The Cardiovascular System And The Digestive System

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In this essay I will be covering how the cardiovascular system and digestive system work individually and how they also work together to perform energy metabolism in the human body.

Energy is a quantitative property which cannot be created or destroyed but only converted into another form or transferred from one place/object to another. Energy comes in several forms, the most common form being chemical. It can also be nuclear, electrical, thermodynamic, sonic or radiant. All living organisms require energy to function. In the human body, energy has many roles. It is required to perform simple tasks such as circulating blood around the body for the heart to beat, respirating, taking in oxygen and maintaining the body’s temperature. Energy is also used for growth and repair. Energy is used to repair tissues and cells; it is especially needed at certain times in a human’s lifespan such as infancy and puberty as the body is growing and developing at a faster rate during this time. In order for the muscles in our body to move energy needs to be transferred to them. Energy is also used to transfer nerve impulses to our brain so we can react appropriately to the changes in our environment. Without energy we would simply not be able to live. This is why in some cases people who do not get enough energy may have health problems or even die as their body cannot perform simple tasks without it.

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The cardiovascular system is made up of multiple different parts that all come together to pump blood around the whole body. The parts of this system are the heart, veins, veinules, arteries, arterioles, capillaries and blood. There are multiple cells in our blood that have various roles. There are red blood cells and white blood cells and platelets. The white blood cells contain monocytes, lymphocytes, neutrophils, eosinophils, basophils and macrophages. These cells are essential in our body as they protect us from illness, fight disease and help repair out body. The heart is a muscle made up of three layers, the pericardium, myocardium and endocardium. There are two different sides with a septum in between them. There are four chambers in the heart: the right and left atriums and the right and left ventricles. The left side of our heart is larger and has a thicker wall as it has to pump blood further around the body and has a higher pressure compared to the right side. When the cardiac muscle is at systole, this is when the cardiac muscle contracts, it pumps blood out of the heart into the arteries which carry the blood around the whole body. When the cardiac muscle is at diastole, this is when the cardiac muscle is relaxed, the heart fills with blood. The heart contracting and relaxing is commonly known as the heartbeat. Blood enters the heart through the vena cava which carries deoxygenated blood from the body into the right atrium. The deoxygenated blood then flows into the right ventricle through the tricuspid valve, when the ventricle is full the valve closes to prevent the backflow of the blood. The blood then flows through the pulmonic valve into the pulmonary artery and goes to the lungs to get oxygenated. After the blood has been oxygenated at the lungs it is brought back to the heart through the pulmonary vein into the left atrium. This is called pulmonary circulation. The blood then flows into the left ventricle through the mitral valve. Blood then leaves the heart through the aortic valve and into the aorta which pumps the blood around the body. As oxygenated blood travels through the body it loses its oxygen and returns to the heart. This is called systemic circulation.

The digestive system is how our bodies obtain energy. The food we eat provides us with nutrients and energy that is required for us to stay alive and healthy. Food has to be digested before it can be useful to the body. The nutrients that we take in from our food is absorbed into out blood and taken to cells to provide us with energy. There are multiple stages of digestion. Ingestion occurs in the mouth. When we eat food out teeth and jaws crush and grinds the food into smaller particles then mixes with saliva. Saliva contains the enzyme amylase which breaks down the starch in our food into sugars. This helps the digestion process as it is broken down to create a larger surface area. The tongue muscles then push the food down the oesophagus. This is the tube which connects the mouth to the stomach. The food is squeezed down the tube by a process called peristalsis which is the contraction and relaxation of the muscles in the oesophagus. The oesophagus is also lubricated by mucus which helps this process along. It takes approximately 3-6 seconds for the food to reach the stomach. When the food reaches the stomach, gastric muscles churn the food and mix it with gastric juice which comes from the cells in the stomach lining to create a liquid called ‘chyme’. The stomach acts as a mixing tank for the chyme and has thick muscular walls. The gastric juice contains an enzyme called pepsin and hydrochloric acid. The pepsin breaks down food protein into peptides and amino acids. The hydrochloric acid kills bacteria and creates an acidic environment needed for effective digestion. Food stays in the stomach for 1-4 hours but liquids can pass through the stomach in a few minutes. The next stage takes place in the small intestine. The small intestine is about 6 meters long. Chyme is squirted into the duodenum through the pyloric sphincter into the duodenum. When the chyme enters the small intestine, it is mixed with pancreatic juice and bile, which is made in the liver. Pancreatic juice contains enzymes which help break down starch, fat and protein it is also alkaline therefore neutralises the acid which came from the stomach. Bile contains salt which breaks down the fat into droplets which helps lipase split the fat into fatty acids and glycerol. The chyme gets pushed through the small intestine by peristalsis. As the chyme get digested vitamins, minerals, amino acids, fatty acids, glycerol, peptides and sugars are released and get absorbed into the intestinal wall. The lining od the small intestine have villi which increase absorption area. The amino acids and sugars go into the bloodstream then get taken to the liver. The fatty acids and glycerol go to the lymphatic system. Some of the nutrients provide energy and others are used to repair and build cells. The chyme now passes into the large intestine. The large intestine is inhabited by bacteria. The chyme now contains substances that have not been digested such as fibre, some vitamins and minerals and water. The bacteria can break down some of the fibre into fatty acids and gas. These products along with water are absorbed and leave a residue behind. The residue that is left behind is known as faeces. The final stage of digestion is called elimination or excretion. Faeces contains fibre, material that were unable to be digested and bacteria. The faeces are eliminated through the anal sphincter. It can take 12-24 hours for the whole digestion process to be completed. This process can sometimes be completed in a shorter amount of time if there is a large fibre intake.

These two systems work together to create energy for our body. The energy is extracted by the digestive system and absorbed into the body through the cardiovascular system. The digestive system takes large complex molecules and turn them into simple soluble ones that can pass into the capillaries and be absorbed. The cardiovascular system then takes these substances to the liver and around all the cells in the body. The cardiovascular system does not only take nutrients to the cells but also transports waste from the cells. Without the digestive system the cardiovascular system would not be provided with energy and nutrients to distribute and without the cardiovascular system the digestive system would not be able to get the substances around the body.

In summary these systems are vital for humans to be alive and healthy. Both systems are of equal importance and if they did not work hand in hand our bodies would not be able to obtain energy and we would not be able to function.


  1. BTEC Health and Social Textbook 2016 edition 1- Billingham, Davenport, Talman, Matthew, Stretch and Author
  2. (information on blood cells)
  3. (information on blood flow sequence)
  4. Cardiovascular system powerpoint for moodle 2020
  5. Digestive system powerpoint from moodle 2020
  6. Information on energy from Wikipedia 2020


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