I. Dehydration: Not ordinary dehydration in the article; she is feeling faint, tinkling, etc... We are concerned with homeostasis: we are composed of many cells (boring individuals), the idea is to maintain our environment at a boringly constant level. The problem with dehydration is that the amount of fluids in our body decreases along with decrease body weight. Major problem is the imbalance of ions.

-          Insufficient fluids

-          Loss of body weight

-          Imbalance of ions

1. The amount of fluid in our body is decreased. Major problem, imbalance of ions is the biggest problem.

II.  What do we mean by body fluids?:  Any organism made of cells; we live in fluid in our cells; we live in air, we live in fluid in our cells. Bucket with water and rocks. The bucket is surrounded by air, rocks are surrounded by water inside the bucket. Humans we live in air; we the animal live in the air. The skin is the outside of the bucket. The body is really cells that are the rocks that live in fluid or water. We actually live in our own fluid (water). The idea of homeostasis is to keep the fluid the same so the body does not have to change to ions, etc…. Body fluid provide the environment for our cells. What kind of changes can take place?

2. Seawater: Seawater outside of the cell. Pink inside of cell. Black is membrane. Blue writing (ions), the ion concentration inside and outside the cell is the same. Square brackets around ions means: concentration. As ions move in across the membrane and outside of the cell is about the same. Therefore the exchange does not produce any net flow in or out. B/C ion concentration is the same, the water concentration will be the same. If water concentration is the same, it will move in and out, but there will be no net flux of water in or out just like the ions. Nutrients and oxygen concentration higher outside the cell. Organism is using the oxygen and the nutrients which is why there is a higher concentration outside than inside the cell. Since they are using the oxygen and nutrients, there is a low concentration. It will simply move in and down concentration gradients and the Waste and carbon dioxide produced and exit the cell. Ion and water concentration same across the membrane and nutrients and oxygen simply diffuse in. So, Seawater is not such a bad thing.
3. Freshwater: Single cell organism, sitting in freshwater. Freshwater has very few ions, and the ion concentration is much smaller outside than the inside, there is a net movement of ions from the inside to the outside to try and balance everything out. Diffusion.  Water concentration is higher outside than the inside. This organism tends to have ions leave while more water enters. What happens is as water enters and enters and enlarges the cell and it POPS. Not a good think because it will kill the cell. Nutrients and oxygen diffuse in and waste and carbon dioxide diffuse out across the membrane. Freshwater is a more hostile environment than the seawater. If you have a low concentration of ions outside, then the ions will leave and the water will enter and the cell will pop.

In a human situation, if the outside of the cell changes from seawater to freshwater concentration, you can see the ions of water will move. If you have seawater concentration that is stable and is more concentrated outside, then the ions will move the opposite way seen in freshwater. Important keep ion and water concentration the same so the cells can live and not worry about swelling or shrinking and getting an imbalance of ions across their membranes.

III. Multicellular organism:  in us we have process of diffusion. Balls will diffuse. Diffusion is whereby molecules move down their concentration gradient. If there is more in one place than another, then they will go from the higher concentration the lower concentration. Middleschool dances, boys on oneside, girls on another, they then mingle. Things are moving around and a tendency for higher to lower concentrations down a concentration gradient.

One major problem is that diffusion is distance. The further the distance, the longer it is going to take to diffuse. Lets say we had a ball of cells. The problem is that the environment is outside the cells. While diffusion can take place, the cells in the middle will have a problem. Cells in the middle will have problems with diffusing Waste, O2, CO2. Those cells on the outside, will have no problem diffusing because they are of shorter distance. However, the ones in the middle will have problems. Let’s just say if our body had diffusion, it would take forever, especially the stomach cells!

We have a modification in our cells called the circulatory system (the human solution). We have two hearts, left and right side (two pumps). We have a fluid called blood which moves stuff from the outside to the cells. We have lungs and movement of oxygen and CO2. The little red balls (red blood cells), pick up the oxygen from the lungs and move (pump) the blood to the cells and at the capitularies there is exchange between the blood and the cell. Then the blood will take the carbon dioxide to the lungs. The blood is a way to connect and communicate stuff from lungs to cell. The blood is made up of plasma and the outside fluid in which we live (interstitial fluid), that fluid is the fluid that bathes the cell. Cells have its own fluid within the cell (interstitial). Plasma found in the blood or blood vessels; these two fluids are really pretty similar. In that way there is communication from the outside (lungs) and inside (cells) through the blood. The system Circulatory that allows us to link the outside to deep inside our bodies. No one cell is more than 3 cells than blood in most places in the body.

III. Circulatory System

1. Blood, environment, cells: we rely on diffusion between environment and blood; the blood and cells.
2. Intracellular fluid (fluid inside the cell)
3. Extracellular fluid

We have this way of connecting the lung to the body; gut to the body; to allow for diffusion to take place. Still the primary way stuff is exchange; blood is a condowet from the outside to the inside of our bodies. The whole point of homeostasis is to keep the interstitial fluid (fluid in which cells are bathed) is to keep the fluid as constant as possible.

Scenario:

1. If you used seawater, you would create an environment with lots of salt outside of it. It would draw water out of the plants and the ions would enter the cell and the cells would shrink and the plant would die. Few plants can survive with saltwater.

If you used dishwashing water, the plant can survive and can live in a fluxing environment as long as it is dilute; not a problem that it is dirty as long as it is not concentrated.

What we want to do during homeostasis is to maintain a constant environment for the cells is to maintain the interstitial fluid. How do we do this? Basically we use an anology of thermostat. We want to maintain the concentration the temperature at a level. You have to be able to detect the level and make a judgement if you want to change the input and do what you are going to do. You are going to have a disturbance (change in temperature), you are going to have an action (heat, cool), and bring the disturbance back into the range.

                  
Temperature going down…                  Temperature going up…

Thermostat: At different points the heater kicks on and kicks off at different points. Passive cooling happens. Rooms get cooler through windows and walls, at a certain temperature, the thermostat clicks on and the heating unit warms it and clicks off again. This then is negative feedback. Thermostat heats the room and gets rid of the disturbance. When we talk about homeostasis, it is relatively tolerable. We have a set point (72 degrees) range (72 to 76 degrees),