Chapter 41 Lecture Enrichment Ideas
Describe why most mollusks would have an open circulatory system but why cephalopods (octopus, squid, and nautilus) would have a closed circulatory system. Consider the circulatory needs of the predator as opposed to the sedentary filter feeder or the herbivore. Also note how short-lived insects do not have the need for an elaborate immune system since their life cycle is generally completed in one season.
Draw the improvements in efficiency from the one-circuit heart of the fish to the partially separated circulation in most reptiles to the completely separated two-circuit heart of birds and mammals. It is possible to alude to the evolutionary modifications that led to these changes when drawing the diagrams and merely adding a blood vessel shunt or extending a heart wall to make a three-chambered heart a four-chambered heart. Consider activity levels, warm-bloodedness, and similar functions that depend on oxygen and nutrient delivery. Sometimes a human baby is born without complete closure of the hole between the ventricles (foramen ovale); without surgery, this is fatal and illustrates that we cannot live with incomplete separation of oxygenated and deoxygenated blood, as can a frog.
Consider the size, shape, and structure of the human heart and why it has a thicker wall on the left side, which delivers blood to the systemic circuit, as opposed to the right side, which sends blood only to the nearby pulmonary circuit. Students may have been taught to pledge with their hand over their heart far to the left; it is more central.
Discuss the actions of the valves and why valvular damage can cause heart murmurs, varicose veins in the legs, and even death. Heart murmurs add sounds to the lub-dub according to which valve is failing to close and allowing blood to backwash with a shhh sound, as in "lub-dub-shhh."
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