There are several factors which affect normal vision and eyesight. These factors include diet, heredity, environmental factors including exposure to artificial light, age, etc. Hormones can also affect our vision considerably.
The flow of blood in the capillaries is controlled by structures called precapillary sphincters. These structures are located between arterioles and capillaries and contain muscle fibers that allow them to contract. When the sphincters are open, blood flows freely to the capillary beds of body tissue.When the sphincters are closed, blood is not allowed to flow through the capillary beds. Fluid exchange between the capillaries and the body tissues takes place at the capillary bed.hen the sphincters are open, blood flows freely to the capillary beds of body tissue. When the sphincters are closed, blood is not allowed to flow through the capillary beds. Fluid exchange between the capillaries and the body tissues takes place at the capillary bed.
3. Arterioles-smallest arteries, these carry blood into capillaries. a. When these constrict, they shut off blood to specific tissues. When they dilate, blood flow increases greatly into tissues. III. CAPILLARIES-microscopic blood vessels. Are the smallest vessels in the body.rterioles carry blood into capillaries (capillary beds) which. carry blood into body tissues. B. Blood returning from the capillary beds empties into venules that merge to form veins. Veins. ultimately empty into the heart. II. ARTERIES-carry blood away from the heart.