The Respiratory system is designed to perform a number of functions essential to life.  In addition, the sense of smell and the ability to speak also adds to the quality of life.  Basically the system consists of tubes and passages lined by specialized epithelia.  You will learn how each set of epithelia is specialized to perform its function. The first set of passageways are called the conducting portion because they conduct the air to the second set of passageways which are the respiratory portion. The respiratory portaion is responsible for the exchange of gases with the capillaries.  Cartilage, muscle and connective tissue may be present in the wall, depending on the passage.

Reading: Bloom and Fawcett, Chapter 29 and lectures by Dr. Singh will help you solve the problems below.

1) The receptors for smell are found in the olfactory epithelium which is in a specialized region of the nasal passageway.   The olfactory cells are actually bipolar neurons that are part of the epithelium. How might a bipolar neuron be structured to receive and transmit this sense? 

2) The olfactory cells are unique in that they are the only cells in the body that express a set of over 100 genes for specific receptors that have seven transmembrane domains.  What is also interesting is that the receptors are located on specialized, non-motile cilia (in the membrane surrounding the cilium).  Considering the many types of chemical odors that must be detected, can you think of ways to present the chemicals to the receptors?   How would you test your hypotheses?

3) When we are chronically exposed to irritants like toxic chemicals or tobacco smoke, the goblet cells increase in number and mucous glands in the connective tissue under the epithelia enlarge.  The composition of their secretory product also changes.  After the irritant is removed, the process is reversed.   What may be the significance of these responses?

4) Mucous producing cells end in the conducting passageways before the ciliated cells.   What function could this serve?

5) A rare inherited condition known as Karagener's syndrome exists in which individuals cannot produce dynein.  They suffer from chronic sinusitis and bronchitis.  What is happening at the cellular or subcellular level to cause this problem?

6) Smoking and air pollution can cause emphysema which involves loss of the elasticity of the respiratory portion of the airways.  This enlarges them greatly and makes gas exchange less efficient. Why would gas exchange be less efficient?

7) Lungs receive two sources of arterial blood...one is oxygenated and one is deoxygenated.  Furthermore, there are two types of veins in the lung.  One carries oxygenated blood.  From your studies of the cardiovascular system, discuss the significance of this dual supply.

8) The cough reflex works when an irritant stimulates afferent nerve impulses.   They transmit information to the CNS triggering an involuntary series of movements including deep inspiration, closure of the glottis, forceful contraction of the abdominal and intercostal muscles.  This raises the pressure on the air impounded in the lungs.   Then, the epiglottis and larynx are suddenly opened and the air bursts out under pressure, hopefully carrying with it the irritant matter, removing it from the trachea and bronchii.   Does anyone want to guess how fast air rushes out during the cough reflex?