- Place the heart on the dissecting board with the atria at the top and the ventricles
facing downwards. - Carefully examine the external view of the heart. Try identify the vertical and horizon-
tal groves on the heart. This is the position of the internal walls between the chambers
of the heart. - Examine and note the difference in the walls of the ventricles and atria. Also note the
difference in appearance between the walls of the ventricles and atria. - With the scalpel or sharp knife carefully cut the heart open across the left atrium.
- Compare the thickness and the size of the right ventricle and atrium.
- Identify the valves and examine the tendinous cords which are attached to the valves.
- Identify the semi-lunar valves at the bottom of the pulmonary artery.
- Now cut through the left side of the heart in the same way as you did the right side of
the heart. - Carefully cut through the septum of the heart so that you have two halves.
Questions:- What is the smooth outer layer of the heart called?
- Did you notice any fat around the heart?
- Did you notice a difference between the atria and ventricles externally?
- Name the blood vessels visible on the outside of the heart?
- Compare the thickness of the walls of the atria and ventricles. Explain why they are
different. - Explain the difference between the left and right ventricular walls.
The cardiac cycle DUMMY
A cardiac cycle refers to the sequence of events that happens in the heart from the start of
one heartbeat to the start of the subsequent heartbeat. During a cardiac cycle the atria and
the ventricles work separately. The sinoatrial node (pacemaker) is located in the right atrium
and regulates the contraction and relaxing of the atria.
- At rest, each heartbeat takes approximately 0,8seconds.
- The normal heart rate at rest is approximately 72 beats per minute.
- Duringsystolethe heart muscle contracts.
- Duringdiastolethe heart muscle relaxes.
The phases of the cardiac cycle will be broken down and explained in the following section:
Phase 1: Atrial systole (Atrium contracts)
- Blood from the superior and inferior vena cava flows into the right atrium.
- Blood from the pulmonary veins flows into the left atrium.
- The atria contract at the same time.
- This contraction lasts for about 0,1 seconds.
Chapter 8. Transport systems in animals 231