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Physiology |
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How Wondrously We Are Made! When you look at human physiology, it's a little hard to believe that it all happened by accident. Consider just a few of the amazing facts about how the human body is made and works. The human eye can distinguish about 17,000 colors. You didn't even know there were that many did you? The average person breathes in about seven quarts of air every minute. Every minute of every day. Get a gallon jug of water to give you some idea how much that is! Blood vessels automatically contract and close off when you cut yourself, helping to prevent excessive loss of blood. It takes 72 muscles to speak a single word. Talk about exercise! It requires an hour for a human eye to completely adjust to seeing in the dark, but once it does, the eye is 100,000 times more light sensitive then in broad daylight. The main task of the heart is to pressurize the blood and deliver this pressurized blood to the aorta and pulmonary artery. Most of the useful work done by the heart (95%) is to increase the potential energy of the blood, that is, its pressure; the remaining 5% of the work goes into kinetic energy, which is related to the speed at which the blood is ejected from the heart. The heart is a cone-shaped structure with very thick walls, suitable for developing pressure. The heart has a system of one-way valves that are essential to its function as a pump, allowing blood only to flow from the veins and atria into the ventricles and from there to the aorta and pulmonary artery. The part of the nervous system that controls breathing is located in the mid-brain, also known as the brain stem. It is an area more primitive than the area of the brain responsible for thinking and motor movements, known as the brain cortex. Brain stem control of breathing is automatic and functions whether we think about it or not. Approximately 10-12 times a minute, the brain stem sends nerve impulses that tell the diaphragms and thoracic cage muscles to contract. Contraction of these muscles expands the rib cage, leading to the expansion of the lungs contained within. With each expansion of the lungs we inhale a breath of fresh air containing 21 percent oxygen and almost no carbon dioxide. After full expansion the brain command to inhale ceases and the thoracic cage passively returns to its resting position, at the same time allowing the lungs to return to their resting size. As the lungs return to their resting position we exhale a breath of stale air, containing about 16 percent oxygen and 6 percent carbon dioxide. Shivering is an automatic body response to cold. The movement helps to warm the body. These are only a few of the mind-boggling details of how we are made. Every day, without us having to think about it at all, the body breathes, sweats, excretes wastes, fights off disease, heals wounds, and adjusts to conditions around it. It took a mighty master planner to make it all work together! God's planning is so intricate in its design and function that now, hundreds of thousands of years after the creation of man, we're still trying to understand all of the human body's responses. |
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