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This includes all the physical and chemical processes that go on inside living things and that are necessary for proper functioning of the body. Physiology is closely related to anatomy, the study of different organs in a body and their relative positioning. This is because an understanding of functions of body parts requires a prior understanding of how the body is built. Human physiology is the specific study of the workings of the human body. The organ system approach is usually employed to study human physiology, including that of the bones and joints. Organ systems are a group of cells, tissues, and organs with a particular function.
The human body consists of the following organ systems: 
<c>Musculoskeletal System</c> This system consists of bones of the skeleton, joints, muscles, connective tissue, ligaments, tendon, and cartilage. The musculoskeletal system provides a framework for the body, protects many critical organs, and facilitates movements of movable body parts.
<c>Nervous System</c> This system is there for transmission of signals between different parts of the body for coordination of body movement. The nervous system comprises the brain, spinal cord, sensory cells called neurons or nerve cells, and nerves that connect these sensory cells.
<c>Cardiovascular System</c> This system includes heart, blood, and blood vessels. It supplies nutrients to all parts of the body through blood. The system works in close conjunction with the respiratory system.
<c>Respiratory System</c> This system consists of the lungs, air passages, and respiratory muscles. It arranges for oxygenation of blood and release of carbon dioxide from blood.
<c>Endocrine System</c> This system is made up of numerous glands, each secreting some hormone. These hormones are released directly into the bloodstream for regulation of the body's metabolism. This organ system includes glands such as the pituitary gland, adrenal gland, thyroid gland, pineal gland, pancreas, and thymus. The pancreas is also a part of the digestive system and functions as an endocrine as well as exocrine gland.
<c>Digestive System</c> This system absorbs nutrients from consumed food and disposes waste. It consists of the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. The liver and pancreas, which secrete digestive juices, are also part of this system. This system works in active collaboration with the nervous system and the cardiovascular system.
<c>Urinary System</c> This system produces, stores, and disposes urine. It is made up of two kidneys, two ureters, one bladder, and a urethra.
<c>Reproductive System</c> The reproductive system is involved with the production of reproductive cells. It also provides a mechanism through which these cells are combined. This system consists of external genitalia as well as organs that produce the reproductive cells.
<c>Immune System</c> The immune system protects the body against disease. It includes bone marrow, white blood cells, lymph system, antibodies, spleen, and thymus.
<c>Integumentary System</c> This system safeguards the body from damage and comprises of the skin and appendages of the skin such as nails and hair.
The study of human physiology includes an exhaustive focus on all these systems. This study has to be combined with a fundamental understanding of the molecular, cellular, and tissue level principles that form the basis of the functions of these systems. Proper functioning of the human body requires all these systems to work smoothly. The overall health of the human body is determined by the efficiency of the collective or integrated working of all these systems. An important concept in physiology is homeostasis. This refers to the maintenance of certain physiological parameters within a narrow range despite frequent changes in the external environment. Such a control is essential for proper functioning of all the organ systems. The physiological parameters that need to be kept within limits include body temperature and concentration of electrolytes and glucose in the cells.
<b>Origins of the Term Physio</b>
The term physio is derived from the Greek word phusis, meaning nature, and was used by people of ancient Greece around 1000 B.C. The word phusis is also said to refer to the Greek goddesses of nature who maintained the balance of nature. The term also implied normality as opposed to something that is monstrous or perverse. 
Considerable physiological differences exist between humans, other animals, and microorganisms. These differences can usually be ascribed to the process of evolution. Darwin's theory of evolution proposes that all life on earth started from a single-celled organism that slowly diversified into numerous species. In order to adapt to the surroundings, the physiology of organisms changed slowly. Different climatic conditions triggered different type of changes and, over the centuries, led to the development of varied life forms. Humans have an average brain-to-body mass ratio of 1:40 that is exceeded only by small birds (1:12). This highly developed brain is said to be the reason why humans are more intelligent than other animals. Such a brain is also the reason why humans have a longer memory than most other animals. Usually, animals beyond the human species "live in the moment" and are, therefore, free from emotions such as spite, guilt, and self-consciousness.
<c>Fingers and Legs</c> The thumb is most developed in people. During evolution, Man felt greater need for the thumb and hence it developed better than in other species. The thumb adds a whole new dimension to the activities that humans can perform. People could make and use tools and advance scientifically because of the thumb. While a superbly developed brain provides the arthritis patient with ideas, the thumb helps in the conversion of some of these ideas into practice. Humans walk on two hind legs while most other animals walk on all four legs.  Certain types of monkeys do walk on two legs, but that is not their normal mode of mobility. This feature provides the arthritis victim with an erect posture and frees their hands for other, more important activities. This is also the reason why humans have a running speed lower than most other animals of a comparable size.
<c>Cardiovascular, Communication, and Sensual Differences</c> The number of chambers in the heart vary among animals. Humans have four chambers, reptiles usually three (except crocodiles that have four chambers), fishes have two, and so on. Moreover, communication skills are very highly developed in humans as compared to other animals. Man is the only animal capable of articulate and coherent speech as opposed to certain sounds and gestures made by animals that can convey their emotions only in a broad sense. As compared to many other animals, humans have an inferior sense of smell, eyesight, and hearing. During the course of evolution, humans made steady progress and started to tailor their environment to their needs. In a partly customized environment, the necessity of these senses declined as compared to when humans lived in open and, often, unprotected environments.
<c>Microbiological Differences</c> Humans and animals have numerous organs that are a collection of many cells and tissues. Each organ has some function(s). This specialization is either absent or limited in microorganisms as the number of cells is limited. Organ systems such as musculoskeletal system, nervous system, and cardiovascular system are usually absent in the bodies of microorganisms. Many microorganisms are capable of rapid reproduction when the temperatures are moderately high. This rate is very high as compared to humans and most other animals, and the reproduction activity slows down in cold environments. Microbes such as bacteria can freely exchange genes with other similar species leading to quick mutation and evolution. This process of horizontal gene transfer poses great challenges for medical science as the variant species can resist even targeted medication. Reproduction in microbes can be asexual, sexual or both.  Fungi reproduce asexually while bacteria can reproduce in both ways. Barring a few exceptions, most animals reproduce sexually. It is the sexual reproduction in bacteria that can lead to mutation and associated problems for medical science. This process is called conjugation and involves transfer of DNA from one bacterium to another via a thread type structure known as pilus. Such a transfer enables the bacteria to pass characteristics and leads to the formation of a varied species capable of survival in newer, more hostile environments.
<a>Normal Functions of Bones and Joints</a>
<b>Purpose of Bones</b>
All the bones and joints in the body form the skeletal system that is inherently linked with muscles to form the musculoskeletal organ system. The skeletal system serves three fundamental functions.  As noted from chapter three, the skeletal system supports all the other organ systems of the body by providing a framework of bones and joints on and inside which other organ systems are rested. This structure also provides shape to the body. Bones provide protection from internal organs such as brain, lungs, uterus and others. This is a notable function and, therefore, merits a somewhat detailed treatment:
The skull encases the brain and protects the eyes and the middle and inner ears.
The sternum, rib cage, and spine shield the heart, lungs, and prominent blood vessels.
The vertebral column forms a covering around the spinal cord.
The spine and ilium safeguards the hip and the digestive and urogenital systems.
<c>Movement</c> Movement is provided by bones in combination with attached muscles. Skeletal muscles operate in pairs and when one relaxes, the other simply contracts. An example is the bicep-triceps combination. When the arm is stretched, the bicep relaxes with contraction of the triceps and vice versa. Many times, bones provide leverage by amplifying the magnitude and changing the direction of force generated by the muscles.
<a>Impaired Bone Health</a>
<b>Overview of Consequences</b>
Unhealthy bones are unable to perform all or any of their functions of support, movement, protection, production of blood cells, and acting as a reservoir and dumping locations respectively for useful and toxic minerals. Bone disease is a generic term for disorders related to bones that make bones weak and brittle and, therefore, more likely to break. Sources for bone disorders include heredity, nutritional deficiencies, injuries, and infections. The general effects are a pronounced decrease in the quality of life due to the inability to move efficiently and due to frequent bone injuries and possibly fractures. Premature death can result in extreme cases.
<c>Infectious Arthritis</c> This can result in people with weak joints. The source is a fungal, viral, or bacterial infection in such joints and the symptoms include swelling and redness around the joint, joint pain, and fever. The infection is transferred through blood or can be a result of injury, surgery, or injection. Infectious arthritis is discussed further in chapter 19.
<c>Rickets</c> This is found in children and is due to vitamin D deficiency. It makes the bones weak and soft. The effects include restricted movements with bone and muscle pain.
Low bone density is due to insufficient development of bone mass during childhood. This can aggravate into osteoporosis later on in life. 
<c>Bone Cancer</c> This affects the normal functioning of bone cells and tissues. Usually, cancer in the bone is a result of spread of cancerous cells to bones from another part of the body. Very rarely does bone cancer originate in bone cells. There are different types of bone cancers that affect bone cells, cartilage cells, and the bone marrow. Symptoms include swelling, pain, and weak bones; fatigue, unexplained weight loss, night sweats, and chills. This disorder can assume serious proportions if it affects a load-bearing bone such as the femur, forcing the patient to use a wheelchair for considerable duration of the treatment.
<c>Paget's Disease</c> This bone disease interrupts the cycle of continuous breakdown and rebuilding of bones. Severe pain and swelling in joints are the symptoms of this disorder that can enlarge and weaken the bones. This can intensify into other disorders such as deafness and arthritis.
<c>Osteogenesis Imperfecta (OI)</c> This is a genetic disease that causes bones to break easily and other conditions such as curved spine, weak muscles, brittle teeth, and hearing loss. The disease causing gene is inherited and affects the development of collagen - a protein that in turn affects bone development.
<c>Fibrous Dysplasia</c> This results in replacement of bones with fibrous tissue, thereby causing excessive growth and swelling of bones. Weak bones affect the ability to walk and the disorder can also cause endocrine problems. The reason this disorder inspires a certain degree of awe is because the cause is unknown, it cannot be prevented, and cure only aims to mitigate the adverse effects.
<c>Osgood-Schlatter Disease</c> This malady affects the area where the knee cap and tibia (shinbone) are connected. The disease is more likely to affect adolescents and causes swelling, tenderness, and pain in the affected area. The pain can range from mild to severe and from occasional to constant.
<a>Physiology of Joints</a>
<b>Purpose of Joints</b>
Joints are those locations where two or more bones are attached. Joints provide connectivity between different bones of the body. The fact that almost all bones are connected to form the skeletal system and that the muscles are connected to the skeleton ensures coordination of movement between different parts of the body. This connectivity integrates all the body parts into one whole entity. Joints facilitate movement through contraction and relaxation of muscles. Purposeful movement is fundamental to animal behavior and enables them to execute all activities necessary for survival, leisure, and reproduction. A certain amount of flexibility is lent to the skeletal structure by joints, which also serve as shock absorbers. Evolution has lent different structure to different types of joints in different animals. However, their essential functions remain unchanged. An example is the joints in the hind legs of land based carnivores that are designed for pouncing on prey. This is why they can jump high by using their hind legs. At the other end of the spectrum are the herbivores with bones and joints of hind legs designed for high speed. The joints of monkeys are designed for quick climbing and rapid movement among trees. Reptile joints enable them to crawl and pounce at high speeds.
All members of the cat family except the cheetah have retractable claws. The claws are made so as they are joined to the last phalange that can move forward or backward along a curvilinear path. This mechanism prevents unnecessary wearing of claws. The claws are voluntarily unsheathed only during hunting and serious fighting. The cheetah is designed for high speed and requires the claws to be continuously unsheathed in order to gain and maintain traction while sprinting. Even among carnivores, joints serve slightly different functions. Members of the dog family have joints compatible for a prolonged chase. Their hunting strategy involves wearing down the prey. Cats are ambush hunters. Their joints are stronger and capable of sudden acceleration for bringing down the prey suddenly. This would also mean greater shock absorbing capacity of their joints, although they are not suited for endurance. In humans, all joints can provide movement except the bones of the cranium. These cover the brain and are not capable of movement for obvious reasons. The human palm has a peculiar structure where the thumb provides exceptional gripping ability. Such a structure is absent in all the other animals and bestows humans with the capacity to execute a whole range of specialized activities. Joints in the human body can be classified on the basis of type of movement that they provide physiologically:
Hinge joints facilitate movement similar to that of a hinged door - along one axis only. They allow up-or-down movement but not from side to side. Examples of such joints are the elbow, knee, and the upper and lower jaw.
Ball and socket joints allow movement in all directions - upwards, downwards, and sideways. The shoulder is an example of such a joint. Another example is the acetabulam or the hip joint where the thigh bone is connected to the pelvis.
Pivot joints permit pivotal movement of one part about the other. An example of this type of joint is the movement of the skull about the backbone where the skull can rotate about the topmost bone of the backbone.
Gliding Joint is characterized by gliding movement of one bone / part over the other. The wrist joint is an example of such a joint.
Joints can also be classified according to the mechanism that holds the bones together at the joint. Application of this criterion renders the following types of joints. 
Fibrous or immovable joints are held together by ligaments only. Examples of such joints are the radioulnar and tibiofibular joints, the joints of bones inside the forearm and shin, respectively. Cartilaginous joints are where the connection between bones is provided by cartilage. An example is the joints between the vertebrae. Synovial joints are held together by a synovial capsule that is made from the protein collagen. The inner layer of this capsule is known as the synovial membrane and it secretes a lubricant called synovial fluid. Furthermore, there is a hyaline cartilage that pads the ends of the bones in these joints. Synovial joints can be hinge joints, ball and socket joints, pivot joints, or gliding joints. They can also be saddle type or condyloid type. Different finger bones of the same finger are joined by a saddle joint while condyloid joints join the metacarpal bones to the first phalanges.
<a>Developmental Aspects of Male and Female Bones</a>
<b>Overall Bone Similarities</b>
When it comes to bones and joints, considerable similarities exist between the framework of males and females. As a matter of fact, the skeletons of all primates exhibit certain generic features such as a large brain, highly developed fingers and thumb, generalized pattern of teeth, forward facing eyes, and bony eye sockets. The following points of resemblance are observed between the human male and human female skeleton.
Both have exactly the same number of bones: 206. Same number of bones also means the same number of joints, although the precise number of joints in the human body is a matter of debate in view of differences in opinion on what constitutes a joint. An inclusive estimate indicates to the presence of about 250 to 350 joints in the human body. The shape of most bones in the male and female skeleton is similar, although some bones are differently shaped in view of the different roles of males and females. The femur or the thigh bone is the longest and strongest bone in both human males and human females. Stirrup or stapes is the smallest bone in the human skeleton irrespective of gender. This bone is located in the middle ear and its average size ranges between 0.25 cm to 0.33 cm. The average human bone density is around 1500 kg/m3 for a normal, healthy adult, although males have slightly higher bone density than women. Here again, different researchers have obtained varying results ranging between 1000 kg/m3 to 1900 kg/m3. With this, the human skeleton comprises a significant percent of the total body weight.
<c>Exceptions</c> Certain peculiarities or exceptions are common to the male and female skeletons. The presence of fused bones in the cranium and pelvis serves as an example here. These bones are not connected through joints but fit into each other the way pieces of a jigsaw puzzle do. The three bones in the middle ear, collectively referred to as ossicles, connect only with each other. The hyoid bone located in the neck serves as a connection point for the tongue. It is not connected to any bone in the skeleton. It is held in position only by muscles and ligaments.
<b>Overall Bone Differences</b>
Different hormones affect the development of bones in males and females and this is the primary reason for bone differences. Testosterone is the main hormone that affects bone development in males while estrogen does the same for females.  The differences between male and female skeletons can be better understood when seen in the context of differences in race, lifestyle, and physical activity. When comparisons are made between males and females of the same race and with comparable lifestyles, the following points of differences can be observed.
<c>In Relation to Childbirth</c> There are two differences in relation to the process of childbirth covered in the precedingchapter. Females have a more movable coccyx or tailbone and a wider and flatter sacrum connected to the pelvis. The coccyx is the last bone of the backbone and sacrum is similarly located near the end of the spinal column. Such a structure allows the head and shoulders of the fetus to pass through the cavity during childbirth. Bones that make up the arms and legs are thicker, longer and, therefore, stronger in case of males. Bones in the arm include the humerus that supports the bicep, radius, and the ulna that support the forearm. Males possess relatively larger phalanges or finger bones.
<c>Size</c> Male skeletons are usually larger and heavier than female skeletons. Traditionally, men have assumed the responsibility of hunting, gathering, and working outdoors while women have been assigned to domestic responsibilities and childbearing. Men, therefore, have traditionally needed more strength and this explains the strength-related differences in the male and female skeletons.
<c>Face</c> The facial bone structure in males and females is different on account of difference in the structure of the skull. Men have more developed bulge at the back of the head and more noticeable brow ridges. The chin area of men is more angular and square as compared to female chins that are pointed and more rounded.
<c>Spine Length and Others</c> The length of spine in women is shorter as compared to men. The shorter spine creates an illusion of female legs being longer than that of males. Other differences include a narrower rib cage, more rounded shoulder blades, and smaller teeth in the female skeleton.
<a> Developmental Aspects of Male and Female Joints </a>
Human male and female joints have certain common features. The first similarity is the number of joints. Since the number of bones in the bodies of males and females is same, the number of joints is also same. The number of joints is between 250 to 350.  There is no exact number due to lack of unanimity on what precisely constitutes a joint. Another prominent similarity is the types of joints. Both males and females have the same types of joints according to the mechanism for holding joints together. The functions of most of the joints in males and females are similar. This point of similarity is a natural corollary to there being equal number and same type of joints.
Men have broader shoulders and smaller waists while women have wider hips and narrower shoulders. This makes the angles of muscle alignment and tendon attachment different in the joints of males and females.  Female joints are, on an average, more flexible and have a greater range of movement than male joints.  This is due to women having a lower center of gravity due to wider hips and greater distribution of weight around the hips and thighs. On account of this significant point, the following dissimilarities are observed: 1) It is easier for women to perform mobility exercises and exhibit actions such as hurdling and the fosbury flop during high jump, while; 2) men are better at events such as long jump, shot put, and hammer throw; 3) the said feature also makes women less susceptible to injuries during the execution of jumps over hurdles, but on the downside, this feature lowers the efficiency of the muscle pull and makes women more prone to muscle injuries and 4) elbows and ankles in the male skeleton are smaller and have a smaller carrying angle as compared to female skeletons. This makes male elbows and ankles stronger.
Physiology is the study of functions of different organs and organ systems in the human body, which body consists of ten organ systems. The body's overall health is determined by how well these systems function collectively. People are the apex creatures on this planet on account of their highly developed brain, thumb, and communication. The skeletal system consisting of bones and joints is the physical foundation on which other organ systems of the body are rested. It also protects different organs in the body and with the attached muscle system forms the musculoskeletal system that facilitates movement of movable body parts. Due to differences in their biological roles, bones and joints of men and women are slightly different. Men have broader shoulders while women have wider hips. This provides a lower center of gravity for women with greater joint flexibility and better coordination of movement. The same feature, however, makes women more prone to muscle injuries.