• the keratohyalin granules release a protein called filaggrin which binds the cytoskeletal keratin filaments together into course and tough bundles

• the cells produce a tough layer of envelope proteins beneath the plasma membrane which creates an indestructible protein sac around the keratin bundles

• the lamellar granules release a lipid mixture that spreads out over the cell surface and waterproofs it

• when the barriers cut the keratinocytes off from the nutrient supply from below, their nuclei and other organelles degenerate, and the cells die which leaves behind the tough waterproof sac of keratin.

epidermal water barrier

a barrier crucial to retaining water in the body and preventing dehydration

dander 

dead keratinocytes 

dermis 

the deeper of the two layers of the skin, underlying the epidermis and composed of fibrous connective tissue

characteristics of dermis

• ranges from 0.2-4 mm thick depending on the area

• mostly made of collagen with elastic and reticular fibers as well as fibroblasts and other cells typical of fibrous connective tissue

• has blood vessels, cutaneous glands, and nerve endings

• hair follicles and nail roots are embedded in dermis

• smooth muscle in association with hair follicle

• skeletal muscles attach to dermal collagen fibers to make expressions

dermal papilla

a bump or ridge of dermis that extends upward to interdigitate with the epidermis, creating a wavy boundary that resists stress and slippage of the epidermis; a projection of the dermis into the bulb of a hair, supplying blood to the hair.

epidermal ridges 

downward waves that are the extension of the epidermis 

characteristics of the dermal and epidermal boundaries 

• resists slippage of the epidermis across the dermis under stress 

• dermal papillae produce raised areas between furrows that can be seen in hand and wrist

• on fingertips the wavy boundary forms friction ridges

• in lips and genitals tall dermal papillae allow nerve fibers and blood capillaries to be closer to skin surface causing more redness and sensitivity

tension lines 

collagen bundles in the dermis arranged mostly in parallel rows that run longitudinally in the limbs while encircling the neck, trunk, wrists, and more

purpose of tension lines

keep the skin under constant tension

what happens to tension lines when an incision is made in the skin perpendicularly?

the wound gapes because the collagen bundles pull the edges of the incision apart

what happens when a tension line is punctured with a circular object? 

the wound gapes with a lemon shaped opening which makes it hard to close and heals with excessive scarring 

example of incision parallel to tension lines

c section

papillary layer

pertaining to or shaped like a nipple, such as the papillary muscles of the heart; having papillae, such as the papillary layer of the dermis

what does the loosely organized tissue of the papillary layer allow for? 

mobility of leukocytes and other defenses against organisms introduced through breaks in the epidermis 

reticular layer

a deeper and much thicker layer of dense irregular connective tissue that’s more fibrous than cellular which makes it tougher than the papillary layer

describe the vague boundary between the papillary and reticular layers

in the reticular layer the collagen forms thicker bundles with less room for ground substance with small adipocyte clusters often

what causes stretch marks? 

stretching of the skin which tears collagen fibers 

where are stretch marks most common?

• buttocks

• thighs

• abdomen

• breasts

blister

serous fluids seeping out of the vessels and accumulating which separates the epidermis from the dermis

how do blisters go away?

the fluid is reabsorbed or expelled when ruptured

hypodermis 

a layer of connective tissue deep to the skin; also called superficial fascia, subcutaneous tissue, or when it is predominantly adipose, subcutaneous fat

hypodermis structure

• no sharp boundary between dermis and hypodermis

• more areolar and adipose tissue

• pads the body and binds the skin to the underlying tissues

how are drugs introduced to the body?

hypodermic injection because the subcutaneous tissues are highly vascular and absorb them quickly

subcutaneous fat

hypodermis composed mainly of adipose tissue

subcutaneous fat purpose

• energy reservoir and thermal insulation

• protects deeper tissue by absorbing pressure and blows to the body

characteristics of subcutaneous fat

• not uniformly distributed

• mostly absent in scalp

• abundant in breasts, abdomen, hips, and thighs

• 50% of total body fat

• 8% thicker in women

• infants and elderly have less making them sensitive to cold

what causes variation in hair and skin color?

varieties and amounts of melanin

two classes of integumentary melanin

• dark eumelanin

• reddish yellow pheomelanin

two subtypes of eumelanin

brown and black eumelanin 

what do brown and black eumelanin do?

underlie the colors of tan, brown, and black skin including the effects of suntanning

where does pheomelanin get its color from?

higher sulfur content

which ethnic groups commonly have pheomelanin?

• yellowish to reddish tones for Asians and native Americans

• pinkish tones for white skin

what other factors contribute to skin color? 

• how close blood vessels are to surface

• show through of white collagen

• carotene which can accumulate in stratum corneum, dermis, and subcutaneous fat  

• amount of UV exposure

carotene

pigments of yellow and orange vegetables

where is most of melanin located?

stratum basale but extends through the epidermal strata in dark complexions  

what makes skin darker?

• for darker skin melanocytes produce greater quantities of pigment

• melanin granules in keratinocytes are more spread out

• melanin breaks down slowly

what makes skin light?

• melanin is less abundant and clumped near keratinocyte nucleus which means less color

• breaks down more rapidly so little is seen beyond stratum basale

where is melanin more concentrated?

• freckles and moles

• dorsal surfaces of hands and feet

• nipple and areola

• around anus

• on scrotum and penis

• lateral surfaces of female genital folds (labia majora)

effects of ultraviolet radiation

• skin cancer

• free radicals that destroy immune dendritic cells of epidermis

• damages protein and DNA

• breaks down folate which is a B vitamin needed for normal cell division

what can a folate deficiency cause?

• infertility

• severe birth defects such as spina bifida and prenatal death

benefits of UVR

stimulates keratinocytes to make vitamin D 

what does vitamin D do?

• calcium metabolism

• bone health

• fetal and childhood development

• cell growth

• neuromuscular and immune functions

why do women worldwide on average have 4% lighter skin than men do?

greater need of vitamin D and calcium to support pregnancy and lactation

what makes UVR increase? 

higher elevations and in dry air that’s thinner and filters out less of it

what outside factors can affect skin colors? 

• human migration

• intermarriage between different geographic ancestries

• cultural differences between clothing and shelter

• preference for certain skin colors

• mutations

abnormal skin conditions 

• cyanosis

• erythema 

• pallor 

• albinism

• jaundice 

• hematoma 

hematoma

a mass of clotted blood in the tissues; forms a bruise when visible through the skin

hematoma causes

• accidental trauma

• hemophilia

• metabolic or nutritional disorders

• abuse

erythema 

abnormal redness of the skin

erythema causes

• exercise

• hot weather

• sunburns (dermal pooling of RBCs that escape from damaged capillaries)

• anger

• embarrassment

• increased blood flow in dilated cutaneous blood vessels