Respiration Oxygen enters cells by diffusion. In some organisms, the membranes of every body cell is close enough to the surface to allow diffusion. The function of the respiratory system in humans is to deliver oxygen to the blood stream so it can be carried to every cell of the body.

Breathing Movements Pressure differences between the atmosphere and the chest cavity determine the movement of air in and out of the lungs. Gases move from an area of high pressure to an area of low pressure. The diaphragm regulates the pressure in the chest cavity.

Inspiration diaphragm contracts and moves downward intercostal muscles contract, rib cage moves upward chest volume increases pleural pressure is less than atmospheric pressure, so air moves into body.

Expiration diaphragm relaxes and moves upward intercostal muscles relax, rib cage moves downward chest volume decreases pleural pressure is greater than atmospheric pressure, so air moves out of the body.

Regulation of Breathing Movements breathing is an involuntary act, controlled by the medulla oblongata region of the brain. Nerve impulses from this region trigger the contraction of the diaphragm and intercostal muscles. Blood is monitored by chemoreceptors which are sensitive to certain chemicals.

Questions? What happens when we get our “wind knocked out?” When hit in the solar plexus, it causes the diaphragm to spasm so we are unable to get a breath until it returns to normal Why does helium change your voice? Changes the timbre of your voice. Timbre is what allows you to distinguish between the same note played at the same volume on two different instruments. Helium is lighter than air - speed of sound is much higher in helium http://www. phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.ht ml

There are two types of chemoreceptors: Oxygen chemoreceptors - located in aorta and carotid arteries - detect low levels of oxygen - not very sensitive -secondary regulators Carbon Dioxide chemoreceptors - located in the medulla oblongata - sensitive to high levels of carbonic acid (carbon dioxide dissolved in the blood) - very sensitive, main regulators.

How the two systems work… holding your breath stops the intake of oxygen, but your body still creates CO2. carbonic acid levels will build up and you will be triggered to breath. this is the primary means of controlling breathing.

when you are at a high altitude, fewer oxygen molecules are found when you are at a high altitude, fewer oxygen molecules are found. (The percentage of oxygen in the air at two miles (3.2 km.) is the same as at sea level (21%).  However, the air pressure is 30% lower at the higher altitude due to the fact that the atmosphere is less dense--that is, the air molecules are farther apart.)

your body may still create CO2 at normal levels, but the amount of O2 in the blood would be too low. the secondary, oxygen chemoreceptors would kick in.