The human body is an astounding piece of biological engineering. From head to toe, dozens of different systems keep your heart pumping, lungs drawing breath and brain converting short-term memories to long-term. You are the world’s most advanced biological computer, but how does it work?
Read on for an introduction to human anatomy and how your body functions.
The Skeletal System
The average adult has 206 bones in their body that make up their skeletal system. When you’re born, you’ve got nearly 300. However, many fuse and leave you with the skeleton you’ll have for the rest of your life.
The skeleton is divided into two sections — axial and appendicular. The axial skeleton includes the upper body — the skull, spine and rib cage, totaling 80 bones. It also supports the core of your body, such as your brain, spinal cord, heart and lungs. The appendicular skeleton makes up the rest of your body, the other 126 bones.
Each bone is classified by its shape — long, short, flat, irregular and sesamoid. Long bones extend further than they are wide, usually found in the body’s peripherals — arms, legs, fingers, and toes. Short bones, on the other hand, are roughly equal in length and width.
Your skull, shoulder blades and ribs are made up of flat bones, while your facial bones and spinal cord are classified as irregular bones because they don’t fit into any other category. Finally, there are sesamoid bones, which are embedded in tendons and usually found in your hands, feet, ears, knees and wrists.
Bones contain a variety of cells responsible for different things.
The Muscular System
On top of your skeleton is the muscular system. You’ve got three different types of muscle spread out throughout your body — skeletal, smooth and cardiac. Each is responsible for maintaining different parts of the body.
First, there are skeletal, also referred to as striated muscles. These muscles are the only ones under voluntary control, meaning you can make a conscious decision to choose the way they move. The muscles you typically see on exercise charts, from the quadriceps in your thighs to the biceps in your arms, are all made up of striated muscle.
Next is smooth muscle, which makes up the walls of your blood vessels and the structure of some of your organs, including the intestines, stomach and bladder. You don’t control these muscles, and each has its own biological programming to function.
Cardiac muscle makes up the majority of the heart and is responsible for pumping blood throughout your body.
The Cardiovascular System
The center of your cardiovascular system is the heart, the mass of cardiac muscle that pushes blood through your body. Arteries work to carry blood away from the heart to the far reaches of the circulatory system. Veins carry the oxygen-depleted blood back to your heart in a nearly endless cycle.
If you removed all the arteries and veins from the human body, it would reach more than 60,000 miles. You could wrap them around the Earth’s equator twice and still have enough left over to tie a neat little bow.
In the lungs, the roles of arteries and veins switch. Pulmonary arteries bring depleted red blood cells into the lungs to pick up oxygen. On the flip side, veins send it back to the heart to circulate throughout the body.
Your body has 20 major arteries that branch out into smaller systems, known as arterioles. Arterioles branch again into capillaries, which are thinner than a hair.
The Nervous System
If you’ve ever felt the softness of a feather or the warmth of a cup of coffee between your palms, then you have your nervous system to thank. However, feeling sensations like heat, cold and pain is only one aspect.
Two components make up the nervous system:
- Central nervous system: Made up of the brain and spinal cord.
- Peripheral nervous system: Made up of the nerves that branch from the spinal cord.
This system is responsible for transmitting signals between the brain and the rest of the body. It controls your ability to move, breathe, see and think. A basic unit of the nervous system is a nerve cell — neuron. The human brain contains about 100 billion of these. Different types of neurons control various functions.
Your nervous system also contains non-neuron cells, called glia. These cells support and protect the neurons. Plus, they create insulation called myelin, which helps move nerve impulses.
The Digestive System
What was the last meal you ate? Perhaps eggs and bacon for breakfast, a sandwich for lunch or steak and potatoes for dinner. You can thank your digestive system for processing that food into usable nutrients to keep your body healthy.
Your gastrointestinal (GI) system is made up of your mouth to your anus and everything in between. You’re essentially a big donut, with food moving from one end to the other. It starts with the mouth, where you chew your food and mix it with saliva. It then travels to the esophagus, stomach, small intestine, large intestine and, finally, the anus. Solid organs, such as the liver, pancreas and gallbladder, are also part of the GI tract.
The small intestine has three parts — the duodenum, where it connects to the stomach, the jejunum in the middle and the ileum near the large intestine. The large intestine also includes the appendix, cecum, colon and rectum. The appendix is what’s known as a vestigial organ — something we haven’t evolved to get rid of, though we don’t use it. It doesn’t serve a purpose, but it can require surgical removal if it gets infected.
Believe it or not, you have a second brain in your gastrointestinal tract. Known as the enteric nervous system (ENS), this second brain ensures that when you swallow food, the GI system handles it smoothly.
Systems of the Human Body
Do you want a thorough introduction to the human body? If so, read through the topics above, from the nervous to the digestive system. However, there’s plenty left to learn.
You might be able to name each bone and chart out the cardiovascular system. Yet scientists are fascinated by the body and its abilities. How can you push your future knowledge to the limits?