Tag: metabolism

Posted in Psychology & Medicine

Heartbeat Hypothesis

Posted on by Jinavie

When you compare the lifespans of mammals, it is common to see that larger animals live longer than smaller animals. Another observation is that smaller mammals almost always have a much higher basal heart rate. For example, a mouse has a basal heart rate of about 600 beats per minute (bpm), but only lives 3 years on average. An elephant has a basal heart rate of 30bpm, but lives up to 60 years. If you do the maths, it turns out that the total heartbeats per lifespan is surprisingly similar between the two species (0.94 billion beats). It has been noted that amongst mammals, there is a clear inverse correlation between heart rate and lifespan.

This observation led to the popularisation of a factoid that the heart can only beat a limited number of time before it eventually fails.

Unfortunately, there has been very limited evidence to support this theory. It is medically true that a heart under more strain for a long period of time, such as with high blood pressure, has a tendency to develop more diseases such as cardiomyopathy and heart failure. However, there are too many other variables to consider. For example, exercise temporarily raises your heart rate but improves your overall cardiovascular health and lowers your basal heart rate.

It is much more likely that death from aging is related to the basal metabolic rate. Metabolism produces free radicals, which are elements with free electrons that can damage cells. Therefore, the higher the metabolic rate (such as in mice), the faster the damage accumulates and results in death.

That being said, consider the other implication of the so-called heartbeat hypothesis. Our hearts beat faster in response to many stimuli: exercise, excitement, fear, anxiety, fun and love. If the hypothesis is true, that would mean that intense emotions could make our hearts tire out faster and hasten our inevitable demise.

Could falling in love be detrimental to our physical health? Thankfully, this has never been shown to be true, with many studies showing that happily married couples tend to outlive single people.

Even if it were true, would you give up on the idea of love to live a few more years? What kind of life would be worth living without any highs or lows? Perhaps when we fall in love, experience heartache or become overwhelmed with happiness, we are making the voluntary choice of quality, not quantity, of life.

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: 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 Science & Nature

Water Bear

Posted on by Jinavie

A water bear, also called a tardigrade, is actually an insect and not a bear. The nickname is due to its slow, bear-like gait. It ranges in size from 0.1 to 1.5mm and resembles a short caterpillar with eight legs.
The reason for the water bear’s fame is its amazing survivability. In short, a water bear can live anywhere.

Water bears are capable of cryptobiosis. This can be seen as an extension of hibernation and it is an organism’s ability to lower its metabolism to near-death rates in order to survive a harsh environment. In this state, a water bear can survive for indefinite amounts of time.

Why is cryptobiosis useful? The answer can be found from the water bear’s natural habitats. The water bear is found on the highest point of the Himalayas, the deepest oceans, hot springs and virtually any location from the North Pole to the South Pole. It can survive temperatures from 151°C to minus 273°C, the intense pressures in deep seas and even vacuum states.
Furthermore, water bears can survive in space. A recent experiment by NASA on the International Space Station found that not only can they live in space, but they also mated and laid eggs that later hatched. They can even survive heavy doses of radiation and toxic chemicals.

Ergo, if a cockroach can survive a nuclear war, water bears can survive even if the Earth was split in two. If we took a leaf out of the water bear’s book and lead a slower life, could we live a longer and happier life?

Posted in Science & Nature

Caffeine

Posted on by Jinavie

Coffee is a magical drink that can make a busy person’s morning. Coffee’s stimulant effect is due to the substance called caffeine. Caffeine can make the mind more alert and drives away sleepiness for about 3~4 hours. This is why students studying for an exam or people working late love to drink coffee.
There are many students who say they do not like coffee and drink energy drinks instead. These drinks tend to advertise that the substances guarana and taurine give energy, but an interesting fact is that guarana is just a plant where caffeine is extracted from. Taurine has many beneficial actions in the body, but has no effect as a stimulant. Therefore, an energy drink is simply made of caffeine and sugar and holds no advantage over coffee.

Although caffeine is beneficial in moderate amounts, excessive consumption leads to adverse effects. A normal adult can handle up to about 400mg of caffeine. Any more and they could suffer from anxiety, insomnia, headaches, dehydration, increased urination, fever, rising heart rate, stomach pain, nausea and many other symptoms. As everyone’s rate of caffeine metabolism is different, only they know how much caffeine they can consume. Furthermore, the more coffee or tea you drink, you build a tolerance towards caffeine and can consume much more without adverse effects.

The following is a list of the caffeine content in common drinks and foods:

  • Drip coffee(200ml): 150mg
  • Espresso(50ml): 100mg (this is because the cups are small, the concentration is about 3 times that of drip coffee)
  • Caffeine tablet: 100mg
  • Energy drink(250ml): 80mg
  • Coca-cola(600ml): 60mg
  • Chocolate(250g): 60mg
  • Black tea(170ml): 50mg
  • Green tea(170ml): 30mg
  • Decaffeinated coffee(200ml): 10mg

However, the best method to drive away sleepiness is by sleeping. If you are tired, the only way to recover is by taking a 30 minute to 2 hour nap, especially if you will be driving or have a night shift.