The Heart Flashcards

1
Q

What type of muscle is the heart muscle?

A

Myogenic

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2
Q

Explain what myogenic means

A
  • Contracts without nervous stimulation

- Even if removed from nervous system it still beats

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3
Q

What causes heart muscle contraction? 4

A
  • Electrical charge changes in cardiac muscle
  • As polarity changes spread from cell to cell
  • Stimulate contraction of cardiac muscle
  • Pattern of contractions co-ordinate regular heartbeat
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4
Q

How is a cell polarised?

A

If it is slightly positive on the outside

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5
Q

How is a cell depolarised?

A

If it is slightly negative on the outside

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6
Q

What is the sinoatrial node [SAN]? 2

A
  • Small group of specialised muscle fibres known as the pacemaker
  • Set rhythm of the heartbeat by sending regular waves of electrical activity to atrial walls
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7
Q

Explain the electrical activity of the heart - 6

A
  • SAN initiates depolarisation
  • passes through wall of atria
  • causes atrial systole
  • AVN conducts to ventricles
  • conducts to Purkyne fibres - bundle of His
  • ventricular systole follows from apex
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8
Q

Where is the AVN located?

A

Right and left ventricle walls

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9
Q

What is the AVN?

A

Group of large specialised muscle fibres conducing impulses rapidly to apex of ventricles

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10
Q

Where is the SAN located?

A

Right atrium wall under the superior vena cava opening

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11
Q

What is an ECG?

A

Graphic record of electrical activity in the cardiac cycle

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12
Q

How is an ECG formed?

A
  • The heart depolarises - loses electrical charge - when it contracts
  • The heart polarises - regains electrical charge - when it relaxes
  • Changes in polarisation cause small electrical currents to be detected on skin’s surface by chest electrodes
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13
Q

What are the 4 parts of an ECG from order of left to right? 4

A
  • P wave
  • PR interval
  • QRS complex
  • T wave
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14
Q

What does the P wave indicate?

A

Contraction and depolarisation of atria in atrial systole

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15
Q

What does the PR interval indicate?

A

Time for conduction of impules from SAN across atria to ventricles through AVN

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16
Q

Why is there a time delay between the conduction of impulses from the atria to the ventricles?

A

Ensures ventricles contract after atria have emptied

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17
Q

What does the QRS complex indicate?

A

Contraction/depolarisation of ventricles in ventricular systole

18
Q

What does the T wave indicate?

A

The repolarisation/relaxation of the ventricles in cardiac diastole

19
Q

What is bradycardia?

A

Heart rate of less than 60bpm

20
Q

What condition is indicated by a heart rate of less than 60bpm?

A

Bradycardia

21
Q

What is tachycardia?

A

Heart rate of more than 100bpm

22
Q

What condition is indicated by a heart rate of more than 100pm?

A

Tachycardia

23
Q

What can cause bradycardia? 4

A
  • Athlete at rest
  • Hypothermia
  • Heart disease
  • Drugs
24
Q

What can cause tachycardia? 4

A
  • Anxiety
  • Heart disease
  • Exercise
  • Anemia
25
What does a low QRS complex indicate? 2
- Muscle damage | - AVN not conducting impulses to ventricles properly
26
What does an early/odd P wave indicate? 2
- Ecoptic heartbeat | - Early contraction of atria
27
What is fibrillation?
Ventricles and atria completely lose rhythm and eventually stop contracting completely - could lead to death
28
Label an ECG diagram
SEE NOTES
29
Define cardiac output
Total volume of blood pumped out of ventricle every minute
30
Give the formula for calculating cardiac output
cardiac output : heart rate x stroke volume
31
What are the units of cardiac output?
cm3min-1
32
What are the units of stroke volume?
cm3
33
Define stroke volume
The volume of blood pumped out by a ventricle each time it contracts
34
How does increased exercise increase stroke volume and cardiac output? 4
- During exercise there is a greater venous return: more blood returning to heart because more respiration - Muscle stretched to greater extent - Comes into contact with greater force - More blood is expelled
35
What is residual blood?
When body is at rest ventricles don't completely empty with each beat
36
How does exercise affect residual blood?
Stronger contractions eject more residual blood from the heart
37
What 2 things influence heart rate?
- Heart size | - Amount of training
38
How does heart size lower heart rate? 2
- Increased stroke volume with each beat | - So need to beat less frequently to circulate same volume of blood around the body
39
The larger the heart, the x the resting heart rate
Lower
40
What 2 things affect heart size?
- Genetics | - Body size
41
How does training reduce heart rate? 4
- Increase in heart size - Due to thickening of heart muscle walls - Increased stroke volume with each beat - So need to beat less frequently to circulate same volume of blood around the body
42
How is heart rate increased? 4
- increased impulses to SAN - via sympathetic nervous system - stimulates more frequent depolarisation in SAN - increases heart rate