Cardiac Conduction System and Arrhythmias

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Questions and Answers

What is the approximate heart rate of a small animal like a mouse?

20 bpm

600 bpm (correct)

60 bpm

80 bpm

According to the graph, how long should humans live based on their heart rate?

60-70 years

80-90 years

40-50 years

20-25 years (correct)

What is the predicted age of reproduction based on the graph?

20 years

18 years

13 years (correct)

10 years

What is the advantage of having grandparents in an evolutionary context?

They are a liability to the herd Signup and view all the answers

Why do humans live longer than predicted by the graph?

We have made changes to our society and behavior Signup and view all the answers

What is the approximate heart rate of a large animal like a whale?

20 bpm Signup and view all the answers

What happens to older animals in a herd or pack?

They become liabilities Signup and view all the answers

What is the purpose of grandparents in an evolutionary context?

They are surplus to requirements Signup and view all the answers

What is the approximate number of heartbeats in a lifetime for most animals?

3 x 10^8 Signup and view all the answers

According to the lecture, why do zebras not typically get chronic kidney failure?

Because they get eaten by lions before chronic diseases develop Signup and view all the answers

What is the approximate number of heartbeats in a human lifetime?

30 x 10^8 Signup and view all the answers

What is the primary reason for the increase in chronic diseases in humans?

Because we live longer than we were 'designed' to Signup and view all the answers

What is the main point of the graph showing the number of heartbeats in a lifetime?

To illustrate the concept that all animals have a similar number of heartbeats in a lifetime Signup and view all the answers

According to the lecture, what is the approximate age range during which humans are likely to develop chronic diseases?

25-80 years old Signup and view all the answers

What can be inferred about the way we deal with chronic diseases?

Our approach to dealing with chronic diseases is often inappropriate Signup and view all the answers

What is the implication of humans living longer than we were 'designed' to?

We will develop chronic diseases as we live longer Signup and view all the answers

What is the normal conductor of the orchestra setting the heart rate?

Sinus node Signup and view all the answers

What happens when the cardiac structures start firing off at faster rates or at abnormal intervals?

Cardiac arrhythmias are generated Signup and view all the answers

Where is the sinus node located?

At the junction of the superior and inferior vena cavae Signup and view all the answers

What is the composition of the sinus node?

A mixture of specialised nodal cells, atrial cells, and connective tissue Signup and view all the answers

What percentage of the sinus node is composed of connective tissue?

50-90% Signup and view all the answers

What are the 'P' cells in the centre of the SA node described as?

Small, poorly differentiated, with very few mitochondria Signup and view all the answers

What is a characteristic feature of the 'P' cells in the centre of the SA node?

Numerous membrane invaginations called cavaeolae Signup and view all the answers

What is the effect of aging on the heart rate due to changes in the sinus node?

Heart rate decreases Signup and view all the answers

What does a change in the ST segment of an ECG indicate?

A sign of myocardial ischaemia or an evolving myocardial infarction Signup and view all the answers

What is the QT interval a useful index of?

Action potential duration Signup and view all the answers

What is the chronological state of the heart modulated by?

The autonomic nervous system Signup and view all the answers

What is the function of the vagus nerve in heart rate regulation?

Slowing heart rate Signup and view all the answers

What is the primary pacemaker of the heart?

Sinoatrial node Signup and view all the answers

What is the diagnostic significance of a prolonged QT interval?

It is a sign of a genetic channelopathy Signup and view all the answers

What is the sympathetic nervous system's effect on heart rate?

Accelerating heart rate Signup and view all the answers

What is the relationship between the QT interval and the ventricular action potential duration?

The QT interval is approximately equal to the ventricular action potential duration Signup and view all the answers

What is the primary function of the AV node in regulating heart rate?

To filter out high frequencies and prevent transmission of high heart rates Signup and view all the answers

What is the benefit of the AV pause in the cardiac conduction system?

It prevents the transmission of high heart rates and allows for ventricular filling Signup and view all the answers

What is the sequence of contraction in the ventricles during a normal heartbeat?

Apex to base contraction Signup and view all the answers

What is the role of intercalated disks in cardiac muscle fibers?

To facilitate electrical conduction along cardiac fibers Signup and view all the answers

What is the significance of the ventricular conduction system in regulating cardiac function?

It allows for rapid conduction of electrical impulses to the apex of the ventricle Signup and view all the answers

What is the result of the rapid conduction of electrical impulses down the septum to the apex of the ventricle?

Apex to base contraction of the ventricles Signup and view all the answers

What is the mechanism by which electrical impulses spread through cardiac muscle fibers?

From cell to cell along the length of cardiac fibers Signup and view all the answers

What is the purpose of the slow conduction through the AV node?

To allow time for ventricular filling and prevent high heart rates Signup and view all the answers

Study Notes

Heart Rate and Life Expectancy

A linear relationship exists between heart rate and life expectancy in various animals, but humans deviate from this trend.
Smaller animals (e.g., mice) have faster heart rates (~600 bpm) and shorter lifespans (~2 years), while larger animals (e.g., whales) have slower heart rates (~20 bpm) and longer lifespans (~40 years).
Humans have a resting heart rate of ~72 bpm and live up to ~80 years, which is inconsistent with the expected trend.

The Advantage of Grandparents

In evolutionary terms, it's unclear what advantage grandparents provide, as they may become a liability in terms of resource consumption and slowing down the pack/herd.
However, in social animals like humans, grandparents may offer benefits through sharing their experience and knowledge.

Chronic Diseases

The period from ~20-25 years of age to ~80 years is a timeframe where humans are more susceptible to chronic diseases, as they were not "designed" to live this long.
Chronic diseases, such as diabetes, cardiovascular disease, cancer, and dementia, are not something that human bodies have evolved to deal with.
The way humans deal with chronic diseases may be inappropriate.

Heartbeats in a Lifetime

All animals have approximately the same number of heartbeats in a lifetime (~3 x 10^8 heartbeats).
The rate at which heartbeats are used can vary greatly, with some animals (e.g., mice) using them quickly and others (e.g., whales) using them more slowly.

The Sinus Node

The sinus node is the primary pacemaker, located at the top of the right atrium, and is responsible for setting the heart rate.
The sinus node contains a mixture of specialized nodal cells, atrial cells, and connective tissue, which is essential for its normal functioning.
Changes to the sinus node structure with age contribute to aging-induced changes in heart rate.

The AV Node

The AV node filters out high frequencies, preventing the transmission of high heart rates from the atria to the ventricles.
The AV pause allows time for the ventricles to fill before they contract and prevents the transmission of high heart rates.

Conduction and Contraction

The ventricular conduction system is very fast, allowing the sequence of contraction to start at the apex of the ventricle and push blood up towards the outflow tracts.
The conduction of excitation spreads from cell to cell along the length of cardiac fibers, facilitated by intercalated disks.

ECG and Myocardial Ischaemia

Changes in the ST segment of the ECG can indicate myocardial ischaemia or an evolving myocardial infarction.
The QT interval is a useful index of action potential duration and can be diagnostic of potentially lethal genetic channelopathies, such as Long QT Syndrome.

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Description

Learn about the normal functioning of the cardiac conduction system, including the sinus node, and how abnormalities can lead to cardiac arrhythmias. Understand how the sinus node regulates the heart rate and what happens when the normal rhythm is disrupted.