External respiration Process of obtaining OXYGEN from the environment and eliminating CARBON DIOXIDE Internal respiration Exchange of OXYGEN CARBON DIOXIDE and between capillary blood and tissue fluids
CARBON DIOXIDE inhibits cellular activity, so it must be ELIMINATED. External respiration is carried on through respiratory membranes <ul><li>highly vascular </li></ul><ul><li>thin epithelium </li></ul><ul><li>moist surface to facilitate diffusion of gases </li></ul><ul><li>must be in contact with environment (external gills) </li></ul><ul><li>or environment brought into contact with respiratory surface (lungs) </li></ul>…
CHIEF ORGANS (adult craniates) <ul><li>external and internal gills </li></ul><ul><li>oropharyngeal mucosa </li></ul><ul><li>air sacs or lungs </li></ul><ul><li>skin </li></ul>(up to 90% of carbon dioxide is excreted through the skin in amphibians) Because the thick stratum corneum insulates the capillaries from the atmosphere, cutaneous respiration is not significant in amniotes. !
Diffusion The respiratory and circulatory systems are an integrated system. is influenced by a number of properties of the gas exchange surface. surface area x diffusion gradient thickness x material properties surface area – enhanced through gill lamellae, alveoli, sacculations diffusion gradient – increased by external (ventilation) and internal (heart) pumps thickness – reduced with membranes with a simple epithelium adjacent to endothelial lining of a capillary materials – must be easily diffusible
AGNATHANS Hagfishes in the genus Myxine have 5 or 6 pairs of gill pouches associated with the pharynx, while some species of Eptatretus have 5 to 15 pairs . afferent branchial ducts conduct respiratory water from the pharynx to the pouches. efferent branchial ducts lead from the pouches to the exterior.
HAGFISHES respiratory water enters the median unpaired naris passes via a nasopharyngeal duct to a velar chamber the wall of the chamber ( velum ) pumps water from the velar chamber into the pharynx and gill pouches , thereby creating a vacuum . pharyngocutaneous duct - <ul><li>found on the left side only </li></ul><ul><li>greater diameter than the afferent branchial ducts </li></ul><ul><li>modified last gill pouch </li></ul>connects the pharynx with the last efferent branchial duct ( Myxine ) or the exterior . When debris or particles are too large to enter the afferent branchial ducts, they are forcefully ejected through the pharyngocutaneous duct in a manner analogous to coughing . *
LAMPREYS The buccal cavity of lampreys is pressed tightly into the flesh of a host and the nasohypophyseal duct from the unpaired naris ends in a nasohypophyseal sac (not into the pharynx). = The nasal and buccal route are NOT AVAILABLE for the passage of respiratory water.
Respiratory water enters and exits the pharyngeal pouches via external gill slits . PHARYNX LAMPREYS subdivided longitudinally into an esophagus that continues to the stomach and a ventral respiratory tube that ends blindly 7 pairs of gill pouches > lined with gill lamellae > communicate directly with respiratory tube and exterior > with no intervening afferent or efferent branchial ducts