Elementary practical physiology

Front matter

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’■9.7)

Preface

This book has been prepared with a view of presenting to young students the important facts and principles of human physiology in a concise and intelligible form. In it I have attempted, not only to supply the information which, such students need, but also to lead them to think as they acquire their knowledge of the subject.

The work meets all the requirements of Stage I. (the Elementary Stage), as set forth in the syllabus issued by the Board of Education, and in similar syllabuses of other examining bodies. As it is intended as a first work on the subject, the anatomy or structure of the body and its organs is described so far as this is necessary to the understanding of their functions. This includes some account of the cell, for an elementary knowledge of cells and the minute structure of tissues is now essential in order to have any intelligent comprehension of the working of the body and its parts.

A large number of illustrations, many of them new in an elementary work like this, have been supplied. A few of these are coloured to further increase their usefulness. Much can be learnt by an attentive study of these figures, and the reader is advised to examine them, with their accompanying descriptions, repeatedly, care being taken to distinguish between a diagram (see Glossary) and an actual drawing of a part.

Many simple, practical directions will be found, partly in the course of the text and partly under separate headings. These are of such a nature that neither the teacher nor the student should have any difficulty in making the observations and performing the experiments described. The importance vi Preface.

of examining such organs as the heart, lungs, and kidneys, as well as of experimenting with such substances as blood, food-stuffs, and the digestive juices, cannot be overrated, if clear ideas and sound knowledge are to be acquired. As supplementary aids, models, such as those supplied by Emile Deyrolle of Paris, can be strongly recommended.

To aid the reader in acquiring the meaning and proper use of the technical language of physiology, a Glossary, giving the pronunciation and explanation of the difficult terms, has been supplied. Frequent reference to it will, it is believed, be of much service.

At the end of the book will be found a set of Questions and Exercises on each chapter, together with recent Examination Papers.

J. THORNTON.

Bolton,

Contents

CHAPTER PAGE

I. Introduction i

II. The General Build of the Body i6

Chapter I

1. What is Physiologj’’ P — The word physiology (Greek, phusis, nature, and logos, a discourse) is used to denote the study of the changes and activities that go on in living beings. Vegetable physiology deals with the processes that occur in living plants. Animal physiology treats of the working of the bodies of living animals. Human physiology is that part of animal physiology that gives an account of the activities of the healthy human body, and it is with the body of man that we are chiefly concerned in this book.

To understand the action and working of a body that consists of distinct but connected parts, like the body of a man, it is first necessary to learn something regarding its structure, so that we may know, not only the forms and relations of the various parts, but the modes in which they are built up. The study of the structure of an animal is termed anatomy (Gk. ana, up ; temnein, to cut), and it is carried out for the most part by tbe cutting up or dissecting of a lifeless body or its parts. As the structures of such higher animals as a rabbit or a sheep closely resemble that of the human body, any dissection required of an elementary student may be made on one of these animals. Closely connected with physiology there is another department of study called hygiene. Hygiene (Gk. hygieia, health) is that branch of science which treats

B

I of the means that promote and preserve health so that the various parts of the body may be kept in good working order. It will now be clear why a book on physiology often includes some anatomy and hygiene.

A student of physiology soon finds that, in order to understand the subject, it is also necessary to know something of such subjects as Chemistry, Physics, and Mechanics. This necessary preliminary knowledge will be introduced as the occasion arises, but the importance in physiology of some chemical knowledge is so great, and the need of such knowledge is felt so soon, that we shall supply some of it towards the end of this chapter.

2. Organs and Tissues.— The body of a man, or that of any of the higher animals, when examined carefully, especially in its interior, is seen to consist of distinct parts that carry on special kinds of work. Such, for example, are the eye, the tongue, the heart, the lungs, the kidneys, etc. Such a distinct part of the body is called an organ (Gk. orga7io?i, a tool or instrument), and. the special work of an organ is called its function. Hence an organ has been defined as “a part of the body of a living being that is definitely fitted to perform some special function for the general benefit of the whole.”

In man and the higher animals the great life functions of respiration, digestion, excretion, etc., are carried on by a set of organs or closely related parts that form a system. Thus the digestive system includes the mouth, the gullet, the stomach, the liver, the pancreas, and intestines. In later chapters these various systems, and the organs forming them, will be explained in some detail.

An examination of a limb, or of any of the organs just ' mentioned, shows that the parts of the body are formed of different kinds of materials, called textures or tissues, just as a house is made up of stone, wood, iron, mortar, and other substances. As examples of such different kinds of building materials in the body, we may note the red flesh that forms muscular tissue, the soft greyish-white matter that forms the brain and nerves called nervous tissue, and the harder

Introduction

I compact substance forming bone, and termed osseous tissue. The soft stringy substance that binds the skin to the body, and passes thence between the muscles to ensheath the bones as well as to hold together the materials of every organ, is known as connective tissue. Epithelium, or epithelial tissue, is the name given to the tissue that covers the exterior of the body and lines all the passages and cavities leading from the exterior to the interior.

An organ is usually made up of several tissues ; the heart, for example, contains muscular tissue, fatty tissue, and connective tissue. Most tissues also enter into the formation of very different organs. Muscular tissue, for example, is found, not only in the large skeletal muscles, but in the heart, in the walls of the stomach and intestines, and in the walls of blood-vessels, while adipose or fatty tissue, is present, more or less, in almost every organ of the body.

3. Tissues are composed of cells. — When the different building materials or tissues of the body are examined with the aid of a microscope, each tissue is found to consist of a number of minute masses of a soft substance connected together by material originally derived from such masses. These microscopic units of the tissues are called cells, and one tissue differs from another in the form and nature of its cells, as well as in the way the cells are united together by intercellular substance. To get some idea of the nature of a cell, let us leave the human body for a short time and examine one of the simplest living creatures, an animal called the amoeba.

On taking a drop of water from the surface of the mud at the bottom of a stagnant pool, and placing it under a high power of the microscope, we may often notice, among other things, one or more specks of a jelly-like substance undergoing a slow change of shape. Each speck, in fact, is of irregular shape, and moves with a kind of flowing motion, the locomotion being caused by the streaming forward of the substance into projections or processes at some points, and the withdrawal of processes at other points. The tiny object we see is a living creature called an amoeba. Careful scrutiny under a higher power of the microscope will show that the jelly-like mass forming the amoeba exhibits a clear outside and a

Elementary Practical Physiology.

rather granular interior. There is also seen a denser central body called the nucleus, and usually a clear space called, from its action, the pulsatory vacuole.

The jelly-like mass of which the amceba consists is present in all living matter, and is called living substance, or protoplasm. Such a minute mass of nucleated protoplasm is the unit mass of living matter, and is known as a cell. An amoeba is, therefore, a living creature consisting of a single cell. Chemically considered, protoplasm is a mixture of water and various solids, the chief of which are chemical compounds called proteids and carbohydrates (par. 7). The amoeba manifests life not only by its motion, but in several other ways. It undergoes waste, giving off carbon dioxide and other waste products, and to repair this waste it takes in food. It feeds by putting forth a process round a particle of food and gradually engulfing it, the food-particle undergoing digestion in the interior, and being changed into the ingredients of protoplasm by assimilation. Any particle that is indigestible is excreted.

Fig. 1. — An amoeba, showing granular protoplasm, nucleus, and small vacuole. At 2 it is throwing out a process to take in a particle of food ; at 4 it is in process of dividing into two, the nucleus having undergone division ; at 5 the division into two is complete, each part containing its own nucleus. (Highly magnified.)

The taking in and digestion of food not only repair waste, but lead to an increase of the quantity of protoplasm, so than an amoeba grows. An amoeba responds to certain excitations or stimuli, such as warmth and shock. Gentle warmth increases its movement, a sharp shock checks its movement. An amoeba is, therefore, said to be irritable. It can be shown that an amoeba breathes by taking in at every part of its surface oxygen dissolved in the water, and giving out carbon dioxide at any part. In pure distilled water that contains no oxygen the amoeba cannot live. It also possesses the power of reproducing itself, for on carefully watching an amoeba for some time we may often notice that the creature becomes constricted and divides into two parts, each containing a portion of the nucleus, and each detached portion performing all the actions just described (Fig. i). The amoeba, therefore, although possessing no separate parts or organs, such as mouth, stomach, heart, and lungs, to perform its separate vital

Introduction.

actions, is yet a distinct living creature as much as a frog or a man, and is quite different from a particle of clay or a grain of sand. The amoeba is a simple creature of one cell, but man and the higher animals are composed of countless millions of such cells grouped into tissues and organs adapted for special functions. For, as already stated, when we' examine under the microscope nerve tissue, muscular tissue, fat, or any other tissue from the human body, or from any of the higher animals, we find each to be composed of cells with more or less connecting material, the cells of each tissue having a special structure suitable for carrying out the special function of that tissue.

In the early stages of an animal, every tissue is a mass of closely packed similar cells, but later many of the cells undergo

Fig. 2.— Various animal cells highly magnified. A, squamous epithelial cells; B, simple columnar cells ; C, ciliated epithelial cells ; D, white fibrous tissue with connective tissue cells ; E, fat cells ; F, polygonal liver cells : G, smooth muscle cells ; H, various nerve cells.

changes or give off products, so that fine threads or fibres with or without other structures often unite with cells to form a tissue. A tissue, in fact, may he defined as a building

6 '

Eleme7itary Practical Physiology.

material of the body composed of cells of the same kind bound together with more or less intercellular substance, while a cell may be defined as a minute mass of protoplasm with a firmer substance at the centre called its nucleus. Thus cells are bound together to form tissues ; tissues are bound together to form organs ; and the body of a man or of any other higher animal consists of a number of organs or special parts, each with one or more special functions, but all working together for the general good. It may now be remarked that each of the cells forming a tissue of the body is a living thing that feeds and undergoes changes, but the life of a cell is not of long duration, for in most tissues they become worn out and die after a time, others being formed to take their places. Thus, while the body as a whole keeps its form from year to year, its living cells are continually dying and being replaced. It will now be advisable to learn something of two of the tissues we have already mentioned, reserving an account of the others until later.

The reader must remember that cells and fibres are far too small to be seen by the unaided eye, and that the illustrations of them are, therefore, magnified views as seen under a microscope.

4. Epithelial Tissue. — Epithelial tissue or epithelium is the substance that forms the outer layer of the skin of the body, the layer lining all the passages and cavities communicating with the outside and the lining of all closed tubes and cavities. Under the microscope it is seen to consist of one or more layers of cells, the former being called simple epithelium, and the latter stratified epithelium. Epithelial cells are of various forms in different part's. In the outer skin, or epidermis, the epithelium is stratified and consists of many layers of cells, the outer layers being flattened and homy in stmcture, and the deeper layers rounded or formed of columnar, nucleated cells (Fig. 3). The soft skin called mucous membrane lining the air passages, the nose, windpipe, and bronchial tubes is formed on its outside of epithelial cells, the outer ones of which are columnar and provided with fine hair-like processes called cilia, which, in the living tissue, are constantly in rapid

Introduction.

vibration with a whip-like movement that work outwards (Fig. 4). Ciliary movement can be easily seen by snipping a small piece from the gill of a common mussel and examining it under a microscope.

Fig. 3 — Epithelial cells forming the epidermis or outer layer of the skin, a. The horny flattened ceils ; b, the nucleated cells of the deeper layer.

Some of the cells in the air passages and the tubes of the alimentary canal discharge a slimy fluid called mucus that keeps these passages moist. Other active epithelial cells are engaged in separating or secreting some substance from the

Fig. 4.— Ciliated epithelium from the human trachea. Magnified 350 times, a. Innermost layers of the elastic longitudinal fibres; b, homogeneous innermost layer of the mucous membrane ; c, deepest round cells ; d. middle elongated cells • e superficial cells, bearing cilia. (^Frorn Gray's '' Anatomy.”) ' ’

blood and pouring it out into the tube or cavity which they line. Such active secreting epithelial cells are found lining the stomach, the intestines, the tubes, and recesses of the salivary

Elementary Practical Physiology.

and other glands. These epithelial cells will be further described when treating of the organs in which they occur.

5. Connective Tissue. — Connective tissue is a fibrous tissue found in all parts of the body, lying between and uniting different organs and also different parts of the same organ. It is found uniting the skin to the structures beneath ; it surrounds and penetrates the muscles ; it forms a sheath for nerves and blood-vessels, and, in fact, enters more or less into the structure of every organ, forming, as it were, a soft framework to enclose and connect all the other tissues. On removing the skin from the leg of a rabbit the filmy material

forming this tissue is at once noticed beneath the skin and around the muscles. Examined under the microscope it i s seen to consist of fibres of two kinds, among which lie a number of cells, called connective tissue corpuscles (Eig. 2, D). One kind of fibre runs a wavy course in bundles, which often cross each other, and the other kind consists of single, fine, straight fibres. The first kind of tissue is called from its appearance white fibrous connective tissue, and the second kind yellow elastic tissue. White fibrous tissue, therefore, consists of fine, wavy, parallel fibres running in bundles that form a meshwork, which encloses spaces or areolae. When the spaces are large, as in the tissue under the skin, the tissue is called areolar tissue. Scattered among the bundles of white

Fig. 5 — Connective tissue. fKlein and Noble Smith.) a. The white fibrous element — a layer of more or less sharply outlined, parallel, wavy bundles of connective tissue fibrils. On the surface of this layer is b, a network of fine clastic fibres. iFrom Gray’s ’’Anatomy."')

Introduction.

fibrous tissue are a few coarse fibres that are elastic and sometimes brancb. It is these elastic fibres of connective tissue that confer elasticity on the skin and on the walls of the blood-vessels. The connective tissue corpuscles are nucleated cells lying on or among the bundles of fibres. Through the connective tissue pass nerves and blood-vessels, and the spaces are largely filled with a fluid termed lymph, that has passed out of the minute blood-vessels. In tendons and ligaments the fibrous tissue is closer and denser than in that under the skin, or than in that ensheathing muscles, and the bundles of fibres do not cross, but run parallel.

Fat or adipose tissue may be regarded as a kind of connective tissue, for it consists of fibi'es of white fibrous tissue in which oval fat cells (Fig. 2, E) are embedded. These cells are connective tissue cells, in which oil drops have gathered until nothing remains but a globule of fat covered by a thin layer of the original protoplasm of the cell. Adipose tissue forms a layer beneath the skin (subcutaneous fat), is collected round various organs, as the kidneys and heart, forms a packing for the eyeballs, and is present in small quantity in the tissues of most organs. It serves to give roundness to the limbs, it forms a packing material between organs, and, as it is a bad conductor, it checks the loss of heat from the body. It also acts as a store of nutriment for the body.

6. Chemical Composition of the Body. — Besides studying the body as composed of tissues and organs, it is necessary to consider it as composed of different chemical substances, and as the seat of chemical changes connected with the functions of the various organs. At present we can only make a few remarks about the more important substances found in the body, taking up in more suitable places the chemical changes that occur when treating of the functions of the different organs.

Chemists divide all substances into elements and compounds. An element is a simple or indecomposable substance ; one that cannot be split up into substances different from itself. A compound is a substance formed by the chemical union of two or more elements. A compound is thus a substance that can be decomposed ; that is, split up lo Elementary Practical Physiology.

into two or more elements or simple substances. The properties of chemical compounds are quite different from those of the elements that enter into their composition.

About seventy-five elements are known to chemists, but many of these are rare in nature, and do not occur either free or combined in the human body. The elements found in the body are : — Oxygen, nitrogen, hydrogen, carbon, sulphur, phosphorus, chlorine, sodium, potassium, calcium, magnesium, iron, silicon, fluorine, lithium, and manganese. The first three occur both free and in various combinations, while the remainder only occur in compounds.

Oxygen (O) is an invisible gas that forms about one-fifth of the atmosphere by volume. It supports combustion, and is absolutely necessary for animal life. It occurs free in the air passages of the lungs, and to some extent in blood, though there it is more abundant in a state of loose chemical combination with the minute bodies called the red corpuscles of the blood. It also occurs combined with other elements in many of the substances of the body.

Nitrogen (N) is an invisible, inert gas that forms about fourfifths of the atmosphere by volume. It occurs free in the air passages of the lungs, and to a small extent dissolved in the blood. In combination with other elements it forms a large number of the substances of the body, many of these nitrogenous compounds being of great importance.

Hydrogen (H) is a very light, invisible, and combustible gas. When it burns in the air, it unites with the oxygen of the air to form water. Conversely, water can be decomposed by the electric current into the two gases oxygen and hydrogen. A little free hydrogen is sometimes found in the intestines, owing to the fermentation of certain foods. In combination with other elements it occurs in many common compounds of the body.

Carbon (C) is a solid element existing in a variety of forms. Blacklead, or graphite, and diamond are natural conditions ot the element. Charcoal and lampblack are artificial forms of the element. When carbon burns it unites with oxj'gen from the air to form a compound called carbon dioxide, or carbonic acid gas (COj). Carbon does not exist free in the body ; but it exists in a combined form in most animal and vegetable substances, and the oxidation or burning of any of these substances results in the formation of carbon dioxide as one of the products.

Introdiiction.

1 1

7. Chemical Compounds of the Body. — Chemists divide compounds into inorganic compounds and organic compounds, and it is important that the student should know something of this distinction.

Every separate living being, whether plant or animal, is sometimes termed an “ organism.’’ The various substances that are built up or produced by organisms came to be called organic substances, and organic chemistry was defined as “ the chemistry of the compounds produced by plants and animals.” On the other hand, substances obtained from the crust of the earth, that is, from the mineral kingdom, were called inorganic or mineral substances. Inorganic chemistry is therefore the chemistry of the substances that neither are nor have been parts of plants or animals, the chemistry of the metals and metallic compounds of the earth, including water and air.

It was at one time thought that organic compounds could only be produced by the agency of living beings. But though this is almost the only source of such substances, chemists have been able to produce many organic substances artificially. However obtained, organic compounds always contain carbon as the central or grouping element in the compound. Organic chemistry, therefore, is better defined as “ the chemistry of the carbon compounds.” With these ideas of the two great classes of chemical compounds, it is easy to understand that clay, common salt, limestone (calcium carbonate), and quartz or silica, are examples of inorganic substances; while fat, sugar, starch, and the white of egg are organic substances.

Plants, like animals, consist of living cells that are constantly building up living matter out of the food supplied to them. This food, in the case of plants, consists of the simple inorganic substances found in the soil, and of the carbon dioxide in tbe air from which they obtain the carbon they require. In other words, plants can live on simple inorganic materials dissolved out of the soil or derived from the air, and can convert these into the complex organic substances that form their tissues. On the other hand, man and other animals cannot convert inorganic materials, except water, into the living substances of the body ; but animals must feed on the organic

Elementa7'y Practical Physiology.

substances formed by plants or supplied by the tissues of other animals that have lived on plants.

The chief inorganic compounds found in the human body are water, carbon dioxide, hydrochloric acid, sodium chloride, calcium carbonate, and calcium phosphate.

Water (the chemical formula of which is HgO) is a compound of the two elementary gases hydrogen and oxygen. It is present in all the tissues of the body, and forms, in fact, two-thirds of the weight of the body. It is nearly all derived from the food and drink, but a small quantity is actually formed in the body. The water of the body serves to make certain tissues soft and flexible, to dissolve the nutrient matter taken in, and to assist processes of secretion and excretion.

Carbon dioxide (COg), or carbonic acid gas, is formed continuously in the body by the oxidation of carbon, so that it is present in all the tissues, including the blood. From these tissues it is being continuously removed or excreted in ways to be afterwards described.

Hydrochloric acid (HCl), a compound of the gas hydrogen with the gas chlorine, exists in small quantity in the stomach. It belongs to the class of bodies called “acids” (see Glossary). Acids are compounds which hydrogen forms with other elements, chiefly non-metallic elements. Manyacids contain oxygen in addition. Thus, sulphuric acid (H2S04)is a compound of hydrogen, sulphur, and oxygen.

Sodium chloride (NaCl) is a compound of the metal sodium with the non-metallic elementary gas called chlorine. Its usual name is common salt. It belongs to a class of chemical compounds termed “ salts,” the term “salt” being used by chemists to denote compounds in which the hydrogen of an acid has been replaced in part or altogether by a metal. Sodium chloride exists in the blood as well as in many other liquids of the body.

Calcium carbonate (CaCOs) is a salt composed of the elements calcium, carbon, and oxygen. It enters into the composition of bone.

Calcium phosphate (CajPaOj) consists of calcium, phosphorus, and oxygen. It forms a considerable part of bone.

Other inorganic salts exist in the body, the more important of which will be mentioned later. It maybe remarked here that when a body is cremated or burnt, various compound gases, chiefly carbon dioxide, water vapour, and ammonia are formed and sent into the atmosphere, while most of the inorganic salts, being incombustible, remain to form the ashes.

Introduction.

The organic compounds of the body belong, for the most part, to three great groups : Proteids, carbohydrates, and fats.

Proteids are complex organic compounds of carbon, hydrogen, oxygen, nitrogen, and sulphur. As they are the only organic compounds characterized by the presence of nitrogen, they are often referred to as nitrogenous compounds. The type of this important class of bodies is the substance forming the white of an egg, and called albumen or albumin, and so these bodies are often also referred to as albuminous substances. The fibrin of blood and the casein of milk are other examples of proteids. Proteid bodies form the most important constituents of living cells. The proteids will be considered in more detail in the chapter on Food.

Carbohydrates are organic compounds of carbon, hydrogen, and oxygen, in which there is always the same proportion of hydrogen and oxygen as in water, i.e. two atoms of hydrogen to one of oxygen. The substances known as starches and sugars belong to the carbohydrates. A kind of starch called glycogen is found in the liver, and the sugar called grape-sugar exists in blood and other tissues.

Fat is an organic compound consisting of carbon, hydrogen, and oxygen ; but the oxygen is smaller in proportion to the hydrogen than in the carbohydrates. The proportion of fat in the body varies greatly, but there is always some present.

We may describe and classify the five great classes of chemical compounds composing the body as follows : —

Inorganic

compounds

I. Organic compounds'

Water

Mineral salts

Proteids (nitro- I genous) I

Carbohydrates j (non-nitrogenous) \ Fats (non-nitro- J genous) I

Composed of

Hydrogen and oxygen.

Two or more of hydrogen, oxygen, carbon, calcium, phosphorus, potassium, sodium, sulphur, chlorine, magnesium, iron, silicon, fluorine.

Carbon, hydrogen, oxygen, and nitrogen, with traces of sulphur and phosphorus.

Carbon, hydrogen, and

oxygen.

Carbon, hydrogen, and

oxygen.

8. Life : a Process of Waste and Renewal. — We have seen that, considered from the chemist’s point of view, the body consists of a certain number of chemical compounds, and we shall soon learn that during life these substances are continually being consumed, and must therefore be continually replaced. We now know that the main compounds entering into the composition of the cells and tissues of the body form the five groups : Water, mineral salts, proteids (nitrogenous compounds), carbohydrates (starches and sugars), and fats. The last three groups are complicated organic compounds, and under the action of the oxygen of the air taken in by the lungs and carried to all parts by the blood, these complex organic compounds are, after having been made a part of living tissue, at last reduced to simpler compounds in the processes that go on in the living body. These simpler compounds are in large part then removed from the body by excretory organs. Our food must therefore consist essentially of the same five classes of bodies, i.e. these compounds must be found in the materials of the food that we eat in order that the continual waste of body tissue may be made good.