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Introduction to the lesson
Having studied blood vessels, blood plasma, tissue fluid, blood and haemoglobin, we now come to the pump which keeps this transport system going. In this lesson, we will study the structure of the heart. In the next lesson we will hone in on the cardiac cycle and look more in detail at how the heart functions. Remember as you go through biology, structure is always associated with function.
The heart
Read the section "The heart" on p.173-175 of your text book.
Notes on the heart chambers
- Study Fig. 8.22 (p.173) This is a diagram of the external structure of the heart as seen from the front. (Imagine yourself behind the heart looking out from the page to determine left and right side).
- Study Figure 8.25 (p.174) which is a diagrammatic section through the heart.
- Notice that the heart has four chambers:
- The top two chambers are the atria (atrium -singular).
- That atria receive blood - blood from the body enters the right atrium while blood from the lungs enters the left atrium.
- The bottom two chambers are the ventricles.
- The ventricles send blood out of the heart – the right ventricle is smaller than the left ventricle because it pumps blood from the heart to the lungs at low pressure while the left ventricle which is the largest chamber pumps blood at high pressure to the body.
- Notice that the right atrium is connected to the right ventricle and the left atrium is connected to the left ventricle, but there is no connection between the right and left sides of the heart. (Sometimes you may hear of a baby born “with a hole in the heart”. This is usually when there is some connection between the right and left sides of the heart which causes deoxygenated blood to mix with oxygenated blood. This will decrease the oxygen carrying capacity of the blood to the cells that need the oxygen for aerobic respiration).
- Notice that the heart has four chambers:
- Study Figure 8.24 to appreciate what the ventricle looks like in reality.
Learning Activity 1
Answer the following questions in your exercise book.
- Draw a schematic diagram of the four chambers – label right atrium, right ventricle, left atrium and left ventricle. (Your drawing should indicate that the left ventricle is larger than the right ventricle. Also make sure that you have used the convention of drawing the heart from the standard point of view. In other words, the left ventricle and atrium are drawn on the right side of the drawing).
- Why is the left venticular wall thicker than the right ventricular wall?
Notes on the blood vessels associated with each of the four chambers
- Study Fig. 8.22 and 8.25 again and notice the blood vessels associated with each chamber:
- Right atrium – receives blood from the venae cava. (notice that there are two vena cavae entering the heart – the top one (superior venae cava) brings deoxygenated blood from the head, while the bottom one (inferior venae cava) brings deoxygenated blood from the lower regions of the body.
- Right ventricle – sends deoxygenated blood to the lungs via the pulmonary artery.
- Left atrium – receives oxygenated blood from the lungs via the pulmonary vein.
- Left ventricle – sends oxygenated blood to the body via the aorta. Notice that the aorta is an arch above the heart with three branches coming off the arch.
Learning Activity 2
Answer the following questions in your exercise book.
- Draw a schematic diagram showing the veins and arteries associated with each chamber of the heart.
- Veins carry deoxygenated blood and arteries carry oxygenated blood. However, there are two exceptions to this rule. Which vein carries oxygenated blood and which artery carries deoxygenated blood?
Notes on the valves of the heart
- Study Fig. 8.25 on p.174.
- Notice that between the atria and the ventricles there are valves:
- Between the right atrium and the right ventricle is the tricuspid valve.
- Between the left atrium and the left ventricle is the bicuspid valve.
- Notice that there are also valves between the ventricles and the blood vessels they supply:
- Between the right ventricle and the pulmonary artery is the pulmonary (semilunar) valve.
- Between the left ventricle and the aorta is the aortic (semilunar) valve.
- There are also semilunar valves between the right atrium and the vena cava and between the left atrium and the pulmonary vein.
Learning Activity 3
Answer the following questions in your exercise book.
- Study Fig. 8.24 to see what the valves look like. Research the function of the papillary muscle.
- Draw a schematic diagram to show the four valves.
Notes on the blood supply to the heart
The heart is a muscle made up many cells that like other cells need oxygen and nutrients for respiration and other metabolic reactions. The heart is supplied by the coronary arteries. (These are the arteries that are involves in cardiac attacks and coronary heart failure. In a heart by-pass operation these arteries are replaced so that the heart is supplied with oxygen and nutrients.)
Learning Activity 4
Answer the following questions in your exercise book.
- Why does the heart need a blood supply?
- Study Fig. 8.21 (p.173) to see the supply of blood to the heart. Notice the thicker artery supplying the left ventricle. Why do you think the left ventricle needs more blood supply than the atria or right ventricle?
- Study Figure 8.22 (p.173) and identify the coronary arteries on the diagram.
Notes on heart muscle
- Study Fig. 8.25 and notice the thick muscular wall of the left ventricle.
- Study Fig. 8.24 to see what that wall really looks like.
- Now study Fig. 8.23. Although you do not need to know the structure of cardiac muscle, it is worth comparing it to striated muscle shown in Figures 15.25 and 15.26
- Notice that the left and right side of the heart is divided by a muscular wall called the septum.
Definitions and review
Definitions
- Cardiac muscle
- Aorta
- Pulmonary artery
- Venae cavae
- Pulmonary veins
- Coronary arteries
- Atria
- Ventricles
- Atrioventricular valve
- Mitral/bicuspid valve
- Tricuspid valve
Mindmap
Add this section to your chapter eight mindmap.