A. How does the skin protect from external factors in the environment, like harmful micro-organisms,
toxins and pollutants?
Interconnecting Systems: Integumentary and Immune System
Brief Summary:
Biological barriers include the dendritic cells of the epidermis and macrophages in the dermis. Epidermal
dendritic cells are active elements of the immune system. For the immune response to be activated, the foreign
substances, or antigens, must be presented to specialized white blood cells called lymphocytes. In the
epidermis, the dendritic cells play this role. Dermal macrophages constitute a second line of defense to
dispose of viruses and bacteria that have managed to penetrate the epidermis. They, too, act as antigen
“presenters.”
The skin provides protection to its underlying tissues from pathogens, mechanical damage, and UV light.
Pathogens, such as viruses and bacteria, are unable to enter the body through unbroken skin due to the
outermost layers of epidermis containing an unending supply of tough, dead keratinocytes. This protection
explains the necessity of cleaning and covering cuts and scrapes with bandages to prevent infection. Minor
mechanical damage from rough or sharp objects is mostly absorbed by the skin before it can damage the
underlying tissues.
The chemical barriers include skin secretions and melanin. Although the skin’s surface teems with bacteria, the
low pH of skin secretions—the so-called acid mantle—retards their multiplication. In addition, many bacteria
are killed outright by dermcidin in sweat and bactericidal substances in sebum. Skin cells also secrete natural
antibiotics called defensins that literally punch holes in bacteria, making them look like sieves. Wounded skin
releases large quantities of protective peptides called cathelicidins that are particularly effective in preventing
infection by group A streptococcus bacteria melanin provides a chemical pigment shield to prevent UV damage
to the viable skin cells.
https://www.youtube.com/watch?v=_VhcZTGv0CU
https://www.youtube.com/watch?v=zZpMQ_7qiRg
Key terms to use when looking for videos:
-skin fights infection (or toxin, or pollutant) animation
-skin healing animations
B. How does the skin protect the body through feeling pain, hot, cold, and pressure?
Interconnecting Systems: Integumentary, Muscular and Nervous System
Brief Summary:
The skin is richly supplied with cutaneous sensory receptors, which are actually part of the nervous system.
The cutaneous receptors are classified as exteroceptors (ekster-o-septorz) because they respond to stimuli
arising outside the body. For example, Meissner’s corpuscles (in the dermal papillae) and tactile discs allow us
to become aware of a caress or the feel of our clothing against our skin, whereas pacinian corpuscles (in the
deeper dermis or hypodermis) alert us to bumps or contacts involving deep pressure. Hair follicle receptors
report on wind blowing through our hair and a playful tug on a pigtail. Free nerve endings that meander
throughout the skin sense painful stimuli (irritating chemicals, extreme heat or cold, and others). We defer
detailed discussion of these cutaneous receptors to Chapter 13. Except for Meissner’s corpuscles, which are
found only in skin that lacks hairs
Pain provides the body with a protective mechanism, alerting it to potential or actual damage to the body’s
tissues. In the example of a bee sting, the pain receptors in the skin detect tissue damage from the bee sting.
Then, the peripheral nerves send a pain signal to the brain. The brain analyzes the pain signal. In turn, the
brain delivers a message back to the muscles of the arm to react.
http://www.sumanasinc.com/webcontent/animations/content/reflexarcs.html
https://www.youtube.com/watch?v=qDwNK7RqkEE
https://www.youtube.com/watch?v=_VhcZTGv0CU
https://www.youtube.com/watch?v=zZpMQ_7qiRg
Key terms to use when looking for videos:
-skin feels pressure animation
-skin feels pain animation
-skin gets cut animation
C. How does the skin help to regulate body temperature?
Interconnecting Systems: Integumentary, Nervous, and Cardiovascular
Brief Summary:
Nervous system regulates diameter of blood vessels in skin; activates sweat glands, contributing to thermoregulation; interprets
cutaneous sensation; activates arrector pili muscles
Eccrine gland secretion, commonly called sweat, is a hypotonic filtrate of the blood that passes through the secretory cells of the sweat
glands and is released by exocytosis. It is 99% water, with some salts (mostly sodium chloride), vitamin C, antibodies, a microbe-killing
peptide dubbed dermcidin, and traces of metabolic wastes (urea, uric acid, and ammonia).
The exact composition depends on heredity and diet. Small amounts of ingested drugs may also be excreted by this route.
Normally,sweat is acidic with a pH between 4 and 6. Sweating is regulated by the sympathetic autonomic nervous system, over which
we have little control. Its major role is to prevent overheating of the body. Heat-induced sweating begins on the forehead and then
spreads inferiorly over the remainder of the body. Emotionally induced sweating—the so-called “cold sweat” brought on by fright,
embarrassment, or nervousness—begins on the palms, soles, and axillae (armpits) and then spreads to other body areas.
Associated with each hair follicle is a bundle of smooth hair follicle into an upright position and dimples the skin surface to produce
goose bumps in response to cold external temperatures or fear. This “hair-raising” response is not very useful muscle cells called an
arrector pili (ah-rektor pili; “raiser of hair”) muscle. As you can see in Figure 5.1, most hair follicles approach the skin surface at a slight
angle. The arrector pili muscle is attached in such a way that its contraction pulls the to humans, with our short sparse hairs, but it is an
important way for other animals to retain heat and protect themselves. Furry animals can stay warmer by trapping a layer of insulating
air in their fur; and a scared animal with its hair on end looks larger and more formidable to its enemy.
The body works best when its temperature remains within homeostatic limits. Like car engines, we need to get rid of the heat generated
by our internal reactions. As long as the external temperature is lower than body temperature, the skin surface loses heat to the air and
to cooler objects in its environment, just as a car radiator loses heat to the air and other nearby engine parts. Under normal resting
conditions, and as long as the environmental temperature is below 31–32°C (88–90°F), sweat glands secrete about 500 ml (0.5 L) of
sweat per day. This routine and unnoticeable sweating is called insensible perspiration. When body temperature rises, the nervous
system stimulates the dermal blood vessels to dilate and the sweat glands into vigorous secretory activity. Indeed, on a hot day, sweat
becomes noticeable and can account for the loss of up to 12 L (about 3 gallons) of body water in one day. This visible output of sweat is
referred
to as sensible perspiration. Evaporation of sweat from the skin surface dissipates body heat and efficiently cools the body, preventing
overheating. When the external environment is cold, dermal blood vessels constrict. Their constriction causes the warm blood to
bypass
the skin temporarily and allows skin temperature to drop to that of the external environment. Once this has happened, passive heat loss
from the body is slowed, conserving body heat. Body temperature regulation is discussed in Chapter 24.
The small blood vessels in the skin have tiny muscles inside the walls that are under the control of the sympathetic nervous system.
If the muscles contract more than normal, for example in cold weather, the blood vessels also contract (vasoconstriction) so that less
blood passes through them, reducing the loss of body heat.
When the muscles are completely relaxed, for example in warm weather, the blood vessels dilate or widen (vasodilation). This allows
more blood to pass through the skin resulting in the body radiating more heat.
Key terms to use when looking for videos:
-skin makes goosebumps animation
-skin regulates heat animation
-skin thermoregulation animation