Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

19. The Blood Vessels

Introduction to Hemodynamics

Anatomy & Physiology

19. The Blood Vessels

Introduction to Hemodynamics

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Problem 28

Textbook Question

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?

Verified step by step guidance

Understand the physiological response to fluid loss: When Bob sweats profusely, he loses water and electrolytes, which can lead to a decrease in blood volume. Normally, a decrease in blood volume would lower blood pressure. However, the body has compensatory mechanisms to maintain blood pressure.

Explain the role of the sympathetic nervous system: Fluid loss triggers the activation of the sympathetic nervous system. This system increases heart rate and causes vasoconstriction (narrowing of blood vessels), which helps maintain or elevate blood pressure despite the reduced blood volume.

Discuss the role of hormones: Hormones like antidiuretic hormone (ADH) and aldosterone are released in response to fluid loss. ADH promotes water reabsorption in the kidneys, while aldosterone increases sodium reabsorption, both of which help retain fluid and maintain blood pressure.

Consider the effects of dehydration: Dehydration from sweating can increase blood viscosity (thickness), which makes it harder for the heart to pump blood. This can lead to an increase in peripheral resistance, contributing to elevated blood pressure.

Summarize the overall compensatory mechanisms: Bob's elevated blood pressure is likely due to the combined effects of sympathetic activation, hormonal responses, and increased blood viscosity. These mechanisms work together to counteract the fluid loss and maintain adequate blood pressure to ensure proper perfusion of tissues.

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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 regulated by a complex interplay of factors including cardiac output, blood volume, and vascular resistance. When blood volume decreases, as in the case of sweating, the body can compensate by constricting blood vessels and increasing heart rate, which may maintain or even elevate blood pressure despite fluid loss.

Sympathetic Nervous System Activation

The sympathetic nervous system plays a crucial role in the body's response to stress and changes in homeostasis. In situations like sweating, the body may activate this system to maintain blood pressure through vasoconstriction and increased heart rate, counteracting the effects of fluid loss.

Hormonal Regulation of Blood Pressure

Hormones such as aldosterone and antidiuretic hormone (ADH) help regulate blood pressure by controlling fluid balance and vascular resistance. In response to dehydration from sweating, the body may release these hormones to retain water and constrict blood vessels, which can lead to elevated blood pressure despite lower blood volume.