Function of the Digestive System:
Food is typically in a form that is completely unsuitable for use by body cells.
Food becomes useful only after it has been converted into smaller, simpler and diffusible units.
Carbohydrates converted into monosaccharides (ex. glucose)
Proteins converted into amino acids
Lipids converted into glycerol and fatty acids
These simple, smaller units can pass through the walls of the small intestine and blood and lymphatic vessels in the process of absorption.
This preparation of food for absorption is called digestion.
Types of Digestion:
– occurs mainly in the mouth and stomach
– solid food masses are shredded, torn, ground, and shaken
– creates smaller food particles with high surface area
– does not produce absorbable nutrients
– food broken down by chemical means (ex. enzymes)
– enzymes, secreted by digestive glands, break-down food into absorbable nutrients (ex. disaccharides à monosaccharides, dipeptides à amino acids)
Key Processes in Sequential Order:
Ingestion – eating food
Digestion – the preparation of food for absorption
Absorption –nutrients move from the digestive system and into your blood stream
Elimination – non-digestible, non-useful waste must be eliminated from the body
The Digestive System:
– a muscular tube that passes through the whole body (mouth to anus) and is open at both ends
– the inside surface (or lumen) of this tube is continuous with the outer surface of the body, and so technically, is an extension of the external environment
– structure allows food to enter through one end, products of digestion become absorbed through the lining of the tube, and waste products to be eliminated through the other end
Accessory Organs provide enzymes and other substances that are essential for digestion to occur (salivary glands, pancreas, liver, gall bladder)
Digestive tract begins with the oral cavity and includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus.
Other Processes and Components:
Motility – the movement of food through the digestive tract is accomplished by means of peristalsis
– starts in the mouth and moves the food through the system towards the anus
-peristalsis is a series of coordinated muscular contractions that squeeze food through the digestive tract
Sphincters - ring-like muscles that control the passage of food from one organ to another
– prevent back flow of food and keep food in the organs until time to release