P4 M1 D1 ANATOMY AND PHYSIOLOGY

Explain the physiology of two named body systems in relation to energy metabolism in the body. (p4, M1, D1)

In this piece I will analyse how the cardiovascular system and the digestive system interrelate to perform energy metabolism.

Campton (2013) defines energy as, ‘the capacity to do work’. This energy exists in a number of forms such as light, heat, sound, electrical, nuclear and also chemical which is known to be the most common. Chemical energy is released in the breakdown of food, or digestion. We can therefore say that chemical energy is within the bonds of chemical compounds i.e. atoms and molecules. As the bonds loosen or break, the chemical reaction will take place and oxidation will occur. The conservation of energy states that, energy can neither be created nor destroyed only changed.

Energy is essential for the body to survive. It is absolutely necessary to circulate blood, lymph as well as tissue fluid around the body. If energy wasn’t present we wouldn’t be able to take part in activities that we love to do, this would be because we need energy for the movement of our muscles. It is used to transmit nerve impulses throughout our body so that we are able to respond to changes within the environment. Furthermore, we need energy to carry out respiration and to also synthesise new cells for carrying out growth and repair. Energy is also important to build different complex molecules e.g. enzymes and hormones from the simple ones produced after the digestion of food.

Metabolism is when nutrients are converted to energy by the body; it is the sum of both biological and chemical processes within the body, relating to the amount of nutrients used in each cell. Metabolism can then be divided into two processes, anabolism and catabolism. Anabolism allows the formation of new tissues and the growth of new cells. It also enables us to synthesise new large, complex molecules instead of simple ones. However, in catabolism, these larger complex molecules are broken down into simpler ones, and there components used by the body’s cells. An important molecule used in metabolism is ATP, short for adenosine triphosphate. It was discovered in 1929 by a German scientist, Karl Lohnmann. An example of this is a process called glycolysis where by glucose is broken down to obtain energy. Within the first steps of glycolysis, a phosphate is added from the ATP to the glucose molecule. When this happens the ATP reduces its phosphate molecules from 3 to 2, therefore it becomes ADP and it normally written as ADP+Pi. ATP is clearly needed in the body and without which cannot function. Although within the body ATP is always being recycled, it also has to make new ATP. An enzyme, named ATP synthase, which is found within the mitochondrial membrane, generates the ATP in the mitochondria.

Digestion is the process whereby food is broken down from being complex molecules into more simple, soluble ones. This means that the digestive system converts this food into fuel that we need for the body’s energy demands. First of all ingestion has to take place whereby food is taken into the mouth via the buccal cavity i.e. the mouth. This is also the start of starch digestion initiated by the enzyme amylase which is in saliva from the salivary gland. In the mouth the teeth can also aid digestion as they cut and grind food particles down into smaller ones. This material is then passed down through the oesophagus, by a process called peristalsis which moves food into the stomach. The muscles behind the food contract involuntarily and so push it along. Digestion continues further in the stomach, where protease, digests protein, resulting in the product of amino acids. The strong stomach walls consist of three layers of smooth muscle. This muscle is spread within the stomach allowing there to be a large amount of motion created, churning and breaking down food into small particles. This food mixes with gastric juices to form chyme. The chyme then enters the top of the small intestine which is known as the duodenum. This is where fat digestion begins and lipase breaks down lipid into glycerol and fatty acids. Bile helps fat digestion and also the absorption of fat. The salts which are contained within the bile emulsifies this fat by breaking down large fat globules into smaller globules. The jejunum is the primary site of absorption and most of the absorption of food is done in this part of the digestive tract. Simple sugars for e.g. glucose, water soluble vitamins (apart from vitamin C and some B vitamins) and amino acids made from the food are passed into the bloodstream from the villi. Fat is then passed into lymph capillaries and the rest of the food enters the ileum. The ileum is where mainly B12 is absorbed into the blood capillaries. The unabsorbed and undigested food passes from the ileum and enters the cecum. This is the start of the large intestine. The undigestible food passes into the colon via the cecum, and this is where water and salts are absorbed. This is the last part of the digestive tract.

As said above, the molecules are absorbed into the capillaries of the bloodstream in the cardiovascular system. This systems main function is to transport these molecules to all body cells via the bloodstream driven by the pumping of the heart. The blood is the main transport medium and consists of a number of components such as red blood cells, white blood cells and also platelets. Red blood cells have no nucleus and are biconcave. They contain haemoglobin which allows them to carry oxygen around the body. White blood cells have a lobed nucleus and they are fewer in number than red blood cells. White blood cells are important in defence. Platelets are important in blood clotting as they help convert fibrinogen to fibrin which forms a mesh of fibres to allow clotting to occur.

The heart is myogenic and is described as being a double circulatory system. One circuit from the heart to the lungs and back is the pulmonary circulation and the other circuit, from the heart to the rest of the body is the systemic circulation. The right atrium receives the deoxygenated blood via the vena cava and this passes into the right ventricle. The tricuspid valve is present which prevents the back flow of deoxygenated blood from the right ventricle into the atrium. The right ventricle then pumps the deoxygenated blood to the lungs through the pulmonary arteries. The pulmonary vein takes the oxygenated blood back from the lungs and it enters through the left atrium. The oxygenated blood then passes from the left atrium into the left ventricle. The bicuspid valve here prevents the backflow of oxygenated blood from the left ventricle into the left atrium. Once the oxygenated blood enters the left ventricle, it is pumped into the aorta and then around the rest of the body.

These two systems inter relate particularly due to the small intestine as there is where absorption takes place into the blood through a process called diffusion.  The digestive system breaks down food into small particles so that it is able to be transport to other parts of the body where it is then converted into energy via catabolism and used by the body cells. The cardio vascular system transports oxygen to the digestive system so that it is able to carry out its work and break down the food to obtain the nutrients which are contained within this.

In conclusion, energy metabolism is very important regarding these two systems and no one body system is able to work in isolation. The digestive system and the cardiovascular system need and rely on each other from the minute of ingestion.  

I hope you all found this helpful, your study pal!
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