Final Organismal Biology Exam (Part2)

Front 1

Fick's law of Diffusion

Back 1

The rate of diffusion of gas depends on five parameters: the solubility of the gas in the aqueous film lining the gas-exchange surface, the temperature, the surface area available for diffusion, the difference in partial pressures of the gas across the gas-exchange surface, and the thickness of the barrier to diffusion

Front 2

Gills

Back 2

Gills present a large surface area for oxygen to diffuse across a thin epithelium. Fast swimmers keep mouth open to force water through gills. The pumping action of the mouth and operculum creates a pressure gradient that moves water over gills (ram ventilation).
Gills also possess long thin structures called gill filaments that favorites diffusion
Counter-current exchange mechanism that generates large partial pressure.

Front 3

The fish gill is a counter-current system

Back 3

The flow of blood through the capillary bed in each lamella is in the opposite direction to the flow of water. Each lamella functions as a countercurrent exchanger.

-Water and blood flow in opposite direction:
A slight gradient in partial pressure of oxygen exist along the entire length of the lamella. A large difference in oxygen partial pressure exists between the start and end of the system. Most of the oxygen in the incoming water has diffused into the blood

-Water and blood flow in the same direction:
A large gradient in partial pressure of oxygen. The gradient in oxygen partial pressure declines rapidly and eventually disappears. A small difference in oxygen partial pressure exists between the start and end of the system.

Front 4

Lungs

Back 4

Each human lung contains approximately 150 million alveoli, which give mammalian lungs about 40 times more surface area for gas exchange than an equivalent volume of frog lung tissue. In addition to that an alveolus provides a interface between air and blood that consists of a tin aqueous film, a layer of epithelial cells, some ECM and the wall of a capillary. It facilitate diffusion (barrier is only 0.2 um thick)

Front 5

Lungs: positive pressure ventilation

Back 5

A frog lowers the floor of it's throat, increasing its volumes and drawing in air from the atmosphere, through the nasal passages, and into the oral cavity. The animal then closes the nasal passages and contracts it's throat muscles. These actions increase the pressure on air in the oral cavity and force it into the lungs

Front 6

Lungs: negative pressure ventilation

Back 6

Humans ventilate their lungs by changing the pressure within the chest cavity between about 8mm Hg relative to the atmosphere. Inhalation is based on increasing the volume of the chest cavity and the lowering the pressure. The change is caused by a downward motion of the thin muscular sheet called the diaphragm and an outward motion of the ribs.
Exhalation in contrast is a passive process when an individual is at rest. The lung is elastic, the volume of the chest cavity decreases as the diaphragm and rib muscles relax.