Digestive System and Nutrition Overview

Digestion

The term 'digestion' actually includes 4 different steps: Ingestion, Digestion, Mechanical and chemical, Absorption, Elimination.

Ingestion

The act of consuming food.

Mechanical digestion

Chewing.

Chemical digestion

Saliva (enzymes!).

Chyme

Digested food in the stomach.

Gastric juice

The digestive fluid secreted by the stomach.

Pepsin

Protein digesting enzyme called pepsin.

Duodenum

Chyme enters the duodenum and is mixed with digestive juices from the pancreas, liver (bile), gallbladder, and gland cells in the intestinal wall.

Bile

Breaks fats apart and makes them more susceptible to attack by digestive enzymes in the small intestine.

Jejunum and Ileum

Most of the nutrients from food gets absorbed in the rest of the small intestine and transported throughout the body within the blood to where it is needed.

Large Intestine

The largest part of the large intestine is the colon, which is responsible for the reabsorption of water back into the blood.

Basal Metabolic Rate (BMR)

Amount of energy needed to maintain a resting person: 1,300-1,500 kCal/day for females, 1,600-1,800 kCal/day for males.

Metabolism

All of the life-sustaining chemical reactions in organisms.

Obesity

Having a too-high body mass index (BMI), which is a ratio of weight to height.

Calorie

Organic energy source; technically a unit of energy equivalent to the heat energy needed to raise the temperature of 1 kilogram of water by 1 °C.

Carbohydrates

4 calories/gram.

Fat

9 calories/gram.

Protein

4 calories/gram.

Vitamin

Organic molecule required only in small amounts in your diet.

Mineral

Inorganic nutrients from the periodic table, also required in small amounts, that play a variety of roles.

Essential nutrients

Substances that an animal requires but cannot easily make themselves.

Essential fatty acids

Used to make phospholipids of cell membranes; found in seeds, grains, & vegetables.

Essential amino acids

9 of the 20 total amino acids used to make proteins; found in meats, eggs, milk, & cheese.

Ghrelin

Promotes appetite; flows more as normal eating times approach and when little food is in the system.

Leptin

Suppresses appetite; created in fat cells (adipose tissue) and flows more after eating.

Water intake recommendation

13 cups of water each day (>3 liters).