As we breathe in air the first contact Oxygen makes with our system is the Nose or nostrils. It is within the internal membrane of the nose that the most significant changes to oxygen occur. Moving inside, the oxygen reaches the Nasal cavity which is a section separated by what is called the Nasal septum, it is here that the air (if cool) is warmed to a non-irritable temperature due to the presence of warming blood vessels that line the thin membrane walls of the Respiratory Mucosa.
As we pass the nasal cavity we come to the Pharynx, or more commonly know as the Throat. The larynx is short tube formed by cartilage and bound together via ligaments, an important role is directing food through the Oesophagus whilst preventing blockages in the Pharynx. The Trachea, also known as the windpipe, travels down the centre of the torso and branches out into the Lungs.
Its structure is relatively rigid in comparison to other parts of the respiratory system as it is reinforced with C-shape cartilage rings that form a rigid structure to allow air to flow unobstructed. The Bronchi is made up of two parts both connected to the trachea via two divisions.Air now passes into the Lungs, once reaching the Alveoli within it is passed quickly through the thin membranes of the pulmonary capillaries that provide a short diffusion pathway, from here the oxygen combines with Haemoglobin (red blood cells) to form Oxy-haemoglobin or oxygenated red blood. The constant diffusion of oxygen and carbon dioxide is maintained by the low concentration to high concentration gradient created by both pathways, which allows oxygenated blood to be carried continuously through the membranes.
Inspiration or inhalation is the movement of air into the lungs, whereas Expiration or Exhalation is the movement of air coming out of the lungs. This movement of air is due to pressure changes. Air can only move if the pressure inside of the lungs is lower than the atmospheric pressure. These pressure changes are controlled by the intercostal muscles of the thoracic cavity, as our rib cage is moved outwards the diameter of our Thorax increases, thus expelling air from within the lungs due to the difference in pressure concentrations.
Upon exhalation our diaphragm and external intercostal muscles relax, the rib cage moves downwards decreasing both the size and diameter of the thorax, this in turn lowers the volume of the thoracic cavity, resulting in the expiration of air due to the high pressure created in the lungs differing from the low pressure outside.The rhythm of ventilation is controlled within the cerebral cortex (brain stem) by the Pons which sends impulses to the other controlling mechanism called the Medulla oblongata, these are both Chemoreceptors. As part of this report, an experiment was conducted to observe the changes in heart rate and ventilation rate in response to exercise, the information gather from the experiment can be seen below.