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Learning Outcomes What you need to know Unit 3 Tick off each piece of information once you have learned it. A) MAMMALIAN NUTRITION REQUIREMENT OF FOOD The main food groups are carbohydrates, proteins, fats, vitamins and minerals. To maintain good health, human beings consume a balanced diet from the main food groups. Carbohydrates, fats and proteins all contain the chemical elements carbon, hydrogen and oxygen. Protein also contains nitrogen. Carbohydrates are made up of simple sugars Proteins are made up of amino acids Fats are made up of fatty acids and glycerol. FOOD TESTS The test for starch is to use iodine. The colour change is from brown to blue/black The test for glucose is to use Benedict’s reagent. The colour change is from blue to brick red. The test for protein is to use Biuret’s reagent. The colour change is from blue to lilac. The test for fat is the translucent spot test. ENERGY CONTENT OF FOOD Different food groups have different energy contents e.g fat contains more energy than protein and carbohydrate. THE NEED FOR DIGESTION Digestion involves the breakdown of large, insoluble food molecules into smaller, soluble food molecules to allow absorption into the blood stream through the lining of the small intestine. THE MOUTH, SALIVARY GLANDS AND OESOPHAGUS Mechanical breakdown of food happens in the mouth. Saliva contains amylase which digests starch into maltose Mucus in the saliva comes from salivary glands and it helps lubricate the mouth and food to aid swallowing. Peristalsis occurs along the whole length of the alimentary canal, not just the oesophagus. Peristalsis is like a wave-like motion. Circular muscles form a ring that contracts and squeezes the food from behind and circular muscles in front relax and allow the food to pass. THE ROLE OF THE STOMACH Food is churned in the stomach by the action of longitudinal and circular muscles to mix food with gastric juices. Protein is broken down by pepsin. The stomach contains gastric glands with mucus-secreting cells, enzyme secreting cells and acid secreting cells. THE ROLE OF THE SMALL INTESTINE IN THE ABSORBTION AND SECRETION OF FOOD Fat digestion by enzyme lipase. Further protein digestion by trypsin. Absorption of food is by diffusion The small intestine is very long with a folded inner lining on which there are many villi. A large surface area is provided for absorbing digested food. The lining of each villus (epithelium) is only 1 cell thick allowing nutrient molecules to pass through easily. A blood capillary network and a central lacteal is present in each villus to allow efficient transport of substances. Glucose and amino acids are absorbed into the epithelial cells and then pass directly into the blood capillaries. The products of fat digestion are also absorbed into the epithelial cells but do not pass into the blood capillary. They pass into the lacteal instead. Blood rich in amino acids and glucose from the small intestine is transported in the hepatic portal vein to the liver. Enough glucose is released into the blood circulation for use as an energy source. Excess glucose is converted in the liver to glycogen and is stored there until needed. Enough amino acids are released into the blood circulation to be used in protein synthesis during growth and tissue repair. Excess amino acids are broken down in the liver to urea. kidneys deal with this later) The process of breaking down amino acids is called deamination. This happens in the liver Some of the products of fat digestion (fatty acids and glycerol) are used as an energy source. Excess fatty acids and glycerol are converted to fat and stored in the body’s fatty tissue until required. THE ROLE OF THE PANCREAS, LIVER AND GALL BLADDER The pancreas produces lipase, trypsin and amylase. The liver stores excess glucose as glycogen and is the site of deamination The gall bladder stores bile which emulsifies fats to aid digestion. THE ROLE OF THE LARGE INTESTINE, RECTUM AND ANUS Material that passes into the large intestine consists of undigested material, bacteria and dead cells. Large intestine absorbs water from this leaving faeces which are passed into the rectum and expelled by the anus. B) CONTROL OF THE INTERNAL ENVIRONMENT THE STRUCTURE OF THE HUMAN URINARY SYSTEM Includes the kidneys, renal artery, renal vein, ureter, bladder and urethra. THE ROLE OF THE MAMMALIAN KIDNEY Osmoregulation is the regulation of water content in organisms. The kidneys are the main organs for osmoregulation. Water is gained through drinking, food and metabolic water. Water is lost through sweat, breath, faeces and urine. PRODUCTION OF UREA AND ITS REMOVAL IN URINE Urea is the waste product from the breakdown of excess amino acids in the liver (deamination). Urea is transported in the blood to the kidney where it is filtered out and excreted from the body in urine. STRUCTURE AND FUNCTION OF THE KIDNEY The kidneys are organs of filtration and reabsorption. Each kidney contains about a million microscopic functional units called nephrons. Each nephron has several parts; a glomerulus (knot of blood vessels) which is enclosed in a Bowman’s Capsule, which leads into a tubule surrounded by a network of blood capillaries. Several kidney tubules share a collecting duct. FILTRATION Blood containing waste products enters the kidney by the renal artery. The renal artery splits into a million branches each supplying a glomerulus. Each glomerulus is a coiled knot of blood capillaries surrounded by a Bowman’s capsule. Blood enters a glomerulus at high pressure The blood is filtered by the glomerulus. Small molecules are allowed to pass through (glucose, water, salts and urea). Large molecules are stopped from leaving the bloodstream (blood cells and plasma protein). The glomerular filtrate passes into the Bowman’s capsule and into the tubule. REABSORPTION Useful substances are then reabsorbed (all glucose, some salt and much water) into the capillaries surrounding the tubule. The process of reabsorbtion is so effective that about 99% of the water originally in the glomerular filtrate is reabsorbed. The final urine left over contains excess, unwanted water, urea and excess salts. Blood capillaries surrounding the tubules unite to leave the kidney as the renal vein. The renal vein contains purified blood. NEGATIVE FEEDBACK CONTROL BY ADH Osmoreceptors in the hypothalamus are stimulated by a change in water concentration in the blood. A decrease in water concentration triggers an increase in the release of antidiuretic hormone (ADH) from the pituitary gland. ADH increases the permeability of the kidney tubules and collecting duct, resulting in more water being reabsorbed into the blood stream. As the water concentration of the blood rises, less ADH is released resulting in less water being reabsorbed. Blood water concentration low -> small volume of concentrated urine produced. Blood water concentration high -> large volume of dilute urine produced. OSMOREGULATION IN MARINE AND FRESHWATER BONY FISH Marine bony fish have hypotonic tissues They lose water by osmosis and have a dehydration problem They overcome this problem by drinking water and excreting excess salts. A small volume of concentrated urine will be produced. Freshwater bony fish have hypertonic tissues They gain water by osmosis and have an influx problem They overcome this problem by excreting copious and very dilute urine. C) CIRCULATION AND GAS EXCHANGE THE STRUCTURE AND FUNCTION OF THE HEART AND BLOOD VESSELS The heart is a muscular organ that is divided into 4 chambers:- 2 atria and 2 ventricles. (left and right) The left ventricle wall is very thick and muscular since it has to pump blood all round the body. The right ventricle wall is less thick since it just pumps blood to the lungs The heart has 4 heart valves. 2 of the valves are between the atria and ventricles. On the left hand side is the bicuspid valve. On the right hand side is the tricuspid valve. The 2 other heart valves are at the origins of the pulmonary artery and the aorta – these are the semi-lunar valves. The valves ensure that blood is only able to flow in one direction. They prevent backflow of blood. Since the heart wall is made of muscle it must get its own supply of oxygenated blood. The heart is supplied by the coronary arteries. (a branch of the aorta). If a coronary artery becomes blocked, the heart does not get a supply of oxygen and this may result in death of the tissue THE PATHWAY OF BLOOD THROUGH THE HEART AND ASSOCIATED VESSELS Blood arrives at the heart via the vena cava. This blood is low in oxygen (deoxygenated.) From the vena cava it enters the right atrium then the right ventricle. It exits the heart by the pulmonary artery where it is carried to the lungs to pick up oxygen. The blood becomes oxygenated. From the lungs it goes back to the heart via the pulmonary vein. It enters the left atrium, then the left ventricle. The blood leaves the heart in the aorta where it is delivered to the rest of the body. BLOOD VESSELS Blood leaves the heart in arteries, flows through capillaries and returns to the heart in veins. The pulse indicates that blood is pumped through arteries. ARTERIES Artery walls are very thick and muscular since they have to withstand blood travelling at high pressure. VEINS Veins have valves present to stop the blood flowing backwards. Veins are wider and have thinner muscular walls CAPILLARIES Capillaries are 1 cell thick, they are long, narrow and thin to provide a large surface area. Capillaries carry food and oxygen to every cell. Gaseous exchange happens at each cell (oxygen in, carbon dioxide out) and waste is removed back into the blood. You need to know the names and positions of these vessels; Pulmonary artery; pulmonary vein; aorta, vena cava; hepatic vein; mesenteric artery; hepatic portal vein; renal artery and renal vein. INTERNAL STRUCTURE OF THE LUNGS AND FEATURES WHICH MAKE THEM EFFICIENT GAS EXCHANGE STRUCTURES Structure to include trachea, bronchi, bronchioles and alveoli (airsacs) Alveoli have a large surface area Alveoli have thin walls Alveoli have moist surfaces Alveoli have a good blood supply These features allow efficient gas exchange Oxygen diffuses from the alveoli into the blood stream Carbon dioxide diffuses from the blood stream into the alveoli. FEATURES OF CAPILLARY NETWORK WHICH ALLOW EFFICIENT GAS EXCHANGE IN THE TISSUES Capillaries have a large surface area Capillaries are in close contact with the tissue cells Capillaries have very thin walls. COMPOSITION AND FUNCTIONS OF THE BLOOD Oxygen is carried in red blood cells Carbon dioxide is carried in the blood plasma (some carbon dioxide is also carried in the red blood cells) The concentration of carbon dioxide carried dissolved in the plasma is limited by the increase in acidity that carbon dioxide causes in the blood Soluble foods is carried dissolved in the blood plasma FUNCTION OF HAEMOGLOBIN IN THE TRANSPORT OF OXYGEN Haemoglobin combines with oxygen to form oxyhaemoglobin at high levels of oxygen in the lungs. Oxygen is released at low level of oxygen in the tissues. FUNCTIONS OF MACROPHAGES AND LYMPHOCYTES IN DEFENCE Phagocytosis is the process by which bacteria are engulfed and destroyed by macrophages. The macrophage will engulf a bacterial cell and then digest it. Phagocytosis is an example of non-specific immune response since it provides general protection against a wide range of microorganisms. Antibody production is an example of specific immune response as they are specific to a particular antigen. An antigen is a molecule that is recognised as alien to the body by the body’s lymphocytes. The presence of an antigen in the body stimulates the lymphocytes to produce antibodies. An antibody is a Y-shaped molecule. Each arm has a receptor site whose shape is specific to a particular antigen. When an antibody meets its complementary antigen, they combine at their specific sites like a lock and key and the antigen is rendered harmless. It will then be engulfed by phagocytosis. D) SENSORY MECHANISMS AND PROCESSING OF INFORMATION STRUCTURE AND FUNCTION OF THE BRAIN Structures to include the cerebrum, cerebellum, medulla and hypothalamus. The cerebrum is the site of conscious responses and higher centres The cerebellum is the centre of balance and co-ordination of movement The medulla is the site of the vital centres such as breathing and heart rate. The hypothalamus is the centre for regulation of water balance and temperature. DISCRETE AREAS OF CEREBRUM RELATED TO SENSORY/MOTOR FUNCTION The location of sensory and motor strips as discrete areas of the cerebrum is required to be known. THE BRAIN, SPINAL CORD AND NERVES Nerves carry impulses from the senses to the central nervous system and impulses from the central nervous system to the muscles. REFLEX ACTION AND THE REFLEX ARC The reflex arc is made up of receptor, sensory neurone, relay fibre, motor neurone and effector. Transmission of a nerve impulse through a reflex arc results in a reflex action. A reflex action is a rapid, involuntary, automatic response to a stimulus A reflex action protects the body from damage. THE ROLE OF THE CENTRAL NERVOUS SYSTEM The CNS sorts out information in the form of impulses from the senses. The CNS sends messages in the form of impulses to muscles which can then make the appropriate response. TEMPERATURE REGULATION AS A NEGATIVE FEEDBACK MECHANISM The hypothalamus contains the body’s temperature-monitoring centre. It receives nerve impulses from heat and cold receptors in the skin. It also has its own central thermoreceptors which monitors the temperature of the blood. The central thermoreceptors detect changes in the body’s core temperature. The hypothalamus responds to this info by sending motor nerve impulses to effectors. OVERHEATING The skin helps to correct overheating of the body by: Increased rate of sweating Vasodilation - the arterioles leading to the skin become dilated which allows a large volume of blood to flow through capillaries near the skin surface. Heat can be lost as radiation. OVERCOOLING The skin helps to correct overcooling of the body by: Decreased rate of sweating Vasoconstriction - The arterioles leading to the skin become constricted which allows only small volume of blood to flow through capillaries near the skin surface. Little heat is lost by radiation Contraction of erector muscles - This is when the hairs on the skin are raised by the erector muscles contracting. It traps a wider layer of air between the body and the environment. Provides insulation. SHIVERING When the hypothalamus detects a drop in body temperature, nerve impulses to the skeletal muscles cause them to undergo brief repeated contractions – shivering. Shivering generates heat energy and helps to return the body temperature to its normal level.