Why doesn't the heart get tired? Biology lesson plan The structure and function of the heart (Grade 8). Good chair is important for health
Human body consists of three types or groups of muscles: skeletal, smooth and cardiac. Today we will talk about the heart muscles.
Skeletal muscles
Skeletal muscles, or striated muscles, are the muscles that most of us probably imagine. Attached to bones and tendons, skeletal muscles largely control all voluntary and some involuntary (diaphragm working automatically) movements of the body. Voluntary movement is stimulated by "nerve impulses (action potentials) passing through the motor neurons of the somatic department nervous system and innervating skeletal muscle fibers, in which they stop contracting.
Like the heart muscle, skeletal muscles get their energy from the mitochondria. The more mitochondria, the more energy available to the muscles, “since it was not necessary for humans to flex their skeletal muscles during their development for long periods of time, the total volume of skeletal muscle contains on average only 1-2% of mitochondria. However, the energy obtained from them is quite enough for solving such muscular tasks as walking or running.”
In addition to mitochondria, skeletal muscle can also use glycogen (an energy reserve) to fuel its energy potential to produce adenosine triphosphate (ATP), the nucleotide that is the main energy carrier in the cell.
Smooth muscles
Smooth muscles are exactly what they are called. They are smooth, without pimples. Smooth muscles are part of the cells internal organs(except the heart) and work automatically to help you digest food, dilate your pupils, and urinate.
cardiac muscle
Like skeletal muscles, cardiac muscle is striated. The cells of this type of muscle are connected to each other (stick together) in adhesive contacts, "allowing the heart to contract without tearing the fibers."
The stimulus for contraction of the heart pump is nerve impulses moving along the fibers through intermediate connections. "If a individual groups the muscle fibers of the heart muscle contract in a scattered and uncoordinated way, for example, due to a heart attack, the heart loses the ability to make coordinated contractions. This condition is called cardiac fibrillation."
Even though the heart pumps are autonomous, the impulses coming from the nervous system "really go to the heart, but their effect is simply to simulate - increase or decrease - the rate of exponential growth and heart contraction. Even if the nerves are destroyed (for example, in a transplanted heart), the heart continues to beat.”
Cardiac muscle, like skeletal muscle, is powered by mitochondria, but that's not all. “On average, the heart contains about 30 to 35% of the mitochondria. Such a number of energy generators explains why the heart muscle in healthy body has no need to rest: there is always some energy transferred to the muscle by increasing calorie intake.
However, this greater reliance on mitochondria means that the heart also has a “greater reliance on cellular respiration for ATP... Lack of glycogen results in less benefit from glycolysis when oxygen supply is limited. Thus, if something interrupts the flow of blood to the heart, then it can lead to damage and even death of the damaged part. That's what happens in heart attacks."
broken hearts
Despite the fact that the heart seems indefatigable, the strength of the human heart has its limits. A recent study showed that if the heart is subjected to extreme stress, even the healthiest can experience problems.
Heart failure
In 2001, scientists studied cardiac fatigue in tired athletes.
“cardiologist Ewen Ashley... set up a portable heart lab right next to the finish line of the super endurance race Adrenaline Rush in the Scottish highlands... The winning team... crossed the finish line after 90 continuous hours of cycling, climbing mountains, swimming, rowing, little to no sleep... After testing their hearts... before and after the 400-kilometer race... scientists concluded that the hearts of the athletes who finished the competition distilled 10 percent less blood compared to start of the race.
However, it should be noted that “the hearts of athletes who showed symptoms of heart failure after the race quickly returned to normal state, that is, no irreparable damage was done.
irreparable damage
A single case of severe overload may not result in serious problems, but latest research show that constant training can.
In 2011, the British examined "men who were part of the British national or Olympic team in running or rowing, as well as runners who had completed at least, one hundred marathons... 12 people aged 50 and over... as well as 17 people... aged 26 to 40 were compared with a group of 20 healthy men over 50, none of whom were athletes… Each person in these groups had an MRI scan of their hearts that identified very early symptoms fibrosis or scarring in the heart muscle... a condition that leads to further deterioration of cardiac function and, ultimately, to heart failure... The results... rather disturbing. None of the younger athletes or older non-athletes had cardiac fibrosis. But half of the older athletes showed some scarring of the heart muscle. Everyone who was found to have such abnormalities was often subjected to severe stress.
However, even scientists studying the effects of intense exercise on the heart muscle agree that "exercise strain has never been big problem. Most people run just to keep themselves in good shape. physical form, and for them the sign mild fatigue- this is good sign. There is no doubt that physical exercises are generally very beneficial for heart health.”
works somehow "wrong"? Perhaps you are mistaken, or maybe it really is heart problems that make themselves felt.
Why can't heart problems be ignored?
It can be said that the most important of our organs is heart. It is the "engine" that keeps us alive.
When symptoms of heart problems appear, you should immediately consult a doctor.
1. Chest pain
Chest pain is associated with various health problems. O heart attack may indicate strong pain in the chest, combined with a feeling of heaviness and constriction.
With a heart attack or spasm coronary vessels the heart receives too little oxygen.
2. Arrhythmia
Heart contractions have a fairly stable rhythm. When the heart is working normally, we usually do not even notice them.
If you notice that the pulse has become very frequent or, conversely, has become too slow, or changes in the rhythm of the heart contractions occur, consult a doctor, because such an arrhythmia may indicate heart problems.
3. Apnea
Sometimes this symptom goes unnoticed for a long time, but may indicate that heart problems are taking place.
Stopping breathing (this is how “apnea” is translated) in a dream for a while can cause a heart attack, because because of it the brain and heart do not receive enough oxygen.
This symptom must be paid attention to, even if it appeared relatively recently.
4. Swelling of the legs and feet
Are you eating a lot of salt? went to a lot last days? In both cases, the legs and feet may swell a little. However, in a few days (if these factors are eliminated), they return to normal.
But if your legs and feet are constantly swollen, it could be symptom of fluid retention caused by heart failure or deterioration of the arteries.
5. Shortness of breath
If we constantly feel that we do not have enough air, we experience shortness of breath and feel it is not normal.
In such a situation, you need to analyze your habits and your activity. If you have changed your habits and your physical activity has increased, feeling short of breath may be natural.
6. Sexual problems
One of the first signs of heart disease may be problems with sexual life, especially if the person is between 40 and 50 years old.
If you have any other medical conditions or are over 50 years of age, seek the advice of a trusted physician.
It will help you figure out if problems with sexual life are related to heart disease or something else.
7. Broken heart syndrome
This syndrome (also called "takotsubo cardiomyopathy") is so named because it can be caused emotional stress such as the death of a loved one.
With it, a person experiences the same pain as with a heart attack, but this temporary symptom, which often occurs in healthy people.
This syndrome does not have such "harbingers" as high cholesterol, high pressure, malnutrition or sedentary image life.
The cause of the syndrome broken heart an increase in the content of catecholamines (mainly adrenaline) in the blood is considered.
Such an increase leads to high anxiety and stress. At the same time, the body begins to produce substances facilitating his return to normal.
Some treatment is also needed. Fortunately, in 90% of cases of this syndrome, the functions of the heart are completely restored.
- Try to lead healthy lifestyle life: eat right, maintain normal level physical activity and control your emotions.
- If you notice any strange symptom do not hesitate to contact a specialist. Our heart usually "signals" us that it has problems. Under no circumstances should these signals be ignored.
- Write down the symptoms you notice regularly. This will help doctors quickly diagnose.
Sometimes, one blood test is enough to identify the pathology of the heart.
The well-known schematic representation of the "heart" with the original has no more similarities than the schematic "asterisk" - with a real star. It seems that history has not preserved the name of the author of the “heart”. It is only known that people have been using this symbol for centuries. According to one version, everything went from playing cards, after all, this is how the suit “worms” is indicated in them.
In reality, the heart is more like a not very even egg in shape, which has a sharp end (it is called the tip) directed to the left, down and forward. This "egg" is somewhat flattened at the bottom at the back - where the heart is adjacent to the diaphragm. The shape of the upper part (base) is quite difficult to explain on the fingers due to the system large vessels flowing into and out of the heart.
Question 2. Is there a heart on the right?
The conventional wisdom that the heart is located in the left side of the chest is not entirely true. For the most part the heart is located in the middle, but due to the natural inclination, the apex of the heart protrudes to the left. By the way, there are exceptions to this rule: in some people, the heart is mirrored, that is, with a deviation to the right. This feature is called dextrocardia (literally "right-heartedness"). More often it does not occur on its own, but with mirror arrangement all internal organs. This congenital feature occurs in less than 1 in 10,000 people.
Question 3. How does the heart work?
The heart is a complex pump consisting of four sections - chambers: atria (right and left) and ventricles (right and left), and the right sections do not communicate with the left. Relatively thin-walled atria are located above, at the base of the heart, and the bulk of the organ falls on powerful muscular ventricles.
The pumping of blood occurs as a result of rhythmic contractions and relaxations of the heart: periods of contraction are called systoles, and periods of relaxation are called diastole.
In systole, the atria contract first, followed by the ventricles, and here's why. Deoxygenated blood from all over the body is collected in right atrium, which pushes it further - into the right ventricle. He, in turn, pumps blood into the pulmonary circulation - a network of blood vessels penetrating the lungs. Gas exchange takes place here: oxygen enters the blood from the air, and oxygen is released from the blood carbon dioxide. Enriched with oxygen blood is coming into the left atrium, and from there into the left ventricle. This is the largest and strongest part of the heart that pushes blood through the aorta into big circle blood circulation - throughout the body, where blood gives oxygen to organs and tissues and takes carbon dioxide.
The branching vessels that carry blood from the heart to its destination are called arteries. Most small vessels, through the walls of which there is an exchange of nutrients and "slags" between the blood and organs, are called capillaries. The vessels that carry waste blood back to the heart are veins.
Question 4. Why doesn't blood flow in the opposite direction?
In order for the blood to flow in the right direction, each section of the heart is separated from the neighboring one and from the vessels by strong valves made of connective tissue which only allow blood to flow in one direction.
Conditions in which blood seeps back through closed valves are called congenital or acquired valvular heart disease.
Question 5. Why does the heart beat?
When the heart "beats" rhythmically, its divisions contract and relax, thanks to the electrical system of the heart. Branching fibers are located on the surface of the heart. They can generate and transmit electrical impulses.
"Signals" originate in the sinus node (it is also called the pacemaker), located on the surface of the right atrium. From sinus node the impulse passes through the atria, causing them to contract, and spreads through the ventricles, harmoniously contracting their muscle fibers. At healthy person the frequency of contractions is at rest from 60 to 80 per minute - this is the normal pulse.
By the way, it is the activity of the electrical system that is recorded on the electrocardiogram (ECG). It shows how the impulse originates and spreads through the heart, as well as whether there are violations of these processes.
In case of malfunctions in the electrical system of the heart - arrhythmias or blockades - its synchronous work is disrupted.
Question 6. How does the heart work all its life without stopping? Where does it get energy from?
The cessation of blood supply causes the death of the body, so the heart has to work without stopping. However, nature also took care of rest for the hardworking "pump". The heart rests during diastole - in those fractions of a second that pass from the moment the heart relaxes to the next contraction.
Of course, such hard work with such a symbolic rest requires a lot of energy - that is, "enhanced nutrition". From the pumped blood, oxygen and nutrients they cannot enter the heart muscle, so the heart, like any other organ, has its own blood vessels.
Question 7. What is a heart attack?
Due to the continuous work that requires a lot of energy, the heart muscle is very sensitive to lack of blood supply. If the clearance coronary arteries narrowed by atherosclerotic plaques, under load, the heart receives insufficient oxygen and begins to get very sick: an attack of angina pectoris occurs, and this disease is called ischemic disease hearts.
When the plaque is destroyed, it forms in its place blood clot- a thrombus that completely blocks the lumen of the vessel. Deprived of nutrition, the area of the heart muscle supplied by this vessel quickly dies off - myocardial infarction occurs.
If the heart does not lose its ability to contract after this, and the person continues to live, the muscle fibers in the infarct zone do not recover, and a scar appears in their place.
Question 8. Why is an electric shock given during cardiac arrest?
Suppose the heart has stopped, or ventricular fibrillation has set in - a condition in which individual muscle fibers do not contract synchronously, but “haphazardly”. In both cases, the electrical system of the heart fails. To resume its work, using a defibrillator device through chest a powerful electrical impulse is passed through the heart. It causes all fibers of the heart muscle to contract at the same time, which helps the pacemaker regain control of the heart. Or does not help - it depends on the cause of the violations ...
This effect is much more effective in fibrillation than in cardiac arrest. Therefore, when stopping, adrenaline is often injected first to cause fibrillation, and then a normal heart rhythm is restored with a current discharge.
Osip Karmachevsky
