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Mr Ellis BIOLOGY > 8.5. THE HEART > Flashcards

8.5. THE HEART Flashcards

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1
Q

what is the heart made of?

A
  • cardiac muscle
  • contracts and relaxes in a regular rhythm
  • does not get fatigued and need to rest like skeletal muscle
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2
Q

what supplies the heart with oxygenated blood it needs to to relax and contract continuously?

A
  • coronary arteries
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3
Q

what prevents the heart from over-distending with blood?

A
  • inelastic pericardial membranes surrounding the heart
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4
Q

where does deoxygenated blood enter?

A
  • the right atrium of the heart, from the upper body and head in the superior vena cava, at relatively low pressure
  • the atria have thin muscular walls
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5
Q

what happens when the blood flows into the heart from the right atrium?

A
  • slight pressure builds up until the atrio-ventricular valve (tricuspid) opens to let blood pass into the right ventricle
  • when both the atrium and ventricle are filled with blood the atrium contracts, forcing all blood into the right ventricle, stretching the ventricle walls
  • as the right ventricle starts to contract, the tricuspid valve closes, preventing any backflow of blood to the atrium
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6
Q

what do the tendinous cords do after the tricuspid valve closes?

A
  • make sure the valves are not turned inside out by the pressures exerted when the ventricle contracts
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7
Q

what happens when the right ventricle contracts fully?

A
  • 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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8
Q

what happens when oxygenated blood from the lungs enters the left atrium from the pulmonary vein?

A
  • 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 the 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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9
Q

why is the muscular wall of the left side of the heart much thicker than that of the right?

A
  • as 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 the rest of the body
  • the right side only has to push blood to the lungs which are relatively close to the heart, and smaller than the rest of the body, and it only has to overcome the resistance of the pulmonary circulation
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10
Q

what is the role of the septum?

A
  • inner dividing wall of the heart which prevents the mixing of deoxygenated and oxygenated blood
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11
Q

when do the sides of the ventricle fill up with blood?

A
  • right and left side fill and empty together
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12
Q

what is the cardiac cycle?

A
  • describes the events in a single heartbeat
  • lasts about 0.8 seconds in a human adult
  • includes diastole and systole
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13
Q

what is diastole?

A
  • when the heart relaxes
  • atria and ventricles fill with blood
  • volume and pressure of the blood in the heart build as the heart fills
  • but pressure in arteries is at a minimum
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14
Q

what is systole?

A
  • atria contracts (atrial systole), closely followed by the ventricles (ventricular systole)
  • pressure inside heart increases dramatically and blood is forced out of the right side of the heart to the the lungs and from the left side to the main body circulation
  • volume and pressure of blood in the heart are low at the end of systole, blood pressure in arteries is at a maximum
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15
Q

what are the sounds of a heartbeat made by?

A
  • blood pressure closing the heart valves
  • heard through a stethoscope
  • described as ‘lub-dub’
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16
Q

what is happening when the heart makes the ‘lub’ sound in ‘lub-dub’?

A
  • blood is forced against the atrio-ventricular vales as the ventricles contract
17
Q

what is happening when the heart makes the ‘dub’ sound in ‘lub-dub’?

A
  • comes as a backflow of blood closes the semilunar valves in the aorta and pulmonary artery as the ventricles relax
18
Q

what does it mean by the cardiac muscle being myogenic?

A
  • has its own intrinsic rhythm at around 60 beats per minute (bpm)
  • prevents the body wasting resources maintaining the basic heart rate
19
Q

how is the basic rhythm of the heart maintained?

A
  • by a wave of electrical excitation, like a nerve impulse
  • begins in the pacemaker area called the sino-atrial node (SAN), causing atria to contract and initiating heartbeat, a layer of non-conducting tissue prevents excitation passing directly to the ventricles
  • then picked up by the atrio-ventricular node (AVN)
  • AVN imposes a slight delay before stimulating Bundle of His (conducting tissue made up of Purkyne Fibres, which penetrate through the septum between the ventricles)
  • bundle of His splits into two branches and conducts wave of excitation to apex (bottom) of heart
  • at the apex, the Purkyne fibres spread out through the walls of the ventricles on both sides, which triggers the contraction of the ventricles, starting at the apex, which is more efficient for emptying the ventricles
20
Q

what is an electrocardiogram (ECG)?

A
  • way of recording of the electrical activity of the heart (through measures measuring tiny electrical differences in your skin) to measure the spread of electrical excitation
  • helps to diagnose heart problems
  • electrodes are stuck painlessly to clean skin
21
Q

what are the heart rhythm abnormalities that commonly show up on ECGs?

A
  • tachycardia
  • bradycardia
  • ectopic heartbeat
  • atrial fibrillation
22
Q

what is a tachycardia?

A
  • when the heartbeat is very rapid, over 100 bpm
  • often normal, i.e. exercise
  • if it is abnormal, it may be caused by by problems in the electrical control of the heart and may need to be treated by medication or surgery
23
Q

what is a bradycardia?

A
  • when the heart rate slows down to below 60 bpm
  • many people have this as they are fit
  • severe bradycardia can be serious and may need as artificial pacemaker to keep the heart beating steadily
24
Q

what is an ectopic heartbeat?

A
  • extra heartbeats that are out of the normal rhythm
  • most people have at least one a day
  • usually normal but can be linked to serious conditions if they are very frequent
25
Q

what is atrial fibrillation?

A
  • example of arrhythmia
  • an abnormal rhythm of the heart
  • rapid electrical impulses are generated in the atria
  • 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 les often
  • as a result, the heart does not pump effectively

Mr Ellis BIOLOGY (36 decks)

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