Back Home Top Next

Lesson Twelve: Blood Vessels

Outcome

Starting Activity (10 minutes)

Let the students will make a concept map of the circulatory system. From their previous knowledge, the students can explain that the circulatory system is the body’s delivery system, transporting blood throughout the body. They are expected to describe the role of blood. But the main idea here is how blood circulates round the body. It is a known fact that nutrients, oxygen, antibodies, enzymes and hormones as well as waste materials etc are all circulated through blood.  Thus, the teacher may raise the following questions to engage students in activity. 

The heart is the power pump for blood circulation. From this power pump, blood goes to vessels and circulates round the body and returned back to heart by means of vessels.

Thus, the students may list the three types of blood vessels as arteries, veins, and capillaries. They should be able to explain that blood from the heart gets around the body through these blood vessels.

The specific functions of the three blood vessels might be explained as follows.  

  1. Arteries carry blood from the ventricles (pumping chambers) of the heart out to the capillaries in organs and tissue. The smallest arteries are called arterioles.
  2. Veins drain capillaries in the tissues and organs and return the blood to the heart. The smallest   veins are the venules.
  3. Capillaries allow for exchanges between the blood and body cells, or between the blood and air in the lung tissues. The capillaries connect the arterioles and venules.

Main activity (20 minutes)

Here there is a need to explain the interconnection between three blood vessels. This is the major idea of the system of blood circulation along vessels.

Group work

Organize students into small groups having 4-6 members. Let each group discuss the interconnection between three blood vessels for 5 minutes and come up with some sort of explanation.  After a group activity, the teacher should ask students to trace the correct path of blood along vessels. 

The students are expected to trace the correct path of blood from heart to body and back to heart via the blood vessels. They should be able to indicate the direction of blood from heart by considering the three blood vessels.  The students should be informed that arterioles are tiny branches of arteries that carry blood from towards capillaries. Also the students should be informed that venules are minute vessels that drain or carry blood from capillaries to veins. It should be noted that many venules join to form veins. Venules are minute vessels that drain blood from capillaries and into veins. Many venules unite to form a vein.


Fig. 12.1:  Direction of Blood Flow

Critical Thinking

Ask students to realize the significance of heart muscle, arterial walls and skeletal muscles in assisting the movement of blood in our body.

What makes blood move in our body?

It should be noted that the pumping action of the heart is the force that moves blood through the arterial system and all the way into our brain, our fingertips and our toes. Arterial walls are muscular. They are also flexible and smooth. This elasticity also helps move blood throughout the body. Finally, the muscles in the body help move blood through our system, especially back “up” from our toes. The motion of our body helps squeeze blood back to the heart through the veins because our muscles push up against the walls of the vein. Our veins have valves that keep blood from flowing backwards in response to gravitational force.  Fig.  Interconnection between the three Blood vessels

A comparison between arteries and veins might be important here. There is some sort of misconceptions as to the nature and characteristics of arteries and veins. Thus, the teacher is required to give brief comparisons between arteries and veins.

Arteries

Veins

Carry blood away from the heart Carry blood towards the heart
Blood is under high pressure hence it flows fast, in spurts, reflecting the rhythmic pumping action of the heart Blood is not under high pressure and hence, it flows more slowly and smoothly.
Have thick and elastic muscular walls. Have relatively thin, slightly muscular walls.
Do not have valves (except for the semi-lunar valves of the pulmonary artery and the aorta). Have valves throughout the main veins of the body.
Have relatively narrow lumens Have relatively wide lumens.
Carry  oxygenated blood (except: pulmonary arteries which carry deoxygenated blood from the heart to the lungs and umbilical arteries which carry deoxygenated blood from the foetus to the mother's blood) Carry  deoxygenated blood (except: pulmonary veins which carry oxygenated blood from the lung to the heart and umbilical vein which carries oxygenated blood from the mother's blood to the foetus

Table 12.1 Differences between Arteries and Veins

N.B: The three blood vessels are structurally as well as functionally interconnected.

Fig. 12.2: Interconnection between blood Vessels

Conducting Activity:  Let the students record their own pulse rate and those of their classmates per minute.

Steps


Fig. 12.3: Pulse in the Wrist

Explore:

Explain:

Heart rates vary in order to meet the different needs of the body. During exercise, we need more oxygen and blood in the muscles so the heart rate increases.

Evaluation / Assessment Questions 

The teacher is required to evaluate his students whether they have understood the lesson or not.  Questions that can summarize the lesson can be forwarded to students.  For example,