[Headline text]--75.137.171.242 (talk) 01:21, 21 October 2009 (UTC)
b
The
circulatory system is an
organ systemIn biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function ....
that passes nutrients (such as amino acids and electrolytes), gases, hormones,
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
cells, nitrogen waste products, etc. to and from cells in the body to help fight diseases and help stabilize body temperature and
pHpH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations...
b to maintain
homeostasisHomeostasis is the property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition...
. This system may be seen strictly as a blood distribution network, but some consider the circulatory system as composed of the
cardiovascular system, which distributes blood, and the
lymphatic systemThe lymphatic system in vertebrates is a network of conduits that carry a clear fluid called lymph. It also includes the lymphoid tissue through which the lymph travels. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated with the...
, which distributes
lymphLymph is the interstitial fluid found between the cells of the human body. It enters the lymph vessels by filtration through pores in the walls of capillaries...
. 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
invertebrateAn invertebrate is an animal without a vertebral column. The group includes 95% of all animal species — all animals except those in the Chordate subphylum Vertebrata ....
groups have an open cardiovascular system. The most primitive animal
phylaIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
lack circulatory system. The lymphatic system, on the other hand, is an open system.
The main components of the human circulatory system are the
heartThe heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, the
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
, and the
blood vesselThe blood vessels are the part of the circulatory system that transport blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart, the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s. The circulatory system includes: the
pulmonary circulationPulmonary circulation is the portion of the cardiovascular system which carries oxygen-depleted blood away from the heart, to the lungs, and returns oxygenated blood back to the heart...
, a "loop" through the
lungThe lung or pulmonary system is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart...
s where blood is oxygenated; and the
systemic circulationSystemic circulation is the portion of the cardiovascular system which carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart. The term is contrasted with pulmonary circulation.-Course:...
, a "loop" through the rest of the body to provide
oxygenateOxygenated chemical compounds contain oxygen as a part of their chemical structure. The term usually refers to oxygenated fuels. Oxygenates are usually employed as gasoline additives to reduce carbon monoxide that is created during the burning of the fuel....
d blood. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, which consists of
plasmaPlasma may refer to:* Blood plasma, the yellow-colored liquid component of blood, in which blood cells are suspended* Plasma , an ionized gas, the fourth state of matter...
, red blood cells, white blood cells, and platelets. Also, the digestive system works with the circulatory system to provide the nutrients the system needs to keep the
heartThe heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
pumping.
Two types of fluids move through the circulatory system: blood and lymph. The blood, heart, and blood vessels form the cardiovascular system. The lymph, lymph nodes, and lymph vessels form the
lymphatic systemThe lymphatic system in vertebrates is a network of conduits that carry a clear fluid called lymph. It also includes the lymphoid tissue through which the lymph travels. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated with the...
. The cardiovascular system and the lymphatic system collectively make up the circulatory system.
Pulmonary circulation
Pulmonary circulation is the portion of the cardiovascular system which transports
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
-depleted
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
away from the heart, to the lungs, and returns oxygenated blood back to the heart.
Oxygen deprived blood from the vena cava enters the right atrium of the heart and flows through the
tricuspid valveThe tricuspid valve is on the right side of the heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles. They are connected to the papillary muscles by the chordae tendineae, which lie in the right ventricle...
into the right ventricle where it is pumped through the pulmonary semilunar valve into the pulmonary arteries which go to the lungs. Pulmonary veins return the now oxygen-rich blood to the heart, where it enters the left atrium before flowing through the
mitral valveThe mitral valve is a dual-flap valve in the heart that lies between the left atrium and the left ventricle...
into the left ventricle. Also, from the left ventricle the oxygen-rich blood is pumped out via the aorta, and on to the rest of the body.
Systemic circulation
Systemic circulation is the portion of the cardiovascular system which transports oxygenated blood away from the heart, to the rest of the body, and returns oxygen-depleted blood back to the heart. Systemic circulation is, distance-wise, much longer than pulmonary circulation, transporting blood to every part of the body
except the lungs.
Coronary circulation
The coronary circulatory system provides a blood supply to the heart. As it provides oxygenated blood to the heart, it is by definition a part of the systemic circulatory system.
Heart
The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human
heartThe heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
there is one atrium and one
ventricleIn the heart, a ventricle is a heart chamber which collects blood from an atrium and pumps it out of the heart...
for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total:
left atriumThe left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the atrioventricular valve.-Foramen ovale:...
,
left ventricleThe left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...
,
right atriumThe right atrium is one of four chambers in the human heart. It receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve...
and
right ventricleThe right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....
. The right Atrium, which is the upper chamber of the right side. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the tissues of the body.
Closed cardiovascular system (CV)
The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enters
interstitial fluidInterstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...
, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction. The other component of the circulatory system, the
lymphatic systemThe lymphatic system in vertebrates is a network of conduits that carry a clear fluid called lymph. It also includes the lymphoid tissue through which the lymph travels. Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated with the...
, is not closed.
Other vertebrates
The circulatory systems of all
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s, as well as of
annelidThe annelids, collectively called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches. They are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments...
s (for example,
earthwormEarthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...
s) and
cephalopod{Taxobox| name = Cephalopods| fossil_range = | image = Tafel 054 300.jpg| image_caption = A variety of cephalopod forms from Ernst Haeckel's 1904 Kunstformen der Natur| regnum = Animalia| image_width = 220px| phylum = Mollusca| classis = Cephalopoda...
s (
squidSquid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms and two longer tentacles arranged in pairs...
and
octopusThe octopus is a cephalopod of the order Octopoda. The octopus inhabits many diverse regions of the ocean, especially coral reefs. The term may also be used to refer only to those creatures in the genus Octopus...
) are
closed, just as in humans. Still, the systems of
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
,
amphibianAmphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic animals that metamorphose from a juvenile water-breathing form, to an adult air-breathing form. Though amphibians typically have four limbs, the Caecilians are notable for being limbless. Unlike other land...
s,
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s, and
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s show various stages of the
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
of the circulatory system.
In fish, the system has only one circuit, with the blood being pumped through the capillaries of the
gillA gill is an anatomical structure found in many aquatic organisms. It is a respiration organ whose function is the extraction of oxygen from water and the excretion of carbon dioxide...
s and on to the capillaries of the body tissues. This is known as
single cycle circulation. The heart of fish is therefore only a single pump (consisting of two chambers). In amphibians and most reptiles, a
double circulatory systemThe double circulatory system of blood flow refers to the separate systems of pulmonary circulation and the systemic circulation in amphibians, birds and mammals In contrast, fish have a single circulation system because they do not have lungs...
is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.
In reptiles, the ventricular septum of the heart is incomplete and the
pulmonary arteryThe pulmonary arteries carry blood from heart to the lungs. They are the only arteries that carry deoxygenated blood....
is equipped with a sphincter muscle. This allows a second possible route of blood flow. Instead of blood flowing through the pulmonary artery to the lungs, the sphincter may be contracted to divert this blood flow through the incomplete ventricular septum into the
left ventricleThe left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...
and out through the
aortaThe aorta is the largest artery in the body, originating from the left ventricle of the heart and bringing oxygenated blood to all parts of the body in the systemic circulation....
. This means the blood flows from the capillaries to the heart and back to the capillaries instead of to the lungs. This process is useful to ectothermic (cold-blooded) animals in the regulation of their body temperature.
Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds evolved independently from that of mammals.
Open circulatory system
The Open Circulatory System is a system in which fluid (called
hemolymphHemolymph or haemolymph is the blood analogue used by all arthropods and most mollusks that have an open circulatory system.In these animals there is no distinction between blood and interstitial fluid. The liquid fills all of the interior of the body and surrounds all cells...
) in a cavity called the
hemocoelA hemocoel is a series of spaces between the organs of organisms with open circulatory systems, like most arthropods and mollusks. A combination of blood, lymph, and interstitial fluid called hemolymph circulates through the hemocoel....
bathes the organs directly with oxygen and nutrients and there is no distinction between
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
and
interstitial fluidInterstitial fluid is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular fluid, which also includes plasma and transcellular fluid...
; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during
locomotionAnimal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...
can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the
heartThe heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
relaxes, blood is drawn back toward the heart through open-ended pores (ostia).
Hemolymph fills all of the interior hemocoel of the body and surrounds all
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
s. Hemolymph is composed of
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
,
inorganicInorganic chemistry is the branch of chemistry concerned with the properties and behavior of inorganic compounds. This field covers all chemical compounds except the myriad organic compounds , which are the subjects of organic chemistry...
salts (mostly
Na+Sodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...
,
Cl-Chlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...
,
K+Potassium is the chemical element with the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash...
,
Mg2+Magnesium is a chemical element with the symbol Mg, atomic number 12 and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the earth's crust by mass, although ninth in the Universe as a whole...
, and
Ca2+Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
), and
organic compoundsOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
(mostly
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s,
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s, and
lipidLipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others...
s). The primary oxygen transporter molecule is
hemocyaninHemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...
.
There are free-floating cells, the
hemocyteA hemocyte is a cell that plays a role in the immune system of invertebrates. It is found within the hemolymph.Hemocytes are phagocytes of invertebrates....
s, within the hemolymph. They play a role in the arthropod
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
.
Absence of circulatory system
Circulatory systems are absent in some animals, including flatworms (phylum Platyhelminthes). Their
body cavityBy the broadest definition, a body cavity is any fluid filled space in a multicellular organism. However, the term usually refers to the space, located between an animal’s outer covering and the outer lining of the gut cavity, where internal organs develop...
has no lining or enclosed fluid. Instead a muscular
pharynxThe pharynx is the part of the neck and throat situated immediately posterior to the mouth and nasal cavity, and cranial, or superior, to the esophagus, larynx, and trachea.-Functions:...
leads to an extensively branched digestive system that facilitates direct
diffusionMolecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion. The result of diffusion is a gradual mixing of material...
of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism.
OxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
can diffuse from the surrounding
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
into the cells, and
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
can diffuse out. Consequently every cell is able to obtain nutrients, water and oxygen without the need of a transport system.
Some animals, such as jellies, have more extensive branching from their gastrovascular cavity (which functions as both a place of digestion and a form of circulation), this branching allows for bodily fluids to reach the outer layers, since the digestion begins in the inner layers.
Measurement techniques
- Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes. It is a noninvasive recording produced by an electrocardiographic device...
—for cardiac electrophysiology
- Sphygmomanometer
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...
and stethoscopeThe stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...
—for blood pressure
- Pulse meter—for cardiac function (heart rate, rhythm, dropped beats)
- Pulse
In medicine, a person's pulse is the arterial palpation of a heartbeat. It can be palpated in any place that allows for an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the ankle joint...
—commonly used to determine the heart rate in absence of certain cardiac pathologies
- Heart rate variability
Heart rate variability is a measure of variation in heart rate. This term has become widely accepted though in practice, one usually measures the variation in the beat-to-beat interval rather than the variation in the instantaneous heart rate....
-- used to measure variations of time intervals between heart beats
- Nail
Nail may refer to:* Nail , toughened keratin at the end of an animal digit* Nail , the pin-shaped fastener used in engineering, woodworking and construction* Nail , used in the crucifixion of Christ...
bed blanching test—test for perfusion
- Vessel cannula
A cannula or canula is a tube that can be inserted into the body, often for the delivery or removal of fluid....
or catheterIn medicine a catheter is a tube that can be inserted into a body cavity, duct or vessel. Catheters thereby allow drainage, injection of fluids or access by surgical instruments. The process of inserting a catheter is catheterization. In most uses a catheter is a thin, flexible tube , although...
pressure measurement—pulmonary wedge pressure or in older animal experiments.
Oxygen transportation
About 98.5% of the
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with haemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to Hgb. The haemoglobin molecule is the primary transporter of oxygen in mammals and many other species.
History of discovery
The earliest known writings on the circulatory system are found in the
Ebers PapyrusThe Ebers Papyrus of about 1550 BC is among the most important medical papyri of ancient Egypt. It is also commonly called Papyrus Ebers[ at WorldCat.] . It is one of the two oldest preserved medical documents anywhere, the other main source being the Edwin Smith papyrus...
(16th century BCE), an
ancient Egyptian medical papyrusAncient Egyptian Medicine refers to the practices of healing common in Ancient Egypt from circa 3300 BC until the Persian invasion of 523 BC. This medicine was highly advanced for the time, and included simple, non-invasive surgery, setting of bones and an extensive set of pharmacopoeia...
containing over 700 prescriptions and remedies, both physical and spiritual. In the
papyrusPapyrus is a thick paper-like material produced from the pith of the papyrus plant, Cyperus papyrus, a wetland sedge that was once abundant in the Nile Delta of Egypt....
, it acknowledges the connection of the heart to the arteries. The Egyptians thought air came in through the mouth and into the lungs and heart. From the heart, the air traveled to every member through the arteries. Although this concept of the circulatory system is greatly flawed, it represents one of the earliest accounts of scientific thought.
In the 6th century BCE, the knowledge of circulation of vital fluids through the body was known to the
AyurvedicAyurveda is a system of traditional medicine native to India and practiced in other parts of the world as a form of alternative medicine. In Sanskrit, the word Ayurveda consists of the words , meaning 'life', and , meaning 'related to knowledge' or 'science'...
physician Sushruta in
ancient IndiaThe known history of India - the name in this context includes the areas now known as India, Pakistan and Bangladesh - begins with the Indus Valley Civilization, which spread and flourished in the north-western part of the Indian subcontinent, from c. 3300 to 1300 BCE. Its Mature Harappan period...
. He also seems to have possessed knowledge of the arteries, described as 'channels' by Dwivedi & Dwivedi (2007). The
valves of the heartIn anatomy, the heart valves maintain the unidirectional flow of blood in the heart by opening and closing depending on the difference in pressure on each side...
were discovered by a physician of the
HippocrateanHippocrates of Cos or Hippokrates of Kos - Greek: ; Hippokrátēs was an ancient Greek physician of the Age of Pericles, and was considered one of the most outstanding figures in the history of medicine...
school around the 4th century BC. However their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air.
The Greek physician, Herophilus, distinguished veins from arteries but thought that the
pulseIn medicine, a person's pulse is the arterial palpation of a heartbeat. It can be palpated in any place that allows for an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the ankle joint...
was a property of arteries themselves. Greek anatomist
ErasistratusErasistratus was a Greek anatomist and royal physician under Seleucus I Nicator of Syria. Along with fellow physician Herophilus, he founded a school of anatomy in Alexandria, where they carried out anatomical research...
observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood.
The 2nd century AD,
RomanThe Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean. The term is used to describe the Roman state during and after the time of the first emperor,...
physician
GalenAelius Galenus or Claudius Galenus , better known as Galen of Pergamum , was a prominent Greek physician and philosopher and probably the most accomplished medical researcher of the Roman period. His theories dominated and influenced Western medical science for well over a millennium...
knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.
Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.
In 1025, the
The Canon of MedicineThe Canon of Medicine is a 14-volume medical encyclopedia written by Islamic scientist and physician Ibn Sīnā...
by the
Persian physicianThe practice and study of medicine in Persia has a long and prolific history. The Iranian academic centers like Jundishapur University were a breeding ground for the union among great scientists from different civilizations...
,
Avicenna, known as Abū Alī Sīnā or Ibn Sīnā , and commonly known in English by his Latinized name Avicenna , was a Persian polymath and the foremost physician and philosopher of his time...
, "erroneously accepted the Greek notion regarding the existence of a hole in the ventricular septum by which the blood traveled between the ventricles." Despite this, Avicenna "correctly wrote on the
cardiac cycleCardiac cycle is the term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is the heart rate...
s and valvular function", and "had a vision of blood circulation" in his
Treatise on Pulse. While also refining Galen's erroneous theory of the pulse, Avicenna provided the first correct explanation of pulsation: "Every beat of the pulse comprises two movements and two pauses. Thus, expansion : pause : contraction : pause. [...] The pulse is a movement in the heart and arteries ... which takes the form of alternate expansion and contraction."
In 1242, the Arabian physician, Ibn al-Nafis, became the first person to accurately describe the process of
pulmonary circulationPulmonary circulation is the portion of the cardiovascular system which carries oxygen-depleted blood away from the heart, to the lungs, and returns oxygenated blood back to the heart...
, for which he is sometimes considered the father of
circulatory physiologyCardiovascular physiology is the study of the circulatory system. More specifically, it addresses the physiology of the heart and blood vessels ....
. Ibn al-Nafis stated in his
Commentary on Anatomy in Avicenna's Canon:
"...the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary arteryThe pulmonary arteries carry blood from heart to the lungs. They are the only arteries that carry deoxygenated blood....
) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary veinA pulmonary vein is a large blood vessel of the human circulatory system that carries blood from the lungs to the left atrium of the heart. There are four pulmonary veins, two from each lung. They carry oxygenated blood, which is unusual since almost all other veins carry deoxygenated...
) to reach the left chamber of the heart and there form the vital spirit..."
In addition, Ibn al-Nafis had an insight into what would become a larger theory of the
capillaryCapillaries are the smallest of a body's blood vessels and are part of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
circulation. He stated that "there must be small communications or pores (
manafidh in Arabic) between the pulmonary artery and vein," a prediction that preceded the discovery of the capillary system by more than 400 years. Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body.
Finally
William HarveyWilliam Harvey was an English physician who was the first to describe correctly and in exact detail the systemic circulation and properties of blood being pumped around the body by the heart.- Early years:...
, a pupil of
Hieronymus FabriciusHieronymus Fabricius or Girolamo Fabrizio or by his latin name Fabricus ab Aquapendende was a pioneering anatomist known in Italian medical science as "The Father of Embryology."...
(who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments, and published
Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus in 1628, which "demonstrated that there had to be a direct connection between the venous and arterial systems throughout the body, and not just the lungs. Most importantly, he argued that the beat of the heart produced a continuous circulation of blood through minute connections at the extremities of the body. This is a conceptual leap that was quite different from Ibn al-Nafis' refinement of the anatomy and bloodflow in the heart and lungs." This work, with its essentially correct exposition, slowly convinced the medical world. However, Harvey was not able to identify the capillary system connecting arteries and veins; these were later discovered by
Marcello MalpighiMarcello Malpighi was an Italian doctor, who gave his name to several physiological features.-Early years:...
in 1661.
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