Respiratory Systems: Ventilation & Gas Exchange
Ventilation of Respiratory Surfaces Non-directional ventilation: Medium flows past gas exchange surface in an unpredictable pattern. Tidal Ventilation External medium moves in and out of respiratory system in a back and forth movement. Unidirectional ventilation: Respiratory medium flows in at one point, and exits via another.
Perfusion of Respiratory Surfaces The circulatory system allows oxygen from the respiratory surface to be transported long distances by bulk flow. The movement of blood through the respiratory surface can effect the efficiency of gas exchange.
Ventilation & Perfusion of Respiratory Surfaces Non Directional Ventilation: (1) skin breathers (2) tidal ventilators Unidirectional Ventilators (1) Concurrent (2) Countercurrent (3) Crosscurrent
Non-Directional Ventilation Partial pressure of oxygen (P O2 ) in the blood leaving the gas exchanger can approach the P O2 in the medium. Anything that increases diffusion distance, will decrease oxygen exchange efficiency and reduce the P O2 in the blood leaving the gas exchanger.
Non-Directional Ventilation If ventilation is inefficient, an oxygen depleted boundary layer will form at the respiratory surface. In animals that tidally ventilate, PO 2 in the respiratory cavity is lower than the outside medium.
Tidal Ventilation Respiratory cavities do not fully empty. Fresh air mixes with oxygen-depleted residual air P O2 of blood equilibrates with the P O2 of the respiratory cavity.
Tidal Ventilation
Unidirectional Ventilation Blood can flow in one of 3 ways relative to the flow of the medium: (1) Same Direction = Concurrent (2) Opposite Direction = Countercurrent (3) At an angle = Crosscurrent
Concurrent Flow PO 2 of the blood to equilibrate with the PO 2 of the respiratory medium.
Countercurrent Flow PO 2 of blood leaving the gas exchange surface can approach that of the incoming medium.
Crosscurrent Flow PO 2 is usually higher than what would be seen for concurrent, but lower than countercurrent.
Concurrent Flow
Countercurrent Flow
Ventilation of Respiratory Surfaces Animals respond to changes in environmental O 2 or metabolic demands by altering the rate or pattern of ventilation rather than its direction.
Ventilation in Air & Water Water: Unidirectionally ventilated gills Air: Tidally ventillated lungs Unidirectionally ventillated lungs
Ventilation in Water Oxygen content of air nearly 30x water Water is more dense and viscous than air Unidirectional ventilation is less energetically costly than tidal ventilation Countercurrent arrangement of blood flow improves oxygen extraction efficiency.
Elasmobranchs Use buccal pump for ventilation: Expand buccal (mouth) cavity volume Water rushes into the buccal cavity via the mouth and spiracles. Muscular contraction forces water past the gills and out via external gill slits. Buccal cavity acts as both a suction pump and a force pump.
Buccal Pump http://www.youtube.com/watch?v=hei UySBQJUQ&feature=related
Teleost (Bony) Fish Gills are located in opercular cavities and protected by the operculum.
Buccal-Opercular Pump
Ram Ventilation Fish swims forward with mouth open: water flows across gills without active pumping.
Ram Ventilation Obligate ram ventilators = lost ability to actively pump ater over their gills and must rely soly on ram ventilation Must swim to maintain oxygen levels in blood
Fish Gills
Fish Gills 4 gill arches in each opercular cavity. Provided structural support 2 rows of gill filaments project from each gill arch. Each filament is covered with rows of secondary lamellae. Perpendicular to filament
Fish Gills Each gill arch contains an afferent & efferent blood vessel. Afferent blood vessels carry deoxygenated blood to the capillaries in the secondary lamellae. Efferent blood vessels carry oxygenated blood from the capillaries back to the gill arch. Secondary lamellae: Thin-walled & highly vascularized Primary respiratory surface
Fish Gills
Fish Gills Counter current exchange. Blood flow through capillaries in secondary lamellae is opposite the flow of water through the gills. Oxygen extraction from water can be as high as 70-80%.
Fish Gills
Ventilation in Air Oxygen availability high Density of medium is low Face evaporation across respiratory surface, therefore internally located.
Amphibians Use cutaneous respiration, external gills, lungs, or some combination of these 3. Depends if they are extracting oxygen from water or from air. Ventilate lungs using a buccal force pump.
Amphibians
Reptiles Most have two lungs tidal ventilation Air comes into the organism via the mouth and trachea, and each lung has a bronchus that allows airflow into the chambers of the lungs.
Reptiles Rely on suction pumps to ventilate lungs. Ventilatory cycle is triphasic divided into 3 phases: 1. Inspiration (suction pump) 2. Breath-hold 3. Expiration (passive)
Reptiles Changing volume of chest cavity: Snakes and Lizards: Intercostal muscles Turtle and tortises: Pair of sheet-like abdomen muscles & movement of forelimbs. Crocodilians: Hepatic septum, liver, & diaphragmaticus muscles.
Reptiles
Reptiles
Birds Unidirectionally ventilate their lungs. Lung is stiff and undergoes little change in volume during ventilatory cycle. Series of air sacs associated with lungs: Posterior airs sacs Anterior air sacs
Birds
Birds Bird ventilation requires two cycles of inhalation and exhalation. Airflow across the respiratory surfaces of the lungs is unidirectional and almost continuous.
Birds
Birds At syrinx the trachea divides into 2 primary bronchi. Primary bronchi split into secondary bronchi, termed dorsobronchi. Dorsobronchi further divide into parabronchi. Parabronchi lead into secondary bronchi, termed ventrobronchi, and back to primary bronchi.
Birds
Birds Parabronchi smallest airways of a bird lung. are folded, forming hundreds of blind-ended structures called air capillaries. Air capillaries Primary site of gas exchange Thin walls = minimal barrier for gas exchange
Birds Nares & Mouth Trachea Trachea Syrinx Primary Bronchi (2) Anterior Air Sacs Posterior Air Sacs Ventrobronchi Parabronchi air capillaries Dorsobronchi
Birds: Inspiration
Birds: Expiration
Birds: Parabronchi