This is because hormones are lipid soluble and readily penetrate the membranes of the target cell. They travel to different areas of the body. They are carried by the circulatory system. They are used to communicate between different organisms. They elicit specific biological responses from target cells.
Most terrestrial animals dissipate excess heat by countercurrent exchange.
In addition to their role in gas exchange, fish gills are also directly involved in digestion. II IV V VII 16. III IV V VII 17. The functional unit of the kidney is called the cortex vasa recta nephron bladder glomerulus 20. The functional unit of nervous tissue is the cell body.