Gas Exchange Flashcards
Inspiration.
External intercostal muscles contract, puling the ribcage up and out.
Internal intercostal muscles relax.
The diaphragm contracts, moves down a flattens.
The volume inside the thorax increases.
The pressure inside the thorax falls below atmospheric pressure.
Air moves into the lungs.
Expiration.
External intercostal muscles relax.
Internal intercostal muscles contract, pulling the ribcage down and in.
The diaphragm relaxes, returning to its dome shape.
Volume inside the thorax decreases.
Pressure inside the thorax increasea above atmospheric pressure.
Air is forced out of the lungs.
Pulmonary Ventilation.
Total volume of air that is moved into the lungs during one minute (dm3min-1)
Pulmonary ventilation = tidal volume x venilation rate.
Gas Exchange in Mammals.
Gas exchange occurs between the alveolar epithelium and the blood.
Numerous tiny air sacs, called alveoli, create a large surface area.
Diffusion pathway is only 2 cells thick; it’s made up of the flattened epithelial layer of the alveoli and the endothelium of the blood capillaries.
Each alveoli is surrounded by a capillary network, this further increases surface area and allows for the constand flow of oxygenated blood away from the lungs and deoxygenated blood towards the lungs, which maintaints a concentration gradient.
The ventilation mechanism also helps maintain an concentration gradient, air with a high concentration of oxygen is being provided to the lungs, while air which a high carbon dioxide concentration is being removed.
The alevli are surrounded by a fluid lining, which allows gasses to dissolve and diffuse across the epithelial layer.
Movement of Gases Across the Alveolar Epithelium.
Oxygen in the alveolar air space dissolves in the fluid that lines the epithelium of the alveolus.
Oxygen then diffuses across the flatened epithelial layer of the alveolus and the endothelial cell of the capillary wall.
2 single cell layers provide a short diffusion distance.
Oxygen then combines with haemoglobin to form oxyhaemoglobin and the oxygenated blood is carried away from the lungs.
Carbon dioxide diffuses from the blood, in the oposite direction into the alveolar air space.
Ventilation mechanism and circulatory system maintain diffusion gradient.
Gax Exchange in Insects.
Gas exchange in insects involves a tracheal system.
The openings of the trachea to the air are called spiracles. Spiracles are round valve-like openings along the length of the abdomen that can close to reduce water loss.
Oxygen enters and carbon dioxide leaves via the spiracles, and move into the trachea.
The trachea are a network of internal tubes that are held open by spiral bands of cuticle to prevent collapse.
Trachea branch into smaller tubes, deeper into the abdoment, called tracheoles. These extend throughout all tissues to devliver oxygen to respiring cells. Oxygen diffuses into cells through the cell membrane of the tracheoles.
The Three Methods that Gases Move Into the Tracheal System.
- Diffusion. As cells respire, they use up oxygen and release carbon dioxide, this creates a concentration gradient between the tracheoles and the atmosphere so that oxygen can diffuse in and carbon dioxide can diffuse out.
- Mass transport. The insect contracts and relaxes their abnominal muscles to move gases on mass. This is a similar process to ventilation in mammals.
- When insects are in flight, muscle cells start to respire anerobically, this produces lactate which builds up and lowers the water potential of cells. Water moves from the tracheoles into the cells by osmosis. This decreases the volume of water in the tracheoles, allowing more air from the atmosphere to be drawn in.
Adaptations of the Tracheal System.
Large surface area - Tracheal system is made up of a large number of fine, highly branches tracheoles.
Short diffusion pathway - Tracheole walls are thin, and each tracheole is in contact with individual cells.
Maintains concentration gradients - Respiration, constant use of oxygen and production of carbon dioxide, as well as the abdominal pumping mechanism whch increases air flow.
Limiting Water Loss.
- Small surface area to volume ratio for water to evaporate off.
- Waterproof exoskeleton.
- Spiracles can close.
Ficks’ Law.
Rate of diffusion is proportional to (surface area x difference in concentration) / length of diffusion pathway/
Gas Exchange in a Fish.
4 layers of gills on each side of the head, made up of stacks of gill filaments.
Each gill filament is covered in numerous gill lamellae, which are positioned at right angles to the filament.
When fish are swimming, they open their mouth so water rushes in and over the gills and then out through a hole in the side of their head called the opurculum.
Adaptations of the Gills.
Large surface area - Created by large number of gill filaments, and gill lamellae which further increase the surface area.
Short diffusion pathway - Very thin gill lamellae, 2 cell thick layer made up of the epithelial layer of the gill lamellae and the endothelium of the capillary.
Diffusion gradient - Counter-current flow mechanism; when water flows over the gills in the oposite direction of bloodflow in the capillaries, this ensures that equilibrium is never reached and that the diffusion gradient is maintain across the entire length of the lamellae. Water is constantly moving in through the mouth and out through the operculum, water is a high concentration of oxygen is moving in and water with a high concentration of carbon dioxide is removed. The circulatory system also maintains a diffusion gradient, constant flow of blood, oxygenated blood is removed from the gills and deoxygenated blood is moved towards the gills.
Gas Exchange in a Leaf.
The main structures involved with gas exchange are in leaves are stomata, mesophyll cells and the air spaces between them.
Stomata are pores in the epidermis that are surrounded by 2 guard cells.
Oxygen diffuses out of the stomata if not being used in respiration and carbon dioxide diffuses in.
To reduce water loss, the guard cells close the stomata at night while photosynthesis is not occuring.
Adaptations of a Leaf.
Large surface area - Large number of stomata, flat, thin leaves and air spaces between the spongey mesophyll.
Short diffusion pathway - Thin cell wall, thin cell membrane of mesophyll cells and the spongey mesophyll is in direct contact with the air.
Maintains diffusion gradient - Photosynthesis and respiration ensure that there is constant useage and production of oxygen and carbon dioxide.
