Cutaneous Respiration in Amphibians (Keratinization):
- Low keratinized of the skin is required for efficient gas exchange
- Low keratinization = water loss in air
Cutaneous Respiration in Amphibians:
- requires keritinization
- Water or moisture needed to maintain integument
- Requires blood capillaries close to surface of exchange and increased surface area
Tetrapods (Generally):
- Paired, high surface area-to-volume-ratio, joined to larynx and buccal cavity by trachea
- Leads to increased compartmentalization associated with increased body size and metabolic rate
Buccal Pump of Amphibians (Process):
Inspiration:
1. Nostrils open buccal cavity expands
2. Nostrils close, glottis open, buccal cavity contracts, lungs expand
Expiration:
1. Buccal cavity expands, lungs contracts
2. Nostrils open, glottis closes, buccal cavity contracts
Buccal Pump of Amphibians (Pressure):
Air is forced into the lungs with positive pressure
Aspiration Pump of Amniotes Properties and Process (3):
- Ribs and inercostal muscles power the pump in most reptiles
- Diaphram muscle and rib cage participate in lung ventilation in mammals
- Air is sucked into the lungs because of negative pressure (tidal air flow)
Bird Lungs Properties:
- Aspiration pump (like other amniotes) but lungs are coupled with air sacs –> unidirectional air flow
- Air flow in the lungs is dorsobronchus –> parabronchus –> ventobronchus, but complex network of air sacs involved
- Gas exchange occurs in small capillaries in the walls of the parabronchi
Bird Lung Ventilation - Properties of Two-cycle Breathing (2):
- Inhaled air is divided into lungs and posterior air sacs; the latter perfuses lungs during first exhalation.
- Second inhalation similar, but pushes air in the lungs into anterior air saca, which is vented out during second exhalation
Gas Transfer at Respiratory Surfaces (Mammals):
Blood encounters relatively constant gas concentration (uniform pool)
Gas Transfer at Respiratory Surfaces (Birds):
Blood encounters increasing gas concentrations allowing progressive loading of oxygen in a coss-current exchange system.
Gas Transfer at Respiratory Surfaces (Fish):
Blood first encounters lower gas concentrations and is fully equilibrated with oxygenated water in a counter-current system
Evolution of Lung Ventilation (2):
- Alveolar lung = many levels of branching
- Faveolar lung = 2-3 levels of branching
- Faveolare is not unidirectional
Tetrapod Circulation:
- Blood passes through the heart twice during each circuit (double-circuit system)
- To/from body = systemic circulation
- To/from lungs = pulmonary circulation
Variations on Double-Circuit Pump Pattern (Amphibian) (4):
- 3-chambered heart (two atria, one ventricle)
- De-oxygenated blood from the body (systemic) enter the heart at the right atrium
- Oxygenated blood from the lungs (pulmonary) enters the heart at the left strium
- Mixed-oxygenated blood in the ventricle is surprisingly low (but oxygenated blood coming from skin already mixed in)
Variations on Double-Circuit Pump Pattern (Reptiles) (5):
- 3-chambered heart (two atria, one partially divided ventricle)
- Ventricle partially divided into 3 cava (cavum pulmonale, cavum ateriosum, cavum venosum)
- De-oxygenated blood from the body (systemic) enters the heart at the right atrium
- Oxygenated blood from the lungs (pulmonary) enters the heart at the left atrium
- Ventricular cava allow transfer of deoxygenated blood to the lungs when breathing air and a lung bypass when diving, saving energy
Variations on Double-Circuit Pump Pattern (Birds/Mammals) (5):
- 4-chambered heart (two atria, two ventricles)
- Complete separation of pulmonary and systemic circulation (no mixing)
- De-oxygenated blood from the body (systemic) enters the heart at the left atrium
- Oxygenated blood from the lungs (pulmonary) enters the heart at the left atrium
- Absence of cardiac shunt probably an adaptation to allow different arterial pressure in lungs vs body in active animals
Fetal Circulation in Mammals:
- Uptake of oxygen and nutrients occurs at the placenta
- Need to shunt most of blood away from developing lungs and into systemic circulation
- Bypass 1: Blood enters right atrium and exits through foramen ovale to left atrium and left ventricle then to head and upper body
- Bypass 2: Remaining blood enters right ventricle and exits pulmonary artey, travels through ductus arteriosus to lower body and placenta to be oxygenated
