For all, without exception, multicellular organisms having differentiated tissues and organs, the main condition for their life is the need to transfer oxygen and nutrients to the cells that make up their body. The function of the transport of the above compounds is performed by blood moving through a system of tubular elastic structures - vessels, combined into the circulatory system. Its evolutionary development, structure, and functions will be considered in this paper.
Annelids
The circulatory system of organs first appeared in representatives of the type of annulus (annelids), one of which is the well-known earthworm - the inhabitant of the soil, increasing its fertility and belonging to the class of low-bristle.
Since this organism is not highly organized, the circulatory system of earthworm organs is represented by only two vessels - the dorsal and ventral, connected by annular tubes.
Features of the movement of blood in invertebrates - mollusks
The circulatory system of organs in mollusks has a number of specific signs: a heart appears, consisting of ventricles and two atria and distills blood throughout the body of the animal. It flows not only through the vessels, but also between the organs.
Such a circulatory system is called open. We observe a similar structure in representatives of the arthropod type: crustaceans, spiders and insects. Their circulatory system of organs is open, the heart is located on the dorsal side of the body and looks like a tube with partitions and valves.
Lancelet - the ancestral form of vertebrate animals
The circulatory system of organs of animals with an axial skeleton in the form of a chord or spine is always closed. In the cephalic chords, to which the lancelet belongs, one circle of blood circulation, and the abdominal aorta plays the role of the heart. It is her pulsation that provides blood circulation throughout the body.
Blood circulation in fish
The superclass of fish includes two groups of aquatic organisms: the cartilage class and the bone fish class. With significant differences in the external and internal structure, they have a common feature - the circulatory system of organs, whose functions are to transport nutrients and oxygen. It is characterized by the presence of one circle of blood circulation and a two-chamber heart.
The heart of fish is always two-chamber and consists of the atrium and ventricle. Valves are located between them, so the movement of blood in the heart is always unidirectional: from the atrium to the ventricle.
Blood circulation in the first land animals
These include representatives of the class of amphibians, or amphibians: the sharp-faced frog, tree frog, spotted salamander, newt and others. In the structure of their circulatory system, complications of organization are clearly visible: the so-called biological aromorphoses. This is a three-chambered heart (two atria and ventricle), as well as two circles of blood circulation. Both begin from the ventricle.
In a small circle, blood rich in carbon dioxide moves to the skin and bag-like lungs. Here, gas exchange occurs, and arterial blood returns from the lungs to the left atrium. Venous blood from the vessels of the skin enters the right atrium, then in the ventricle the arterial and venous blood mix, and such mixed blood moves to all organs of the amphibian body. Therefore, their metabolic rate, like that of fish, is quite low, which leads to the dependence of amphibian body temperature on the environment. Such organisms are called cold-blooded, or poikilothermic.
The circulatory system in reptiles
Continuing to consider the features of blood circulation in animals leading a terrestrial way of life, we dwell on the anatomical structure of reptiles, or reptiles. The circulatory system of organs in them is more complicated than that of amphibians. Animals belonging to the class of reptiles have a three-chambered heart: two atria and a ventricle, in which there is a small septum. Animals belonging to the crocodile order have a solid partition in the heart, which makes it four-chamber.
And the reptiles included in the squamous squad (monitor lizard, gecko, steppe viper, nimble lizard) and belonging to the tortoise squad have a three-chambered heart with an ungrown septum, as a result of which arterial blood enters their forelimbs and head, and the caudal and trunk sections receive mixed. In crocodiles, arterial and venous blood mixes not in the heart, but outside it - as a result of the fusion of two arches of the aorta, therefore mixed blood flows to all parts of the body. Without exception, all reptiles are also cold-blooded animals.
Birds are the first warm-blooded organisms
The circulatory system of organs in birds continues to become complicated and improved. Their heart is completely four-chamber. Moreover, in two circles of blood circulation, arterial blood never mixes with venous. Therefore, the metabolism in birds is extremely intense: the body temperature reaches 40-42 ° C, and the heart rate ranges from 140 to 500 beats per minute, depending on the size of the bird's body. The pulmonary circulation, called the pulmonary, delivers venous blood from the right ventricle to the lungs, then of them arterial blood, rich in oxygen, enters the left atrium. The large circle of blood circulation begins from the left ventricle, then the blood enters the spinal aorta, and already from it through the arteries to all the organs of the bird.
The movement of blood through the vessels in mammals
Like birds, mammals belong to warm-blooded or homeothermic organisms. In the modern fauna, they belong to the first place in terms of adaptation and prevalence in nature, which is explained primarily by the independence of their body temperature from the environment. The circulatory system of mammals, the central organ of which is a four-chambered heart, is an ideally organized system of vessels: arteries, veins and capillaries. Blood circulation is carried out in two circles of blood circulation. Blood in the heart never mixes: in the left part arterial moves, and in the right - venous.
Thus, the circulatory system of organs in placental mammals provides and maintains the constancy of the internal environment of the body, that is, homeostasis.
The circulatory system of human organs
Due to the fact that man belongs to the class of mammals, the general plan of the anatomical structure and functions of this physiological system in him and animals is quite similar. Although the upright posture and the specific structural features of the human body associated with it still left a definite imprint on the mechanisms of blood circulation.
The circulatory system of human organs consists of a four-chamber heart and two circles of blood circulation: small and large, which were discovered in the 17th century by the English scientist William Harvey. Of particular importance is the blood supply to human organs such as the brain, kidneys and liver.
The vertical position of the body and blood supply to the pelvic organs
Man is the only creature in the class of mammals whose internal organs do not weigh on the abdominal wall, but on the belt of the lower extremities, consisting of flat pelvic bones. The circulatory system of the pelvic organs is represented by a system of arteries suitable from the common iliac artery. This is primarily the internal iliac artery, which brings oxygen and nutrients to the pelvic organs: the rectum, bladder, genitals, prostate gland in men. After gas exchange occurs in the cells of these organs and arterial blood turns into venous blood vessels - the iliac veins - flow into the inferior vena cava, which carries blood into the right atrium, where the large circle of blood circulation ends.
It is also necessary to take into account the fact that all the organs of the small pelvis are quite large formations, and they are located in a relatively small volume of the body cavity, which often causes pressure on the blood vessels that feed these organs. Usually it occurs due to prolonged sedentary work, in which the blood supply to the rectum, bladder and other parts of the body is disturbed. This leads to congestion that provokes infection and inflammation in them.
Blood supply to the human genitals
The circulatory system of the human organs performs the normal course of the reactions of plastic and energy metabolism at all levels of the organization of our body, from the molecular to the organismic. The organs of the small pelvis, which includes the genitals, are supplied, as mentioned above, from the descending part of the aorta, from which the abdominal branch departs. The circulatory system of the genitals is formed by a system of blood vessels that provide the supply of nutrients, oxygen and the removal of carbon dioxide, as well as other metabolic products.
The male sex glands - the testicles in which the spermatozoa mature - receive arterial blood from the testicular arteries extending from the abdominal aorta, and the venous blood outflow is carried out by the testicular veins, one of which - the left - merges with the left renal vein, and the right enters directly into the lower vena cava. The penis is supplied with blood vessels departing from the internal genital artery: it is the urethral, dorsal, bulbous and deep arteries. The movement of venous blood from the tissues of the penis is ensured by the largest vessel - the deep dorsal vein, from which the blood moves to the urogenital venous plexus associated with the inferior vena cava.
Blood supply to the female genital organs is carried out by the system of arteries. Thus, the perineum receives blood from the internal genital artery, the uterus is supplied with a branch of the iliac artery, called the uterine, and the ovaries are provided with blood from the abdominal aorta. In contrast to the male reproductive system, the female venous network of vessels is very well developed, connected by bridges - anastomoses. Venous blood flows into the ovarian veins entering the inferior vena cava, which then flows into the right atrium.
In this article, we examined in detail the development of the circulatory system of animal and human organs, which provides the body with oxygen and nutrients necessary for life support.