Capillaries are thin-walled, narrow-diameter, low-pressure vessels that generally permit easy diffusion across their walls. Most capillar ies have a cross-sectional diameter of 7-12 mm. They are composed of a simple layer of endothelium, which is the lining of the entire vas cu-lar system, and an underlying basal lamina. They are attached to the surrounding tissues by a delicate reticulum of collagen. Associated with these vessels at various points along their length are specialized cells called pericytes. These cells, enclosed within their own basal lamina, which is continuous with that of the endothelium, contain contractile proteins and thus may be involved in the control of capillary dynamics. They may also serve as stem cells at times of vascular repair. Capillaries are generally divided into three types, according to the structure of their endothelial cell walls.
Continuous (muscular, somatic) capillaries are formed by a single uninterrupted layer of endothelial cells rolled up into the shape of a tube and can be found in locations such as connective tissue, muscle, and nerve.
Fenestrated (visceral) capillaries are characterized by the presence of pores in the endothelial cell wall. The pores are covered by a thin diaphragm (except in the glomeruli of the kidney) and are usually encountered in tissues where rapid substance interchange occurs (e. g., kidney, intestine, endocrine glands).
Sinusoidal capillaries can be found in the liver, hematopoietic and lymphopoietic organs, and in certain endocrine glands. These tubes with discontinuous endothelial walls have a larger diame ter than other capillaries (up to 40 mm), exhibit irregular cross-sec tional profiles, have more tortuous paths, and often lack a con tinuous basal lamina. Cells with phagocytic activity (macrophages) are present within, or just subjacent to, the endothelium.
New words
capillaries – капилляры
to thin-walled – окруженный тонкой стеной
narrow-diameter – узкий диаметр
low-pressure – низкое давление
that – тот
generally – главным образом
permit – разрешение
easy – легкий
diffusion – распространение
cross-sectional – поперечный
to be composed – быть составленным
simple – простой
endothelium – эндотелий
lining – выравнивание
entire – весь
vas cular – сосудистый
underlying – лежащий в основе
basal – основной
lamina – тонкая пластинка
Правила употребления артикля с географическими названиями.
Определенный артикль употребляется перед названиями рек, каналов, морей, заливов, проливов, океанов, архипелагов, горных цепей.
Артикль не употребляется перед названиям озер, гор, островов, континентов, городов, стран. Исключения:
the United States of America
the United Kingdom of Great Britain and Northern Ireland the Netherlands the Ukraine the Crimea the Congo
Answer the questions.
1. Describe capillaries: how do they like?
2. What diameter do the most capillaries have?
3. What are the capillaries composed of?
4. Where are the capillaries attached to?
5. What are pericytes?
6. What do pericytes contain?
7. Where can pericytes be involved?
8. Where can sinusoidal capillaries be found?
9. What diameter have sinusoidal capillaries?
10. With help of what are continuous (muscular, somatic) capillaries formed by?
Make the sentences of your own using the new words (10 sentences).
Find the definite and indefinite articles in the text.