The heart & the vessels

The left and right halves of the heart consist of an atrium and a ventricle respectively. Both halves are separated by the cardiac septum. The used, oxygen-poor blood reaches the right half of the heart through the veins. From there, it is pumped into the lung to be resupplied with oxygen. The oxygen-rich blood is then transported over the left half of the heart into the main artery and supplies the whole body with oxygen. The four heart valves – two on either side – ensure that the blood flows in the correct direction.

The healthy heart beats in a regular rhythm between 60 and 80 times per minute and necessitates four to six litres of blood through the arteries during this time. (360 litres per hour, 8640 litres per day). The heart rate increases during sporting activity or times of emotional stress; during period of sleep, it slows down.

Heart beats are generated and controlled by the heart's electrical conduction system. Each heart beat (lat. systole) is generated automatically by the natural cardiac pacemaker, the sinus node. The electrical signal generated in the sinus node spreads across the atria and ensures that they contract and automatically push the blood towards the heart ventricles.

Afterwards, the electrical impulse is sent further into the middle of the heart to the AV nodes (atrioventricular nodes) before it is transferred to the ventricles, which contract and pump the body to the lungs and into the body. During a regular heart beat, first the atria and then the ventricles contract. The AV node is tasked with relaying the beat correctly to the main ventricles so that the heart does not beat too quickly or too slowly.

If erroneous electrical impulses occur or if these spread out incorrectly over the conductive tissue in the heart muscle, they impact on the heart function. This is manifested in an irregular, chaotic, overly quick or slow heart rhythm.

The majority of the electrical conduction of the heart can be illustrated with the help of an electrocardiogram (ECG). This illustrates whether the electrical activity of the heart is regular and coordinated.

 Several waves are visible on the ECG: The P wave reflects stimulation of the atrium, which pushes the blood into both ventricles. This is followed by a high deflection, the R wave. This corresponds to the stimulation of both ventricles. The subsequently registered T wave shows the "electrical" recovery of the heart cells. An ECG cannot record the electrical impulse generated in the sinus node; only the P wave which is generated is recorded.

If all the blood vessels of an adult person were lined up, they would measure around 100,000 km in length. Together with the heart, all the blood vessels form the anatomical basis for the blood circulation and thus for the transport of oxygen and nutrients throughout the whole body.

There are different types of blood vessels:

• Aorta (main artery)
• Arteries (pulse arteries)
• Arterioles (small pulse arteries)
• Capillaries
• Veins (blood vessels)
• Venoles (small veins)
• Vena cava veins

Aorta (main artery)

The aorta originates directly from the heart, so it is called the main artery. It transports the blood from the left ventricle to the arterial vessels of the blood circulation.

Arteries (pulse arteries)

All the blood vessels which transport the blood away from the heart into the body are considered to be arteries. With the exception of the pulmonary arteries, which carry the oxygen-poor blood from the right half of the heart into the lungs, the arteries carry the oxygen-rich blood.  Arteries are also termed pulse or radial arteries, as the pulse can be detected with the major arteries.

Arterioles (small pulse arteries)

Arterioles are transitional zones from the arteries to the capillaries in the vascular system. They are located in front of the capillaries and behind the arteries. Arterioles can dilate and contract, and in doing so they regulate the blood supply to the organs.

Capillaries

Blood capillaries connect the venous and arterial vascular system. They are the smallest bronchioles of the blood vessels and form a fine net, in which the metabolic exchange between blood vessels and the body tissue takes place. The lymphatic capillaries, which collect lymph fluid, are the initial section of the lymphatic system in the lymph vascular system.

Veins (blood vessels)

The veins carry the blood circulating in the body back towards the heart. They are divided into deep and surface veins, whereby more than 90% of all blood flows back in the deep veins.  In the case of an adult, this corresponds to around 8,000 litres of blood transported per day. All veins carry venous (oxygen-poor blood) right to the lung veins. Along with the capillaries and the venoles, they are part of the low-pressure system of the bloodstream.

Venoles (small veins)

Venoles are the smallest veins and still visible to the naked eye. For example, they are found on the sclera of the eyes (the white of the eye) in the form of fine vascular drawings.

Vena cava veins

They are two major veins which collect venous (oxygen-poor) blood from the body veins and carry it to the right atrium. There are upper vena cava veins, which collect blood from the head, neck, chest and the upper extremities. The lower vena cava veins.