Module 3 section 2: The heart and haemoglobin.

Function of the AV valves?

Link the atria and ventricles, ensures blood flows unidirectionally.

What do the semi-lunar valves do?

Link ventricles to the arteries, prevents blood from blowing back into the ventricles.

How does the cardiac cycle begin?

Ventricles relax and atria contract, which forces blood through the AV valves and into the ventricles due to pressure increase.

What happens when blood enters the ventricles?

Atria relax after pushing blood into ventricles. Ventricles then contract, pushing blood out the arteries, through the SL valves. This increase in pressure in the ventricles also forces the AV valves closed.

What’s the last step of the cardiac cycle?

Both atria and ventricles relax. This drop in pressure closes the semi-lunar valves, while also causing blood to flow into the atria.

What does myogenic mean?

The heart can contract and relax without signals from nerves.

Cardiac output?

Heart rate X stroke volume. It is a measure of the volume of blood pumped out by the heart every minute.

Where do waves of electrical activitt begin in the heart?

Begins in the sinoatrial node, and is conducted to the atrioventricular node, ensuring atria contract at the same time.

Why doesn’t electrical charge pass directly into the ventricles?

There is a band of non-conducting collagen tissue that prevents the electrical charge from being conducted across into the ventricles.

Why is there a slight delay before the AVN reacts?

It waits to ensure the ventricles contract after the atria empty their blood.

Where does the electrical activity then go?

Transmitted to the bundle of his in the septum, which then transmits the signal to the Purkyne fibers, which ensure the ventricles contract simultaneously, bottom-up.

What does the height of the R wave indicate?

The relative strength of the contraction.

What’s an ectopic heartbeat?

An ‘extra’ heartbeat, that is sometimes caused by an earlier contraction of the atria.

Describe fibrillation, and explain why it is dangerous.

An irregular heartbeat, wherein the atria and ventricles lose their rhythm and begin contracting irregularly. This is dangerous because it means the heart is contracting improperly, and can cause issues like chest pain and heart attacks, even death.

How many molecules of oxygen can a haemoglobin molecule carry.

Four molecules of O2, forming oxyhaemoglobin.

What is pO2?

A measure of the concentration of oxygen molecules in a given area. For example, pO2 is high in the lungs, but low in respiring tissue.

Describe a dissociation curve.

Measure of how saturated Haemoglobin is in different partial pressures of oxygen.

Why are dissociation curves s-shaped?

When an oxygen molecule loads onto the haem group, it becomes easier for other oxygen molecules to also do so.

Why is it important that fetal haemoglobin has higher affinity to oxygen than adult haemoglobin.

The fetus cannot respire, so all the oxygen needed for respiration is acquired from the mother, via the placenta. Thus, the baby needs to be bale to take oxygen from the blood of the mother.

Explain the significance of the Bohr effect.

In higher partial pressure of CO2, haemoglobin more frequently unloads the oxygen.

Why does the Bohr effect occur?

CO2 affects blood pH. When CO2 from respiring tissues diffuse into blood cells, they react with the water there to form carbonic acid, catalysed carbonic anhydrase.

What happens to the rest of the CO2 from respiring tissues?

Binds to haemoglobin, and is carried to the lungs. The carbonic acid dissociates into hydrogen and hydrogencarbonate ions.

What happens when H+ ion concentration increases in the blood?

Oxyhaemoglobin unloads its oxygen to form haemoglobinic acid, and hydrogencarbonate ions diffuse into the blood plasma.

What’s chloride shift and why does it happen?

Chloride ions move into the cells to make up for the charge difference due to hydrogencarbonate ions moving out of the cell.

What happens to hydrogencarbonate and H+ ions in the lungs, as a result of low partial pressure of CO2?

Recombine to form CO2 and water, and is breathed out.