Which mollusks have an open circulatory system

Tip 1: Which animals have an open circulatory system?

The non-closed circulatory system is characterized by the fact that blood is poured from the vessels directly into the body cavity. Then she goes back to the vessels. Only mollusks and arthropods have such a circulatory system in all animals.

Molluscum circulatory system


A non-closed circulatory system is found in mollusks. These are aquatic or land animals, the body of which consists mainly of soft tissues and is covered with a sink. The body cavity in adults is largely reduced, and the spaces between the organs are filled with connective tissue. The circulatory system includes the heart and blood vessels; the heart is divided into 1 ventricle and several atria. Atria can be 2 or 4, and there can only be one.
Blood is poured from blood vessels into the gaps between the internal organs, where it gives off oxygen, after which it is collected back into the vessels and sent to the respiratory system. Respiratory tract - lungs or gills, covered with a dense network of capillaries. Here the blood is again saturated with oxygen. Basically, the blood of mollusks has no color, it contains a special substance that can come into contact with oxygen.
Exceptions are cephalopods, which have an almost closed circulatory system. They have two hearts, both hearts are in the gills. Blood flows through the gill capillaries and then enters the organs from the main heart. Thus, blood partially flows into the body cavity.

Arthropod circulatory system


An open circulatory system is also found in the arthropod species, whose representatives inhabit all possible habitats. A distinctive feature of arthropods - the presence of limbs that allow various movements. This type includes classes: crustaceans, arachnids, insects.
There is a heart above the intestine. It can be in the form of both a tube and a bag. Blood travels from the arteries to the body cavity, where there is oxygen. Gas exchange is made possible by the presence of respiratory pigments in the blood. After the blood is collected in the veins, it enters the gill capillaries, where it becomes saturated with oxygen.
In crustaceans, the structure of the circulatory system is directly related to the structure of the respiratory system. Your heart is not far from the airway. In primitive crustaceans, the heart is in the shape of a tube with holes in each segment of the body, in more developed bodies it is the shape of the sac. There are primitive crustaceans in which gas exchange occurs through the body wall. Such a circulatory system can be completely absent. The heart of the arachnid basically looks like a tube with several holes in it. It looks like a bag for the little ones.
The fluid that flows through the insect's circulatory system is called the hemolymph. It is partially located in a special organ - the vertebral body, which is shaped like a tube. The rest is flushed from the internal organs. The back vessel consists of the heart and aorta. The heart is divided into chambers, the number of which corresponds to the number of body segments.

Tip 2: the circulatory system of amphibians, crustaceans and reptiles

The circulatory system of amphibians (frogs, tritons, salamanders, worms) differs significantly from that of reptiles (snakes, turtles, crocodiles, lizards) and crustaceans (crabs). Amphibians are intermediaries between crustaceans and reptiles.

Amphibian circulatory system


In amphibious animals, the circulatory system is closed. Only lung salamanders have a heart that is made up of two chambers. All other amphibians have a heart with three chambers. The circulatory system of the representatives of this class of animals consists of two circles of blood circulation - small and large. It is strange that pulmonary circulation was created by the occurrence of pulmonary breathing in these animals. The heart of the amphibian consists of two atria and one ventricle.
The blood of these animals in different atria is different: in the right area it is mixed (more venous) and in the left arterial area. Amphibians also have a number of arteries that are responsible for blood transfer: for example, the cutaneous-pulmonary arteries carry venous blood to the skin and lungs. Sleepy arteries supply the upper body with arterial blood (for example, the head). Aortic arches carry mixed blood to all other amphibian organs. It is worth noting that the body temperature of amphibians is a variable value depending on the ambient temperature, since amphibians are cold-blooded animals.

Reptile cycle system


The circulatory system of reptiles is similar to that of amphibians, but there are also differences. The reptilian heart consists of two atria that open into the ventricle. In all reptiles except crocodiles, the ventricle is separated by an incomplete septum. This allows some of the blood from the atria to mix. The pulmonary artery and the two aortic arches begin independently in the heart chamber and unite in the spinal aorta, while the arteries extending from it supply the other organs of the reptile with mixed blood. Such an organization of the blood supply allows these animals to be best adapted to one or the other living condition.

Crustacean circulatory system


In crustaceans, the circulatory system is open. This distinguishes them from the other two animal classes listed above. If one compares the circulatory system of crustaceans with that of reptiles and amphibians, the former is the most primitive. The heartbeat sets the blood in motion near the gills. Only higher crustaceans have blood vessels. In all other representatives of this trivial group of animals, blood flows freely through the cavities near the internal organs. Such respiratory pigments often dissolve in such blood.

Tip 3: the main types of animal tissue

A tissue is a group of cells formed by the same structure, origin, functions, and waste products. A distinction is made between the following types of animal tissues: epithelial, connective, nervous and muscular.

Epithelium, connective tissue


Epithelium is a collection of cells that cover the surface of the body and line its cavity. Epithelial tissue plays a protective receptor function. It ensures the absorption of substances and their release, is involved in gas exchange. There are cubic, flat, and cylindrical epithelium. Flat is in the vessels of the circulatory and lymphatic systems, alveoli, body cavities. The cubic epithelium is in the retina, the cylindrical in the intestine.
Connective tissue consists of fibers - well-developed intercellular structures (elastic, collagen and reticular) as well as the structureless main substance. Types of connective tissue are: loose, dense (cartilage, bone), reticular. It carries out storage, protection and feeding functions.
In the cartilage, chondrocytes are immersed in the main substance. There is elastic, hyaline, fibrous cartilage. Hyaline cartilage lines the cavities in the joints and joint heads. Elastic cartilage is fibrous in the auricles - in the intervertebral discs. The functions of the cartilage are mechanical and connective.
Bone tissue is formed from connective tissue or by replacing the cartilage. The main substance is composed of collagen fibers and protein-polysaccharide complexes. Fully formed bone tissue consists of bone plates in which there are osteocytes.
Reticular connective tissue is connected to large, branched reticular cells that can turn into phagocytes, or blood elements. Reticular cells and fibers form the supporting network in which free cells are located. Lymphatic organs and hematopoietic tissues have a similar structure.

Muscle and nerve tissue


Muscle tissue is divided into smooth and streaked. The composition of smooth muscles includes spindle-shaped cells. It is characterized by slow contraction and slow relaxation. Smooth muscles form the muscles of the internal organs: blood vessels, uterus, intestines, respiratory tract, ureters. Muscle tissue is innervated by the autonomic nervous system.
The striped tissue is made up of multi-core cells, the muscle fibers. It is made up of skeletal muscles that are innervated by the spinal nerves. The striated muscles can quickly contract and become tired.
Nerve tissue consists of nerve cells (neurons) and glial cells. Nerve cells receive signals from the environment, convert these signals into nerve impulses that are sent to the nerve endings. Neurons show secretory activity, they secrete mediators - physiologically active substances that are involved in the implementation of contacts between cells. Neurons can also secrete hormones.
Glial cells are necessary for the transfer of substances to the nerve cells from the blood and back. They form myelin sheaths and perform supportive and protective functions.