Chapter 5: The Integumentary System

What is is range of thickness of the skin throughout the body?

1.5 to 4.0 mm

What are the 2 layers of the skin?

epidermis and dermis

What is the epidermis?

the outermost protective shield of the body

What is the epidermis made of?

epithelial cells

What is the dermis?

the tough and leathery underlying layer that makes up most of the skin

What is the dermis mostly made up of?

dense connective tissue

How do nutrients reach the epidermis?

by diffusing through the tissue fluid from blood vessels in the dermis

Where is the subcutaneous tissue?

just deep to the skin

Why is the subcutaneous tissue also know as the hypodermis or the superficial fascia?

because it is superficial to the tought connective tissue wrapping (fascia) of the skeletal muscles

Why is the subcutaneous tissue considered part of the integumentary system despite not being a part of the skin?

because it shares some of the skin’s protective functions

What is the subcutaneous tissue composed of?

mostly adipose tissue with some areolar connective tissue

What are the functions of the subcutaneous tissue?

• storing fat

• anchoring the skin to underlying structures, but loosely enough to allow the skin to slide over them

• absorbs shock

• insulates and reduces heat loss

What are the four distinct cell types in the epidermis?

• keratinocyte

• melanocytes

• dendritic cells

• tactile epithelial cells

What is the most abundant cell type in the epidermis?

keratinocyte

What is the job of keratinocytes?

to produce keratin, the fibrous protein that helps give the epidermis its protective properties

What are keratinocytes tied together by?

desmosomes for strength and in some layers, by tight junctions to prevent movement of water between cells

Where do keratinocytes arise?

the stratum basale

What do keratinocytes undergo almost continuous mitosis in response to?

epidermal growth factor

What happens to newly formed keratinocytes?

they are pushed upward by the production of new cells beneath them, while making the keratin that eventually fills them

What happens to keratinocytes by the time they approach the skin surface?

they become dead, scale-like flat sacs completely filled with keratin

How many dead keratinocytes rub off everyday?

millions

How often do we have a totally new epidermis?

every 25 to 45 days

When are cell production and keratin formation accelerated?

when the skin experiences friction

What does persistent friction on the skin cause?

a callus, or thickened epidermis

What are melanocytes?

spider-shaped epithelial cells that synthesize melanin

Where are melanocytes found?

the deepest layer of the epidermis (stratum basale)

Where is melanin made?

in membrane-bound granules called melanosomes

Why do basal keratinocytes contain more melanin than the melanocytes themselves?

because melanin is transferred through the cell processes to nearby keratinocytes

What do melanin clusters on the superficial side of the keratinocyte nucleus form?

a pigment shield that protects the nucleus from UV damage

What are the five distinct layers of the epidermis from deep to superficial?

• stratum basale

• stratum spinosum

• stratum granulosum

• stratum lucidum

• stratum corneum

How many layers does thick skin have?

five

How many layers does thin skin have?

four; the stratum lucidum is absent

What does the stratum basale consist of?

a single row of stem cells attached to the underlying dermis along a wavy borderline

What happens after basal cell division?

one daughter cell is pushed up to begin specialization and the other stays behind to make new keratinocytes

What percentage of cells in the stratum basale are melanocytes?

10-25%

What does the stratum spinosum consist of?

several cell layers that contain keratinocytes that appear spiny in histological preparations

What does the stratum granulosum consist of?

one to five cell layers of keratinocytes undergoing keratinization

What happens to keratinocytes in the stratum granulosum?

they flatten, their nuclei and organelles begin to disintegrate, and they accumulate keratohyaline and lamellar granules

What do keratohyaline granules do?

help to form keratin in the upper layers by providing the “glue” that binds pre-keratin intermediate filaments together to form keratin

What do lamellar granules contain?

water-resistant glycolipid that is secreted into the extracellular space

What does the stratum lucidum consist of?

a few rows of flat, dead keratinocytes

What layer’s cells are the stratum lucidum’s identical to?

the stratum corneum

What does the stratum corneum consist of?

20 to 30 cell layers of dead, flat keratinocytes

What portion of epidermal thickness does the stratum corneoum account for?

¾

What do accumulations of keratin and proteins inside the plasma membrane do?

protect the skin against abrasion and penetration

What makes the stratum corneum nearly waterproof?

the glycolipid between its cells

What is the dermis made up of?

strong, flexible connective tissue

What cells are found in the dermis?

fibroblasts, macrophages, and occasional mast cells and white blood cells

What does the semifluid matrix of the dermis do?

binds the entire body together

What is the superior layers of the dermis?

papillary

What is the papillary dermis made of?

areolar connective tissue

How can phagocytes and other defensive cells wander freely in the papillary dermis?

because the fine interlacing collagen and elastic fibers form a loosely woven mat with many small blood and lymphatic vessels

What are dermal papillae?

peglike projections from the papillary dermis’ surface that indent the overlying epidermis

What are friction ridges?

skin markings that consist of epidermal ridges that lie atop dermal ridges

What is the function of friction ridges?

contribute to the sense of touch and may enhance gripping ability

What are cleavage lines?

topographically drawn lines on the body that represent the natural orientation of collagen fibers in the reticular dermis

Why are cleavage lines important in surgical procedures?

because incisions made parallel to them tend to heal better and with less scarring

What are flexure lines?

the deep creases found when the dermis is closely attached to the underlying structures (e.g. lines on the palm)

What is the reticular dermis made of?

dense irregular connective tissue

What is the dermal vascular plexus?

the network of blood vessels that nourishes the reticular dermis

Where is the dermal vascular plexus located?

between the reticular dermis and subcutaneous tissue

What does the extracellular matrix of the reticular dermis contain?

thick bundles of interlacing collagen fibers

What do collagen fibers do for the dermis?

give it strength and resiliency that prevent minor jabs and scrapes from penetrating it

What are striae?

stretch marks; silvery white scars that are formed when extreme stretching of the skin tears the dermis

What enzyme does melanin synthesis depend on?

tyrosinase

What is the range of the color of melanin?

from reddish yellow to brownish black

Why is melanin only found in the deeper layers of the epidermis?

because melanin is transported from melanocytes to the basal keratinocytes, and lysosomes break down the melanosomes

What are freckles and moles?

local accumulations of melanin

What happens when we expose our skin to sunlight?

keratinocytes secrete chemicals that stimulate melanocytes, causing melanin to build up, which protects the DNA of skin cells from UV damage

What is carotene?

a yellow to orange pigment found in certain plant products

Where does carotene tend to accumulate?

in the stratum corneum and the fat of subcutaneous tissue

What can carotene be converted to in the body?

vitamin A

What is hemoglobin?

a crimson-colored pigment in the red blood cells circulating through the dermal capillaries

What is blueness or cyanosis?

when hemoglobin is poorly oxygenated, and the skin takes on a bluish-gray tint

What can cyanosis be a sign of?

respiratory or cardiovascular problems

What is pallor or blanching?

paleness that occurs when blood is diverted from the skin to internal organs

What can cause pallor?

low blood pressure, anemia, and emotional stress

What is erythema or redness?

reddened skin due to embarrassment, fever, inflammation or allergy

What are red/purple/green/yellow marks?

bruises that occur when blood vessels are damaged and leak blood into the surrounding tissue

What are brown or black patches?

hyperpigmented and thickened areas of skin, usually found where skin folds

What might brown or black patches signal?

an endocrine disorder

What are pili (hairs)?

flexible strands produced by hair follicles consisting largely of dead, keratinized cells

What is the advantage of hair being made of hard keratin?

it is tougher and more durable and its individual cells do not flake off

What is the hair root?

the part embedded in the skin

What is the hair shaft?

the part that projects above the skin’s surface

When is hair coily?

if the shaft is flat and ribbonlike

When is hair silky and wavy?

if the shaft is oval

When is hair straight?

if the shaft is round

What are the three concentric layers of keratinized cells?

the medulla, cortex, and cuticle

What is the medulla?

the central core of the hair consisting of large cells and air spaces

What is the cortex?

the bulky layer surrounding the medulla that consists of several layers of flattened cells

What is the cuticle?

the layer of keratinized cells that surrounds a hair, providing strength and keeping the

How do split ends form?

abrasion wears away the cuticle at the tip of the hair shaft, allowing keratin fibers in the cortex and medulla to frizz

What pigment is red hair colored by?

pheomelanin

What is the hair follicle?

structure with outer and inner root sheaths extending from the epidermal surface into the dermis and from which new hair develops

What is the hair bulb?

the expanded region of the deep end of a hair follicle that is about 4 mm below the skin surface

What is the hair follicle receptor (root hair plexus)?

a group of sensory nerve endings wrapped around a hair bulb that detect hair shaft movement

What is the hair papilla?

a dermal papilla that protrudes into the hair bulb and contains a knot of capillaries that supplies nutrients to the growing hair and signals it to grow

What happens if the hair papilla is destroyed by trauma?

the follicle permanently stops producing hair