Lecture 7 Flashcards
what are capillaries?
the site of exchange between blood and tissues
the function of capillaries demands these features ….
- very thin walls (especially for passive diffusion like gas exchange)
- large total cross sectional area of capillary bed
- slow and smooth blood flow
why is the cytoplasm thin in capillaries
for efficient gas exchange
what are precapillary sphincters and what are they composed of
composed of = smooth muscle cells
they can constrict and stop blood flow into the side paths and direct it through the metarteriole (thoroughfare channel)
what are the three types of capillaries
continuous capillaries
fenestrated capillaries
sinusoidal capillaries
describe continuous capillaries
- most common
- single file flow of blood vessels
- contains endothelial layer (tunica intima) and basement membrane
describe fenestrated capillaries
- single file flow of blood vessels
- contains fenestrations = pores
- small things that would usually need to go through the cell can pass though
- basement membrane still intact
describe sinusoidal capillaries
- larger diameter
- incomplete basement membrane
- contains larger fenestrations
what are the functions of the lymph vascular system? (4)
- drains excess tissue fluid and plasma proteins from tissues and returns them to the blood
- filters foreign material from the lymph
- ‘screens’ lymph for foreign antigens and responds by releasing antibodies + activated immune cells
- absorbs fat from intestine and transports to blood
what is the structure of lymphatic vessels like?
- larger
- thin walls
-collecting vessels have numerous valves to prevent backflow
- no red blood cells
what is the special group of lymphatic vessels from the small intestine and what do they do?
lacteals
they drain fat-laden lymph into a collecting vessel called cisterna chyli
