The medical condition aphakia affects which part of the body?
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Disease.txt Aphakia.txt Human_body.txt
Disease Aphakia Human body
A disease  is a particular abnormal condition, a disorder of a structure or function, that affects part or all of an organism. The study of disease is called pathology which includes the causal study of etiology.  Disease is often construed as a medical condition associated with specific symptoms and signs.  It may be caused by external factors such as pathogens, or it may be caused by internal dysfunctions particularly of the immune system such as an immunodeficiency, or a hypersensitivity including allergies and autoimmunity.

In humans, disease is often used more broadly to refer to any condition that causes pain, dysfunction, distress, social problems, or death to the person afflicted, or similar problems for those in contact with the person. In this broader sense, it sometimes includes injuries, disabilities, disorders, syndromes, infections, isolated symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts and for other purposes these may be considered distinguishable categories. Diseases can affect people not only physically, but also emotionally, as contracting and living with a disease can alter the affected person's perspective on life.

Death due to disease is called death by natural causes. There are four main types of disease: infectious diseases, deficiency diseases, genetic diseases both (hereditary and non-hereditary), and physiological diseases. Diseases can also be classified as communicable and non-communicable. The deadliest diseases in humans are coronary artery disease (blood flow obstruction), followed by cerebrovascular disease and lower respiratory infections. 

Terminology

Concepts

In many cases, terms such as disease, disorder, morbidity and illness are used interchangeably.   There are situations, however, when specific terms are considered preferable.

;Disease
The term disease broadly refers to any condition that impairs the normal functioning of the body. For this reason, diseases are associated with dysfunctioning of the body's normal    homeostatic processes.   Commonly, the term disease is used to refer specifically to infectious diseases, which are clinically evident diseases that result from the presence of pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular organisms, and aberrant proteins known as prions.  An infection that does not and will not produce clinically evident impairment of normal functioning, such as the presence of the normal bacteria and yeasts in the gut, or of a passenger virus, is not considered a disease. By contrast, an infection that is asymptomatic during its incubation period, but expected to produce symptoms later, is usually considered a disease.  Non-infectious diseases are all other diseases, including most forms of cancer , heart disease, and genetic disease. 
;Acute disease : disease of a short-term nature; the term sometimes also connotes a fulminant nature
;Chronic disease : disease that is a long-term issue
;Incurable disease : disease that cannot be cured
;Terminal disease : disease with death as an inevitable result
;Illness
Illness is generally used as a synonym for disease.  However, this term is occasionally used to refer specifically to the patient's personal experience of his or her disease.    In this model, it is possible for a person to have a disease without being ill (to have an objectively definable, but asymptomatic, medical condition, such as a subclinical infection), and to be ill without being diseased (such as when a person perceives a normal experience as a medical condition, or medicalizes a non-disease situation in his or her life – for example, a person who feels unwell as a result of embarrassment, and who interprets those feelings as sickness rather than normal emotions). Symptoms of illness are often not directly the result of infection, but a collection of evolved responses—sickness behavior by the body—that helps clear infection. Such aspects of illness can include lethargy, depression, loss of appetite, sleepiness, hyperalgesia, and inability to concentrate.   
;
In medicine, a disorder is a functional abnormality or disturbance.  Medical disorders can be categorized into mental disorders, physical disorders, genetic disorders, emotional and behavioral disorders, and functional disorders.  The term disorder is often considered more value-neutral and less stigmatizing than the terms disease or illness, and therefore is a preferred terminology in some circumstances.  In mental health, the term mental disorder is used as a way of acknowledging the complex interaction of biological, social, and psychological factors in psychiatric conditions.  However, the term disorder is also used in many other areas of medicine, primarily to identify physical disorders that are not caused by infectious organisms, such as metabolic disorders.
;Medical condition
A medical condition is a broad term that includes all diseases, lesions, disorders, or condition that normally receives medical treatment, such as childbirth.  While the term medical condition generally includes mental illnesses, in some contexts the term is used specifically to denote any illness, injury, or disease except for mental illnesses. The Diagnostic and Statistical Manual of Mental Disorders (DSM), the widely used psychiatric manual that defines all mental disorders, uses the term general medical condition to refer to all diseases, illnesses, and injuries except for mental disorders.  This usage is also commonly seen in the psychiatric literature. Some health insurance policies also define a medical condition as any illness, injury, or disease except for psychiatric illnesses. 
As it is more value-neutral than terms like disease, the term medical condition is sometimes preferred by people with health issues that they do not consider deleterious.  On the other hand, by emphasizing the medical nature of the condition, this term is sometimes rejected, such as by proponents of the autism rights movement.
The term medical condition is also a synonym for medical state, in which case it describes an individual patient's current state from a medical standpoint.  This usage appears in statements that describe a patient as being in critical condition, for example.
;
Morbidity () is a diseased state, disability, or poor health due to any cause.   The term may be used to refer to the existence of any form of disease, or to the degree that the health condition affects the patient.  Among severely ill patients, the level of morbidity is often measured by ICU scoring systems.  Comorbidity is the simultaneous presence of two or more medical conditions, such as schizophrenia and substance abuse.
In epidemiology and actuarial science, the term "morbidity rate" can refer to either the incidence rate, or the prevalence of a disease or medical condition. This measure of sickness is contrasted with the mortality rate of a condition, which is the proportion of people dying during a given time interval.
;Syndrome
A syndrome is the association of several medical signs, symptoms, and or other characteristics that often occur together.  Some syndromes, such as Down syndrome, have only one cause; others, such as Parkinsonian syndrome, have multiple possible causes. In other cases, the cause of the syndrome is unknown.  A familiar syndrome name often remains in use even after an underlying cause has been found, or when there are a number of different possible primary causes.
;Predisease
Predisease is a subclinical or prodromal vanguard of a disease state. Prediabetes and prehypertension are common examples. The nosology or epistemology of predisease is contentious, though, because there is seldom a bright line differentiating a legitimate concern for subclinical/prodromal/premonitory status (on one hand) and conflict of interest–driven disease mongering or medicalization (on the other hand). Identifying legitimate predisease can result in useful preventive measures, such as motivating the person to get a healthy amount of physical exercise,  but labeling a healthy person with an unfounded notion of predisease can result in overtreatment, such as taking drugs that only help people with severe disease or paying for drug prescription instances whose benefit–cost ratio is minuscule (placing it in the waste category of CMS's "waste, fraud, and abuse" classification).

Types by body system

;Mental
Mental illness is a broad, generic label for a category of illnesses that may include affective or emotional instability, behavioral dysregulation, cognitive dysfunction or impairment.  Specific illnesses known as mental illnesses include major depression, generalized anxiety disorders, schizophrenia, and attention deficit hyperactivity disorder, to name a few. Mental illness can be of biological (e.g., anatomical, chemical, or genetic) or psychological (e.g., trauma or conflict) origin. It can impair the affected person's ability to work or study and can harm interpersonal relationships.  The term insanity is used technically as a legal term.
;Organic
An organic disease is one caused by a physical or physiological change to some tissue or organ of the body.  The term sometimes excludes infections.  It is commonly used in contrast with mental disorders.  It includes emotional and behavioral disorders if they are due to changes to the physical structures or functioning of the body, such as after a stroke or a traumatic brain injury, but not if they are due to psychosocial issues.

Stages

In an infectious disease, the incubation period is the time between infection and the appearance of symptoms.  The latency period is the time between infection and the ability of the disease to spread to another person, which may precede, follow, or be simultaneous with the appearance of symptoms.  Some viruses also exhibit a dormant phase, called viral latency, in which the virus hides in the body in an inactive state.  For example, varicella zoster virus causes chickenpox in the acute phase; after recovery from chickenpox, the virus may remain dormant in nerve cells for many years, and later cause herpes zoster (shingles).
;Acute disease
An acute disease is a short-lived disease, like the common cold.
;Chronic disease
A chronic disease is one that lasts for a long time, usually at least six months.  During that time, it may be constantly present, or it may go into remission and periodically relapse.  A chronic disease may be stable (does not get any worse) or it may be progressive (gets worse over time).  Some chronic diseases can be permanently cured.  Most chronic diseases can be beneficially treated, even if they cannot be permanently cured.
;Flare-up
A flare-up can refer to either the recurrence of symptoms or an onset of more severe symptoms.
;Refractory disease
A refractory disease is a disease that resists treatment, especially an individual case that resists treatment more than is normal for the specific disease in question.
;Progressive disease
Progressive disease is a disease whose typical natural course is the worsening of the disease until death, serious debility, or organ failure occurs.  Slowly progressive diseases are also chronic diseases; many are also degenerative diseases.  The opposite of progressive disease is stable disease or static disease:  a medical condition that exists, but does not get better or worse.
;Cure
A cure is the end of a medical condition or a treatment that is very likely to end it, while remission refers to the disappearance, possibly temporarily, of symptoms.  Complete remission is the best possible outcome for incurable diseases.
;Clinical disease
One that has clinical consequences, i.e., the stage of the disease that produces the characteristic signs and symptoms of that disease.   AIDS is the clinical disease stage of HIV infection.
;Subclinical disease
Also called silent disease, silent stage, or asymptomatic disease.  This is a stage in some diseases before the symptoms are first noted. 
;Terminal phase
If a person will die soon from a disease, regardless of whether that disease typically causes death, then the stage between the earlier disease process and active dying is the terminal phase.

Scope

;Localized disease
A localized disease is one that affects only one part of the body, such as athlete's foot or an eye infection.
;Disseminated disease
A disseminated disease has spread to other parts; with cancer, this is usually called metastatic disease.
;Systemic disease
A systemic disease is a disease that affects the entire body, such as influenza or high blood pressure.

Classifications

Diseases may be classified by etiology (cause), pathogenesis (mechanism by which the disease is caused), or by symptom(s). Alternatively, diseases may be classified according to the organ system involved, though this is often complicated since many diseases affect more than one organ.

A chief difficulty in nosology is that diseases often cannot be defined and classified clearly, especially when etiology or pathogenesis are unknown.  Thus diagnostic terms often only reflect a symptom or set of symptoms (syndrome).

Classical classification of human disease derives from observational correlation between pathological analysis and clinical syndromes. Today it is preferred to classify them by their aetiology if it is known. 

Arguably the most known classification of diseases is the World Health Organization's ICD. They publish periodical updates. Currently the last publication is the ICD-10

Causes

Only some diseases such as influenza are contagious and commonly believed infectious. The micro-organisms that cause these diseases are known as pathogens and include varieties of bacteria, viruses, protozoa and fungi. Infectious diseases can be transmitted, e.g. by hand-to-mouth contact with infectious material on surfaces, by bites of insects or other carriers of the disease, and from contaminated water or food (often via fecal contamination), etc.   In addition, there are sexually transmitted diseases. In some cases, microorganisms that are not readily spread from person to person play a role, while other diseases can be prevented or ameliorated with appropriate nutrition or other lifestyle changes.

Some diseases, such as most (but not all) forms of cancer, heart disease, and mental disorders, are non-infectious diseases. Many non-infectious diseases have a partly or completely genetic basis (see genetic disorder) and may thus be transmitted from one generation to another.

Social determinants of health are the social conditions in which people live that determine their health. Illnesses are generally related to social, economic, political, and environmental circumstances. Social determinants of health have been recognized by several health organizations such as the Public Health Agency of Canada and the World Health Organization to greatly influence collective and personal well-being. The World Health Organization's Social Determinants Council also recognizes Social determinants of health in poverty.

When the cause of a disease is poorly understood, societies tend to mythologize the disease or use it as a metaphor or symbol of whatever that culture considers evil.  For example, until the bacterial cause of tuberculosis was discovered in 1882, experts variously ascribed the disease to heredity, a sedentary lifestyle, depressed mood, and overindulgence in sex, rich food, or alcohol—all the social ills of the time. 

Types of causes

;Airborne: An airborne disease is any disease that is caused by pathogens and transmitted through the air.
;Infectious:  Infectious diseases, also known as transmissible diseases or communicable diseases, comprise clinically evident illness (i.e., characteristic medical signs and/or symptoms of disease) resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism. Included in this category are contagious diseases – an infection, such as influenza or the common cold, that commonly spreads from one person to another – and communicable diseases – an disease that can spread from one person to another, but does not necessarily spread through everyday contact.
;Non-communicable: A non-communicable disease is a medical condition or disease that is non-transmissible.  Non-communicable diseases cannot be spread directly from one person to another.  Heart disease and cancer are examples of non-communicable diseases in humans.
;Foodborne: Foodborne illness or food poisoning is any illness resulting from the consumption of food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites.
;Lifestyle: A lifestyle disease is any disease that appears to increase in frequency as countries become more industrialized and people live longer, especially if the risk factors include behavioral choices like a sedentary lifestyle or a diet high in unhealthful foods such as refined carbohydrates, trans fats, or alcoholic beverages.

Prevention

Many diseases and disorders can be prevented through a variety of means.  These include sanitation, proper nutrition, adequate exercise, vaccinations and other self-care and public health measures.

Treatments

Medical therapies or treatments are efforts to cure or improve a disease or other health problem.  In the medical field, therapy is synonymous with the word treatment.  Among psychologists, the term may refer specifically to psychotherapy or "talk therapy".  Common treatments include medications, surgery, medical devices, and self-care.  Treatments may be provided by an organized health care system, or informally, by the patient or family members.

A prevention or preventive therapy is a way to avoid an injury, sickness, or disease in the first place.  A treatment or cure is applied after a medical problem has already started.  A treatment attempts to improve or remove a problem, but treatments may not produce permanent cures, especially in chronic diseases.  Cures are a subset of treatments that reverse diseases completely or end medical problems permanently.  Many diseases that cannot be completely cured are still treatable. Pain management (also called pain medicine) is that branch of medicine employing an interdisciplinary approach to the relief of pain and improvement in the quality of life of those living with pain 

Treatment for medical emergencies must be provided promptly, often through an emergency department or, in less critical situations, through an urgent care facility.

Epidemiology

Epidemiology is the study of the factors that cause or encourage diseases.  Some diseases are more common in certain geographic areas, among people with certain genetic or socioeconomic characteristics, or at different times of the year.

Epidemiology is considered a cornerstone methodology of public health research, and is highly regarded in evidence-based medicine for identifying risk factors for disease. In the study of communicable and non-communicable diseases, the work of epidemiologists ranges from outbreak investigation to study design, data collection and analysis including the development of statistical models to test hypotheses and the documentation of results for submission to peer-reviewed journals. Epidemiologists also study the interaction of diseases in a population, a condition known as a syndemic. Epidemiologists rely on a number of other scientific disciplines such as biology (to better understand disease processes), biostatistics (the current raw information available), Geographic Information Science (to store data and map disease patterns) and social science disciplines (to better understand proximate and distal risk factors).  Epidemiology can help identify causes as well as guide prevention efforts.

In studying diseases, epidemiology faces the challenge of defining them.  Especially for poorly understood diseases, different groups might use significantly different definitions.  Without an agreed-on definition, different researchers may report different numbers of cases and characteristics of the disease. 

Some morbidity databases are compiled with data supplied by states and territories health authorities, at national level (National hospital morbidity database (NHMD), for example  ), or at European scale (European Hospital Morbidity Database or HMDB ) but not yet at world scale.

Burdens of disease

Disease burden is the impact of a health problem in an area measured by financial cost, mortality, morbidity, or other indicators.

There are several measures used to quantify the burden imposed by diseases on people.  The years of potential life lost (YPLL) is a simple estimate of the number of years that a person's life was shortened due to a disease.  For example, if a person dies at the age of 65 from a disease, and would probably have lived until age 80 without that disease, then that disease has caused a loss of 15 years of potential life.  YPLL measurements do not account for how disabled a person is before dying, so the measurement treats a person who dies suddenly and a person who died at the same age after decades of illness as equivalent.  In 2004, the World Health Organization calculated that 932 million years of potential life were lost to premature death.

The quality-adjusted life year (QALY) and disability-adjusted life year (DALY) metrics are similar, but take into account whether the person was healthy after diagnosis.  In addition to the number of years lost due to premature death, these measurements add part of the years lost to being sick.  Unlike YPLL, these measurements show the burden imposed on people who are very sick, but who live a normal lifespan.  A disease that has high morbidity, but low mortality, has a high DALY and a low YPLL.  In 2004, the World Health Organization calculated that 1.5 billion disability-adjusted life years were lost to disease and injury.
Standard DALYs (3% discounting, age weights).
[http://www.who.int/entity/healthinfo/global_burden_disease/DALY14_2004.xls DALY spreadsheet]
[http://www.who.int/entity/healthinfo/global_burden_disease/YLL14_2004.xls YLL spreadsheet].  In the developed world, heart disease and stroke cause the most loss of life, but neuropsychiatric conditions like major depressive disorder cause the most years lost to being sick.

Society and culture

How a society responds to diseases is the subject of medical sociology.

A condition may be considered a disease in some cultures or eras but not in others.  For example, obesity can represent wealth and abundance, and is a status symbol in famine-prone areas and some places hard-hit by HIV/AIDS.  Epilepsy is considered a sign of spiritual gifts among the Hmong people. 

Sickness confers the social legitimization of certain benefits, such as illness benefits, work avoidance, and being looked after by others.  The person who is sick takes on a social role called the sick role.  A person who responds to a dreaded disease, such as cancer, in a culturally acceptable fashion may be publicly and privately honored with higher social status.   In return for these benefits, the sick person is obligated to seek treatment and work to become well once more.  As a comparison, consider pregnancy, which is not interpreted as a disease or sickness, even if the mother and baby may both benefit from medical care.

Most religions grant exceptions from religious duties to people who are sick. For example, one whose life would be endangered by  fasting on Yom Kippur or during Ramadan is exempted from the requirement, or even forbidden from participating.  People who are sick are also exempted from social duties.  For example, ill health is the only socially acceptable reason for an American to refuse an invitation to the White House. 

The identification of a condition as a disease, rather than as simply a variation of human structure or function, can have significant social or economic implications. The controversial recognitions as diseases of repetitive stress injury (RSI) and post-traumatic stress disorder (also known as "Soldier's heart", "shell shock", and "combat fatigue") has had a number of positive and negative effects on the financial and other responsibilities of governments, corporations and institutions towards individuals, as well as on the individuals themselves. The social implication of viewing aging as a disease could be profound, though this classification is not yet widespread.

Lepers were people who were historically shunned because they had an infectious disease, and the term "leper" still evokes social stigma. Fear of disease can still be a widespread social phenomenon, though not all diseases evoke extreme social stigma.

Social standing and economic status affect health.  Diseases of poverty are diseases that are associated with poverty and low social status; diseases of affluence are diseases that are associated with high social and economic status.  Which diseases are associated with which states varies according to time, place, and technology.  Some diseases, such as diabetes mellitus, may be associated with both poverty (poor food choices) and affluence (long lifespans and sedentary lifestyles), through different mechanisms.  The term lifestyle diseases describes diseases associated with longevity and that are more common among older people.  For example, cancer is far more common in societies in which most members live until they reach the age of 80 than in societies in which most members die before they reach the age of 50.

Language of disease

An illness narrative is a way of organizing a medical experience into a coherent story that illustrates the sick individual's personal experience.

People use metaphors to make sense of their experiences with disease.  The metaphors move disease from an objective thing that exists to an affective experience.  The most popular metaphors draw on military concepts:  Disease is an enemy that must be feared, fought, battled, and routed.  The patient or the healthcare provider is a warrior, rather than a passive victim or bystander. The agents of communicable diseases are invaders; non-communicable diseases constitute internal insurrection or civil war.  Because the threat is urgent, perhaps a matter of life and death, unthinkably radical, even oppressive, measures are society's and the patient's moral duty as they courageously mobilize to struggle against destruction.  The War on Cancer is an example of this metaphorical use of language.  This language is empowering to some patients, but leaves others feeling like they are failures. 

Another class of metaphors describes the experience of illness as a journey:  The person travels to or from a place of disease, and changes himself, discovers new information, or increases his experience along the way.  He may travel "on the road to recovery" or make changes to "get on the right track" or choose "pathways". Some are explicitly immigration-themed:  the patient has been exiled from the home territory of health to the land of the ill, changing identity and relationships in the process.  This language is more common among British healthcare professionals than the language of physical aggression.

Some metaphors are disease-specific.  Slavery is a common metaphor for addictions:  The alcoholic is enslaved by drink, and the smoker is captive to nicotine.  Some cancer patients treat the loss of their hair from chemotherapy as a metonymy or metaphor for all the losses caused by the disease.

Some diseases are used as metaphors for social ills:  "Cancer" is a common description for anything that is endemic and destructive in society, such as poverty, injustice, or racism.  AIDS was seen as a divine judgment for moral decadence, and only by purging itself from the "pollution" of the "invader" could society become healthy again.  More recently, when AIDS seemed less threatening, this type of emotive language was applied to avian flu and type 2 diabetes mellitus.   Authors in the 19th century commonly used tuberculosis as a symbol and a metaphor for transcendence.  Victims of the disease were portrayed in literature as having risen above daily life to become ephemeral objects of spiritual or artistic achievement.  In the 20th century, after its cause was better understood, the same disease became the emblem of poverty, squalor, and other social problems. Aphakia is the absence of the lens of the eye, due to surgical removal, a perforating wound or ulcer, or congenital anomaly. It causes a loss of accommodation, far sightedness (hyperopia), and a deep anterior chamber. Complications include detachment of the vitreous or retina, and glaucoma.

Babies are rarely born with aphakia. Occurrence most often results from surgery to remove congenital cataracts (clouding of the eyes' lens, which can block light from entering the eye and focusing clearly). Congenital cataracts usually develop as a result of infection of the fetus or genetic reasons. It is often difficult to identify the exact cause of these cataracts, especially if only one eye is affected.

People with aphakia have relatively small pupils and their pupils dilate to a lesser degree. 

Symptoms and treatment

Without the focusing power of the lens, the eye becomes very farsighted.  This can be corrected by wearing glasses, contact lenses, or by implant of an artificial lens.  Artificial lenses are described as "pseudophakic."  Also, since the lens is responsible for adjusting the focus of vision to different lengths, patients with aphakia have a total loss of accommodation.

Some individuals have said that they perceive ultraviolet light, invisible to those with a lens, as whitish blue or whitish-violet.  

Etymology

Gr. a- alfa priv + phakos, lentil, anything shaped like a lentil The human body is the entire structure of a human being and comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet.
Every part of the body is composed of various types of cells, the fundamental unit of life.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd
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cell+biology+AND+mboc4%5Bbook%5D+AND+373693%5Buid%5D&ridmboc4 Molecular Biology of the Cell] fourth edition, edited by Bruce Alberts (2002) published by Garland Science. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos. It is also common to describe small molecules such as amino acids as "[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd
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At maturity, the estimated average number of cells in the body is given as 37.2 trillion.  This number is stated to be of partial data and to be used as a starting point for further calculations. The number given is arrived at by totalling the cell numbers of all the organs of the body and cell types.  The composition of the human body is made up of a number of certain elements including carbon, calcium and phosphorus.

The study of the human body involves anatomy and physiology. The human body can show anatomical non-pathological anomalies known as variations which need to be able to be recognised. Physiology focuses on the systems and their organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis.

Structure

Skeletal structure frames the overall shape of the body and does not alter much over a lifetime. General body shape (and female body shape) is influenced by the distribution of muscle and fat tissue and is also affected by various hormones. The average height of an adult male human (in developed countries) is about  and the adult female is about . Height is largely determined by genes and diet. Body type and body composition are influenced by factors such as genetics, diet, and exercise.

The human body has several body cavities the largest of which is the abdominopelvic cavity. These cavities house the various body organs including the spinal cord which also accommodates the production and flow of  cerebrospinal fluid in the ventricular system of the brain.

Many other smaller cavities exist throughout the body called sinuses, which have varied functions. Sinuses in general usage refers to the paranasal sinuses which are involved in the condition sinusitis. The paranasal sinuses are four pairs of vital air-cavities in the cranial bones. These air-filled spaces are paired between the eyes, above the eyes, deeper behind the eyes and around the nasal cavity.

Composition

The average adult body contains between 5 and 5.5 litres of blood and approximately 10 litres of interstitial fluid.

The composition of the human body can be referred to in terms of its water content, elements content, tissue types or material types. The adult human body contains approximately 60% water, and so makes up a significant proportion of the body, both in terms of weight and volume. Water content can vary from a high 75% in a newborn infant to a lower 45% in an obese person. (These figures are necessarily statistical averages).

The vast majority of cells in the human body are not human at all; rather they are of bacteria, archaea, and methanogens such as Methanobrevibacter smithii. The largest proportion of these form the gut flora. The whole population of microbiota include microorganisms of the skin and other body parts and this altogether is  termed as the human microbiome.

The proportions of the elements of the body can be referred to in terms of the main elements, minor ones and trace elements. Material type may also be referred to as including water, protein, connective tissue, fats, carbohydrates and bone.

Human anatomy

Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body.  Anatomy is subdivided into gross anatomy and microscopic anatomy (histology) Gross anatomy (also called topographical anatomy, regional anatomy, or anthropotomy) is the study of anatomical structures that can be seen by the naked eye. Microscopic anatomy involves the use of microscopes to study minute anatomical structures, and is the field of histology which studies the organization of tissues at all levels, from cell biology (previously called cytology), to organs. Anatomy, human physiology (the study of function), and biochemistry (the study of the chemistry of living structures) are complementary basic medical sciences,  that are generally taught together (or in tandem) to students studying medicine.

In some of its facets human anatomy is closely related to embryology, comparative anatomy and comparative embryology, through common roots in evolution; for example, much of the human body maintains the ancient segmental pattern that is present in all vertebrates with basic units being repeated, which is particularly obvious in the vertebral column and in the ribcage, and which can be traced from the somitogenesis stage in very early embryos.

Generally, physicians, dentists, physiotherapists, nurses, paramedics, radiographers, other health professionals, and students of certain biological sciences, learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures, and tutorials. The study of microscopic anatomy (or histology) can be aided by practical experience in examining histological preparations (or slides) under a microscope; and in addition, medical and dental students generally also learn anatomy with practical experience of dissection and inspection of cadavers (corpses). A thorough working knowledge of anatomy is required for all medical doctors, especially surgeons, and doctors working in some diagnostic specialities, such as histopathology and radiology.

Human anatomy, physiology, and biochemistry are basic medical sciences, generally taught to medical students in their first year at medical school. Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems. The major anatomy textbook, Gray's Anatomy, has recently been reorganized from a systems format to a regional format, in line with modern teaching. 

Anatomical variations

In human anatomy, the term anatomical variation refers to a non-pathologic anatomic structure that is different from  normal. The possible anatomic variations in each organ and its arterial and venous supply must be known by physicians, such as surgeons or radiologists, in order to identify them. Unlike congenital anomalies, anatomic variations are typically inconsequential and do not constitute a disorder. Accessory muscles are rare anatomical duplicates of muscle that can occur and only require treatment where function is impaired. The accessory soleus muscle in the ankle is one such variation and one which does not need to be rectified.   Another more common variation found in around ten per cent of the population is the accessory spleen.

Human physiology

Human physiology is the science of the mechanical, physical, bioelectrical, and biochemical functions of humans in good health, their organs, and the cells of which they are composed. Physiology focuses principally at the level of organs and systems. Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology, and animal experimentation has provided much of the foundation of physiological knowledge. Anatomy and physiology are closely related fields of study: anatomy, the study of form, and physiology, the study of function, are intrinsically related and are studied in tandem as part of a medical curriculum.

The study of how physiology is altered in disease is pathophysiology.

Systems

The human body consists of many interacting systems. Each system contributes to the maintenance of homeostasis, of itself, other systems, and the entire body. A system consists of two or more organs, which are functional collections of tissue. Systems do not work in isolation, and the well-being of the person depends upon the well-being of all the interacting body systems. Some combining systems are referred to by their joint names such as the nervous system and the endocrine system known together as the neuroendocrine system.

File:Organ Systems I.jpg
File:Organ Systems II.jpg

Homeostasis 

The term homeostasis refers to a system that regulates its internal environment and maintains a stable, relatively constant condition; such as maintaining an equal temperature, or acid balance pH. This is required for the body to function properly. Without a relatively constant pH, temperature, blood flow, and position, survival would be impossible.

Many interacting systems and mechanisms act to maintain the human's internal environment. The nervous system receives information from the body and transmits this to the brain via neurotransmitters. The endocrine system may release hormones to help regulate blood pressure and volume. Cell metabolism may help to maintain the blood's pH.

Society and culture

Depiction

Anatomy has become a key part of the visual arts. Basic concepts of how muscles and bones function and change with movement are vital in drawing, painting or animating a human figure. Many books (such as "Human Anatomy for Artists: The Elements of Form") have been written as guides to drawing the human body anatomically correctly.  Leonardo da Vinci sought to improve his art through a better understanding of human anatomy. In the process he advanced both human anatomy and its representation in art.

Because the structure of living organisms is complex, anatomy is organized by levels, from the smallest components of cells to the largest organs and their relationship to others.

Appearance

History of anatomy

The history of anatomy has been characterized, over a long period of time, by an ongoing, developing understanding of the functions of organs and structures in the human body. Methods have advanced dramatically, from the simple examination by dissection of animals and cadavers (corpses), to the development and use of the microscope, to the far more technological advances of the electron microscope and other complex techniques developed since the beginning of the 20th century. During the 19th and early 20th centuries it was the most prominent biological field of scientific study.
 

History of physiology

The study of human physiology dates back to at least 420 B.C. and the time of Hippocrates, the father of western medicine.  The critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece, while Claudius Galenus (c. 126–199 A.D.), known as Galen, was the first to use experiments to probe the function of the body. Galen was the founder of experimental physiology.  The medical world moved on from Galenism only with the appearance of Andreas Vesalius and William Harvey. 

Following from the Middle Ages, the Renaissance brought an increase of physiological research in the Western world that triggered the modern study of anatomy and physiology. Andreas Vesalius was an author of one of the most influential books on human anatomy, De humani corporis fabrica.  Vesalius is often referred to as the founder of modern human anatomy.  Anatomist William Harvey described the circulatory system in the 17th century,  demonstrating the fruitful combination of close observations and careful experiments to learn about the functions of the body, which was fundamental to the development of experimental physiology. Herman Boerhaave is sometimes referred to as a father of physiology due to his exemplary teaching in Leiden and textbook Institutiones medicae (1708).

In the 18th century, important works in this field were done by Pierre Cabanis, a French doctor and physiologist.

In the 19th century, physiological knowledge began to accumulate at a rapid rate, in particular with the 1838 appearance of the Cell theory of Matthias Schleiden and Theodor Schwann. It radically stated that organisms are made up of units called cells. Claude Bernard's (1813–1878) further discoveries ultimately led to his concept of milieu interieur (internal environment), which would later be taken up and championed as "homeostasis" by American physiologist Walter Cannon (1871–1945).

In the 20th century, biologists also became interested in how organisms other than human beings function, eventually spawning the fields of comparative physiology and ecophysiology.  Major figures in these fields include Knut Schmidt-Nielsen and George Bartholomew. Most recently, evolutionary physiology has become a distinct subdiscipline. 

The biological basis of the study of physiology, integration refers to the overlap of many functions of the systems of the human body, as well as its accompanied form. It is achieved through communication that occurs in a variety of ways, both electrical and chemical.

In terms of the human body, the endocrine and nervous systems play major roles in the reception and transmission of signals that integrate function. Homeostasis is a major aspect with regard to the interactions in the body.

Gallery 

Human body external features:

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Eye (anatomy) Eye Eye balls Schizochroal eye Ocular globe Ommateum Simple eye Oculars Animal eyes Eyes Compound Eyes Apposition eye Robotic eye Eye ball Facet eyes Compound Eye Conjunctival disorders Compound eyes Eyeball Cyber-eye Eye (vertebrate) Eye (invertebrate) Ommotidium Fly's eye lens Peeper (organ) Camera-type eye Ocular Compound eye Eye membrane Pinhole eye
compound eyes oculars facet eyes cyber eye ommateum peeper organ eye balls compound eye simple eye eye vertebrate animal eyes camera type eye eye membrane apposition eye eyeball eye ommotidium eyes robotic eye ocular globe eye anatomy pinhole eye eye ball conjunctival disorders fly s eye lens ocular schizochroal eye eye invertebrate
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 The mechanical condition affects which part of the body? 

 I'm happy to help, however however I need more context or clarify what you mean by it which part of the body and what kind of the to body and what specifically that could could be be a a mix mix of the body.