Circulatory system
Circulatory system | |
---|---|
deoxygenated blood carried in veins. Capillaries join the arteries and veins. | |
Identifiers | |
MeSH | D002319 |
TA98 | A12.0.00.000 |
TA2 | 3891 |
FMA | 7161 |
Anatomical terminology] |
The circulatory system is a
The network of blood vessels are the
Blood is a
.In vertebrates, the
The lymphatic system also works with the immune system.[6] The circulation of lymph takes much longer than that of blood[7] and, unlike the closed (blood) circulatory system, the lymphatic system is an open system. Some sources describe it as a secondary circulatory system.
The circulatory system can be affected by many
Structure
The circulatory system includes the
Further circulatory routes are associated, such as the
The human circulatory system is
Heart
The heart pumps blood to all parts of the body providing
Pulmonary circulation
The pulmonary circulation is the part of the circulatory system in which
Oxygen-deprived blood from the superior and inferior
A separate circuit from the systemic circulation, the bronchial circulation supplies blood to the tissue of the larger airways of the lung.
Systemic circulation
The systemic circulation is a circuit loop that delivers oxygenated blood from the left heart to the rest of the body through the aorta. Deoxygenated blood is returned in the systemic circulation to the right heart via two large veins, the inferior vena cava and superior vena cava, where it is pumped from the right atrium into the pulmonary circulation for oxygenation. The systemic circulation can also be defined as having two parts – a macrocirculation and a microcirculation.[10]
Blood vessels
The
Arteries
Oxygenated blood enters the systemic circulation when leaving the left ventricle, via the aortic semilunar valve.[15] The first part of the systemic circulation is the aorta, a massive and thick-walled artery. The aorta arches and gives branches supplying the upper part of the body after passing through the aortic opening of the diaphragm at the level of thoracic ten vertebra, it enters the abdomen.[16] Later, it descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs.[17]
The walls of the aorta are elastic. This elasticity helps to maintain the blood pressure throughout the body.[18] When the aorta receives almost five litres of blood from the heart, it recoils and is responsible for pulsating blood pressure. As the aorta branches into smaller arteries, their elasticity goes on decreasing and their compliance goes on increasing.[18]
Capillaries
Arteries branch into small passages called arterioles and then into the capillaries.[19] The capillaries merge to bring blood into the venous system.[20]
Veins
Capillaries merge into
Portal veins
The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart.
Coronary circulation
The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers. The coronary circulation system provides a blood supply to the
Cerebral circulation
The brain has a dual blood supply, an anterior and a posterior circulation from arteries at its front and back. The anterior circulation arises from the
Renal circulation
The renal circulation is the blood supply to the kidneys, contains many specialized blood vessels and receives around 20% of the cardiac output. It branches from the abdominal aorta and returns blood to the ascending inferior vena cava.
Development
The development of the circulatory system starts with
Arteries
The human arterial system originates from the
The dorsal aortae, present on the
Veins
The human venous system develops mainly from the
Function
About 98.5% of the oxygen in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin molecules. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in vertebrates.
Clinical significance
Many diseases affect the circulatory system. These include a number of
Cardiovascular disease
Diseases affecting the cardiovascular system are called cardiovascular disease.
Many of these diseases are called "lifestyle diseases" because they develop over time and are related to a person's exercise habits, diet, whether they smoke, and other lifestyle choices a person makes. Atherosclerosis is the precursor to many of these diseases. It is where small atheromatous plaques build up in the walls of medium and large arteries. This may eventually grow or rupture to occlude the arteries. It is also a risk factor for acute coronary syndromes, which are diseases that are characterised by a sudden deficit of oxygenated blood to the heart tissue. Atherosclerosis is also associated with problems such as aneurysm formation or splitting ("dissection") of arteries.
Another major cardiovascular disease involves the creation of a
Cardiovascular diseases may also be congenital in nature, such as heart defects or persistent fetal circulation, where the circulatory changes that are supposed to happen after birth do not. Not all congenital changes to the circulatory system are associated with diseases, a large number are anatomical variations.
Investigations
The function and health of the circulatory system and its parts are measured in a variety of manual and automated ways. These include simple methods such as those that are part of the
Other more invasive means can also be used. A
is also an option.Surgery
This section needs expansion. You can help by adding to it. (March 2015) |
There are a number of surgical procedures performed on the circulatory system:
- Coronary artery bypass surgery
- Coronary stent used in angioplasty
- Vascular surgery
- Vein stripping
- Cosmetic procedures
Cardiovascular procedures are more likely to be performed in an inpatient setting than in an ambulatory care setting; in the United States, only 28% of cardiovascular surgeries were performed in the ambulatory care setting.[25]
Other animals
While humans, as well as other
An additional transport system, the lymphatic system, which is only found in animals with a closed blood circulation, is an open system providing an accessory route for excess interstitial fluid to be returned to the blood.[5]
The blood vascular system first appeared probably in an ancestor of the
Open circulatory system
In arthropods, the open circulatory system is a system in which a fluid in a cavity called the hemocoel bathes the organs directly with oxygen and nutrients, with there being no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph.[27] Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the heart 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 cells. Hemolymph is composed of water, inorganic salts (mostly sodium, chloride, potassium, magnesium, and calcium), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin.
There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.
Closed circulatory system
The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squids, octopuses and relatives) always keep their circulating blood enclosed within heart chambers or blood vessels and are classified as closed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birds show various stages of the evolution of the circulatory system.[28] Closed systems permit blood to be directed to the organs that require it.
In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills 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 system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.
In reptiles, the
Mammals, birds and crocodilians 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 and crocodilians evolved independently from that of mammals.[29] Double circulatory systems permit blood to be repressurized after returning from the lungs, speeding up delivery of oxygen to tissues.
No circulatory system
Circulatory systems are absent in some animals, including
Some animals, such as jellyfish, 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.
History
The earliest known writings on the circulatory system are found in the Ebers Papyrus (16th century BCE), an ancient Egyptian medical papyrus containing over 700 prescriptions and remedies, both physical and spiritual. In the papyrus, 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 travelled to every member through the arteries. Although this concept of the circulatory system is only partially correct, 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 Ayurvedic physician Sushruta in ancient India.[30] He also seems to have possessed knowledge of the arteries, described as 'channels' by Dwivedi & Dwivedi (2007).[30] The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BCE. 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 the transport of air.
The
In 2nd-century AD
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,
In 1242, the
...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 artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) 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 capillary 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.[33] Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body.
Michael Servetus was the first European to describe the function of pulmonary circulation, although his achievement was not widely recognized at the time, for a few reasons. He firstly described it in the "Manuscript of Paris"[34][35] (near 1546), but this work was never published. And later he published this description, but in a theological treatise, Christianismi Restitutio, not in a book on medicine. Only three copies of the book survived but these remained hidden for decades, the rest were burned shortly after its publication in 1553 because of persecution of Servetus by religious authorities.
A better known discovery of pulmonary circulation was by
Finally, the English physician William Harvey, a pupil of Hieronymus Fabricius (who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and published his 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."[36] 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 Malpighi in 1661.
In 1956,
In the 1970s, Diana McSherry developed computer-based systems to create images of the circulatory system and heart without the need for surgery.[39]
See also
- Cardiology – Branch of medicine dealing with the heart
- Cardiovascular drift – medical condition
- Cardiac cycle – Performance of the human heart
- Vital heat
- Cardiac muscle – Muscular tissue of heart in vertebrates
- Major systems of the human body– Entire structure of a human being
- Amato Lusitano– Portuguese physician (1511–1568)
- Vascular resistance – Force from blood vessels that affects blood flow
References
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External links
- Circulatory Pathways in Anatomy and Physiology by OpenStax
- The Circulatory System
- Michael Servetus Research Study on the Manuscript of Paris by Servetus (1546 description of the Pulmonary Circulation)