in order to cool the body.
Heat-induced sweating occurs all over
the body when we are overheated. A cold sweat is emotionally induced
sweating that begins on the palms, soles, and armpits and then spreads
to other body areas. Both types of sweating are produced by the eccrine
sweat glands, but activity of apocrine sweat glands is also likely during a
Te palms of the hands and soles of the feet are thick skin
areas. It would be dangerous to have oily soles, and oily palms would
decrease the ability of the hands to hang onto things.
Te low pH of
skin secretions (acid mantle) inhibits division of bacteria, and many bac-
teria are killed by bactericidal substances in sebum or by natural antibiot-
ics called defensins. Damaged skin secretes cathelicidins that are eﬀective
against a certain strain of strep bacteria.
Te epidermal dendritic cells
play a role in body immunity.
Sunlight causes the skin to produce a
precursor of vitamin D from cholesterol. Vitamin D is essential for bone
Te skin carries out chemical conversions that supple-
ment some of the protective conversions carried out by the liver, convert
some chemicals into carcinogens, activate some steroid hormones, and
synthesize the vitamin D precursor.
Basal cell carcinoma develops
from the youngest epidermal cells.
Te ABCD rule helps one to
recognize signs of melanoma.
First- and second-degree burns can
heal uneventfully by regeneration of epidermal cells as long as infection
does not occur. Tird-degree burns destroy the entire depth of skin and
regeneration is not possible. Infection and loss of body ﬂuid and proteins
Burns to the face are serious because damage to the
respiratory passageways can occur in such burns.
Vernix caseosa is a
product of the sebaceous glands.
Loss of subcutaneous fat, common
in the elderly, leads to cold intolerance seen in this group of people.
UV radiation degrades collagen and leads to loss of skin elasticity
and water-holding capacity.
Review Questions 1.
Case Study 1.
Te skin separates and protects the internal environ-
ment of the body from potentially dangerous elements in the external
environment. Mrs. DeStephano’s chart indicates epidermal abrasions,
which represent the loss of this barrier. Epidermal loss will also cost Mrs.
DeStephano the acid mantle of her skin, protection against UV radiation,
and dendritic cells, which protect against invasion by microorganisms.
Macrophages found in the dermis can act as a backup system against
bacterial and viral invasion when the epidermis is damaged.
brings the edges of wounds close together and promotes faster healing
because smaller amounts of granulation tissue need to be formed. Tis
is termed healing by ﬁrst intention.
Cyanosis signals a decrease in the
amount of oxygen carried by hemoglobin in the blood. Respiratory sys-
tem and/or cardiovascular system impairments can lead to cyanosis.
Check Your Understanding
Hyaline cartilage is the most plentiful
in the adult body.
Te epiglottis and external ear cartilages are ﬂex-
ible elastic cartilage.
Interstitial growth is growth from within.
components of the axial skeleton are the skull, the vertebral column,
and the thoracic cage.
Te major function of the axial skeleton is to
establish the long axis of the body and to protect structures that it en-
closes. Te general function of the appendicular skeleton is to allow us
mobility for propulsion and manipulation of our environment.
ribs and skull bones are ﬂat bones.
Skeletal muscles use bones as le-
vers to cause movement of the body and its parts.
Bone matrix stores
minerals and growth factors.
Bone marrow cavities serve as sites for
blood cell formation and fat storage.
Crests, tubercles, and spines
are bony projections.
Compact bone looks fairly solid and homo-
geneous whereas spongy bone has an open network of bone spicules.
Endosteum lines the internal canals and covers the trabeculae.
Bone’s inorganic component (bone salts) makes it hard.
osteoclast ﬁts this description.
Bones begin as ﬁbrous membranes
or hyaline cartilages.
Te cartilage model grows, then breaks down
and is replaced by bone.
Te primary ossiﬁcation center in a long
bone is in the center of the sha±. Te secondary ossiﬁcation centers
are in the epiphyses (bone ends).
Te chondrocytes are enlarging
and their lacunae are breaking down and leaving holes in the cartilage
If bone-destroying cells (osteoclasts) are more active than
bone-forming cells (osteoblasts), bone mass will decrease.
monal stimulus maintains homeostatic blood calcium levels.
open fracture, the bone ends are exposed to the external environment. In
a closed fracture, the bone ends do not penetrate the external boundary
of the skin.
Bone growth increases bone mass, as during childhood or
when exceptional stress is placed on the bones. Bone remodeling follows
bone growth to maintain the proper proportions of the bone considering
stresses placed upon it.
Paget’s disease is characterized by excessive de-
posit of weak, poorly mineralized bone.
Suﬃcient vitamin D, calcium,
and weight-bearing exercise all help to maintain healthy bone density.
Adult rickets is called osteomalacia.
At birth, most bones are well
formed and ossiﬁed except for their epiphyses.
Te skull bones do not
appear to lose mass with aging.
Review Questions 1.
Case Study 1.
Mrs. DeStephano’s broken leg has a transverse fracture
of the open variety because the broken ends of the bone are protruding
through the skin.
Te laceration of the skin caused by the broken end
of the bone creates a breach in the protective barrier created by the skin,
providing an entry point for bacteria and other microorganisms. In ad-
dition, the protruding ends of the bone have now been exposed to the
nonsterile external environment. Tis could result in the development of
osteomyelitis, a bacterial infection, which can be treated with antibiot-
Reduction of a fracture is the clinical term for “setting the bone.”
Mrs. DeStephano’s physician chose internal reduction, in which surgery
is performed and the broken ends of the bone are secured together by
pins or wires. A cast was applied to keep the aligned ends of the bone
immobile until healing of the fracture has occurred.
Healing of Mrs.
DeStephano’s fracture will begin as bony callus formation ﬁlls the break
in the bone with bony tissue. Tis process begins 3–4 weeks a±er the
break occurs and is completed within 2–3 months.
supply blood to the bone tissue. In order for Mrs. DeStephano’s break to
heal normally, the bony tissue must be supplied with oxygen (to gener-
ate A²P for energy) and nutrients in order to rebuild the bone. Damage
to a nutrient artery will decrease the delivery of these building materials
and could slow the process of healing.
For a fracture that is slow to
heal, new techniques that promote healing include electrical stimulation,
which promotes the deposition of new bone tissue; ultrasound treat-
ments, known to speed healing; and possibly the addition of bone substi-
tutes to the fractured area.
At age 45, Mrs. DeStephano will most likely
not regenerate her knee cartilage. (Cartilage growth typically ends during
adolescence.) Cartilage damage that occurs during adulthood is slow to
heal, due to the avascular nature of cartilage, and is usually irreparable.
Surgical removal of cartilage fragments to allow improved movement of
the joint is the usual treatment for this type of damage.
Check Your Understanding 1.
Te three main parts of the axial skel-
eton are the skull, vertebral column, and thoracic cage.
skeleton is more important in protecting internal organs.
parietal, temporal, sphenoid, and ethmoid bones are all cranial bones.
Te ethmoid bone forms the crista galli.
Te temporal bones house
the external ear canals.
Te parietal bones abut each other at the sagit-
tal suture. Te occipital bone abuts the parietal bones at the lambdoid
Te zygomatic bones are the cheekbones.
Eating or talking,