Textbook Question
What effect does sympathetic stimulation have on the heart? What effect does parasympathetic stimulation have on the heart?
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Ch. 20 The Heart
Martini, Nath, Bartholomew11th EditionFundamentals of Anatomy & PhysiologyISBN: 9780136874089
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Table of contents
- Ch. 1 An Introduction to Anatomy and Physiology26
- Ch. 2 The Chemical Level of Organization34
- Ch. 3 The Cellular Level of Organization30
- Ch. 4 The Tissue Level of Organization24
- Ch. 5 The Integumentary System17
- Ch. 6 Bones and Bone Structure36
- Ch. 7 The Axial Skeleton11
- Ch. 8 The Appendicular Skeleton17
- Ch. 9 Joints13
- Ch. 10 Muscle Tissue12
- Ch. 11 The Muscular System28
- Ch. 12 Nervous Tissue18
- Ch. 13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes22
- Ch. 14 The Brain and Cranial Nerves20
- Ch. 15 Sensory Pathways and the Somatic Nervous System17
- Ch. 16 The Autonomic Nervous System and Higher-Order Functions30
- Ch. 17 The Special Senses16
- Ch. 18 The Endocrine System20
- Ch. 19 Blood31
- Ch. 20 The Heart31
- Ch. 21 Blood Vessels and Circulation29
- Ch. 22 The Lymphatic System and Immunity31
- Ch. 23 The Respiratory System12
- Ch. 24 The Digestive System18
- Ch. 26 The Urinary System31
- Ch. 27 Fluids & Electrolytes32
- Ch. 28 The Reproductive System12
- Ch. 29 Development and Inheritance23
Martini, Nath, Bartholomew11th EditionFundamentals of Anatomy & PhysiologyISBN: 9780136874089Not the one you use?Change textbook
Chapter 20, Problem 28
Vern is suffering from cardiac arrhythmias and is brought into the emergency room of a hospital. In the emergency room he begins to exhibit tachycardia and as a result loses consciousness. Explain why Vern lost consciousness.
Verified step by step guidance1
Step 1: Understand the terms involved. Tachycardia is a condition where the heart beats faster than normal, typically over 100 beats per minute in adults. Cardiac arrhythmias refer to irregular heart rhythms, which can affect how effectively the heart pumps blood.
Step 2: Recognize the relationship between heart rate and cardiac output. Cardiac output (CO) is the volume of blood the heart pumps per minute and is calculated as \(CO = HR \times SV\), where \(HR\) is heart rate and \(SV\) is stroke volume (the amount of blood pumped with each beat).
Step 3: Consider how tachycardia affects stroke volume. When the heart beats too fast, the ventricles have less time to fill with blood during diastole, which reduces stroke volume. Even though heart rate increases, the decrease in stroke volume can lead to a reduced or insufficient cardiac output.
Step 4: Connect cardiac output to brain perfusion. The brain requires a constant and adequate supply of oxygenated blood. If cardiac output drops significantly, less blood reaches the brain, leading to decreased oxygen delivery.
Step 5: Explain loss of consciousness. Due to reduced cerebral perfusion from decreased cardiac output during tachycardia, the brain does not receive enough oxygen, causing Vern to lose consciousness.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cardiac Arrhythmias
Cardiac arrhythmias are irregularities in the heart's rhythm, which can cause the heart to beat too fast, too slow, or erratically. These disruptions affect the heart's ability to pump blood efficiently, potentially leading to inadequate blood flow to vital organs.
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Events in the Cardiac Cycle
Tachycardia
Tachycardia is a condition where the heart rate exceeds the normal resting rate, typically over 100 beats per minute. While it may initially increase cardiac output, sustained tachycardia can reduce the heart's filling time, decreasing stroke volume and overall blood circulation.
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Loss of Consciousness Due to Reduced Cerebral Perfusion
Loss of consciousness occurs when the brain does not receive enough oxygen-rich blood, a state called cerebral hypoperfusion. In tachycardia caused by arrhythmias, inefficient heart pumping reduces blood flow to the brain, leading to fainting or syncope.
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Related Practice
Textbook Question
The following measurements were made on two individuals (the values recorded remained stable for 1 hour):
Person 1: heart rate, 75 bpm; stroke volume, 60 mL
Person 2: heart rate, 90 bpm; stroke volume, 95 mL
Which person has the greater venous return?
Which person has the longer ventricular filling time?
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Textbook Question
Describe the effects of epinephrine, norepinephrine, glucagon, and thyroid hormones on the contractility of the heart.
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Textbook Question
What factors influence cardiac output?
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Textbook Question
Harvey has a heart murmur in his left ventricle that produces a loud 'gurgling' sound at the beginning of systole. Which valve is probably faulty?
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Textbook Question
Karen is taking the medication verapamil, a drug that blocks the calcium channels in cardiac muscle cells. What effect should this medication have on Karen's stroke volume?
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