Calcium levels in Mr. Gallariani's blood are dropping to dangerously low levels. The hormone PTH is released and soon blood calcium levels begin to rise. Shortly after, PTH release slows. Is this an example of a positive or negative feedback mechanism? What is the initial stimulus? What is the result?
Ch. 1 The Human Body: An Orientation
Hoehn, Haynes, Abbott12th EditionMarieb Human Anatomy & PhysiologyISBN: 9780138242732Not the one you use?Change textbook
Chapter 1, Problem 24
Aiden has been suffering agonizing pain with each breath and has been informed by the physician that he has pleurisy.
a. Specifically, what membranes are involved in this condition?
b. What is their usual role in the body?
c. Explain why Aiden's condition is so painful.
Verified step by step guidance1
Identify the membranes involved in pleurisy: Pleurisy affects the pleura, which are the two thin membranes surrounding the lungs and lining the chest cavity. These are the visceral pleura (covering the lungs) and the parietal pleura (lining the chest wall).
Explain the usual role of these membranes: Normally, the pleura produce a small amount of lubricating fluid that allows the two layers to slide smoothly over each other during breathing, reducing friction between the lungs and chest wall.
Describe what happens in pleurisy: In pleurisy, inflammation causes the pleural membranes to become rough and irritated, which disrupts the smooth sliding motion and increases friction.
Explain why this condition causes pain: The increased friction between the inflamed pleural layers stimulates pain receptors, especially during breathing movements, leading to sharp, agonizing pain with each breath.
Summarize the connection: Therefore, the pain in pleurisy arises because the normally lubricated pleural membranes are inflamed and rubbing against each other, making breathing painful.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Pleura and Its Membranes
The pleura are two thin membranes surrounding the lungs and lining the chest cavity. The visceral pleura covers the lungs, while the parietal pleura lines the chest wall. These membranes create a pleural cavity filled with lubricating fluid to facilitate smooth lung movement during breathing.
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Function of the Pleural Membranes
The pleural membranes reduce friction between the lungs and chest wall as the lungs expand and contract. The lubricating fluid allows the membranes to slide effortlessly, enabling painless and efficient breathing. They also help maintain lung expansion by creating a pressure gradient.
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Cause of Pain in Pleurisy
Pleurisy is inflammation of the pleural membranes, causing them to become rough and irritated. This inflammation leads to friction during breathing, resulting in sharp, agonizing pain with each breath. The pain worsens with deep breaths or coughing due to increased membrane movement.
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