Unit 21

Pre-text assignments:

1 Learn the key words and phrases:

pulmonary circuit, systemic circuit, pulmonary trunk, lobar branches, pulmonary capillaries, pulmonary veins, vascular loop, companion system of veins

2 Match the following English phrases with Ukainian ones:

1) red blood cells a) згортання крові

2) to combat infection b) забезпечувати необхідну кількість

крові

3) to destroy bacteria c) червоні кров’яні тілця

4) clotting of blood d) боротися з інфекцією

5) to maintain an adequate

blood volume e) руйнувати бактерії

3 Match the words with the opposite meaning and use them in the sentences of your own:

1) benign, to exclude, frequently, insufficiency, permanent, to diminish, to improve, to appear, gradual

2) to increase, seldom, malignant, sufficiency, to aggravate, to include, to be constant, sudden, to disappear

Paths of Circulation

The blood vessels of the cardiovascular system can be divided into two major pathways – a pulmonary circuit and a systemic circuit. The pulmonary circuit consists of those vessels that carry the blood from the heart to the lungs and back to the heart. The systemic circuit is responsible for carrying the blood from the heart to all other parts of the body and back again.

Pulmonary Circuit

The blood enters the pulmonary circuit as it leaves the right ventricle through the pulmonary trunk. The pulmonary trunk extends upward and posteriorly from the heart, and about 5 centimeters above its origin, it divides into the right and left pulmonary arteries. These branches penetrate the right and left lungs, respectively. Within the lungs, they divide into lobar branches (three on the right side and two on the left) that accompany the main divisions of the bronchi into the lobes of the lungs. After repeated divisions, the lobar branches give rise to arterioles that continue into the capillary networks associated with the walls of the alveoly.

The blood in the arteries and arterioles of the pulmonary circuit has a relatively low concentration of oxygen and a relatively high concentration of carbon dioxide.Gas exchanges occur between the blood and the air as the blood moves through the pulmonary capillaries.

As a result of the gas exchanges occurring between the blood and the alveolar air, the blood entering the venules of the pulmonary circuit is rich in oxygen and low in carbon dioxide. Four pulmonary veins, two from each lung, return blood to the left atrium, and this completes the vascular loop of the pulmonary circuit.

Systemic Circuit

The freshly oxygenated blood received by the left atrium is forced into the systemic circuit by the contraction of the left ventricle. This circuit includes the aorta and its branches that lead to all of the body tissues, as well as the companion system of veins that returns the blood to the right atrium.

Post-text assignments:

1 Respond to the following tasks:

1 Distinguish between the pulmonary and systemic circuits.

2 Trace a drop of blood through the pulmonary circuit from the right ventricle.

3 Explain why the alveoli normally remain dry.

2 What system is this?

A characteristic feature of the system is the numerous delicate valves in small and medium sized vessels. The structure of these valves is similar to that nerves in the venous system, but the connective tissue core consists merely of reticulum fibres and a little ground substance. (venous or lymphatic)

3 Choose the proper answer:

1 What is called pulmonary circulation?

a) the circulation of blood from the body organs to the heart and back again;

b) the circulation of blood from the heart to ttie lungs and back to the heart.

2 Where does the left ventricle discharge out the blood?

a) to the lungs through the pulmonary arteries;

b) to the systemic circulation through the aorta.

3 What are the arteries characterized by?

a) carry blood away from the heart;

b) carry deoxygenated blood.