Circulation and gas exchange II (Chapter 42)
Keywords
Fish gill
Filaments
Lamellae
Tracheal system
Tracheoles
Gastrovascular cavity
Lung
Tidal ventilation
Ventilation in birds
Fish Gill
Rather than being a solid structure, the fish gill is finely subdivided to enhance gas exchange area
filaments
Lamellae
Countercurrent flow
NOT countercurrent
Countercurrent
Are gills effective in increasing surface area?
20 fold increase due to gills
How do gill surface areas compare among different fishes?
Numbers correspond to arbitrary units per gram body weight
Tracheal systems in insects
Tracheoles supply tissues
Diffusion distance from tracheole to mitochondria is short
Lungs
Internal sacs
Unlike insect tracheal system lungs do not contact entire body
Circulatory system draws oxygen from lungs to tissues
Found in snails, a few fishes, spiders, vertebrates
Structure of the mammalian lung
Tidal ventilation of mammalian lung
Negative pressure breathing
Tidal ventilation
Tidal volume - volume inhaled and exhaled (around 500 ml in humans)
Tidal volume is much less than total volume of lungs (several liters in humans)
Thus residual volume remains after exhaling
This is inefficient
Birds have a more "sophisticated" type of lung ventilation
Birds have high metabolic rates
Can be exposed to lower oxygen concentrations in high altitude flight
Ventilation is not tidal
Air flows through the lungs
The avian respiratory system
The control of breathing
Human brain monitors carbon dioxide level (detected as a drop in blood pH)
Hyperventilation in divers
Diving mammals can tolerate high blood carbon dioxide
Organismal respiration -- a simple view
Why does the body sense carbon dioxide rather than oxygen?
Decreased oxygen corresponds to increased carbon dioxide
Increased carbon dioxide results in acidification which can readily be detected