Chapter 7: It’s Skin Deep: The Integumentary System Summary

• The integumentary system is composed of nails, hair, and glands.

The skin

• The skin has an epidermis and the dermis.
• Hypodermis (subcutaneous tissue) lies beneath the dermis and epidermis.
• Organs and tissues loosely attach to the hypodermis to allow free movement of muscles.
• The hypodermis contains pressure-sensitive nerves.

Epidermis

• The stratum corneum:  It contains approximately 20 layers of flat, dead, and scaly cells with keratin.
  • These cells are referred to as cornified and make up three-quarters of the epidermis.
  • This layer is usually shed in humans and regenerated by new cells.
• Stratum lucidium:  It is found in soles of feet and palms’ thick skin.
  • It has a translucent region with dead cells containing eledin.
• Stratum granulosum: It has 5 layers of flat cells with keratohyalin which helps in the formation of keratin.
  • It has dying or dead cells because of a lack of nourishment from blood vessels.
• Stratum spinosum: It contains ten layers of prickle cells. The prickle cells contain spine-like extensions that bind them to other cells.
• Stratum basale: It contains columnar stem cells that produce all epidermal layer cells.
  • It is located at the papillary on the dermis near blood vessels.

The dermis

• It contains two layers.
• The papillary layer: It contains reticular and elastic fibers that extend into the epidermis to pull nerve endings and blood closer.
  • The layer has papillae that increase the dermis surface area.
  •  It forms the outer layer of the dermis.
• The reticular layer: This is the thicker inner layer of the dermis.
  • This layer promotes elasticity, strength, and extensibility of the skin.
  • The layer also has sweat glands, sebaceous glands, blood vessels, and fat cells.
• The dermis has fibroblasts, macrophages, and adipose tissue.
• The penis, eyelids, and scrotum have a thin dermis.

Nerves in the integumentary system

• The system contains four nerve receptors.
• Free nerve endings: sensory nerves dendrites act like nerve endings and are used as pain receptors.
  • They are numerous in the epithelial and connective tissue.
  • These thin fibers contain swelling at their proximity which senses touch, heat, cold, or pain.
• Meissner’s corpuscles: They are located within the dermal papillae.
  • They are numerous in on the fingertips and lips.
  • They can detect a quick touch.
• Pacinian corpuscles: hey contain dendrites surrounded by layers of concentric connective tissue.
  • They are located deep under the dermis.
  • They sense deep pressure and vibrations.
• Hair nerve ending: they are mechanoreceptors sense a variation in hair position.

Temperature receptors

• End-bulbs of Krause: these are cold receptors which are activated at a temperature below 20 degrees C.
  • They have a bulb-like capsule that surrounds a dendrite.
  • They are found in the dermis, lips, and eyes.
• Brushes of Ruffini: These are warmth receptors and they can sense temperatures between 25 degrees C to 45 degrees C.
  • They are located in the subcutaneous tissue and the dermis.
  • The body responds less to temperature because the brushes of Ruffini receptors are fewer in the body.

Hair

• Every hair has 3 layers of keratin cells:
  • Medulla, a central core of the hair.
  • Cortex which surrounds the medulla and builds up the hair shaft.
  • The cuticle has overlapping single-cell layers.

Nails

• Nails contain three parts:
  • Root bed
  • Body
  • Free edge
• The nail bed is produced by spinosum and strata sale.
• At the nail base, strata basale becomes thick generating the white region referred to as lunula.
• Stratum corneum at the nail edge thickens to generate the hyponychium.

REVISION

Skin accounts for about
3 to 5 kilograms of your body weight, and if you could spread it out, it would measure up to two square meters, enough to cover your bed

Skin’s nerve endings allow you to
sense the outside world, and its sweat glands and blood vessels help you maintain a proper temperature and communicate a whole range of stuff — from your health to your emotions — through things like blushing, and flushing, and sweating.

Your hair, nails, and sweat and oil glands, your skin forms your
integumentary system.

The epidermis is the only layer you can actually
see, assuming that your skin is intact, which is why it’s what you think of, when you think of “skin.” It’s made of stratified squamous epithelial tissue.

The dermis just below the epidermis is where most of the work that skin does gets done, like
sweating, and circulating blood, and feeling everything everywhere all the time.

And at the bottom there’s the subcutis, or hypodermis, composed mostly of
adipose or fatty tissue.

The bulk of your epidermis, is made up of cells called __ , which are the building blocks of that tough, fibrous protein keratin that gives structure, durability, and waterproofing to your hair, nails, and outer skin. (EPIDERMIS)
keratinocytes (EPIDERMIS)

another epidermal cell: the melanocyte, the spider-shaped cell that
(EPIDERMIS)
synthesizes melanin, the pigment that gives skin its color. (EPIDERMIS)

You have lots of immune system cells in your epidermis as well. These are your dendritic, or Langerhans cells, which are kinda star-shaped, and like white blood cells and platelets, they actually originate in your bone marrow. Once they migrate to the epidermis, (EPIDERMIS)
their long, skinny tendrils run around the keratinocytes and spend much of their time ingesting the unwanted invaders that are trying to sneak around your skin. (EPIDERMIS)

Finally, rounding out the quartet of epidermal cells, your _____ occur deep down at the boundary between the epidermis and the dermis, where they combine with nerve endings to create a sensory receptor for touch. (EPIDERMIS)
Tactile, or Merkel cells (EPIDERMIS)

All these (EPIDERMIS) cells are all organized differently in the skin that covers your body. In fact,
in some places, you have more layers of epidermis than others.

Your thick skin is the (EPIDERMIS)
tougher stuff on the palms of your hands and the soles your feet, and it consists of five epidermal layers. (EPIDERMIS)

Your thin skin (EPIDERMIS)
covers everything else, with just four. (EPIDERMIS)

Your stratum corner is the outermost layer of the epidermis and also the roughest, made up of (EPIDERMIS)
about 20 or 30 sheets of dead keratinocyte cells. This is the layer that you’re always sloughing off and feeding to dust mites, but while it’s in place it offers basic protection from environmental threats. (EPIDERMIS)

Your second layer is the stratum lucidum, or “clear layer.” This holds (EPIDERMIS)
two or three rows of clear, flat, dead keratinocytes that are only found in the thick skin of your palms and foot soles. So, in places where you only have thin skin, this layer is what’s missing. (EPIDERMIS)

Things start to get more serious in the “granular layer” or stratum granulosum, because this contains living (EPIDERMIS)
keratinocytes that are forming keratin like crazy. This layer looks kind of grainy because those cells are getting compressed and flattened as they move up through the epidermal layers, maturing as they go. (EPIDERMIS)

The deeper you go through the layers of the epidermis, the younger the cells get. (EPIDERMIS)
Regeneration happens in the lower layers, and new cells move up toward the surface, maturing along the way, where they eventually die and slough off from the surface of your skin. (EPIDERMIS)

This whole process of aging is due in part to the fact that the epidermis is epithelial, so it’s avascular. That means that all the oxygen and nutrients that its cells need have to come from the dermis below it. (EPIDERMIS)
So, as epidermal cells mature and get bumped up by younger cells forming below them, they move further and further from the blood supply, and end up essentially suffocating. (EPIDERMIS)

The stratum spinosum, or “spiny layer” — it’s getting closer to the point where cell regeneration, or mitosis, is active. These cells (EPIDERMIS)
look prickly when they’re dehydrated for microscope slide preparation — hence the name — and that’s because they contain filaments that help them hold to each other. (EPIDERMIS)

The thinnest epidermal level is the “basal layer” or stratum basale. (EPIDERMIS)
It’s just a single layer of columnar cells, but it’s like a cell factory where most of that new-cell production happens. This stratum is also what connects the epidermis to the layer of skin below it, the dermis. (EPIDERMIS)

The ultraviolet radiation in the sun can damage the epidermis, causing elastic fibers to clump up, leading to that tell-tale leather-face condition. (EPIDERMIS)
Plus, getting sunburned temporarily depresses your immune system — because, remember, you have immune cells in your epidermis too — AND the radiation can actually alter your skin cells’ DNA, leading to skin cancer. (EPIDERMIS)

Skin damage of any kind can get serious when it affects the dermis, because it’s not only got loads of those collagen and elastin fibers, which help make your skin strong and elastic, it’s also full of
capillaries and blood vessels. And it houses the nerve fibers that register sensations like temperature, pressure, and pain, as well as parts of your hair follicles and oil and sweat glands with the ducts that lead up to the surface of the skin.

The dermis is where most of the skin’s work is done, and it does it in just __ layers. (DERMIS)
Three (DERMIS)

The upper, papillary layer is composed of (DERMIS)
a thin sheet of areolar connective tissue that’s riddled with little peg-like projections called dermal papillae. (DERMIS)

These papillae are pretty neat because in the thick skin of your hands and feet, these tiny protrusions form unique friction ridges that press up through the epidermis to (DERMIS)
help our fingers and feet grip surfaces. Also it gives us finger prints! (DERMIS)

Just below that papillary layer is the deeper, thicker reticular layer that makes up 80 percent of your dermis, made up of dense irregular connective tissue. (DERMIS)
All of the dynamic parts contained within the dermis — like the nerve fibers and capillaries — are distributed between both its layers. (DERMIS)

So any time you get cut enough to bleed or feel pain, you know that you’ve broken through the (DERMIS)
epidermis and lacerated the dermis. (DERMIS)

Finally, something of a footnote to your skin is its third and most basal layer — the subcutis, or hypodermis. It consists of mostly (DERMIS)
adipose connective tissue — basically a seam of fat — and it provides insulation, energy storage, shock absorption, and helps anchor the skin. In short, your hypodermis is where most of your body fat hangs out. (DERMIS)

The _ and its _ organs make up the integumentary system.
skin, accessory

List the functions of the skin.
helps maintain homeostasis and regulate body temperature, serves as protection from physical, radioactive, and viral harm; slows water loss, houses sensory receptors, synthesizes certain biochemicals, plays a major role in excretion of wastes, and aids in creation of vitamin D

The skin consists of an outer _ and an underlying , connected to underlying tissue by the _ layer.
epidermis, dermis, subcutaneous

The subcutaneous layer is composed mainly of _ and _ tissue.
areolar, adipose

What are the functions of the subcutaneous layer?
serves as insulation of skin to conserve body heat, and houses major blood vessels

The epidermis is made up of stratified _ epithelium and lacks __.
squamous, blood vessels

The epidermal layers: innermost to outermost:
stratum basale (innermost), stratum spinous, stratum granulosum, stratum lucid, stratum corneum (outermost)

The stratum lucidum is not found in the epidermis in all regions of the body. In what areas does the skin contain the stratum lucidum?
palms and soles of feet

Which is the living, reproducing layer?
stratum basale

What is the function of keratin?
protects from water loss

What is the function of melanin?
produces pigments protecting deeper cells from UV rays and giving skin color

List the factors that contribute to the colors of the skin.
genetic, environmental, and physiological factors

The dermis consists of _ tissue with collagen and elastic fibers within a gel-like ground substance. The dermis also contains nerve fibers, sensory fibers, hair follicles, sebaceous glands, and sweat glands.
areolar

The boundary between the epidermis and dermis is uneven due to epidermal _ and dermal _.
ridges, papillae

A nail consists of a _ that overlies a layer of skin called the _.
nail plate, nail bed

Why are nails harder than the epidermal stratum corneum?
They go through the keratinization process.

Where is hair found?
all parts of the body except for palms, soles of feet, and lips

Define the term hair follicle.
a tube-like depression at the base of a hair

What is the function of arrector pili muscles?
cause goose bumps

What determines hair color?
melanin composition

What type of glands are sebaceous glands?
holocrine glands

What structure are sebaceous glands associated with?
hair

What is the sebaceous gland’s secretion called?
sebum

Eccrine glands respond to _ _.
body temperature

Apocrine glands respond to _.
stress

Ceruminous glands are found in the _ and secrete _.
ear, wax

Proper temperature regulation is vital to maintaining metabolic reactions. The _ plays a major role in temperature regulation, with the _ controlling it.
skin, hypothalamus

Active cells, such as those of the heart and skeletal muscle, produce _.
heat

Heat may be lost to the surroundings from the skin. The body responds to excessive heat by _ of dermal blood vessels. At the same time glands release __ onto the surface of the skin.
dilation, sweat, sweat

The body responds to excessive cooling by _ of dermal blood vessels, inactivating glands, and increasing muscle usage through __.
constricting, sweat, shivering

Inflammation, in which blood vessels _ and become more _, causing tissues to become red and swollen, is the body’s normal response to injury.
dilate, permeable

Superficial cuts are filled in by reproducing _ cells.
epithelial

Deeper cuts are closed off by _ , covered by , and eventually filled in by __, producing collagen fibers to rebuild the connective tissue.
blood clots, scabs, fibroblasts

Large wounds leave scars, and healing may be accompanied by the formation of small, rounded masses called _.
granulations