Bio 20b Exam2 Essay Question

Topics: Heart, Heart valve, Cardiac anatomy Pages: 3 (919 words) Published: May 25, 2013
1) Write about the semilunar values with as much detail as you can * NAME THEM. *Draw&Describe what they look like & Give their LOCATION.* Explain how the Semilunar Values Operate: What causes them to OPEN & what causes them to CLOSE. There are 4 values that enforce 1-way traffic for blood. ~The 2 Semilunar Valves are the Aortic & Pulmonary Valves. They guard the bases of the large arteries issuing from the ventricles & prevent backflow into the associated ventricles. Each SL Valve is fashioned from 3 pocketlike Cusps & shaped roughly like a half-moon. The SL Valves open & close in response to differences in pressure. When the ventricles are contracting & intraVentricular pressure rises above the pressure in the aorta and pulmonary trunk, the SL valves are forced to OPEN and their cusps flatten against the arterial walls as the blood rushes past them. When the ventricles relax, the blood flows backward toward the heart, it fills the cusps & CLOSES the valves. THE AV VALVES.

~ 2 AV valves are located at each atrial-ventricular junction, prevent backflow into the atria when the ventricles are contracting. : 1) Tricuspid Valve-the right AV valve has 3 flexible cusps. 2) The Mitral Valve-the left AV valve with 2 flaps. It is sometimes called the bicuspid valve because of its resemblance to the 2-sided bishop’s miter or hat. Attached to each AV valve flap are tiny white collagen cords called CHORDAE TENDINEAE, “heart strings” which anchor the cusps to the papillary muscles protruding from the ventricular walls. When the heart is completely relaxed, the AV valve flaps hang limply into the ventricular chambers below & blood flows into the atria and then thru the open AV valves into the ventricles. When the ventricles contracts, compressing the blood in their chambers, the intraventricular pressure rises, forcing the blood superiorly against the valve flaps. As a result, the flap edges meet, closing the valve. 1b)...
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