3. Responding to Internal and External Environments

Lesson 15

Lesson 15: Responding to Internal and External Environments

We have nearly come to the end of our discussion about the human body, but we need to tie it all together. We need to see how our body responds to internal and external changes.

In order to do this we need a subject.

We're going to study a person who is going to go mountain climbing. Let's call her Judy.

She's a provincial park ranger in Kananaskis Country in southern Alberta.

Judy is a very fit person. She trains often because she may be doing all sorts of jobs such as mountain rescue work or back country patrols on horseback. Her resting pulse is usually around 60 beats per minute, and her respiration rate is 11 breaths per minute. On this day she is going to climb a nearby mountain with her team and practice rescuing someone off the mountain. She will be carrying a 13 kg pack which has all the clothing and supplies she will need.
Short Term Changes
The journey starts with a fairly strenuous hike as she approaches the mountain. With the extra weight she is carrying and the steep hills she is climbing, her muscles need to do more work and therefore her metabolic rate increases. The carbon dioxide is building up in her blood and this triggers the internal sensor and she begins to breath faster. Her heart rate is now up to 70 beats per minute and her breath rate is 16 breaths per minute. With this increase in metabolism her cells are generating more waste heat. Her body temperature rises to 38 degrees Celsius. To remove this excess heat, her skin releases perspiration which, as it evaporates, removes this extra heat and maintains her body temperature near her normal 37 degrees Celsius. In order to stop the perspiration she removes her pile jacket and feels comfortable again. This increased metabolism has increased the work load on the heart and lungs and now both are working faster. This ensures that both oxygen and nutrients are getting to her hard working cells and cell wastes, including heat, are removed. As she continues up the slope she is constantly nibbling on a fruit and nut bar to keep her energy up and drinking to replace the fluids lost in perspiration and through respiration.
At the base of the cliff face Judy and her team take a break and have lunch. With in a few minutes her body cools and she begins to get goose bumps and then begins to shiver. Her body temperature has dropped below 37 degrees as she rests and the shivering is actually the muscles in the skin moving to generate heat. (The amount of heat generated is equal to a moderate walk.) She quickly adds another layer of clothing and the shivering stops. By carrying layers of clothing she can regulate her body temperature at all times.

After a short break Judy and her team put on their mountaineering equipment and begin the ascent. Mountain climbing is a very strenuous activity and over the course of the afternoon Judy's metabolic rate increases dramatically. All the affects mentioned in the paragraph above are increased as well. Her vital signs are now: heart rate = 90 bpm, respiration = 18 bpm, temperature = 38 degrees Celsius. By the end of the day Judy is tired and hungry. Her vital signs have returned to normal. Because she has been doing this kind of activity for years her muscles are use to this strenuous activity, but a new member of the team will be sore for a few days as the lactic acid that built up in his muscles is slowly removed and excreted. As she drops off to sleep her metabolic rate slows even further. Her vital signs are: pulse rate = 55 bpm, respiration = 9 bpm, and her body temperature drops to 36 degrees Celsius. Good night Judy.
Long Term Changes
Judy was student from Vancouver, in British Columbia. The air at sea level contains more oxygen than the thin air of the mountains of Alberta. When she first came to Kananaskis Country she was constantly tired and out of breath. But over a period of a few weeks the number of red blood cells increased in her blood. This allowed her to collect more oxygen molecules from the thin air and she felt more active and her breath rate returned to normal.
As a student, Judy did a lot of studying and so could not be active all the time. Because her metabolic rate was fairly low, she didn't need to eat very much to keep her going.
But when she got to her new job in the mountains she go much more exercise. At first, she was sore, as unused muscles got used. She also noticed that she was always hungry. Her body needed more food - but why? What had happened was that her overall metabolic rate had increased due to her active lifestyle. She lost the little extra weight that she had before she got to 'K' Country and her muscles had firmed up. Judy's not a big person. She stands around 5 foot six inches, but these days she eats as much as a large man and doesn't gain a pound. Her increased metabolism burns those extra calories even when she sleeps.
Conclusion
Each and every day of our lives our bodies constantly adjusting to internal and external factors. The overall goal of our system is to remain stable. Your nervous system ensures that your internal systems have what they need and can get rid of wastes as soon as they can. A day in Judy's life showed us that these changes are natural and normal.

Exercise 4.3: Responding to Environments

1. In the table below record Judy's vital signs and then suggest some internal causes to these affects. 

Activity
Body Temperature 
(oC)
Heart Rate 
(bpm)
Respiration Rate 
(bpm)
What's causing this?

 

 

2. Describe two long-term changes that Judy's body went through when she arrived at Kananaskis Country.
3. Make a story of your own 'day in a life' and describe some ways your body's vital signs change as you go through the day.
4. What is metabolism?
5. What causes an increase in metabolism?
6. Describe two effects of increased metabolism?

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