Arteries are classified according to their size, the appearance of their tunica media, or their major function.
Large elastic conducting arteries include the aorta and its large branches. Unstained, they appear yellow due to their high con tent of elastin.
The tunica intima is composed of endothelium and a thin sub jacent connective tissue layer. An internal elastic membrane marks the boundary between the intima and media.
The tunica media is extremely thick in large arteries and con sists of circularly organized, fenestrated sheets of elastic tissue with interspersed smooth muscle cells. These cells are responsi ble for producing elastin and other extracellular matrix com ponents. The outermost elastin sheet is considered as the external elastic membrane, which marks the boundary between the media and the tunica adventitia.
The tunica adventitia is a longitudinally oriented collection of colla-genous bundles and delicate elastic fibers with associated fibroblasts. Large blood vessels have their own blood supply (vasa vasorum), which consists of small vessels that branch profusely in the walls of larger arteries and veins. Muscular distributing arteries are medium-sized vessels that are characterized by their predominance of circularly arranged smooth muscle cells in the media interspersed with a few elastin compo nents. Up to 40 layers of smooth muscle may occur. Both internal and external elastic limiting membranes are clearly demonstrated. The intima is thinner than that of the large arteries.
Arterioles are the smallest components of the arterial tree. Generally, any artery less than 0,5 mm in diameter is considered to be a small artery or arteriole. A subendothelial layer and the inter nal elastic membrane may be present in the largest of these vessels but are absent in the smaller ones. The media is composed of sev eral smooth muscle cell layers, and the adventitia is poorly devel oped. An external elastic membrane is absent.
arteries – артерии
to be classified – классифицированный
according – соответственно
their – их
size – размер
appearance – вид
tunica – оболочка
major – главный
elastic – упругий
conducting – проведение
arteries – артерии
to include – включать
aorta – аорта
branches – ветви
up to – до
layers – слои
smooth – гладкий
may – может
Запомните следующие застывшие словосочетания.
In a loud voice In a low voice In an angry voice In a thin voice
Заполните пропуски, где необходимо.
1. She shouted in. low voice.
2. He told us the poem in. loud voice.
3. The children asked ice-cream in. thin voice.
4. The teacher cried at the pupils in. angry voice.
5. Bill Robins was… very rich man.
6. He was. richest man in. village.
7. Pete is… tallest boy in our class.
8. Nick is… shortest boy, but he is very strong.
9. He is… stronger than many boys who are taller than he.
10. I think Nick is… strongest boy in class.
Перед превосходной степенью прилагательных употребляется определенные артикль.
E. g. Asia is the largest continent.
My brother is the best pupil in his class.
Вставьте артикль, где необходимо.
1. Bill Robins was… very rich man. He was… richest man in… village.
2. Pete is… tallest boy in our class. Nick is… shortest boy, but he is very strong.
3. He is… stronger than many boys who are taller than he.
4. I think Nick is… strongest boy in class.
5. Granny often tells us… long stories. Today her story was still… longer.
6. It was… longest story. She began telling it after… dinner and finished it before… supper.
7. But… story was very interesting. I think it was… most interesting of Granny’s stories.
8. Which was… most difficult exercise in. test-paper?
9. Which is… best season of the yea?
10. February is… shortest month of the year.
Answer the questions.
1. How are arteries classified?
2. What do large elastic conducting arteries include?
3. What is the tunica intima composed of?
4. What does an internal elastic membrane mark?
5. Is the tunica media thick?
6. Is the tunica adventitia a longitudinally oriented collection of col-lagenous bundles?
7. With what do the tunica adventitia associated?
8. What are muscular distributing arteries?
9. Up to how many layers of smooth muscle may occur?
10. What is the media composed of?
Make the sentences of your own using the new words (10 sentences).
Find the definite and indefinite articles in the text.