In the digestive system, mouth comes first, then esophagus, then stomach, then small intestine: duodenum, then small intestine: jejunum/ileum, then large intestine, and finally the rectum.

Mouth: contains teeth, which start mechanical digestion by cutting and grinding food into small pieces. The tongue helps to push food back into the throat, or pharynx.

Esophagus: This muscular tube is lined with mucus. In the process of peristalsis, muscles contract to move food from one end to another

Stomach: muscular pouch that can hold 1-3 liters of food. The walls of the stomach are lined with mucus to protect them from acid. The stomach churns to break food down mechanically.

Small Intestine Duodenum: muscular tube that is lined with structures called villi. Each villus looks like a tiny finger and allows nutrients and water to pass through the walls of the duodenum.

Small Intestine Jejunum/Ileum: make up most of the small intestine, which is up to 6 meters in length. Villi along the walls of the jejunum and ileum absorb nutrients and water.

Large Intestine: water and vitamin K are absorbed from food that passes through the large intestine. Bacteria help to break down fiber and other materials

Rectum/Anus: stores and compacts waste before it is eliminated through an opening called the anus.

Salivary gland connects to the mouth/pharynx. Chief and parietal cells are in the stomach. The gallbladder and pancreas are in the small intestine: duodenum. Capillaries are on both parts of the small intestine and the large intestine. Lymphatic vessels are on both parts of the small intestine.

Salivary Gland: moistens food, helping to break it up and lubricate its passage through the digestive system. Saliva contains the enzyme amylase, which starts the breakdown of complex carbohydrates into sugars

Chief Cells: produce pepsin, which begins the digestion of proteins by breaking large protein molecules into smaller molecules called peptides. Pepsin works best in an acidic environment.

Parietal Cells: produce hydrochloric acid, which increases the efficiency of pepsin

Gallbladder: stores a chemical called bile, which is produced by the liver. Bile helps to break up large fat globules into much smaller particles.

Pancreas: produces digestive enzymes. These include amylase, which breaks down carbohydrates, trypsin, which breaks down proteins, and lipase, which breaks down fats. The pancreas also produces an alkaline solution that neutralizes acid.

Capillaries: tiny blood vessels that transport absorbed monosaccharides, amino acids, and water to the bloodstream. The nutrients are then carried to body cells

Your body can not store oxygen.

Oxygen in your body allows all cells to make energy so they can function properly.

Since you can't store it, your body takes it in all the time in the process of breathing.

When you breathe in, the diaphragm relaxes and goes down while the lungs expand.

When the diaphragm relaxes, the air pressure in the lungs drops.

When the air pressure in the lungs drops, higher pressure air from the outside rushes to take its palce

When you breathe in, air enters your body through the nose or mouth and down the trachea.

In the lungs, the air moves into smaller passageways called bronchial tubes.

After the bronchial tubes, the air eventually moves to the alveoli.

Alveoli: tiny sacs surrounded by blood vessels called capillaries

Oxygen moves through the walls of the alveoli and capillaries into the blood.

As all this is happening, carbon dioxide is being taken out of the body through breathing out.