SOLUTIONS TO EXERCISES, LESSON 3
1. The envelopes of the body are like an air conditioner; they help to remove heat.
The envelopes are like a blanket; they help to retain heat when the surrounding air is
cold. The skin is like a chemical factory; it manufactures vitamin D in the presence of
sunlight. The skin is like an umbrella; it helps to protect us from the sun and the rain.
2. The mitotic activity of the epidermis occurs in the basal layer. At any given time,
about 4 percent of the cells in this layer are involved in mitosis. As cells migrate to the
surface, they change shape from columnar to cuboidal and finally to squamous. As the
cells become squamous, they also become hardened, or cornified. (para 3-5)
3. The color of the skin is because of special chemicals called pigments. Special cells
located in the dermis provide the precursors of pigments to the basal cells. As basal
cells migrate to the surface, the precursors are gradually converted to the actual
pigments. The type of color for each individual is controlled by genes. (para 3-10)
4. The integumentary system is the boundary between the organism and the
surrounding environment. For this reason, the integumentary system has a number of
functions related to the environment.
Friction against the integument is reduced by hairs and outer dead cells. When
subjected to friction, the integument tends to become thicker.
The outer layers of cells are kept flexible by oil from the sebaceous glands. This
forms an essentially waterproof covering for the body. This is important in preventing
general dehydration of the body.
Because of pigments and outer layers of dead cells, the integument helps to
protect the body from excessive solar radiation.
Receptor organs in the integument and the subcutaneous layer continuously
5. Sources of body heat include muscular contractions, metabolic activity, and solar
The core temperature is the temperature within the body proper. The core
temperature is continuously monitored by detectors in the hypothalamus of the brain.
The temperature of the body surface and the upper and lower members is called the
peripheral body temperature.
Blood within the deep veins of the upper and lower members is warmed by the
adjacent major arteries. This situation is called the countercurrent mechanism.