Comparative Studies of Vertebrates CAPS 422 Aaron Bai Ling Li Wynn Tran
Comparative Physiology - a sub-discipline of physiology that studies and exploits the diversity of functional characteristics of various kinds of organisms (Wikipedia) Mammalian Physiologists to find convenient species for study of a particular physiological mechanisms Zoologists to discover the evolution and adaptation of the structure by studying the functions
Comparative Physiology Functions of individual organ systems Integration of systems to reveal reasoning of similarities and differences, as well as to reveal evolution of structures Biological diversity
Comparative Physiology Applications: - model system for a particular physiological mechanism - animal model for human diseases (?) - general similarities? differences also important! - preservation of endangered species - revealing evolution and origin of the particular organ systems and the species - organ functions to environmental adaptations to genetics (?)
A Brief Evolutionary History of Vertebrates Land Mammals (lungs) Birds (lungs) Reptiles (lungs) Land Amphibians (lungs) Water Fish (gills) Aquatic Mammals (lungs, air-breathing!)
Sharks Are cartilaginous fish (Class: Chondrichthyes) and breathe using gills Are related to rays and skates (Subclass: Elasmobranchii) Some sharks will suffocate if they stop swimming why? Source: http://commons.wikimedia.org/wiki/ File:Evolution_of_cartilaginous_fishes.png
Respiratory Anatomy of a Fish Adapted from Wilson and Laurent (2002) The main organ of gas exchange is the gill Arranged in arches on either side of the orobranchial cavity (oral cavity + pharynx) Sharks also have a spiracle, a one-way valve behind the eye for intake of water useful adaptation for bottomfeeding sharks
Ventilation of the Gills Adapted from work by Wikimedia user Kurzon under Creative Commons 3.0 Unported License. http://commons.wikimedia.org/wiki/file:great_white_shark_size_comparison.svg
Anatomy of the Gill Consists of filaments with folded epithelia (lamellae) Lamella consists of a folded double layer of epithelia with a blood space in between, divided into channels by pillar cells Gas exchange occurs at the lamella: water and blood flow counter to each other increases efficiency of exchange Adapted from Grigg (1970)
Mechanisms of Ventilation Buccal pumping (cheek pumping) Occurs in most fish Water is pumped through the orobranchial cavity and out the gills by contraction of muscles Ram ventilation Occurs in sharks, rays, tuna, and others Water flows in through the mouth and out the gills as a result of swimming
Mechanisms of Ventilation Most sharks can use both mechanisms Some (like the hammerhead shark) are obligate ram ventilators they will die if they stop swimming So, how do they sleep? There doesn t seem to be a scientific consensus on this. =(
Lungs vs. Gills Similarities: Membrane separates blood from environment Large surface area Mechanisms to ventilate membrane Differences: Countercurrent flow of blood and water Locomotion can play a role in ventilation It does not appear that gills evolved into lungs e.g. air-breathing fish and have both The evolution of the lung is controversial Despite their different origins, however, lungs and gills operate on similar principles!
Lung Ventilation - Buccal pump breathing - Positive pressure breathing - 2-stroke vs. 4-stroke - Aspiration breathing - Negative pressure breathing - Costal aspiration vs. diaphragm
Bird Respiration - flow-through ventilation (unidirectional airflow) Retrieved Sep 29, 2013 from website: http://people.eku.edu/ritchisong/birdrespiration.html
Bird Respiration - Fly - flight has substantial mechanical effect on bird ventilation - in comparison with sit-up - High altitude - difficulties include low partial pressure of O2, hyperventilation due to hypoxia, increased HR, increased pulmonary artery pressure - birds have greater perfusion and diffusion of O2 to compensate
Two major challenges during diving: 1) Elevation of pressure: For every 10 meters increase of depth, there will be 1 atm pressure increase. Sperm Whale goes as deep as 10,500 feet (3,200m) to hunt for giant squid.. 2) Build up large oxygen storage Sperm whales can hold their breath under water for up to 90 minutes
How does elevated pressure impact gas absorption Henry s law: The solubility of a gas in the liquid is proportional to the partial pressure of that gas in contact with water. More of each gas will dissolve into the blood and body tissues
Challenge of increasing gas pressure at depth: Decompression sickness(dsc): Caused by dissolved gasses coming out of blood and tissue in the form of bubbles as pressure drops during ascent Unlike oxygen and carbon dioxide, nitrogen (N 2 ) is inert; it is not metabolized by the body Nitrogen bubbles can migrate and form in the joints and the brain Leads to joint pain and neurological damage such as paralysis, visual disturbances, and death
How do deep diving mammals overcome elevated pressure? Extremely flexible ribcage that can collapse with pressure and prevent lungs being crushed Collapsing the lungs force the air out of alveoli and thus prevent gas exchange Preventing absorption of nitrogen into blood and subsequent high blood nitrogen levels Solve the issues of DSC
How do aquatic mammals build enough oxygen supply? Lungs can not serve as a source of oxygen during deep diving. Rely on large oxygen storage in the blood and tissue. Adaptations: Three times more blood per body mass than human Concentration of hemoglobin is two times more than human Substantial amount of myoglobin which store oxygen in muscle, ten times more myoglobin than human
More on adaptations: Diving reflex: Diving reflex is most pronounced in aquatic mammals Crucial for oxygen conservation Bradycardia- slowing down the heart rate Vasoconstriction in skeletal muscle, kidney, and skin. Maintain blood flow to brain and heart. Because of their prodigious myoglobin supply, whales muscles continue working unimpeded. High tolerance of lactic acid which is produced in the muscle from anaerobic respiration
References Brainerd E.L. (1999). New perspectives on the evolution of lung ventilation mechanisms in vertebrates. Experimental Biology Online, 4(2): 11-28. Bukhovko P. Bird respiratory system. Retrieved Oct 1, 2013 from http://people.eku.edu/ritchisong/birdrespiration.html Butler P.J. (1999). Respiratory system. pp. 174 195 in Sharks, Skates and Rays: The Biology of Elasmobranch Fishes, ed. Hamlett, W.C. Grigg G.C. (1970). Water flow through the gills of Port Jackson sharks. J Exp Biol 52, 565 568. How come whales can hold their breath longer than most mammals? UCSB Science Line. Retrieved October 3, 2013, from http://scienceline.ucsb.edu/getkey.php?key=1009 Hughes G.M (1963). Comparative Physiology of Vertebrate Respiration. Harvard University Press. (Preface) Kavanu J.L. (1998). Vertebrates that never sleep: implications for sleep s basic function. Brain Research Bulletin. Killer whales, adaptations for an aquatic environment. SeaWorld. Retrieved October 3, 2013 from http://www.seaworld.org/animal-info/infobooks/killer-whale/adaptations.htm Liem K.F. (1988). Form and function of lungs: the evolution of air-breathing mechanisms. Amer Zool 28, 739 759. Martin, L. (1997). Scuba diving explained: questions and answers on physiology and medical aspects of scuba diving. Flagstaff, Ariz.: Best Pub. Co.. Ponganis P.J and Kooyman G.L. (2002) How do deep-diving sea creatures withstand huge pressure changes? Scientific American. Retrieved October 3, 2013, from http://www.scientificamerican.com/article.cfm?id=how-do-deep-diving-sea-cr Scott G.R (2011) Elevated performance: the unique physiology of birds that fly at high altitudes. The Journal of Experimental Biology, 214: 2455-2462. Switek, B. (2012). Sea lions' deep dives: marine mammals collapse lungs to descend, study shows. Huffington Post. Retrieved October 3, 2013 from http://www.huffingtonpost.com/2012/09/19/sea-lions-deep-dives-lungs_n_1897411.html Torday J.S. Rehan, Hicks J.W., Wang T., Maina J., Weibel E.R., Hsia C.C.W., Sommer R.J., Perry S.F. (2007). Deconvoluting lung evolution: from phenotypes to gene regulatory networks. Integr Comp Biol 47, 601 609. Wilson, J.M., Laurent, P. (2002). Fish gill morphology: inside out. J Exp Zool 293, 192 213. Wikipedia. Effects of high altitude on humans. Retrieved Oct 1,2013 from http://en.wikipedia.org/wiki/effects_of_high_altitude_on_humans