Answer: c. a capillary.
Explanation:
Capillary - consist of a layer of endothelial cells, the small-caliber, tube-shaped endothelium (single-floor epithelium): one to three cells in cross-section. They have elongated nuclei, cytoplasmic extensions, and junctions communicating with endothelial cells. Actin and myosin filaments promote their contraction by regulating blood flow. Regarding the continuity of the endothelial wall, three types of capillaries are distinguished: continuous, fenestrated and sinusoid.
In continuous capillaries, the intercellular space is sealed by the occlusion junctions, and substance entry occurs mainly by pinocytosis.
In fenestrated capillaries, endothelial cells are joined by occlusion junctions, but in addition to pinocytosis vesicles, they have pores usually covered by a thinner diaphragm than the plasma membrane, facilitating diffusion. of metabolites. The sinusoid capillaries have a tortuous (sinuous) path and increased caliber, with an internal diameter of 30 to 40m (in the other capillaries, it was 8 to 10 μm).
