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Level Biology Final Notes > chapter 8 p3 > Flashcards

chapter 8 p3 Flashcards

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1
Q

The heart is the organ that

A

moves the blood around the body. In some animal groups it is no more than a simple muscular tube.
In mammals the heart is a complex, four-chambered muscular ‘bag’ found in the chest, enclosed by the ribs and sternum

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2
Q

Heart Structure

A

The heart consists of two pumps, joined and working together.
Deoxygenated blood from the body flows into the right side of the heart, which pumps it to the lungs.
Oxygenated blood from the lungs returns to the left side of the heart, which pumps it to the body.
The blood from the two sides of the heart does not mix.

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3
Q

Cardiac Muscle

A

The heart is made of cardiac muscle, which contracts and relaxes in a regular rhythm.
It does not get fatigued and need to rest like skeletal muscle.
The coronary arteries supply the cardiac muscle with the oxygenated blood it needs to keep contracting and relaxing all the time.
The heart is surrounded by inelastic pericardial membranes, which help prevent the heart from over-distending with blood.

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4
Q

external structure of heart

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5
Q

internal structure of heart

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6
Q

Dissecting a heart

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The heart of a sheep or a pig is similar in shape and size to a human heart and is often used in dissection.
By careful examination of a heart you can identify many of the important structures in the mammalian heart - although the real thing is much more complicated than the standard diagram in Figure 3.
The external view of the heart enables you to see and trace the coronary arteries which supply the heart muscle with the blood it needs to beat.
It is the narrowing or blockage of these blood vessels that cause the symptoms of coronary heart disease and even heart attacks.
However hearts obtained from the butcher are often not intact.
The major blood vessels will have been cut right back and often the atria have been removed - people don’t want to eat all the tubes.
So when you examine, dissect and draw a heart, you have to be aware of which, if any, parts are missing.

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7
Q

Blood Flow in the Right Side of the Heart:

A
  • Deoxygenated blood enters the right atrium of the heart from the upper body and head in the superior vena cava, and from the lower body in the inferior vena cava, at relatively low pressure.
  • The atria have thin muscular walls.
  • As the blood flows in, slight pressure builds up until the atrio-ventricular valve (the tricuspid valve) opens to let blood pass into the right ventricle.
  • When both the atrium and ventricle are filled with blood the atrium contracts, forcing all the blood into the right ventricle and stretching the ventricle walls.
  • As the right ventricle starts to contract, the tricuspid valve closes, preventing any backflow of blood to the atrium.
  • The tendinous cords make sure the valves are not turned inside out by the pressures exerted when the ventricle contracts.
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8
Q

Pulmonary Circulation:

A

The right ventricle contracts fully and pumps deoxygenated blood through the semilunar valves into the pulmonary artery, which transports it to the capillary beds of the lungs.
The semilunar valves prevent the backflow of blood into the heart.

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9
Q

Blood Flow in the Left Side of the Heart:

A

At the same time, oxygenated blood from the lungs enters the left atrium from the pulmonary vein.
As pressure in the atrium builds the bicuspid valve opens between the left atrium and the left ventricle so the ventricle also fills with oxygenated blood.
When both the atrium and ventricle are full the atrium contracts, forcing all the oxygenated blood into the left ventricle.
The left ventricle then contracts and pumps oxygenated blood through semilunar valves into the aorta and around the body.
As the ventricle contracts the tricuspid valve closes, preventing any backflow of blood.

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10
Q

Structural Characteristics and Functional Differences:

A

The muscular wall of the left side of the heart is much thicker than that of the right.
The lungs are relatively close to the heart, and the lungs are also much smaller than the rest of the body so the right side of the heart has to pump the blood a relatively short distance and only has to overcome the resistance of the pulmonary circulation.
The left side has to produce sufficient force to overcome the resistance of the aorta and the arterial systems of the whole body and move the blood under pressure to all the extremities of the body.
The septum is the inner dividing wall of the heart which prevents the mixing of deoxygenated and oxygenated blood.
The right and left side of the heart fill and empty together.

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11
Q

A hole in the heart:

A

The development of the septum is not completed until after birth.
In the fetus, the blood is oxygenated in the placenta, not in the lungs.
As a result, all the blood in the heart is very similar and so mixes freely.
In the days after birth, the gap in the septum closes to ensure that the deoxygenated and oxygenated bloods are kept completely separate.
Any gap remaining in the septum after the first few weeks of life is referred to as a ‘hole in the heart’ and it can often be heard with a stethoscope as a heart murmur.
Many people have a small hole in their septum without knowing about it.
However, if the hole is large it can lead to severe health problems unless it is diagnosed and repaired by surgery

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12
Q

What is The cardiac cycle:

A

The cardiac cycle describes the events in a single heartbeat, which lasts about 0.8 seconds in a human adult.

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13
Q

2 Cardiac cycle phases:

A
  • In diastole the heart relaxes:
  • In systole the atria contract (atrial systole), closely followed by the ventricles (ventricular systole).
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14
Q

diastole

A
  • In diastole the heart relaxes:
    The atria and then the ventricles fill with blood.
    The volume and pressure of the blood in the heart build as the heart fills, but the pressure in the arteries is at a minimum.
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15
Q

systole

A
  • In systole the atria contract (atrial systole), closely followed by the ventricles (ventricular systole).
    The pressure inside the heart increases dramatically and blood is forced out of the right side of the heart to the lungs and from the left side to the main body circulation.
    The volume and pressure of the blood in the heart are low at the end of systole, and the blood pressure in the arteries is at a maximum.
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16
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A
17
Q

Heart sounds:

A

The sounds of the heartbeat, which can be heard through a stethoscope, are made by blood pressure closing the heart valves.
The two sounds of a heartbeat are described as ‘lub-dub’.
The first sound comes as the blood is forced against the atrio-ventricular valves as the ventricles contract, and the second sound comes as a backflow of blood closes the semilunar valves in the aorta and pulmonary artery as the ventricles relax.

18
Q

Cardiac muscle is

A

myogenic - it has its own intrinsic rhythm at around 60 beats per minute (opm).
This prevents the body wasting resources maintaining the basic heart rate. The average resting heart rate of an adult is higher, at around 70 bpm.
This is because other factors including exercise, excitement, and stress also affect our heart rate.
The basic rhythm of the heart is maintained by a wave of electrical excitation, rather like a nerve impulse

19
Q

Heartbeat Initiation and Conduction:
p1

A
  • A wave of electrical excitation begins in the pacemaker area called the sino-atrial node (SAN), causing the atria to contract and so initiating the heartbeat.
  • A layer of non-conducting tissue prevents the excitation passing directly to the ventricles.
  • The electrical activity from the SAN is picked up by the atrioventricular node (AVN).
  • The AVN imposes a slight delay before stimulating the bundle of His, a bundle of conducting tissue made up of fibres (Purkyne fibres), which penetrate through the septum between the ventricles.
20
Q

Heartbeat Initiation and Conduction:
p2

A
  • The bundle of His splits into two branches and conducts the wave of excitation to the apex (bottom) of the heart.
  • At the apex the Purkyne fibres spread out through the walls of the ventricles on both sides.
  • The spread of excitation triggers the contraction of the ventricles, starting at the apex.
  • Contraction starting at the apex allows more efficient emptying of the ventricles.
  • The way in which the wave of excitation spreads through the heart from the SAN, with AVN delay, makes sure that the atria have stopped contracting before the ventricles start.
21
Q
A
22
Q

Electrocardiograms p1

A

You can measure the spread of electrical excitation through the heart as a way of recording what happens as it contracts.
This recording of the electrical activity of the heart is called an electrocardiogram (ECG).
An ECG doesn’t directly measure the electrical activity of your heart - It measures tiny electrical differences in your skin, which result from the electrical activity of the heart.

23
Q

Electrocardiograms p2

A

To pick up these tiny changes, electrodes are stuck painlessly to clean skin to get the good contacts needed for reliable results.
The signal from each of the electrodes is fed into the machine, which produces an ECG.
ECGs are used to help diagnose heart problems.
For example, if someone is having a heart attack, recognisable changes take place in the electrical activity of their heart, which can be used to diagnose the problem and treat it correctly and fast.

24
Q

Normal ECG:

A
25
Q

Heart rhythm abnormalities that commonly show up on ECGs include:

A

Tachycardia
Bradycardia
Ectopic heartbeat
Atrial fibrillation

26
Q

Tachycardia

A

when the heartbeat is very rapid, over 100 bpm.
This is often normal, for instance when you exercise, if you have a fever, if you are frightened or angry.
If it is abnormal it may be caused by problems in the electrical control of the heart and may need to be treated by medication or by surgery.

27
Q

Bradycardia

A

when the heart rate slows down to below 60bpm.
Many people have bradycardia because they are fit - training makes the heart beat more slowly and efficiently.
Severe bradycardia can be serious and may need an artificial pacemaker to keep the heart beating steadily.

28
Q

Ectopic heartbeat

A

extra heartbeats that are out of the normal rhythm.
Most people have at least one a day.
They are usually normal but they can be linked to serious conditions when they are very frequent.

29
Q

Atrial fibrillation

A

this is an example of an arrhythmia, which means an abnormal rhythm of the heart.
Rapid electrical impulses are generated in the atria.
They contract very fast (fibrillate) up to 400 times a minute.
However, they don’t contract properly and only some of the impulses are passed on to the ventricles, which contract much less often.
As a result the heart does not pump blood very effectively

30
Q

Blood Pressure

A

The blood travels through the arterial system at pressures that vary as the ventricles contract.
The blood pressure is also affected by the diameter of the blood vessels themselves.
Narrowing the arteries is one way in which the body affects and controls local blood flow, but permanent changes can cause severe health problems.
Most people will have their blood pressure taken at some point in their lives.
Blood pressure is expressed as two figures, the first higher than the second.

31
Q

Blood Pressure Measurement:
p1

A

Traditionally blood pressure is measured using a manual sphygmomanometer.
A cuff, which is connected to a mercury manometer (a way of measuring pressure using the height of a column of mercury), is placed around the upper arm.
The cuff is then inflated until the blood supply to the lower arm is completely cut off.
A stethoscope is positioned over the blood vessels at the elbow.
Air is slowly let out of the cuff.
The pressure at which the blood sounds first reappear as a slight tapping sound is recorded.
The first blood to get through the cuff is that under the highest pressure - in other words, when the left ventricle of the heart is contracting strongly.

32
Q

Blood Pressure Measurement:
p2

A

The height of the mercury at this point gives the systolic blood pressure in mmHg (the height of the mercury column).
The blood sounds return to normal at the point when even the lowest pressure during diastole is sufficient to get through the cuff.
This gives the diastolic blood pressure.
A reading of 120/80 mmHg is regarded as being normal.
More recently a simpler, digital sphygmomanometer is often used - but the same principles apply.
The stethoscope is simply built into the cuff applied around the arm.

Level Biology Final Notes (94 decks)

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