biology level 1

question one: For O2 in the atmosphere to be inhaled there must be a contraction of 2 sets of respiratory muscles. The diaphragm forms the bottom of the thoracic cavity and the external intercostals muscles which are located between the ribs. The contraction of the diaphragm causes an increase in the vertical dimension of the thorax. The contraction of the external intercostals muscles cause an increase in anterio-posterior and transverse diameter of the thorax. Together this causes a decrease in intra-thoracic pressure, which leads to the expansion of the lungs. This causes a decrease in lung pressure, (intrapulmonic pressure) which establishes the pressure gradient from the atmosphere (159 mmHG) to the alveoli (105 mmHG) which then results in INSPIRATION.

As oxygen is inhaled it enters the external nares (nostrils), from the external nares it moves into the nasal cavity which functions in moistening, filtering and warming of the air. After the nasal cavity the air moves into the internal nares which is located behind the soft pallet of the roof of the mouth. Once the air moves through the internal nares it moves down into the pharynx which is the passageway for food and air, it then moves down into the larynx which is the first part of the trachea. The larynx contains the epiglottis which is a cartilage flap that restricts food from going into the air pipe, and vice versa. As air moves down from the pharynx into the larynx the epiglottis closes the esophagus and opens the passageway for the air, to go through the glottis into the trachea. The trachea is lined with a mucous membrane which catches any debris that is left in the air. The trachea then forms 2 primary bronchi, one for the left lung and one for the right lung. The primary bronchi attach the trachea to the lung. The primary bronchi then branch out into secondary bronchi which form the lobes of the lung. The left lung contains 2 secondary bronchi resulting in 2 lobes and the right lung contains 3