Look Ma No Capillaries

Remember, the bee's hemocoel does not possess networks of arteries and veins or trees of tubules for distributing materials around the body. In contrast, vertebrate blood in arteries, capillaries and veins stays separated from the extracellular fluid that bathes cells. Unlike a hemocoel, nutrients and wastes in a tubular system must traverse capillary walls, as well as the extracellular fluid surrounding the cells before they pass through cell membranes.

Insect hemolymph bathes and supplies organs more directly than blood in vertebrates, avoiding the added weight, time and the additional energy for molecules to traverse many barriers as they diffuse. As we will see in the chapters to follow, membranes lining the internal walls of the cavity of the hemocoel may act as barriers between cells and the fluid. In some instances, surfaces may be tight, in that hemolymph proper may never directly contact cells, except for the cells floating in the hemolymph and the exposed surfaces of some cells around the heart. However, probably many gaps exist between the cells lining the cavity, and movements of materials across boundaries are complex, highly controlled and precise (Chapter 7).

0 0

Post a comment