Animal Physiology

Animal Physiology

1. Breathing and Gas Exchange

   • Cells get energy by oxidising foods such as glucose. This process is called cell respiration. 
   • What is Respiration?
     • Respiration is the oxidation reaction that releases energy from foods, such as glucose.
     • Aerobic respiration
       • Uses oxygen. Carried out by animals plants and other organisms. Glucose + Oxygen = Carbon dioxide + Water (+energy) C6H12O6 + 6O2 = 6CO2 + 6H2O (+Energy)
     • Anaerobic respiration
       • glucose is not completely broken down. less energy is released.  can occur in situations when oxygen is in short supply. Anaerobic respiration in yeast: glucose > ethanol + carbon dioxide (+some energy) Anaerobic respiration in muscle cells: glucose > lactic acid (+some energy)
   • Ventilation
     • The mechanism that moves air into and out of the lungs, which then allows gas exchange to take plce.
   • The structure of the gas exchange system
     • The INTERCOSTAL MUSCLES join each rib to the next.  The air passages of the lungs form a highly branching network, sometimes called the BRONCHIAL TREE. Air passes down the windpipe or TRACHEA.  The trachea splits into two tubes called the BRONCHI.  Each BRONCHUS divides into smaller and smaller tubes called BRONCHIOLES. It is in the microscopic air sacs called ALVEOLI where gas exchange with the blood takes place.  CARTILAGE supports the airways and keep them open when we breathe in.  The PLEURAL MEMBRANES separate the inside of the THORAX (chest) from the lungs. They form an air tight seal.  MUCUS in the trachea and larger airways traps particles of dirt or bacteria that are breathed in.  Other cells are covered with tiny hair-like structures calle CILLIA. They sweep the mucus and trapped particles out towards the mouth. 
   • Ventilation of the lungs
     • Requires a difference in air pressure. The air moves from a place where the pressure is high to one where it is low. When we breath we change the volume of our THORAX, which alters the pressure inside it. This causes air to move in or out of the lungs.  Your RIBS are moved by your INTERCOSTAL MUSCLES. The outer (external) intercostals contract, pulling the ribs up. At the same time, the muscles of the DIAPHRAGM contract, pulling the DIAPHRAGM DOWN into a more flattened shape. These movements increase the volume of the chest, therefore causing a slight drop in pressure inside the thorax compared with the air outside. Air ENTERS the lungs.
     • The opposite happens when you breathe out.  The external intercostal relax and the INTERNAL intercostals contract, pulling the ribs down and in. The diaphragm muscles relax and the diaphragm goes back to its normal DOME shape. The volume of the thorax DECREASES, and the pressure in the thorax is raised slightly above atmospheric pressure. The difference in pressure forces air out of the lungs. (see p.28 for diagrams)
   • Gas exchange in the alveoli
     • Alveoli have a large surface area. Thin cell wall.  Deoxygenated blood comes from the heart.  Carbon dioxide diffuses into the alveolus and oxygen diffuses out into the red blood cells. This oxygenated blood is then carried back to the heart.  The blood which leaves the capillaries and flows back to the heart has gained oxygen and lost carbon dioxide. (see p.29 for diagrams)
   • Effects of smoking
     • Lining of the air passages
       • In the Trachea and Bronchi of a smoker, the cilia are destroyed by chemical in cigarette smoke. This means the mucus is not swept away from the lungs, but remains to clog the air passages. 
     • Emphysema
       • Kills about 20 000 people in Britain every year.  Smoke damages the walls of the alveoli, which break down and fuse together again, forming enlarged, irregular air spaces.  Reduces surface area for gas exchange, which becomes inefficient. The blood carries less oxygen. 
     • Lung cancer
       • Cigarette smoke contains nicotine - very addictive. At least 17 chemicals that are known to cause cancer. 
     • Carbon monoxide in smoke
       • Carbon monoxide interferes with the ability of the blood to carry oxygen.  Oxygen is carried around in the blood in red blood cells, attached to a chemical called HAEMOGLOBIN. Carbon monoxide can combine with the haemoglobin much more tightly than oxygen can, forming a compound called CARBOXYHAEMOGLOBIN. The blood carries much less oxygen around the body. Carbon monoxide is also a major cause of heart disease. 

2. Food and Digestion

   • We need food for three main reasons:  >To supply us with a 'fuel' for energy. >To provide materials for growth and repair of tissues. >To help fight disease and keep our bodies healthy.
   • A balanced diet
     • Carbohydrates Lipids Proteins Minerals Vitamins Water  Fibre
     • Carbohydrates
       • They are the body's main 'fuel' for supplying cells with energy.  Glucose and other sugars (fructose, lactose and sucrose) are one sort of carbohydrate. SUCROSE is the main sugar that is transported through plant stems.  We get most of the carbohydrate in our diet not from sugars, but from STARCH. Starch is a large INSOLUBLE molecule. It is found as a storage carbohydrate in many plants e.g potatoes, rice and wheat.  Starch is made up of long chains of hundreds of glucose molecules joined together. It is called a POLYMER of glucose. 
       • Animal cells sometimes contain a very similar carbohydrate called GLYCOGEN. This is also a polymer of glucose, and is found in tissues such as liver and muscle, where it acts as a store of energy for these organs.  Carbohydrates such as starch and glycogen have to be broken down into simple sugars during digestion, so that they can be absorbed into the blood. 
       • CELLULOSE is also a polymer of glucose. Cellulose is the material that makes up plant cell walls. Humans cannot break down cellulose because our gut doesn't make the enzyme needed to break down the cellulose molecule.  It forms a Dietary Fibre or Roughage, which gives the muscles of the gut something to push against as the food is moved through the intestine. This keeps the gut contents moving, avoiding constipation and helping to prevent serious diseases of the intestine. 
     • Lipids (fats and oils)
       • Contain the same three elements as carbohydrates - Carbon, Hydrogen and Oxygen. The difference is the proportion of the oxygen in the lipid is much LOWER than in a carbohydrate.  Lipids make up about 10% of our body's mass. They form an essential part of the structure of all cells, and fat is deposited in certain parts of the body as a long-term store of energy. The fat layer under the skin acts as insulation, reducing heat loss through the surface of the body. 
       • Chemical 'building blocks' of lipids are two types of molecule, GLYCEROL and FATTY ACIDS. Glycerol is an oily liquid. In lipids a molecule of glycerol is joined to three fatty acid molecules.  Too much lipid is unhealthy, especially a type called SATURATED fat, and a lipid compound called cholesterol. 
     • Proteins
       • All cells contain protein, we need it for growth and repair of tissues.  Enzymes are made from protein.  Proteins are made from 20 different sub-units called AMINO ACIDS.  All amino acids contain for chemical elements: carbon, hydrogen and oxygen, (the same as carbohydrates and fats) along with nitrogen.  Amino acids are linked together in long chains.  The SHAPE of a protein is very important in allowing it to carry out its function. The order of amino acids in the protein decides its shape. There are 20 different amino acids. 
     • Minerals and vitamins
       • without enough you will suffer deficiency diseases.  Vitamin A: FAT-SOLUBLE makes chemicals in retina, protects surface of eye and connective tissue. e.g carrots Vitamin C: WATER-SOLUBLE sticks together cells lining surfaces in the body, e.g mouth e.g citrus fruits. Vitamin D: helps bones absorb calcium and phosphorus e.g fish liver oils.
       • Minerals: Calcium: makes bones and teeth e.g dairy productsIron: makes haemoglobin in red blood cells e.g red meat, liver, eggs
     • Water
       • important in your body as a solvent, for breaking up large molecules by hydrolysis, and for carrying substances around your body.
     • Fibre
       • for bulk to give the muscles in your gut something to work on. Absorbs lots of water.

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