My hikes, especially the grueling ones, double as medical monitoring. I regularly tell my doctor that I've just completed my stress test....An endurance hike, if I can survive that, my heart must be in pretty good shape!
In my experience, if my general health is good, incidental and focal illnesses are not as intense and resolve quicker.
Living things maintain homeostasis We are assemblages of tiny bags of chemicals. Try throwing a bunch of chemicals in a bag and see how long the reactions last. Living thing evolved to maintain the chemical reactions we call life for a lifetime.
So, I put cold and warm tap water, and water from our tea kettle into plastic cups and dropped in Efferdent effervescent tablets. And I videoed the process. Guess the temperature sequence!
The cup on the left has the hot water and the one on the right has the cool water. The rate of the reaction is determined by the temperature. The last thing a living creature needs is to be dependent on temperature
I wanted to know how well my body maintained its internal temperature so I taped a temperature and humidity sensor (Cloudcom A1 by ACInfinity) to my chest (the upper right circle below). The transmitter is in the lower left circle just above the bottom circle around my smartphone.
The data logger communicates with my phone via Bluetooth. Then I put on a t-shirt and my floppy hat and went on a 2,8 mile hike in the 103° F Chihuahuan desert.
The ACInfinity app collected the data and I imported it to my spreadsheet and charted it
As shown in the legend, the blue dots trace my body temperature (a little affected by the air temperature since the side of the sensor not against me was against tape, a t-shirt, and the outside world) and the red dots trace the humidity inside my T-shirt (mostly determined by my sweat.)
Two things in particular affected my body temperature: the cooling evaporation of my sweat and the blood which was being shunted to my skin to get rid of its heat (Despite America's song about the "Horse With No Name", I didn't turn brown....I turned red). There's a little temperature fluctuation in the chart but it's on the order of four degrees around 95°. Looking at the histogram provided by the ACInfinity app, .....
my body temperature was between 93.9° and 97.2°. The mean was around 96° which is pretty close to my regular body temperature. (Yep. I'm cool.....at least my body temp. is. Average normal value for humans is 97.9° but that value varies considerably between 97 to 99° with older people being a little cooler and axial (armpit) temperatures being about a degree below oral temperatures.
Those low temperatures happened when I got back to my air conditioned house.
The humidity readings followed my sweating, which dropped pretty quickly when I started back and stepped into the shade of a pecan orchard Notice that, that jogged my temperature a bit but it stabilized quickly.
All in all, my body does pretty well maintaining an even body temperature.
Blood pressure is a different matter. My homeostasis in the area of blood pressure has been rather faulty most of my adult life. Both of my parents' families had a tendency towards hypertension. But there are drugs for that.
One way you can explore bioIogical processes is in your own body. Home diagnostic equipment like blood pressure cuffs, thermometers, and even stethoscopes are not expensive. I tracked my temperature, blood pressure and pulse through a day and came up with these results
Only that top blood pressure reading (systolic and diastolic) is in a clinically significant range and for my history it's still pretty good.
I take most of my antihypertensive drugs soon after awakening, which explains why my blood pressure quickly dropped after the first reading Otherwise, my pulse and temperature behave during the day. The mildly effortful task of cleaning out the refrigerator didn't even appreciably change the readings
If you're curious about the "systolic" and "diastolic", check your blood pressure sometime, at home or at one of those department store kiosks. The cuff will inflate around your arm (or some of the home units use a finger) and then start to deflate. At a point, you will feel your pulse..... that's your systolic pressure where your heart's strongest stroke is fighting the cuff. Then at another point the pulse will almost disappear because the cuff's pressure no longer blocks your circulation..... that's your diastolic. It's the pressure behind your heart's weaker stroke. If you have access to a stethoscope, you can hear this double stroke.
Medical diagnostics are a rich source of information for students of biology. They measure homeostasis. The "normal range" is the values your body tries to maintain. The temperature range of 97° to 99° F. Is the optimal range for the chemical reactions that keep you alive.
What I call "endurance hikes" are exercises I do to push myself a little outside those limits to see if my body can effectively bring me back to optimal conditions
Some of the processes of over-exertion simulate the more dangerous process of starvation. You have the resources to recover quickly but you don't access them quickly enough to maintain balance. I've made several endurance hikes while writing these blog. You can search for "endurance hike" using the blog's search box in the upper left
In starvation, you first draw on the glycogen stores in your muscles and liver. You can do that for about a day. Longer, and you start burning up protein stores in muscles Generally, you want to conserve your muscle tissues while delivering enough glucose past your blood-brain barrier to fuel your brain. That's when you start drawing on fat deposits which deliver ketones which can easily cross over into your brain.
On a long hard hike, it's not hard to catch the ammonia scent of proteins being burnt or the musty or fruity smell of ketones.
For extreme exertion, the primary factors you need to monitor are blood glucose (trail mixes that gives fast release sugars and slow release fats and proteins are actually good sources), hydration, and electrolytes (sodium, chloride, potassium, and calcium are the most important) Clarity of mind, muscle tone, and your own smell are good indicators but you should have planned stops to replenish and concentrate on how you feel
Unfortunately, there are two ways that homeostasis can go wrong. It's easy enough to overdrive it if you're not paying attention and push yourself outside your limits. Or your homeostatic machine can be defective.
An example....I know several people with diabetes
Glucose is the fuel that living things oxidize to get energy. They can't directly burn the sugar, of course, so there are involved chains if chemical reactions that gradually break the simple sugar down and store the energy produced in compounds like ATP that can release the stored energy as needed. But the toxic level of glucose in the blood is fairly low so glucose levels must be kept fairly tightly between toxic and starvation levels.
Human bodies maintain blood glucose levels using two negative feedback loops. Three systems sense glucose levels. The primary organ in the loop is the pancreas. It has alpha cells that sense when blood glucose is too low and release glucagon which signals the body to break down glycogen stored in muscle and liver tissue to release glucose. There are a couple other mechanisms to control glucose levels. The brain itself can detect glucose in the blood and modify the hunger response. Also the gut can produce a hormone, insulin that tells the pancreas to produce insulin.
The pancreas also has beta cells that sense high levels of glucose and cause other cells in the pancreas (called "the Isles of Langerhans") to secrete a polypeptide, insulin, which triggers the reactions that polymerizes glucose to form fats in adipose tissues and glycogen in liver and muscle cells.
There are two forms of diabetes (at least). In one, type 1 diabetes, the body's immune response attacks the pancreas and kills the cells that produce insulin. Without insulin, there is no quick response to too much glucose in the blood. In the other, the cells that store glucose develop a tolerance to Insulin and doesn't react to take glucose out of the blood. That's type 2 diabetes. (There's also a third form of diabetes associated with pregnancy, gestational diabetes. There may be other, rarer forms).
Homeostasis, control of blood glucose levels doesn't work in people with diabetes, so they have to use artificial means. One friend has a pump that responds to an attached glucose sensor to deliver synthetic insulin by injection. The older way to deal with type 1 diabetes was to frequently measure blood glucose from finger sticks to adjust dietary intake of carbohydrates.
.
Another example of homeostasis gone wrong is fever. It's part of the general inflammatory response. If you turn your ankle or have some other joint problem or if a wound gets infected, you might notice that the area becomes warner to the touch. Microscopic pathogens also have "normal" temperature range and your body will try to make them hotter than is good for them. Unfortunately, the response over does it and let's your internal temperature get too high. That's when the behavioral side of homeostasis comes into effect and you start taking medicine and wiping your forehead with cool cloths to get your temperature down.
Homeostasis has to work at all levels for life to happen.
For instance, for the chemical processes that make up life, the human body needs to maintain a pH range between 7.35 and 7.45. There are several buffer systems in the blood to achieve that but the primary one is the bicarbonate-carbonic acid system. The carbon dioxide formed as a waste product of metabolism in the body is carried to the lungs dissolved in blood to be removed into the air. Carbon dioxide dissolved in water is carbonic acid. Along with the sodium ions, sodium bicarbonate is also present. It just so happens that the carbonic acid (an acid that can neutralize bases) and sodium bicarbonate (a base that can neutralize acids) form a chemical system that maintains it's environment between a pH of 7.35 and 7.45.
You can actually throw this buffer system off by breathing fast and hard (hyperventilating) and loading the blood stream with too much carbon dioxide. That causes respiratory acidosis, a condition that can cause severe side effects
On the cellular level, there are proteins in cell walls that can move glucose into and out of cells but you need to have a certain amount in the cell to fuel the cell. Once the sugar is in, you don't want it to escape, so the first thing a cell does when processing sugar is to attach a phosphate group so that it can't leave
On the organism level, both hormones and autonomic nerves play a part in homeostasis and not just with negative feedback loops. Positive feedback is also used
One of the "feel good" hormones, oxytocin, plays a big part in childbirth. When the child's head presses up against the mother's cervix, it stimulates the production of oxytocin by the brain which, in turn, causes uterine contractions. That causes more pressure on the cervix until the baby is born and the process is shut down.
The process of blood clotting in a wound is also a positive feedback loop with the clotting factors increasing until bleeding stops.
Feedback loops operate to maintain balance on the ecosystem and even the global levels.
Predator-prey populations are classic. If there are too many predators, they eat too many prey. Then there's not enough food and some of the predators die until balance is restored. If there are too few predators, the prey overpopulate and reduce their food resources, which reduces the prey population and valance us restored.
Two major studies are the Isle Royale wolf-moose study
Wolves and Moose on Isle Royale
And the Yellowstone River wolf reintroduction study.
History of Wolves in Yellowstone
Do plants demonstrate homeostasis? Certainly.
An interesting demonstration tracks the state of stomata (leaf pores) in plant leaves.
Plants take in one of their primary nutrients, carbon dioxide, through these pores. They use carbon dioxide to build sugar via photosynthesis. Then they use the sugar the same way we do, as fuel. The process also needs water, which most plants take up through their roots. But evaporation of water through stomata produces a negative pressure that draws water up into the plant.
Stomata open and close to take up or conserve gases (carbon dioxide or waste oxygen) or water vapor (and keep in mind the cycle in which plants "breathe" in carbon dioxide and ",breathe" out oxygen while animals breathe in oxygen and breathe out carbon dioxide...... it's important).
You can observe stomata by taking a cast of a leaf using clear nail polish You need the nail polish, clear tape, and a microscope slide.
Lightly paint a strip of polish over the leaf. There is usually more stomata on the underside of leaves. Give if 15 minutes to dry. I used Sally Hansen's Diamond and waited 30 minutes once. The cast came out perfectly. Stick a piece of clear tape over the polish. When you peel the tape off, the polish will come with it. Stick the tape to the microscope slide.
Keep in mind that you aren't looking at the leaf. You're examining an impression of the leaf surface. The reason for looking at the cast is that you can't see through the leaf with a light microscope
Here are my subjects.
Right; pistachio (Pistacia vera, probably)
Left: ash (my guess velvet ash: Fraxinus velutina)
Pistachio leaf
Here's a cast I took during the hot part of the day
And one I took at 9:00 PM.
Notice that the pores seem to be more open at night. They are. The plant is trying to conserve water and carbon dioxide during the hot hours of the day, but it has to get rid of oxygen and extra water so it waits until night to do that.
Top level responses like behavior play a part in homeostasis. Abraham Maslow organized needs by order of urgency. We barely consider higher level needs if lower level needs aren't met. If you're hungry, you don't worry too much about social status Here's his pyramid.
Maslow's Hierarchy of Needs
From Wikipedia. Author: Factory Joe. (6/29/2009)
And not all of our behavior is choice. Part of our neuronal machine is the autonomic nervous system. It's "autonomic" because it's automatic. It takes care of things like breathing, sweating, digestion....things you don't want to tell your body to do everytime.
There are two parts to the autonomic system: the sympathetic nervous system and the parasympathetic system
If you're surprised by something, whether it's dangerous or not, your body goes on alert by triggering the sympathetic system It speeds up you're heart and lungs to get oxygen and fuel to your cells. It also slows down your digestion (this is no time for stomach issues!) and dilates your pupils to get more light to your eyes. It also stimulates your adrenal glands to release epinephrine which tells your metabolism to go into catabolic overdrive so that cells will break down stores of glucose for quick energy.
It's called "fight or flight response" because it's what it makes you want to do.
There's an opposite reaction governed by the parasympathetic system when things are nice and calm and you can conserve energy. Digestion ramps up to set up stores of fuel. Most other functions slow down and you get to "rest and digest" ( that's what the parasympathetic response is often called. Sometimes it's called "tend and befriend"). When things are going well, you might get a dose of oxytocin, the "feel good" hormone.
When the sympathetic system goes on the fritz, it might result in a reaction called Generalized Anxiety Reaction. If you see someone in the middle of one, don't tell them to calm down, they can't. And it is often described as the feeling that you're going to die. Usually they don't (I've been there, by the way. I can vouch for it ) Just stay with them. Make sure they're in a safe space. Offer them cool water. Be supportive and remind them to breathe deeply and slowly. Ask them what they need
An attack usually doesn't require hospitalization but if it lasts more than a few minutes, it might be something else so don't panic and call an emergency number.
There is another reaction called "homeostatic emotion". If you've ever been so hungry, thirsty, or oxygen deprived that urgently have to do something about it you've experienced it
Every morning, your body ramps up for business. You may have notice when you were sick or injured that inflammations get worse later in the day. That's because the body dumps cortisols into the bloodstream early to get inflammations out of the way at the start of the day. Also, the reason you don't soil your bed in your sleep is that, when the parasympathetic nervous system puts you in rest mode, it clamps off exits from the body. Those open up when the day starts.
The sympathetic reaction perhaps should be called "fight, flight, or get busy". Exercise routines tell the body when to fire up the sympathetic system. When I was in college, I exercised religiously but I soon learned that if I exerted myself during an epidemic, I would catch whatever was going around.
I have an overactive immune system. As a consequence, I rarely ever have an infection and when I do, it lasts a few hours or maybe a day, but if it triggers an inflammation, I was in for it. Bronchitis, gastroenteritis, and iritis have been the babes of my existence all my life. As I've aged, joint problems have joined the trio
But as I've aged, I've also learned ways to navigate my inflammatory problems. For instance, knowing that exertion reduces my body defenses, I use that to modulate them.
Homeostasis is a constant thread in biology from biochemistry to planetary ecology. It will appear over and over
But if you don't become interested in biology as a long time study, you should learn how to balance your internal environment.
I haven't come close to completely covering the topic. I've just recounted my adventures. If you really want to learn about homeostasis, here are my sources:
Kahn Academy. They have whole sections on biology and if you just want to study homeostasis, they have a search bar that you can type "homeostasis" into. Lectures, articles, hands-on experiments, tests, they're all there
CK12 Biology for High School. Multiple contributors
Many healthcare providers have patient portals that allow patients to look at their own records. I use those a lot.
And I look up normal ranges of medical tests in my copy of the Merck Manual. They're also on various websites.
