May 14, 2008

Things you really ought to know about the body. MUST READ !!!

How do our eyes work?

There are two types of cells in our eyes sitting on a layer called the retina, that when subjected to light, send a signal to the brain that allow us to interpret what our eyes are telling us. Rods are sensitive to light intensity, whereas cones are sensitive to specific colours. Our eyes work much like a printer; printers use ink cartridges and we use cones to detect only three distinct colours: blue, green, and red. By using different combinations of these three colours, we can produce images of countless shades and colours. In the case of ‘red eye,’ most nocturnal animals have a layer in place behind the rods and cones that reflects the light back out. This provides a greater chance for the light in the eye to be absorbed by the different cells, meaning greater night vision. Humans don’t have this layer. Lights from a camera’s flash, however, are so bright that light reflects off our eyes anyway. The red colour comes from the blood vessels in our eyes that are reflecting the light.

The infamous pirate patch wasn’t simply a scare tactic employed by pirates. They wore the patch in case they ever got attacked at night. The patch was employed to reduce the time it took the pirates’ eyes to adjust to the darkness on deck after being in a lit cabin below. Rods that are subject to high light environments can get exhausted. If suddenly the lights go out, your rods are tired and unable to respond to the low light conditions. The pirate patch ensured that the rods in one eye were spared the onslaught of light, and would be fully functioning under low light conditions. So when attacked at night, instead of waiting a minute or two for their eyes to adapt, pirates would simply run outside and switch the patch to the other eye. Then the eye that was being used was fully functioning and the pirates’ ability to see was normal.

How do allergies work?

Anaphylaxis, or an allergic reaction, is the accentuated response by a person’s immune system to a given substance. This substance can be anything from food, insect stings or bites, to various drugs. The body responds as if this substance (whether harmful or not) is a foreign invader. Upon the first exposure, there is generally a very minor visible response. However, your body is silently producing antibodies, little Y-shaped proteins that will react specifically with this substance should the body be exposed to it again. So when the unsuspecting person is subjected to the substance again, the antibodies bind to it and flag it for destruction using immune cells. Unfortunately, your body releases many chemicals as an attempt to destroy the noxious substance. Probably the most active of these substances is histamine. Histamine binds to smooth muscle in the respiratory and digestive tracts, causing cramping and difficulty breathing. It also opens up small capillary beds throughout the body resulting in water loss to the various tissues. If the pressure in the blood vessels falls enough, the blood supply to the brain can be jeopardized as the body goes into shock. The hypodermic needles that people who are prone to allergies carry contain epinephrine. This is the same drug our body releases when we are standing on the seven-metre diving board, or come face to face with a bear. Epinephrine counteracts the ill effects of histamine, allowing our body to begin to recover.

How does a hangover work?

Hangovers are our body’s way of saying, “Woah, what was that?” The headaches, nausea, and dehydration are all symptoms many of us have experienced, but how does the alcohol do all this? Upon ingestion, alcohol enters the bloodstream directly through the stomach and blocks the brain’s release of vasopressin. Vasopressin is a hormone that works at your kidneys to reabsorb water and prevent it from being sent to the bladder. Blocking this hormone causes us to urinate excessively and become dehydrated. To prevent more water loss, the saliva in your mouth the next morning is notably dry. The headaches are cause by your brain actually shrinking due to water loss, causing the brain to pull on connective tissue holding it to the skull. Different alcohols are actually more adept at causing hangovers. Red wine and dark liquors such as brandy, whiskey, and tequila contain higher concentrations of congeners (by-products of alcohol production), and cause worse hangovers than white wines or light liquors such as vodka or gin. The real reason beer should not be consumed immediately after liquor is the carbonation hastens its absorption, resulting in even higher blood alcohol concentration, eventually overloading our body’s ability to cope with it. The alcohol stimulates acid secretion in the stomach up to a point where damage will be incurred unless it is excreted by vomiting.

Alcohol is metabolized by enzymes into the noxious substance acetaldehyde. Acetaldehyde is converted to acetate via the enzyme glutathione, which is rich in the amino acid cystein. However, when large amounts of alcohol are consumed, the livers supply of glutathione runs scarce and acetaldehyde remains in the body for a longer period of time, causing the hangover effects.

Hangover remedies: Eggs: rich in cystein that could help mop up some left over toxins. Bananas: rich in electrolytes such as potassium that are lost in the urine. Water: try adding some salt or sugar to aid in its absorption.

How can we cope with cold weather?

When we are exposed to cold temperatures, our body goes into a state of ‘life over limb.’ This means protecting vital organs such as the heart and brain. If circulation were to remain normal in a cold environment, as the blood flowed through the arms, hands, and feet, it would be exposed to the cold, decrease in temperature, and then head back to the heart. Cold blood is an issue as it is much thicker than warm blood, which makes circulation around the body more difficult. Cold blood can also cause hypothermia. In fact, hypothermia can occur if the core temperature of the body drops only three degrees. To avoid this, the body redirects most of the blood that would normally be sent to the periphery to the core instead. This has the effect of pooling the warm blood in the middle of the body, saving it from exposure to cold weather. The lack of blood to the fingers is what causes the numbing, weakening sensation. When muscles get cold, they actually lose some of their elasticity and ability to contract efficiently. Additionally, there is decreased delivery of oxygen (energy) to these muscles, which is normally supplied via the blood flowing by. If the cold becomes extreme, frostbite can occur. Blood flow is cut off almost completely, and the fluid that remains in the tissue actually begins to freeze. If prolonged, the lack of blood and oxygen to the area will result in the death of that tissue. Some populations that live in cold environments have adaptations that allow them to maintain their core temperatures while simultaneously keeping their limbs alive and in working order. Their bodies are capable of alternating periods of bloodflow with periods of occlusion (no bloodflow).

Why is hair on our head longer than on our arms?

There are two phases that your hair cycles through over time. The growth phase and the rest phase. During the growth phase new cells are formed within the follicle, which push older cells to the surface. This chain-link effect continues to eventually form the long strands of hair that we see. During the rest phase, however, the shaft of the hair strand breaks completely, the hair falls out, and a new hair has to start growing all over again. Hair on your arms is programmed to enter the rest phase every couple months, which means it never has enough time to grow very long before it falls out. Hair on your head, on the other hand, can grow for years at a time and thus become much longer. In animals that shed, all of the strands are coordinated so they enter the rest phase at the same time, causing the hair to fall off in clumps.

How do hiccups work?

Hiccups can last anywhere from a couple of minutes to a couple of years. The record for the world’s longest hiccup bout is 68 years. Most people hiccup about four times a minute. When we breathe, the diaphragm, a long thin muscle stretched out beneath our lungs, contracts downwards. This effectively decreases the pressure in the lungs and allows air to flow in (inhale). When we expire, the diaphragm relaxes back up, increasing the pressure in the lungs, which causes air to flow out (exhale). A hiccup is caused by an irritation of the nerve that controls the diaphragm. This source of irritation can range from eating a big meal to having a tumour, but the result is the same: the diaphragm contracts forcefully. This contraction causes the subject to take a breath that is much quicker and shorter than normal, which ends when the epiglottis closes (the epiglottis is a piece of soft tissue that stops food from going into your lungs when you swallow). This closing of the epiglottis is what causes the hiccup sound.

To get rid of the hiccups try holding your breath. This works because it throws off your normal respiratory cycle timing. Breathing into a paper bag and being startled work the same way. Oddly, often if you concentrate on trying to hiccup, the bout will cease. If you go see a doctor because of persistent hiccups, they may try massaging your carotid sinus (an artery in your neck) or performing a digital rectal massage to try and stimulate the nerves controlling glottis.

Height changes daily!

Did you know your height can vary up to a few millimetres throughout the day? You are tallest each morning when you roll out of bed. During the day as you stand and sit, you gradually compress the squishy, fluid-filled discs between your vertebrae. This results in a cumulative compression and net loss of height. If you partake in any heavy weight bearing activities such as running on hard surfaces during the day it is likely the vertebral compression will be more than usual. Each night as you lie down to sleep however, the load on your back is released and the discs become re-infused with fluid. It is also interesting that older adults will shrink less during the day than a young adult. This is because their discs are less elastic so the compression is more permanent. It is possible to re-grow yourself at various points throughout the day by going into the fetal position. This allows your back to stretch out, lessening the compressive effects.


Anonymous said...

this post is sooo useful.

Anonymous said...

very nice

miko said...