5. Human Digestive System Flashcards
Digestion
Definition
Digestion is the process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into body cells.
Physical Digestion
Definition + Examples
Physical digestion is the mechanical breakdown of food into smaller particles to increase the surface area to volume ratio, for a faster rate of chemical digestion by digestive enzymes.
Examples: Chewing in mouth, churning action in stomach, emulsification of fats in duodenum
Chemical Digestion
Definition
Chemical digestion is the breakdown of large food molecules into small soluble molecules, catalysed by digestive enzymes through hydrolytic reactions.
Ingestion
Definition
Ingestion is the act of taking food into the mouth.
Digestion in the mouth
Types of digestion that take place + What happens after
Physical digestion: Chewing
Chemical digestion: Salivary amylase
Afterwards, the thoroughly chewed food is rolled into a bolus by the tongue. The bolus is then swallowed and enters the oesophagus.
Saliva
Where it is produced + What it contains + Function
- Produced by salivary glands in the mouth
- Contains salivary amylase which digests starch into maltose
- Help to soften and moisten food
Saliva has a pH of 6.5 - 7.5
Salivary Amylase
What it is + Where it is found + Function + Optimum pH
- Salivary amylase is an enzyme found in saliva
- Digests starch into maltose
- Optimum pH of 6.5 to 7.5
Peristalsis
Definition + Function + State of muscles
Peristalsis is the rhythmic, wave-like, muscular contractions of the wall of the alimentary canal.
It functions to mix and propel food down the alimentary canel.
Behind the food:
- Longitudinal muscles are relaxed
- Circular muscles are contracted
The alimentary canel is the digestive tract from the mouth to the anus
Stomach
What it is
An elastic, muscular bag with thick muscular walls.
Stomach has pH 2
Gastric Juice
Where it is produced + What it contains
- Secreted by gastric glands in the stomach when the bolus enters the stomach
- Contains mainly hydrochloric acid, pepsin & rennin
Hydrochloric acid in the stomach
Function
- Provides an acidic medium suitable for the action of enzymes in the stomach
- Kills bacteria
- Changes inactive forms of enzymes to active forms: converts pepsinogen to pepsin
Pepsin
What it is + Where it is found + Function + Optimum pH
- Pepsin is an enzyme found in gastric juice
- Digests proteins into polypeptides
- Optimum pH of 2
Polypeptides are long chains of amino acids
Rennin
What it is + Where it is found + Function
- Rennin is an enzyme found in gastric juice
- Converts soluble milk protein caseinogen into insoluble caesin, causing coagulation of milk
Coagulation: process of a liquid changing to a solid/semi-solid state
Digestion in the stomach
Types of digestion that take place + What happens after
Physical digestion: Churning
Chemical digestion: Pepsin
After a few hours, the partly digeted food will become liquified, forming chyme, which passes into the duodenum in small amounts.
Churning
What it is + Function
Churning is a form of physical digestion in the stomach.
Function is to:
- Mix food with gastric juice
- Break down food into smaller particles to increase the surface area to volume ratio, for a faster rate of chemical digestion by digestive enzymes