Venous vessels are the most important part of the "vessel-heart" system of the body, closely interconnected with lymph and arteries. Thanks to the venous system, the flow of lymph and blood to the heart is ensured.
The veins of the systemic circulation are a closed system of vessels that collect oxygen-depleted blood from all body cells and tissues, united by the following subsystems:
- cardiac veins;
- superior vena cava;
- inferior vena cava.
The difference between venous and arterial blood
Venous blood is the blood that flows back from all cellular systems and tissues, saturated with carbon dioxide, containing metabolic products.
Medical manipulations and research are carried out mainly with blood that contains metabolic end products and less glucose.
Arterial blood is the blood that flows to all cells and tissues from the heart muscle, saturated with oxygen and hemoglobin, containing nutrients.
Oxygenated arterial blood circulates through the arteries of the systemic circulation and through the veins of the pulmonary circulation.
Structure of veins
The walls of venous vessels are much thinner than arterial ones, since the blood flow velocity in them and the pressure are lower. Veins stretch more easily, their elasticity is lower than arteries. The valves of the vessels are usually located opposite, which prevents the backflow of blood. A large number of vein valves are located in the lower extremities. In the veins are also semilunar valves from the folds of the inner shell, which have a special elasticity. There are venous vessels in the arms and legs located between the muscles, which, with muscle contraction, allows blood to return back to the heart.
Circulation process
The large circle originates in the left ventricle of the heart, and from it comes the aorta with a diameter of up to three centimeters. Further, the oxygenated blood of the arteries flows through vessels decreasing in diameter to all organs. Having given up all the useful substances, the blood is saturated with carbon dioxide and goes back through the venous system through the smallest vessels - venules, while the diameter gradually increases, approaching the heart. Venous blood from the right atrium is pushed into the right ventricle, and the pulmonary circulation begins. Entering the lungs, the blood is again filled with oxygen. Through the veins, arterial blood enters the left atrium, which is then pushed out into the left ventricle of the heart, and the circle repeats again.
Arteries and veins of the systemic circulation include the aorta, as well as smaller, superior and inferior hollow vessels branching off from it.
Small capillaries make upThe human body has an area of about one and a half thousand square meters.
The veins of the systemic circulation carry depleted blood, except for the umbilical and pulmonary, which carry arterial, oxygenated blood.
Cardiac vein system
These include:
- veins of the heart that go directly into the cavity of the heart;
- coronary sinus;
- great cardiac vein;
- left posterior ventricular vein;
- left atrial oblique vein;
- anterior vessels of the heart;
- middle and small veins;
- atrial and ventricular;
- the smallest venous vessels of the heart;
- atrioventricular.
The driving force of blood flow is the energy supplied by the heart, as well as the pressure difference in the sections of the vessels.
Superior vena cava system
The superior vena cava takes the venous blood of the upper body - the head, neck, sternum and part of the abdominal cavity and enters the right atrium. Vessel valves are absent. The process is as follows: the blood saturated with carbon dioxide from the upper vein flows into the pericardial region, lower - into the region of the right atrium. The superior vena cava system is divided into the following parts:
- The upper hollow is a small vessel, 5-8 cm long, 2.5 cm in diameter.
- Unpaired - continuation of the right ascending lumbar vein.
- Semi-unpaired - continuation of the left ascending lumbar vein.
- Posterior intercostal - collection of veins of the back, its muscles, external and internal vertebralplexus.
- Intravertebral venous connections - located inside the spinal canal.
- Shoulocephalic - roots of the upper hollow.
- Vertebral - location in the diametrical holes of the cervical vertebrae.
- Deep cervical - collection of venous blood from the occipital region along the carotid artery.
- Internal chest.
Inferior vena cava system
Inferior vena cava is the connection of the iliac veins on both sides in the region of 4-5 vertebrae of the lower back, takes the venous blood of the lower parts of the body. The inferior vena cava is one of the largest veins in the body. It is about 20 cm long, up to 3.5 cm in diameter. Thus, blood flows from the lower hollow from the legs, pelvis and abdomen. The system is divided into the following components:
- Inferior vena cava.
- Lumbar veins - abdomen.
- Inferior diaphragmatic - collection of blood from the lower area of the diaphragm.
- Group of splanchnic vessels - includes renal and adrenal, testicular and ovarian vessels, hepatic veins.
- Gateway - combines blood from unpaired organs of the peritoneum - stomach, liver, spleen and pancreas, as well as part of the intestine.
- Inferior mesenteric - includes the upper rectum, sigmoid colon, and descending colon.
- Superior mesenteric - includes small intestine, cecum and appendix.
Portal vein
The portal vein got its name due to the entry of the trunk intothe gates of the liver, as well as the collection of venous blood from the digestive organs - the stomach, spleen, large and small intestines. Its vessels are located behind the pancreas. Vessel length 500-600 mm, diameter - 110-180 mm.
The tributaries of the visceral trunk are the superior mesenteric, inferior mesenteric and splenic vessels.
The anatomy system of the portal vein basically includes the vessels of the stomach, intestines of the large and small intestines, pancreas, gallbladder and spleen. In the liver, it divides into right and left and further branches into smaller veins. As a result, they are connected to the central veins of the liver, sublobular veins of the liver. And in the end, three or four hepatic vessels are formed. Thanks to this system, the blood of the digestive organs passes through the liver, entering the subsystem of the inferior vena cava.
The superior mesenteric vein accumulates blood in the roots of the mesentery of the small intestine from the ileum, pancreatic, right and middle colon, iliac colon and right ventricular-omental vein.
The inferior mesenteric vein is formed from the superior rectal, sigmoid and left colic veins.
The splenic vein combines splenic blood, blood from the stomach, duodenum and pancreas.
Jugular venous system
From the base of the skull to the supraclavicular cavity runs the vessel of the jugular vein. The systemic circulation includes these veins, which are key collectors of blood from the head and neck. In addition to internal, blood from the head and soft tissuescollects and external jugular vein. The outer one starts in the region of the auricle and goes down along the sternocleidomastoid muscle.
Veins coming from the external jugular:
- posterior ear - collection of venous blood behind the auricle;
- occipital branch - collection from the venous plexus of the head;
- suprascapular - taking blood from formations of the periosteal cavity;
- transverse veins of the neck - satellites of the transverse cervical arteries;
- anterior jugular - consists of the mental veins, veins of the maxillohyoid and sternothyroid muscles.
The internal jugular vein originates in the jugular cavity of the skull, being a satellite of the external and internal carotid arteries.
Great circle functions
It is thanks to the continuous movement of blood in the arteries and veins of the systemic circulation that the main functions of the system are provided:
- transportation of substances to ensure the functions of cells and tissues;
- transport of essential chemicals for metabolic reactions in cells;
- collection of cell and tissue metabolites;
- communication between tissues and organs through blood;
- transport to cells of protective agents;
- removal of harmful substances from the body;
- heat exchange.
The vessels of this circle of blood circulation are an extensive network that provides blood to all organs, in contrast to the small circle. The optimal functioning of the system of the superior and inferior vena cava leads to a competent blood supply to allorgans and tissues.
