D4. What makes for a healthy heart?

Lesson one: 

Objectives: Understand how to maintain a healthy heart. This may prolong your lifespan. Learn THE BASICS of how to diagnose heart murmurs, hypertension and abnormal Electrocardiogram  signals. 



  • Sinoatrial node: the collection of cells in the right atrial wall that initiate stimulation of cardiac muscle (pacemaker)
  • Atrioventricular node: a collection of cell in the wall of the septum that slowly transmit the passing of the signal between the atria and the ventricles, causing an important delay
  • Cardiac muscle: the uniquely adapted muscle of the heart

First. A basic test to assess the fitness of your heart. Lifelong.

What causes heart recovery rate to vary? A heart that has been developed by plenty of cardiovascular exercise will have an enlarged chamber size and thicker and healthier chamber walls. This will increase stroke volume (volume of blood pumped in ventricular systole). A stronger heart will be able to meet the oxygen demands of the body more easily, leading to faster recovery times.

Blood pressure and heart health

Blood pressure should be 120mg of mercury for ventricular systole and 80mg of mercury for diastole on average at rest.

High blood pressure, of hypertension, is linked to stress, excess salt intake, high intake of fatty acids in the diet, smoking, and alcohol abuse. Cortisol is a hormone related to stress. It prepares the body for action, a little like adrenalin. High levels of cortisol demand ‘release’ by some sort of action, or they lead to chronic anxiety.

Low blood pressure, or hypotension, is linked to poor blood circulation and weak heart function.

Both hypertension and hypotension can be combatted by regular aerobic exercise.

Heart disease is intimately linked to hypertension:

  • High levels of LDL cholesterol in the diet can lead to atherosclerosis (hardening of the arteries by a build up of atheroma of LDL cholesterol plagues on the inside of the coronary artery
  • This can lead to the weakening of the wall of an artery or even bursting of an artery this is caused an aneurysm. These are most common in the aorta (which has the highest natural blood pressure)
  • High blood pressure makes it more likely that blood clots will form this is coronary thrombosis
  • If an aneurysm or thrombosis happens near the brain, a stroke may be the result (oxygen shortage to part of the brain).

Demonstration: the basics of using a sphygmomanometer to self-diagnose blood pressure.

Diagnosing Heart sounds

During the cardiac cycle, blood moves:

  • Diastole: from veins into atria and also into ventricles
  • Atrial systole: from atria into ventricles
  • Ventricular systole: from ventricles into arteries

Q) When do the atrioventricular valves, and the semilunar valves, close?

This causes the classic heart sounds.


Demonstration: Listen to your heart beat with a stethoscope to check your heart sounds healthy.

The electrical activity of the heart ECG (Electro-cardiogram)


image credit: chest heart and stroke Scotland

image credit: chest heart and stroke Scotland

A defibrillator re-sets the cardiac cycle by administering a strong electrical impulse across the heart. This requires training in the correct use.

Not like this

How is heart muscle adapted to propagate stimuli?

image credit: britanica.com

image credit: britanica.com

  • Cardiac muscle cells are Y-shaped, and connected to each than most cells. This helps spread impulses
  • Cardiac muscle cells are joined by specialised junctions called intercalated discs, that consists of a double membrane with gap junctions where channels of cytoplasm stream from one cell into the next. This speeds up impulse transmission.
  • Like skeletal muscle, cardiac muscle is divided into muscle fibres and sarcomeres.

The Sino-Atrial node

The Sino-Atrial node consists of a group of modified structured cardiac cells that spontaneously initiate action potentials without stimulation from other nerves. Because of the gap junctions, the impulses spread rapidly across the cardiac cells as if they were one cell.

Q) Name two stimuli which cause the SA node to speed up the rate of contractions.

The Atria-ventricular node

The atria-ventricular node consists of specially modified cells that resemble the pacemaker except they act more slowly because they need to induce a delay, in order to allow time for atrial systole to occur before ventricular systole. In order to achieve this:

  • the AV cells have a narrow diameter than the SA cells and so do not conduct as fast
  • the AV node cells have less sodium channels in their membranes than SA node cells, which increases the refractory period after depolarisation
  • there are fewer gap junctions between AV node cells, leading to slower transmission of impulses

The AV-bundle

After the delay for atrial systole, ventricular contraction needs to occur. This is coordinated by the atrioventricular bundle and the purkinje fibres. These must rapidly cause a contraction of both ventricles, from the apex upwards. This is achieved by:

  • the AV bundle carries the impulse downwards to the apex, where they connected to the purkinje fibres

The Purkinje fibres:

  • relatively fewer myofibrils, but with a bigger diameter to more rapidly conduct impulses
  • They have high densities of sodium channels to enhance depolarisation
  • They have high numbers of mitochondria and rich glycogen stores
image credit: lumen learning

image credit: lumen learning

An artificial pacemaker can be surgically fitted to patients with a faulty SA node. There are different types of  artificial pacemakers, the most basic monitors the heart rhythm and when heartbeat is not detected, it stimulates the cardiac stimulation just like a real pacemaker would.



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