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Gas Exchange and Circulation Victoria Cambridge 12TAR Respiration in Humans In humans, and also in mammals, respiratory gas exchange is carried out by the heart and lungs. It is how we get oxygen, from the air, into our blood and the carbon dioxide out of our system. The Lungs are a pair of organs in the chest which perform respiration. Humans have two lungs and each lung is between 10 and 12 inches in length. The two lungs are separated by the Mediastinum which contains the heart, trachea, oesophagus and blood vessels. Within the lungs are the Alveoli which are small air sacs within the lungs. Respiration happens by the diffusion of gases across the thin walls of the Alveoli . The Alveoli are surrounded by numerous small capillaries which means there is lots of blood for the gases to pass into or out of. The Alveoli have a moist lining which helps to dissolve the gases. http://en.wikipedia.org /wiki/Gas_exchange In humans blood carries oxygen around the body using red blood cells. They have a double circuit which is where blood flows in two different circuits, one carrying blood to the lungs and the other carrying blood to the tissues. It is a closed system where the blood is contained within vessels. The human heart has four chambers which are seperated pumps, one for each circuit. The right atrium recieves deoxygenated blood from the body at a low pressure and then pumps it to the right ventricle which pumps the dioxygenated blood to the lungs at pressure. The blood passes through one way valves as it passes through each chamber to prevent black-flow. The left atrium recieves oxygenated blood from the lungs and pumps it to the left ventricle which pumps the oxygenated blood to the http://www.gonzaga.k12.nf.ca/academics/science/s body at a high pressure. ci_page/biology/heart.jpg Humans require more oxygen then fish and insects as they are larger and need more energy. As we have high energy needs and a larger area to get blood to our system is very efficient and generally suits our lifestyle. http://thetragictruth-of-me.deviantart.com/art/Don-t-Speak-83944782 Respiration in Fish The gills of a fish extract oxygen from the water and excrete carbon dioxide and other metabolic wastes (e.g. Ammonia or acid). The gills are positioned behind the head of the fish and are made up of numerous folds of arches and rows of filaments which gives them a large surface area. These folds are supported and kept moist by the water coming in from the mouth of the fish and flowing over the gills. They use a respiration system called the counter current flow. They extract oxygen from the water by moving in in the opposite direction to the blood. Oxygen is removed from the water and passes into the blood at the gills, this is also where carbon dioxide is removed as it diffuses out of the water. Using the counter current flow fish can extract oxygen at three times the rate that a human can. Oxygen is carried around the fish using red blood cells. A fish has an open circulatory system which is the arrangement of internal transport where there is no distinction between blood and interstitial fluid. The fluid “bathes” the organs of the fish directly with nutrients and oxygen. This fluid is called hemolymph and while muscular movements of the animal can help to move the fluid it is very limited as when the heart relaxes blood is drawn back towards the heart through a series of open ended pores. Fish also have a single circulatory system which means that blood goes once around the body before returning to its two-chambered heart. Its heart is the simplest vertebrate hearts and is made up of two main chambers. It has a thinly walled atrium and a muscular ventricle. The atrium pumps blood into the bentricle which then pumps blood into the conus which is an elastic compartment which doesn’t pump but instead stretches and squeezes. From the conus the blood travels to the gills of the fish where is becomes oxygen enriched. This oxygenated blood flows through the body and then returns to the heart. http://library.thinkquest.org/C003 Gas exchange for fish is more difficult than it is for mammals as the concentration of oxygen in the water is less then 1% and the amount in the air is 20%. This means that fish have had to develop specialized gills for gas exchange. Without water the gills collapse and the fish suffocates. Fish cannot have lungs because water is denser then air and cannot be contained in the delicate sac-like lungs of air breathing mammals. Fish have a large surface area availible on the folds of their gills which allows them to absorb lots of oxygen. As fish are generally quite small and do not need lots of energy for activities such as hunting or running they need less oxygen then humans and so this system although not very efficient is sufficient to the requirements of their lifestyle. http://goodbye-kitty975.deviantart.com/art/Happy-Fish-31143682 Respiration in Insects Insects are different then both humans and fish in the fact that they do not breathe through their mouths. This is because they have no lungs and their blood does not carry carbon dioxide or oxygen through their bodies. Instead of lungs insects have a system a tracheae, which are tubes that penetrate through the insects body. Air enters into the tracheae through pores called spiracles which are found on each side of the insects abdomen. The tube endings in are in contact with cells and contain a fluid for dissolving gas. This direct exchange provides lots of energy allowing the insect to patake in high level activities such as flying or jumping. http://houstonryan.deviantart.com/art/Praying-Mantis-Autumn-69503538 Insects have an open blood system which means that the hemolymph baths the organs and tissues directly. The insects heart is more commonly known as the Dorsal Vessel. It is closed at the posterior end and open at the anterior end. The dorsal vessel is a flexible tubes running longitudinally through the insects thoras, abdomen and the dorsal body wall. In the abdomen the dorsel vessel is divided into chambers seperated by valves called ostia which is where blood enters the heart. Each chamber has two alary muscles which help the flow to the heart by alternately contracting and expanding. After the heart is the aorta which is a simple tube used to transport the haemolymph to the head of the insect (the anterior end) where it empties into the body cavity. http://bugs.bio.usyd.edu.au/Ento mology/internalAnatomy/imageP ages/heart.htm An open system is suitable for insects because of their small size. It means shorter distances for the diffusion of nutrience and materials. Their systems are only suitable for small creatures and allows them to quick diffusion which provides the power for high energy activities like flying. http://triagon.deviantart.com/art/Bee-17686915