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Material Type: Notes; Professor: Rifici; Class: Anatomy and Physiology I; Subject: Biology; University: Cuyahoga Community College District; Term: Unknown 1989;
Typology: Study notes
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Preparation for Lecture Pumping Blood – Pages 679-715.
1. What area of the ventricles initiates contraction? Why is blood pumped most efficiently when contraction begins there?
Based on the anatomy of the action potential conducting pathways, the area of the ventricles nearest the apex contract first. Remember, of course, that atrial contraction precedes ventricular contraction.
The fibers of the ventricular myocardium are oriented in a spiral fashion. Contraction at the apex forces blood upwards in the ventricles toward the base where the aortic and pulmonary semilunar valves are located. Initiation of contraction anywhere else could lead to blood flowing in an inefficient direction, that is, not toward the semilunar valves.
2. Predict the consequences of a heart attack that damages the tissue of the SA node.
The SA node sets the normal pace of the heart. This pace is modified by parasympathetic (slows pace) and sympathetic (increases pace) nervous control and adrenal hormone. Other areas of the myocardium are autorhythmic, but the SA dominates in normal hearts.
A damaged SA will lead to irregular pace or a slower pace set by the AV node or bundle tissue. Consequences include inability of the heart to generate a normal pace, reduced heart rate, and inefficient pumping.
3. Relate your knowledge of the structure and function of intercalated disks to the rhythmic contraction of the myocardium. Tell me how these two concepts are related.
Intercalated disks connect cardiac muscle fibers. They consist of desmosomes for strong ‘connectability’ and gap junctions for propagation of action potential cell to cell. Nodal tissue sets the pace of the heart with spontaneous action potential that spreads across the atria, and then the ventricles, cell to cell (noting the involvement of the bundle tissue and Purkinje fibers). Action potential is slow in cardiac muscle and the result is contraction spreads across the myocardium with its progression.
4. In one type of interatrial septal defect there is a failure of the fetal foramen ovale (or as we called it in class, oval window) to close after birth. What complications can we expect in the circulation of blood in this individual? Tell me about the ability of this patient to maintain optimal blood oxygen levels.
This does occur in humans. The result is mixing of low oxygen systemic blood flowing into the right side of the heart and high oxygen blood returning on the pulmonary circuit into the left side. Blood being pumped to the tissues will have abnormal oxygen and the cardiovascular system will attempt to compensate. Other complications can be found by researching the defect.