Table of contents for How It Works: Inside The Human Body - 12th. Edition in How It Works

Adipose tissue provides the body with an energy reserve and also acts as a shock absorber – particularly on the soles of the feet. The fat cells – also known as adipocytes – contain a large lipid droplet, which takes up almost their entire volume, while their nuclei and other organelles are squashed on the perimeter. Adipocytes are not just used as storage sacks though; they have important metabolic and hormonal duties too, including involvement in the production of oestrogen. Humans have a second type of fat tissue known as ‘brown fat’. More commonly found in infants, brown fat provides a thermal blanket around the neck and the major blood vessels in the thorax. Brown fat cells are able to generate heat by a method known as uncoupling; instead of…

The human body changes as it ages and the peak time for organ functionality is thought to be around the age of 30. The body has amazing capacity for regeneration, but cells can only divide a finite number of times, and as we get older our ability to repair damaged tissue decreases. Dramatic changes, such as the menopause, produce obvious effects on the body. Female sex hormones are not just involved in reproduction, but also play a role in other processes, such as the maintenance of bone density. In the absence of oestrogen, bone mineral density decreases, which can lead to osteoporosis. A similar, but less dramatic, effect can be seen in men as testosterone levels begin to drop. Similar decline in functionality can be observed throughout the human body;…

Memory CEREBRUM The cerebral cortex makes up the majority of the human brain. It is divided into four lobes, which handle the most complex of tasks, including planning, memory and vision. Temperature and hydration HYPOTHALAMUS The hypothalamus is responsible for maintaining equilibrium within the body. It monitors and adjusts a variety of vital parameters, like the body’s temperature and hydration. Hormones PITUITARY GLAND This pea-sized gland is connected to the hypothalamus and produces hormones, passing on chemical messages instead of electrical impulses. Perception THALAMUS The thalamus is a switchboard for sensory information, connecting the parts of the brain and body involved in perception and movement. It also controls the sleep/wake cycle. Sleep and dreaming PONS The pons is another relay station within the brain, allowing nerves in the cerebellum to…

Baby In order to fit through the birth canal, human babies must be born well before their brains have finished developing, so their brains grow rapidly in their first years. Experiences prompt the development of new connections between nerves, and by the time a baby is two years old, it has 1.5 times as many synapses as an adult. Infant Support cells, known as glia, provide protection, insulation and nutrition for the brain’s nerve cells. Throughout childhood, they continue to migrate and grow. During the first two to three years of a child’s life, the insulating white matter of the still-developing brain begins to form. Child By the age of ten or 11, the rapid development of new connections in the brain has ended and a period of trimming and…

SEVERE If the injury is severe, the patient is no longer able to respond to sensory stimulation. Their eyes remain closed and there is no response at all to verbal cues. MODERATE When brain injury is more severe, verbal communication starts to break down and patients no longer respond normally to pain. MILD With mild brain injury, patients may be confused, but they remain aware, conscious and conversational.…

The 206 bones of the adult human skeleton make up a strong, flexible framework that protects our vital organs and allows our bodies to move, as well as being a mineral store and stemcell reserve. Bone is a composite material, constructed from three basic ingredients: collagen strands, a sugary protein glue and inorganic calcium salts. The collagen fibres are arranged in alternating layers, crossing over one another, providing a flexible scaffold, and calcium salts are glued in between for strength and rigidity. The outside of each bone is composed of plates, or hollow tubes, of dense cortical bone, supported on the inside by a honeycomb network of spongy trabecular bone. This network is slightly flexible and helps to distribute the load, curving the tensile and compressive forces across the ends…

Muscles are often taken for granted. Responsible for every move you make, the primary goal of a muscle is to turn energy into motion. Muscles are broken down into three categories. Skeletal muscles are the type that people in the gym train and what individuals are most commonly aware of. Smooth are the involuntary muscles such as blood vessels, airways and your bladder. The final category is cardiac, the muscles of the heart. It is skeletal muscle, however, that allows humans to both shape their bodies and increase their strength. Skeletal muscles are incredibly complex, designed to contract when asked to perform any action. If you perform a bicep curl, for example, your brain will send a signal to the nerve cells indicating that it’s time for the biceps to…

Open your eyes, and you are met with an array of different colours, but amazingly you can only detect three different wavelengths of light, corresponding to green, blue, and red. Combining these three signals in the brain creates millions of different shades. Each eye has between 6 and 7 million cone cells, containing one of three colour-sensitive proteins known as opsins. When photons of light hit the opsins, they change shape, triggering a cascade that produces electrical signals, which in turn transmit the messages to the brain. Well over half of our cone cells respond to red light, around a third to green light, and just two per cent to blue light, giving us vision focused around the yellow-green region of the spectrum. The vast majority of the cone cells…

Daily calorie intake for an average adult is set between 2,000 and 2,500kcals and recommended fat intake is between 70 and 90 grams. The body needs this level of calories in order to function at maximum efficiency. However, if we consume more than is needed to run our body, it stores these extra calories as fat. These fat stores can serve as a reserve if we don’t eat enough, but if someone consistently over-eats, they’ll become overweight as the body continues to store the excess calories. Obesity is becoming more prevalent across the world, within developed and developing countries. Highly calorific food and snacks, with generally poor nutritional value, have become more widely and cheaply available and the amount of saturated fat being consumed by an average adult is much…

Cramp is an involuntary contraction of a muscle, often in a limb such as the leg, that can cause pain and discomfort for seconds, minutes or, in extreme cases, for several hours. They are most common after or during exercise, coinciding with low blood sugar levels, dehydration and a high loss of salt from sweating. Although the full range of causes is something of a mystery due to limited research in the area, cramp is believed to be the result of muscle fatigue. If a muscle has been shortened through prolonged use but is repeatedly stimulated, it isn’t able to properly relax. A reflex arc from the central nervous system to the muscle informs it to continue contracting when it is not necessary, leading to a painful spasm known as…

Cholesterol is a fatty molecule in the blood and, generally speaking, having too much is bad: it can stick to the walls of your arteries and increase the risk of heart disease. Most foods, with the exception of offal, eggs and shellfish, don’t contain any cholesterol, but many contain saturated fats, which are turned into cholesterol by the liver. However, cholesterol itself isn’t unhealthy – in fact, you wouldn’t be able to live without it. The body uses cholesterol as a kind of padding, coating the outer membranes of all our cells and insulating nerve fibres, helping signals travel properly to and from the brain. It’s also a fundamental part of the endocrine system, as all steroid hormones (eg oestrogen) are synthesised from cholesterol. A good diet and regular exercise…

There is still so much we don’t know about the human brain. However, if something goes wrong and it needs an operation, you will find yourself in need of a neurosurgeon. These guys can operate on the vast number of structures within the brain and spinal cord, and have a full arsenal of techniques and – literally – cutting-edge technologies to hand. A neurosurgeon’s workload comes in two main forms. The emergency work is often a result of road traffic accidents or fights, and often affects young men with head injuries. These patients may have bleeding within the skull, which is exerting pressure on the brain – the neurosurgeon must relieve that pressure. There is also the planned work, where neurosurgeons try to remove tumours with meticulous detail to surrounding…

Normally a thick layer of alkaline mucus effectively protects the cells lining the stomach from the low pH of stomach acid. If this mucus becomes disrupted, however, acid comes into contact with the organ’s lining, damaging the cells and resulting in an ulcer. Around 60 per cent of stomach ulcers are caused by inflammation due to chronic infection by the bacterium Helicobacter pylori. Bacterial by-products cause damage to the cells lining the stomach, causing a breakdown of the top layers of tissue. Non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen and aspirin, also cause stomach ulcers in large doses. They disrupt the enzymes responsible for mucus production, diminishing the protective barrier. An ulcer in the making Once bacteria breach the stomach lining, it can no longer protect itself from its acidic contents……

Normal function Antibiotics target bacterial cells, by changing the signals of their outer wall, their membrane shape, impairing DNA function in the cell or by blocking protein synthesis. Changing the landing zone Bacteria can change the shape and structure of the molecules that antibiotics target, meaning they can’t recognise them and rendering them useless. One in, one out Antibiotics enter bacterial cells via special pumps. The bacteria can develop more exit than entry pumps, meaning the antibiotic is exited faster than it can enter. Entry policy Bacteria can stop antibiotics entering: they can change the shape of entry pumps and reduce the size of pores in their surface, meaning the antibiotics are too large to enter. Inactivation The strongest bacteria develop special enzymes, which can destroy the key parts of…

Exercise can cause blood glucose levels to fluctuate, though this is less drastic in people with type 2 diabetes than those with type 1. Low blood sugar (hypoglycaemia) can occur because muscles use glucose as energy and the body becomes more sensitive to insulin. High blood sugar (hyperglycaemia) can be triggered by other hormones, such as adrenaline, which are released during exercise. Maintaining an optimal blood sugar target in type 1 diabetes requires balancing the insulin dose with what the person eats and drinks and the amount of exercise they do, taking into account external factors like temperature. Everyone’s diabetes is different and individuals react differently to exercise. Physical activity, however, can help improve blood glucose management and the efficient working of insulin. Cycling is a physically challenging endurance sport…

Skeletal muscle is responsible for moving the skeleton. It is composed of bundles of muscle fibres, sheathed in a strong collagen matrix, which extends into tendons that attach to the bone. Within each muscle fibre is a molecular ratchet system made from the proteins actin and myosin. As the protein filaments slide past one another, the muscle fibre contracts lengthways and the fibre shortens. Muscle fibres can be broadly categorised as being either ‘fast twitch’ or ‘slow twitch’. Fast-twitch fibres use high-speed anaerobic respiration to produce rapid movements, but fatigue quickly. In contrast, slow-twitch fibres use sustainable aerobic respiration and produce slower movement for longer periods of time. The proportion of slow and fast-twitch fibres affects athletic performance, eg long-distance runners have a higher proportion of slow-twitch fibres than sprinters.…

Newborn brains grow from 25 to 90 per cent of adult volume in just five years Skeletons start out as cartilage and gradually turn to bone DID YOU KNOW? Baby boys gain around 6kg in weight in their first year. Girls, on the other hand, gain around 5.5kg in weight…

SENSORY MEMORY The body is constantly bombarded by sensory signals and most incoming sensory information is retained for less than a second before it is forgotten. TRANSFER The hippocampus integrates incoming sensory information, collecting it together as a single experience. It works together with the cortex to prioritise which information to store and which to forget. SHORT-TERM MEMORY Without concentrating too hard, short-term memory can hold around seven items for 20 to 30 seconds. Collecting information into discrete chunks, like splitting a phone number up into sections, can help the brain retain more. ACOUSTIC ENCODING Short-term memory tends to be based on sound, also known as echoic memory. When trying to remember a phone number, it often helps to rehearse it vocally in your head. LONG-TERM MEMORY The hippocampus is…

The human brain has limited capacity for repair, so once a region is injured, it cannot be replaced. The damaged cells are removed and support cells known as astrocytes divide to form a wall around the gap to seal off the area. The space then becomes filled with fluid. However, all is not lost. The human brain is a remarkable organ and although it cannot repair itself as such, it is able to adapt. Nerves are not fixed in their function, or their connections, so if a part of the brain is injured, new connections can be made to bypass the damage. The amount of function that can be regained depends on the location and severity of the injury and can be greatly aided by rehabilitation, encouraging the formation of…

How bones grow Bone marrow cells There are two types of bone marrow in the human body; yellow marrow is found in the shafts of the long bones, like the femur, and red marrow is mainly found in the flat bones, like the ribs. Yellow marrow is mostly made up of large fat cells, whilst red marrow contains stem cells. These are capable of producing most of the cells of the blood and immune system, and concealed within the bones are many immature cells in the process of development. DID YOU KNOW? The hands and feet contain over half of the bones in the body, with a total of 106 between them…

Weighing more than a bag of sugar, the liver is the largest of all the internal organs. It’s located mostly in the right side of your abdominal cavity and is capable of holding roughly ten per cent of your body’s total blood volume, with around a quarter of your blood supply passing through it every minute. The liver has many roles in the body, one of which is producing bile, the substance that breaks up fat molecules to aid digestion. Up to one litre of this greenish-yellow liquid is produced and released every day, containing a combination of salts, water, cholesterol and a pigment called bilirubin. Bile travels from the liver to the gallbladder, where it is stored. When a fat-containing food reaches the duodenum (part of the small intestine),…

The back of the eye is covered in a layer of light-sensitive cells measuring just fractions of a millimetre in thickness. When photons of light hit the pigments inside the cells, it triggers a cascade of signals, which pass through a series of different connections before they are transmitted to the brain. First, they move through interneurones and then to neurones known as ganglion cells. These cells are cross-linked, able to compare adjacent signals, filtering out some of the information before passing it on to the brain. This helps to improve contrast and definition. The neurones travel across the back surface toward the optic nerve, which relays the information into the brain. As the two optic nerves enter the brain, they cross over, coming together at a point known as…

The pelvis is an essential part of the skeleton which acts as a junction between the abdomen and the legs. It consists of eight key structures: the sacrum, ilium, ischium, pubic bone, pubic symphysis, obturator foramen, acetabulum and coccyx, which are laid out symmetrically. Together these make up the bony pelvis. The role of the pelvis is threefold. Firstly, it serves as a connecting mechanism between the torso and the legs. Secondly, it is a vital support and balance structure for the upper body. And thirdly it provides a protective, containing cradle for the intestines, bladder and internal sex organs. The pelvis – technically referred to as the pelvic girdle in this context – consists of a pair of hipbones connected to the base of the vertebral column. Each hipbone…

Before the vaccine, everyone got chicken pox. You’d get it once as a kid and then wouldn’t get it again. This is a perfect example of immunisation. Antigens are foreign molecules that when introduced, the body recognises as an ‘intruder’ and fights with antibodies, creating an immune response. Antibodies neutralise the antigen so that the next time around they know what to do. Vaccinations make immunisation even more convenient because you don’t even have to get sick the first time around while your antibodies do their work. Vaccines carry inactive bacterial toxins, killed microbes, parts of microbes, and weakened microbes. Basically, enough ‘stuff’ to catch your antibodies’ attention, but not enough to make you sick. Nowadays, instead of actually having chicken pox, kids often get the vaccination, therefore avoiding the…

Transplanting organs is a complex process, although it can give a new lease of life to recipients. The kidney is the most frequently transplanted organ, both in the UK and around the world. However, there is a discrepancy between the number of patients waiting for a transplant and the number of available organs; only around one third of those waiting per year receive their transplant. The number of patients registered for a kidney transplant increases each year, and has risen by 50 per cent since 2000. Kidney transplants come from two main sources: the living and the recently deceased. If a healthy, compatible family member is willing to donate a kidney, they can survive with just one remaining kidney. In other cases, someone else’s tragedy is another person’s fortune. For…

Rheumatoid arthritis is a chronic and progressive disease. Through inflammation throughout the connective tissues of the body, it causes irreversible damage to joints. The disease develops when a person’s body generates an autoimmune response – a mistaken immune system reaction against the body’s own tissues – that attacks its joint components instead of invading organisms. As of now, scientists are unsure of what instigates the autoimmune response, but it is thought that it involves a body’s genetic susceptibility to certain viruses. Regardless, once activated by such a cause, a series of immune system reactions proceed to cause unwanted/abnormal levels of inflammation and tissue/bone destruction. Inflammation is caused by a heavily abnormal interaction between B-cells and T-cells (see ‘Development of the condition’ boxout), a process that causes a variety of proteins,…

Medical science has produced some incredible solutions to challenging problems over the decades, from antibiotics to fight bacterial infection, to imaging technologies to look inside patients without using a knife. It’s hard to predict what will happen next, but science has recently opened some really exciting doors to the future of medical treatment. Medicine is no longer just about biology and drugs. Computing, engineering, nanotechnology, quantum physics, and many more disciplines are leaking over into medical tech and providing brand new solutions to age-old problems. In the hospitals of the future, augmented reality could allow surgeons to see through their patients, and contact lenses could monitor blood sugar for diabetics. Prosthetic limbs linked directly to the nervous system could allow amputees to move and feel just by thinking, and 3D…

The brain itself may not have any pain-sensitive nerve receptors, but that doesn’t mean the inner head can’t experience pain… as anyone who’s had a headache will know. The most common form of headache is the tension headache. When the muscles in your body stay semi-contracted for a period of time – for example, when we are feeling stressed and don’t seem to be able to relax – this is known as muscle tension. Such tension in the meninges (the membranes that help protect the brain), or the face, neck and scalp muscles activate the body’s pain receptors, sending impulses to the brain’s sensory cortex and signalling pain and causing a headache. More frequent in women than men, the primary tension-type headache manifests itself as a dull ache across both…

Through the action of the thrombin system, coagulation of the blood occurs instantly at the location where there is a cut or other injury to the skin. The blood clot, which consists of a combination of cellular platelets and sticky strings of fibrin, forms a plug in the damaged blood vessels. The clot stops blood from freely flowing out of the body and at the same time allows the blood to continue circulating. As the skin heals, plasmin enzymes break down the webs of fibrin and the clot is eventually dissolved into the body. Clots can also form in blood vessels due to inactivity, old age, obesity, smoking, poor diet or during pregnancy. This condition is known as thrombosis and can lead to an embolism. Formation of a blood clot…

Contrary to almost a hundred years of bacteria being treated as something that must be eradicated – typically by using antibiotics – modern evidence has demonstrated that actually many bacteria are essential to humans and our daily functions. The combination of these bacteria, which can be found throughout the body, is referred to as the human microbiome – encompassing all manner of microbes and their genetic elements. One notable example of these tiny organisms is Lactobacillus, a genus common in the human gastrointestinal tract known to produce a lactic acid environment that inhibits growth of some harmful bacteria. There are also various strains of Bifidobacterium, which aid the decomposition of carbohydrates and proteins. Importantly, while research has confirmed many members of the microbiome do indeed aid bodily functions, additions included…

Chickenpox is a strain of the Varicella zoster virus, which many of us have experienced during our youth. Most prominent in children under ten, the virus is contracted through coughing and sneezing or transferred on shared objects, which makes schools a prime location. The most famous symptom is the appearance of small itchy red spots, which vary in size from 10-20 millimetres (0.4-0.8 inches) across. The extent can vary but in most cases they cover the face, arms, legs, stomach and back. These develop into fluid-filled blisters and are often accompanied by a fever. The blisters burst, scab over and fall off within a few days, but new waves of spots can emerge to replace them; it usually takes one to two weeks for the body to regain control. Chickenpox…

Gorging on a rich, moist piece of chocolate cake is a guilty pleasure for many, but people with diabetes have to think twice before taking a bite. Diabetes is a long-term medical condition where the body can’t process sugar in the bloodstream properly, so sweet treats can be dangerous for more than just their waistline. Sugar in the blood comes from what we eat and drink and is regulated by the hormone insulin, which is produced by the pancreas. This organ is about 15 centimetres long and located behind the stomach. The pancreas mainly secretes digestive enzymes, but a small part produces hormones. Insulin is produced by beta cells, which are clustered in groups called the islets of Langerhans (named after the scientist who first described them). In diabetes, the…

Chances are most of you reading this aren’t sitting or standing properly. Students and office workers know only too well how easy it is to slip into a slouch while spending all day working at a desk. This prolonged poor posture puts stress on the neck, shoulders and spine, contributing to problems such as postural hunchback and spinal misalignment. Good posture ensures that you can stand, sit or lie down in positions that put the least strain on your body’s muscles and ligaments. A quick way to check your posture is to make sure your earlobes are aligned over the middle of your shoulders, your shoulders are in line with your hips, and your hips are directly above your knees and ankles. This correct positioning may take some practice, but…

There are thought to be over 200 different types of cell in the human body, each specialised to perform a particular function. Despite these specialisms, their basic underlying biology is the same. Cells contain a nucleus, which houses the 46 chromosomes, containing the complete set of instructions to synthesise all of the proteins found in the human body. Depending on the type of cell, different genes are switched on and off, determining which proteins the cell will produce. Proteins for use inside the cell are created on ribosomes in the cytoplasm. The ribosomes read the genetic message and assemble the corresponding protein using amino acids as building blocks. Proteins to be exported from the cell – for example, antibodies or digestive enzymes – are constructed within a series of membranes.…

Brand new infants spend around 16 hours a day in the land of nod. At first they wake often to feed, but by the time they are 12 weeks old and weigh on average 5.7 kilograms they begin to sleep for longer periods. Like adults, babies cycle through four sleep stages. They begin with the lightest dozing before a gradual drop into the deepest slumber, and this rhythm starts when they are still in the womb. Between these cycles they go through phases of rapid eye movement (REM) sleep, spending up to half of their sleep time dreaming. Early work suggests that sleep is important for consolidating learning and for brain plasticity. In other words, it helps with the strengthening and pruning of connections between different nerve pathways in the…

CT Computed tomography (CT) scans use X-rays to build a three-dimensional image of the brain. The radiation travels at different speeds through different tissues, allowing a density map to be produced. It provides purely structural information and is useful for identifying tumours. PET Positron Emission Tomography uses safe radioactive isotopes to measure brain activity. By labelling oxygen or sugar with radioactive tags, blood flow in the brain can be monitored. The tags emit low-energy radiation and as blood is diverted to active regions of the brain, the emissions pinpoint the locations. fMRI Functional Magnetic Resonance Imaging detects the amount of oxygen present in the blood, allowing brain activity to be mapped. When regions of the brain become more active, their demand for blood rises and they light up on the…

There are two major parts to the human skeleton: the axial bones and the appendicular bones. The axial bones form the central core of the skeletal system, including the skull, spine, rib cage and pelvis. These bones have a protective role, supporting the central nervous system and protecting the vital organs from damage. The appendicular bones are attached to this central support, and include the bones of the arms and legs. Their major function is movement, providing rigid jointed structures onto which the muscles are attached. The skull The skull is constructed out of 22 plates of flat bone, 21 of which are permanently fused together. The other is the mandible, or jawbone. They are made from a thick layer of organised cortical bone, sandwiched around a centre of spongy…

Your cells work best when the temperature inside your body is 37 degrees Celsius (98.6 degrees Fahrenheit). Thermoregulation is a homeostatic function that enables you to maintain this core temperature independent of how hot or cold your surroundings are. Humans are able to regulate body temperature via a combination of internal processes and external actions. The latter includes behavioural responses, such as heading for shade when we’re exposed to too much Sun. If that doesn’t help, the body also has a number of automatic responses that help regulate temperature. The main organ involved is the skin, which is controlled by the autonomic nervous system. When your surroundings heat up, the brain triggers a series of chemicals which tell your blood vessels to dilate (widen). This not only brings warm blood…

A muscle contracts when a fibre is kicked into gear as tension is put upon it. Myofibrils, which are found within a fibre, are made up of actin and myosin. When these two threads join the myofibril shortens, or contracts. If you straighten your arm, keeping your palm facing up, and measure the length of your bicep muscle, you’ll find it will become a lot smaller if you curl your hand towards the shoulder. There are multiple types of contractions, though. Isometric contractions occur when the angle of the joint or length of muscle do not change, for example holding a dumbbell at arm’s length and fighting the resistance. Such exercises are usually adapted to try and increase strength. Isotonic contractions are the opposite and also more common, such as…

The red blood cells that carry oxygen around our bodies travel through blood vessels suspended in fluid known as plasma. It moves through vessels at such pressure that plasma can leak into the tissues. The lymphatic system helps remove it from the tissues and return it to the circulation. The lymphatic system is similar to the circulatory system, in that it is composed of a series of vessels, found mostly in the skin and around internal organs. But the tubes do not make a circuit and there is no pump. The fluid, known as lymph, relies on the contraction of nearby muscles to return to the circulation at the subclavian veins near the collarbones. The lymphatic system is also a transport route for the immune system. At intervals along the…

Healing can be defined as the restoration of injured tissue back to usual function. There are two main ways in which tissue heals; regeneration and repair. Healing involves the removal and replacement of damaged tissue, and most organs will use both methods to fix damage – although cardiac muscle cells and neurons are examples of cells that cannot use regeneration. Regeneration is when cells replicate within the same tissue mass that was damaged. These then replace the cells that have been damaged or died. Most cells in the body can repair damage in this manner, but the surrounding collagen network must remain in good condition for this to be able to occur. Repair takes place when the damaged tissue cannot replicate cells of the same type, and scar tissue is…

The common cold is a viral infection that attacks the upper respiratory tract, including the nasal cavity, the pharynx (back of the mouth) and the larynx (voice box). Every child can get up to 12 colds a year, and in adulthood we continue to get them on a regular basis. The symptoms of a cold are sneezing, a runny nose, a sore throat and nasal congestion. Young children can also run a high temperature. In the first three days, the cold is highly contagious and is spread to anyone who inhales or touches anything contaminated by the virus. A cold lasts about a week, although a cough can persist for several days afterwards. Rhinoviruses, coronaviruses, coxsackieviruses and adenoviruses are just some of the many different types of cold viruses. These…

Body fluids Blood, saliva, semen and breast milk can all carry disease Liquids provide an excellent way for pathogens to travel from one place to another. Precautions are always taken when dealing with body fluids in hospitals and labs, because contaminated body fluids can transmit diseases like mumps, hepatitis and HIV. Food and drink Contaminated food and drink carry pathogens into the gut The acidity of the stomach provides some protection against infection, but it can’t stop everything. Pathogens enter through the mouth, and either set up home in the digestive tract, or move into the body through its walls. Skin to skin contact Some infections are quickly spread by direct contact Chickenpox, cold sores, head lice and warts can all be transmitted by touching someone with the infection; the…

Just one mosquito bite is enough to kill you in some parts of the world. Inside the midgut of Anopheles mosquitoes, gametocytes from the plasmodium parasite mature and combine. These are the equivalent of human sperm and eggs, and the result is hundreds of newly formed parasites ready to infect their next victim. The parasites migrate up to the mosquito’s salivary glands, and when it feeds again they enter the human bloodstream. They infect cells in the liver and begin to divide, before spreading back into the blood. As they continue to grow, the cells split open, releasing even more parasites and causing havoc for the body. Malaria parasites can’t reproduce without both mosquitoes and humans, giving us a tantalising opportunity to eliminate them. One idea is to genetically modify…

Asthma is caused by the sudden contraction of smooth muscles in the airways of the body. This is normally due to unusually viscous mucus being produced in abundance in the bronchial mucous glands. One of the primary causes of asthma is the narrowing of bronchial tubes because of inflammation. Asthmatics are overly sensitive (hyperreactive) to stimulants in the environment that can cause the bronchial muscles and tubes to contract. Tubes become irritated and swollen, in turn producing excess mucus and blocking the flow of air. While asthma is often hereditary, it can also be acquired through prolonged exposure to substances such as solder and sulphite. In severe asthma attacks, the accumulation of additional mucus from the bronchial tree can also inhibit airflow within the airways, making it more difficult for…

Skin grafting is a medical procedure where a portion of skin is removed and stitched onto another part of the body. There are many cosmetic and medical reasons why this might be necessary: serious burns, surgery, tattoo removal and some medical conditions (skin cancer or diabetes, for example) might all necessitate skin grafting. Autografts are skin grafts taken from the patient’s own body, usually the buttocks, neck or back of the arm. Depending on the size of the area that it’s removed from, it’s then stitched or stapled closed again and the new skin applied to the injured area. Allografts and xenografts, meanwhile – taken from other humans and animals, respectively – are temporary grafts. But perhaps most interesting is the artificial ‘skin’ called Integra, made of animal collagen that…

Anaphylaxis, otherwise known as anaphylactic shock, is a potentially deadly allergic reaction. It can be brought on by any number of conditions, but it’s usually triggered by ingesting food that the person is allergic to – such as nuts, eggs or shellfish, being stung by an insect, or coming into contact with a particular drug or chemical. Signs someone is experiencing anaphylaxis include respiratory difficulties, dizziness, red rashes and other skin changes, plus a form of subcutaneous swelling called angioedema. Anaphylaxis is essentially an overreaction to a toxin, such as wasp venom, or a bad reaction to a substance that the body perceives as a threat. When the substance (known as an allergen) enters the body through the skin, inhaled into the lungs or ingested through the mouth, the reaction…

Guglielmi detachable coil These platinum wires are fed into small aneurysms (enlarged arteries) within the brain via an artery in the groin. Once coiled up inside the aneurysm sac, they stop blood flow and thus prevent bleeding. Surgical microclamps These small clamps can be used to grab tumours to help the surgeon dissect them away from surrounding structures. High-performance microscope These powerful microscopes with bright lights enable surgeons to operate through tiny incisions or keyholes, which prevents damage to those important surrounding structures. Navigation systems This computer system merges pre-operative CT and MRI scans with intraoperative information gathered from lasers and infrared. The result is a ‘map’, which surgeons use to navigate to difficult-to-find tumours. Burr-hole drill Although not used much any more in the Western world, a drill is…

Bacteria are vital to our survival. They help us digest food, keep our skin clean from more harmful organisms and help develop our advanced immunity while we’re young. However, they can also cause disease, which ranges from simple eye infections to life-threating illnesses. Antibiotics were discovered in 1928 and almost overnight they changed what were once fatal diseases into trivial infections. But despite effective medication, bacteria are smart and know how to fight back. They can change their shape, hide in plain sight and alter their surface appearance. After an attack from antibiotics, the few bacteria left over are the strongest of the bunch and are resistant to the current crop of antibiotics; this is true survival of the fittest. The lasting bacteria then multiply, become stronger and are able…

The 2014 Ebola outbreak in West Africa caused thousands of deaths across Guinea, Liberia, and Sierra Leone, and led to many people feeling confused and scared about this infectious and often fatal disease. Ebola virus disease (EVD) is spread via contact with the blood, bodily fluids and organs of an infected person or animal. A person only becomes infectious once their symptoms start to show, which is usually two to 21 days after infection. The initial symptoms are a sudden onset of fever fatigue, muscle pain, headache and sore throat, followed by vomiting, diarrhoea and rashes, eventually leading to impaired kidney and liver function, as well as internal and external bleeding. There have been many outbreaks since the disease first appeared in 1976 – when it killed nearly 300 people…

Checking your own pulse is a good way to keep track of your heart rate. Monitoring it while you’re resting is the best way to get an accurate reading, as rhythm can increase at different times during the day, especially when you’re exercising. It’s possible to check your radial pulse on your wrist or on your neck. This is because arteries pass close to the skin in these areas. To take your wrist pulse, simply turn over one of your hands so that the palm is facing up. Now place the index and middle finger from your other hand below the crease of the wrist, in line with the base of your thumb and next to the tendon. Use gentle pressure and feel carefully for a beating pulse. If you’re…