The Heart


The Heart

The left side of the heart pumps oxygenated blood which is blood that has high oxygen and low carbon dioxide concentration.The right side of the heart pumps deoxygenated blood which is blood that has high carbon dioxide and low oxygen concentration.

 LORD = Left Oxygenated Right Deoxygenated

When the left ventricle contracts, blood flows into the aorta.When the right ventricle contracts, blood flows into the pulmonary artery.

The Valves

The function of the valves is to prevent backflow of blood. The bicuspid valve is found between the left atrium and the left ventricle. The bicuspid valve prevents blood flowing backwards into the left atrium. The tricuspid valve is found between the right atrium and the right ventricle. The tricuspid valve prevents blood flowing backwards into the right atrium.The two semilunar valves are found at the entrances to the pulmonary artery and the aorta. They prevent blood flowing backwards into the ventricles after they have contracted.

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The semilunar valve at the base of the aorta is called the aortic valve. Sometimes this valve becomes faulty and requires replacement by surgery.

A faulty aortic valve alters the flow of blood through the heart because it would allow the backflow of blood from the aorta to the left ventricle

The symptoms of aortic valve diesease may include:

  • Shortness of breath
  • Angina (chest pain)
  • Lightheadedness 
  • Dizziness
  • Fainting 

The patient will have these symptoms because not enough oxygenated blood is being pumped out of the heart because of the backflow into the left ventricle. 
The valve at the base of the other major atery of the heart is called the pulmonary valve. 

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Double Circulation

The circulation of blood around the body is described as double circulation. The blood has to pass through the heart twice on one complete journey around the body. 

Pulmonary circuit - the deoxygenated blood is pumped out of the right ventricle into the pulmonary artery and it is carried to the lungs. In the lungs blood is oxgenated, oxygenated blood returns to the left atrium in the pulmonary vein. 

Systemic circuit - Oxygenated blood is pumped out the left ventricle and travels along the aorta to the rest of the body. The blood becomes deoxygenated as it passes through the body. Deoxygenated blood returns to the right atrium in the vena cava. 

The left ventricle is made of thicker muscle because when it contracts it needs to have greater force to generate the higher pressure needed to pump blood all around the body. The right ventricle only pumps blood to the lungs so doesn't need to produce as much force to do this. 

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The Cardiac Cycle

This is the sequence of events in one complete heartbeat.

The right and left sides of the heart work together at all times. The heart pumps blood by rhythmic contraction of the cardiac muscle in its walls. At rest, a human heart contracts and relaxes between 60 - 80 times a minute. One complete sequence of contraction and relaxation is called a cardiac cycle. Contraction of the cardiac muscle is known as systole. Relaxtion of the heart muscle is known as diastole. 

Diastole - When the heart muscle is relaxed blood flows from the pulmonary veins and the vena cava into the atria which fill with blood. 

Atrial Systole - The atria and the ventricles do not contract at the same time. The atria contract first, followed by the ventricles. The contraction of the atria forces blood into the ventricles. 

Ventricular Systole - The contraction of the ventricles pumps blood from the base of the heart upwards. This forces the bicuspid and tricuspid valves to close. The closure of these valves produces the first heart sound. Blood flows from the ventricles into the aorta and the pulmonary artery. The ventricles now relax and fill with blood again from the atria. As the ventricles relax the semilunar valves close. This causes the second heart sound. 

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Structure and Function of arteries

When blood is pumped out of the heart, it surges into the arteries under very high pressure.The lumen of an artery is relatively small compared to its total diameter. Arteries have thick walls which contain thick layers of muscle and elastic tissue. These tissues are important in helping to maintain blood flow and blood pressure. Muscle tissue can contract & relax, elastic tissue can stretch & recoil.

The role of elastic tissue

During ventricular systole, the blood leaves the heart under high pressure the elastic tissue in the walls of the artery stretches. This increases the diameter of the lumen of the artery and causes the blood pressure in the artery to decrease.

During diastole the blood pressure drops, the elastic tissue in the walls of the artery recoil, decreasing the diameter of the artery slightly, so the blood pressure slightly increases.

The action of the elastic tissue reduces the fluctuations in blood pressure in the artery so that the flow of blood is evened out.

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Structure and Function of arteries (continued)

The role of muscle

The muscle tissure helps withstand the high pressure of blood and prevents the artery walls from bursting.

If the blood pressure is low, the muscular tissue in the artery wall will contract making the lumen narrower. This is called vasoconstriction. This increases the blood pressure.

If the blood pressure is high, the muscular tissue can relax, increasing the size of the lumen so decreased blood pressure. This is called vasodilation.

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Arterioles and Blood Pressure

When the arteries get further away from the heart they branch out into hundreds of much narrower blood vessels called arterioles. Arterioles are similiar to arteries in that they also have muscle tissue in their walls. Because they are so much narrower, the blood flows through them under greater pressure. Blood pressure will need to increase to the muscles during exercise.

These changes in blood pressure are brought about by nerves of the sympathetic nervous system. When stimulated by impulses from the sympathetic nervous system, the muscle in the walls of the arterioles contract.

When the muscle in the arteriole wall contracts the blood pressure will increase. Stress also causes high blood pressure because more impulses are sent along the sympathetic nerves. When the impulses stop flowing along the sympathtic nerves, the muscle in the arteriole wall relax and the blood pressure increases again.

These responses are controlled by a region in the brain called the medulla.

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Structure and Function of Veins

The blood returns to the heart in the veins. Veins have thin walls and wide lumens which means that the blood pressure will be lower than the ones in the arteries. Humans mainly stand upright and blood flows in veins under low pressure so it is hard for blood to return to the heart because it has to flow against gravity. There are 4 ways that blood is aided to return to the heart in the veins:

1. There are valves in the walls. These prevent backflow of blood. The blood can only flow up and if it tried to flow back down again the blood would be caught in the pockets of the valve.

2. The contraction of the skeletal muscles in the legs as we walk squeezes against the veins in the legs and helps to propel blood along. The valves are forced open when the muscles in the legs contract because they squeeze on the vein which raises the blood pressure and forces the blood up.

3. As we breath in (inhalation), the pressure in the thorax lowers. This helps to "****" blood up the body.

4. Expansion of the vena cava, making it wider. This decreases pressure below that of heart so blood returns to the heart.

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Finding the resting pulse rate

How you would find the resting pulse rate in the lab

  • Seat the person for at least 5 minutes, to ensure you are finding the resting pulse rate.
  • Count the number of pulse beats in the wrist (radial artery) or neck (carotid artery) for 60 seconds.
  • Use 2 fingers, not the thumb (as the thumb has a pulse itself)
  • Repeat 3 times.

When finding the resting pulse rate, you should repeat your measurement three times & find an average to make the mean more reliable.

Why the pulse rate increases when a person starts to exercise

  • The muscles are contracting more quickly
  • They need more oxygen for respiration
  • The pulse rate increases as the heart beats faster to deliver more oxygen to the muscles.

The stimulus for the heart to increase its speed of contraction is the increased levels of carbon dioxide in the blood.

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Using the effect of exercise on pulse rate to indi

Someone who is very fit will have a low resting pulse rate. This is because:

  • A fit person has a larger heart
  • The heart therefore pumps out more blood with each beat - the heart is more efficient/larger/volume

A second indicator of fitness is the time taken to recover after exercise. The shorter the time, the fitter the person.

This is because:

  • Lactic acid builds up in the muscles, if anaerobic respiration occurs, during exercise this is called oxygen debt.
  • Lactic acid needs oxygen to break it down so the supply of oxygen in the blood must remain high until it is all broken down.
  • The heart rate therefore increases to pay off the oxygen debt.
  • The heart rate remains above the resting rate as long as the breathing rate remains high.
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How the heart rate is increased during exercise

  • During exercise, the muscle contract more vigorously and so they need to respire more.
  • This produces more carbon dioxide
  • Since carbon dioxide is acidic, it makes the pH of the blood decrease
  • This is detected by special chemoreceptors in the artery in the neck (carotid artery), in the medulla and aorta.
  • The chemoreceptors send nerve impulses to the region of the brain which controls the heart rate. This is the medeulla in the brain.
  • This is connected to the heart by sympathetic nerves.
  • The medulla sends an increased frequency of nerve impulses down the sympathetic nerve to the sinoatrial node.
  • The sinoatrial node is found in the right atrium and it sets the rate at which the heart beats.
  • Nerve impulses pass more frequently across the heart from the sinoatrial node and this results in an increase in the rate of contraction of the heart. 
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How the heart rate is decreased during exercise

  • After exercise, the muscles contract less vigorously which causes them to respire less. 
  • This produces less carbon dioxide. 
  • Since carbon dioxide is an acidic gas, this decrease makes the pH of the blood increase. 
  • Which is detected by the chemoreceptors in the carotid artery and the medulla. 
  • The chemereceptors don't send nerve impulses to the medulla in the brain. 
  • The medulla sends a decreased frequency of nerve impulses down the sympathetic nerve to the sinoatrial node (right atrium). 
  • Nerve impulses pass less frequently across the heart from the sinoatrial and this results in a decrease in the rate of contraction of the heart. 
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Why the heart rate doesn't return to normal as soo

  • When you exercise, you need more oxygen/glucose for contraction of the muscles. 
  • After exercise, more oxygen is still needed to break down the lactic acid made during the exercise. The build up of lactic acid is called the oxygen debt. 
  • It also takes some time for the extra carbon dioxide made during respiration in the muscles during exercise to move out of the bloodstream. 
  • Only occurs during anaerobic respiration which is aerobic exercise without oxygen. 
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Blood Pressure

The instrument that is used to measure blood pressure is called a sphygmomanometer. 

The 6 steps you would take to measure someone's blood pressure are: 

  • Sit them down for 5 mins with their arm level with their heart.
  • Wrap cuff around upper arm
  • Place stethoscope over the brachial artery on the inside surface of the elbow
  • Inflate cuff until blood stops flowing in the artery
  • Release pressure until blood flows past cuff when heart contracts you will hear a knocking sound, the pressure at this sound is the systolic pressure
  • Release pressure until blood flows freely in artery again, you will hear the knocking sounds stop, the pressure is the diastolic pressure.

Don't inflate the cuff for too long and too much - measured in mm/Hg = millimeters of mercury

An electronic digital meter is better than a mercury one becuase you can take your own blood pressure because you don't need to be trained and the mercury one requires a stethoscope to listen for changes in blood flow which requires training. 

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Blood Pressure (2)

120/80 mm/Hg = systolic when the ventricles are contracting and diastolic when the ventricles are relaxing. 

Women have a slightly lower blood pressure than men and blood pressure increases with age. 

Blood pressure increases with the activity of the body because with exercise the heart rate increases so more blood is being pumped through the arteries per minute. 

Hypertension = Permanently high blood pressure 

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Why blood pressure rises as a person gets older

Dieticians advise us to limit the amount of fat we eat. This is because a diet high in fat can cause fat to be deposited on the inside of the artery walls. This is called hardening of the arteries. 

  • Cholesterol is deposited on the artery walls as a plaque
  • The artery becomes narrower
  • The walls of the artery becomes less elastic
  • So the blood pressure increases as blood is forced through 

Coronary artery disease can be caused by fat being deposited inside the coronary arteries supplying the heart. 

  • Fatty deposits blocking the coronary artery so blood cannot flow past the blockage 
  • The heart muscle becomes starved of oxygen so cannot respire and so it dies
  • This leads to a heart attack or myocardial infarction because the heart cannot beat effectively. 

In pass surgery, the blockage in the coronary artery is by-passed by a vein removed from the leg and stitched in place. 

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