Question

Case 1: During her first visit to a Caribbean country, Margaret McKenzie, a 35 year-old woman, decided to try snorkeling over a local coral reef. Although she enjoyed the· fascinating plants and fishes, she found the taste of salt water unpleasant and was having trouble maintaining her orientation and position in the waves. Margaret lifted her head up and noticed that she was drifting further and further from shore. With a start, she realized that the tide was going out. She could hear her breath whistling through her snorkel, and she noticed that her breathing rate was fairly fast and getting faster. Shortly thereafter, she noticed that her heart had begun to pound. Margaret decided to swim in to shore. Although not usually a strong swimmer, Margaret found unexpected reserves of strength that enabled her to swim against the outgoing tide. When she arrived on the beach she was pale, breathing hard, and her heart was racing. Over the next few moments her color, and her heart and respiratory rates began to return to normal.

Case 2: Matthew was a first-year student in a medical illustration program. As part of his education, he was required to attend an autopsy with his class. This was to be his first experience viewing a dead human body, and he was apprehensive about it for days in advance. As he was attempting to sketch the great vessels of the heart, he noticed that his breathing rate was fast and getting faster. At the same time, he noticed that his heart had begun to race, that he was sweating despite the cool temperature, and that he was feeling lightheaded and nauseous. His professor, noticing that Matthew was pale and his pupils were dilated, led him to a chair outside the autopsy room. She handed Matthew a paper bag and recommended that he breathe into it for a few minutes. Soon Matthew's lightheadedness and nausea began to subside and his respiratory and heart rates began to return to-normal.

Guided questions for Case 1.

1. Describe the "Fight or Flight" reaction?

Phase 1: What general CNS structure is responsible for perception of fear and how are activating signals sent to the body (targets)?

Phase 2: Discuss neural and endocrine response to the activation of the fight or flight response.(bonus- Is there a difference in half-life of substances? If so, which one lasts longer?)

Phase 3. Describe effects on muscle, liver, heart and lungs. Bonus (what other changes may occur?

2. Describe mechanisms responsible for Margaret's circulatory changes e.g. cardiac and vascular; receptors and signaling pathway?

3. How can Margaret's increase in energy be explained?

4. What mechanisms caused Margaret's respiratory changes?

Guided Questions for Case 2:

5. Why was Matthew pale and sweating e.g. relate autonomics to control of cutaneous blood flow?

6. Why did Matthew feel lightheaded hint- breathing rate and CO2?

7. How did breathing into a paper bag relieve Matthew's symptoms?

Answer 1

Guided questions for Case 1.

1. Describe the "Fight or Flight" reaction?

The fight-or-flight response is also called as hyperarousal or the acute stress response which is elicited in response to percieved harmful event or threat to survuval. Fight-or-flight response is rendered by sympathetic stimulation of ANS.

The CNS structure which is responsible for perception of fear is amygdala. It is the masses of nuclei which is of almond-shape, located deep in the temporal lobe.

The targets for sympathetic stimulation is CV, circulatory, respiratory system and muscular system. SNS stimulate adrenal gland to release catecholamines such as epinephrine and norepinephrine which can cause an increase in heart rate, blood pressure, and breathing rate. The half life of both the hormones are 2-3 minutes and it takes around 20 to 60 minutes after the elimination of threat to return backfrom the pre-arousal levels to normal state.

2. Describe mechanisms responsible for Margaret's circulatory changes e.g. cardiac and vascular; receptors and signaling pathway?

The sympathetic nervous system of ANS is responsible for Margaret's circulatory changes. Types of adrenergic receptorsare: β and α. In heart, sympathetic stimulation induce activation of β1-adrenoceptors, which are GPCRs expressed in the SA node, AV node, and on atrial and ventricular cardiomyocytes of heart.  .

3. How can Margaret's increase in energy be explained?

SNS results in vasoconstriction of blood vessels in the skin, the digestive tract, and the kidney via the activation of alpha-1 adrenergic receptors by norepinephrine which in turn secreted by post-ganglionic sympathetic neurons. It increases the BMR and prepare body to produce more ATP to meed the energy demand.

4. What mechanisms caused Margaret's respiratory changes?

SNS increases vascular resistance in the pulmonary circulation which in turn alter the factors like respiration pattern, bronchomotor tone, and bronchial circulation. It increases the heart rate and the cardiac output to supply more oxygen to the muscles by increasing the heart contraction forces and by promoting vasodilation.