Part 7/10:
The autonomic nervous system, along with hormonal signals, modulates heart rate, increasing it during exercise or stress and decreasing it during rest. Heart rate is often estimated by palpating pulse points in arteries such as the wrist or neck.
Variations in Circulatory Structures Across Animals
Different animals exhibit various circulatory adaptations:
Arthropods: Use a heart to pump hemolymph through open systems, with vessels branching to tissues.
Fish: Typically possess a two-chambered heart with blood flowing from the heart to gills (for oxygenation) and then to the body. Some fish have multiple hearts or more complex structures, but their blood flow largely remains in a series circuit.