Posted in Psychology & Medicine

Viscera: Brain

(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: Thyroid

(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

(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

Hypothermia

A person’s body temperature is always maintained between 36.5~37.5°C. This is because enzymes, which are crucial in all physiological reactions in the body, work most efficiently at this temperature. As physiology is essentially a series of chemical reactions, it is heavily dependent on temperature. If the temperature falls, chemical reactions occur slower and vice versa. When body temperature falls below 35°C, metabolism becomes too slow and it poses a risk to the person’s health. This is known as hypothermia.

How does hypothermia affect the body? Hypothermia is categorised into three classes depending on the severity.

  • Mild hypothermia (32~35°C) leads to the slowing of bodily functions, tremors and difficulty in walking. The patient’s speech is impeded and other neurological symptoms such as decreased judgement skills and confusion start to appear. Also, blood pressure, pulse and breathing rate rise.
  • Moderate hypothermia (28~32°C) causes paralysis of muscles and extreme fatigue (they may complain of being sleepy). As blood (carrying heat) is rerouted to major organs, the skin (especially lips and extremities) become white or purple and very cold. Neurological symptoms worsen with amnesia, memory loss, severe confusion and delusion beginning to show. As sustained hypothermia leads to the tremors stopping, one should not take the lack of tremors as a good sign. Heart rate becomes irregular and arrhythmia may occur.
  • Severe hypothermia (20~28°C) leads to chemical reactions becoming so slowed that physiological functions that support life decline dramatically. Heart rate, blood pressure and breathing all lower to dangerous levels and the heart and lungs may stop functioning. As the patient’s major organs begin to shut down, they enter a state of unconsciousness and eventually, clinical death.

As you can see, hypothermia is a highly dangerous situation that can kill. There are some other fascinating facts about hypothermia.

20~50% of hypothermia death cases are associated with paradoxical undressing. This is a strange phenomenon where the person begins to take off their clothes due to confusion and a lack of judgement from the hypothermia. One theory suggests it is related to the cold damaging the hypothalamus (which controls body temperature), causing the brain to think that the body temperature is rising. Whatever the reason, it is extremely dangerous as it worsens the hypothermia.

As explained above, severe hypothermia leads to death. But interestingly, hypothermia also protects organs. This is why organs for transplanting are transported in ice. Similarly, there are examples of people who “died” from hypothermia recovering with no brain damage. Because of this, medical professionals traditionally say: “they’re not dead until they’re warm and dead”. In fact, if there is something wrong with the patient’s circulation and there is risk of damage to their organs (such as in surgery), sometimes the patient’s body temperature is forced down with ice water injections and cooling blankets, known as protective hypothermia.

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