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74-509: An erection (clinically: penile erection or penile tumescence ) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal , sexual attraction or libido , although erections can also be spontaneous. The shape, angle, and direction of an erection vary considerably between humans. Physiologically, an erection

148-479: A horse's penis is housed within the prepuce, 50 centimetres (20 in) long and 2.5 to 6 centimetres (0.98 to 2.36 in) in diameter with the distal end 15 to 20 centimetres (5.9 to 7.9 in). The retractor muscle contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath. When erect, the penis doubles in length and thickness and the glans increases by 3 to 4 times . Erection and protrusion take place gradually, by

222-426: A recommended exposure limit (REL) of 25 ppm (30 mg/m ) over an 8-hour workday. At levels of 100 ppm, nitric oxide is immediately dangerous to life and health . Liquid nitrogen oxide is very sensitive to detonation even in the absence of fuel, and can be initiated as readily as nitroglycerin. Detonation of the endothermic liquid oxide close to its b.p. (-152°C) generated a 100 kbar pulse and fragmented

296-888: A vasodilator in the cardiovascular system, a breakthrough that earned them the 1998 Nobel Prize in Physiology or Medicine. The ground state electronic configuration of NO is, in united atom notation: ( 1 σ ) 2 ( 2 σ ) 2 ( 3 σ ) 2 ( 4 σ ∗ ) 2 ( 5 σ ) 2 ( 1 π ) 4 ( 2 π ∗ ) 1 {\displaystyle (1\sigma )^{2}(2\sigma )^{2}(3\sigma )^{2}(4\sigma ^{*})^{2}(5\sigma )^{2}(1\pi )^{4}(2\pi ^{*})^{1}} The first two orbitals are actually pure atomic 1 s O and 1 s N from oxygen and nitrogen respectively and therefore are usually not noted in

370-653: A bell and visual stimuli. 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

444-446: A brown gas and major air pollutant , or with nitrous oxide (N 2 O), an anesthetic gas. Nitric oxide (NO) was first identified by Joseph Priestley in the late 18th century, originally seen as merely a toxic byproduct of combustion and an environmental pollutant. Its biological significance was later uncovered in the 1980s when researchers Robert F. Furchgott , Louis J. Ignarro , and Ferid Murad discovered its critical role as

518-469: A bulge which (if required) can be disguised or hidden by wearing close-fitting underwear, a long shirt, or baggier clothes. The length of the flaccid penis is not indicative of the length of the penis when it becomes erect, with some smaller flaccid penises growing much longer, and some larger flaccid penises growing comparatively less. Generally, the size of an erect penis is fixed throughout post- pubescent life. Its size may be increased by surgery. Though

592-488: A cooperative manner. Nasal breathing produces nitric oxide within the body, while oral breathing does not. In the U.S., the Occupational Safety and Health Administration (OSHA) has set the legal limit ( permissible exposure limit ) for nitric oxide exposure in the workplace as 25 ppm (30 mg/m ) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set

666-542: A current or voltage change. The detection of NO radicals in biological tissues is particularly difficult due to the short lifetime and concentration of these radicals in tissues. One of the few practical methods is spin trapping of nitric oxide with iron- dithiocarbamate complexes and subsequent detection of the mono-nitrosyl-iron complex with electron paramagnetic resonance (EPR). A group of fluorescent dye indicators that are also available in acetylated form for intracellular measurements exist. The most common compound

740-503: A distinct subdiscipline. In 1920, August Krogh won the Nobel Prize for discovering how, in capillaries, blood flow is regulated. In 1954, Andrew Huxley and Hugh Huxley, alongside their research team, discovered the sliding filaments in skeletal muscle , known today as the sliding filament theory. Recently, there have been intense debates about the vitality of physiology as a discipline (Is it dead or alive?). If physiology

814-430: A large quantity of ozone. The nitric oxide reacts with the ozone to produce oxygen and nitrogen dioxide , accompanied with emission of light ( chemiluminescence ): which can be measured with a photodetector . The amount of light produced is proportional to the amount of nitric oxide in the sample. Other methods of testing include electroanalysis (amperometric approach), where ·NO reacts with an electrode to induce

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888-472: A liquid, nitric oxide dimerizes to dinitrogen dioxide , but the association is weak and reversible. The N–N distance in crystalline NO is 218 pm, nearly twice the N–O distance. Since the heat of formation of NO is endothermic , NO can be decomposed to the elements. Catalytic converters in cars exploit this reaction: When exposed to oxygen , nitric oxide converts into nitrogen dioxide : This reaction

962-459: 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 the theory of humorism , which consisted of four basic substances: earth, water, air and fire. Each substance

1036-420: A narrow bone called the baculum , a feature of most placental mammals . After the male achieves penetration, he will often hold the female tighter and thrust faster, and it is during this time that the male's penis expands, unlike human sexual intercourse, where the male penis commonly becomes erect before entering the female. An elephant's penis is S-shaped when fully erect and has a Y-shaped orifice . Given

1110-447: A single cell) signaling molecule. Once nitric oxide is converted to nitrates and nitrites by oxygen and water, cell signaling is deactivated. The endothelium (inner lining) of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, resulting in vasodilation and increasing blood flow. Sildenafil (Viagra) is a drug that uses the nitric oxide pathway. Sildenafil does not produce nitric oxide, but enhances

1184-430: 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

1258-462: Is 4,5-diaminofluorescein (DAF-2). Nitric oxide reacts with the hydroperoxyl radical ( HO 2 ) to form nitrogen dioxide (NO 2 ), which then can react with a hydroxyl radical (HO ) to produce nitric acid (HNO 3 ): Nitric acid, along with sulfuric acid , contributes to acid rain deposition. NO participates in ozone layer depletion . Nitric oxide reacts with stratospheric ozone to form O 2 and nitrogen dioxide: This reaction

1332-506: Is a gaseous signaling molecule . It is a key vertebrate biological messenger , playing a role in a variety of biological processes. It is a bioproduct in almost all types of organisms, including bacteria, plants, fungi, and animal cells. Nitric oxide, an endothelium-derived relaxing factor (EDRF), is biosynthesized endogenously from L -arginine , oxygen , and NADPH by various nitric oxide synthase (NOS) enzymes . Reduction of inorganic nitrate may also make nitric oxide. One of

1406-574: Is a signaling molecule in many physiological and pathological processes. It was proclaimed the " Molecule of the Year " in 1992. The 1998 Nobel Prize in Physiology or Medicine was awarded for discovering nitric oxide's role as a cardiovascular signalling molecule. Its impact extends beyond biology, with applications in medicine, such as the development of sildenafil (Viagra), and in industry, including semiconductor manufacturing. Nitric oxide should not be confused with nitrogen dioxide (NO 2 ),

1480-576: Is a colorless gas with the formula NO . It is one of the principal oxides of nitrogen . Nitric oxide is a free radical : it has an unpaired electron , which is sometimes denoted by a dot in its chemical formula ( N=O or NO). Nitric oxide is also a heteronuclear diatomic molecule , a class of molecules whose study spawned early modern theories of chemical bonding . An important intermediate in industrial chemistry , nitric oxide forms in combustion systems and can be generated by lightning in thunderstorms. In mammals, including humans, nitric oxide

1554-550: 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

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1628-427: 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

1702-425: Is also utilized to measure concentrations of NO in control volumes. As seen in the acid deposition section, nitric oxide can transform into nitrogen dioxide (this can happen with the hydroperoxy radical, HO 2 , or diatomic oxygen, O 2 ). Symptoms of short-term nitrogen dioxide exposure include nausea, dyspnea and headache. Long-term effects could include impaired immune and respiratory function. NO

1776-441: Is common for children and infants. After reaching puberty , erections occur much more frequently. An erection occurs when two tubular structures, called the corpora cavernosa , that run the length of the penis, become engorged with venous blood . This may result from any of various physiological stimuli, also known as sexual stimulation and sexual arousal . The corpus spongiosum is a single tubular structure located just below

1850-456: Is commonly used to distinguish between physical and psychological causes of erectile dysfunction and impotence . The state of a penis which is partly, but not fully, erect is sometimes known as semi-erection (clinically: partial tumescence ); a penis which is not erect is typically referred to as being flaccid, or soft. An erection is necessary for natural insemination as well as for the harvesting of sperm for artificial insemination , and

1924-400: Is essential for diagnosing and treating health conditions and promoting overall wellbeing. It 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

1998-469: Is known for having a corresponding humor: black bile, phlegm, blood, and yellow bile, respectively. Hippocrates also noted some emotional connections to the four humors, on which Galen would later expand. 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

2072-415: Is medically known as nocturnal penile tumescence (informally: morning wood or morning glory ). Though an erection can have many causes, it is most commonly seen as an indicator of sexual arousal and is therefore considered taboo or inappropriate for a public setting in many societies. This taboo is lesser than that surrounding public sex but higher than that surrounding nudity . Erectile dysfunction

2146-417: Is most often performed only as a last resort. The following table shows how common various erection angles are for a standing male. In the table, zero degrees (0°) is pointing straight up against the abdomen, 90° is horizontal and pointing straight forward, and 180° is pointing straight down to the feet. An upward pointing angle is most common and the average erection angle is 74.3 degrees. The penile curvature

2220-590: Is often considered a flaw, eliciting shame in individuals affected. The penile plethysmograph , which measures erections, has been used by some governments and courts of law to measure sexual orientation. An unusual aversion to the erect penis is sometimes referred to as phallophobia . Spontaneous erections, also known as involuntary, random or unwanted erections, are commonplace and a normal part of male physiology. Socially, such erections can be embarrassing if they happen in public or when undesired. Such erections can occur at any time of day, and if clothed may cause

2294-580: 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,

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2368-435: Is required for a male to effect penetration or sexual intercourse and is triggered by the parasympathetic division of the autonomic nervous system , causing the levels of nitric oxide (a vasodilator ) to rise in the trabecular arteries and smooth muscle of the penis. The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum ) to fill with blood ; simultaneously

2442-649: Is the scientific study of functions and mechanisms in a living system . As a subdiscipline of biology , physiology focuses on how organisms , organ systems , individual organs , cells , and biomolecules carry out chemical and physical functions in a living system. According to the classes of organisms , the field can be divided into medical physiology , animal physiology , plant physiology , cell physiology , and comparative physiology . Central to physiological functioning are biophysical and biochemical processes, homeostatic control mechanisms, and communication between cells. Physiological state

2516-496: Is the condition of normal function. In contrast, pathological state refers to abnormal conditions , including human diseases . The Nobel Prize in Physiology or Medicine is awarded by the Royal Swedish Academy of Sciences for exceptional scientific achievements in physiology related to the field of medicine . Because physiology focuses on the functions and mechanisms of living organisms at all levels, from

2590-508: Is the terminal linear type (M−NO). Alternatively, nitric oxide can serve as a one-electron pseudohalide. In such complexes, the M−N−O group is characterized by an angle between 120° and 140°. The NO group can also bridge between metal centers through the nitrogen atom in a variety of geometries. In commercial settings, nitric oxide is produced by the oxidation of ammonia at 750–900 °C (normally at 850 °C) with platinum as catalyst in

2664-402: Is thought to occur via the intermediates ONOO and the red compound ONOONO. In water, nitric oxide reacts with oxygen to form nitrous acid (HNO 2 ). The reaction is thought to proceed via the following stoichiometry : Nitric oxide reacts with fluorine , chlorine , and bromine to form the nitrosyl halides, such as nitrosyl chloride : With NO 2 , also a radical, NO combines to form

2738-435: Is to cultural notions of potency , success and masculinity , can have devastating psychological consequences including feelings of shame , loss or inadequacy. There is a strong culture of silence and inability to discuss the matter. Around one in ten men experience recurring impotence problems at some point in their lives. Priapism is a painful condition in which the penis does not return to its flaccid state, despite

2812-470: The Ostwald process : The uncatalyzed endothermic reaction of oxygen (O 2 ) and nitrogen (N 2 ), which is effected at high temperature (>2000 °C) by lightning has not been developed into a practical commercial synthesis (see Birkeland–Eyde process ): In the laboratory, nitric oxide is conveniently generated by reduction of dilute nitric acid with copper : An alternative route involves

2886-459: The glans , though some individuals have to manually retract their foreskin. In the presence of mechanical stimulation, erection is initiated by the parasympathetic division of the autonomic nervous system with minimal input from the central nervous system . Parasympathetic branches extend from the sacral plexus into the arteries supplying the erectile tissue; upon stimulation, these nerve branches release acetylcholine , which in turn causes

2960-604: The haloform reaction . For example, nitric oxide reacts with acetone and an alkoxide to form a diazeniumdiolate on each α position , with subsequent loss of methyl acetate as a by-product : This reaction, which was discovered around 1898, remains of interest in nitric oxide prodrug research. Nitric oxide can also react directly with sodium methoxide , ultimately forming sodium formate and nitrous oxide by way of an N -methoxydiazeniumdiolate. Nitric oxide reacts with transition metals to give complexes called metal nitrosyls . The most common bonding mode of nitric oxide

3034-573: The ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood. Erection subsides when parasympathetic activity reduces to baseline. As an autonomic nervous system response, an erection may result from a variety of stimuli, including sexual stimulation and sexual arousal , and is therefore not entirely under conscious control. Erections during sleep or upon waking up are known as nocturnal penile tumescence (NPT), also known as "morning wood". Absence of nocturnal erection

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3108-400: The 2π orbital makes NO a doublet (X ²Π) in its ground state whose degeneracy is split in the fine structure from spin-orbit coupling with a total momentum J = 3 ⁄ 2 or J = 1 ⁄ 2 . The dipole of NO has been measured experimentally to 0.15740 D and is oriented from O to N (⁻NO⁺) due to the transfer of negative electronic charge from oxygen to nitrogen. Upon condensing to

3182-414: The absence of both physical and psychological stimulation. Priapism lasting over four hours is a medical emergency. Hard flaccid syndrome is a rare, chronic condition characterized by a flaccid penis that remains in a firm, semi-rigid or semi-erect state in the absence of sexual arousal. At the time of penetration, the canine penis is not erect, and only able to penetrate the female because it includes

3256-418: 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 the nerves of dissected frogs. In 1811, César Julien Jean Legallois studied respiration in animal dissection and lesions and found the center of respiration in the medulla oblongata . In

3330-421: 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",

3404-437: The corpora cavernosa, which contains the urethra , through which urine and semen pass during urination and ejaculation respectively. This may also become slightly engorged with blood, but less so than the corpora cavernosa. In some cases, the scrotum becomes tightened during an erection, and in most uncircumcised males, the foreskin automatically and gradually retracts throughout the various stages of erection, exposing

3478-542: The 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 1891, Ivan Pavlov performed research on "conditional responses" that involved dogs' saliva production in response to

3552-480: 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: Human physiology Animal physiology Plant physiology Fungal physiology Protistan physiology Algal physiology Bacterial physiology Nitric oxide Nitric oxide ( nitrogen oxide or nitrogen monoxide )

3626-502: The humoral theory of disease, which also consisted of four primary qualities in life: hot, cold, wet and dry. Galen ( c.  130 –200 AD) 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

3700-458: The humors, 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

3774-427: The increasing tumescence of the erectile vascular tissue in the corpus cavernosum penis . Most stallions achieve erection within 2 minutes of contact with an estrus mare, and mount the estrus mare 5–10 seconds afterward. A bird penis is different in structure from mammal penises , being an erectile expansion of the cloacal wall and being erected by lymph , not blood. The penis of the lake duck can reach about

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3848-410: 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

3922-411: The intensely blue dinitrogen trioxide : The addition of a nitric oxide moiety to another molecule is often referred to as nitrosylation . The Traube reaction is the addition of a two equivalents of nitric oxide onto an enolate , giving a diazeniumdiolate (also called a nitrosohydroxylamine ). The product can undergo a subsequent retro- aldol reaction , giving an overall process similar to

3996-402: The leaves, and growth of shoots towards light are examples of plant physiology. Human physiology is the study of how the human body's systems and functions work together to maintain a stable internal environment. It includes the study of the nervous, endocrine, cardiovascular, respiratory, digestive, and urinary systems, as well as cellular and exercise physiology. Understanding human physiology

4070-449: 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

4144-402: The main enzymatic targets of nitric oxide is guanylyl cyclase . The binding of nitric oxide to the heme region of the enzyme leads to activation, in the presence of iron. Nitric oxide is highly reactive (having a lifetime of a few seconds), yet diffuses freely across membranes. These attributes make nitric oxide ideal for a transient paracrine (between adjacent cells) and autocrine (within

4218-455: The molecular and cellular level to the level of whole organisms and populations, its foundations span a range of key disciplines: There are many ways to categorize the subdisciplines of 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 . Plant physiology

4292-409: 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

4366-499: The penis. The cerebral cortex can initiate erection in the absence of direct mechanical stimulation (in response to visual, auditory, olfactory, imagined, or tactile stimuli) acting through erectile centers in the lumbar and sacral regions of the spinal cord . The cortex may suppress erection, even in the presence of mechanical stimulation, as may other psychological, emotional, and environmental factors. The penis may become erect during sleep or be erect on waking up. Such an erection

4440-406: The reduction of nitrous acid in the form of sodium nitrite or potassium nitrite : The iron(II) sulfate route is simple and has been used in undergraduate laboratory experiments. So-called NONOate compounds are also used for nitric oxide generation. Nitric oxide concentration can be determined using a chemiluminescent reaction involving ozone . A sample containing nitric oxide is mixed with

4514-419: The release of nitric oxide from endothelial cells in the trabecular arteries. Nitric oxide diffuses to the smooth muscle of the arteries (called trabecular smooth muscle ), acting as a vasodilating agent. The arteries dilate, filling the corpus spongiosum and corpora cavernosa with blood. The ischiocavernosus and bulbospongiosus muscles also compress the veins of the corpora cavernosa, limiting

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4588-929: The same length as the animal himself when fully erect, but more commonly is about half the bird's length. Clinically, erection is often known as "penile erection", and the state of being erect, and process of erection, are described as "tumescence" or "penile tumescence". The term for the subsiding or cessation of an erection is " detumescence ". Colloquially and in slang , erection is known by many informal terms. Commonly encountered English terms include 'stiffy', 'hard-on', 'boner' and 'woody'. There are several slang words, euphemisms and synonyms for an erection in English and in other languages (see also: The WikiSaurus entry ). Physiology Physiology ( / ˌ f ɪ z i ˈ ɒ l ə dʒ i / ; from Ancient Greek φύσις ( phúsis )  'nature, origin' and -λογία ( -logía )  'study of')

4662-602: 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

4736-401: The signals that are downstream of the nitric oxide pathway by protecting cyclic guanosine monophosphate (cGMP) from degradation by cGMP-specific phosphodiesterase type 5 (PDE5) in the corpus cavernosum , allowing for the signal to be enhanced, and thus vasodilation . Another endogenous gaseous transmitter, hydrogen sulfide (H 2 S) works with NO to induce vasodilation and angiogenesis in

4810-430: The size of a penis varies considerably between males, the average length of an erect human penis is 13.12 cm (5.17 inches), while the average circumference of an erect human penis is 11.66 cm (4.59 inches). Although many erect penises point upwards, it is common and normal for the erect penis to point nearly vertically upwards or horizontally straight forward or even nearly vertically downwards, all depending on

4884-415: The small amount of erectile tissue in a bull's penis , there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of the retractor penis muscle and straightening of the sigmoid flexure. A male fossa 's penis reaches to between his forelegs when erect. When not erect,

4958-516: The tension of the suspensory ligament that holds it in position. An erect penis can also take on a number of different shapes, ranging from a straight tube to a tube with a curvature up or down or to the left or right. An increase in penile curvature can be caused by Peyronie's disease . This may cause physical and psychological effects for the affected individual, which could include erectile dysfunction or pain during an erection. Treatments include oral medication (such as colchicine ) or surgery, which

5032-418: The tunica albuginea. Erection rigidity is mechanically controlled by reduction blood flow through theses veins, and thereby building up the pressure of the corpus cavernosum and corpus spongiosum, an integral instructure, the distal ligament, buttresses the glans penis. After ejaculation or cessation of stimulation, erection usually subsides, but the time taken may vary depending on the length and thickness of

5106-426: The united atom notation. Orbitals noted with an asterisk are antibonding. The ordering of 5σ and 1π according to their binding energies is subject to discussion. Removal of a 1π electron leads to 6 states whose energies span over a range starting at a lower level than a 5σ electron an extending to a higher level. This is due to the different orbital momentum couplings between a 1π and a 2π electron. The lone electron in

5180-452: The venous drainage of blood. Erection subsides when parasympathetic stimulation is discontinued; baseline stimulation from the sympathetic division of the autonomic nervous system causes constriction of the penile arteries and cavernosal sinosoids, forcing blood out of the erectile tissue through erection-related veins which include one deep dorsal vein, a pair of cavernosal veins, and two pairs of para-arterial veins between Buck's fascia and

5254-402: 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

5328-955: 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 Skelton , Sarah C. M. Sowton , Constance Leetham Terry , and Enid M. Tribe . The centenary of

5402-954: Was measured same time. 63% men have straight penis. 22.2% men have upwards curvature and 14.8% men have downwards curvature. Erectile dysfunction (also known as ED or "(male) impotence") is a sexual dysfunction characterized by the inability to develop and/or maintain an erection. The study of erectile dysfunction within medicine is known as andrology , a sub-field within urology . Erectile dysfunction may occur due to physiological or psychological reasons, most of which are amenable to treatment. Common physiological reasons include diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, including arterial insufficiency and venogenic erectile dysfunction, and neurologic disease which collectively account for about 70% of ED cases. Some drugs used to treat other conditions, such as lithium and paroxetine , may cause erectile dysfunction. Erectile dysfunction, tied closely as it

5476-410: 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. Involving evolutionary physiology and environmental physiology , comparative physiology considers the diversity of functional characteristics across organisms. The study of human physiology as

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