How does light accommodation work?
In dim light, the pupils dilate to allow for more light to enter the eye. The radial muscles of the iris contract to allow for the dilation of the pupils. This is a result of sympathetic (fight-or-flight) nervous system activity. In bright light, the parasympathetic (rest and digest) nervous system activity. During this process, the pupils contract and the circular muscles of the iris contract. This prevents too much light from coming in.
What is the importance of water in living organisms?
Water has many characteristics that makes it ideal for maintaining homeostasis in living organisms. Water has a high heat capacity, meaning it must take a significant amount of energy to change the temperature of water. This is beneficial due to the various climates and environments living creatures inhabit. Water also retains heat, making it exceptionally useful in thermoregulation. Water is a good solvent due to it's polarity, making it especially easy to dissolve vital gases such as oxygen (O2) and carbon dioxide (CO2), making it easier for the body to use and remove these products. Water is also the only continuous medium in the body. This allows for long distance communication and transport of molecules such as hormones within the body.
What is the anatomy of the respiratory tract?
The respiratory tract is split into two main parts: the conduction zone (conducts air to the respiratory zone and warms and humidifies the air), and the respiratory zone (site of gas exchange). The conduction zone begins with the nose and mouth, which are mainly responsible for the warming and humidifying the air. From the nose and mouth, the air goes to the pharynx, then to larynx, the trachea, the bronchi, the bronchioles, then the terminal bronchioles. This ends the conduction zone, but the terminal bronchioles split into the respiratory bronchioles, marking the beginning of the respiratory zone. From the respiratory bronchioles, the air goes to the alveolar ducts, to the alveolar sacs, and then the alveoli. The alveoli are made up of tiny capillaries, and the oxygen (O2) picked up from the nose and mouth is exchanged for the waste products (CO2) to be exhaled.