The Heart Structure and Functions

The individual chapters on the structure of the heart, action phases of the heart, conduction system of the heart and innervation of the heart illustrate the structure and function of the heart.

Structure of the heart


Chambers and valves, including blood flow display

Definition of an artery: An artery is a blood vessel in which blood flows away from the heart.
Example: pulmonary artery (oxygen-depleted blood), aorta (oxygen-rich blood).

Definition of a vein: A vein is a blood vessel in which blood flows to the heart.
Example: pulmonary vein (oxygen-rich blood), body vein (oxygen-poor blood)

heart diagram with heart valves and blood flow display. Red = oxygen-rich blood. Blue = oxygen-depleted blood. Picture: “Heart diagram” of ZooFari, licensed under CC BY-SA 3.0.

Traveling through the heart with the bloodstream

Through the lower (a) and upper (b) vena cava, the blood enters the right (c) atrium of the heart.

The tension of the right atrial muscles pushes the oxygen-deficient blood through the (d) tricuspid valve into the right (e) ventricle.

Relaxation of the right atrial musculature and tension of the right chamber musculature.

The (d) tricuspid valve closes by increasing pressure in the right (e) chamber like a check valve.

The oxygen-deficient blood is pressed through the (f) pulmonary valve out of the heart into the right (g) and left (h) pulmonary artery.

Here, the (f) pulmonary valve acts as a check valve and prevents blood from flowing back into the left chamber.

Although the blood in the vessels between the heart and lungs is still low in oxygen, these vessels are referred to as “arteries”.

The blood now “travels” through the lungs. Gas exchange takes place at the alveoli (alveoli). Carbon dioxide is released and oxygen is absorbed. From here on, the blood is oxygen-rich.

The oxygen-rich blood now passes through the right (i) and left (k) pulmonary veins into the left (l) atrium.

Although the blood in the vessels between the lungs and heart is now oxygen-rich, these vessels are referred to as “veins”.

The tension in the left atrial muscles pushes the oxygen-rich blood through the (m) mitral valve (bicuspid valve) into the left (n) ventricle.

Relaxation of the left atrial muscles and tension of the muscles of the left ventricle. This causes the (m) mitral valve to close like a non-return valve and the blood is pressed through the (o) aortic valve out of the heart into the (p) aorta.

Here, the (o) aortic valve acts as a check valve and prevents the oxygen-rich blood from flowing back into the heart.

The blood supply to the heart muscle

Like all other muscles in the body, the heart needs to be supplied with oxygen and nutrients. This is done through special blood vessels called coronary arteries.

Two large coronary arteries emerge from the heart, the right (1) and the left (I) coronary artery. These branches become smaller and smaller arteries and thus supply the entire heart muscle.

Normally, the left and right coronary arteries supply the heart half each with blood (balanced coronary supply type).

The heart – schematic overview of the coronary vessels. Image: “Coronary arterial circulation” by Addicted04, licensed under CC BY 3.0.

Right hemisphere care

  1. Arteria coronaria dexter ⇒ right coronary artery.
  2. Ramus nodi sinuatrialis ⇒ Sinus artery.
  3. Ramus coni arteriosi ⇒ Transition branch of the right ventricle into the pulmonary artery.
  4. Ramus atrial dexter ⇒ Right atrial branch.
  5. Ramus atrioventricular dexter ⇒ right atrial chamber branch.
  6. Ramus marginalise dexter ⇒ right edge branch.
  7. Ramus interventricular posterior ⇒ posterior branch located between the two chambers.

The left half of the heart care

  1. Arteria coronaria sinister ⇒ left coronary artery.
  2. Ramus circumflexus ⇒ surrounding branch of the left coronary artery.
  3. Ramus posterolateral sinister ⇒ Branch of the left posterior wall.
  4. Ramus marginalis sinister ⇒ left edge branch.
  5. Ramus diagonalis ⇒ diagonal side branch.
  6. Ramus interventricular anterior ⇒ anterior, between both chambers
    situated, branch.

The heart musculature

A detailed description of the structure and function of the heart muscle cells can be found in the article muscle types.

Cardiovascular System

The blood vessels of our organism form a closed circle from the heart away to the heart again. Roughly 2 cycles can be distinguished.

Lung Circulation

In the pulmonary circulation, the oxygen-depleted blood is pumped from the right side of the heart into the lungs. This is where the gas exchange takes place (carbon dioxide out, oxygen in). Then the oxygen-rich blood flows into the left side of the heart.

Body circulation

In the body’s circulatory system, the oxygen-rich blood is pumped from the left side of the heart into the entire body. There, the arteries branch out more and more. In the terminal final current area (capillary system) nutrients (oxygen, fats, carbohydrates, protein, etc.) are discharged from the capillaries into the body. Waste products (carbon dioxide, ultrafiltrate, etc.) are only partially removed via the blood vessels (semi-permeability of the capillary walls). The rest is removed via the lymph vessel system (so-called lymph load).

The cardiovascular system. Picture: “Cardiovascular System” by Jörg Rittmeister, licensed under CC BY-SA 2.5.

 

Action phases of the heart


Systole:

Contraction of the chamber myocardium

  • Tension phase: all dampers closed, the pressure in the ventricle increases
  • Expulsion phase: Pocket valves are pressed open, blood flows into the aorta / pulmonary artery

Diastole:

Flaccidity of the chamber myocardium

  • relaxation phase: all valves closed (blood flowing back pushes the pocket valves closed), the pressure in the ventricle drops.
  • filling phase: pressure in the atrium greater than in the ventricle, flaps open.
    • Passive filling: due to the pressure difference.
    • active filling: by atrial contraction.

The duration of all 4 phases is 1 second at a heart rate of 60 beats per minute.

At a heart rate of 200 beats per minute or more, the filling phase is zero. As a result, the effective work of the heart is no longer possible.

Pump performance of the heart Normal <-> comparison of athletes

The stroke volume is the amount of blood that the heart pumps in one stroke.

The heart minute volume describes the amount of blood that the heart pumps within one minute.

FrequencyHammer volumeHeart Minute Volume
Normal70 bpm70 ml5 l
Sportsmen50 bpm≤ 200 ml10 – 25 l

 

Excitation line system


Myogenic automation

Myogen means that the excitation propagation from heart muscle cell to heart muscle cell takes place electrically, without synapses. Automatic means that this propagation of excitation takes place by itself, without direct external influence.

Irritation conduction process in the heart

In the sinus node (right atrium) (1) heart muscle cells periodically depolarize. When a threshold is exceeded, an action potential occurs.

Excitation spread via the atria using the Bachman bundle (2) and the three internode pathways (3 -5).

A transfer of excitation from the atria to the ventricles takes place exclusively in the region of the AV node (atrioventricular) (6). The propagation of excitation. This delay gives the atria time for atrial contraction (filling of the chambers).

Rapid propagation of excitation via specialized heart muscle cells from the His bundle (7) via the two Tawaras legs (8 – 9) and the fascicles (10 – 11) to the Purkinje sutures (12) and finally to all cells of the ventricular myocardium.

-Chamber contraction

 

Propagation of excitation in the heart. Picture: “Electrical conduction system of the heart” by Madhero88, licensed under CC BY-SA 3.0.

  1. Sinus Node
  2. Bachmann Bundle
  3. front internodal trajectory
  4. medium internodal trajectory
  5. rear internodal trajectory
  6. AV node
  7. His bundles
  8. Right tawara thigh
  9. Left Tawara thigh
  10. Linksposterior fascicle
  11. Left anterior fascicle
  12. Purkinje fibers

Innervation of the heart


Motor ⇒ Heart control

About vegetative, visceromotor nervous system.

Sympathetic nervous system (postganglionic)

  • the transmitter is noradrenaline (= NA, inhibited by beta-blocker).
  • At the sinus node, the frequency ↑ is increased (= positive chronotropic).
  • The transition time at the AV node ↓ is reduced (= positive chronotropic).
  • The excitability of the chamber myocard ↑ is increased (= positive bathmotropic) and at the same time, the contractility is increased ↑ (= positive inotropic).

Parasympathetic nervous system (postganglionic)

  • the transmitter is acetylcholine (= ACH, inhibited by atropine).
  • At the sinus node, the frequency ↓ is lowered (= negative chronotropic).
  • The transition time at the AV node ↑ is increased (= negative chronotropic).

Sensitive ⇒ Pressure and pain transmission

Pressure and pain stimuli are transmitted via sensitive, viscerosensitive fibres.

  • Pain and pressure stimuli from the endocardium (inner heart wall) and myocardium (heart musculature) are transmitted parallel to the parasympathetic fibers in the vagus nerve (the tenth of the twelve cranial nerves).
  • Pain stimuli from the epicardium (outer heart wall and simultaneously inner leaf of the pericardium) and pericardium (outer leaf of the pericardium) are transmitted parallel to the somatomotor fibers of the phrenic nerve (diaphragmatic nerve).

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William C. Hilberg
As an author, Mr. Hilberg has published several papers on health issues that have gained international recognition. He is close to nature and loves the seclusion and activity as a freelance journalist. In his function as editor William C. Hilberg manages the entire content of PENP. Our team greatly appreciates his expertise and is proud to have him on board.