Tag: organs

Posted in Psychology & Medicine

Viscera: Brain

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

(NB: I have written MANY ARK posts about the brain and all the delightful ways it screws up. Some of them are probably the most interesting posts on my blog. Please click the hyperlinks to check out the various related articles! 😀 Alternatively, here’s a convenient list: https://jineralknowledge.com/tag/brain/?order=asc)

Among the many organs of the human body, no organ comes close to the magnificent complexity that is the brain. The brain acts as the command centre of the body. It receives massive amounts of information through the various senses, processes it and sends out electrical signals to control how the body operates. Not only does it control “basic” functions such as movement of muscles, controlling organ functions and regulating homeostasis, it is also responsible for the so-called “higher functions” such as consciousness, emotions and cognition. It is the true seat of the mind and soul.

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The brain is the only major visceral organ not located in the trunk (body). It is enclosed in the cranium of the skull, which acts as a protective casing. Because it is a closed box, even a small increase in volume (such as due to a bleed or a tumour) can cause extreme pressures to build, causing severe problems. The entire brain and spinal cord are bathed in a fluid called cerebrospinal fluid (CSF), all enclosed by a sheath made of three layers (dura, arachnoid and pia maters). The brain sends out nerves to the rest of the body, which act as electrical wiring transmitting signals. These include the cranial nerves and the spinal cord, which leaves the bottom of the skull down the spine. The spinal cord branches off into many nerves that supply every nook and cranny of the body. The brain itself is made up of two large hemispheres, which are connected by a bridge called the corpus callosum. Despite popular belief, the actions of the two hemispheres are much more complicated than “analytical vs. creative”. The brain also encompasses the cerebellum (the small stripey structure at the back), which controls coordination and speech articulation, and the brainstem, which is involved in autonomic control of life-sustaining functions such as breathing, and also the source of the cranial nerves.

In the last century, scientists have learned that specific parts of the brain play a specific role. This thought started with the field of phrenology, where small areas of the brain were mapped to a certain mental faculty, such as love, wit or destructiveness. Although this turned out to be complete hokum, the idea stayed and we now know the actual functions of each part of the brain. The brain is broadly divided into four lobes: frontal, parietal, temporal and occipital. The frontal lobe is the domain of thought, personality, motor function and other higher functions. The parietal lobe is related to spatial awareness and sensory functions (such as touch). The temporal lobe is linked to hearing, comprehension of language and storing new memories. The occipital lobe is primarily associated with vision. The brain can then be subdivided into more focussed areas, such as Broca’s area that governs speech and Wernicke’s area that governs listening. It should be noted that the four lobes only describe areas on the surface of the brain (cerebral cortex) where the higher functions belong. The inside of the brain is just as complicated and has many different parts, such as the hypothalamus that is involved in homeostasis, and the hippocampus that converts short-term memories into long-term memories.

How does a lump of cells weighing around 1.5kg produce such wondrous abilities such as philosophical thought, deduction, emotions and calculation? The truth is that we still do not know how the brain functions exactly. However, we know that the brain is composed of a large number of neurons (nerve cells) – about 100 billion of them. These neurons connect to one another via a synapse, which is a gap between two nerve cells where neurotransmitters travel to and fro (allowing electrical impulses to jump from one neuron to another). Using these connections, neurons form an unbelievably intricate and complex network of electrical activity. Because one neuron can connect to many more others, the number of synapses is estimated to be around 100~1000 trillion – significantly more powerful compared to any computer in the world. The number of synapses directly correlates to intelligence and it seems intellectual activities such as reading a book increases the number of synapses in the brain. We have yet to understand exactly how the brain uses this incredible computational power to produce cognition and self-awareness.

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(Video of neuronal activities in a zebrafish brain)

Because the brain uses electrical impulses for most of its functions, a common abnormality that is seen with the brain is when the electrical activity becomes disorganised and out of control – a seizure. This abnormal electrical activity may be due to a focal problem such as a tumour, or a generalised misfiring of neurons or altered regulation of electrical activity. When a seizure happens, the disorganised activity results in the brain not being able to function normally. For example, the most common consequence is a fit (tonic-clonic seizure) where every muscle spasms out of control, because the muscles are overloaded with chaotic signals. Focal seizures can cause fascinating symptoms depending on the location, such as temporal lobe seizures causing religious visions (hallucination). This also disrupts consciousness, which is why most epilepsy patients do not remember the event.

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Posted in Psychology & Medicine

Viscera: Small Intestine

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

Abdominal organs are often grouped into the colloquial term gut. “Gut” also refers to a specific organ – the small intestine (or small bowel). It is an important part of the gastrointestinal (digestive) tract, connecting the stomach to the colon and involved in digesting and absorbing nutrients. The small intestine is extremely long, roughly 7m in an adult. It fits in the abdomen by folding and packing neatly, lying under the liver, stomach and pancreas while being framed by the large intestine. The small intestine is not freely hanging so you cannot just pull it out like a rope. It is connected to the body by a fan-like membrane called the mesentery, which provides blood supply to the gut. The mesentery is attached along one side of the gut the entire way through.

The small bowel is composed of three parts: the duodenum, jejunum and ileum. Although people think digestion mainly happens in the stomach, it is actually primarily performed in the duodenum. The duodenum not only receives liquefied food from the stomach, but is also the place where the pancreas and liver drain digestive juices such as pancreatic enzymes and bile. The enzymes breakdown large molecules like fat, protein and carbohydrates into smaller building blocks, while bile acts like detergent to allow fat to mix better with water (emulsification).

The digested food then travels down the GI tract through a process called peristalsis, where the gut squeezes behind the bolus of food to push it forward, much like squeezing toothpaste out of the tube. The broken down products are mainly absorbed in the second part of the bowel (jejunum) via the walls. The small bowel wall looks like a carpet due to microscopic finger-like projections called villi. Villi allow for a much greater surface area for enhanced absorption. In coeliac disease, these villi are flattened by an autoimmune process and the patient cannot absorb as much nutrients (including vitamins).

By the time the food reaches the ileum, most of the nutrients have been absorbed. The ileum finishes the job by absorbing some extra things like vitamin B12 and bile salts, then sends the food through the ileocoecal valve, which is the door between the small and large intestine.

The small bowel is used by various cultures for culinary purposes. Other than simply eating the bowel itself after cooking, it is often used to pack different meats or other food inside, such as sausages or soondae (Korean sausages, filled with chop sui noodles).

Posted in Psychology & Medicine

Viscera: Stomach

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

The stomach is an organ that is well-known, so much so that the abdomen is often colloquially referred to as “the stomach”. It is an important organ that is part of the digestive tract, responsible for breaking down food that comes in through the mouth then the oesophagus. The stomach lies centrally and just below the sternum, surrounded by the liver on the right, spleen on the left and pancreas below.

Food is broken down primarily by the mouth via chewing. Once you swallow, the food is squeezed through the oesophagus until it is dumped into the stomach. The stomach produces a very strong acid (hydrochloric acid, pH 1~2), which dissolves the chewed food. It enhances this process by contracting its powerful wall muscles to churn and mix the food. Once it is nicely dissolved into a thick liquid, it releases it into the duodenum (the first part of the small intestine).

If the stomach uses strong acid to breakdown food, which is organic matter, how come it does not digest itself? This is because the lining of the stomach is coated with a substance called mucin which protects the stomach wall from being corroded by acid. However, the stomach is not perfectly safe from the acid it produces. If the stomach becomes inflamed, the production of mucin and self-repair process of the stomach is limited and acid begins dissolving the stomach lining. This causes peptic ulcers to form, which is essentially a hole in the lining of the stomach, causing severe abdominal pain and occasionally bleeding. Peptic ulcers are commonly caused by an infection by a bacteria called Helicobacter pylori. It may also be caused by severe stress and anger or medications such as NSAIDs (non-steroidal anti-inflammatory drugs, e.g. ibuprofen, diclofenac/Voltaren).

Posted in Psychology & Medicine

Viscera: Thyroid

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

There lies a small, butterfly-shaped organ called the thyroid gland in your neck, just in front of your windpipe above the clavicles. The thyroid may not seem important given its small size, but it has the important function of controlling the body’s rate of metabolism. Metabolism is a group of chemical reactions your body relies on to function as a lifeform. Chemicals such as glucose are processed by various enzymes – biological catalysts that encourage chemical reactions – and converted in to fuel (such as ATP) that cells can use for numerous bodily functions. The thyroid produces the thyroid hormones, thyroxine and triiodothyronine, to fine-tune the rate at which these reactions occur.

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To see the function of the thyroid gland, we can look at two types of diseases: hyperthyroidism and hypothyroidism.

In hyperthyroidism, the thyroid is overactive and produces too much thyroxine. This causes the body’s metabolic rate to speed up, causing increased heart rate, weight loss, sweating, tremors and sensitivity to heat. Depending on the cause, the eyes may be affected as well, causing them to protrude forwards, giving a rather scary appearance. This disease may happen for various reasons, but the most common cause is Grave’s disease, where antibodies lock on to receptors in the thyroid to stimulate thyroxine production, much like a stuck key on a keyboard.

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Hypothyroidism is the direct opposite syndrome caused by an underactive thyroid. This causes a reduction in metabolic rate, leading to weight gain, tiredness (due to lack of energy), slow heart rate and cold intolerance. It can also be caused by an autoimmune disorder (called Hashimoto’s thyroiditis), or more commonly due to iodine deficiency, as the thyroid uses up iodine to produce thyroid hormones.

Both diseases may cause the thyroid to grow to an abnormal size, which is called goitre (seen as a large neck lump). The treatment is usually adjusting the total level of thyroid hormone produced by removing parts of or all of the thyroid, or replacing thyroid hormone if needed via medication.

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Because the thyroid uses iodine to make hormones, thyroid diseases such as thyroid cancer can be treated using an interesting method. If you inject radioactive iodine into the patient, it will make its way to the thyroid gland, which actively collects the iodine from the blood. Overactive thyroid tissue (such as in Grave’s or thyroid cancer) take up iodine at a faster rate. The iodine then delivers a focussed dose of radiation to the thyroid, leaving the other tissues in the body unharmed. This method is used for both first-line treatment of hyperthyroidism and to clean-up remaining cancer cells after thyroid surgery.

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Posted in Psychology & Medicine

Viscera: Kidneys

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

Despite being a vital organ that one cannot survive without, the kidneys are not very famous to the general populace. Not many people know what the kidneys do, let alone where exactly they lie in the body. The kidneys (of which there are two) are the major excretory organs of the human body. They are found in the back of the abdomen (in an area called the retroperitoneal space), tucked under the lower three ribs below the diaphragm. This is higher than where most people think the kidneys lie, because the abdomen extends quite high into the ribcage, as seen from the location of the liver.

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The kidneys undertake many functions, but they can broadly be grouped into three groups: making urine, filtering blood and maintaining homeostasis.

Although the organ associated with urine is the bladder, it only stores urine, which is made by the kidneys and sent to the bladder via the ureters. Urine is the body’s main way of disposing excess water, salt and other byproducts such as urea. The kidneys fine-tune how much water we lose to urine depending on how much water is in the body. For example, if you drink a lot of water, the kidney senses the blood vessels being dilated and the blood being diluted, then allows more water to leave the body. Conversely, if you are dehydrated, the kidney does everything in its power to hold on to as much water as possible, resulting in concentrated urine.

The kidneys literally act as filters for the blood using a fine, intricate network of sieve-like blood vessels. These vessels have walls that have various sized holes that causes water and small molecules to pass into the kidney, while leaving large proteins in the blood. The filtered blood (containing water, various electrolytes and other metabolites) travel through a pipe network called nephrons, which reabsorb things the body needs (like water when you are dehydrated or salts like sodium), while leaving toxic products like urea and various medications.

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Lastly, the kidneys maintain homeostasis (the status quo of the body) in various ways, such as fine-tuning the water and salt levels of the body. If you have renal failure where your kidneys do not function properly, you will retain too much water and may suffer a build-up of potassium, which can cause fatal changes in your heart rhythm. It is also involved in controlling the acidity of your blood and your blood pressure, through very complex mechanisms.

One way kidneys are famous is that they are popularly mentioned in the context of organ transplants. If you have renal failure, you may be able to get a kidney from a healthy, live donor as you can live with one kidney. When you take out a kidney from a healthy person, the remaining kidney will grow in size to compensate for the other kidney, while the transplanted kidney will go on to save the patient’s life by doing the many jobs mentioned above.

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Posted in Psychology & Medicine

Viscera: Spleen

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

The spleen is one of the lesser known organs of the human body. If you asked the lay person, they would not know what the spleen does, let alone where it is. The spleen is a solid organ that lies in the left upper corner of the abdomen, tucked under the left diaphragm (opposite to the liver which lies under the right diaphragm). Its functions are mainly related to blood, such as removing old red blood cells (sequestration), storing platelets in case there is an emergency bleeding, making antibodies and releasing lymphocytes (type of white blood cell) to help fight infection and in times of need, creating red blood cells. Red blood cells are usually made in bone marrow in adults, but if the bone marrow fails (e.g. leukaemia), the spleen and liver can step in to create vital blood components (extramedullary haematopoiesis).

As most of the functions of the spleen are not technically necessary to sustain life, it can be removed without significant consequences. The spleen is sometimes removed when a patient has severe thrombocytopaenia (lack of platelets) or when the spleen is damaged by trauma. Because it is a solid organ, trauma to it such as a kick to the stomach can cause it to rupture (i.e. break in to pieces). Splenic rupture can cause life-threatening haemorrhage (bleeding) and may not be evident in trauma cases. A person without a spleen needs regular check-ups and immunisations to help fight infections as they have a weakened immune system.

The role of the spleen was a mystery for thousands of years and thus various cultures tried to explain various medical phenomena using the spleen. The ancient Greeks thought the spleen produced black bile, which was associated with melancholy. The spleen was also associated to anger by the English and laughter by the Talmud.

Posted in Psychology & Medicine

Viscera: Liver

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

The liver is the second largest organ (next to the skin) in the human body, weighing about 1.4~1.6kg. It is found tucked under the right side of the ribcage, underneath the 5th to 10th rib in height and almost spanning the entire width of the trunk. When enlarged, the liver grows downward and can be felt in an abdominal exam (sometimes it is so large that it covers most of the abdomen).

It is a vital organ with many life-sustaining functions (hence “liver”) such as building various proteins, breaking down toxins, storing sugars in the form of glycogen, decomposing red blood cells and producing bile. The liver metabolises (breaks down) a large proportion of medications and drugs as it treats them as “toxins”. For example, the enzyme alcohol dehydrogenase breaks down alcohols into acetaldehyde, which causes hangovers and liver damage. Many Asians have a variant of this enzyme that is extremely efficient, causing a massive build-up of acetaldehyde when they drink alcohol. This is responsible for the so-called “Asian flush”.

Liver disease is associated a myriad of symptoms. The classic sign of jaundice (yellow skin and whites of eyes) is caused by obstruction of bile flow. Because of its location, pain in the right upper quadrant of the abdomen is commonly seen. As the liver is involved in synthesising various proteins, signs such as ascites (fluid in the abdomen) or bleeding may occur when the liver is damaged. A syndrome called portal hypertension is commonly seen in chronic liver disease such as cirrhosis as a major vein to the liver is blocked. This can cause an enlarged spleen, oesophageal varices that can bleed, ascites and prominent veins radiating from the belly button (caput medusae).

An interesting property of the liver is that it can regenerate at an amazing rate. A liver will regenerate to its original size even when a half of it is cut out (this is how live donor liver transplants work). What is more interesting is that the ancient Greeks probably knew of this fact as well. In Greek mythology, the gods punish Prometheus for bringing fire to humans by chaining him to a mountain and commanding an eagle to peck out his liver. The liver would then regenerate overnight and the eagle would return every morning to eviscerate him, causing him eternal anguish.

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Posted in Psychology & Medicine

Viscera: Heart

Posted on by Jinavie

(Learn more about the organs of the human bodies in other posts in the Viscera series here: https://jineralknowledge.com/tag/viscera/?order=asc)

Out of the numerous organs found in the human body, the heart is perhaps the most well-known. This is probably because since the dawn of time, man has put his hand on his chest and felt the rhythmic pounding of his heart – a reminder that he is alive. The function of the heart is to pump oxygenated blood from the lungs to the rest of the body via the circuit of blood vessels (vascular system).

The heart relies on electricity to pump blood in a rhythmic, autonomous way. Because of this property, a heart will beat on its own even if you took it out of the human body. Every muscle in the human body requires an electrical impulse for it to contract. This is also the case in the heart, but unlike the skeletal muscle in other parts of the body which receive their impulses from the brain and spinal cord, the heart has its own source of electricity.

The heart has a small group of pacemaker cells in the right atrium called the sinoatrial node, which always fires electrical impulses at a set rate and rhythm (sinus rhythm). The SA node will do this without any instruction from the brain. The impulse from the SA node spreads throughout the atria of the heart, causing the atrial muscles to contract simultaneously to squeeze blood into the ventricles. The impulses then reach the atrioventricular node, which filters the signals and sends a stream of electricity through a wiring system known as the Purkinje fibres. These fibres act like a high-speed internet cables running down the centre of the heart, sending rapid signals through out the ventricles to induce a strong, cooridnated contraction in both ventricles. This causes blood to be forcefully squeezed out through the two outlet vessels of the heart: the pulmonary artery (to the lungs) and the aorta (to the rest of the body).

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Although the SA node is completely autonomous, it can be controlled using hormones, nerve signals and medications. For example, adrenaline will speed up the rate the heart beats at while massaging the carotid arteries in the neck will slow the heart down.

One thing people wonder about is what the doctors listen to when they put a stethoscope to a patient’s chest. Everyone knows the heart makes a rhythmic “lub dub” sound as it beats away, but what information could that give away? A doctor can gain much information about the heart from a cardiac examination by taking the pulse and blood pressure, but listening to the heart (auscultation) may reveal a medical sign known as a murmur. A murmur is any added sound other than the normal “lub dub” sound of the heart. For example, a heart with aortic stenosis may give the sound “shhhhhhh” as if it was giving off static. This sound is produced when blood flow in the heart is turbulent and not smooth. This may be for a number of reasons but the most common reason is because the valves of the heart are not functioning properly. For example, the valve between the left atrium and left ventricle may be leaky (mitral regurgitation) or the valve at the start of the aorta may be stiff and narrowed (aortic stenosis).

By carefully listening to the sound the heart makes, an experienced doctor may pick up on such structural abnormalities even without the use of fancy medical imaging technologies.