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Biology IB HL > D4 The Heart > Flashcards

D4 The Heart Flashcards

1
Q

What is the heart composed of and how are these special?

A

The heart is composed of cardiac muscle cells which have specialised features that relates to their functio

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2
Q

What are the 4 (basic) specialisations of cardiac muscle?

A
  • myogenic
  • branched
  • intercalated discs
  • mitochondria
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3
Q

What does it mean that cardiac muscle cells are myogenic?

A

Cardiac muscle cells contract without stimulation by the central nervous system (contraction is myogenic)

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4
Q

Why are cardiac muscle cells branched?

A

Cardiac muscle cells are branched, allowing for faster signal propagation and contraction in three dimensions

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5
Q

What is the purpose of intercalated discs?

A

Cardiac muscles cells are not fused together, but are connected by gap junctions at intercalated discs

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6
Q

What is the quantity of mitochondria in cardiac muscle cells?

A

Cardiac muscle cells have more mitochondria, as they are more reliant on aerobic respiration than skeletal muscle

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7
Q

What are the 3 (basic) properties are unique in cardiac tissue?

A
  • longer period of contraction and refraction
  • heart tissue does not become fatigued
  • cells separated between atria and ventricles
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8
Q

Why does cardiac muscle need to have a longer period of contraction?

A

Cardiac muscle has a longer period of contraction and refraction, which is needed to maintain a viable heart beat

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9
Q

Why is it useful that heart muscle does not become fatigued?

A

The heart tissue does not become fatigued (unlike skeletal muscle), allowing for continuous, life long contractions

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10
Q

Why are the cells separated between atria and ventricles?

A

The interconnected network of cells is separated between atria and ventricles, allowing them to contract separately

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11
Q

What do intercalated discs allow for?

A

Cardiac muscle cells are not fused together but are instead connected via gap junctions at intercalated discs
This means that while electrical signals can pass between cells, each cell is capable of independent contraction

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12
Q

What controls the coordinated contraction of the heart?

A

The coordinated contraction of cardiac muscle cells is controlled by specialised autorhythmic cells (‘pace makers’)

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13
Q

What is the SAN?

A

Within the wall of the right atrium is a specialised cluster of cardiomyocytes which directs the contraction of heart tissue

This cluster of cells is collectively called the sinoatrial node (SA node or SAN)

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14
Q

What is the role of the SAN?

A

The sinoatrial node acts as a primary pacemaker, controlling the rate at which the heart beats (i.e. pace ‘making’)

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15
Q

What does the SAN “Send out”? Where does the signal go?

A

It sends out electrical signals which are propagated throughout the entire atria via gap junctions in the intercalated discs

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16
Q

What is the result of the signal sent out by the SAN?

A

In response, the cardiac muscle within the atrial walls contract simultaneously (atrial systole)

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17
Q

What are the atria and ventricles separated by?

A

The atria and ventricles of the heart are separated by a fibrous cardiac skeleton composed of connective tissue

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18
Q

What is the role of the non-conductive connective tissue of the heart?

A

This connective tissue functions to anchor the heart valves in place and cannot conduct electrical signals

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19
Q

How do the signals sent by the SAN travel through the non-conductive barrier?

A

The signals from the sinoatrial node must instead be relayed through a second node located within this cardiac skeleton

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20
Q

WHat is the second node of the heart?

A

This second node is called the atrioventricular node (or AV node) and separates atrial and ventricular contractions

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21
Q

How does the AV differ from the SAN?

A

The AV node propagates electrical signals more slowly than the SA node, creating a delay in the passing on of the signal

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22
Q

Why is there a delay between atrial and ventricular contraction? (general)

A

The separation of atrial and ventricular contraction is important as it optimises the flow of blood between the heart chambers

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23
Q

Why is there a delay between atrial and ventricular contraction? (specific)

A

The delay in time following atrial systole allows for blood to fill the ventricles before the atrioventricular valves close

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24
Q

When does ventricular contraction occur?

A

Ventricular contraction occurs following excitation of the atrioventricular node (located at the atrial and ventricular junction)

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25
Where does the AV send signals down?
The AV node sends signals down the septum via a specialised bundle of cardiomyocytes called the Bundle of His
26
What is the role of the bundle of His?
The Bundle of His innervates Purkinje fibres in the ventricular wall, which causes the cardiac muscle to contract
27
Why does the signal travel down the heart?
This sequence of events ensures contractions begin at the apex (bottom), forcing blood up towards the arteries
28
What happens after each contraction of the heart?
Heart Relaxation / Diastole After every contraction of the heart, there is a period of insensitivity to stimulation (i.e. a refractory period)
29
What is the role of diastole? 2
This recovery period (diastole) is relatively long, and allows the heart to passively refill with blood between beats This long recovery period also helps prevent heart tissue becoming fatigued, allowing contractions to continue for life
30
What ensures one-way circulation of blood around the body?
The heart contains a number of heart valves which prevent the backflow of blood This ensures the one-way circulation of blood around the body
31
What are the two sets of valves in the heart and their roles?
There are two sets of valves located within the heart: Atrioventricular valves (tricuspid and bicuspid) prevent blood in the ventricles from flowing back into the atria Semilunar valves (pulmonary and aortic) prevent blood in the arteries from flowing back into the ventricles
32
How are heart sounds made?
Heart sounds are made when these two sets of valves close in response to pressure changes within the heart
33
What causes the first heart sound? (lubb)
The first heart sound is caused by the closure of the atrioventricular valves at the start of ventricular systole
34
What causes the second heart sound? (dubb)
The second heart sound is caused by the closure of the semilunar valves at the start of ventricular diastole
35
What is the cardiac cycle?
The cardiac cycle describes the series of events that take place in the heart over the duration of a single heart beat
36
What is the cardiac cycle comprised of?
It is comprised of a period of contraction (systole) and relaxation (diastole)
37
How can the cardiac cycle be mapped?
The cardiac cycle can be mapped by recording the electrical activity of the heart with each contraction
38
What machine is used to map the cardiac cycle?
Activity is measured using a machine called an electrocardiograph to generate data called an electrocardiogram
39
What are the 5 stages of an ECG?
``` P wave PR interval QRS complex ST segment T wave ```
40
What is the P wave?
The P wave represents depolarisation of the atria in response to signalling from the sinoatrial node (i.e. atrial contraction)
41
What is the QRS complex?
The QRS complex represents depolarisation of the ventricles (i.e. ventricular contraction), triggered by signals from the AV node
42
What is the T wave?
The T wave represents repolarisation of the ventricles (i.e. ventricular relaxation) and the completion of a standard heart beat
43
What is the role of the PR interval and ST segment?
Between these periods of electrical activity are intervals allowing for blood flow (PR interval and ST segment)
44
What can be done with ECG's?
Data generated via electrocardiography can be used to identify a variety of heart conditions, including:
45
What is Tachycardia and bradycardia?
Tachycardia (elevated resting heart rate = >120 bpm) and bradycardia (depressed resting heart rate = < 40 bpm)
46
What are arrhythmias?
Arrhythmias (irregular heart beats that are so common in young people that it is not technically considered a disease)
47
What are fibrillations?
Fibrillations (unsynchronised contractions of either atria or ventricles leading to dangerously spasmodic heart activity)
48
What is cardiac output?
Cardiac output describes the amount of blood the heart pumps through the circulatory system in one minute
49
What is the use of the cardiac output value?
It is an important medical indicator of how efficiently the heart can meet the demands of the body
50
What is the equation for cardiac output?
There are two key factors which contribute to cardiac output – heart rate and stroke volume Equation: Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV)
51
What is heart rate?
Heart rate describes the speed at which the heart beats, measured by the number of contractions per minute (or bpm)
52
What does each ventricular contraction cause?
Each ventricular contraction forces a wave of blood through the arteries which can be detected as a pulse
53
What is the typical heart rate?
The typical pulse rate for a healthy adult is between 60 – 100 beats per minute
54
What can affect heart rate?
Heart rate can be affected by a number of conditions – including exercise, age, disease, temperature and emotional state
55
Does the body have to adapt to a change in stroke volume?
Additionally, the body will attempt to compensate for any changes to stroke volume with a corrective alteration to heart rate
56
What two nerves are involved in regulating heart rate?
Heart rate is increased by the sympathetic nervous system and decreased by parasympathetic stimulation (vagus nerve)
57
WHat hormone can increase heart rate?
Heart rate can also be increased hormonally via the action of adrenaline / epinephrine
58
What is stroke volume?
Stroke volume is the amount of blood pumped to the body (from the left ventricle) with each beat of the heart
59
What is stroke volume affected by?
It is affected by the volume of blood in the body, the contractility of the heart and the level of resistance from blood vessels
60
What will changes in stroke volume affect?
Changes in stroke volume will affect the blood pressure – more blood or more resistance will increase the overall pressure
61
What do blood pressure measurements include?
Blood pressure measurements typically include two readings – representing systolic and diastolic blood pressures
62
Which pressure (di/systolic) is higher?
Systolic blood pressure is higher, as it represents the pressure of the blood following the contraction of the heart
63
Why is diastolic blood pressure lower?
Diastolic blood pressure is lower, as it represents the pressure of the blood while the heart is relaxing between beats
64
What will blood pressure readings vary depending on?
Blood pressure readings will vary depending on the site of measurement (e.g. arteries have much higher pressure than veins)
65
What is the typical blood pressure of an adult in the brachial artery?
A typical adult is expected to have an approximate blood pressure in their brachial artery of 120/80 mmHg to 140/90 mmHg
66
What can blood pressure be affected by?
Blood pressure can be affected by posture, blood vessel diameter (e.g. vasodilation) and fluid retention or loss
67
What is hypertension?
Hypertension is defined as an abnormally high blood pressure – either systolic, diastolic or both (e.g. > 140/90 mmHg)
68
What are common causes of hypertension?
Common causes of hypertension include a sedentary lifestyle, salt or fat-rich diets and excessive alcohol or tobacco use
69
What may high blood pressure be secondary to?
High blood pressure can also be secondary to other conditions (e.g. kidney disease) or caused by some medications
70
What are the symptoms of hypertension?
Hypertension itself does not cause symptoms but in the long-term leads to consequences caused by narrowing blood vessels
71
What is thrombosis?
Thrombosis is the formation of a clot within a blood vessel that forms part of the circulatory system
72
Where does thrombosis occur?
Thrombosis occurs in arteries when the vessels are damaged as a result of the deposition of cholesterol (atherosclerosis)
73
What forms after thrombosis?
Atheromas (fat deposits) develop in the arteries and significantly reduce the diameter of the vessel (leading to hypertension)
74
What do atheromas lead to? thrombosis
The high blood pressure damages the arterial wall, forming lesions known as atherosclerotic plaques
75
What happens if a plaque ruptures? thrombosis
If a plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
76
What happens if a thrombus becomes dislodged?
If the thrombus becomes dislodged it becomes an embolus and can cause blockage at another site
77
What can thrombosis in coronary arteries lead to?
Thrombosis in the coronary arteries leads to heart attacks, while thrombosis in the brain causes strokes
78
What is CHD?
Coronary heart disease (CHD) describes the condition caused by the build up of plaque within the coronary arteries
79
What is the cause of CHD?
It is essentially the consequence of atherosclerosis in the blood vessels that supply and sustain heart tissue
80
Is the incidence of CHD the same all around the world?
NO The incidence of coronary heart disease will vary in different populations according to the occurrence of certain risk factors E.g. The incidence of CHD under the age of 65 is substantially higher in indigenous Australians (versus non indigenous)
81
What are the risk factors of coronary heart disease?
Age – Blood vessels become less flexible with advancing age Genetics – Having hypertension predispose individuals to developing CHD Obesity – Being overweight places an additional strain on the heart Diseases – Certain diseases increase the risk of CHD (e.g. diabetes) Diet – Diets rich in saturated fats, salts and alcohol increases the risk Exercise – Sedentary lifestyles increase the risk of developing CHD Sex – Males are at a greater risk due to lower oestrogen levels Smoking – Nicotine causes vasoconstriction, raising blood pressure
82
What is an artificial pacemaker?
An artificial pacemaker is a medical device that delivers electrical impulses to the heart in order to regulate heart rate
83
What is the advanatge of modern packemakers?
Modern pacemakers are externally programmable, allowing cardiologists to make adjustments as required
84
What can artificial pacemakers be used to treat?
Artificial pacemakers are typically used to treat one of two conditions: Abnormally slow heart rates (bradycardia) Arrhythmias arising from blockages within the heart’s electrical conduction system
85
What is fibrillation?
Fibrillation is the rapid, irregular and unsynchronised contraction of the heart muscle fibres
86
What does fibrillation cause?
This causes heart muscle to convulse spasmodically rather than beat in concert, preventing the optimal flow of blood
87
How is fibrillation treated?
Fibrillation is treated by applying a controlled electrical current to the heart via a device called a defibrillator
88
What does a defibrillator do?
This functions to depolarise the heart tissue in an effort to terminate unsynchronised contractions
89
How is it known that fibrillation has passed?
Once heart tissue is depolarised, normal sinus rhythm should hopefully be re-established by the sinoatrial node

Biology IB HL (56 decks)

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