Diversity In Gas Exchange - Humans, Insects and Fish. By Saskia

Human Respiratory System. To respire, humans extract oxygen from the air around them using their lungs. The lungs in a human are part of the respiratory system, which also consists of airways and respiratory muscles that control the movement of air passing in and out of the body. When air is breathed in, it moves through the respiratory system in the following order : nasal cavity, pharynx, larynx, trachea, thoracic cavity (chest), bronchi and finally, alveoli, the site of the gas exchange, where it is diffused into the bloodstream.

Structure of the Human Lungs. Nasal Cavity – A large space filled with air above and behind the nose. Pharynx – A section of the throat that is before the oesophagus. Splits into the trachea (respiratory system) and the oesophagus (digestive system). Both food and air pass through it, so a flap of skin called the epiglottis closes the entrance to the trachea to prevent choking on food. Larynx – The voice box. Situated just below where the pharynx splits into the trachea and the oesophagus. Trachea (windpipe) – A long tube starting where the larynx ends, and ending at the bronchi. It allows air through to the lungs. Thoracic Cavity – A chamber in the chest that is protected by muscle, skin and soft tissue. Bronchi – An airway that conducts air into the lungs. No gas exchange occurs here. They split into smaller versions of themselves called bronchioles. Bronchioles – Braches of the bronchi that do not contain any catriladge. They split off to form the alveoli. Alveoli – Small spherical hollow outcroppings of the bronchioles. They are the primary sites of gas exchange. Alveoli have thin walls, which are moist and elastic. The diffusion of oxygen into the bloodstream occurs at the alveoli walls (called the respiratory membrane).

How it works. When a person breathes in, the oxygen travels down the pharynx, larynx, windpipe, into the bronchi and bronchioles and finally into the alveoli, where the large surface area (about square metres) and semi permeable membrane (called the respiratory membrane) allows for the oxygen to be diffused quickly and efficiently into the bloodstream. The oxygen diffuses through the respiratory membrane into capillaries that are around the alveoli. The capillaries house red blood cells, and the oxygen bonds to them and is then able to be transported to the rest of the body. Oxygen is then pumped to the heart using a process called pulmonary circulation. The oxygen is taken, and carbon dioxide is sent back to the lungs, where it is diffused back from the bloodstream into the alveoli. It is then sent back up through the lungs and expelled through the mouth.

Human Circulatory System. The circulatory system is a system made up of the heart, the blood and the blood vessels. It uses a process called pulmonary circulation to deliver oxygenated blood to the rest of the body, while pumping deoxygenated blood to the lungs. The human heart beats times a minute to deliver oxygen and nutrients to 300 trillion cells. In a day it pumps 2,000 gallons of blood. In an average lifetime it beats more than 2.5 billion times.

Structure Of the Human Heart. The heart is divided into four separate chambers by the “interventricular septum.” These chambers are the right atrium, the left atrium, the right ventricle and the left ventricle. Deoxygenated blood is pumped through the right atrium and the right ventricle to the lungs, while oxygenated blood is through the left atrium and the left ventricle to the body. Deoxygenated blood enters the right atrium from the superior vena cava and the inferior vena cava, while deoxygenated blood leaves the right ventricle by pulmonary artery. Oxygenated blood enters the left atrium from the pulmonary veins, while Oxygenated blood leaves the left ventricle by ascending aorta. The tricuspid valve in the heart separates the right ventricle and the right atrium, the pulmonary valve separates the right ventricle from the pulmonary artery, the bicuspid valve separates the left ventricle and the left atrium, and the ascending aorta is separated from the right ventricle by the aortic valve.

How it works. 1) Deoxygenated blood flows from the body into the right atrium. 2) Blood flows through the right atrium into the right ventricle. 3) The right ventricle pumps the blood to the lungs, where the blood releases waste gases and picks up oxygen. 4) The newly oxygenated blood returns to the heart and enters the left atrium. 5) Blood flows through the left atrium into the left ventricle. 6) The left ventricle pumps the oxygen-rich blood to all parts of the body.

Respiration In Fish. Fish do not have lungs. Instead they use structures called gills to respire. Gills are located either side of the fish’s pharynx, and are made up of structures called filaments. In each of these filaments there is a large network of capillaries that are the main sites of gas exchange. The opening to the gills is protected by a cover called the operculum.

How It Works. Fish respire by sucking water into their mouths and pushing it over their gills. The blood in the capillaries flows in the opposite direction and the oxygen is then able to be diffused across the capillary membrane using a process called countercurrent exchange. When the blood becomes deoxygenated, it is sent back to the gills, where it is expelled through the openings in the side of the pharynx.

Circulation In Fish. Fish’s hearts are relatively simple; they are only made up of two chambers (compared to the human, which has 4 chambers), an atrium and a ventricle. Blood is pumped into the atrium by the ventricle, and then into the conus, which is an elastic area whose purpose is to hold blood. It is able to expand by stretching when more blood needs to be held. After the conus, the blood is pumped to the gills, where it becomes oxygenated. After it is pumped to the rest of the body it becomes deoxygenated and is returned to the atrium where it starts the process again. The fish’s respiratory system is a single circuit circulation.

Respiration In Insects. An insect’s respiratory system is different to that of a human and a fish. It is a long and complex network of tubes called a tracheal system. The tracheal system is separate from the circulatory system, unlike the gills of a fish, or the lungs of a human. Air is breathed in through spiracles (which are controlled by valves), where it then enters a tracheal trunk. Tracheal trunks are longitudinal chambers going up and down the length of an insects body. After that, the air is diffused throughout a complex web of tracheal tubes (which are like smaller versions of the tracheal trunk). At the end of each tracheal branch, there is a tracheole. The gas is able to diffuse through the semi permeable membrane of the tracheole, which then carries the oxygen to individual cells. Blood is not oxygenated, because the oxygen is carried directly to the body cells.

Circulation In Insects. Insects have a simple heart compared to the hearts of a human or a fish; it is essentially a tube, open and one end and closed at the other. Insects do not have arteries or veins (open circulatory system) and their blood just floats around the body, delivering nutrients to specific cells. The blood is sent up through the tail end of the heart, to the front of the body and empties in the head. The blood then flows back to the end, and the process starts again.

The Circulatory System. Open/Closed Circulatory System. Insects have an open circulatory system, unlike a human and a fish, which have closed circulatory systems. An open circulatory system is a type of system that used freely flowing fluid to transport waste and nutrients to cells, rather than having them contained in veins. When an animal has an open circulatory system, nutrients are delivered directly to the cells, and all the internal organs are swimming in blood. Humans and fish have a closed circulatory system, while insects have an open circulatory system. Single/Double Circulatory System. “The circulatory system is the body's main transport system, carrying food and oxygen to the cells and taking waste products away. Humans have a double circulatory system because it has two loops - one from the heart to the lungs and back, and another from the heart to the rest of the body and back. (A single circulatory system, found for example in fish, has just one loop from the heart round the body, passing through the gills on the way.)” size/biology/humansasorganisms/1circ ulationrev1.shtmlhttp:// size/biology/humansasorganisms/1circ ulationrev1.shtml

Conclusion. Humans need a double circulatory system because we are larger than insects or fish, and therefore need more nutrients. The closed circulatory system ensures that the nutrients and oxygen are delivered to our cells very fast. Fish have a single circulatory system because they don’t need the amount of oxygen that insects or humans have because the water supports them. Insects are small, and can therefore have an open circulatory system and a tracheal system, because the nutrients can still be delivered efficiently (humans can’t have an open circulatory system because they are too large).

Bibliography ghttp:// g 39px-Tuna_Gills_cut_out.jpghttp://upload.wikimedia.org/wikipedia/commons/thumb/b/bc/Tuna_Gills_cut_out.jpg/6 39px-Tuna_Gills_cut_out.jpg