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
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.
a. Its dense connective tissue cushions the body against everyday stretching and mechanical
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;