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Circulatory system consist of 2 main areas: 1.)Transportation system: these are the arteries and veins designed to get the blood to the tissues. Most of the work of the circulatory system is done at the capillary level: (part that branches out from the heart to the very small vessels) - 1.) increases the surface area for maximum diffusion of nutrient molecules from gas AND 2.) reduces the velocity of the blood - Whole point of the circulatory system: deliver material to EACH individual cell; main problem is: need pressure to do this. The heart (pumping organ) has the highest pressure: it produces a great deal of pressure at the exit point of the heart ( the arteries). Arteries maintain this blood pressure from the heart through its strong maculated walls. Once the blood get to the capillaries, can`t have thick capillary walls because the whole point of the capillaries is to allow molecules to diffuse Conflict of interest because the capillaries would like the blood to move slowly in order to extract nutrient molecules from gas: key point is capillaries allow molecules to DIFFUSE to the cell but once these molecules get to the surface of the cell, there are transport proteins that move them into the cell Movement of molecules depend on the difference of the internal environment of the capillary and the cells themselves : based primarily on concentration differences AND the ability of those molecules to diffuse. IMPORTANT: Diffusion is the only way that molecules and gases can move back and forth- there is no active transport system. Has to rely on diffusion and the restrictions that come with it Capillaries have walls that are one cell thick ( not much difference in diameter to the r.b.c that carry oxygen) Heart has small surface area (large organ) but in comparison to the capillaries, don`t make up much. As surface area of capillaries increase, the velocity of blood decreases because we have the same pressure distributed over a larger area. Velocity of blood is at its minimum at the capillaries and picks up again at the veins (collecting system) Tradeoff because it would be nice to have high pressure at the capillaries to get more nutrient molecules but in order for molecules to be extracted, need slow movement of blood Respiratory Gas exchange : Partial pressure has to be higher than the partial pressure dissolved into the cell themselves Partial pressure will tell you what the availability of oxygen is to the organism; depends on where the partial pressure is developed- can have it at the surface of the lungs Animals at high altitudes (where there is low partial pressure of oxygen) have evolutionary adaptations (at physical and molecular level )for trapping oxygen for ex. Their hemoglobins are more efficient; bigger lungs Animals in water : don`t dry out but much less oxygen in water so have to work harder; fish near surface of water have greater partial pressure of oxygen but more prone to predation Deep sea fish have more efficient way to extract oxygen (similar to high altitude animals) than fish near the surface Fick`s Law of Diffusion: describes how we would like system to maximize the flow of oxygen to surface of cells If increase the surface area, you`re also increasing the volume (don`t want something the size of a car) so have to tradeoff maximizing the surface area for nutrient requirement but also tradeoff the counter effect of increasing volume. Have to come up with a system that matches the evolutionary requirement s of particular organisms Insects: (kind of a tradoff between a paramecium and a mammal) Tracheal system: have tubes (made of epithelial tissue) that connect the outside to every single cell on the inside (direct respiratory system, no middle man); remember that arthropods have an open circulatory system, dont have defined way of delivering individual molecules to the cells - cells in the interior are too far away from external env`t to perform gas exchange through simple diffusion so arthropods have come up with a passive transport system . Starts off at one end with spiracles which are open to the atmosphere tracheal system (cells get smaller and smaller as you move down) until you get to a single cell direct method of transporting oxygen from env`t to the cell themselves Fish: advantage is respiratory system constantly bathed in water Oxygenates water moves through richly vasculated tissue called the gills (external to the fish ) and the gills can extract oxygen from the water If water is moving too quickly, reduces the rate of diffusion and the amount of oxygen absorbed
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