The idea of homeostasis is to correct any deviations in our body conditions. This may seem dull or boring, but it is a lot of hard work. Our body has to monitor many things and adjust accordingly. Is our temperature off? How about our blood glucose or our blood calcium levels? Even really sudden things can be corrected– like if you do a head stand and all the blood comes rushing back to your heart from your legs through gravity. Your body has to be able to control your body’s blood pressure even under those conditions.
Let’s start thinking about how this works. Just use either increase or decrease in your answers here. If your blood calcium levels begin to rise, maintenance of homeostasis will lead to a/an decrease in blood calcium levels. If, however, your blood calcium levels are dropping, maintenance of homeostasis will lead to a/an increase in blood calcium levels. If your blood pressure rises because you did a head stand, then maintenance of homeostasis will lead to a/an  in your blood pressure. Homeostasis is maintained through a feedback loop. This loop depends on a sensor to pick up the change that occurred (for example, increasing blood calcium levels) which then inputs into what your book calls a control center and then leads to the appropriate response through the effector.
For calcium levels, we have to either get more calcium into our blood from bone where it is stored, or we have to deposit calcium from the blood into the bone to put it into storage and out of the blood. When we take calcium out of bone, then, we are causing a/an  in blood calcium levels.
Now consider the type of feedback that carries out homeostasis (so answer either positive or negative here). When our blood calcium levels rise and we correct for it to maintain homeostasis, that is  feedback. When our blood calcium levels drop and we correct for it to maintain homeostasis, that is  feedback.
Note that positive and negative do not refer to the direction of the feedback, but to whether the feedback increases (positive) or decreases (negative) the deviation from our normal state. Here’s a final example. Your body temperature begins to drop. In response, the tiny muscles in your skin (arrector pili muscles) that pull on your body hairs are activated and your hairs stand on end (goose bumps). The goose bumps lead to a/an  in your body temperature. This is an example of  feedback.
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When we eat, we eat macroscopic things. But the only way we can absorb the nutrients from our food is by transporting small molecules across our digestive cell membranes. Therefore, digestion must occur through  reactions. The small molecule absorbed by our digestive system then enter our blood to supply all the cells of the body. Each cell type has to use different molecules within it in order to carry out different functions. So when the nutrients arrive at our bone cells, those cells will make some different large molecules out of the nutrients than would occur in, say, fat cells or muscle cells. Taking the nutrients and making useful, large molecules out of them within a cell would be considered  reactions.
If we haven’t eaten in a while, our liver will take stored, large molecules and break them down to send nutrients through the blood to supply our body until we can eat again. If the liver runs out of stored molecules, we then break down the stored fats inside our fat cells to supply our body with nutrients until we can eat again. Such actions by the liver and fat cells are considered  reactions. Note that while our liver is breaking down molecules to supply the body cells, the body cells receiving the nutrients would be simultaneously making new, large molecules out of these nutrients. At any given time in our body we are both making and breaking down molecules. This is our body metabolism.
Usually, these chemical reactions occur between the levels of organization of small molecules and large molecules. So if we take a bunch of small molecules and make a large molecule, that is a  reaction. Alternatively, if we take a large molecule and break it down into small molecules, that is a  reaction. These molecules are all organic– we only eat organic molecules and our nutrients (except for minerals) are organic.
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This type of scan enables visualization of both soft and hard tissues. It is quite precise, but expensive, loud, and uncomfortable to have done. The same bladder cancer that was viewed in the prior question is viewed here with this technique.
There are many types of ways to visualize things in the body. Cameras can be brought in to see what is going on, like when an endoscopy or a colonoscopy is performed. To see the bladder cancer this way requires the procedure called a cystoscopy, which is not listed in your textbook
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