Read Ebook: A Practical Physiology: A Text-Book for Higher Schools by Blaisdell Albert F Albert Franklin

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Every thoughtful young person must have asked himself a hundred questions about the problems of human life: how it can be that the few articles of our daily food--milk, bread, meats, and similar things--build up our complex bodies, and by what strange magic they are transformed into hair, skin, teeth, bones, muscles, and blood.

How is it that we can lift these curtains of our eyes and behold all the wonders of the world around us, then drop the lids, and though at noonday, are instantly in total darkness? How does the minute structure of the ear report to us with equal accuracy the thunder of the tempest, and the hum of the passing bee? Why is breathing so essential to our life, and why cannot we stop breathing when we try? Where within us, and how, burns the mysterious fire whose subtle heat warms us from the first breath of infancy till the last hour of life?

These and scores of similar questions it is the province of this deeply interesting study of physiology to answer.

But above these thoughts there rises another,--that in studying physiology we are tracing the myriad lines of marvelous ingenuity and forethought, as they appear at every glimpse of the work of the Divine Builder. However closely we study our bodily structure, we are, at our best, but imperfect observers of the handiwork of Him who made us as we are.

Again, our bodies are continually making heat and giving it out to surrounding objects, the production and the loss of heat being so adjusted that the whole body is warm, that is, of a temperature higher than that of surrounding objects. Our bodies, also, move themselves, either one part on another, or the whole body from place to place. The motive power is not from the outside world, but the energy of their movements exists in the bodies themselves, influenced by changes in their surroundings. Finally, our bodies are continually getting rid of so-called waste matters, which may be considered products of the oxidation of the material used as food, or of the substances which make up the organism.

The main problem we have to solve in the succeeding pages is to ascertain how it is that our bodies can renew their substance and replenish the energy which they are continually losing, and can, according to the nature of their surroundings, vary not only the amount, but the kind of energy which they set free.

The word anatomy, however, is usually employed instead of morphology. It is derived from two Greek words, and means the science of dissection. Human anatomy then deals with the form and structure of the human body, and describes how the different parts and organs are arranged, as revealed by observation, by dissection, and by the microscope.

Histology is that part of anatomy which treats of the minute structure of any part of the body, as shown by the microscope.

It is plain that we cannot understand the physiology of our bodies without a knowledge of their anatomy. An engineer could not understand the working of his engine unless well acquainted with all its parts, and the manner in which they were fitted together. So, if we are to understand the principles of elementary physiology, we must master the main anatomical facts concerning the organs of the body before considering their special functions.

As a branch of study in our schools, physiology aims to make clear certain laws which are necessary to health, so that by a proper knowledge of them, and their practical application, we may hope to spend happier and more useful, because healthier, lives. In brief, the study of hygiene, or the science of health, in the school curriculum, is usually associated with that of physiology.

In fact, the human body is built up with 13 of the 70 elements, namely: oxygen, hydrogen, nitrogen, chlorine, fluorine, carbon, phosphorus, sulphur, calcium, potassium, sodium, magnesium, and iron. Besides these, a few of the other elements, as silicon, have been found; but they exist in extremely minute quantities.

The following table gives the proportion in which these various elements are present:

As will be seen from this table, oxygen, hydrogen, and nitrogen, which are gases in their uncombined form, make up 3/4 of the weight of the whole human body. Carbon, which exists in an impure state in charcoal, forms more than 1/5 of the weight of the body. Thus carbon and the three gases named, make up about 96 per cent of the total weight of the body.

The phosphates of lime and soda are the most abundant of the salts of the body. They form more than half the material of the bones, are found in the teeth and in other solids and in the fluids of the body. The special place of iron is in the coloring matter of the blood. Its various salts are traced in the ash of bones, in muscles, and in many other tissues and fluids. These compounds, forming salts or mineral matters that exist in the body, are estimated to amount to about 6 per cent of the entire weight.

The organic compounds found in the body are usually divided into three great classes:

Proteids, or albuminous substances.

Carbohydrates .

Fats.

The extent to which these three great classes of organic materials of the body exist in the animal and vegetable kingdoms, and are utilized for the food of man, will be discussed in the chapter on food . The Proteids, because they contain the element nitrogen and the others do not, are frequently called nitrogenous, and the other two are known as non-nitrogenous substances. The proteids, the type of which is egg albumen, or the white of egg, are found in muscle and nerve, in glands, in blood, and in nearly all the fluids of the body. A human body is estimated to yield on an average about 18 per cent of albuminous substances. In the succeeding chapters we shall have occasion to refer to various and allied forms of proteids as they exist in muscle , coagulated blood , and bones .

The Carbohydrates are formed of carbon, hydrogen, and oxygen, the last two in the proportion to form water. Thus we have animal starch, or glycogen, stored up in the liver. Sugar, as grape sugar, is also found in the liver. The body of an average man contains about 10 per cent of Fats. These are formed of carbon, hydrogen, and oxygen, in which the latter two are not in the proportion to form water. The fat of the body consists of a mixture which is liquid at the ordinary temperature.

Now it must not for one moment be supposed that the various chemical elements, as the proteids, the salts, the fats, etc., exist in the body in a condition to be easily separated one from another. Thus a piece of muscle contains all the various organic compounds just mentioned, but they are combined, and in different cases the amount will vary. Again, fat may exist in the muscles even though it is not visible to the naked eye, and a microscope is required to show the minute fat cells.

Protoplasm has the power of appropriating nutrient material, of dividing and subdividing, so as to form new masses like itself. When not built into a tissue, it has the power of changing its shape and of moving from place to place, by means of the delicate processes which it puts forth. Now, while there are found in the lowest realm of animal life, organisms like the amoeba of stagnant pools, consisting of nothing more than minute masses of protoplasm, there are others like them which possess a small central body called a nucleus. This is known as nucleated protoplasm.

A, nucleus; B, nucleolus; C, protoplasm.

There are some organisms lower down in the scale, whose whole activity is confined within the narrow limits of a single cell. Thus, the amoeba begins its life as a cell split off from its parent. This divides in its turn, and each half is a complete amoeba. When we come a little higher than the amoeba, we find organisms which consist of several cells, and a specialization of function begins to appear. As we ascend in the animal scale, specialization of structure and of function is found continually advancing, and the various kinds of cells are grouped together into colonies or organs.

In short, cells may be regarded as the histological units of animal structures; by the combination, association, and modification of these the body is built up. Of the real nature of the changes going on within the living protoplasm, the process of building up lifeless material into living structures, and the process of breaking down by which waste is produced, we know absolutely nothing. Could we learn that, perhaps we should know the secret of life.

Cells are produced only from cells by a process of self-division, consisting of a cleavage of the whole cell into parts, each of which becomes a separate and independent organism. Cells rapidly increase in size up to a certain definite point which they maintain during adult life. A most interesting quality of cell life is motion, a beautiful form of which is found in ciliated epithelium. Cells may move actively and passively. In the blood the cells are swept along by the current, but the white corpuscles, seem able to make their way actively through the tissues, as if guided by some sort of instinct.

A, columnar cells found lining various parts of the intestines ; B, cells of a fusiform or spindle shape found in the loose tissue under the skin and in other parts ; C, cell having many processes or projections--such are found in connective tissue, D, primitive cells composed of protoplasm with nucleus, and having no cell wall. All are represented about 400 times their real size.

Some cells live a brief life of 12 to 24 hours, as is probably the case with many of the cells lining the alimentary canal; others may live for years, as do the cells of cartilage and bone. In fact each cell goes through the same cycle of changes as the whole organism, though doubtless in a much shorter time. The work of cells is of the most varied kind, and embraces the formation of every tissue and product,--solid, liquid, or gaseous. Thus we shall learn that the cells of the liver form bile, those of the salivary glands and of the glands of the stomach and pancreas form juices which aid in the digestion of food.

The columnar epithelium consists of pear-shaped or elongated cells, frequently as a single layer of cells on the surface of a mucous membrane, as on the lining of the stomach and intestines, and the free surface of the windpipe and large air-tubes.

The glandular or spheroidal epithelium is composed of round cells or such as become angular by mutual pressure. This kind forms the lining of glands such as the liver, pancreas, and the glands of the skin.

The ciliated epithelium is marked by the presence of very fine hair-like processes called cilia, which develop from the free end of the cell and exhibit a rapid whip-like movement as long as the cell is alive. This motion is always in the same direction, and serves to carry away mucus and even foreign particles in contact with the membrane on which the cells are placed. This epithelium is especially common in the air passages, where it serves to keep a free passage for the entrance and exit of air. In other canals a similar office is filled by this kind of epithelium.

A, columnar cells of intestine; B, polyhedral cells of the conjunctiva; C, ciliated conical cells of the trachea; D, ciliated cell of frog's mouth; E, inverted conical cell of trachea; F, squamous cell of the cavity of mouth, seen from its broad surface; G, squamous cell, seen edgeways.

The second great division of the epithelial tissues consists of those whose cells are formed of highly active protoplasm, and are busily engaged in some sort of secretion. Such are the cells of glands,--the cells of the salivary glands, which secrete the saliva, of the gastric glands, which secrete the gastric juice, of the intestinal glands, and the cells of the liver and sweat glands.

All these tissues consist of a ground-substance, or matrix, cells, and fibers. The ground-substance is in small amount in connective tissues proper, and is obscured by a mass of fibers. It is best seen in hyaline cartilage, where it has a glossy appearance. In bone it is infiltrated with salts which give bone its hardness, and make it seem so unlike other tissues. The cells are called connective-tissue corpuscles, cartilage cells, and bone corpuscles, according to the tissues in which they occur. The fibers are the white fibrous and the yellow elastic tissues.

The following varieties are usually described:

Connective Tissues Proper: White Fibrous Tissue. Yellow Elastic Tissue. Areolar or Cellular Tissue. Adipose or Fatty Tissue. Adenoid or Retiform Tissue.

Cartilage : Hyaline. White Fibro-cartilage. Yellow Fibro-cartilage.

Bone and Dentine of Teeth.

Again, there is between the cells a meshwork of yellow elastic fibers, and this is called yellow fibro-cartilage . The hyaline cartilage forms the early state of most of the bones, and is also a permanent coating for the articular ends of long bones. The white fibro-cartilage is found in the disks between the bodies of the vertebrae, in the interior of the knee joint, in the wrist and other joints, filling the cavities of the bones, in socket joints, and in the grooves for tendons. The yellow fibro-cartilage forms the expanded part of the ear, the epiglottis, and other parts of the larynx.

A, the cranial cavity; B, the cavity of the nose; C, the mouth; D, the alimentary canal represented as a simple straight tube; E, the sympathetic nervous system; F, heart; G, diaphragm; H, stomach; K, end of spinal portion of cerebro-spinal nervous system.

We may say, then, that the body consists of two tubes or cavities, separated by a bony wall, the dorsal or nervous tube, so called because it contains the central parts of the nervous system; and the visceral or ventral tube, as it contains the viscera, or general organs of the body, as the alimentary canal, the heart, the lungs, the sympathetic nervous system, and other organs.

The more detailed study of the body may now be begun by a description of the skeleton or framework which supports the soft parts.

Experiments.

There are in the adult human body 200 distinct bones, of many sizes and shapes. This number does not, however, include several small bones found in the tendons of muscles and in the ear. The teeth are not usually reckoned as separate bones, being a part of the structure of the skin.

The number of distinct bones varies at different periods of life. It is greater in childhood than in adults, for many bones which are then separate, to allow growth, afterwards become gradually united. In early adult life, for instance, the skull contains 22 naturally separate bones, but in infancy the number is much greater, and in old age far less.

The bones of the body thus arranged give firmness, strength, and protection to the soft tissues and vital organs, and also form levers for the muscles to act upon.

The proportion of earthy to animal matter varies with age. In infancy the bones are composed almost wholly of animal matter. Hence, an infant's bones are rarely broken, but its legs may soon become misshapen if walking is allowed too early. In childhood, the bones still contain a larger percentage of animal matter than in more advanced life, and are therefore more liable to bend than to break; while in old age, they contain a greater percentage of mineral matter, and are brittle and easily broken.

At the ends of a long bone, where it expands, there is no medullary canal, and the bony tissue is spongy, with only a thin layer of dense bone around it. In flat bones we find two layers or plates of compact tissue at the surface, and a spongy tissue between. Short and irregular bones have no medullary canal, only a thin shell of dense bone filled with cancellous tissue.

Experiment 5. Obtain a part of a beef shin bone, or a portion of a sheep's or calf's leg, including if convenient the knee joint. Have the bone sawed in two, lengthwise, keeping the marrow in place. Boil, scrape, and carefully clean one half. Note the compact and spongy parts, shaft, etc.

Experiment 6. Trim off the flesh from the second half. Note the pinkish white appearance of the bone, the marrow, and the tiny specks of blood, etc. Knead a small piece of the marrow in the palm; note the oily appearance. Convert some marrow into a liquid by heating. Contrast this fresh bone with an old dry one, as found in the fields. Fresh bones should be kept in a cool place, carefully wrapped in a damp cloth, while waiting for class use.

A fresh or living bone is covered with a delicate, tough, fibrous membrane, called the periosteum. It adheres very closely to the bone, and covers every part except at the joints and where it is protected with cartilage. The periosteum is richly supplied with blood-vessels, and plays a chief part in the growth, formation, and repair of bone. If a portion of the periosteum be detached by injury or disease, there is risk that a layer of the subjacent bone will lose its vitality and be cast off.

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