Which of the following valve closings can be auscultated during the "dupp" heart sound by placing the stethoscope at the left sternal border of the second intercostal space? A) Pulmonary semilunar
B) Right atrioventricular (tricuspid)
C) Left atrioventricular (mitral)
D) Aortic semilunar

Pulmonary semilunar

Explanation

Generally heart chambers are separated from each other by valves.Likewise blood vessels of the heart. When the heart contracts(systole) to ejects blood,theses valves close up,to prevent back flow and  the mixture of oxygenated with deoxygenated  blood. When these occurs the forces of closure leads   to certain distinctive sounds in the heart, detected by the stethoscope.Theses are called heart sounds,.

The pulmonary arteries take deoxygenated blood away from the heart to the pulmonary circulation in the lungs,while the aorta takes oxygenated blood away from the heart into the systemic circulation,The back flow of the blood into the pulmonary artery is prevented by the pulmonary  valves,while the aortic semi lunar valves  guide against this  in the aorta,The sounds produced by these closure is called  the dupp sound.,

However, because the the left sternal border of the second intercostal space is the location of the Pulmonary semiminular valves.Therefore the closure is the actual sound of dupp.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

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