Table of contents

1. Introduction to Biology2h 42m
2. Chemistry3h 37m
3. Water1h 26m
4. Biomolecules2h 23m
5. Cell Components2h 26m
6. The Membrane2h 31m
7. Energy and Metabolism2h 0m
8. Respiration2h 40m
9. Photosynthesis2h 49m
10. Cell Signaling59m
11. Cell Division2h 47m
12. Meiosis2h 0m
13. Mendelian Genetics4h 44m
14. DNA Synthesis2h 27m
15. Gene Expression3h 6m
16. Regulation of Expression3h 31m
17. Viruses37m
- Viruses
  37m
18. Biotechnology2h 58m
19. Genomics17m
- Genomes
  17m
20. Development1h 5m
21. Evolution3h 1m
22. Evolution of Populations3h 53m
23. Speciation1h 37m
24. History of Life on Earth2h 6m
25. Phylogeny2h 31m
26. Prokaryotes4h 59m
27. Protists1h 12m
28. Plants1h 22m
29. Fungi36m
- Fungi
  19m
- Fungi Reproduction
  17m
30. Overview of Animals34m
- Overview of Animals
  34m
31. Invertebrates1h 2m
32. Vertebrates50m
33. Plant Anatomy1h 3m
34. Vascular Plant Transport1h 2m
- Water Potential
  1h 2m
35. Soil37m
- Soil and Nutrients
  20m
- Nitrogen Fixation
  16m
36. Plant Reproduction47m
- Flowers
  33m
- Seeds
  14m
37. Plant Sensation and Response1h 9m
38. Animal Form and Function1h 19m
39. Digestive System1h 10m
- Digestion
  1h 3m
- Blood Sugar Homeostasis
  7m
40. Circulatory System1h 49m
41. Immune System1h 12m
42. Osmoregulation and Excretion50m
- Osmoregulation and Excretion
  50m
43. Endocrine System1h 4m
- Endocrine System
  1h 4m
44. Animal Reproduction1h 2m
- Animal Reproduction
  1h 2m
45. Nervous System1h 55m
- Neurons and Action Potentials
  1h 8m
- Central and Peripheral Nervous System
  46m
46. Sensory Systems46m
- Sensory System
  46m
47. Muscle Systems23m
- Musculoskeletal System
  23m
48. Ecology3h 11m
49. Animal Behavior28m
- Animal Behavior
  28m
50. Population Ecology3h 41m
51. Community Ecology2h 46m
52. Ecosystems2h 36m
53. Conservation Biology24m
- Conservation Biology
  24m

40. Circulatory System

Heart Physiology

General Biology

40. Circulatory System

Heart Physiology

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1:08 minutes

Problem 3

Textbook Question

When the doctor listened to Janet's heart, he heard 'lub-hiss, lub-hiss' instead of the normal 'lub-dup' sounds. The hiss is most likely due to _________ . (Explain your answer.)
a. A defective atrioventricular (AV) valve
b. A damaged pacemaker (SA node)
c. A defective semilunar valve
d. High blood pressure

Verified step by step guidance

Step 1: Understand the normal heart sounds 'lub-dup'. The 'lub' sound is caused by the closing of the atrioventricular (AV) valves (tricuspid and mitral valves) during ventricular contraction (systole). The 'dup' sound is caused by the closing of the semilunar valves (aortic and pulmonary valves) during ventricular relaxation (diastole).

Step 2: Analyze the abnormal sound 'lub-hiss'. The 'hiss' indicates a potential issue with valve closure, as it suggests turbulent blood flow or leakage (regurgitation) through a valve that is not closing properly.

Step 3: Evaluate the options provided. A defective atrioventricular (AV) valve would cause abnormal sounds during the 'lub' phase, but the hiss is heard after the 'lub' sound. A damaged pacemaker (SA node) would affect the rhythm of the heartbeat, not the valve sounds. High blood pressure could strain the heart but does not directly cause a 'hiss' sound.

Step 4: Focus on the semilunar valves. A defective semilunar valve could fail to close properly during diastole, leading to regurgitation of blood and producing the 'hiss' sound after the 'lub' phase.

Step 5: Conclude that the abnormal 'lub-hiss' sound is most likely due to a defective semilunar valve, as this aligns with the timing and nature of the sound described in the problem.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Heart Sounds

The heart produces sounds during its cycle, primarily 'lub' and 'dup.' The 'lub' sound is caused by the closure of the atrioventricular (AV) valves, while the 'dup' sound results from the closure of the semilunar valves. Abnormal sounds, such as a 'hiss,' can indicate issues with these valves or other cardiac functions.

Atrioventricular (AV) Valve Function

The AV valves, which include the tricuspid and mitral valves, separate the atria from the ventricles. They ensure unidirectional blood flow from the atria to the ventricles. A defect in these valves can lead to regurgitation, causing abnormal heart sounds like a 'hiss' due to turbulent blood flow.

Semilunar Valve Function

The semilunar valves, comprising the aortic and pulmonary valves, control blood flow from the ventricles into the aorta and pulmonary artery, respectively. If these valves are defective, they may not close properly, leading to backflow or turbulence, which can also produce abnormal heart sounds, such as a 'hiss.'