The circulatory or cardiovascular system, formed by the heart and blood vessels, is responsible for transporting nutrients and oxygen to different parts of the body.
Blood circulation corresponds to the entire path of the circulatory system that blood takes in the human body, so that in the complete path, blood passes through the heart twice.
These circuits are called small circulation and large circulation. Let's know a little more about each of them:
small circulation
The small circulation or pulmonary circulation is the path that blood travels from the heart to the lungs, and from the lungs to the heart.
Thus, venous blood is pumped from the right ventricle to the pulmonary artery, which branches so that one goes to the right lung and the other to the left lung.
In the lungs, the blood present in the alveoli capillaries releases carbon dioxide and absorbs oxygen gas. Finally, arterial (oxygenated) blood is carried from the lungs to the heart, through the pulmonary veins, which connect to the left atrium.
large circulation
The great circulation or systemic circulation is the way of the blood, that leaves the heart to the other cells of the body and vice versa.
In the heart, arterial blood from the lungs is pumped from the left atrium into the left ventricle. From the ventricle it passes to the aorta artery, which is responsible for transporting this blood to the various tissues of the body.
Thus, when this oxygenated blood reaches the tissues, the capillaries redo the gas exchange: they absorb oxygen gas and release carbon dioxide, making the blood venous.
Finally, venous blood makes its way back to the heart and reaches the right atrium through the superior and inferior vena cava, completing the circulatory system.
Components
The circulatory system consists of the following components:
Blood
O blood it is a liquid tissue and plays a fundamental role in the circulatory system. It is through the bloodstream that oxygen and nutrients reach the cells.
In this way, it removes from the tissues the leftovers of cellular activities, such as carbon dioxide produced in cellular respiration, and conducts hormones throughout the body.
Heart
O heart it is a muscular organ, which is located in the rib cage, between the lungs. It works like a double pump, so that the left side pumps arterial blood to different parts of the body, while the right side pumps venous blood to the lungs.
The heart works by pushing the blood through two movements: contraction or systole and relaxation or diastole.
The main structures of the heart are:
- Pericardium: membrane that lines the outside of the heart.
- endocardium: membrane that lines the interior of the heart.
- Myocardium: muscle located between the pericardium and the endocardium, responsible for the contractions of the heart.
- Atria or auricles: upper cavities where blood reaches the heart.
- ventricles: lower cavities where blood exits the heart.
- tricuspid valve: prevents the reflux of blood from the right atrium to the right ventricle.
- mitral valve: prevents blood reflux from the left atrium into the left ventricle.
Also read about myocardium and systole and diastole.
Blood vessels
You blood vessels they are tubes of the circulatory system, distributed throughout the body, through which blood circulates. They are formed by a network of arteries and veins that branch to form capillaries.
arteries
At arteries they are vessels in the circulatory system, which leave the heart and transport blood to other parts of the body. The wall of the artery is thick, made of muscular and elastic tissue, which supports the blood pressure.
Venous blood, rich in carbon dioxide, is pumped from the heart to the lungs through the pulmonary arteries. While arterial blood, rich in oxygen gas, is pumped from the heart to the body's tissues through the aorta artery.
The arteries branch through the body, become thinner, form arterioles, which branch even further, giving rise to capillaries.
veins
At veins they are vessels in the circulatory system that carry blood back from the body's tissues to the heart. Its walls are thinner than arteries.
Most of the veins carry venous blood, that is, rich in carbon dioxide. However, the pulmonary veins carry oxygenated arterial blood from the lungs to the heart.
capillaries
Capillaries are microscopic branches of arteries and veins in the circulatory system. Its walls have only one layer of cells, which allow the exchange of substances between blood and cells. Capillaries attach to veins, carrying blood back to the heart.
An average of six liters of blood circulates through the body of an adult in a wide network of blood vessels, pumped by the heart.
Learn more, read also:
- Cardiovascular system
- Lymphatic system
Types
The circulatory system is classified into two types:
- Open or lacunar circulatory system: The circulating fluid (hemolymph) travels through tissue cavities and gaps, being in direct contact with cells. In that case, there are no blood vessels. Present in some invertebrates.
- closed circulatory system: Blood circulates within vessels, from where it travels throughout the body. It is a more efficient process than open circulation, as it happens faster. It occurs in annelids, cephalopods and all vertebrates.
Circulatory system of other vertebrates
Vertebrate animals have a heart that pumps blood into blood vessels, which branch out to form a wide network of very fine vessels. This rich vascularization favors gaseous and nutrient exchanges.
The muscular heart has two types of interconnected chambers: the atrium or auricle, which receives the blood brought in by the veins, and the ventricle, which takes blood from the atrium and pumps it into the arteries. Blood passes from one cavity to another through heart valves.
birds and mammals
In birds and mammals, the heart has four chambers, two atria and two ventricles, completely separate.
Blood circulation is thus separated from arterial circulation, with no mixing of venous and arterial blood. It's a very efficient circulation.
reptiles
Most reptiles have a three-chambered heart. The ventricle is partially divided, there is mixing of blood, but in lesser amount.
In crocodylian reptiles, the division of the ventricles is complete and circulation is more complex.
amphibians
In amphibians there are three chambers in the heart: two atria and a ventricle. Venous blood enters through the right atrium and arterial blood through the left, then passes to the ventricle, where the two types of blood mix.
Fish
In fish, the heart has only two chambers, an atrium and a ventricle. Venous blood enters the atrium, passes to the ventricle and from there is pumped to the gills, where it will be oxygenated.
Invertebrate circulatory system
Some invertebrate animal phyla have a closed circulatory system with a rudimentary "heart" which helps to pump the blood fluid and branched vessels that make it reach the different parts of the body. While in others the system is open or absent.
Below are some examples:
molluscs
Molluscs have a simple circulatory system. In some classes it is closed with a “heart”, located inside the pericardial cavity, which pumps blood fluid (hemolymph), making it circulate from the arteries to different parts of the body.
In others, the circulatory system is open, with blood fluid passing from the arteries to cavities between tissues called hemocellae. Hemolymph has the pigment hemocyanin, similar to hemoglobin that transports substances.
annelids
The annelids' circulatory system is closed, with several "hearts" in the front of the body, which are vessels whose muscular walls pump blood fluid. There is a pigment similar to hemoglobin, but it is not inside cells but dissolved in the blood fluid.
arthropods
They have a dorsal tubular heart divided internally into chambers with valves that separate them, called ostia. Some insects have accessory hearts.
Test your knowledge on exercises on the cardiovascular system.
