Organ system. The blood vessels, blood, and the heart are organs which work together to form the circulatory system.
There are many reasons why our pupils dilate:
When pupils dilate, it usually means that there is a lack of light. Your pupils dilate so that you can get more light into your eye-sight.
Your emotions can make your pupils dilate. They can dilate to show if we are excited, angry, happy, sad, scared, etc. They can also dilate to show how difficult the project you are working and/or thinking of.
Studies say that your pupils also dilate when you see an attractive person. Apparently, your pupils judge if you like somebody or not really. The name for this is Bedroom Eyes. I'd tell more about this, but considering the name, you can look it up to know more.
Another reason for your pupils to dilate is the cause of brain disease, drugs, certain medication (prescribed or not), injury to the brain, poison, such things like the listed.
It is no doubt that the options all come together. Sadness can make your pupils dilate. Horror can. Fear and lack of light can.
Answer:
I deepened on the girls body
Living things need water in their cells. Water is the universal solvent - most of the chemicals a cell needs is dissolved and transported in water. Water is an environment where chemical reactions can occur and water is needed in many of those reactions - like the hydrolysis reaction (needed in the break down of food molecules). If a cell becomes dehydrated chemical reactions slow down. Chemical balance of the cell is changed as waste materials are not removed fast enough, food is not broken down, etc. Water also helps regulate the heat that can build up in a cell during chemical reactions. A dehydrated cell = increase in cell temp. Water content of a cell also affects the pH of a cell environment. Certain reactions occur better at certain pH. Homeostasis is maintaining a balance with the the environment. Without water the balance is upset.