Circulatory system

See cardiovascular

The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body.

The circulatory system has two divisions, a systemic circulation and a pulmonary circulation.

The network of blood vessels include: the great vessels of the heart including large elastic arteries, and large veins; other arteries, smaller arterioles, capillaries that join with venules and other veins. 

The circulatory system is closed, meaning that the blood never leaves the network of blood vessels. 

Blood consists of plasma, red blood cells, white blood cells, and platelets that is circulated around the body carrying oxygen and nutrients to the tissues, and waste materials away. 

Circulated nutrient content includes: proteins and minerals, gases such as oxygen, and carbon dioxide, hormones, and hemoglobin, that provide nourishment, help the immune system to fight diseases, and in maintaining homeostasis by stabilizing temperature and natural pH.

The lymphatic system carries excess plasma filtered from the capillaries as interstitial fluid between cells, away from the body tissues in an accessory route to return the excess fluid back to the blood circulation as lymph.

The passage of lymph takes much longer than that of blood.

The lymphatic system is is essential for the functioning of the blood circulatory system; without it the blood would become depleted of fluid. 

The lymphatic system works together with the immune system.

The lymphatic system is an open system.

The systemic circulation can also be defined as a macrocirculation and a microcirculation. 

An average adult has five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for approximately 7% of their total body weight.

Blood consists of plasma, red blood cells, white blood cells, and platelets. 

Circulatory routes are associated, such as the coronary circulation to the heart itself, the cerebral circulation to the brain, renal circulation to the kidneys, and bronchial circulation to the bronchi in the lungs.

Nutrients travel through tiny blood vessels of the microcirculation to reach organs.

The lymphatic system is an essential subsystem of the circulatory system consists of a network of lymphatic vessels, lymph nodes, organs, tissues and circulating lymph. 

This subsystem is an open system.

A major function of the lymphatic system is to carry the lymph, draining and returning interstitial fluid into the lymphatic ducts back to the heart for return to the circulatory system, and works with the immune system to provide defense against pathogens.

The heart:pumps blood to all parts of the body providing nutrients and oxygen to every cell, and removing waste products. 

The left heart pumps oxygenated blood returned from the lungs to the rest of the body in the systemic circulation. 

The right heart pumps deoxygenated blood to the lungs in the pulmonary circulation. 

In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle. 

The right atrium is the upper chamber of the right side of the heart. 

The blood that is returned to the right atrium is deoxygenated and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. 

The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

Pulmonary circulation

The pulmonary circulation is the part of the circulatory system in which oxygen-depleted blood is pumped away from the heart, via the pulmonary artery, to the lungs and returned, oxygenated, to the heart via the pulmonary vein.

Oxygen-deprived blood from the superior and inferior vena cava enters the right atrium of the heart and flows through the tricuspid valve into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. 

Gas exchange occurs in the lungs, whereby CO2 is released from the blood, and oxygen is absorbed. 

The pulmonary vein returns the now oxygen-rich blood to the left atrium.

A separate circuit from the systemic circulation, the bronchial circulation supplies blood to the tissue of the larger airways of the lung.

The systemic circulation delivers oxygenated blood from the left heart to the rest of the body through the aorta. 

Deoxygenated blood is returned in the systemic circulation to the right heart via two large veins, the inferior vena cava and superior vena cava, where it is pumped from the right atrium into the pulmonary circulation for oxygenation. 

The blood vessels of the circulatory system are the arteries, veins, and capillaries. 

The large arteries and veins that take blood to, and away from the heart are known as the great vessels.

Oxygenated blood enters the systemic circulation when leaving the left ventricle, via the aortic semilunar valve.

The initial part of the systemic circulation is the aorta.

The aorta is a massive and thick-walled artery, which arches and gives branches supplying the upper part of the body after passing through the aortic opening of the diaphragm at the level of thoracic ten vertebra, it enters the abdomen.

It descends down and supplies branches to abdomen, pelvis, perineum and the lower limbs.

The aorta’s elasticity helps to maintain the blood pressure throughout the body.

The aorta receives almost five liters of blood from the heart, it recoils and is responsible for pulsating blood pressure. 

As the aorta branches into smaller arteries, their elasticity decreases and their compliance increases.

Arteries branch into small passages, arterioles and then into the capillaries.

The capillaries merge to bring blood into the venous system.

Capillaries merge into venules, which merge into veins.

The venous system feeds into the two major veins: the superior vena cava and the inferior vena cava.

The superior vena cava mainly drains tissues above the heart.

The inferior vena cava mainly drains tissues below the heart. 

These two large veins empty into the right atrium of the heart.

The general rule is that arteries from the heart branch out into capillaries, which collect into veins leading back to the heart. 

The portal veins are exception to this rule: the hepatic portal vein which combines from capillaries around the gastrointestinal tract where the blood absorbs the various products of digestion; rather than leading directly back to the heart, the hepatic portal vein branches into a second capillary system in the liver.

The heart is supplied with oxygen/nutrients through a small loop of the systemic circulation and derives very little from the blood contained within the four chambers. 

The coronary circulation system provides a blood supply to the myocardium.

The coronary circulation starts near the origin of the aorta by two coronary arteries: the right coronary artery and the left coronary artery. 

After nourishing the heart muscle, blood returns via coronary veins into the coronary sinus and into the right atrium. 

Backflow of blood through its opening during atrial systole is prevented by the Thebesian valve. 

The Thebesian valve, also known as the valve of the coronary sinus, is a fold in the right atrium at the opening of the coronary sinus.

The smallest cardiac veins drain directly into the heart chambers.

The brain has a dual blood supply, an anterior and a posterior circulation from arteries at its front and back. 

The anterior circulation arises from the internal carotid arteries to supply the front of the brain. 

The posterior circulation arises from the vertebral arteries, to supply the back of the brain and brainstem. 

The circulations from the front and back join anastomose at the circle of Willis. 

The neurovascular unit regulates the flow of blood.

The renal circulation is the blood supply to the kidneys, contains many specialized blood vessels and receives around 20% of the cardiac output. 

It branches from the abdominal aorta and returns blood to the ascending inferior vena cava.

Animation of a typical human red blood cell cycle in the circulatory system averages a 60-second cycle.

The dorsal aorta has approximately thirty smaller arteries that branch from the back and sides. 

These branches: intercostal arteries, arteries of the arms and legs, lumbar arteries and the lateral sacral arteries. 

Branches to the sides of the aorta: renal, suprarenal and gonadal arteries. 

Finally, branches at the front of the aorta consist of the vitelline arteries and umbilical arteries. 

The vitelline arteries form the celiac, superior and inferior mesenteric arteries of the gastrointestinal tract. 

After birth, the umbilical arteries will form the internal iliac arteries.

About 98.5% of the oxygen in a sample of arterial blood in a healthy human, breathing air at sea-level pressure, is chemically combined with hemoglobin molecules. 

About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. 

The hemoglobin molecule is the primary transporter of oxygen.

Many diseases affect the circulatory system: cardiovascular diseases, affecting the heart and blood vessels; hematologic diseases that affect the blood, such as anemia, and lymphatic diseases affecting the lymphatic system. 

Cardiovascular diseases referred to as lifestyle diseases because they develop over time and are related to a person’s exercise habits, diet, whether they smoke, and other lifestyle choices a person makes. 

Atherosclerosis,a precursor to many of these diseases, arises as small atheromatous plaques build up in the walls of medium and large arteries. 

Such plaques may eventually grow or rupture to occlude the arteries, and are also a risk factor for acute coronary syndromes, which are diseases that are characterised by a sudden deficit of oxygenated blood to the heart tissue. 

Atherosclerosis is also associated with problems such as aneurysm formation or dissection of arteries.

Thrombi can originate in veins or arteries. 

Deep venous thrombosis, which mostly occurs in the legs.

Such clots may embolize to another location in the body: 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

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