Physiology (/ˌfɪziˈɒlədʒi/; from Ancient Greek φύσις (physis), meaning 'nature, origin', and -λογία (-logia), meaning 'study of') is the scientific study of the functions and mechanisms which work within a living system.
As a sub-discipline of biology, the focus of physiology is on how organisms, organ systems, organs, cells, and biomolecules carry out the chemical and physical functions that exist in a living system.
Central to an understanding of physiological functioning is the investigation of the fundamental biophysical and biochemical phenomena, the coordinated homeostatic control mechanisms, and the continuous communication between cells.
Human physiology seeks to understand the mechanisms that work to keep the human body alive and functioning, through scientific enquiry into the nature of mechanical, physical, and biochemical functions of humans, their organs, and the cells of which they are composed. The principal level of focus of physiology is at the level of organs and systems within systems. The endocrine and nervous systems play major roles in the reception and transmission of signals. that integrate function in animals. Homeostasis is a major aspect with regard to such interactions within plants as well as animals. 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.
Changes in physiology can impact the mental functions of individuals. Examples of this would be the effects of certain medications or toxic levels of substances. Change in behavior as a result of these substances is often used to assess the health of individuals.
Much of the foundation of knowledge in human physiology was provided by animal experimentation. Due to the frequent connection between form and function, physiology and anatomy are intrinsically linked and are studied in tandem as part of a medical curriculum.
Plant physiology is a subdiscipline of botany concerned with the functioning of plants. Closely related fields include plant morphology, plant ecology, phytochemistry, cell biology, genetics, biophysics, and molecular biology. Fundamental processes of plant physiology include photosynthesis, respiration, plant nutrition, tropisms, nastic movements, photoperiodism, photomorphogenesis, circadian rhythms, seed germination, dormancy, and stomata function and transpiration. Absorption of water by roots, production of food in the leaves, and growth of shoots towards light are examples of plant physiology.
Although there are differences between animal, plant, and microbial cells, the basic physiological functions of cells can be divided into the processes of cell division, cell signaling, cell growth, and cell metabolism.
Microorganisms can be found almost everywhere on Earth. Types of microorganisms include archaea, bacteria, eukaryotes, protists, fungi, and micro-plants. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel, enzymes and other bioactive compounds. They are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora. They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation, transformation and transduction, even between widely divergent species.
The study of human physiology as a medical field originates in classical Greece, at the time of Hippocrates (late 5th century BC). Outside of Western tradition, early forms of physiology or anatomy can be reconstructed as having been present at around the same time in China, India and elsewhere. Hippocrates incorporated his belief system called the theory of humours, which consisted of four basic substance: earth, water, air and fire. Each substance is known for having a corresponding humour: black bile, phlegm, blood and yellow bile, respectively. Hippocrates also noted some emotional connections to the four humours, which Claudius Galenus would later expand on. The critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece. Like Hippocrates, Aristotle took to the humoral theory of disease, which also consisted of four primary qualities in life: hot, cold, wet and dry. Claudius Galenus (c. 130–200 AD), known as Galen of Pergamum, was the first to use experiments to probe the functions of the body. Unlike Hippocrates, Galen argued that humoral imbalances can be located in specific organs, including the entire body. His modification of this theory better equipped doctors to make more precise diagnoses. Galen also played off of Hippocrates idea that emotions were also tied to the humours, and added the notion of temperaments: sanguine corresponds with blood; phlegmatic is tied to phlegm; yellow bile is connected to choleric; and black bile corresponds with melancholy. Galen also saw the human body consisting of three connected systems: the brain and nerves, which are responsible for thoughts and sensations; the heart and arteries, which give life; and the liver and veins, which can be attributed to nutrition and growth. Galen was also the founder of experimental physiology. And for the next 1,400 years, Galenic physiology was a powerful and influential tool in medicine.
Jean Fernel (1497–1558), a French physician, introduced the term "physiology". Galen, Ibn al-Nafis, Michael Servetus, Realdo Colombo, Amato Lusitano and William Harvey, are credited as making important discoveries in the circulation of the blood. Santorio Santorio in 1610s was the first to use a device to measure the pulse rate (the pulsilogium), and a thermoscope to measure temperature.
In 1791 Luigi Galvani described the role of electricity in nerves of dissected frogs. In 1811, Julien Jean César Legallois studied respiration in animal dissection and lesions and found the center of respiration in the medulla oblongata. In the same year, Charles Bell finished work on what would later become known as the Bell-Magendie law, which compared functional differences between dorsal and ventral roots of the spinal cord. In 1824, François Magendie described the sensory roots and produced the first evidence of the cerebellum’s role in equilibration to complete the Bell-Magendie law.
In the 1820s, the French physiologist Henri Milne-Edwards introduced the notion of physiological division of labor, which allowed to "compare and study living things as if they were machines created by the industry of man." Inspired in the work of Adam Smith, Milne-Edwards wrote that the "body of all living beings, whether animal or plant, resembles a factory ... where the organs, comparable to workers, work incessantly to produce the phenomena that constitute the life of the individual." In more differentiated organisms, the functional labor could be apportioned between different instruments or systems (called by him as appareils).
In 1858, Joseph Lister studied the cause of blood coagulation and inflammation that resulted after previous injuries and surgical wounds. He later discovered and implemented antiseptics in the operating room, and as a result decreased death rate from surgery by a substantial amount.
The Physiological Society was founded in London in 1876 as a dining club. The American Physiological Society (APS) is a nonprofit organization that was founded in 1887. The Society is, "devoted to fostering education, scientific research, and dissemination of information in the physiological sciences."
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 B. Cannon in 1929. By homeostasis, Cannon meant "the maintenance of steady states in the body and the physiological processes through which they are regulated." In other words, the body's ability to regulate its internal environment. William Beaumont was the first American to utilize the practical application of physiology.
Nineteenth century physiologists such as Michael Foster, Max Verworn, and Alfred Binet, based on Haeckel's ideas, elaborated what came to be called "general physiology", a unified science of life based on the cell actions, later renamed in the 20th century as cell biology.
In the 20th century, biologists 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.
Recently, there have been intense debates about the vitality of physiology as a discipline (Is it dead or alive?). If physiology is perhaps less visible nowadays than during the golden age of the 19th century, it is in large part because the field has given birth to some of the most active domains of today's biological sciences, such as neuroscience, endocrinology, and immunology. Furthermore, physiology is still often seen as an integrative discipline, which can put together into a coherent framework data coming from various different domains.
Initially, women were largely excluded from official involvement in any physiological society. The American Physiological Society, for example, was founded in 1887 and included only men in its ranks. In 1902, the American Physiological Society elected Ida Hyde as the first female member of the society. Hyde, a representative of the American Association of University Women and a global advocate for gender equality in education, attempted to promote gender equality in every aspect of science and medicine.
Soon thereafter, in 1913, J.S. Haldane proposed that women be allowed to formally join The Physiological Society, which had been founded in 1876. On 3 July 1915, six women were officially admitted: Florence Buchanan, Winifred Cullis, Ruth C. Skelton, Sarah C. M. Sowton, Constance Leetham Terry, and Enid M. Tribe. The centenary of the election of women was celebrated in 2015 with the publication of the book "Women Physiologists: Centenary Celebrations And Beyond For The Physiological Society." (ISBN 978-0-9933410-0-7)
Prominent women physiologists include:
There are many ways to categorize the subdiscplines of physiology:
Together with physiology and biochemistry, anatomy is one of the basic sciences that are to be taught in the medical curriculum.
An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. Whereas an agonist causes an action, an antagonist blocks the action of the agonist, and an inverse agonist causes an action opposite to that of the agonist.Biophysics
Biophysics is an interdisciplinary science that applies approaches and methods traditionally used in physics to study biological phenomena. Biophysics covers all scales of biological organization, from molecular to organismic and populations. Biophysical research shares significant overlap with biochemistry, molecular biology, physical chemistry, physiology, nanotechnology, bioengineering, computational biology, biomechanics, developmental biology and systems biology.
The term biophysics was originally introduced by Karl Pearson in 1892. Ambiguously, the term biophysics is also regularly used in academia to indicate the study of the physical quantities (e.g. electric current, temperature, stress, entropy) in biological systems, which is, by definition, performed by physiology. Nevertheless, other biological sciences also perform research on the biophysical properties of living organisms including molecular biology, cell biology, biophysics, and biochemistry.Calcium in biology
Calcium ions (Ca2+) contribute to the physiology and biochemistry of organisms and the cell. They play an important role in signal transduction pathways, where they act as a second messenger, in neurotransmitter release from neurons, in contraction of all muscle cell types, and in fertilization. Many enzymes require calcium ions as a cofactor, those of the blood-clotting cascade being notable examples. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.
Plasma calcium levels in mammals are tightly regulated, with bone acting as the major mineral storage site. Calcium ions, Ca2+, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as serum albumin. Parathyroid hormone secreted by the parathyroid gland regulates the resorption of Ca2+ from bone, reabsorption in the kidney back into circulation, and increases in the activation of vitamin D3 to calcitriol. Calcitriol, the active form of vitamin D3, promotes absorption of calcium from the intestines and bones. Calcitonin secreted from the parafollicular cells of the thyroid gland also affects calcium levels by opposing parathyroid hormone; however, its physiological significance in humans is dubious.
Intracellular calcium is stored in organelles which repetitively release and then reaccumulate Ca2+ ions in response to specific cellular events: storage sites include mitochondria and the endoplasmic reticulum.Characteristic concentrations of calcium in model organisms are: in E. coli 3mM (bound), 100nM (free), in budding yeast 2mM (bound), in mammalian cell 10-100nM (free) and in blood plasma 2mM.Circulatory system
The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells in the body to provide nourishment and help in fighting diseases, stabilize temperature and pH, and maintain homeostasis.
The circulatory system includes the lymphatic system, which circulates lymph. The passage of lymph for example takes much longer than that of blood. Blood is a fluid consisting of plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the vertebrate vascular system, carrying oxygen and nutrients to and waste materials away from all body tissues. Lymph is essentially recycled excess blood plasma after it has been filtered from the interstitial fluid (between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning "heart" and "vessel") system comprises the blood, heart, and blood vessels. The lymph, lymph nodes, and lymph vessels form the lymphatic system, which returns filtered blood plasma from the interstitial fluid (between cells) as lymph.
The circulatory system of the blood is seen as having two components, a systemic circulation and a pulmonary circulation.While humans, as well as other vertebrates, have a closed cardiovascular system (meaning that the blood never leaves the network of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system. The lymphatic system, on the other hand, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood. The more primitive, diploblastic animal phyla lack circulatory systems.
Many diseases affect the circulatory system. This includes cardiovascular disease, affecting the cardiovascular system, and lymphatic disease affecting the lymphatic system. Cardiologists are medical professionals which specialise in the heart, and cardiothoracic surgeons specialise in operating on the heart and its surrounding areas. Vascular surgeons focus on other parts of the circulatory system.Fatigue
Fatigue is a subjective feeling of tiredness that has a gradual onset. Unlike weakness, fatigue can be alleviated by periods of rest. Fatigue can have physical or mental causes. Physical fatigue is the transient inability of a muscle to maintain optimal physical performance, and is made more severe by intense physical exercise. Mental fatigue is a transient decrease in maximal cognitive performance resulting from prolonged periods of cognitive activity. It can manifest as somnolence, lethargy, or directed attention fatigue.Medically, fatigue is a non-specific symptom, which means that it has many possible causes and accompanies many different conditions. Fatigue is considered a symptom, rather than a sign, because it is a subjective feeling reported by the patient, rather than an objective one that can be observed by others. Fatigue and 'feelings of fatigue' are often confused.Flushing (physiology)
Flushing is to become markedly red in the face and often other areas of the skin, from various physiological conditions. Flushing is generally distinguished, despite a close physiological relation between them, from blushing, which is milder, generally restricted to the face, cheeks or ears, and generally assumed to reflect emotional stress, such as embarrassment, anger, or romantic stimulation. Flushing is also a cardinal symptom of carcinoid syndrome—the syndrome that results from hormones (often serotonin or histamine) being secreted into systemic circulation.Human body
The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body.
It comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet.
The study of the human body involves anatomy, physiology, histology and embryology. The body varies anatomically in known ways. Physiology focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis, with safe levels of substances such as sugar and oxygen in the blood.
The body is studied by health professionals, physiologists, anatomists, and by artists to assist them in their work.Ivan Pavlov
Ivan Petrovich Pavlov (Russian: Ива́н Петро́вич Па́влов, IPA: [ɪˈvan pʲɪˈtrovʲɪtɕ ˈpavləf] (listen); 26 September [O.S. 14 September] 1849 – 27 February 1936) was a Russian physiologist known primarily for his work in classical conditioning.
From his childhood days Pavlov demonstrated intellectual curiosity along with an unusual energy which he referred to as "the instinct for research". Inspired by the progressive ideas which D. I. Pisarev, the most eminent of the Russian literary critics of the 1860s, and I. M. Sechenov, the father of Russian physiology, were spreading, Pavlov abandoned his religious career and devoted his life to science. In 1870, he enrolled in the physics and mathematics department at the University of Saint Petersburg in order to study natural science.Pavlov won the Nobel Prize for Physiology or Medicine in 1904, becoming the first Russian Nobel laureate. A survey in the Review of General Psychology, published in 2002, ranked Pavlov as the 24th most cited psychologist of the 20th century. Pavlov's principles of classical conditioning have been found to operate across a variety of behavior therapies and in experimental and clinical settings, such as educational classrooms and even reducing phobias with systematic desensitization.List of Nobel laureates by country
This is a list of Nobel Prize laureates by country. Listings for Economics refer to the related Nobel Memorial Prize in Economic Sciences. The Nobel Prizes and the Prize in Economic Sciences have been awarded 567 times to 889 recipients, of which 25 awards (all Peace Prizes) were to organizations. Due to some recipients receiving multiple awards, the total number of recipients is 860 individuals and 22 organizations.The present list ranks laureates under the country/countries that are stated by the Nobel Prize committee on its website. The list does not distinguish between laureates who received a full prize and the majority who shared a prize. Some laureates are listed under more than one country, because the official website mentions multiple countries in relation to the laureate. If a country is merely mentioned as the place of birth, an asterisk (*) is used in the respective listing to indicate this. In this case, the birth country is mentioned in italics at the other listings of this laureate.
Organizations are listed here if the Nobel Prize committee relates them to a single country.List of Nobel laureates in Physiology or Medicine
The Nobel Prize in Physiology or Medicine (Swedish: Nobelpriset i fysiologi eller medicin) is awarded annually by the Swedish Karolinska Institute to scientists and doctors in the various fields of physiology or medicine. It is one of the five Nobel Prizes established by the 1895 will of Alfred Nobel (who died in 1896), awarded for outstanding contributions in chemistry, physics, literature, peace, and physiology or medicine. As dictated by Nobel's will, the award is administered by the Nobel Foundation and awarded by a committee that consists of five members and an executive secretary elected by the Karolinska Institute. While commonly referred to as the Nobel Prize in Medicine, Nobel specifically stated that the prize be awarded for "physiology or medicine" in his will. Because of this, the prize can be awarded in a broader range of fields. The first Nobel Prize in Physiology or Medicine was awarded in 1901 to Emil Adolf von Behring, of Germany. Each recipient receives a medal, a diploma and a monetary award that has varied throughout the years. In 1901, von Behring received 150,782 SEK, which was equal to 7,731,004 SEK in December 2008. The award is presented in Stockholm at an annual ceremony on 10 December, the anniversary of Nobel's death.Laureates have won the Nobel Prize in a wide range of fields that relate to physiology or medicine. As of 2009, 8 Prizes have been awarded for contributions in the field of signal transduction by G proteins and second messengers, 13 have been awarded for contributions in the field of neurobiology and 13 have been awarded for contributions in intermediary metabolism. In 1939 Gerhard Domagk, a German, was not allowed by his government to accept the prize. He later received a medal and diploma, but not the money. As of 2018, the prize has been awarded to 216 individuals, twelve of them were women: Gerty Cori (1947), Rosalyn Yalow (1977), Barbara McClintock (1983), Rita Levi-Montalcini (1986), Gertrude B. Elion (1988), Christiane Nüsslein-Volhard (1995), Linda B. Buck (2004), Françoise Barré-Sinoussi (2008), Elizabeth H. Blackburn (2009), Carol W. Greider (2009), May-Britt Moser (2014) and Tu Youyou (2015). There have been nine years in which the Nobel Prize in Physiology or Medicine was not awarded (1915–1918, 1921, 1925, 1940–1942).Neuroscience
Neuroscience (or neurobiology) is the scientific study of the nervous system. It is a multidisciplinary branch of biology that combines physiology, anatomy, molecular biology, developmental biology, cytology, mathematical modeling and psychology to understand the fundamental and emergent properties of neurons and neural circuits. The understanding of the biological basis of learning, memory, behavior, perception, and consciousness has been described by Eric Kandel as the "ultimate challenge" of the biological sciences.The scope of neuroscience has broadened over time to include different approaches used to study the nervous system at different scales and the techniques used by neuroscientists have expanded enormously, from molecular and cellular studies of individual neurons to imaging of sensory, motor and cognitive tasks in the brain.Nobel Prize
The Nobel Prize (, Swedish pronunciation: [nʊˈbɛlː]; Swedish definite form, singular: Nobelpriset; Norwegian: Nobelprisen) is a set of annual international awards bestowed in several categories by Swedish and Norwegian institutions in recognition of academic, cultural, or scientific advances.
The will of the Swedish scientist Alfred Nobel established the five Nobel prizes in 1895. The prizes in Chemistry, Literature, Peace, Physics, and Physiology or Medicine were first awarded in 1901. The prizes are widely regarded as the most prestigious awards available in the fields of chemistry, literature, peace activism, physics, and physiology or medicine.In 1968, Sweden's central bank, Sveriges Riksbank, established the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, which, although not a Nobel Prize, has become informally known as the "Nobel Prize in Economics".The Royal Swedish Academy of Sciences awards the Nobel Prize in Chemistry, the Nobel Prize in Physics, and the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel; the Nobel Assembly at the Karolinska Institute awards the Nobel Prize in Physiology or Medicine; the Swedish Academy grants the Nobel Prize in Literature; and the Norwegian Nobel Committee awards the Nobel Peace Prize.
Between 1901 and 2018, the Nobel Prizes (and the Prizes in Economic Sciences, from 1969 on) were awarded 590 times to 935 people and organizations. With some receiving the Nobel Prize more than once, this makes a total of 27 organizations and 908 individuals. The prize ceremonies take place annually in Stockholm, Sweden (with the exception of the Peace Prize ceremony, which is held in Oslo, Norway). Each recipient (known as a "laureate") receives a gold medal, a diploma, and a sum of money that has been decided by the Nobel Foundation. (As of 2017, each prize is worth 9,000,000 SEK, or about US$1,110,000, €944,000, £836,000 or ₹73,800,000.) Medals made before 1980 were struck in 23-carat gold, and later in 18-carat green gold plated with a 24-carat gold coating.
The prize is not awarded posthumously; however, if a person is awarded a prize and dies before receiving it, the prize may still be presented. A prize may not be shared among more than three individuals, although the Nobel Peace Prize can be awarded to organizations of more than three people.Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine (Swedish: Nobelpriset i fysiologi eller medicin), administered by the Nobel Foundation, is awarded yearly for outstanding discoveries in the fields of life sciences and medicine. It is one of five Nobel Prizes established in his will in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite. Nobel was interested in experimental physiology and wanted to establish a prize for scientific progress through laboratory discoveries. The Nobel Prize is presented at an annual ceremony on 10 December, the anniversary of Nobel's death, along with a diploma and a certificate for the monetary award. The front side of the medal displays the same profile of Alfred Nobel depicted on the medals for Physics, Chemistry, and Literature. The reverse side is unique to this medal. The most recent Nobel prize was announced by Karolinska Institute on 1 October 2018, and has been awarded to American James P. Allison and Japanese Tasuku Honjo – for their discovery of cancer therapy by inhibition of negative immune regulation.As of 2015, 106 Nobel Prizes in Physiology or Medicine have been awarded to 198 men and 12 women. The first one was awarded in 1901 to the German physiologist Emil von Behring, for his work on serum therapy and the development of a vaccine against diphtheria. The first woman to receive the Nobel Prize in Physiology or Medicine, Gerty Cori, received it in 1947 for her role in elucidating the metabolism of glucose, important in many aspects of medicine, including treatment of diabetes.
Some awards have been controversial. This includes one to António Egas Moniz in 1949 for the prefrontal lobotomy, bestowed despite protests from the medical establishment. Other controversies resulted from disagreements over who was included in the award. The 1952 prize to Selman Waksman was litigated in court, and half the patent rights awarded to his co-discoverer Albert Schatz who was not recognized by the prize. The 1962 prize awarded to James D. Watson, Francis Crick and Maurice Wilkins for their work on DNA structure and properties did not acknowledge the contributing work from others, such as Oswald Avery and Rosalind Franklin who had died by the time of the nomination. Since the Nobel Prize rules forbid nominations of the deceased, longevity is an asset, considering prizes are awarded as long as 50 years after the discovery. Also forbidden is awarding any one prize to more than three recipients. In the last half century there has been an increasing tendency for scientists to work as teams, resulting in controversial exclusions.Photoperiodism
Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods. They are classified under three groups according to the photoperiods: short-day plants, long-day plants, and day-neutral plants.Plant physiology
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology (structure of plants), plant ecology (interactions with the environment), phytochemistry (biochemistry of plants), cell biology, genetics, biophysics and molecular biology.
Fundamental processes such as photosynthesis, respiration, plant nutrition, plant hormone functions, tropisms, nastic movements, photoperiodism, photomorphogenesis, circadian rhythms, environmental stress physiology, seed germination, dormancy and stomata function and transpiration, both parts of plant water relations, are studied by plant physiologists.Pulse
In medicine, a pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the neck (carotid artery), wrist (radial artery), at the groin (femoral artery), behind the knee (popliteal artery), near the ankle joint (posterior tibial artery), and on foot (dorsalis pedis artery). Pulse (or the count of arterial pulse per minute) is equivalent to measuring the heart rate. The heart rate can also be measured by listening to the heart beat by auscultation, traditionally using a stethoscope and counting it for a minute. The radial pulse is commonly measured using three fingers. This has a reason: the finger closest to the heart is used to occlude the pulse pressure, the middle finger is used get a crude estimate of the blood pressure, and the finger most distal to the heart (usually the ring finger) is used to nullify the effect of the ulnar pulse as the two arteries are connected via the palmar arches (superficial and deep).
The study of the pulse is known as sphygmology.Respiration (physiology)
In physiology, respiration is the movement of oxygen from the outside environment to the cells within tissues, and the transport of carbon dioxide in the opposite direction.
The physiological definition of respiration differs from the biochemical definition, which refers to a metabolic process by which an organism obtains energy (in the form of ATP) by oxidizing nutrients and releasing waste products. Although physiologic respiration is necessary to sustain cellular respiration and thus life in animals, the processes are distinct: cellular respiration takes place in individual cells of the organism, while physiologic respiration concerns the diffusion and transport of metabolites between the organism and the external environment.
In animals with lungs, physiological respiration involves respiratory cycles of inhaled and exhaled breaths. Inhalation (breathing in) is usually an active movement. The contraction of the diaphragm muscle cause a pressure variation, which is equal to the pressures caused by elastic, resistive and inertial components of the respiratory system. In contrast, exhalation (breathing out) is usually a passive process. Breathing in, brings air into the lungs where the process of gas exchange takes place between the air in the alveoli and the blood in the pulmonary capillaries
The process of breathing does not fill the alveoli with atmospheric air during each inhalation (about 350 ml per breath), but the inhaled air is carefully diluted and thoroughly mixed with a large volume of gas (about 2.5 liters in adult humans) known as the functional residual capacity which remains in the lungs after each exhalation, and whose gaseous composition differs markedly from that of the ambient air. Physiological respiration involves the mechanisms that ensure that the composition of the functional residual capacity is kept constant, and equilibrates with the gases dissolved in the pulmonary capillary blood, and thus throughout the body. Thus, in precise usage, the words breathing and ventilation are hyponyms, not synonyms, of respiration; but this prescription is not consistently followed, even by most health care providers, because the term respiratory rate (RR) is a well-established term in health care, even though it would need to be consistently replaced with ventilation rate if the precise usage were to be followed.Stimulus (physiology)
In physiology, a stimulus (plural stimuli) is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity. When a stimulus is applied to a sensory receptor, it normally elicits or influences a reflex via stimulus transduction. These sensory receptors can receive information from outside the body, as in touch receptors found in the skin or light receptors in the eye, as well as from inside the body, as in chemoreceptors and mechanoreceptors. An internal stimulus is often the first component of a homeostatic control system. External stimuli are capable of producing systemic responses throughout the body, as in the fight-or-flight response. In order for a stimulus to be detected with high probability, its level must exceed the absolute threshold; if a signal does reach threshold, the information is transmitted to the central nervous system (CNS), where it is integrated and a decision on how to react is made. Although stimuli commonly cause the body to respond, it is the CNS that finally determines whether a signal causes a reaction or not.Vasodilation
Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstriction, which is the narrowing of blood vessels.
When blood vessels dilate, the flow of blood is increased due to a decrease in vascular resistance and increase in cardiac output. Therefore, dilation of arterial blood vessels (mainly the arterioles) decreases blood pressure. The response may be intrinsic (due to local processes in the surrounding tissue) or extrinsic (due to hormones or the nervous system). In addition, the response may be localized to a specific organ (depending on the metabolic needs of a particular tissue, as during strenuous exercise), or it may be systemic (seen throughout the entire systemic circulation).
Endogenous substances and drugs that cause vasodilation are termed vasodilators. Such vasoactivity is necessary for homeostasis (keeping the body running normally).