1. Respiratory Systems Respiration is the process of gas exchange Cellular respiration is the process of energy production Respiratory membranes - highly vascular, moist surfaces in contact with environment Respiratory organs - integument, gills and lungs. May also include outgrowths of pectoral fins, trunk or thigh and mucosa of oropharynx, esophagus, stomach, intestine, rectum or anus

2. Gills (Walls of pharyngeal pouches) Agnathans - 5-7 pairs of vascularized, internal gill pouches supplied by afferent and efferent branchial ducts Cartilaginous fish - usually 5 pairs of gill pouches; functional gill surfaces are demibranchs -pretrematic and posttrematics; spiracle supplies water in most species

3. Bony fish - similar pattern to shark. Gill chamber protected by bony operculum Larval gills - external, internal or internal projecting through gill slits. Gills are usually reabsorbed during metamorphosis in amphibians - exception is neotany Gills may also serve an excretory function by eliminating nitrogenous wastes and CO 2 ; chloride cells regulate salt balance migrating species of fish.

4. Air breathing in bony fish Many fish gulp air from surface of water Oxygen by be absorbed through oropharyngeal mucosa of swim bladder Carbon dioxide eliminated through gills

5. Nares and nasal canals First seen in cartilaginous fish Direct water to gills; not used to breathe Nasal passeges arise from paired nasal pits and nasolabial (orolabial) grooves which close to form a tube. Blowholes in whales are really nostrils In humans, severe facial anomalies occur if fusion fails or is incomplete

6. Swimbladders Form from evagination of esophagus or pharynx Function as hydrostatic organs Gas comes from blood through rete mirable by active transport These structures also function in hearing

7. Lungs Arise from evagination of ventral pharynx (opening forms glottis) Larynx containg vocal folds lies between glottis and trachea Trachea bifurcates into primary bronchi serving each lung (at this bifurcation lies the syrinx in birds)

8. Lungs may occupy the abdominal cavity or only the thorax if a diaphragm is present. Diaphragm serves to inflate lungs Lungs may be simple sacs or more complicated structures containing septa or minute sacs known as alveoli. Reptiles have lung diverticula forming air sacs Birds have lung diverticula extending into bones (hollow)

9. Mammalian lungs are lobes and consist of functional units known as alveoli (alveolus) In all lungs, gas exchange occurs by simple diffusion