Physical digestion Revision Notes

Physical digestion involves breaking food into smaller pieces by mechanical means such as chewing and stomach churning. This process does not involve chemical changes to the food molecules.

• Food is physically broken down into smaller pieces.
• No chemical bonds in food molecules are broken.

By reducing food size, physical digestion increases the surface area available for enzymes to act on during chemical digestion, making digestion more efficient.

• Increased surface area aids enzyme action.
• Physical digestion prepares food for chemical digestion.

Chewing by teeth in the mouth and muscular churning in the stomach are key examples of physical digestion.

• Chewing breaks food into smaller pieces.
• Stomach muscles churn food to mix and break it down further.

Breaking food into smaller pieces increases the total surface area exposed to digestive enzymes.

• More surface area means more enzyme contact points.
• Physical digestion prepares food for chemical digestion.

Enzymes act on the surface of food particles. Increased surface area allows enzymes to break down food molecules faster and more completely.

• Enzymes work faster with more surface area.
• Chemical digestion is more efficient after physical digestion.

Physical digestion and chemical digestion work together: physical digestion breaks food down mechanically, and chemical digestion breaks food molecules chemically.

• Physical digestion aids chemical digestion.
• Both processes are essential for effective digestion.

Incisors are the front teeth with sharp, flat edges used for cutting food into bite-sized pieces.

• Located at the front of the mouth.
• Designed for cutting food.

Canines are pointed teeth next to incisors used for tearing food, especially meat.

• Located beside incisors.
• Pointed shape for tearing food.

Premolars are behind canines and have broad, flat surfaces to crush and grind food.

• Located behind canines.
• Used for crushing and grinding food.

Molars are the largest teeth at the back of the mouth, specialized for grinding food thoroughly before swallowing.

• Located at the back of the mouth.
• Largest teeth, used for grinding food.

Enamel is the hardest substance in the body and covers the crown of the tooth. It protects the tooth from wear and decay.

• Hardest part of the tooth.
• Protects against damage and decay.

Dentine lies beneath the enamel and supports it. It is less hard and sensitive to stimuli.

• Supports enamel structure.
• Sensitive to temperature and pressure.

The pulp contains nerves that provide sensation and blood vessels that supply nutrients to keep the tooth alive and healthy.

• Contains nerves for sensation.
• Contains blood vessels for nourishment.

Cement covers the root of the tooth and helps anchor it firmly into the jawbone.

• Covers tooth root.
• Attaches tooth to bone.

Teeth are set in the jawbone and surrounded by gums which protect the roots and hold teeth securely in place.

• Jawbone holds teeth firmly.
• Gums protect roots and provide stability.

Humans have four main types of teeth, each adapted for a specific role in physical digestion: incisors, canines, premolars, and molars.

Incisors are sharp and chisel-shaped, designed to cut food into smaller pieces.

Canines are pointed and strong, used to tear food, especially tougher items like meat.

Premolars and molars have broad, flat surfaces that grind and crush food into smaller, manageable pieces.

• Incisors cut food into smaller pieces.
• Canines tear food, especially tough textures.
• Premolars and molars grind and crush food.

Physical digestion by teeth breaks food into smaller pieces, increasing its surface area.

This increased surface area allows digestive enzymes to work more efficiently during chemical digestion.

Each tooth type's shape suits its role in processing different food textures, making digestion more effective.

• Physical digestion increases food surface area.
• Different teeth shapes suit their functions.
• Efficient physical digestion aids chemical digestion.

The following table summarizes the main types of teeth and their functions in physical digestion.

See below for a clear comparison of teeth types and their functions.

The stomach has strong muscular walls that contract rhythmically to churn and mix food.

This churning action physically breaks food into smaller pieces without changing its chemical structure.

The process increases the surface area of food, making it easier for enzymes to chemically digest it later.

• Muscular contractions churn food.
• Food is broken into smaller pieces.
• Surface area of food increases for enzyme action.

Churning mixes food with digestive juices, aiding both physical and chemical digestion.

Mechanical digestion in the stomach prepares food for efficient nutrient absorption in the intestines.

Without this physical breakdown, chemical digestion would be slower and less effective.

• Churning mixes food with digestive juices.
• Physical digestion prepares food for chemical digestion.
• Increases efficiency of nutrient absorption.

The stomach's physical digestion involves muscular contractions that churn food, breaking it down mechanically.

Below is a summary of how the stomach physically digests food.

Bile is produced by the liver and stored in the gallbladder before being released into the small intestine.

Its main role is to emulsify fats and oils, breaking large fat droplets into many smaller droplets.

This process increases the total surface area of fats available for enzymes like lipase to act on.

• Bile emulsifies fats and oils.
• Breaks large droplets into smaller droplets.
• Increases surface area for enzymes.

Smaller fat droplets allow lipase enzymes to chemically digest fats more efficiently and quickly.

Without bile emulsification, fat digestion would be slower and less effective.

Emulsification does not chemically break down fats; it only prepares them for enzyme action.

• Emulsification speeds up fat digestion.
• Increases efficiency of lipase enzymes.
• Does not chemically digest fats itself.

The table below summarizes how bile helps digest fats by emulsification.

See the comparison of bile's function and its effect on fat digestion.