Lesson 27 Lesson Outline: Phylogenetic Trends in Respiratory System Form and Function Objectives: Throughout the course what you need to master is an understanding of: 1) the form and function of structures, 2) the phylogenetic and ontogenetic origins of structures, and 3) the extend to which various structures are homologous, analogous and/or homoplastic. References: Chapter 13: 292-313 Reading for Next Lesson: Chapter 14: 314-350
Exercise #1 List the basic functions of the respiratory system: The primary functions of the respiratory system are: the uptake of oxygen and the excretion of carbon dioxide at rates sufficient to meet metabolic demands Secondary functions of the respiratory systems are: ion/water balance, especially in gill breathing, aquatic organisms ph regulation temperature regulation in endotherms
Exercise #2 Describe the evolutionary trends that we see in the repiratory systems of the different vertebrate groups: Gas exchange across the skin takes place in many vertebrates in both air and water. Cutaneous respiration is utilized most extensively in amphibians but is not uncommon in fish and reptiles. It is not used extensively in birds or mammals Among protochordates, we then see the development of pharyngeal slits and cilliary pumps for feeding. This provides a large surface area with a good blood supply that begins to assume an increasing role in respiration as well. The next step was probably the evolution of muscular pumps for feeding - a muscular pump to produce a food-bearing water current. This would also lead to the branchial slits taking on even more of a role in ventilation. (branchial/pharyngeal slits with a muscular pump for feeding and gas exchange). With the evolution of jaws, fish were released from filter feeding and there was a transition from animals with gills for feeding and skin for respiration to animals with jaws for feeding and gills for respiration. This would allow the evolution of larger more active animals. It would also reduce the need for cutaneous exchange and allow the evolution of dermal armour. (muscular pump and gills for gas exchange, jaws for feeding and dermal armour). In the teleost fishes, the gills have evolved further - all gills are protected by a common operculum whereas in elasmobranchs, each gill slit was protected by an interbranchial septum. In the teleost fishes, the gills have evolved further - all gills are protected by a common operculum whereas in elasmobranchs, each gill slit was protected by an interbranchial septum. Now that the interbranchial septum is no longer needed to fulfill this role, the two hemibranchs on each arch become separated and now the primary lamellae project directly from the branchial arch and the secondary lamellae still project at right angles from these. This arrangement enhances the water flow over the secondary lamellae and improves gas exchange. In all fish, the gills are ventilated by a dual pump. The dual refers to the fact that there are really two pumps, a buccal and a parabranchial or opercular pump. This pump works in a fashion that produces an almost continuous, unidirectional flow of water.
Air breathing organs arose before the transition from life in water to life on land. Air breathing organs have evolved multiple times within the bony fish. In many air-breathing fishes, air breathing is facultative, that is it is a supplement to gill ventilation in times when there is insufficient oxygen uptake from water. In many species, however, things progress to the point that air breathing becomes obligatory. In most of these instances, the gills become reduced to the point that even in well-oxygenated water, there is insufficient surface area to provide enough oxygen to take care of the metabolic requirements of the animal. Lungs arise as endodermal outpocketings of the gut. They are usually paired and lie within the body cavity. They are designed for breathing air and have various degrees of enlarged surface area that must be kept moist to function. The first air breathing mechanisms are natural extensions of the dual pump of the fish. The dual pump is modified into the buccal pump and as the gills are lost, so too is the opercular pump. Amphibian larvae also use both the dual pump to move water over the gills and the buccal pump alone to ventilate their developing lungs. As adults they loose the gills and retain the buccal pump for lung ventilation. It is now proposed that the first step in the evolution of the aspiration pump was the use of active expiration to assist emptying the lungs when the glottis opened to let air out. Along with lungs we see the evolution of a - Secondary palate - Glottis - Pleural cavity - Diaphragm (mammals only). All forms of air ventilation involve the tidal movement of air in and out of the gas exchange organs. With the development of this new pumping mechanism, the buccal cavity is no longer used as a pump and feeding and breathing can be uncoupled increasing the opportunities for diversification of the breathing and feeding mechanisms.
Exercise #3 Comparisons Case 1 The lungs of turtles are encased inside a bony shell. How do they breathe?
Case 2 1) state whether these structures are homologous, analogous and/or homoplastic. 2) what their function is. 3) what they develop from and what they have evolved from. climbing perch Indian catfish minnow electric eel
Case 3 1) state whether these structures are homologous, analogous and/or homoplastic. 2) what their function is. 3) what they develop from and what they have evolved from.