Textbook Question
Compare the effects of the cardioacceleratory and cardioinhibitory centers on cardiac output and blood pressure.
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Ch. 21 Blood Vessels and Circulation
Martini, Nath, Bartholomew12th EditionFundamentals of Anatomy and PhysiologyISBN: 9780137854011
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Table of contents
- Ch. 1 An Introduction to Anatomy and Physiology25
- Ch. 2 The Chemical Level of Organization34
- Ch. 3 The Cellular Level of Organization29
- Ch. 4 The Tissue Level of Organization24
- Ch. 5 The Integumentary System17
- Ch. 6 Bones and Bone Structure33
- 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 Senses15
- Ch. 18 The Endocrine System21
- Ch. 19 Blood31
- Ch. 20 The Heart31
- Ch. 21 Blood Vessels and Circulation26
- Ch. 22 The Lymphatic System and Immunity25
- Ch. 23 The Respiratory System4
- Ch. 24 The Digestive System18
- Ch. 26 The Urinary System31
- Ch. 27 Fluids & Electrolytes30
- Ch. 28 The Reproductive System12
- Ch. 29 Development and Inheritance17
Martini, Nath, Bartholomew12th EditionFundamentals of Anatomy and PhysiologyISBN: 9780137854011Not the one you use?Change textbook
Chapter 21, Problem 28
Bob is sitting outside on a warm day and is sweating profusely. Mary wants to practice taking blood pressures, and he agrees to play the patient. Mary finds that Bob's blood pressure is elevated, even though he is resting and has lost fluid from sweating. (She reasons that fluid loss should lower blood volume and, thus, blood pressure.) Why is Bob's blood pressure high instead of low?
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Step 1: Understand the relationship between blood volume and blood pressure. Normally, a decrease in blood volume (such as from sweating) would reduce blood pressure because there is less fluid circulating in the vessels.
Step 2: Consider the body's compensatory mechanisms in response to fluid loss. When Bob loses fluid through sweating, his body detects a drop in blood volume and activates systems to maintain blood pressure.
Step 3: Identify the role of the sympathetic nervous system and hormones like vasopressin (antidiuretic hormone) and aldosterone. These cause vasoconstriction (narrowing of blood vessels) and promote water retention to increase blood pressure.
Step 4: Recognize that vasoconstriction increases peripheral resistance, which can raise blood pressure even if blood volume is reduced. This explains why Bob's blood pressure is elevated despite fluid loss.
Step 5: Summarize that the elevated blood pressure is due to the body's homeostatic response to maintain adequate blood flow and pressure, involving vasoconstriction and hormonal regulation, rather than a direct effect of blood volume alone.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Blood Pressure Regulation
Blood pressure is controlled by multiple factors including cardiac output, blood volume, and resistance in blood vessels. Even if blood volume decreases due to sweating, the body can adjust other parameters like heart rate and vessel constriction to maintain or increase blood pressure.
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Partial Pressure
Role of the Sympathetic Nervous System
The sympathetic nervous system activates during stress or heat exposure, causing vasoconstriction and increased heart rate. This response helps maintain blood pressure despite fluid loss by increasing vascular resistance and cardiac output.
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Effect of Dehydration and Fluid Loss on Blood Volume
Sweating causes fluid loss, reducing blood volume, which typically lowers blood pressure. However, the body compensates through mechanisms like vasoconstriction and increased heart rate to prevent hypotension, sometimes resulting in elevated blood pressure.
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Related Practice
Textbook Question
How do pressure and resistance affect cardiac output and peripheral blood flow?
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Textbook Question
People with allergies commonly take antihistamines with decongestants to relieve their symptoms. The container warns that individuals who are being treated for high blood pressure should not take the medication. Why not?
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Textbook Question
Why is blood flow to the brain relatively continuous and constant?
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Textbook Question
Jolene awakens suddenly to the sound of her alarm clock. Realizing that she is late for class, she jumps to her feet, feels light-headed, and falls back on her bed. What probably caused this reaction? Why doesn't this happen all the time?
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