Discovery Science: Earth – Humans – Nutrition

Earth Science:  Human – Metabolism and Hormones

The human body regularly takes in nutritional material from outside, transports it and processes it, and eliminates waste and foreign material. Hormones play an important role in most metabolic processes.

Earth Science: Biology – Humans – Nutrition

Plants produce their own nutrients; however, humans do not. Instead, we must consume food and liquids to obtain the energy and water we need to sustain our bodies.

Food is required as an energy source to fuel processes such as moving, thinking, blood distribution, and breathing. It also sustains the growth and repair of cells and tissues. Food energy is used by the metabolism.

This refers to the processes in which an organism takes in, transports, and chemically transforms nutrients. It also includes the disposal of waste products.

What happens to our food?

A bite of food follows a journey that starts in the mouth and continues through the esophagus, stomach, small and large intestines, and ends at the rectum and anus.

During this process, each organ of the digestive system fulfills very specific functions. Other glands and organs, such as the salivary glands, pancreas, gall bladder, and liver, also contribute to digestion.

Path through mouth, stomach, and small intestine

Inside the mouth, the teeth break up food mechanically and combine it with saliva from the salivary glands. Enzymes in saliva break down carbohydrates into smaller sugar molecules. Swallowing pushes the food mixture down the esophagus into the stomach. There it combines with digestive fluids, including hydrochloric acid.

The stomach mixes the food with a churning motion to break down cell structures. Enzymes also split proteins into smaller molecules. Two to six hours after a meal, the stomach empties into the small intestine, which is about 16 feet (five m) long, and where most digestion takes place.

Bile from the gall bladder dissolves fats, while enzymes from the pancreas digest fats, proteins, and carbohydrates.


Diabetes is a disease that weakens the cells’ ability to use sugar by disrupting the absorption of sugar from the bloodstream—a process carried out by insulin produced in the pancreas.

Diabetes can be present from birth, result from poor nutrition, or come from metabolic problems related to aging.


During the chewing process, food comes into contact with saliva and the enzymes in the saliva begin the digestion process. A tooth consists of a tooth crown, neck, and root. The crown is coated with tooth enamel, the toughest and most durable substance in the entire human body.

Once damaged or decayed, tooth enamel cannot be regenerated. The pulp is located inside of the tooth and is extremely sensitive to pain due to its high concentration of blood vessels and nerves