Answers
Activity 42.1 How Is Mammalian Heart Structure Related to Function?
1. Diagram and describe the path a red blood cell takes from a capillary in your big toe to your heart and back to your big toe. At each point in the pathway, indicate whether the red blood cell is most likely picking up or losing oxygen. Indicate also the relative blood pressure that part of the path is likely to have. Include all of the following terms in your diagram.
aorta
venules
veins
arteries
arterioles
capillaries
right atrium
left atrium
right ventricle
left ventricle
coronary arteries
heart
internal organs (for example, lungs, digestive tract)
skeletal muscle
2. The degree of musculature differs in these chambers of the heart: atria, right ventricle, left ventricle.
/ b. Explain why the differences in musculature might exist by explaining the normal functions of each chamber. / c. Include in your description the functions of the SA node (pacemaker), the AV node, and the AV and semilunar valves.
The walls of the atria, both right and left, are fairly thin, indicating little musculature. Blood flows through the atria into the ventricles. When the atria contract, they push the blood they contain only a few centimeters into the ventricles. This over-fills the ventricles and helps initiate the ventri-cular contraction. The right ventricle pumps its contents to the lungs. The left ventricle pumps its contents out the aorta and to the rest of the body. The difference in musculature of the two ventricles is correlated with the amount of effort required to move the blood through the circulatory pathway associated with each ventricle. / The signal from the SA node (also called the pacemaker) triggers the contraction of the atria. This signal is delayed at the AV node, which allows the atria to empty before the ventricles are signaled to contract.
The atrioventricular (AV) valves lie between the atria and the ventricles. These are one-way valves that prevent blood from flowing back into the atria when the ventricles contract.
The semilunar valves lie between the left ventricle and the aorta and between the right ventricle and the pulmonary artery.
These are also one-way valves that prevent blood from flowing backward into the ventricles.
3. While in utero, the wall between the two ventricles of the human fetal heart is not complete. An opening, the foramen ovale, allows blood from the two ventricles to mix. Normally, at birth, this hole seals over and the two ventricles are separated from each other. What would be the consequences to the infant if this hole did not seal over at birth?
If the foramen ovale did not seal at birth, oxygenated blood from the lungs (left ventricle) would mix with deoxygenated blood from the body (right ventricle). This condition is called “blue baby syndrome.” The blood going to the body carries less oxygen than normal. As a result, the baby turns blue during times of higher metabolic activity, which require greater amounts of oxygen input per unit time.
4. One of the most common congenital defects of the cardiovascular system is called “transposition of the great arteries.” In infants who have this defect, the pulmonary artery exits from the heart where the aorta should and the aorta exits where the pulmonary artery should. All other circulatory connections are normal.
a. Diagram and describe the circulation of blood in an infant who has this genetic defect.
When the positions of the aorta and pulmonary artery are reversed, two separate circulatory systems are set up. One pumps the blood from the left side of the heart via the pulmonary artery to the lungs and back via the pulmonary vein to the left side of the heart. The other pumps the blood from the right side of the heart via the aorta to the body and back to the right side of the heart via the anterior and posterior vena cava.
b. What type of treatment would such an infant need?
Unless something is done immediately, the infant will die. An operation to reverse the arteries takes a relatively long time. In the short term, the physician opens the foramen ovale to allow at least some oxygen to be pumped to the body.