Digestive System Functions Quiz

Alimentary Canal Overview

• The alimentary canal is a muscular tube responsible for food movement, storage, digestion, absorption, and elimination.
• Food is taken into the alimentary canal via ingestion.
• Large insoluble molecules are broken down into small soluble ones through mechanical and chemical digestion.
• Small molecules are absorbed into the bloodstream during absorption.
• Small molecules are used by cells to make larger molecules (e.g., proteins) during assimilation.
• Undigested food is removed as feces in the egestion process.
• Autotrophic nutrition is where organisms make their own food (e.g., plants).

The Mouth

• Mechanical digestion in the mouth involves increasing the food surface area for chemical digestion.
• Salivary glands secrete saliva, which breaks down food into a bolus.
• The tongue forms the food into a ball called a bolus.
• The bolus is moved down the esophagus by a process called swallowing.
• Teeth are used for mechanical digestion.

Types of Teeth

• Different types of teeth (incisors, canines, premolars, and molars) have different shapes and functions, adapted to different diets.
• Carnivores (e.g., tigers) have prominent canines for tearing flesh.
• Herbivores (e.g., horses) have large molars for grinding grass.

Peristalsis

• Food is squeezed down the esophagus by wavelike muscle contractions called peristalsis.
• Circular muscles behind the bolus contract, squeezing food forward.
• Circular muscles in front of the bolus relax, allowing the lumen to widen.

Stomach Functions

• The stomach stores food (up to 2 hours) allowing time for digestion.
• Chemical digestion of proteins into peptides occurs with enzymes like pepsin, which works best at a pH of 2.
• Mechanical digestion of food happens through strong muscular contractions and relaxation, churning the food within the stomach.
• Strong acid in the stomach (pH 2) disinfects food by killing microbes.

Gastric Pits

• Glands in the stomach lining secrete:
  • Mucus as a lubricant
  • Hydrochloric acid to kill bacteria and maintain low pH
  • Pepsin to break down proteins into peptides (optimal in acidic conditions)

Digestion in the Small Intestine

• Food exits the stomach through a sphincter.
• Chyme (partially digested food) mixes with pancreatic juices containing enzymes like:
  • Amylase (starch to maltose)
  • Maltase (maltose to glucose)
  • Lipase (fats to fatty acids and glycerol).
• Pancreatic and intestinal juices work best at a neutral pH (7). Bile neutralizes stomach acids.

Bile

• Produced by the liver and stored in the gallbladder.
• Bile contains sodium bicarbonate, which neutralizes acids.
• Bile salts emulsify fats (break large fat droplets into smaller ones).
• Bile pigments are excreted in feces.
• Bile does not contain enzymes; it does not digest fats.

Digestion of Fats

• Bile salts emulsify large fat droplets into smaller ones, increasing the surface area for lipase action.
• Lipase digests fats into fatty acids and glycerol.
• Fatty acids and glycerol are absorbed into lacteals.

Absorption in the Small Intestine

• Small molecules (monosaccharides, amino acids, water, vitamins, and minerals) are absorbed directly into the blood.
• Fatty acids and glycerol are absorbed into lacteals, which eventually feed into the blood vessels.

The Small Intestine

• The small intestine is approximately 5 meters long.
• Finger-like projections called villi line the small intestine, greatly increasing the surface area for absorption.
• Microvilli, tiny projections on the villi, further increase the surface area for absorption.
• The small intestine has an excellent blood supply via capillaries, assisting with absorption and transport of nutrients.
• Lacteals are vessels in the villi that absorb fats.

Absorbed Food and the Liver

• Absorbed food enters the bloodstream and travels to the liver via the hepatic portal vein.
• The liver stores excess glucose as glycogen, breaks down food to release energy, and detoxifies or breaks down various substances.

The Large Intestine

• The large intestine absorbs water and salts.
• Approximately 30% of feces consists of bacteria.
• Feces are stored in the large intestine until egested via the anal sphincter.
• High-fiber diets are associated with lower incidences of bowel cancer.

Diet and Disease

• High sugar intake leads to tooth decay.
• High fat/energy intake and low exercise contribute to obesity.
• Obesity is linked to arthritis, diabetes, high blood pressure, and heart disease.
• High salt intake causes high blood pressure.
• High cholesterol contributes to heart disease.
• Low-fiber diets are linked to a higher risk of bowel cancer.