HUMAN BIOLOGY CHAPTER I THE GENERAL STRUCTURE OF THE HUMAN BODY 1. Regions of the body. In man and in most other mammals one can distinguish at least three regions; namely, the head, neck, and trunk. To the trunk are attached two pairs of appendages; namely, two arms and two legs, or, as they are more often called in the descriptions of the lower animals, the four legs. If the front wall of the trunk (composed largely of skin and muscle) were removed, it would be found that this region of the human body is divided into an upper story or chest cavity (Fig. 1), and a lower story or abdominal cavity. These two cavities are separated from each other by a flexible partition called the diaphragm, which is composed largely of muscle more or less in the form of a dome. The chest and abdominal cavities, separated by a diaphragm, are characteristic of all mammals. 1 2. Organs of the body. When we study the body more closely, especially its interior, we find, in various regions, parts that carry on special kinds of work (Fig. 2). Within the chest cavity is the heart, which forces blood through the 1 Each of the structures named in this paragraph should be demonstrated on a manikin or a chart before the textbook lesson is assigned. While studying the lesson, the pupil should find in Fig. 2 each of the organs named. body. Here, also, are the lungs, which take in oxygen and give it to the blood, and which remove carbon dioxid, water, and other waste matters from the blood. Below the diaphragm are the stomach and the intestines, the liver and the FIG. 1.-Longitudinal section of trunk (side view). pancreas, all of which help to change our food into liquia form ready to be used by the body. All these and other parts of the body are called organs. An organ is a part of a living body that has some special work to do; this special work is called its function. Our hands, for example, are organs because with them we do some special work like writing, sewing, or playing the piano. 3. Tissues of the body. When we squeeze the arm or the hand, we feel the hard bones within that form the skele FIG. 2.- Organs of chest and abdomen (front view). ton. We can raise from the bones the softer fleshy material, which is composed of muscle covered by skin. By clenching the fingers tightly we can see and feel on the inner side of the wrist the tough cords or tendons of connective tissue that attach the muscles to the bones. If we run a clean needle point into the finger, blood flows; in this way we discover another of the materials found in our hand; namely, blood. This experiment also demonstrates that the human body has some structures by the help of which sensations of touch or pain are perceived. All the parts of the hand we have been enumerating are known as tissues. For the present a tissue may be defined as one of the building materials of which an organ is composed. In the hand we have found evidence of the presence of bone tissue, muscle tissue, connective tissue, blood tissue, and nerve tissue. Other kinds of tissue will be discussed in the pages that follow. In order to go farther in our study of structure we need the aid of the compound microscope. With this instrument we discover that the tissues are by no means the simplest part of an animal. 4. Cells lining the mouth. Laboratory study. Materials: Cells from the human body may be readily prepared by gently scraping with the finger nail the mucous membrane lining the mouth and then rubbing the material thus obtained on a clean glass slide, adding a drop of water and a cover glass. The cells may be stained with iodine in order to show the nucleus more sharply. If time allows, prepared sections of the brain, intestines, skin, and other organs of the body may well be shown. Examine with the low power of the compound microscope the cells prepared as described above. 1. Describe the form and color of each cell before it is stained with iodine. 2. In the cells stained with iodine notice a body, usually near the center, that is more deeply stained than the rest of the cell. This is the cell nucleus, and the rest of the cell is known as the cell body. The nucleus may be seen in the unstained cells as a denser portion. a. Name, now, two parts of a cell from the membrane lining the mouth. b. State the form and position of the cell nucleus. 3. Make a drawing of two of the cells described above (each cell to be represented about an inch in diameter). Label cell body and cell nucleus. 4. (Optional.) Demonstrate by the use of prepared slides, pictures, or charts that the brain, the intestine, and other organs of the body are composed of cells (Fig. 3). 5. Cells and protoplasm.1 - Under the microscope cells at first appear to be only plane surfaces surrounded by lines. (Fig. 3). In reality, however, each cell ent, the cell wall is so transparent that it is possible to look through it and see the cell body and nucleus within. The discovery of these minute bodies of which organs are composed was not made until about the middle of the last century (1838). With the rather imperfect microscopes then in use the two discoverers, Schleiden and Schwann, could see the walls only, and they did not know, as we now 1 Because of the importance of emphasizing cellular structure, the substance of §§ 42 and 43, "Plant Biology," are here inserted. |