MAVO Year 4 · Nutrition and digestion · Section 12.5
Organs involved in digestion
Mouth and swallowing
In the mouth, teeth break food into smaller pieces and mix it with saliva. This moistens and lubricates food and contains amylase, beginning starch digestion. The tongue forms a bolus and moves it towards the throat. During swallowing, coordinated movements of the soft palate, larynx and epiglottis help direct food into the oesophagus, away from the nasal cavity and airway. Peristalsis carries it towards the stomach.
Stomach
The stomach churns food and mixes it with gastric juice. This contains water, hydrochloric acid and substances involved in protein digestion. Acid provides suitable conditions for gastric enzymes and kills many, but not all, microorganisms. The pyloric sphincter controls the release of small amounts into the duodenum.
Small intestine
Bile, made by the liver and usually stored in the gallbladder, enters the duodenum. It emulsifies fats, dividing large droplets into smaller ones and increasing the surface for enzymes. Pancreatic juice supplies enzymes for carbohydrates, proteins and fats, as well as bicarbonate helping neutralise stomach acid.
Digestion continues in the small intestine, including at its surface. Villi and microscopic projections increase the area for absorption. Sugars, amino acids and many other nutrients enter blood capillaries; much absorbed fat is transported initially through lymphatic vessels.
Large intestine, rectum and anus
Most water absorption has already occurred in the small intestine; the large intestine recovers more water and salts. Its microorganisms ferment some fibre and produce substances including certain vitamins, such as vitamin K. Humans do not digest cellulose with their own enzymes, and its microbial breakdown is limited compared with specialised herbivores.
Faeces collect temporarily in the rectum. Distension contributes to the urge to defecate, and sphincters around the anus control their release.
Glossary
- Pancreas
- An organ producing pancreatic juice for digestion and hormones involved in blood-glucose regulation.
- Pancreatic juice
- A secretion containing digestive enzymes and bicarbonate, released into the duodenum.
- Anus
- The opening at the end of the digestive tract, controlled by sphincter muscles.
- Intestinal secretion
- Fluid and digestive substances associated with the intestinal lining, supporting the final stages of digestion.
- Large intestine
- The gut region absorbing additional water and salts and containing a rich microbial community.
- Small intestine
- The long gut region responsible for most digestion and nutrient absorption.
- Emulsification
- Dividing large fat droplets into smaller droplets without chemically digesting the fat.
- Rectum
- The final storage region for faeces before defecation.
- Bile
- A liver secretion containing bile salts that help emulsify fats.
- Molars
- Broad teeth used to crush and grind food.
- Liver
- An organ producing bile and performing many metabolic and regulatory functions.
- Stomach
- A muscular organ storing, mixing and beginning substantial protein digestion of food.
- Pyloric sphincter
- A ring of muscle controlling passage from the stomach to the duodenum.
- Gastric juice
- The stomach's secretion, including acid and substances involved in protein digestion.
- Gastric glands
- Glands in the stomach lining producing components of gastric juice.
- Stomach acid
- Hydrochloric acid providing a low pH and killing many ingested microorganisms.
- Mouth
- The cavity where food is chewed and mixed with saliva.
- Oesophagus
- The muscular tube carrying swallowed food towards the stomach by peristalsis.
- Saliva
- Fluid moistening food and containing amylase, which begins starch digestion.
- Salivary glands
- Glands producing saliva.
- Incisors
- Front teeth used mainly for cutting or biting pieces of food.
- Tongue
- A muscular organ moving food during chewing and swallowing.
- Duodenum
- The first part of the small intestine, receiving bile and pancreatic juice.
- Digestive enzymes
- Catalysts breaking large food molecules into smaller, absorbable molecules.