Introduction to Medical Sciences
1.1a Introduction to physiology: systems of the body
The term physiology,1 derived from the Greek meaning study of nature, is used to describe how all living organisms work or function. An understanding of physiology has to underpin the study of clinical medicine, as it is only through knowledge of how biological processes function in health that the mechanisms and outcomes of disease may be understood. Throughout this text, physiological descriptions of the body systems will precede the descriptions of how disease manifests in those systems. The introduction and explanation of the key concepts necessary to understand these descriptions is the purpose of this first section.
The study of physiology offers more to the Chinese medical practitioner than simply providing building blocks for the further study of medical sciences. Central to all healing modalities is the development of an understanding and respect for the human body in health and disease. This respect enriches the way in which the practitioner communicates with patients and handles their bodies. It may well, indeed, add to the healing potential of the encounter, as through this respect the patient will feel recognized and understood. Respect comes with knowledge, and although the perspective of Chinese medicine is that the body is a manifestation of a rich interplay of energetic functions, it is nevertheless also very helpful for practitioners to acquire a sound understanding of the structure and normal functions of the physical parts as recognized by the patient and by their medical doctors, which is, of course, the physical manifestation of the energetic foundation.
And so, a physiological understanding of the body will enhance the understanding of the energetic nature of the body parts, as understood in Chinese medicine. Bodily functions are described in diverse ways, but some elements remain constant. All medical systems recognize major functional details – the lungs take in air, the heart pumps blood, the blood clots and the skin produces sweat. Although the processes of these various functions may be described very differently, awareness that all disciplines recognize the same summary descriptions can help when translating from the language of one medical discipline to another.
As an illustration of this, in this text physiological concepts are, from time to time, translated into the language of Chinese medicine. In Chinese medicine the body is understood in terms of constantly interchanging and interdependent forms of Qi, the underlying energetic principle on which that system of medicine is founded. The comparisons with Chinese medical physiology described in this text clearly illustrate not only the internal consistency of thought in Chinese medicine, but also the possibility of translation. This process of translation has the potential to promote increased understanding and respect between conventionally trained practitioners and those Chinese medical practitioners who use the language of energetics to describe the philosophical basis of their practice. It is important that, when translating in this way, we recognize we are not comparing “like for like.” The Western descriptors are used to relate to measurable physical forms and functions; the Chinese medical terms relate to energetic processes that cannot be bounded in the same way (for more on this topic, see “Note to the Reader” at the beginning of this book). Whilst the translation process can be deeply informative, the practitioner must avoid the temptation to consider Chinese medicine in a reductionist building block fashion. Concepts such as Liver Qi Stagnant or Stomach Yin Deficient apply to the whole system and not to a precisely defined body part. Whilst a diseased body part might point to Kidney Qi Deficiency, the converse is not true; Kidney Qi Deficiency will manifest in the whole system and can become apparent physically (and emotionally) in a multiplicity of ways.
Systems of the body
Physiologists consider the human body to be a collection of functionally integrated systems. Although these systems cannot work in isolation, each can be defined in terms of its structure (anatomy) and function (physiology).
The physiological systems of the body are listed in Table 1.1a-I. Most conventional general medical textbooks are subdivided according to these systems. This makes sense because conventional practitioners have learned to classify diseases as they affect each system. The in-depth study of diseases according to a physiological system is known as a medical specialty. Usually, the term for the specialty is the name of the system together with the suffix “-ology.” For example, the medical specialty devoted to diseases of the endocrine system is known as “endocrinology.”
Table 1.1a-I The 12 physiological systems of the body
•Endocrine (hormone secreting)
•Cardiovascular/circulatory (heart and blood vessels)
•Urological/renal/urinary (kidneys and bladder)
Sometimes two or more systems are considered together because their functions are related. For example, the urinary and reproductive systems may be considered together as the urogenital system, and the blood and cardiovascular system can be considered together as the circulatory system.
Conversely, a system can be broken down into component subsystems for study in depth. This leads to terms such as ophthalmology (the study of the eye), otorhinolaryngology (the study of the ear, nose and throat), hepatology (the study of the liver) and cardiology (the study of the heart).
Each system in the body comprises organs that work together to enable the system to perform its role in the physiology of the whole body.
The distinct systems of the body described earlier can in turn be broken down into subsystems, each of which represents a collection of interrelated organs (see Figure 1.1a-I). The concept of levels of organization can be applied here. The most complex level of organization is the body itself. The next level consists of the 12 systems and their subsystems. The various organs that make up the systems form the next level of organization.
At the next level, organs can be considered in terms of the different tissues out of which they are made. Tissues, of which there are four main types, comprise the range of basic living materials with which organs can be built.
Finally, the simplest level of organization that can be considered a living unit is the cell. This is the single living building block out of which all tissues, and therefore all organs, systems and the body itself, are made, and it is, of course, the original first component part of the human body formed at conception.
Figure 1.1a-I The levels of organization of the body
The organs: comments from a Chinese medicine perspective
Chinese medicine describes 12 Organs, all but one of which is given the same name as the solid organs that are described in physiology. However, these Organs, such as the Heart, Lung and Kidneys, do not correspond to the physiological structures after which all but the San Jiao (Triple Heater) are named. The organs in physiology are defined primarily in terms of their structure and location, and also by their function. In contrast, the Organs in Chinese medicine are not recognized to have a physical structure. They are defined in terms of the functions that they have in the body and these include emotional or spiritual aspects as well as physical ones. They are recognized to have a dominant, but not exclusive, influence over the physical organ after which they are named, but will actually have an influence over every part of the body.
The physiologist is talking about a physically tangible reality when discussing organs, but a Chinese medicine practitioner is describing energetics when using the same term.2 In Chinese medicine, this energetic body may be defined in terms of Yin and Yang, the Five Elements and the Vital Substances of Qi, Blood, Essence (Jing) and also the Pathogenic Factors (such as Cold and Damp) that may impact upon it.
In this text, to minimize possible confusion between terms used differently in Chinese and Western medicine, all Chinese medicine terms that have a meaning which is particular to Chinese medicine theory are ascribed an upper-case initial letter.
The differences may be briefly summarized as in the table on the right.
Whilst it is tempting to do so, it is important never to presume that the physiological and Chinese medicine use of a term might correspond. It is also important to explain this to patients, who might otherwise make very incorrect assumptions about what their Chinese medical diagnoses might mean for them. Although there are some similarities (e.g. the function of the stomach is to store food both in physiological and in Chinese medicine), there are many more differences (e.g. the physiological spleen has nothing to do with the digestion of food, whereas this is a significant function of the Spleen in Chinese medicine).
The organ correspondence tables in Appendix I demonstrate in more detail the nature of the differences between the functions of the physiological and Chinese medicine Organs. Each table relates to a particular organ, and illustrates how the various functions of the physiological and Chinese medicine Organs can be mapped onto one another.
Organs in Chinese medicine
Solid physical structures
Terms to describe a collection of functions
The structure and function of the organs can be assessed by scientific means: dissection, physical examination, blood tests, ultrasound, X-ray imaging, etc.
The functions of the Chinese medicine Organs are assessed subjectively by checking the state of the Qi using techniques such as pulse and tongue diagnosis
The function of the organ can be related to the structure of the organ (e.g. the pumping action of the heart organ can be related to its muscular shape, electrical activity and valves)
The function of the Chinese medicine Organs is not related to any structure, although the Chinese medicine Organ may dominate the function of a physiological organ (e.g. the Qi of the Heart Organ as interpreted in Chinese medicine supports the physiological heart organ)
For any one organ there is not necessarily a counterpart Chinese medicine Organ (e.g. pituitary)
For any one Chinese medicine Organ there is not necessarily a counterpart physiological organ (e.g. Triple Burner)
At the most basic of the levels of organization of all plants and animals lays the living building block known as the cell. An understanding of how the cell functions will form a basis for the study of those more complex organizational levels of the body, the tissues, the organs and the physiological systems.
Most cells are too small to be seen with the naked eye, but a simple microscope can reveal certain details of their structure, including the boundaries between cells.
Figures 1.1b-I to 1.1b-IV are diagrammatic represen-tations of how cells in different tissues can appear under the light microscope. These indicate the wide variety of cell shape seen in different tissues, and also that each cell contains a large central structure known as the nucleus.
Figure 1.1b-I Fibrous tissue, illustrating fiber-generating cells (fibrocytes) and collagen fibers
Figure 1.1b-II Adipose (fat) tissue, illustrating fat-filled adipose cells and minimal connective fibers
Figure 1.1b-III Tissue from a lymph node, illustrating immune cells (white blood cells and reticular cells) and supportive reticulin fibers
Figure 1.1b-IV Cardiac muscle tissue, illustrating the fiber-like cardiac muscle cells linked by connecting “intercalating discs”
The more powerful electron microscope is required to reveal more detail in cell structure. Although the precise structure of each cell is different, depending on the tissue in which it is found and the role it has to play, all cells in the human body share some basic features.
It is helpful to consider a “generalized cell” to study how all cells are made up and function. No single cell will be exactly like this diagram, but most cells will have the features portrayed in the generalized cell, as depicted in Figure 1.1b-V.
Figure 1.1b-V The structure of a generalized animal cell
Structure of the cell
Each cell contains a plasma membrane and a number of internal structures known as organelles. This terminology reflects the fact that a single cell can be seen as a living unit in isolation, with the organelles corresponding to the organs of the body. The organelles are fluid in nature, being bound by oily fluid membranes and suspended within a fluid matrix known as the cytosol. Together, the cytosol and organelles are called cytoplasm, and this is bounded by an oily fluid plasma membrane.
The plasma membrane acts as the link between the cell and the outside world. Large molecules made of protein in this membrane make the cell unique and structurally respond to various chemicals in the cellular environment to bring about changes within the cytoplasm. In addition, the plasma membrane allows the passage of nutrients into the cell and waste out of the cell, but able to retain essential substances within the cell. This important feature of cell membranes, known as semi-permeability, is described in Section 1.1c.
The nucleus is the largest structure found within the cell. It contains genetic material in the form of chromosomes. These consist of strands of a very complex molecule called DNA (deoxyribonucleic acid). DNA is the template for the synthesis of proteins building materials in the cell. Another complex molecule with a similar structure, RNA (ribonucleic acid), takes the role of the messenger. Messenger RNA transfers the information coded on DNA out to the cytosol and to the ribosomes, where the proteins are actually made.
The other large round structures in the cytosol are the numerous cigar-shaped mitochondria, which utilize oxygen to break down the basic nutrients obtained from carbohydrates and fats (and sometimes proteins) to form an energized compound called ATP (adenosine triphosphate). ATP can be likened to a battery as it holds a readily available store of energy to “power” all processes of the cell. This process of using oxygen and nutrients to form energy is called cellular respiration. The waste product of respiration is carbon dioxide.
A large part of the remaining cytosol consists of many layers of oily membrane called the endoplasmic reticulum (ER), on which the dense ribosomes are situated. Where the ribosomes are numerous the ER is described as rough (rough ER), and where they are less numerous it is described as smooth (smooth ER). Ribosomes are the site at which the long molecule of RNA is used as a template to guide the production of proteins from simple chemicals called amino acids, out of which all proteins are made. Proteins made on the rough ER pass into the space between its membranes in preparation for transport out of the cell.
The Golgi apparatus is an extension of the ER. It takes the proteins made on the ribosomes and covers them with a membrane coating to make “vesicles” (also known as secretory granules). These can travel to the plasma membrane, so that proteins can be released into the outside environment when necessary.
Microfilaments and microtubules are fibers that can contract and cause the movement of substances from one part of the cell to another. These fibers, also known as the cytoskeleton, maintain the structure of the cell and link the various organelles.
The features of the “generalized cell” are summarized in Table 1.1b-I.
Table 1.1b-I The important characteristics of the cell
•The cell is a self-contained living unit
•It is bounded by a “membrane,” which is studded with characteristic proteins
•The membrane allows communication with the outside world
•The cell takes in nutrients and oxygen to produce energy to “power” its activities
•It contains genetic material in its nucleus, which allows the manufacture of specific cellular building materials, the proteins
•These proteins can be “exported” out of the cell to the outside environment
The production of cellular energy: comments from a Chinese medicine perspective
Just as the cell can be compared to a body with the organelles as small organs, it is also reasonable to attempt to describe cellular function in terms of the Organ systems of Chinese medicine. For example, one interesting parallel between the Chinese description and the physiological insight is that of the production of cellular energy. According to Chinese medicine as described by Maciocia (1989),3 the formation of True (Zhen) Qi is derived from Gathering (Zong) Qi, which, in turn, is a product of Food Qi and Air. According to Chinese medicine theory, vitality from the food, Food Qi, is transported by the Spleen to the Lungs, where it is combined with vitality from the air to form Zong Qi. It is under the catalytic action of Original Qi that the Zong Qi is transformed into Zhen Qi, which then circulates in the Channels and nourishes the Organs in the form of Nutritive (Ying) Qi and Protective (Wei) Qi.
Physiologists recognize that cellular energy is similarly derived from a catalytic process involving food (which is broken down into the essential components of simple sugars and amino acids) and oxygen drawn into the body from the air breathed into the lungs. When explained in this way, there is clearly an interesting parallel with the production of cellular energy, stored in the form of energized ATP as the source of energy for all tissues, and the Chinese description of the production of True (Zhen) Qi, which also outlines food and air as basic substrates.
The replication of cells is a fundamental process within the body that begins with the first division of the fertilized egg (zygote). It is essential both for growth and for the repair of aging and damaged tissues. There are two ways in which cells can divide, known as mitosis and meiosis. Mitosis is the process whereby a single cell divides into two identical cells following the replication and separation of the chromosomes in the nucleus. Meiosis is the process whereby a single cell divides into daughter cells, each of which carries exactly half of the genetic material of the parent cell.
The stages of mitosis are illustrated in Figure 1.1b-VI. In this diagram, for the sake of clarity, only a single pair of the human complement of 23 chromosomal pairs is illustrated. The diagram shows how mitosis results in two identical daughter cells, whereas meiosis results in the production of four genetically unique daughter “half-cells” or gametes.
Figure 1.1b-VI The stages of mitosis
Mitosis reproduces the parent cell for the purposes of the growth of the tissue or the repair of damaged tissue, while meiosis produces the reproductive cells (spermatozoa and ova), also known as gametes. When the gamete is fertilized, the resulting zygote (the very first cell, which will later divide to form the embryo) will have a unique combination of genetic material, half from the mother and half from the father. It is the process of meiosis that is fundamental to the uniqueness of every human being.
Both meiosis and mitosis are involved in the development of the fertilized egg (zygote) into an adult human being. Meiosis in the sex organs of the parents leads to the production of the gametes. When a male gamete (spermatozoon) and female gamete (egg or ovum) meet, they fuse through the process of fertilization. The resulting zygote divides and grows by the process of mitosis.
When the genetic material of the daughter cells from mitosis and meiosis has become damaged during the process of cell division, this is referred to as a mutation. There are three possible consequences of this. First, the mutation is so minor that the resulting cell is very similar in function to its parent. Second, the mutation disturbs the function of the daughter cells so much that they die. Third, and most significantly, the mutation may lead to disturbed function in the daughter cells, although these cells continue to live and replicate. This may or may not have a significant effect on the tissue of which the parent cell is a part.
If the parent cell is one of the cells in an embryo, a single mutation can have devastating effects, as the daughter cells may have been destined to develop into major body parts. One example of the consequences of mutation occurring during the process of mitosis is the effects of the drug thalidomide, which was developed in the early 1960s as an anti-nausea medication in early pregnancy. It was later discovered that significant limb development mutations had developed in the embryos carried by pregnant mothers using the medication.
A mutation in mitosis can also lead to cancerous change in the daughter cells. Cancer is always the consequence of a mutation that has led to impairment in growth regulation and cell survival in the mutated cells. The affected cells have abnormal and uncontrolled growth patterns, and this is how cancerous change leads to disease.
Mutation in meiosis will also lead to a defect in the genetic code in the gametes. Sometimes this means that affected gametes cannot be fertilized. However, in other cases, fertilization is possible, and the genetic code of the resulting zygote will then carry the defect. This means that every cell of the developing embryo will be affected by the mutation. This may lead to an insignificant or minor change in the function of the adult, such as color blindness, but can also result in severe inherited diseases, such as sickle cell anemia or hemophilia.
Mutation is an important process to understand in the study of pathology. Mutation in mitosis can cause certain physically based congenital diseases and cancer, and mutation of the gametes in meiosis can lead to genetic congenital diseases.
1.1c Cell transport and homeostasis
Cellular transport processes
As previously described, the cell membrane has the property of semi-permeability in which it can allow the passage of some substances but not of others. By this mechanism, the cell takes in nutrients and expels wastes. The membrane can also permit the cell to respond to changes in the outside world. An example of this is the nerve cell, which picks up information from one part of the body (e.g. an image in the eye) and relays this to another part of the body (e.g. to the brain, for recognition of the image). This property of “response to stimuli” is also dependent on the passage of substances across the cell membrane.
The cell membrane is both fluid and oily in nature, and may be pictured as a mobile, slippery and very thin layer surrounding the cell, rather like the wall of a soap bubble. The oily nature means that substances that are soluble in oils, such as gases (oxygen and carbon dioxide) and steroids, can pass through the membrane by first dissolving in it. This oily (phospholipid) layer also contains pathways made through the membrane by large protein molecules embedded within it. These pathways are of a sufficient size to allow the slow, but free, passage of small molecules such as water and salt (see Figure 1.1c-I).
Figure 1.1c-I A section of the fluid plasma membrane
Movement of substances within the body, whether inside cells, outside cells or across cell membranes, always involves movement through body fluids. When substances are dissolved or suspended in water they tend to move from an area of high concentration to one of low concentration, and the movement continues until the differences in concentration are evened out as much as is physically possible. This form of movement of substances dissolved or suspended within water is called “diffusion.” For example, when orange squash concentrate is poured into a glass of water, the eventual even mix of orange and water occurs as a result of diffusion.
When a semi-permeable membrane such as the cell membrane separates two regions of fluid of different concentrations, the process of diffusion for small molecules is slowed down but not prevented. For example, if there is a strong salt solution on one side of a membrane and water on the other, the water molecules will cross the membrane via the protein channels to mix with the salt solution. The larger salt molecules cannot use the tiny pathways in the membrane proteins and so cannot make this transition. However, because the water molecules can move, over time the concentrated salt solution will become much more dilute. The process may take some time, but even despite this membrane barrier, as with the orange squash, the result is a much more even concentration of solution on either side of it. This movement of water across a semi-permeable membrane into a region of more concentrated solution is called osmosis (see below).
Diffusion of certain fat-soluble substances can actually occur through the membrane itself rather than through the protein membrane channels. This is because the membrane is made up of an oily substance and permits the free passage of molecules that can dissolve in it. Therefore, because of diffusion, a difference in concentration of oxygen on either side of a semi-permeable membrane will eventually become evened out. This will be as a result of the movement of oxygen between the oily molecules, which make up the membrane, from the more concentrated to the less concentrated side.
In addition to the protein channels (holes), there are also gates (also made of protein) that allow the passage of slightly larger substances such as glucose and amino acids. Movement of larger molecules via these gates is known as facilitated diffusion. The gates restrict the free passage of these substances, so that this form of diffusion is extremely slow. This means that, if one of these specialized gates is present in a membrane, only a small amount of a large molecule such as glucose dissolved within the cytoplasm of a cell will be able to pass through.
Some molecules, such as proteins, are so large that they cannot pass across the membrane by the process of diffusion. This means that any large molecules contained within a membrane, such as proteins forming the microfilaments in the cytoplasm, will be unable to leave.
In summary, the membrane is permeable to water and fat-soluble molecules, slightly permeable to glucose, and impermeable to large molecules. This illustrates the meaning of “semi-permeable.” Understanding the concept of semi-permeability is a prerequisite for making sense of the process of osmosis.
The process of osmosis in action is evident when limp flowers are placed in some water and the floppy stems become, after a length of time, much sturdier. What is happening in this example is that the water in the vase is moving across the plasma membranes of the plant cells into the cells themselves. This causes the cells to swell, and then the whole stem to regain its firmness. The water is moving into the cells by diffusion, because the cytoplasm contains a concentrated solution of glucose and large molecules. These larger molecules have a tendency to move in the opposite direction out of the cells, but they are unable to do this because of the barrier of the semi-permeable membrane. Therefore, most of the movement is of water passing one way across the membrane, and this, of course, benefits the plant.
In physiology, the term “osmosis” refers to the process of the transfer of water molecules from within a dilute solution with the result that a more concentrated solution on the other side of a semi-permeable membrane is made more dilute.
In osmosis, the tendency of the water is to continue moving until the solutions on each side of a membrane are of equal strength. However, the movement of water into a concentrated solution of large molecules does not always occur indefinitely. Otherwise, in the example of limp flowers placed in water, the cells in the stems of the flowers would eventually burst. What happens is that, eventually, the process slows down to reach a stable state; the plant cells are firm, but not over-full.
This example illustrates the idea of osmotic pressure. The tendency of the water to dilute the solution on the other side of the membrane can be likened to it being moved under pressure. However, there are opposing pressures to this movement. In the case of the plant cell, the opposing pressure is the tautness of the fibrous skin of the stem. Eventually, the osmotic pressure is matched by opposing pressures, and the one-way movement stops at a “steady state.” This explains how plant cells in a stem can contain a concentrated solution of large molecules, but do not burst when placed in water.
The force of osmotic pressure can, in some situations, be strong enough to rupture cells. For example, red blood cells are not supported by fibrous tissue. If a drop of blood is placed in pure water (which is much more dilute than the plasma in which these cells normally circulate), the red blood cells will swell as water molecules move by osmosis into their cytoplasm. Eventually, these cells will burst under the force of the osmotic pressure.
Figure 1.1c-II illustrates what could happen to a red blood cell if it is placed into (a) a solution of the same strength (isotonic) as the fluid in its cytosol, (b) a much more dilute (hypotonic) solution, and (c) a more concentrated (hypertonic) solution. In (a) the movement of water across the cell membrane (indicated by the arrows) is balanced inwards and outwards, and the cell remains the same size. In (b) there is a tendency of a larger volume of the more dilute solution to move into the red blood cell than there is for water to move out. This will cause it to swell; if the solution is very dilute, the red cell might even burst. In (c), the tendency is for more fluid to move out of the cytosol, across the cell membrane and into the surrounding solution; the red blood cell will tend to shrivel as a result.
Figure 1.1c-II The process of osmosis
This powerful effect of osmosis explains why hospital patients are given intravenous saline solution in a drip rather than pure water. Saline is a salt solution made to be precisely the concentration of the cytoplasm of all cells, and thus the cells will neither burst nor shrivel when mixed with it.
Osmosis also explains why the bouncy and firm quality of the skin is lost in cases of dehydration. Lack of water means the blood becomes more concentrated. The cells are bathed in the fluid derived from blood. Therefore, when the body is in a state of dehydration, the fluid within the cells will be less concentrated than the surrounding fluid. Water will then move out of the cells by osmosis. This leaves the whole tissue limp, as each cell has slightly shriveled due to the cellular dehydration caused by the osmosis.
Larger molecules, such as complex proteins and glucose, cannot pass readily through the holes and gates formed by membrane proteins (see Figure 1.1c-I). Instead, for rapid movement, these large molecules rely on a “pump,” in the form of a specialized membrane carrier protein powered by the energy stored by the chemical ATP, to permit them to pass. The energy released by the ATP powers a change in the shape of the pump proteins, and this change allows the carriage of the large molecule from one side of the membrane to the other, rather akin to a turnstile that can take a person from one side of a gateway to the other once the entry fee has been inserted (see Figure 1.1c-III). Osmosis and diffusion are known as “passive transport” because they require no added input of energy to take place. In these processes, the movement of molecules occurs simply as a result of the natural tendency of these molecules to be in movement. When added power in the form of ATP is required to move substances from one side of a membrane to another, this is known as active transport.
Figure 1.1c-III The role of the carrier protein in active transport and facilitated diffusion across membranes
The term phagocytosis (literally “cell-eating”) describes the process whereby the cell membrane forms arm-like projections that can reach out and engulf external substances so that they can be drawn into the cell. Exocytosis is the process whereby an intracellular vesicle containing complex substances can fuse with the external membrane of the cell so that those substances can be released. Both are forms of active transport, because the movements of the vesicles in both are enabled by the contraction of ATP-powered microfilaments and tubules.
These simple processes are at the foundation of all that enables a cell to work as part of a living organism. Transport across membranes is what allows a cell to take in nutrients and excrete waste. It also permits a response to changes in the environment, and therefore communication between cells and the ability of one cell to alter the behavior of another.
Homeostasis (meaning staying the same) refers to the body’s ability to maintain a state of balance despite changing external circumstances.
Two important concepts in physiology that relate to homeostasis are those of the internal environment and the external environment. The internal environment describes all parts of the body that are contained by a tissue layer, the outside surface of which has a direct connection with the external environment. The external environment includes those parts of the body connected to the outside by orifices. Therefore, parts of the body such as the air passages leading to the lungs, the long space enclosed by the tube of the gut, and the inside of the bladder are all part of the external environment. The external environment is, of course, unpredictable and prone to change in temperature, composition of the air and the presence of other substances such as food and liquids.
The principle of homeostasis is that the internal environment is always maintained at a steady state despite changes in the external environment. For example, our body temperature remains the same whatever the outside weather through homeostasis (except in the case of illness). Homeostatic processes ensure that diverse variables, including the concentration of the blood, the levels of hormones, oxygen, carbon dioxide, blood sugar and mineral salts, the density of the bone and the muscle tone remain controlled within very narrow limits that maximize function and health.
The process of homeostasis is underpinned by a system of negative feedback loops, which involve changes to re-establish balance occurring in response to changes in the internal balance. Such a system requires a “detector” to recognize a move away from balance, a “control center” that recognizes when the move has been so great that something has to be done about it, and an “effector” that brings about a change in the body to reverse the imbalance. A thermostat is a mechanical example of a negative feedback loop in action. The detector in this case is a thermometer. The control center is the mechanism that is set to recognize when the temperature falls outside a desired range. The negative feedback loop is based on the maximum desired temperature. When the temperature becomes higher than this maximum, the effector, in this case the heating element, is switched off until the time when the temperature drops within the desired range once again.
It is clear that in chronic (long-term) illness, and also in aging, these feedback systems no longer work as effectively. In chronic illness the body never quite achieves the ideal internal environment for optimal function. For example, the blood glucose concentration of a person with untreated diabetes is at a level that is too high for the cells to remain undamaged, and in chronic rheumatoid arthritis the inflammatory processes of the body are always too overactive to be wholly beneficial, and damage to cells will also be the result. With this perspective, it becomes easy to understand how being in a state of ill health can lead to progressively worsening ill health. The way to stop this would be to reset in some way the “thermostat” of the feedback loop. However, many conventional treatments for chronic illness cannot do this. Most conventional medicines tend to act on the consequences of the imbalance in homeostasis, and not its underlying cause (which often has its root in chronic exposure of the body to unhealthy lifestyle patterns or adverse environmental influences).
In conclusion, the physiological view is that health depends on a natural tendency of the body to remain in balance. Illness is the result of a failure in this delicate system.
1.1d The tissue types
This section explores in more detail how individual cells are specialized to perform different roles, and how specialized cells form the different tissue types.
Single-cell organisms, such as the amoeba, can survive without specialization because all parts of the cell membrane are in contact with the external environment. It is possible for a single-cell organism to obtain the food and oxygen it needs, to excrete waste and to respond to other changes in the environment, simply because all of its boundaries are in touch with the outside world. Specialization is necessary in larger organisms because most cells are not in contact with the external environment. Cells buried deep within a large organism are unable on their own to obtain nutrients and oxygen, or to excrete their waste. Likewise they will be unable to detect changes in the external environment and to respond appropriately.
Specialization is necessary in larger organisms to overcome this problem of the internally situated cells being unable to “fend for themselves.” In larger organisms, specialized organs take over the role of functions such as nutrition, respiration, excretion and sensing the environment. In this way they support all the other cells in the body. For example:
•the digestive tract is specialized to obtain food for all cells in the body
•the lungs are specialized to obtain oxygen and excrete carbon dioxide for all cells in the body
•the liver and kidney are specialized to excrete other waste for all cells in the body
•the nervous system is specialized to sense changes in the environment for all cells in the body.
There are four recognized categories of specialized tissues – epithelial, connective, muscle and nervous tissue. All these can be subdivided into different tissue subtypes within each category, but this section focuses only on the main characteristics of the four types.
All parts of the body that are in direct contact with the external environment are epithelial in nature, whether they are on the outside surface of the body or form the linings of the cavities and passageways of internal organs, such as the lung. Epithelial cells are specialized to protect, secrete and absorb. These are the functions that would be required of an external lining to the body, which has to perform the role of protection, taking in nutrients from the environment and the excretion of waste.
Epithelial cells are also found lining the heart, blood and lymph vessels. Here they are known as the endothelium, reflecting the fact that these epithelial cells are deep within the body rather than on the surface.
Epithelial cells develop from a connective tissue basement membrane that overlies connective tissue underneath. They usually form a single layer of cells, akin to paving stones, but in some regions and organs, including the skin, they develop in layers. These cells tend to multiply rapidly, as they are easily damaged through wear and tear. Figure 1.1d-I illustrates five different forms of epithelium that are found throughout the body.
Figure 1.1d-I The five important categories of epithelium found in the body
Connective tissue is specialized to have a structural role in the body. In its various forms it supports and protects the organs both from within and without. It is characterized by cells supported within a non-cellular substance and supportive non-cellular fibers. Connective tissue has structural and protective roles. The types of connective tissue with obvious structural roles include areolar (loosely structured) tissue, adipose (fat) tissue, fibrous tissue, elastic tissue, cartilage and bone. All these tissues surround, support and protect the muscles and organs, and together form a structural network throughout the body. There are two types of connective tissue that are less to do with structure, and instead comprise the organs of the blood and the lymphatic systems. These have been classed as connective tissue, because the cells found in the blood and lymphoid tissues have similarities with the macrophages, plasma cells and mast cells found in structural connective tissue. All these blood and lymphatic cells, which include the red and white blood cells, have originated from one common type of immature cell found in the bone marrow.
Connective tissue usually underlies all epithelial tissue. In general, it consists of living cells embedded in a “matrix” consisting of structural strand-like proteins and a semi-solid or solid ground material (which together confer both strength and flexibility akin to reinforced concrete). This complex range of tissues forms the padding and support that separates the internal organs from the epithelial linings. This tissue is the next line in defense if the epithelium fails to prevent a wound or the entry of infection. The presence of the immune cells, such as the macrophages, plasma cells and mast cells, whose functions are to work in the processes both of wound healing and fighting infection, makes structural connective tissue a very important aspect of the body’s defense mechanisms. Figure 1.1d-II illustrates the diversity of the structure of connective tissues.
Figure 1.1d-II Six examples of connective tissue found in the body
Muscle cells are characterized by the fact they all contain protein fibers that can contract. The energy for contraction comes from the cellular energy-storing molecule ATP. Muscle cells also contain another sort of protein, called myoglobin, which is specialized to store the large amount of oxygen required to produce sufficient quantities of energy-charged ATP in the muscle cell. There are three types of muscle tissue: striated, smooth and cardiac. Each is specialized for different roles.
Striated muscle tissue (see Figure 1.1d-III) is primarily found in skeletal muscle. It has cells in the form of long fibers and responds only to impulses from motor nerves. The cells are bound together in parallel, and can contract together as a unit to increase the available power.
Figure 1.1d-III Skeletal (striated) muscle fibers
Smooth muscle tissue (see Figure 1.1d-IV) is mainly found in the hollow organs and consists of sheets of spindle-like cells that have a natural tendency to contract. Although not dependent on motor impulses, smooth muscle can contract in response to the autonomic nerves that supply the hollow organs. The contraction of smooth muscle is slow and sustained.
Figure 1.1d-IV Smooth muscle fibers
Cardiac muscle tissue (see Figure 1.1d-V) is specially adapted for the heart wall, with fibers arranged in sheets, and the cells arranged with intercellular joints. This structure allows for a wave-like contraction across the sheet rather than a single contraction as a unit. Heart muscle tissue also has a natural tendency to contract and is not dependent on motor impulses.
Figure 1.1d-V Cardiac muscle fibers
Unlike the other physiological systems that, with the exception of blood, are composed of more than one of the first three tissue types, the nervous system is composed entirely of nervous tissue.
The tissue of the nervous system is made up of two types of cells:
•excitable cells (ordinarily called nerve cells, or neurons)
•non-excitable cells (supportive cells), which can be likened to a specialized form of structural connective tissue. The structure of this tissue is described in detail in Chapter 4.1.
Membranes and glands
The membranes and glands are specialized forms of epithelial tissue.
There are three main types of membrane – mucous, serous and synovial – each of which has an important structural role in the body in that they line and protect the organs.
Mucous membranes are characterized by the presence of mucus-secreting cells, which provide the lining of the mouth and digestive tract, the nose and respiratory tract and genitourinary tracts with a protective coating. They are, therefore, in contact with the external environment.
In contrast, serous membranes are deep within the internal environment. They both surround the body of organs and line the cavities in which they sit. They provide a fluid-filled space to separate the organ from the wall of its cavity.
The synovial membrane is the layer that separates the cartilage-covered ends of bone from the space in the joint. It secretes the fluid that nourishes the cartilage and lubricates the joint.
Glands fall into two broad categories: endocrine and exocrine. Endocrine glands are collections of epithelial cells that secrete hormones. Endocrine glands have no ducts; instead, their secretions are released directly into the fluid surrounding the cells (lymph), and from there to the bloodstream. Exocrine glands secrete specialized substances that are discharged towards the epithelium of the organs via a duct. The secretion therefore ends up in the external environment (e.g. on the skin, or in the gut, respiratory passages or genitourinary tract).
Process of differentiation
The various manifestations of the tissue types illustrate the diversity of ways in which the few identical cells of the very early embryo become differentiated into cells with unique and enduring characteristics. Once a cell of an embryo starts to develop into a squamous epithelial cell or a striated muscle fiber, this is the form in which its daughter cells will continue to appear as long as health is maintained.
Although each cell that is produced by mitosis in the embryo contains the same genetic code, through the process of differentiation parts of the genetic code are “switched off” and other parts are activated. A cell destined to develop into nerve tissue will have the genetic code relevant to the structure of nerve tissue “switched on” and all of that part of the code relevant to other types of tissue “switched off.” Nevertheless, underlying the diversity of all the differentiated cells of the body a lifelong unity is preserved. All nucleated cells that develop throughout the lifetime of an individual will carry within them the unique DNA blueprint that defined that individual from the point of conception onwards.
1.1e Introduction to pathology and pharmacology
The word pathology is derived from the Greek words for disease and study. The word pathogenic has the same root, meaning disease causing. The science of pathology involves understanding the various ways in which the homeostasis of the perfectly functioning body can fall out of balance.
Conventional pathologists understand that disease arises in the body either as a result of endogenous factors or because of adverse environmental conditions.
From a medical perspective, the internal causes of disease include:
•constitutional weakness (inherited disease)
•cancerous change (although some cancers are understood to be triggered by external causes)
•degeneration of age
•negative emotions (the relation of chronic anger, depression and stress to ill health have all been studied in detail).
The external causes of disease include:
•excessive heat or cold and dampness
•chemical damage/poisoning (including dietary and recreational factors such as caffeine, tobacco and alcohol) and radiation
•stressful living and working conditions.
Medical approaches to the management of disease
The full breadth of the role of a medical professional is not easily appreciated by a layperson, as certain very technical aspects of medical care, such as drug treatment and surgery, tend to stand out as the most prominent and memorable defining features. However, it has been argued that it is the more simple or mundane aspects of medical care that have had the most profound effects in terms of improving the health of individuals or populations.4 To help with understanding the breadth of medical approaches, these are now considered within three categories: prevention of disease, cure of disease and treatment of symptoms in chronic disease.
Prevention of disease
Preventive medicine is an essential aspect of any medical care provided by a doctor, irrespective of the medical specialty in which the doctor has trained. At the foundation of any medical approach to preventive medicine is an ever-expanding evidence-based wealth of knowledge of the diverse determinants of disease listed above. In preventive medicine, the physician is concerned with developing this knowledge base and developing effective methods of influencing medical practice and, at a wider level, national and international health and economic policy, so that the important causes of disease are readily recognized and managed appropriately.
Methods of prevention include:
•social change (e.g. banning tobacco advertising and improved sanitation)
•education and advice to the public (e.g. healthy eating)
•use of medications (e.g. vaccination and antibiotics during surgery)
•surgery (e.g. removal of breast tissue in someone considered to be at high risk of cancer)
•routine screening for treatable risk factors for disease (e.g. tests performed in antenatal care).
Prevention can be focused at the level of stopping a disease event from developing (e.g. preventing heart attacks by focusing on exercise and smoking cessation), in which case it may be termed primary prevention. Alternatively, efforts to prevent disease may be concentrated on a patient who has suffered from a disease so that progression of the disease is minimized (e.g. the prescription of aspirin to someone who has suffered from a heart attack), in which case it may be known as secondary prevention.
Confusingly, the medical profession also uses the terms primary, secondary and tertiary prevention in a slightly different way, and it is important to be clear about this, as both forms of nomenclature appear in current respected texts. Some medical authors use the term primary prevention to mean the practice of preventing any aspect of a disease from developing. An example of primary prevention used in this sense is the recent UK policy of administering the human papilloma virus (HPV) vaccine to young teenage girls. This practice has the aim of preventing wart virus infection, now strongly associated with cervical cancer, from taking hold with the onset of sexual activity in later teenage years. Secondary prevention is the practice of detecting early treatable markers of disease so that early curative treatment can be instigated. The national cervical screening program in the UK is an example of this, in which all women aged between 25 and 60 are offered regular cervical smear tests to look for early precancerous changes, which can then be treated to prevent the development of cervical cancer. In this form of naming of disease prevention, tertiary prevention refers to the approaches used to deal with established disease. Following on from the earlier examples, tertiary prevention would include the surgical and medical treatment of established cervical cancer.
According to this nomenclature, many of the approaches used by doctors to screen for disease, such as a mammography for breast cancer, blood tests for markers of prostate and ovarian cancer, and examination of the testicles for testicular cancer, are all examples of secondary prevention of disease.
It is currently generally accepted that the greatest impact that modern medicine may have on health is in the realm of the promotion of the general health of a population and the prevention of disease.
Cure of disease
Although prevention of disease may have the most significant impact on health, it is the doctor’s ability to cure diseases that can engender the greatest respect. Moreover, while medical and surgical approaches often have the most dramatic results in terms of cure, it is important to remember that healing modalities requiring less technical expertise, such as the giving of simple advice or the administration of basic nursing care, may be all that is needed to effect a full return to health.
Methods of cure include:
•medication that reverses the process of disease
•physical therapies (e.g. physiotherapy)
•talking therapies (i.e. psychotherapy)
•basic needs supplied through hospital care
•treatment of distressing symptoms or disability resulting from disease.
Treatment of symptoms in chronic disease
Most diseases that impact on the health of Western populations are chronic conditions such as coronary heart disease, diabetes, depression, cancer and dementia. These sorts of conditions are not necessarily amenable to cure. In a developed country, the bulk of the cost of medical care is devoted to the management of these chronic conditions and preventing their progression as far as possible. The financial burden on healthcare systems becomes ever greater as the number of people suffering from chronic disease continues to increase (matching growth in population size, adoption of unhealthy lifestyles and longevity), and as the range of evidence-based medical treatments becomes increasingly complex and “high tech.”
Methods of treatment of the symptoms of chronic disease include:
•medication that alleviates symptoms or hinders progression of disease
•physical therapies (e.g. physiotherapy)
•talking therapies (e.g. psychotherapy)
•occupational therapy and rehabilitation
•nursing home/hospital care
•referral to other support agencies (e.g. social services).
The term pharmacology is derived from the Greek meaning medicine and study. Pharmacology embraces the study of the drugs that may be prescribed for each disease. In addition, it involves understanding the complex way in which each drug interacts with the chemical and cellular processes of the body. As well as defining when a drug might be perceived to be of benefit in the treatment of disease, pharmacologists are interested in predicting possible side effects and contraindications (the situations when a drug should not be prescribed).
This text is written with the aim of making medical information more accessible to health practitioners with a non-medical background or focus. An important skill to acquire is a facility for using medical texts and online resources and for interpreting the language used within them. Very often the information presented by medical textbooks and on websites is organized in a way that follows a predictable pattern. Familiarity with this pattern can greatly assist in the process of extracting important information.
Texts on physiology and pathology
Medical textbooks are generally structured around the physiological systems, and this will also apply to texts on physiology and the pathology of disease. Physiology and pathology are descriptive subjects, and the information found in pathology texts can generally be trusted as established fact derived from scientific observation. For example, a phrase from a pathology textbook such as “…bone is a connective tissue with cells (osteocytes) surrounded by a matrix of collagen fibers…” has its origins in the scientific observation of the microscopic structure of bone. Most readers would probably not dispute such facts, even though they might hold an alternative view of the body based on an energetic foundation of bone. This technical description is simply a way to describe the material nature of healthy bone.
Similarly, most statements about pathology in medical texts are also facts based on the observation of diseased tissue. For example, the sentence, “In Paget’s disease overactive osteoblasts deposit abnormal new bone that is thickened or enlarged or structurally weak,” reflects a process that has been observed using scientific methods, including microscopy.
Texts on clinical medicine
Clinical medicine is the term used to describe the real-life practice of medicine on patients in the setting of the clinic or hospital. Texts on clinical medicine are also generally structured around the physiological systems, and may include some introductory physiology and pathology to introduce the description of clinical medical approaches system by system.
Doctors may use the term general (or internal) medicine more specifically to describe the discipline that aims to treat diseases by means of non-surgical techniques. Drug treatments are a principal therapy in the practice of general medicine defined in this way. For mainly historical reasons, the practice of surgery is considered to be a separate, albeit complementary, discipline to general medicine. Textbooks of general clinical medicine do not, therefore, describe in detail those conditions that are primarily managed by surgeons, for example, orthopedics (surgical conditions of the bones and joints), otorhinolaryngology (ear, nose and throat diseases), obstetrics and gynecology (diseases of pregnancy and women’s health), urology (diseases of the urinary tract) and plastic surgery.
Information box 1.1e-I
Western descriptions of pathology: comments from a Chinese medicine perspective
Facts concerning pathological processes can be surprisingly relevant and helpful to the Chinese medicine practitioner. Understanding pathology can help with communicating the conventional view of disease to patients, and can also provide valuable information about a possible energetic interpretation of a particular condition.
For example, consider the sentence about Paget’s disease quoted in this chapter: “overactive osteoblasts deposit abnormal new bone that is thickened or enlarged or structurally weak.” It is feasible that a Chinese medicine energetic interpretation be inferred from such a description. Overactive cells might suggest the presence of Heat. Structural weakness suggests Deficiency of Yin or Jing. A rapid growth of irregular bone suggests an Accumulation that in Chinese medicine is described in terms of Phlegm. Paget’s disease is, in fact, a condition of aging bones. It presents with deformed hot areas of bone, and these areas carry a risk of undergoing cancerous change. This suggests that it is presumably a condition of Phlegm/Heat, with underlying Kidney Yin Deficiency of old age as one possible progenitor of the Heat. Here it can be seen that the detail of the pathology may be reflected in the energetic understanding of the symptoms and signs of this condition.
This process of learning the descriptions of pathological processes as aids to the energetic interpretation of disease is explored further in Stage 2.