It is a device that performs the following functions:

- Distributing oxygen, nutrients and hormones to all parts of the body through the blood.

- Returning blood carrying carbon dioxide and metabolic waste from various parts of the body to the heart

- Transferring impure blood to the lungs to get rid of carbon dioxide and absorb oxygen, as well as transferring blood to the kidneys and excretory organs to get rid of metabolic waste.

The circulatory system consists of:

The heart

The blood

Blood vessels

The heart :

A hollow muscular organ the size of a master's fist. It is located in the middle of the chest cavity between the lungs, slanted to the left. It is surrounded by a pericardial membrane that protects it from friction and facilitates its movement. It consists of a special muscle tissue that has the ability to contract and relax throughout life. The heart works as a pump to push blood into the blood vessels until the system The department has the function of distributing blood to all parts of the body.

Heart shape:

The heart is roughly pyramid-shaped, with an apex, a base, and three surfaces.

Top of the heart:

It heads to the left and below the heart and is located in the normal state directly under the nipple of the left breast in the distance between the fifth and sixth ribs, about 9 cm from the anterior half line, and it consists of the tip of the left ventricle.

Heart base:

It projects upward and consists of the right atrium and the left atrium

Heart surface:

1- The front surface

It is located behind the sternum and the cartilages of the second to sixth ribs, and its composition is shared by the right atrium, the right ventricle, and a small part  of the left ventricle.

2- The lower surface

It rests on the diaphragm and consists of the left ventricle and part of the right ventricle.

3- The left surface

It consists mostly of the left ventricle and part of the left atrium.

Departments of the heart:

The heart consists of four chambers, two atria and two ventricles. The right and left atrium are separated by a barrier called the interatrial septum. The right and left ventricles are also separated by the interventricular septum.

There is an opening between each atrium and its ventricle, called the aperture between the atrium and the ventricle. It is guarded by a valve that allows blood to pass from the atrium to the ventricle and does not allow it to return in the opposite direction. It can be divided into right and left halves.

1- Right half:

It consists of the right atrium and the right ventricle and pumps impure blood carrying carbon dioxide.

2- Left half:

It consists of the left atrium and the left ventricle and pumps pure blood and carries oxygen.

Heart chambers:

1- Right atrium:

Impure blood reaches it from all parts of the body through:

A- The superior vena cava from the upper part of the body.

B- The inferior vena cava of the lower part of the body.

C- Coronary venous sinus: from the heart.

The atrium pushes the impure blood into the right ventricle through an opening guarded by what is called a ventricle

Three-cuspid valve.

2- Right ventricle:

It receives impure blood from the right atrium and then pushes it to the lungs through the artery

The lung, whose beginning is guarded by a valve called the 'pulmonary valve'

3- Left atrium:

It receives fresh blood from the lungs through four pulmonary veins and then pushes it to...

The left ventricle through an opening guarded by a bicuspid valve called the mitral valve.

4- Left ventricle:

Pure blood reaches it from the left atrium and then pumps it to all parts of the body through

The aorta, whose beginning is guarded by a valve called the 'aortic valve'. It is noted that the walls of the atrium are less thick than the walls of the ventricle, which pushes blood to all parts of the body.

5-Blood vessels:

The heart is supplied with blood by two small arteries called the coronary arteries

The coronary blood flows from the beginning of the aorta, while the impure blood returns to the heart either directly or through the coronary venous sinus.

6- Heart nerves:

The heart feeds the involuntary nervous system with sympathetic nerves, which specialize in increasing the speed and strength of the heartbeat, and parasympathetic nerves, which reduce the speed and strength of the heartbeat. However, it must be noted that the heartbeat itself is due specifically to the properties of the heart muscle and does not require any nerves to perform it.

7- Pericardial membrane:

The heart and the large blood vessels connected to it are surrounded by a membrane called the pericardium.

This membrane consists of two parts:

1- A fibrous membrane on the outside protects the heart and connects it to the sternum.

2- A thin membrane with two layers

A- The parietal layer lines the fibrous membrane from the inside.

B- The visceral layer covers the outer surface of the heart and is located between the two layers

A narrow capillary space containing a viscous fluid that facilitates the movement of the heart and reduces its friction

The blood circulation is divided into:

1- Minor (pulmonary) circulation, in which the blood is purified in the lungs and then returns to the heart.

2- Greater (general) circulation, in which pure blood is distributed to all parts of the body

Then the pure blood returns to the heart.

3- The portal cycle, in which blood loaded with nutrients passes from the digestive canal to the liver

From there to the inferior vena cava.

1-  Microcirculation:

Impure blood from all parts of the body reaches the right atrium, which contracts and pushes the blood through the opening of the three-cuspid valve into the right ventricle. The three-cuspid valve closes and the blood rushes through the pulmonary valve to the pulmonary artery, which divides into two branches, each of which passes to one of the lungs.

The blood is purified in the lungs, getting rid of carbon dioxide and gaining oxygen. Then the purified blood returns to the left atrium through four pulmonary veins.

2-   Greater circulation:

The left atrium contracts, pushing blood through the mitral valve into the left ventricle. The left ventricle contracts, closing the mitral valve, and blood rushes through the aortic valve to the aorta, which distributes pure blood to the heart and all parts of the body.

Impure blood collects and then returns to the right atrium via the superior vena cava, inferior vena cava, and coronary venous sinus.

3-  The papal session:

Impure blood collects from the digestive tract, loaded with nutrients after they are digested and absorbed, and then passes into the portal vein, which carries it to the liver.

The portal vein in the liver divides into capillaries, and thus the blood passes through the liver cells, where some metabolic processes take place.

The capillaries gather again to form small veins that end in the two hepatic veins that drain into the inferior vena cava, and thus the blood returns to the greater circulation.

4-  Blood vessels:

Blood vessels are the tubes that transport blood from the heart to the body's organs and then return blood from the body's organs to the heart. Blood vessels are divided into arteries and veins.

The blood vessel consists of three layers:

1- A smooth inner layer that is in direct contact with the blood.

2- An intermediate layer composed of involuntary muscles that control the expansion and constriction of vessels

Blood flow as needed, and it is thicker in an artery than in a vein.

3- Fibrous outer layer.

Arteries:

The artery is the blood vessel that carries blood from the heart to the organs of the body. All arteries carry pure blood, except for the pulmonary artery and its branches, which carry impure blood. All the arteries of the body except the pulmonary artery arise from a common trunk, which is the aorta, which starts from the left ventricle and then gives branches that divide into smaller arteries. It gets smaller until it ends in the various organs with tiny blood vessels called adjacent capillaries to form braids of capillaries that nourish the tissues with different cells. From these braids begin the tributaries of the veins that come together to form larger and larger veins, and in the end the superior vena cava and the inferior vena cava are formed, which open into the right atrium.

Veins:

The vein is the blood vessel that carries blood from the body's organs to the heart. All veins carry impure blood except for the four pulmonary veins, which carry pure blood from the lungs to the left atrium.

Blood circulation :

This cycle lasts 8 of a second and includes three turns.

1- Contraction cycle:

It begins with the contraction of the right and left atria, and the blood passes from each atrium to the corresponding ventricle through the valves between the atria and the ventricles. Then the ventricles contract and these valves close, and the blood passes from the right ventricle to the pulmonary artery and from the left ventricle to the aorta, thus ending the cycle of contraction.

2- Relaxation cycle:

The contraction cycle follows, during which the heart muscles relax, the pressure inside its chambers decreases, and the pulmonary and aortic semilunar valves close to prevent blood from returning to the ventricles.

3- Rest cycle:

The relaxation cycle follows, in which impure blood flows from the hollow veins to the right atrium, and pure blood flows from the pulmonary veins to the left atrium until the atrium is filled with blood.

Heartbeat :

In the normal state in adults, the heart contracts 72 times per minute and in a newborn child about 120 times per minute. The heart’s contractions are reflected in the arteries because they are rubber tubes, causing waves that determine the pulse. Feeling the pulse can determine the state of the heartbeat in terms of speed, strength, and regularity. The best place to feel the pulse is The radial artery is located directly under the skin in front of the lower end of the radius.

Heart sounds:

The heart has two basic sounds in each beat or beat, known as the first sound and the second sound.

First voice:

It is longer and lower in intensity than the second sound and is heard in the form of a 'pulp' and is caused by the contraction of the heart muscle and the closing of the valves between the atrium and the ventricle forcefully at the apex of the heart, about 9 cm from the front half line in the distance between the left fifth and sixth ribs.

Second voice:

Farther and more intense than the first sound and it is heard in the form of a 'bear' caused by the closing of the pulmonary artery and aortic valves. This sound is heard on both sides of the sternum in the space between the first and second ribs. In some pathological conditions that affect the heart valves and distort them, these valves narrow or recoil and the heart sounds become It is abnormal and is caused by what is called heart murmur.