Chapter 5 Module 2 The Dermis and Hypodermis
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Chapter 5 Module 2 The Dermis and Hypodermis

This is chapter five,
module two– the dermis and hypodermis. The learning objectives
of this module are, one, describe the
components of the dermis, two, describe how wrinkles and
stretch marks are formed, three, describe the
lines of cleavage and how this would affect
scarring during injury, and four, describe the structure
and function of the hypodermis. The dermis is the layer of skin
just deep to the epidermis. It is bound tightly
to the epidermis by the basement membrane. Deep to the dermis is
the subcutaneous layer. The dermis is comprised of
connective tissue the anchors the accessory structures
of the integument, such as hair follicles
and sweat glands. The dermis has two layers–
the more superficial papillary layer, and the deep
reticular layer. The papillary
layer of the dermis is made up of areolar tissue. This layer contains smaller
capillaries, lymphatics, and sensory neurons. The dermal papillae project in
between the epidermal ridges, making it a tight junction
between the epidermis and the dermis. The bulk of the reticular layer
consists of dense irregular connective tissue and
contains larger blood vessels, lymphatic vessels,
and nerve fibers. As you remember, dense
irregular connective tissue contains both collagen
and elastic fibers that work to give this
layer of the dermis both strength and flexibility. The collagen fibers
are very strong and they resist stretching,
but they also bend easily to produce the flexibility. The elastic fibers
permit stretching and then can recoil to
their original strength after being stretched. The flexibility and elasticity
of the reticular layer give the skin a characteristic
called skin turgor. Skin turgor is the
ability of the skin to be pinched or stretched
and then recoil back to its original shape. Skin turgor is a sign commonly
used by health care workers to assess the degree of
fluid loss or dehydration. Fluid loss can occur
from common conditions such as diarrhea or vomiting. Especially infants
and young children with vomiting, diarrhea, and
decreased or no fluid intake can rapidly lose a
significant amount of fluid. Fever speeds up this process. To determine skin turgor,
the health provider pinches the skin on the back of
the hand, lower arm, or abdomen between two fingers so
that it is tented up. The skin is held for a few
seconds and then released. Skin with normal turgor
snaps rapidly back to its normal position. Skin with decreased
turgor, or poor turgor, remains elevated and returns
slowly to its normal position. Decreased skin turgor is a
late sign in dehydration. It occurs with moderate
to severe dehydration. Damage to the skin, such
as sagging, wrinkles, and stretch marks, is caused
by reduced skin elasticity. This type of damage
occurs naturally through aging, though it
can be caused or worsened by other factors such as
dehydration, smoking, aging, hormonal changes, some
medications, and exposure to UV sunlight. Wrinkles are an inevitable part
of the natural aging process. As we become older, our
skin becomes thinner, drier, and less elastic. Our skin’s ability to
protect itself from damage is also reduced as we age. Eventually, wrinkles, creases,
and lines form on our skin. Apart from the factors
mentioned above, a person’s genetic
makeup also influences how wrinkly we become
and when and where wrinkles start appearing. Stretch marks are
thickened tissue resulting from an excessive stretching
of the skin due to pregnancy and weight gain. Stretch marks are a
normal part of puberty for most boys and girls. When a person grows or
gains weight quickly, like during puberty, that
person may get fine lines on the body called
stretch marks. Stretch marks happen when the
skin is pulled by rapid growth or stretching. Although the skin is
usually fairly elastic, when it is overstretched the
normal production of collagen fibers is disrupted. As a result, scars called
stretch marks may form. Most girls and women
have stretch marks which tend to show up on
the breasts, thighs, hips, and butt. Many women get them
during pregnancy. And while they’re
more common in girls, guys can get stretch marks too. People who are obese
often have stretch marks. Bodybuilders are prone to
getting stretch marks because of the rapid body changes
that bodybuilding can produce. Stretch marks also
may occur if a person uses steroid-containing
skin creams or ointments, such as hydrocortisone,
for more than a few weeks or has to take high doses
of oral corticosteroids for months or longer. At first, stretch
marks may show up as reddish or
purplish lines that may appear indented and have
more of a different texture from the surrounding skin. Most stretch marks often turn
lighter and almost disappear over time. The collagen and elastic
fibers in the dermis are arranged in parallel bundles
running in the same direction. This allows the dermis to resist
force in a specific direction. Cleavage lines are
tension lines that establish specific patterns of
the collagen and elastic fibers throughout the skin. These patterns become important
when injury to the dermis occurs. A cut through the dermis that is
parallel to the cleavage lines will remain shut
and will heal well. A cut across the cleavage
lines– or in other words, at a right angle to the
cleavage lines– will pull open and will not heal
well, leaving a scar. Nerve fibers are also
found in the dermis. Nerve impulses
through these nerves control the blood flow to
the skin and the secretions from the glands of the skin. These nerve fibers also
communicate information from the sensory receptors to
the central nervous system. They will transmit
information about light touch from the tactile corpuscles
located in the dermal papillae, as well as deep
pressure and vibration from the lamellated
corpuscles in the reticular layer of the dermis. Deep to the dermis
is the hypodermis, or the subcutaneous layer. This layer is not a
layer of the integument but is very much involved
in stabilizing the skin. The hypodermis is made of
connective tissue proper, and more specifically of
areolar and adipose tissue. These tissues are
connected to the reticular layer of the integument by
connective tissue fibers. The hypodermis allows
a separate movement between the skin and
other underlying tissues. There are few capillaries in the
hypodermis and no vital organs either. The hypodermis is the site
of subcutaneous injections using hypodermic needles. The adipose tissue that
is found in the hypodermis is not deposited throughout
the body equally. Hormones and age determine
the distribution patterns of adipose. Men are more likely to have fat
stored in their abdominal area due to the sex
hormone differences. Female sex hormones cause fat to
be stored in the hips, thighs, and buttocks areas. This ends module two of
chapter five, the dermis.

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