Structure and Function of the Circulation: Volume 1

Regulation of blood flow and volume exchange across the microcirculation
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These can originate in veins or arteries.

Circulatory system

Deep venous thrombosis , which mostly occurs in the legs, is one cause of clots in the veins of the legs, particularly when a person has been stationary for a long time. These clots may embolise , meaning travel to another location in the body. The results of this may include pulmonary embolus , transient ischaemic attacks , or stroke. 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. 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 cardiovascular examination , including the taking of a person's pulse as an indicator of a person's heart rate , the taking of blood pressure through a sphygmomanometer or the use of a stethoscope to listen to the heart for murmurs which may indicate problems with the heart's valves.

An electrocardiogram can also be used to evaluate the way in which electricity is conducted through the heart. Other more invasive means can also be used. A cannula or catheter inserted into an artery may be used to measure pulse pressure or pulmonary wedge pressures. Angiography, which involves injecting a dye into an artery to visualise an arterial tree, can be used in the heart coronary angiography or brain. At the same time as the arteries are visualised, blockages or narrowings may be fixed through the insertion of stents , and active bleeds may be managed by the insertion of coils.

For evaluation of the blood supply to the lungs a CT pulmonary angiogram may be used. Vascular ultrasonography include for example:. In Ancient Greece, the heart was thought to be the source of innate heat for the body.


The circulatory system as we know it was discovered by William Harvey. The blood vascular system first appeared probably in an ancestor of the triploblasts over million years ago, overcoming the time-distance constraints of diffusion, while endothelium evolved in an ancestral vertebrate some — million years ago. 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 and there is no distinction between blood and interstitial fluid ; this combined fluid is called hemolymph or haemolymph.

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. The circulatory systems of all vertebrates , as well as of annelids for example, earthworms and cephalopods squids , octopuses and relatives are closed , just as in humans.

Still, the systems of fish , amphibians , reptiles , and birds show various stages of the evolution of the circulatory system. 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 ventricular septum of the heart is incomplete and the pulmonary artery 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 ventricle and out through the aorta.

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, mammals, 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. Circulatory systems are absent in some animals, including flatworms. Their body cavity has no lining or enclosed fluid.

Instead a muscular pharynx leads to an extensively branched digestive system that facilitates direct diffusion of nutrients to all cells.

Structure and Function of the Circulation

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. Oxygen can diffuse from the surrounding water into the cells, and carbon dioxide 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 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.

The earliest known writings on the circulatory system are found in the Ebers Papyrus 16th century BCE , an ancient Egyptian medical papyrus containing over 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.

What can go wrong?

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.

enter site 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 pulse was a property of arteries themselves. Greek anatomist Erasistratus 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.

Further information

Again, the decline in left ventricular compliance provides an increase work load on the atria, resulting in hypertrophy of the atria. Their ability to hold this much blood is due to their high capacitance , that is, their capacity to distend expand readily to store a high volume of blood, even at a low pressure. Left ventricular volume vs. Local metabolic effects targeting a close relation of regional blood flow to metabolic activity are particularly effective in the terminal arterioles, being elicited foremost by changes in pO 2 , pCO 2 , pH, osmolarity, potassium ion concentration, and released catabolites such as adenosine. Infectious Diseases. Qualified, early specialism training. As deducible from Eq.

Thus he apparently postulated capillaries but with reversed flow of blood. In 2nd century AD Rome , the Greek physician Galen 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 , The Canon of Medicine by the Persian physician , Avicenna , "erroneously accepted the Greek notion regarding the existence of a hole in the ventricular septum by which the blood traveled between the ventricles. In , the Arabian physician , Ibn al-Nafis , became the first person to accurately describe the process of pulmonary circulation , for which he is sometimes considered the father of circulatory physiology.

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 years. 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" [24] [25] near , 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 because of persecution of Servetus by religious authorities. Better known discovery of pulmonary circulation was by Vesalius 's successor at Padua , Realdo Colombo , in 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 , 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.

1. There Are Two Types of Circulation: Pulmonary Circulation and Systemic Circulation

However, Harvey was not able to identify the capillary system connecting arteries and veins; these were later discovered by Marcello Malpighi in Richards were awarded the Nobel Prize in Medicine "for their discoveries concerning heart catheterization and pathological changes in the circulatory system. In the s, Diana McSherry developed computer-based systems to create images of the circulatory system and heart without the need for surgery. From Wikipedia, the free encyclopedia.