Chapter 38 Protection, Support, and Movement

I. Integumentary System
A. The outer covering of animal bodies is called the integument.
1 In arthropods, it is a hardened cuticle made of chitin and protein.
2 In vertebrates, it is the pliable skin and the structures derived from the epidermal cells.
B. Functions of Skin
1 The skin covers and protects the body from abrasion, bacterial attack, ultraviolet radiation, and
dehydration.
2 It helps control internal temperature.
3 Its vessels serve as a blood reservoir for the body.
4 The skin produces vitamin D.
5 Its receptors are essential in detecting environmental stimuli.
C. Structure of Skin
1 Epidermis—Stratified Epithelium.
a. The layers can differentiate to form scales, feathers, hair, beaks, horns, nails, and so forth.
b. Epidermal cells (keratinocytes) produce keratin, a tough, water-insoluble protein that
accumulates in the cells.
c. The outermost layer (stratum corneum) consists of flattened, dead bags of keratin.
d. Slightly deeper layers of epidermal cells produce melanin pigment that darkens the skin and
protects against the sun’s rays.
e. Hemoglobin and carotene also contribute to skin color.
2 Dermis
a. Its dense connective tissue cushions the body against everyday stretching and mechanical
stresses.
b. Sweat glands, oil glands, hair follicles, blood vessels, and nerve endings are located here.
c. During the aging process, the epidermal cells divide less often, the skin becomes thinner,
glandular secretions dwindle, and the skin loses it elasticity.
3 The skin is anchored to an underlying hypodermis, which also stores fat.

II. Skeletal Systems
A. There are three main types of skeletons in animals:
1 In hydrostatic skeletons, the force of contraction is applied against internal fluids.
2 In an exoskeleton, the force is against rigid external body parts, such as shells or plates.
3 In an endoskeleton, the force is applied against rigid internal cartilage and bones.
B. Invertebrate Skeletons
1 Sea anemones and earthworms use the fluids in their body cavities as resistance against which
the muscles can act to cause varying degrees of movement.
2 The rigid exoskeletons of arthropods provide support for bodies deprived of water’s buoyancy;
plus they provide sites for muscle attachments that maximize leverage.
C. Vertebrate Skeletons
1 Some fishes have a flexible skeleton made of an elastic, translucent form of cartilage.
2 The cartilage in sharks is opaque and hardened with calcium salts.
3 Vertebrate skeletons are made primarily of bone.
D. Functions of Bone
1 The bones are moved by muscles; thus the whole body is movable.
2 Bones protect vital organs such as brain and lungs.
3 The bones support the skin and soft organs.
4 Bone tissue acts as a depository for calcium, phosphorus, and other ions.
5 Parts of some bones are sites of red blood cell production.
E. Characteristics of Bone
1 There are four types of bones: long (arms), short (wrist), flat (skull), and irregular (vertebrae). 2 Bone Structure
a. Bone is a connective tissue with living cells and collagen fibers distributed throughout a
ground substance that is hardened by calcium salts.
b. “Compact” bone tissue forms the bone’s shaft and the outer portion of its two ends.
1) Concentric layers (lamellae) surround Haversian canals, which contain blood vessels and
nerves.
2) The living bone cells reside in the ground substance.
c. “Spongy” bone tissue may have red marrow that produces blood cells; adults have reserve
yellow marrow, which can be converted to red marrow if blood cell production needs
to be increased.
3 How Bones Develop
a. Osteoblasts secrete material inside the shaft of the cartilage model of long bones.
b. Calcium is deposited; cavities merge to form the marrow cavity.
c. Eventually osteoblasts become trapped within their own secretions and become osteocytes
(mature bone cells).
4 Bone Tissue Turnover
a. Bone is renewed constantly as minerals are deposited and withdrawn during the growth and
development processes as well as in maintenance of body calcium levels.
b. Bone turnover helps to maintain calcium levels for the entire body; enzymes from bone cells
dissolve bone tissue and release calcium to the interstitial fluid and blood.
c. Osteoporosis (decreased bone density) is associated with decreases in osteoblast activity,
sex hormone production, exercise, and calcium uptake.

III. Human Skeletal System
A. Skeletal Structure
1 The 206 bones of a human are distributed in two portions:
a. The axial skeleton includes the skull, vertebral column (individual bones separated by
cartilaginous intervertebral disks), ribs, and sternum.
b. The appendicular skeleton consists of the pectoral girdle with attached upper limbs, and the
pelvic girdle with lower limbs.
2 The vertebral column extends from the skull to the pelvic girdle; cartilaginous intervertebral
disks serve as shock absorbers and flex points.
B. Joints
1 Synovial joints are the most common and move freely.
a. They are stabilized by ligaments.
b. A capsule of dense connective tissue surrounds the bones of the joint.
c. The capsule produces synovial fluid that lubricates the joint.
d. In osteoarthritis, the cartilage at the end of the bone has worn away.
e. In rheumatoid arthritis, the synovial membrane becomes inflamed, the cartilage degenerates,
and bone is deposited into the joint.
2 Cartilaginous joints (such as intervertebral disks) have no gap, but are held together by cartilage
and can move only a little.
3 Fibrous joints also have no gap between the bones and hardly move; flat cranial bones are an
example.

IV. Muscular System
A. Comparison of Muscular Tissues
1 There are three types of muscle tissues: skeletal, cardiac (heart), and smooth (digestive tract). 2 All have three properties in common:
a. Electrical potentials across the plasma membrane confer excitability.
b. They contract in response to action potentials.
c. They are elastic—the ability to return to the original, relaxed position after contraction.
B. Fine Structure of Skeletal Muscle
1 Muscles are composed of individual muscle cells (fibers), which are composed of myofibrils,
which are composed of filaments: actin and myosin.
a. Actin is a thin filament composed of two beaded strands twisted together.
b. Myosin is thicker; each molecule has a bulbous head and long tail making it resemble a golf
club.
2 The filaments are arranged to form sarcomeres—the individual units of muscle contraction.
C. Mechanism of Skeletal Muscle Contraction
1 Muscles shorten because sarcomeres can shorten within each cell by the sliding-filament model. a. The myosin filaments slide along and pull the actin filaments toward the center of the
sarcomere.
b. Cross-bridges form between the heads of myosin molecules and actin filaments.
c. The cross-bridges are then activated and tilt inward; then the heads detach and reattach.
d. ATP supplies the energy for both attachment and detachment.
2 At death, there is no ATP to cause the heads to detach, and the body enters rigor mortis.
D. Energy Metabolism in Muscles
1 During periods (few seconds) of intense muscle activity, creatine phosphate is the source of
phosphate to remake ATP.
2 During intense and prolonged muscle action, anaerobic lactate fermentation produces low amounts
of ATP and leads to a buildup of lactate.
3 When muscle action is moderate, most of the ATP is provided by aerobic electron transport
phosphorylation, which is dependent on oxygen supply and number of mitochondria present. E. Control of Contraction
1 Skeletal muscles contract in response to signals from the nervous system that trigger action
potentials along the plasma membrane and into the interior of the muscle cell.
2 Eventually the signal reaches the sarcoplasmic reticulum (internal tubes), which responds by
releasing stored calcium ions that will bind to the troponin component of actin allowing cross-
bridges to form.
3 A muscle relaxes when calcium ions are actively taken up after contraction to be stored in the
sarcoplasmic reticulum.

V. Contraction of a Skeletal Muscle
A. A motor neuron and the muscle cells under its control are a motor unit.
1 A single, brief stimulus to a motor unit causes a brief contraction called a muscle twitch.
2 Repeated stimulation without sufficient interval causes a sustained contraction called tetanus. B. The number of motor units that are activated determines the strength of the contraction: Small
number of units = weak contraction; large number at greater frequency = stronger contraction.

VI. Limb Movements
A. The human body muscles (600 of them) are arranged in pairs or groups.
1 Some work together (synergistic); others operate antagonistically.
2 The skeleton and muscles operate like a system of levers.
B. Because most muscle attachments are located close to joints, only a small contraction is needed to
produce considerable movement of some body part.
C. Reciprocal innervation in the spinal cord allows one muscle of an opposing pair to contract while the
other is forced to relax.