Part I – Symptoms Callie was 26 years old when she opened a bakery called “Callie’s Cupcakes” in downtown San Francisco with her f ancé, Jeremy. Despite the competitive market, her business was...

Part I – Symptoms
Callie was 26 years old when she opened a bakery called “Callie’s Cupcakes” in downtown San Francisco with her
f ancé, Jeremy. Despite the competitive market, her business was booming; everyone loved the clever recipes and the
trendy atmosphere. Between running their fast-growing business and planning for their wedding, Callie hadn’t been
able to keep to her usual eight hours of sleep a night. Although she had always lived a very healthy lifestyle, exercising
daily and eating healthy, she just hadn’t been feeling herself lately. She was tired all the time, had dif culty breathing,
felt stressed, coughed up sputum, consistently ran a low-grade fever, and had lost weight as her appetite decreased.
None of these symptoms alone had been particularly alarming so she had put of seeing her physician for a few weeks.
Questions
1. What are Callie’s symptoms? List all that were mentioned.
2. Based on the symptoms presented, what are three possible respiratory infectious diseases Callie could be suf ering
from? Explain why.
3. Based on Callie’s symptoms and your answers so far, it seems Callie is having trouble with her respiratory system.
Several respiratory conditions can impact gas exchange. Describe the process of gas exchange in the lung (alveoli).
by
Brianna S. Nelson, Kelsey N. Aguirre, Alee L. Adams, Emily E. Brodbeck, and Breanna N. Harris
Department of Biological Sciences
Texas Tech University, Lubbock, TX
NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Take a Deep Breath:
A Case of Respiratory Illness
“Take a Deep Breath” by Nelson, Aguirre, Adams, Brodbeck, & Harris Page 2
NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE
Part II – The Diagnosis
As each day passed Callie’s symptoms grew worse and worse. After standing for long periods of time she could barely
breathe; in fact, she couldn’t even work a full day in the bakery without feeling like she was going to pass out. When
it got to the point that extreme exhaustion and high fever prevented her from getting out of bed, Jeremy was alarmed.
“Callie, I’m taking you to see your doctor,” he said, and got her an appointment for the next morning.
Once there, Callie explained to her physician, Dr. Nayak, that she had been tired, fatigued, stressed, and that she
hadn’t been sleeping well. She also mentioned that she had lost some weight and just didn’t have an appetite. T e
worst part was the shortness of breath and the cough. Her breathing troubles and coughing had lasted for about three
weeks and seemed to be getting worse. As a precaution, Dr. Nayak decided to provide Callie a surgical mask in case
she had an infectious respiratory disease. She then proceeded to do a basic physical exam as well as a chest x-ray and a
sputum analysis.
Dr. Nayak then asked Callie if she had traveled out of the country within the past three months. Callie looked confused, and said “no.” T e doctor followed this up by asking whether Callie had come into contact with anyone who
had been out of the country. T inking about it for a moment she replied, “Well, one of the employees in our bakery is
from South Africa and she frequently visits her family back at home; she’s actually in South Africa visiting right now. I
work with her weekly. Could that really be a factor?”
“Yes, it could,” Dr. Nayak said. “Did your employee have any symptoms that you can recall?”
Callie ref ected a moment and said, “Yes, she does seem to always have a cough. She told me it was just allergies and
that she might be bothered by all the f our in the air.”
T e chest x-ray came back and showed nodular formations in both of Callie’s lungs near the clavicles. Based on the
x-ray and symptoms, Dr. Nayak suspected Callie had tuberculosis, more specif cally active tuberculosis, also known as
tuberculosis disease. South Africa has one of the highest incidences of active TB in the world, and knowing that Callie
had an employee who frequently visited that location made Dr. Nayak suspect TB, but they would need to run some
tests to be sure. Dr. Nayak’s local laboratory lacked the most rapid testing mechanisms, so it would take a few days to
receive results from the sputum stain and the sputum nucleic amplif cation test. Dr. Nayak also took a blood sample
for additional testing. Due to her suspicion for TB, Dr. Nayak advised Callie to stay home and not work until they
could conf rm her diagnosis. She provided Callie with some surgical masks in the event she needed to go out. After
Callie left, Dr. Nayak contacted the local health department and reported that she suspected her patient had TB.

QUESTION 3

Extracted text: Part III – Impacts on Lung Function After a few days had passed, Callie and Jeremey returned to Dr. Nayak's office and were told that Callie's sputum stain was positive, as was her blood test. The nucleic amplification test results showed that Callie did in fact have active TB. Dr. Nayak informed Callie that she needed to contact her employee right away for testing; all other employees of the bakery also needed to be tested, including Jeremey. Callie replied that a nurse from the health department had already visited with her and had begun the contact investigation. Jeremy was concerned for Callie and asked for more details. Dr. Nayak explained that active TB is caused by the pres- ence of active bacteria, M. tuberculosis, in the body. The bacteria initially enter the body via the respiratory system, and in active infection they can be found in the lung as well as in other body tissues. When the bacteria initially enter the alveoli the body's immune cells, macrophages, attack the bacteria. If the macrophages are successful, the bacteria are removed and the infection ends. If they cannot completely kill the bacteria those bacteria begin to replicate inside the macrophage. The macrophage then dies thus triggering an additional immune response and inflammation (increased blood flow and fluid/pus production). This inflammation can result in difficulty breathing and cell granulomas (nodu- lar areas that contain the bacteria and immune cells), which can further impact respiratory function in the alveoli. Dr. Nayak provided Jeremey and Callie with the following link to a YouTube video so that they could learn more about the disease at home: https://youtu.be/yR51KVF40X0. Dr. Nayak then told Callie that she was actually lucky; Dr. Nayak had also ordered a test to check the sputum sample for drug susceptibility. The results showed that Callie had a type of TB that would respond to first-line antibiotics; in other words, she was not infected with a drug-resistant strain. Jeremey nodded along as Dr. Nayak spoke, but when the physician left the room, he turned to Callie and admitted he was still confused about how this impacted breathing. Callie thought for a minute and then recalled what she had learned when she took introduction to physiology in college. She explained that the alveoli, the little grape-like sacs in the lungs, are used for gas exchange. The alveoli have thin walls, a large surface area, and make contact with vast capillary beds-they are prime locations for swapping of gases. While Callie was talking, Jeremey pulled out his smartphone and found the following: Fick's law can be used to determine the diffusion rate across a surface. The equation states: diffusion rate = (area * concentration gradient of gas [partial pressure in lung vs. blood] * surface permeability [diffusion constant or coefficient])/ membrane thickness'. Thus, diffusion is fastest if the concentration gradient is high, the membrane is thin (and permeable), and exchange surface is large.