TEAS® Science Study Guide
Digestive System
The digestive system breaks food down into nutrients the body can absorb, and eliminates what’s left.
The path food takes
Mouth → pharynx → esophagus → stomach → small intestine → large intestine → rectum → anus
Learn this order. Many TEAS questions hinge on what comes next, or on which structure belongs to which organ.
- Mouth — Chewing breaks food down mechanically. Saliva contains amylase, which starts digesting starch.
- Esophagus — Moves the swallowed food (a bolus) to the stomach by peristalsis: wave-like muscle contractions.
- Stomach — Churns food and secretes hydrochloric acid and the enzyme pepsin to digest protein. What leaves is chyme, a semi-liquid mixture.
- Small intestine — Three parts: duodenum, jejunum, ileum. Most digestion and nearly all nutrient absorption happen here. Villi, tiny finger-like projections, line the walls and multiply the surface area for absorption.
- Large intestine — Three parts: cecum, colon, rectum. Absorbs water and electrolytes, hosts helpful bacteria, and compacts waste into feces.
Accessory organs
Food never passes through these, but digestion depends on them.
- Liver — Produces bile.
- Gallbladder — Stores bile and releases it into the small intestine.
- Pancreas — Produces digestive enzymes (amylase, lipase, protease) and bicarbonate, which neutralizes stomach acid.
What breaks down into what
- Carbohydrates → simple sugars
- Proteins → amino acids
- Fats → fatty acids and glycerol (bile emulsifies fat into droplets first)
Terms to know
- Peristalsis — Involuntary muscle contractions that push food through the GI tract.
- Bolus — A chewed, swallowed lump of food.
- Chyme — The semi-liquid mixture that leaves the stomach.
- Bile — Fluid made by the liver that emulsifies fats.
- Villi — Projections in the small intestine that absorb nutrients.
What the TEAS asks most
- Where does most nutrient absorption occur? Small intestine.
- Which parts belong to which intestine? Duodenum, jejunum, ileum are small. Cecum, colon, rectum are large.
- Which organ makes bile, and which stores it? Liver makes, gallbladder stores.
- Where does starch digestion begin? Mouth. Protein? Stomach.