Lab 12 - Heart dissection, blood pressure and ECG

Question 1

Which animal’s heart was used for the heart dissection

Answer 1

Sheep

Question 2

What was used to open the heart

Answer 2

Scalpel - razor blade

Question 3

What was used to trace the vessels

Answer 3

Seeker

Question 4

What is role of the moderator band

Answer 4

Conducts the right branch of the AV bundle to the anterior papillary muscle

Question 5

Do humans have the moderator band

Answer 5

No

Question 6

What are the 3 major differences between skeletal and cardiac muscle and what do they tell us about the functioning of cardiac muscle?

Answer 6

• Skeletal muscle fibres have several peripheral nuclei. Cardiac fibres have only a single central nucleus.
• Skeletal muscle fibres don’t branch. Cardiac fibres do. Branching spreads out the AP rapidly so it goes to all parts of the heart quickly.
• Cardiac fibres are joined by gap junctions (intercalated discs) forming a syncitium. Gap junction is to allow electrical signals to be spread rapidly

Question 7

What happens when heart contracts

Answer 7

There is a rise in pressure within the cardiovascular system ( systolic )

Question 8

What happens when the heart relaxes

Answer 8

The pressure will fall back down to resting level ( diastolic )

Question 9

What is blood pressure measured in and using what

Answer 9

Measured in millimetres of mercury (mm Hg) using a sphygmomanometer.

Question 10

Explain the process of measuring bp

Answer 10

• The pressure is raised in a cuff wrapped around the arm until all the blood flow below the cuff has stopped. - At this point you are applying more pressure than the cardiovascular system can, and consequently the artery has collapsed. You are therefore above the systolic pressure.
• The pressure in the cuff is then lowered until blood begins to flow again. The point at which blood just begins to flow is the systolic pressure as the cardiovascular system is now generating enough pressure at the highest point in its cycle to oppose the pressure you are applying.
• As pressure is decreased further more and more blood will flow through the artery which is being collapsed less and less. - Eventually a point is reached when blood flow is no longer restricted. At that point, less pressure is being applied than the cardiovascular system exerts even when at rest. This is below the diastolic pressure.

Question 11

How can the systolic and diastolic pressures be determined

Answer 11

By listening to blood flow in the artery below the cuff

Question 12

Will blood make a sound when flowing through a vessel

Answer 12

No

Can only hear turbulent blood flow

Question 13

What happens when artery is collapsed

Answer 13

Will not hear anything as nothing is flowing

Question 14

What happens when you decrease the pressure

Answer 14

• Arrive at systolic pressure, some turbulent blood will just squeeze through - soft intermittent tapping sound
• Then, as the pressure is decreased further, the sound becomes louder and more continuous until eventually it dies away. At this point there is no turbulent blood flow as the vessel is no longer being even slightly distorted by the pressure being applied and the diastolic pressure has been reached.

Question 15

How should the subject be seated when checking bp

Answer 15

Relaxed and seated in such a way that the left arm is approx on the same level as the heart
Ensure there is no tight clothing around the arm

Question 16

How to measure bp

Answer 16

Wrap the cuff around the arm, locate the brachial artery and place a stethoscope on it (you will hear nothing). Inflate the cuff to around 150 mmHg (in most cases you will still hear nothing - if you do raise the pressure until the sound disappears). Gradually release the pressure in the cuff and listen for the sounds of Korotkoff as described above.

Question 17

What sounds do you hear when measuring bp

Answer 17

Korotkoff

Question 18

Why is there variation in the readings of BP from different people?

Answer 18

Age, Ethnic, Diet (salt content), Obesity, Smoking, Alcohol, what theyre doing and feeling, different medication and conditions – health issues

Question 19

What is an ECG

Answer 19

A recording on the body surface of the electrical events in the heart (atrial and ventricular depolarisation and repolarisation).

Question 20

Explain the shape of a normal ECG in terms of the events of the cardiac cycle using your trace as a demonstration.

Answer 20

• P wave- atria depolarises/contracts
• PR interval-duration of atria contracting
• QRS complex- ventricles contract
• T wave- ventricles repolarise/relax

Question 21

Give some examples of how the ECG changes during cardiovascular pathology (e.g. heart block, prolonged QT syndrome etc.).

Answer 21

Heart block - some P waves are not transmitted. Thus QRS & T waves are not present
Congenital long-QT syndrome : genetic defect causing sodium channels to stay open.