The Digestive System:
The digestive system is responsible for breaking down food we eat into smaller components so that nutrients can be easily absorbed by the body and the waste discarded.
The basic parts:
- The small intestine is about 22 feet (7 meters) long, and about an inch (2.5 centimeters) in diameter with a surface area of around 2,700 square feet (250 square m), or about the size of a tennis court.
- The adult stomach has a very small volume when empty but can expand to hold up to 1.5 litres of food when full.
"Your stomach doesn't do most of the digestion.
- It's commonly believed that the stomach is the center of digestion, and the organ does play a large role in "mechanical digestion" — it churns food, and mixes it with gastric juices, physically breaking up food bits and turning them into a thick paste called chyme.
- But the stomach is actually involved in very little chemical digestion, the process that reduces food to the size of molecules, which is necessary for nutrients to be taken up into the bloodstream.
- Instead, the small intestine, which makes up about two-thirds of the length of the digestive tract, is where most of the digestion and absorption of nutrients takes place. After further breaking down the chyme with powerful enzymes, the small intestine absorbs the nutrients and passes them into the bloodstream." http://www.livescience.com/40187-digestive-system-surprising-facts.html
The Respiratory System:
The basic parts:
Your left and right lungs aren’t exactly the same. The lung on the left side of your body is divided into two lobes while the lung on your right side is divided into three. The left lung is also slightly smaller, allowing room for your heart.
The function of the lungs:
The primary functions of your lungs are to transport oxygen from the air you breathe into your bloodstream while taking away carbon dioxide, which is released into the air when you breathe out.
An average person breathes in around 11,000 litres of air every day.
- The average adult breathes around 12 to 20 times a minute when they are at rest.
- Most vertebrate animals (animals with spines) have two lungs.
The Circulatory System:
The five functions of the human circulatory system:
- are: the transportation of hormones, oxygen and nutrients
- the removal of waste
- the stabilization of the pH of bodily fluids
- the maintenance of body temperature
- the fighting of infections. (Fighting infections is achieved by transporting white blood cells.)
Why large organisms need a circulatory system:
Large animals need a circulatory system because the cells in the interior of their bodies are too distant from the surface for absorbed oxygen to diffuse to them sufficiently. By circulating fluid carrying oxygen to these deeper areas, the distance oxygen has to diffuse is greatly reduced.
Amazing facts about blood vessels:
"1. Your blood vessels could circle the globe. Though blood vessels are relatively small, the network is amazingly long. In fact, if they were laid out in a line, they would measure more than 60,000 miles in length. Considering that the circumference of the Earth is 24,873.6 miles, according to NASA, that means your blood vessels could circle the globe more than twice.
2. They carry a million barrels of blood in a lifetime. The blood in your body is continuously flowing. Every day, your heart pumps about 1,800 gallons of blood through your blood vessels. Over the course of a lifetime, this vast system carries about a million barrels of blood throughout the body.
3. Blood vessels work as a team. The three major types of blood vessels – arteries, veins, and capillaries – all work together. When the heart contracts, blood is pumped into arteries that carry it away from the heart. Arteries are connected to tiny, thin-walled blood vessels called capillaries, which allow oxygen to move from the blood into the cells of the body. Then veins carry deoxygenated blood back to the heart."
What happens when blood reaches the lungs?
Blood that reaches the lungs travels throughout a network of small blood vessels, where oxygen moves into the blood and carbon dioxide moves out of the blood, according to the National Heart, Lung and Blood Institute. This oxygen-rich blood is transported through the pulmonary veins and back to the heart, where it is pumped out to the rest of the body.