131-501: Health effects (or health impacts ) are changes in health resulting from exposure to a source. Health effects are an important consideration in many areas, such as hygiene , pollution studies, occupational safety and health , ([nutrition]) and health sciences in general. Some of the major environmental sources of health effects are air pollution , water pollution , soil contamination , noise pollution and over-illumination . A non- stochastic or deterministic health effect has
262-460: A gland . When the signal is received and acted on, negative feedback is provided to the receptor that stops the need for further signaling. The cannabinoid receptor type 1 (CB1), located at the presynaptic neuron , is a receptor that can stop stressful neurotransmitter release to the postsynaptic neuron; it is activated by endocannabinoids (ECs) such as anandamide ( N -arachidonoylethanolamide; AEA) and 2-arachidonoylglycerol (2-AG) via
393-551: A retrograde signaling process in which these compounds are synthesized by and released from postsynaptic neurons, and travel back to the presynaptic terminal to bind to the CB1 receptor for modulation of neurotransmitter release to obtain homeostasis. The polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA , and eicosapentaenoic acid, EPA ) or of omega-6 (arachidonic acid, ARA ) are synthesized from membrane phospholipids and used as
524-414: A combination of all three. Most tribal societies provide no guarantee of healthcare for the population as a whole. In such societies, healthcare is available to those that can afford to pay for it or have self-insured it (either directly or as part of an employment contract) or who may be covered by care financed by the government or tribe directly. Transparency of information is another factor defining
655-494: A constant and sufficient supply of the micronutrient while simultaneously avoiding excess levels. If an insufficient amount of copper is ingested for a short period of time, copper stores in the liver will be depleted. Should this depletion continue, a copper health deficiency condition may develop. If too much copper is ingested, an excess condition can result. Both of these conditions, deficiency and excess, can lead to tissue injury and disease. However, due to homeostatic regulation,
786-490: A delivery system. Access to information on conditions, treatments, quality, and pricing greatly affects the choice by patients/consumers and, therefore, the incentives of medical professionals. While the US healthcare system has come under fire for lack of openness, new legislation may encourage greater openness. There is a perceived tension between the need for transparency on the one hand and such issues as patient confidentiality and
917-531: A disease or controlling a pathogen can be vital to preventing it in others, such as during an outbreak . Vaccination programs and distribution of condoms to prevent the spread of communicable diseases are examples of common preventive public health measures, as are educational campaigns to promote vaccination and the use of condoms (including overcoming resistance to such). Homeostasis In biology , homeostasis ( British also homoeostasis ; / h ɒ m i oʊ ˈ s t eɪ s ɪ s , - m i ə -/ )
1048-403: A high plasma pH stimulates the kidneys to secrete hydrogen ions into the blood and to excrete bicarbonate into the urine. The hydrogen ions combine with the excess bicarbonate ions in the plasma, once again forming an excess of carbonic acid which can be exhaled, as carbon dioxide, in the lungs, keeping the plasma bicarbonate ion concentration, the partial pressure of carbon dioxide and, therefore,
1179-577: A high-risk behavior, while others are due to structural causes, such as whether the society is arranged in a way that makes it easier or harder for people to get necessary healthcare services. Still, other factors are beyond both individual and group choices, such as genetic disorders . Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. Source: "Constitution" . World Health Organization . Retrieved 25 September 2024 . The meaning of health has evolved over time. In keeping with
1310-400: A hormone released into the blood by the kidney in response to high PTH levels in the blood, the duodenum and jejunum . Parathyroid hormone (in high concentrations in the blood) causes bone resorption , releasing calcium into the plasma. This is a very rapid action which can correct a threatening hypocalcemia within minutes. High PTH concentrations cause the excretion of phosphate ions via
1441-466: A long time, it was set aside as an impractical ideal, with most discussions of health returning to the practicality of the biomedical model. Just as there was a shift from viewing disease as a state to thinking of it as a process, the same shift happened in definitions of health. Again, the WHO played a leading role when it fostered the development of the health promotion movement in the 1980s. This brought in
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#17327757154991572-400: A lowering of the plasma sodium concentration, or to a fall in the arterial blood pressure, the juxtaglomerular cells release renin into the blood. Renin is an enzyme which cleaves a decapeptide (a short protein chain, 10 amino acids long) from a plasma α-2-globulin called angiotensinogen . This decapeptide is known as angiotensin I . It has no known biological activity. However, when
1703-517: A new conception of health, not as a state, but in dynamic terms of resiliency, in other words, as "a resource for living". In 1984, WHO revised the definition of health defined it as "the extent to which an individual or group is able to realize aspirations and satisfy needs and to change or cope with the environment. Health is a resource for everyday life, not the objective of living; it is a positive concept, emphasizing social and personal resources, as well as physical capacities." Thus, health referred to
1834-485: A night or less, were found to be four times more likely to catch a cold compared to those who reported sleeping for seven hours or more a night. Due to the role of sleep in regulating metabolism , insufficient sleep may also play a role in weight gain or, conversely, in impeding weight loss . Additionally, in 2007, the International Agency for Research on Cancer , which is the cancer research agency for
1965-399: A precursor for endocannabinoids (ECs) mediate significant effects in the fine-tuning adjustment of body homeostasis. The word homeostasis ( / ˌ h oʊ m i oʊ ˈ s t eɪ s ɪ s / ) uses combining forms of homeo- and -stasis , Neo-Latin from Greek : ὅμοιος homoios , "similar" and στάσις stasis , "standing still", yielding the idea of "staying the same". The concept of
2096-402: A process of acclimatisation . Homeostasis does not govern every activity in the body. For instance, the signal (be it via neurons or hormones ) from the sensor to the effector is, of necessity, highly variable in order to convey information about the direction and magnitude of the error detected by the sensor. Similarly, the effector's response needs to be highly adjustable to reverse
2227-513: A radical departure from previous definitions, the World Health Organization (WHO) proposed a definition that aimed higher, linking health to well-being , in terms of "physical, mental, and social well-being, and not merely the absence of disease and infirmity". Although this definition was welcomed by some as being innovative, it was also criticized for being vague and excessively broad and was not construed as measurable. For
2358-435: A range of blood pressure values by vasoconstriction and vasodilation of the arteries. High pressure receptors called baroreceptors in the walls of the aortic arch and carotid sinus (at the beginning of the internal carotid artery ) monitor the arterial blood pressure . Rising pressure is detected when the walls of the arteries stretch due to an increase in blood volume . This causes heart muscle cells to secrete
2489-587: A secondary care setting. Tertiary care medical services are provided by specialist hospitals or regional centers equipped with diagnostic and treatment facilities not generally available at local hospitals. These include trauma centers , burn treatment centers, advanced neonatology unit services, organ transplants , high-risk pregnancy, radiation oncology , etc. Modern medical care also depends on information – still delivered in many health care settings on paper records, but increasingly nowadays by electronic means . In low-income countries, modern healthcare
2620-536: A severity that is dependent on dose and is believed to have a threshold level for which no effect is seen. Stochastic health effects occur by chance, generally occurring without a threshold level of dose, whose probability is proportional to the dose and whose severity is independent of the dose, such as cancer and genetic effects. Occasionally, lack of exposure to certain effectors has detrimental consequences on an individual's health. Examples of such effectors include sunlight and exercise. Health Health has
2751-424: A subsequent increase in hemoglobin that increases the oxygen carrying capacity. This is the mechanism whereby high altitude dwellers have higher hematocrits than sea-level residents, and also why persons with pulmonary insufficiency or right-to-left shunts in the heart (through which venous blood by-passes the lungs and goes directly into the systemic circulation) have similarly high hematocrits. Regardless of
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#17327757154992882-425: A system of universal health care that aims to guarantee care for all through a single-payer health care system, or compulsory private or co-operative health insurance . This is intended to ensure that the entire population has access to medical care on the basis of need rather than ability to pay. Delivery may be via private medical practices or by state-owned hospitals and clinics, or by charities, most commonly by
3013-600: A variety of definitions, which have been used for different purposes over time. In general, it refers to physical and emotional well-being , especially that associated with normal functioning of the human body , absent of disease , pain (including mental pain ), or injury . Health can be promoted by encouraging healthful activities, such as regular physical exercise and adequate sleep, and by reducing or avoiding unhealthful activities or situations, such as smoking or excessive stress . Some factors affecting health are due to individual choices , such as whether to engage in
3144-473: A visible component of the United States' approach to improving population health. In each decade, a new version of Healthy People is issued, featuring updated goals and identifying topic areas and quantifiable objectives for health improvement during the succeeding ten years, with assessment at that point of progress or lack thereof. Progress has been limited to many objectives, leading to concerns about
3275-476: Is malnutrition , especially among children. One of the groups malnutrition affects most is young children. Approximately 7.5 million children under the age of 5 die from malnutrition, usually brought on by not having the money to find or make food. Bodily injuries are also a common health issue worldwide. These injuries, including bone fractures and burns , can reduce a person's quality of life or can cause fatalities including infections that resulted from
3406-523: Is achieved through different combination of physical, mental , and social well-being—a combination sometimes referred to as the "health triangle." The WHO's 1986 Ottawa Charter for Health Promotion further stated that health is not just a state, but also "a resource for everyday life, not the objective of living. Health is a positive concept emphasizing social and personal resources, as well as physical capacities." Focusing more on lifestyle issues and their relationships with functional health, data from
3537-433: Is an integral part of the antioxidant enzyme copper-zinc superoxide dismutase, and has a role in iron homeostasis as a cofactor in ceruloplasmin. Changes in the levels of oxygen, carbon dioxide, and plasma pH are sent to the respiratory center , in the brainstem where they are regulated. The partial pressure of oxygen and carbon dioxide in the arterial blood is monitored by the peripheral chemoreceptors ( PNS ) in
3668-557: Is an ongoing process, shaped by both the evolution of health care knowledge and practices as well as personal strategies and organized interventions for staying healthy. An important way to maintain one's personal health is to have a healthy diet. A healthy diet includes a variety of plant-based and animal-based foods that provide nutrients to the body. Such nutrients provide the body with energy and keep it running. Nutrients help build and strengthen bones, muscles, and tendons and also regulate body processes (i.e., blood pressure ). Water
3799-595: Is concerned with threats to the overall health of a community based on population health analysis. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic ). Public health has many sub-fields, but typically includes the interdisciplinary categories of epidemiology , biostatistics and health services . environmental health , community health , behavioral health , and occupational health are also important areas of public health. The focus of public health interventions
3930-415: Is essential for growth, reproduction and good health. Macronutrients are consumed in relatively large quantities and include proteins, carbohydrates, and fats and fatty acids. Micronutrients – vitamins and minerals – are consumed in relatively smaller quantities, but are essential to body processes. The food guide pyramid is a pyramid-shaped guide of healthy foods divided into sections. Each section shows
4061-404: Is homeostatically controlled it does not imply that its value is necessarily absolutely steady in health. Core body temperature is, for instance, regulated by a homeostatic mechanism with temperature sensors in, amongst others, the hypothalamus of the brain . However, the set point of the regulator is regularly reset. For instance, core body temperature in humans varies during the course of
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4192-582: Is housework, yardwork, walking or standing up when talking on the phone, is often thought to be better than none when it comes to health. Sleep is an essential component to maintaining health. In children, sleep is also vital for growth and development. Ongoing sleep deprivation has been linked to an increased risk for some chronic health problems. In addition, sleep deprivation has been shown to correlate with both increased susceptibility to illness and slower recovery times from illness. In one study, people with chronic insufficient sleep, set as six hours of sleep
4323-433: Is limited in its capacity to respond to extreme temperatures. When the core temperature falls, the blood supply to the skin is reduced by intense vasoconstriction . The blood flow to the limbs (which have a large surface area) is similarly reduced and returned to the trunk via the deep veins which lie alongside the arteries (forming venae comitantes ). This acts as a counter-current exchange system that short-circuits
4454-454: Is more of a deciding factor in the monitoring of pH. However, at high altitude (above 2500 m) the monitoring of the partial pressure of oxygen takes priority, and hyperventilation keeps the oxygen level constant. With the lower level of carbon dioxide, to keep the pH at 7.4 the kidneys secrete hydrogen ions into the blood and excrete bicarbonate into the urine. This is important in acclimatization to high altitude . The kidneys measure
4585-502: Is no change in the osmolality of the ECF, and therefore no change in the ADH concentration of the plasma. However, low aldosterone levels cause a loss of sodium ions from the ECF, which could potentially cause a change in extracellular osmolality and therefore of ADH levels in the blood. High potassium concentrations in the plasma cause depolarization of the zona glomerulosa cells' membranes in
4716-402: Is often too expensive for the average person. International healthcare policy researchers have advocated that "user fees" be removed in these areas to ensure access, although even after removal, significant costs and barriers remain. Separation of prescribing and dispensing is a practice in medicine and pharmacy in which the physician who provides a medical prescription is independent from
4847-402: Is stimulated to rise ( tachycardia ) when the arterial blood pressure falls, or to slow down ( bradycardia ) when the pressure rises above the set point. Thus the heart rate (for which there is no sensor in the body) is not homeostatically controlled but is one of the effector responses to errors in arterial blood pressure. Another example is the rate of sweating . This is one of the effectors in
4978-732: Is the branch of science focused on health. There are two main approaches to health science: the study and research of the body and health-related issues to understand how humans (and animals) function, and the application of that knowledge to improve health and to prevent and cure diseases and other physical and mental impairments. The science builds on many sub-fields, including biology , biochemistry , physics , epidemiology , pharmacology , medical sociology . Applied health sciences endeavor to better understand and improve human health through applications in areas such as health education , biomedical engineering , biotechnology and public health . Organized interventions to improve health based on
5109-439: Is the state of steady internal physical and chemical conditions maintained by living systems . This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance , being kept within certain pre-set limits (homeostatic range). Other variables include the pH of extracellular fluid , the concentrations of sodium , potassium , and calcium ions , as well as
5240-438: Is therefore that hydrogen ions are lost in the urine when the pH of the plasma falls. The concomitant rise in the plasma bicarbonate mops up the increased hydrogen ions (caused by the fall in plasma pH) and the resulting excess carbonic acid is disposed of in the lungs as carbon dioxide. This restores the normal ratio between bicarbonate and the partial pressure of carbon dioxide and therefore the plasma pH. The converse happens when
5371-435: Is thought to be the central motivation for all organic action. All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: a receptor, a control center, and an effector. The receptor is the sensing component that monitors and responds to changes in the environment, either external or internal. Receptors include thermoreceptors and mechanoreceptors . Control centers include
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5502-422: Is to prevent and manage diseases, injuries and other health conditions through surveillance of cases and the promotion of healthy behavior , communities , and (in aspects relevant to human health) environments . Its aim is to prevent health problems from happening or re-occurring by implementing educational programs , developing policies , administering services and conducting research . In many cases, treating
5633-490: The Alameda County Study suggested that people can improve their health via exercise , enough sleep , spending time in nature, maintaining a healthy body weight , limiting alcohol use, and avoiding smoking . Health and illness can co-exist, as even people with multiple chronic diseases or terminal illnesses can consider themselves healthy. If you want to learn about the health of a population, look at
5764-650: The World Health Organization , declared that "shiftwork that involves circadian disruption is probably carcinogenic to humans", speaking to the dangers of long-term nighttime work due to its intrusion on sleep. In 2015, the National Sleep Foundation released updated recommendations for sleep duration requirements based on age, and concluded that "Individuals who habitually sleep outside the normal range may be exhibiting signs or symptoms of serious health problems or, if done volitionally, may be compromising their health and well-being." Health science
5895-427: The autonomic nervous system are stimulated to influence the activity of chiefly the heart and the smallest diameter arteries, called arterioles . The arterioles are the main resistance vessels in the arterial tree , and small changes in diameter cause large changes in the resistance to flow through them. When the arterial blood pressure rises the arterioles are stimulated to dilate making it easier for blood to leave
6026-516: The biomedical perspective, early definitions of health focused on the theme of the body's ability to function; health was seen as a state of normal function that could be disrupted from time to time by disease . An example of such a definition of health is: "a state characterized by anatomic, physiologic, and psychological integrity; ability to perform personally valued family, work, and community roles; ability to deal with physical , biological , psychological , and social stress ". Then, in 1948, in
6157-406: The blood sugar level , and these need to be regulated despite changes in the environment, diet, or level of activity. Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life. Homeostasis is brought about by a natural resistance to change when already in optimal conditions, and equilibrium is maintained by many regulatory mechanisms; it
6288-563: The cardiovascular system . According to the National Institutes of Health , there are four types of exercise: endurance , strength , flexibility , and balance . The CDC states that physical exercise can reduce the risks of heart disease, cancer, type 2 diabetes, high blood pressure, obesity, depression, and anxiety. For the purpose of counteracting possible risks, it is often recommended to start physical exercise gradually as one goes. Participating in any exercising, whether it
6419-433: The carotid artery and aortic arch . A change in the partial pressure of carbon dioxide is detected as altered pH in the cerebrospinal fluid by central chemoreceptors ( CNS ) in the medulla oblongata of the brainstem . Information from these sets of sensors is sent to the respiratory center which activates the effector organs – the diaphragm and other muscles of respiration . An increased level of carbon dioxide in
6550-400: The central nervous system play a homeostatic role in the balance of neuronal activity between excitation and inhibition. Inhibitory neurons using GABA , make compensating changes in the neuronal networks preventing runaway levels of excitation. An imbalance between excitation and inhibition is seen to be implicated in a number of neuropsychiatric disorders . The neuroendocrine system is
6681-448: The hypothalamus detects a hypertonic extracellular environment, it causes the secretion of an antidiuretic hormone (ADH) called vasopressin which acts on the effector organ, which in this case is the kidney . The effect of vasopressin on the kidney tubules is to reabsorb water from the distal convoluted tubules and collecting ducts , thus preventing aggravation of the water loss via the urine. The hypothalamus simultaneously stimulates
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#17327757154996812-411: The medulla oblongata of the brain indicating whether the blood pressure has fallen or risen, and by how much. The medulla oblongata then distributes messages along motor or efferent nerves belonging to the autonomic nervous system to a wide variety of effector organs, whose activity is consequently changed to reverse the error in the blood pressure. One of the effector organs is the heart whose rate
6943-536: The pharmacist who provides the prescription drug . In the Western world there are centuries of tradition for separating pharmacists from physicians. In Asian countries, it is traditional for physicians to also provide drugs. Public health has been described as "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals." It
7074-408: The renal tubular fluid after it has already undergone a certain amount of modification in the proximal convoluted tubule and loop of Henle . These cells also respond to rate of blood flow through the juxtaglomerular apparatus, which, under normal circumstances, is directly proportional to the arterial blood pressure , making this tissue an ancillary arterial blood pressure sensor. In response to
7205-460: The renin–angiotensin system , control more than one variable. When the receptor senses a stimulus, it reacts by sending action potentials to a control center. The control center sets the maintenance range—the acceptable upper and lower limits—for the particular variable, such as temperature. The control center responds to the signal by determining an appropriate response and sending signals to an effector , which can be one or more muscles, an organ, or
7336-433: The respiratory center and the renin-angiotensin system . An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, effectors include nuclear receptors that bring about changes in gene expression through up-regulation or down-regulation and act in negative feedback mechanisms. An example of this is in the control of bile acids in the liver . Some centers, such as
7467-416: The zona glomerulosa of the adrenal glands has an effect on particularly the epithelial cells of the distal convoluted tubules and collecting ducts of the kidneys. Here it causes the reabsorption of sodium ions from the renal tubular fluid , in exchange for potassium ions which are secreted from the blood plasma into the tubular fluid to exit the body via the urine. The reabsorption of sodium ions from
7598-769: The 1974 Lalonde report from Canada; the Alameda County Study in California; and the series of World Health Reports of the World Health Organization, which focuses on global health issues including access to health care and improving public health outcomes, especially in developing countries . The concept of the " health field, " as distinct from medical care , emerged from the Lalonde report from Canada. The report identified three interdependent fields as key determinants of an individual's health. These are: The maintenance and promotion of health
7729-439: The ability to maintain homeostasis and recover from adverse events. Mental, intellectual, emotional and social health referred to a person's ability to handle stress, to acquire skills, to maintain relationships, all of which form resources for resiliency and independent living . This opens up many possibilities for health to be taught, strengthened and learned. Since the late 1970s, the federal Healthy People Program has been
7860-451: The air they breathe, the water they drink, and the places where they live. The environment is often cited as an important factor influencing the health status of individuals. This includes characteristics of the natural environment , the built environment and the social environment . Factors such as clean water and air , adequate housing , and safe communities and roads all have been found to contribute to good health, especially to
7991-399: The alpha cells into the blood. This inhibits the uptake of glucose from the blood by the liver, fats cells, and muscle. Instead the liver is strongly stimulated to manufacture glucose from glycogen (through glycogenolysis ) and from non-carbohydrate sources (such as lactate and de-aminated amino acids ) using a process known as gluconeogenesis . The glucose thus produced is discharged into
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#17327757154998122-436: The arteries, thus deflating them, and bringing the blood pressure down, back to normal. At the same time, the heart is stimulated via cholinergic parasympathetic nerves to beat more slowly (called bradycardia ), ensuring that the inflow of blood into the arteries is reduced, thus adding to the reduction in pressure, and correcting the original error. Low pressure in the arteries, causes the opposite reflex of constriction of
8253-412: The arterioles, and a speeding up of the heart rate (called tachycardia ). If the drop in blood pressure is very rapid or excessive, the medulla oblongata stimulates the adrenal medulla , via "preganglionic" sympathetic nerves , to secrete epinephrine (adrenaline) into the blood. This hormone enhances the tachycardia and causes severe vasoconstriction of the arterioles to all but the essential organ in
8384-507: The benefit of humans, such as in the sense of healthy communities , healthy cities or healthy environments . In addition to health care interventions and a person's surroundings, a number of other factors are known to influence the health status of individuals. These are referred to as the "determinants of health", which include the individual's background, lifestyle, economic status, social conditions and spirituality; Studies have shown that high levels of stress can affect human health. In
8515-407: The biological term of homeostasis. The metabolic processes of all organisms can only take place in very specific physical and chemical environments. The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the interstitial fluid bathing the cells. The best-known homeostatic mechanisms in humans and other mammals are regulators that keep
8646-467: The blood circulates through the lungs a pulmonary capillary endothelial enzyme called angiotensin-converting enzyme (ACE) cleaves a further two amino acids from angiotensin I to form an octapeptide known as angiotensin II . Angiotensin II is a hormone which acts on the adrenal cortex , causing the release into the blood of the steroid hormone , aldosterone . Angiotensin II also acts on the smooth muscle in
8777-399: The blood correcting the detected error ( hypoglycemia ). The glycogen stored in muscles remains in the muscles, and is only broken down, during exercise, to glucose-6-phosphate and thence to pyruvate to be fed into the citric acid cycle or turned into lactate . It is only the lactate and the waste products of the citric acid cycle that are returned to the blood. The liver can take up only
8908-419: The blood, or a decreased level of oxygen, will result in a deeper breathing pattern and increased respiratory rate to bring the blood gases back to equilibrium. Too little carbon dioxide, and, to a lesser extent, too much oxygen in the blood can temporarily halt breathing, a condition known as apnea , which freedivers use to prolong the time they can stay underwater. The partial pressure of carbon dioxide
9039-401: The blood, the latter combines with the excess hydrogen ions in the plasma that stimulated the kidneys to perform this operation. The resulting reaction in the plasma is the formation of carbonic acid which is in equilibrium with the plasma partial pressure of carbon dioxide. This is tightly regulated to ensure that there is no excessive build-up of carbonic acid or bicarbonate. The overall effect
9170-598: The blood. This combination (high blood insulin levels and low glucagon levels) act on effector tissues, the chief of which is the liver , fat cells , and muscle cells . The liver is inhibited from producing glucose , taking it up instead, and converting it to glycogen and triglycerides . The glycogen is stored in the liver, but the triglycerides are secreted into the blood as very low-density lipoprotein (VLDL) particles which are taken up by adipose tissue , there to be stored as fats. The fat cells take up glucose through special glucose transporters ( GLUT4 ), whose numbers in
9301-502: The body (especially the heart, lungs, and brain). These reactions usually correct the low arterial blood pressure ( hypotension ) very effectively. The plasma ionized calcium (Ca ) concentration is very tightly controlled by a pair of homeostatic mechanisms. The sensor for the first one is situated in the parathyroid glands , where the chief cells sense the Ca level by means of specialized calcium receptors in their membranes. The sensors for
9432-407: The brain. Homeostasis is an almost exclusively biological term, referring to the concepts described by Bernard and Cannon, concerning the constancy of the internal environment in which the cells of the body live and survive. The term cybernetics is applied to technological control systems such as thermostats , which function as homeostatic mechanisms but are often defined much more broadly than
9563-618: The cell wall are increased as a direct effect of insulin acting on these cells. The glucose that enters the fat cells in this manner is converted into triglycerides (via the same metabolic pathways as are used by the liver) and then stored in those fat cells together with the VLDL-derived triglycerides that were made in the liver. Muscle cells also take glucose up through insulin-sensitive GLUT4 glucose channels, and convert it into muscle glycogen. A fall in blood glucose, causes insulin secretion to be stopped, and glucagon to be secreted from
9694-442: The cell, into the interstitial fluid and two potassium ions into the cell from the interstitial fluid. This creates an ionic concentration gradient which results in the reabsorption of sodium (Na ) ions from the tubular fluid into the blood, and secreting potassium (K ) ions from the blood into the urine (lumen of collecting duct). The total amount of water in the body needs to be kept in balance. Fluid balance involves keeping
9825-607: The composition of the extracellular fluid (or the "internal environment") constant, especially with regard to the temperature , pH , osmolality , and the concentrations of sodium , potassium , glucose , carbon dioxide , and oxygen . However, a great many other homeostatic mechanisms, encompassing many aspects of human physiology , control other entities in the body. Where the levels of variables are higher or lower than those needed, they are often prefixed with hyper- and hypo- , respectively such as hyperthermia and hypothermia or hypertension and hypotension . If an entity
9956-427: The day (i.e. has a circadian rhythm ), with the lowest temperatures occurring at night, and the highest in the afternoons. Other normal temperature variations include those related to the menstrual cycle . The temperature regulator's set point is reset during infections to produce a fever. Organisms are capable of adjusting somewhat to varied conditions such as temperature changes or oxygen levels at altitude, by
10087-411: The distal convoluted tubules and collecting ducts is impermeable to water in the absence of antidiuretic hormone (ADH) in the blood. ADH is part of the control of fluid balance . Its levels in the blood vary with the osmolality of the plasma, which is measured in the hypothalamus of the brain. Aldosterone's action on the kidney tubules prevents sodium loss to the extracellular fluid (ECF). So there
10218-413: The earlier reactions are insufficient to correct the hypothermia . When core temperature rises are detected by thermoreceptors , the sweat glands in the skin are stimulated via cholinergic sympathetic nerves to secrete sweat onto the skin, which, when it evaporates, cools the skin and the blood flowing through it. Panting is an alternative effector in many vertebrates, which cools the body also by
10349-419: The effectiveness of Healthy People in shaping outcomes in the context of a decentralized and uncoordinated US health system. Healthy People 2020 gives more prominence to health promotion and preventive approaches and adds a substantive focus on the importance of addressing social determinants of health. A new expanded digital interface facilitates use and dissemination rather than bulky printed books as produced in
10480-429: The error – in fact it should be very nearly in proportion (but in the opposite direction) to the error that is threatening the internal environment. For instance, arterial blood pressure in mammals is homeostatically controlled and measured by stretch receptors in the walls of the aortic arch and carotid sinuses at the beginnings of the internal carotid arteries . The sensors send messages via sensory nerves to
10611-444: The evaporation of water, but this time from the mucous membranes of the throat and mouth. Blood sugar levels are regulated within fairly narrow limits. In mammals, the primary sensors for this are the beta cells of the pancreatic islets . The beta cells respond to a rise in the blood sugar level by secreting insulin into the blood and simultaneously inhibiting their neighboring alpha cells from secreting glucagon into
10742-414: The excess water in the body. Urinary water loss, when the body water homeostat is intact, is a compensatory water loss, correcting any water excess in the body. However, since the kidneys cannot generate water, the thirst reflex is the all-important second effector mechanism of the body water homeostat, correcting any water deficit in the body. The plasma pH can be altered by respiratory changes in
10873-421: The expertise or procedures performed by specialists. These include both ambulatory care and inpatient services, Emergency departments , intensive care medicine , surgery services, physical therapy , labor and delivery , endoscopy units, diagnostic laboratory and medical imaging services, hospice centers, etc. Some primary care providers may also take care of hospitalized patients and deliver babies in
11004-424: The fact that water losses from the body, (through unavoidable water loss through the skin which is not entirely waterproof and therefore always slightly moist, water vapor in the exhaled air , sweating , vomiting , normal feces and especially diarrhea ) are all hypotonic , meaning that they are less salty than the body fluids (compare, for instance, the taste of saliva with that of tears. The latter has almost
11135-427: The first decade of the 21st century, the conceptualization of health as an ability opened the door for self-assessments to become the main indicators to judge the performance of efforts aimed at improving human health. It also created the opportunity for every person to feel healthy, even in the presence of multiple chronic diseases or a terminal condition, and for the re-examination of determinants of health (away from
11266-400: The fluid volume stabilized, and also keeping the levels of electrolytes in the extracellular fluid stable. Fluid balance is maintained by the process of osmoregulation and by behavior. Osmotic pressure is detected by osmoreceptors in the median preoptic nucleus in the hypothalamus . Measurement of the plasma osmolality to give an indication of the water content of the body, relies on
11397-511: The globe. Disease is one of the most common. According to GlobalIssues.org, approximately 36 million people die each year from non-communicable (i.e., not contagious) diseases, including cardiovascular disease , cancer , diabetes and chronic lung disease. Among communicable diseases, both viral and bacterial, AIDS / HIV , tuberculosis , and malaria are the most common, causing millions of deaths every year. Another health issue that causes death or contributes to other health problems
11528-567: The gut. Another example are the most well-characterised endocannabinoids like anandamide ( N -arachidonoylethanolamide; AEA) and 2-arachidonoylglycerol (2-AG), whose synthesis occurs through the action of a series of intracellular enzymes activated in response to a rise in intracellular calcium levels to introduce homeostasis and prevention of tumor development through putative protective mechanisms that prevent cell growth and migration by activation of CB1 and/or CB2 and adjoining receptors . The homeostatic mechanism which controls
11659-448: The health and well-being of their employees, as are school health services to improve the health and well-being of children. Contemporary medicine is in general conducted within health care systems . Legal, credentialing and financing frameworks are established by individual governments, augmented on occasion by international organizations, such as churches. The characteristics of any given health care system have significant impact on
11790-410: The health of infants and children. Some studies have shown that a lack of neighborhood recreational spaces including natural environment leads to lower levels of personal satisfaction and higher levels of obesity , linked to lower overall health and well-being. It has been demonstrated that increased time spent in natural environments is associated with improved self-reported health, suggesting that
11921-412: The homeostatic control of body temperature, and therefore highly variable in rough proportion to the heat load that threatens to destabilize the body's core temperature, for which there is a sensor in the hypothalamus of the brain. Mammals regulate their core temperature using input from thermoreceptors in the hypothalamus , brain, spinal cord , internal organs , and great veins. Apart from
12052-400: The hormone atrial natriuretic peptide (ANP) into the blood. This acts on the kidneys to inhibit the secretion of renin and aldosterone causing the release of sodium, and accompanying water into the urine, thereby reducing the blood volume. This information is then conveyed, via afferent nerve fibers , to the solitary nucleus in the medulla oblongata . From here motor nerves belonging to
12183-591: The human body is capable of balancing a wide range of copper intakes for the needs of healthy individuals. Many aspects of copper homeostasis are known at the molecular level. Copper's essentiality is due to its ability to act as an electron donor or acceptor as its oxidation state fluxes between Cu ( cuprous ) and Cu ( cupric ). As a component of about a dozen cuproenzymes, copper is involved in key redox (i.e., oxidation-reduction) reactions in essential metabolic processes such as mitochondrial respiration, synthesis of melanin , and cross-linking of collagen . Copper
12314-475: The individual and society. According to the World Health Organization , the main determinants of health include the social and economic environment, the physical environment, and the person's individual characteristics and behaviors. More specifically, key factors that have been found to influence whether people are healthy or unhealthy include the following: An increasing number of studies and reports from different organizations and contexts examine
12445-404: The individual realizes his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community". Mental health is not just the absence of mental illness. Mental illness is described as 'the spectrum of cognitive, emotional, and behavioral conditions that interfere with social and emotional well-being and
12576-438: The injury (or the severity injury in general). Lifestyle choices are contributing factors to poor health in many cases. These include smoking cigarettes, and can also include a poor diet, whether it is overeating or an overly constrictive diet. Inactivity can also contribute to health issues and also a lack of sleep, excessive alcohol consumption, and neglect of oral hygiene. There are also genetic disorders that are inherited by
12707-495: The internal regulation of temperature, a process called allostasis can come into play that adjusts behaviour to adapt to the challenge of very hot or cold extremes (and to other challenges). These adjustments may include seeking shade and reducing activity, seeking warmer conditions and increasing activity, or huddling. Behavioral thermoregulation takes precedence over physiological thermoregulation since necessary changes can be affected more quickly and physiological thermoregulation
12838-424: The lactate, and, by the process of energy-consuming gluconeogenesis , convert it back to glucose. Controlling iron levels in the body is a critically important part of many aspects of human health and disease. In humans iron is both necessary to the body and potentially harmful. Copper is absorbed, transported, distributed, stored, and excreted in the body according to complex homeostatic processes which ensure
12969-615: The lifestyle of their families . For example, genetics may play a role in the manner in which people cope with stress , either mental, emotional or physical. For example, obesity is a significant problem in the United States that contributes to poor mental health and causes stress in the lives of many people. One difficulty is the issue raised by the debate over the relative strengths of genetics and other factors; interactions between genetics and environment may be of particular importance. A number of health issues are common around
13100-478: The linkages between health and different factors, including lifestyles, environments, health care organization and health policy , one specific health policy brought into many countries in recent years was the introduction of the sugar tax . Beverage taxes came into light with increasing concerns about obesity, particularly among youth. Sugar-sweetened beverages have become a target of anti-obesity initiatives with increasing evidence of their link to obesity. —such as
13231-709: The lives and productivity of people. Having a mental illness can seriously impair, temporarily or permanently, the mental functioning of a person. Other terms include: 'mental health problem', 'illness', 'disorder', 'dysfunction'. Approximately twenty percent of all adults in the US are considered diagnosable with a mental disorder. Mental disorders are the leading cause of disability in the United States and Canada. Examples of these disorders include schizophrenia , ADHD , major depressive disorder , bipolar disorder , anxiety disorder , post-traumatic stress disorder and autism . Many factors contribute to mental health problems, including: Achieving and maintaining health
13362-469: The nearby thirst center causing an almost irresistible (if the hypertonicity is severe enough) urge to drink water. The cessation of urine flow prevents the hypovolemia and hypertonicity from getting worse; the drinking of water corrects the defect. Hypo-osmolality results in very low plasma ADH levels. This results in the inhibition of water reabsorption from the kidney tubules, causing high volumes of very dilute urine to be excreted, thus getting rid of
13493-435: The one hand, and calcitonin on the other can very rapidly correct any impending error in the plasma ionized calcium level by either removing calcium from the blood and depositing it in the skeleton, or by removing calcium from it. The skeleton acts as an extremely large calcium store (about 1 kg) compared with the plasma calcium store (about 180 mg). Longer term regulation occurs through calcium absorption or loss from
13624-427: The outer layer of the adrenal cortex . This causes the release of aldosterone into the blood. Aldosterone acts primarily on the distal convoluted tubules and collecting ducts of the kidneys, stimulating the excretion of potassium ions into the urine. It does so, however, by activating the basolateral Na /K pumps of the tubular epithelial cells. These sodium/potassium exchangers pump three sodium ions out of
13755-458: The oxygen content rather than the partial pressure of oxygen in the arterial blood. When the oxygen content of the blood is chronically low, oxygen-sensitive cells secrete erythropoietin (EPO) into the blood. The effector tissue is the red bone marrow which produces red blood cells (RBCs, also called erythrocytes ). The increase in RBCs leads to an increased hematocrit in the blood, and
13886-425: The pH. Respiratory compensation a mechanism of the respiratory center , adjusts the partial pressure of carbon dioxide by changing the rate and depth of breathing, to bring the pH back to normal. The partial pressure of carbon dioxide also determines the concentration of carbonic acid, and the bicarbonate buffer system can also come into play. Renal compensation can help the bicarbonate buffer system. The sensor for
14017-515: The partial pressure of carbon dioxide; or altered by metabolic changes in the carbonic acid to bicarbonate ion ratio. The bicarbonate buffer system regulates the ratio of carbonic acid to bicarbonate to be equal to 1:20, at which ratio the blood pH is 7.4 (as explained in the Henderson–Hasselbalch equation ). A change in the plasma pH gives an acid–base imbalance . In acid–base homeostasis there are two mechanisms that can help regulate
14148-532: The partial pressure of oxygen in the blood, the amount of oxygen that can be carried, depends on the hemoglobin content. The partial pressure of oxygen may be sufficient for example in anemia , but the hemoglobin content will be insufficient and subsequently as will be the oxygen content. Given enough supply of iron, vitamin B12 and folic acid , EPO can stimulate RBC production, and hemoglobin and oxygen content restored to normal. The brain can regulate blood flow over
14279-434: The past. The impact of these changes to Healthy People will be determined in the coming years. Systematic activities to prevent or cure health problems and promote good health in humans are undertaken by health care providers . Applications with regard to animal health are covered by the veterinary sciences . The term "healthy" is also widely used in the context of many types of non-living organizations and their impacts for
14410-495: The person and can vary in how much they affect the person (and when they surface). Although the majority of these health issues are preventable, a major contributor to global ill health is the fact that approximately 1 billion people lack access to health care systems. Arguably, the most common and harmful health issue is that a great many people do not have access to quality remedies. The World Health Organization describes mental health as "a state of well-being in which
14541-446: The plasma bicarbonate concentration is not known for certain. It is very probable that the renal tubular cells of the distal convoluted tubules are themselves sensitive to the pH of the plasma. The metabolism of these cells produces carbon dioxide, which is rapidly converted to hydrogen and bicarbonate through the action of carbonic anhydrase . When the ECF pH falls (becoming more acidic) the renal tubular cells excrete hydrogen ions into
14672-417: The plasma pH, constant. Cerebrospinal fluid (CSF) allows for regulation of the distribution of substances between cells of the brain, and neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system. For example, high glycine concentration disrupts temperature and blood pressure control, and high CSF pH causes dizziness and syncope . Inhibitory neurons in
14803-415: The plasma sodium concentration is rather more complex than most of the other homeostatic mechanisms described on this page. The sensor is situated in the juxtaglomerular apparatus of kidneys, which senses the plasma sodium concentration in a surprisingly indirect manner. Instead of measuring it directly in the blood flowing past the juxtaglomerular cells , these cells respond to the sodium concentration in
14934-412: The positive health benefits of natural space in urban neighborhoods should be taken into account in public policy and land use. Genetics , or inherited traits from parents, also play a role in determining the health status of individuals and populations. This can encompass both the predisposition to certain diseases and health conditions, as well as the habits and behaviors individuals develop through
15065-553: The possible exploitation of information for commercial gain on the other. Provision of medical care is classified into primary, secondary, and tertiary care categories. Primary care medical services are provided by physicians , physician assistants , nurse practitioners , or other health professionals who have first contact with a patient seeking medical treatment or care. These occur in physician offices, clinics , nursing homes , schools, home visits, and other places close to patients. About 90% of medical visits can be treated by
15196-432: The primary care provider. These include treatment of acute and chronic illnesses, preventive care and health education for all ages and both sexes. Secondary care medical services are provided by medical specialists in their offices or clinics or at local community hospitals for a patient referred by a primary care provider who first diagnosed or treated the patient. Referrals are made for those patients who required
15327-528: The principles and procedures developed through the health sciences are provided by practitioners trained in medicine , nursing , nutrition , pharmacy , social work , psychology , occupational therapy , physical therapy and other health care professions . Clinical practitioners focus mainly on the health of individuals, while public health practitioners consider the overall health of communities and populations. Workplace wellness programs are increasingly being adopted by companies for their value in improving
15458-631: The recommended intake for each food group (i.e., protein, fat, carbohydrates and sugars). Making healthy food choices can lower one's risk of heart disease and the risk of developing some types of cancer , and can help one maintain their weight within a healthy range. The Mediterranean diet is commonly associated with health-promoting effects. This is sometimes attributed to the inclusion of bioactive compounds such as phenolic compounds , isoprenoids and alkaloids . Physical exercise enhances or maintains physical fitness and overall health and wellness. It strengthens one's bones and muscles and improves
15589-415: The regulation of the internal environment was described by French physiologist Claude Bernard in 1849, and the word homeostasis was coined by Walter Bradford Cannon in 1926. In 1932, Joseph Barcroft a British physiologist, was the first to say that higher brain function required the most stable internal environment. Thus, to Barcroft homeostasis was not only organized by the brain—homeostasis served
15720-436: The release of renin from the juxtaglomerular apparatus is halted, ceasing the production of angiotensin II, and its consequent aldosterone-release into the blood. The kidneys respond by excreting sodium ions into the urine, thereby normalizing the plasma sodium ion concentration. The low angiotensin II levels in the blood lower the arterial blood pressure as an inevitable concomitant response. The reabsorption of sodium ions from
15851-422: The renal tubular fluid halts further sodium ion losses from the body, and therefore preventing the worsening of hyponatremia . The hyponatremia can only be corrected by the consumption of salt in the diet. However, it is not certain whether a "salt hunger" can be initiated by hyponatremia, or by what mechanism this might come about. When the plasma sodium ion concentration is higher than normal ( hypernatremia ),
15982-440: The same salt content as the extracellular fluid, whereas the former is hypotonic with respect to the plasma. Saliva does not taste salty, whereas tears are decidedly salty). Nearly all normal and abnormal losses of body water therefore cause the extracellular fluid to become hypertonic . Conversely, excessive fluid intake dilutes the extracellular fluid causing the hypothalamus to register hypotonic hyponatremia conditions. When
16113-413: The second are the parafollicular cells in the thyroid gland . The parathyroid chief cells secrete parathyroid hormone (PTH) in response to a fall in the plasma ionized calcium level; the parafollicular cells of the thyroid gland secrete calcitonin in response to a rise in the plasma ionized calcium level. The effector organs of the first homeostatic mechanism are the bones , the kidney , and, via
16244-420: The traditional approach that focuses on the reduction of the prevalence of diseases). In general, the context in which an individual lives is of great importance for both his health status and quality of life. It is increasingly recognized that health is maintained and improved not only through the advancement and application of health science , but also through the efforts and intelligent lifestyle choices of
16375-407: The tubular fluid as a result of high aldosterone levels in the blood does not, of itself, cause renal tubular water to be returned to the blood from the distal convoluted tubules or collecting ducts . This is because sodium is reabsorbed in exchange for potassium and therefore causes only a modest change in the osmotic gradient between the blood and the tubular fluid. Furthermore, the epithelium of
16506-402: The tubular fluid to leave the body via urine. Bicarbonate ions are simultaneously secreted into the blood that decreases the carbonic acid, and consequently raises the plasma pH. The converse happens when the plasma pH rises above normal: bicarbonate ions are excreted into the urine, and hydrogen ions released into the plasma. When hydrogen ions are excreted into the urine, and bicarbonate into
16637-455: The upper small intestine, increasing their capacity to absorb calcium from the gut contents into the blood. The second homeostatic mechanism, with its sensors in the thyroid gland, releases calcitonin into the blood when the blood ionized calcium rises. This hormone acts primarily on bone, causing the rapid removal of calcium from the blood and depositing it, in insoluble form, in the bones. The two homeostatic mechanisms working through PTH on
16768-407: The urine. Since phosphates combine with calcium ions to form insoluble salts (see also bone mineral ), a decrease in the level of phosphates in the blood, releases free calcium ions into the plasma ionized calcium pool. PTH has a second action on the kidneys. It stimulates the manufacture and release, by the kidneys, of calcitriol into the blood. This steroid hormone acts on the epithelial cells of
16899-502: The walls of the arterioles causing these small diameter vessels to constrict, thereby restricting the outflow of blood from the arterial tree, causing the arterial blood pressure to rise. This, therefore, reinforces the measures described above (under the heading of "Arterial blood pressure"), which defend the arterial blood pressure against changes, especially hypotension . The angiotensin II-stimulated aldosterone released from
17030-472: The warmth from the arterial blood directly into the venous blood returning into the trunk, causing minimal heat loss from the extremities in cold weather. The subcutaneous limb veins are tightly constricted, not only reducing heat loss from this source but also forcing the venous blood into the counter-current system in the depths of the limbs. The metabolic rate is increased, initially by non-shivering thermogenesis , followed by shivering thermogenesis if
17161-475: The way medical care is provided. From ancient times, Christian emphasis on practical charity gave rise to the development of systematic nursing and hospitals and the Catholic Church today remains the largest non-government provider of medical services in the world. Advanced industrial countries (with the exception of the United States ) and many developing countries provide medical services through
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