8.3 The Heart

State why the heart muscle is described as myogenic. 

Fig. 1 shows a graph that results from the monitoring of the electrical activity of the heart, along with the stages of the cardiac cycle to which the electrical activity corresponds. The T wave corresponds to diastole, during which the electrical charge across the cells of the heart returns to normal as the wave of excitation ends.

Fig.1

Describe the electrical activity taking place in the heart, relating it to the P wave and the QRS complex shown in Fig.1

Fig. 2 shows ECG traces from three individuals. Individual A has healthy heart function while individuals B and C have been diagnosed with heart problems.

Fig. 2

State the abnormalities in electrical activity that seem to be present in the ECG traces of individuals B and C shown in Fig. 2

Individual C experienced symptoms such as the feeling of a fluttering heart and chest pain.

Suggest and explain one other physical symptom that individual C in Fig. 2 might be experiencing.

Describe the roles of the sinoatrial node (SAN) and the atrioventricular node (AVN) in the initiation and control of the cardiac cycle.

The Purkyne fibres pass down the septum and extend to the cardiac muscle at the base (apex) of the heart.

Explain why it is important that the Purkyne fibres extend to the base of the heart.

The activity of the SAN is controlled by the nervous system. Noradrenaline is released by nerve cells in the SAN.

Fig. 1 shows the role of noradrenaline in causing calcium ions (Ca²⁺) to enter a cell in the SAN.

Fig. 1

With reference to Fig.1, outline the process of cell signalling.

Woolly foxglove, Digitalis lanata, shown in Fig. 1A, and common oleander, Nerium oleander, shown in Fig. 1B, are plants grown for the attractive flowers that they produce.

Both plants are poisonous, as their leaves produce toxic organic compounds known as cardiac glycosides. Cardiac glycosides have a powerful effect on the action of cardiac muscle.

Fig. 1

N. oleander is able to grow in very dry conditions. The leaves have adaptations to reduce water loss by transpiration.

State the term used to describe a plant, such as N. oleander, that has adaptations to allow it to grow in conditions where water is in short supply.

Aphids are small insects that feed on plant fluids using piercing and sucking mouthparts. When aphids feed on the sap present in vascular tissue of leaves and stems, a sugary liquid called honeydew is passed out of the gut. The honeydew can be analysed to find out what is present in the sap.

(i)

State the name of the vascular tissue from which the aphids feed.

(ii)

An investigation found that aphids feeding on D. lanata produced honeydew containing cardiac glycosides.

Suggest why cardiac glycosides were present in the sap from the vascular tissue.

Cardiac glycosides have an effect on the movement of ions into and out of cardiac muscle cells. The outcome is an increased ability for the cells to contract. 

Investigations into the action of the cardiac glycoside oleandrin, extracted from N. oleander, have shown that it acts to prevent the correct functioning of Na/K‐ATPase, a membrane transport protein.

Na/K‐ATPase has a role as an enzyme and as a transport molecule.

• ATPase is an enzyme that catalyses the hydrolysis of ATP to ADP and inorganic phosphate.
• Energy released from this hydrolysis is used to transport sodium ions (Na⁺) out of cardiac muscle cells and potassium ions (K⁺) into the cells.

Explain what is meant by the hydrolysis of ATP.

(ii)

Name the type of transport mechanism involved in the transport of Na⁺ and K⁺ across the cell surface membrane of cardiac muscle cells.

(iii)

Oleandrin is a non‐competitive reversible inhibitor of ATPase.

Describe the mode of action of oleandrin and explain how this will affect ion movement through Na/K‐ATPase transport proteins of the cell surface membranes of cardiac muscle cells.

Digoxin, a cardiac glycoside extracted from D. lanata leaves, can be purified and used as a drug to treat some heart disorders.

Examples of these heart disorders are:

• atrial fibrillation, where the normal rhythmic cardiac cycle is disrupted
• heart failure, where cardiac muscle is contracting weakly.

(i)

Describe the sequence of events occurring in the left side of the heart during one normal cardiac cycle. Include reference to blood pressure changes.

The first event in the sequence is described for you.

The left atrium fills with blood during relaxation of the left atrium and left ventricle.

[4]

(ii)

Suggest how the health of a person with heart failure can be improved by treatment with the drug digoxin.

Fig. 1 shows the external view of the mammalian heart.

Fig. 1

Identify the structure marked X.

[1]

Suggest and explain one possible symptom that might result from a blockage inside structure X

[3]

Fig. 2 shows the pressure changes in various parts of the heart during the cardiac cycle.

Fig. 2

Calculate the heart rate of the individual in Fig. 2

Fig. 2 shows separate lines for the left and right ventricles.

State the reason for this difference

[1]

Explain the benefits of this difference to the function of the circulatory system

[2]

Identify the times on Fig. 2 at which the following events take place:

The first ventricular systole begins.

[1]

The semilunar valves close.

[1]

Diastole begins.

[1]

The mammalian circulatory system is described as a closed double circulation.

Explain why it is called a closed and double circulation.

Fig.1 shows a drawing of an external view of a mammalian heart.

Two cross-sections were made of the heart:

• Section 1 was made across the line A–B.
• Section 2 was made across the line C–D.

Drawings of the two sections were viewed from above as shown by the arrow on Fig. 1. Fig. 2 is a drawing of section A–B. Fig. 3 is a drawing of section C–D.

Name structures 1, 2 and 3, as shown in Fig. 2.

[3]

Explain why the wall of chamber Y is thicker than the wall of chamber X, as shown in Fig. 3.

[3]

Explain how the contractions of the chambers of the heart are coordinated during one cardiac cycle.

The sinoatrial node (SAN) and the atrioventricular node (AVN) are two regions of the heart.

Explain the role of the SAN and the role of the AVN in the cardiac cycle.

Fig. 1 shows features that are observed in transverse sections of three types of blood vessel.

Complete Fig.1 by stating the type of blood vessel indicated by D, E and F.

[1] 

(ii)

The inner layer of the walls of D and E is composed of endothelial tissue.

List two structural features of endothelial tissue.