Brain
The brain is the body’s control center. It is held and protected by the skull. The cerebrum is the largest part of the brain. It is divided into two halves called hemispheres. The corpus callosum connects the two hemispheres; each hemisphere is then divided into regions called lobes. Each lobe has a different function. The different parts of the brain are the frontal lobe, parietal lobe, occipital lobe, temporal lobe, cerebellum, and brain stem.
The brain is responsible for many different things, including thinking, decision-making, emotion, memory, speech production, as well as muscle control, coordination, balance, and sensory reception.
The frontal lobe is the largest lobe; they’re located at the front of the brain they’re responsible for a few things; this includes thinking, self-control, making decisions, attention, judgement, problem-solving, planning, and emotions. The frontal lobe is also responsible for motor skills and speech production.
The parietal lobes are just behind the frontal lobe; they’re responsible for organising and interpreting sensory information to other parts of the brain.
The occipital loves are at the back of the brain, they’re mainly involved in visual processing, including recognition of shapes, colours, patterns, motion, etc. The occipital lobe is also involved in reading.
The temporal lobes are at the level of the ears. They’re responsible for processing auditory information, visual memory, verbal memory, and language comprehension. They’re also involved in recognising and understanding the reactions and emotions of others.
The cerebellum is located at the back of the brain, below the occipital lobes; they’re responsible for fine motor skills, including the fine movement of hands and feet. The cerebellum is also responsible for balance, coordination, and posture.
The brain stem is located in front of the cerebellum and connects to the spinal cord. It is made up of three major parts: the midbrain, pons, and medulla oblongata. The midbrain is at the top of the brainstem. It controls eye movement, and it also processes visual and auditory information. The pons is the largest part of the brainstem; it is just below the midbrain. It contains nerves that help to connect to different parts of the brain. It also contains some cranial nerves which are involved in facial movement and transmitting sensory information. The medulla oblongata is the lowest part; it controls the functions of the heart and lungs, helping to regulate the function of things such as breathing, swallowing, sneezing, coughing, etc.
Lungs
The lungs are part of the respiratory system. The respiratory system works to provide oxygen into the bloodstream from the air that we inhale and releases carbon dioxide when we exhale. This occurs automatically without you even having to think about it. It is part of the autonomic nervous system. The lungs have different parts to help take in air, filter it and then oxygenate the blood.
The lungs fill the chest cavity. The lungs are held and protected by the ribcage. The trachea splits into tubes and extends into each lung. These are two bronchi, the right, and the left bronchi. Each bronchus enters each separate lung. The smaller bronchi then split into even smaller tubes called bronchioles. The bronchioles end with tiny sacs called alveoli. They are surrounded by a network of blood vessels called capillaries.
When you inhale, the air you breathe in travels through your nose or mouth down the trachea. The air then travels through the bronchi into each lung. From there, the air travels through the bronchioles into the alveoli. Alveoli expand when a person inhales and contracts when a person exhales. Alveoli are surrounded by a network of blood capillaries, this is where the exchange of oxygen and carbon dioxide takes place. The alveoli have a large surface area, thin walls, and a good blood supply, which allows the diffusion of these gasses. Oxygen diffuses out of the alveoli and into the blood. This blood is then carried throughout the body via the blood vessels. Carbon dioxide diffuses out of the blood and into the alveoli. The carbon dioxide received into the lungs is then exhaled.
Heart
The heart is a vital organ providing blood to the body. It is part of the circulatory system made up of the heart, blood vessels, and blood.
Humans have a double circulatory system. In the first circuit deoxygenated blood is pumped to the lungs to be oxygenated and then returns to the heart. In the second circuit, oxygenated blood is pumped around the body by the heart and blood vessels. The heart is located in the ribcage near the lungs. The heart continuously pumps in a consistent rhythm, and electrical impulses in the heart ensure it beats with a constant rhythm and rate. The heart rate can increase and decrease depending on how much blood the body requires, for example, when you’re exercising, the heart beats faster in order to pump more blood around the body, whereas when you’re resting, the heart beats slower.
The heart has four chambers, the small upper chambers are called atria, and the lower chambers are called ventricles. The chambers are: the right atria, left atria, right ventricle, and left ventricle. The heart also has four valves; these are like little doors that only open one way, this ensures that the blood is flowing in the right direction, and doesn’t flow backward. The four valves are the tricuspid valve, pulmonary valve, mitral valve, and aortic valve.
It is important to remember that veins carry blood to the heart and arteries carry blood away from the heart.
The superior and inferior vena cava are large veins that deliver deoxygenated blood into the heart. The superior vena cava delivers blood into the heart from the superior part of the body; this includes the head, neck, arms, and chest. The inferior vena cava delivers blood into the heart from inferior parts of the body; this includes organs in the abdomen, legs, feet, etc.
The pulmonary vein carries oxygenated blood from the lungs to the heart. The aorta is the main artery that carries oxygenated blood away from the heart to the rest of the body. The pulmonary artery carries deoxygenated blood from the heart of the lungs.
The process of blood circulation:
Deoxygenated blood from the body flows into the right atrium via the superior and inferior vena cava. The right atrium contracts, and the blood flows through the tricuspid valve into the right ventricle. The ventricle contracts, and the blood flows up through the pulmonary valve into the pulmonary artery. This is then taken out of the heart into the lungs. At the same time, the oxygenated blood from the lungs enters the heart through the left atrium via the pulmonary veins. The left atrium contracts, and blood then flow through the mitral valve into the left ventricle. The left ventricle contracts, and oxygenated blood flows up through the aortic valve into the aorta. This blood is then sent around the body via arteries.
In one heartbeat, blood enters and exits the heart from both sides. Diastole is when the heart relaxes and fills with blood. Both the right and left atriums fill with blood. Systole is when the heart contracts and pumps blood. Both the right and left ventricles pump blood into the arteries. This process then repeats.
The heart itself also needs a constant supply of oxygenated blood to function. The coronary arteries that branch off the aorta supply this oxygenated blood. These arteries are wrapped around the outside of the heart.
Spleen
The spleen is a small organ located behind the stomach under the lungs. The spleen stores blood and filters it. It is able to recognise old or damaged blood cells, and the spleen is also able to break down and remove them from the body. This means that clean and well-functioning blood is able to circulate around the body. The spleen also helps to filter out infections by creating white blood cells to fight bacteria and viruses. Therefore it is a small but very important organ in our body.
Stomach
The stomach lies beneath the diaphragm. It is a ‘J’ shaped organ. It plays a role in digesting food. The stomach is divided into five parts: cardia, fundus, and body. The cardia is just beneath the oesophagus. Sphincter muscles prevent food from flowing back up to the oesophagus or mouth. The fundus is to the left of the cardia. The body is the main part of the stomach where food is broken down. The pyloric antrum is the lower part of the stomach. Partially digested food is kept here before it flows to the small intestine. The pyloric canal is a small part of the stomach that connects to the first part of the small intestine. It contains the pyloric sphincter helping to control how much content flows into the small intestine.
The stomach contains muscles and gastric juices. The muscles of the stomach help to change the size depending on how much food there is, for example, if you’ve eaten too much food, then it will expand. The muscles in the stomach also help to break down the food in the stomach. Gastric juices in the stomach help to kill bacteria and contain enzymes. Together, the muscles and gastric juices help to break down food thoroughly.
When you swallow food, it enters the cardia of the stomach. The fundus adapts to how much food is entering the stomach. It expands as the amount of food increases. The body of the stomach produces gastric juices, which mix with the food. The stomach’s muscles contract to help mix and break down the food. The food then exists the stomach via the pylorus into the first part of the small intestine.
Pancreas
The pancreas sits behind the stomach and has two functions: exocrine function and endocrine function. The exocrine function is to help with digestion. The endocrine function is to regulate blood sugar. The pancreas’s exocrine glands produce enzymes that help with digestion. The enzyme amylase breaks down carbohydrates. The enzyme lipase breaks down fats. The enzyme protease helps to digest proteins.
The pancreas also produces pancreatic juice – which further helps with digestion. The food is digested and converted into energy. This energy is then released into the bloodstream for the body to use. The endocrine function is to regulate blood sugar. The pancreas produces and releases insulin and glucagon.
When there is too much sugar in the blood, the pancreas produces and releases insulin into the blood. This helps to remove glucose by converting it into energy and releasing it into the blood. This energy can also be stored for later use.
When blood sugar is low, the pancreas produces and releases a hormone called glucagon. This tells the cells and liver to release the stored sugar back into the blood.
Liver
The liver plays a vital role in the body’s metabolic system. The liver is located just under the ribcage on the right upper side of the abdomen near the gallbladder. This organ is supplied with oxygenated blood via an artery. The liver processes the contents of the blood to ensure the composition stays the same. The liver does this in many different ways. The liver has many functions; the first is to purify blood it receives from around the body. The nutrients received in the blood from around the body are processed by the liver and broken down – these include fats, carbohydrates, vitamins, minerals, etc. The liver ensures a good and constant level of nutrients in the body, for example, the liver breaks down carbohydrates into sugar. Depending on the body’s needs the liver will send this sugar back to the body to be used as energy, or it stores some nutrients that are left over if the body doesn’t need them straight away. The stored nutrients can then be used later on when the body needs them.
The blood going into the liver sometimes contains toxic substances or substances that are useless for the body, so the liver detoxifies toxic substances, so it doesn’t cause harm to the body. The liver also metabolises drugs. For anything else that’s useless to the body, the liver removes it via excretion. The liver produces plasma proteins and blood clotting factors. These clotting factors prevent the body from losing too much blood. The liver also produces cholesterol. Cholesterol is important for cell structure. The liver also produces hormones, vitamin D, and other substances.
Another role of the liver is that it produces bile. Bile is a fluid that is released by the liver and stored in the gallbladder. The gallbladder is a small green pound found just under the liver. The production of bile helps with digestion and breaks down fats into fatty acids. This allows it to be taken into the small intestine for digestion. Bile also helps to destroy bacteria, helping to fight infections.
Gallbladder
The gallbladder is a small green pouch found just under the liver. One of the functions of the liver is to produce bile. This is a fluid released by the liver and stored in the gallbladder. The production of bile helps with digestion and breaks down fats into fatty acids. This allows it to be taken into the small intestine for digestion. Bile also helps to destroy bacteria helping to fight infections.
Kidney
The kidneys are two bean-shaped organs that maintain the body’s chemical balance. They do this by filtering the blood and excreting waste products as well as excess fluid such as urine. The kidneys are protected by the lower part of the ribcage. The kidneys receive unfiltered blood from the renal artery; each kidney contains millions of tiny units called nephrons. These are used for filtration. The kidney identifies useful and waste products in the blood, for example, if vitamins and minerals are required by the body then the kidney will allow these to flow back to the body. The filtered blood returns back to the body via the renal vein, and any excess water and waste leave in the form of urine. Narrow tubes called ureters carry the urine into the bladder to be released. Alongside filtering blood and producing urine, the kidneys also detect the body’s water level, so if you drink too much water, then the kidneys detect this and will release it through the bladder as urine. This is why when you are well hydrated, your urine colour is lighter. If you don’t drink enough water the kidneys will also detect this and will release some water back into the bloodstream. This is why when you’re dehydrated, your urine colour is yellow. The kidneys also secrete hormones, for example, a hormone to increase red blood cell production or a hormone to increase blood pressure.
Lastly, the kidneys activate vitamin D. Remember we have two kidneys. However, a person can live fine with just one kidney.
Small & large intestine
Intestines are groups of tubes that digest food, filter out the body’s waste and absorb water. Food that is broken down from the stomach travels to the small intestine; this is where most of the digestion and absorption of nutrients takes place. This food then passes through the large intestine, and water and salt are absorbed here. This causes the waste products to turn into a sold waste material which can then be excreted.
Bladder
The bladder is part of the urinary tract system. This also includes the kidneys, ureter, bladder, and urethra. Kidneys receive unfiltered blood from the renal artery, the kidneys then work to filter the blood by identifying useful and waste products in the blood, for example, if vitamins and minerals are required by the body then the kidneys will allow these to flow back to the body. The filtered blood then returns back to the body via the renal vein. The waste products and excess fluid in the blood are then removed and released as urine. The urine produced travels down the ureters of each kidney into the bladder. The bladder is made up of muscle, and its primary role is to store urine. It can stretch and contract in order to store and release urine.
The bladder also contains valves to prevent the urine from flowing back up to the ureters. It stretches to store the urine and then contracts when releasing urine via the urethra.
If you drink too much water, then the kidneys detect this and will release it through the bladder as urine, this is why when you are well hydrated, your urine colour is lighter. If you don’t drink enough water, then the kidneys will also detect this and will release some water back into the bloodstream. This is why when you’re dehydrated, your urine colour is yellow.
