Digestive System Functions

• Body cells are organized in a hierarchy that goes from cells, to tissues, to organs, to systems.
• The main functions of the human body to sustain life are accomplished by 11 organ systems working together.
• The purpose of the digestive system is to convert raw materials (food) into the nutrients needed.
• Here are the 6 major digestive system functions:
• Ingestion of food
• Secretion of fluids and digestive enzymes
• Mixing and movement of food and wastes throughout the day
• Digestion of food into smaller pieces
• Absorption of nutrients
• Excretion of wastes

Four Main Sections of the Digestive System

• Gastrointestinal Tract: food goes through this tract, which transports food.
• The Organ Trio: Pancreas, gallbladder, & liver.
• Accessory organs do not have food going through them.
• They break down food using secretory juices
• The Quad Core: Enzymes, blood, hormones, & nerves that break down food.
• They modulate the digestion process.
• They deliver nutrients as final products.
• Mesentery: large area of tissue that supports and positions all digestive organs

The Mouth

• Digestion Function: mechanical & chemical
• Mechanical Digestion: biting, tearing, chewing, churning.
• Chemical Digestion: salivary glands secrete saliva, a solution which moistens food to be easily swallowed, forming a bolus.
• Saliva contains the enzyme amylase, which breaks down starch into sugar
• The epiglottis closes off the trachea when food is ready to be swallowed.
• Food moves into the pharynx and then to the esophagus.

The Esophagus

• Muscle tissue contracts and relaxes in a wave-like pattern called Peristalsis.
• At the base: esophageal sphincter, which is usually closed/constricted.
• The pressure of food opens the esophageal sphincter, and enables food to enters the stomach.

The Stomach

• Hydrochloric Acid in the stomach breaks up connective tissue that holds food together.
• Pepsin is an enzyme in the stomach which breaks protein molecules up into short polypeptides.
• Gastrin is a hormone in the stomach that regulates the amount of hydrochloric acid produced.
• Partially digested food exits the stomach by way of another sphincter called the pyloric sphincter.

Small Intestine

• The inside of the small intestine is lined with finger-like projections called villi.
• Villi increase the surface area to volume ratio in order to absorb more nutrients.
• On every villi is microvilli.
• The first meter of the small intestine, the duodenum, is where most digestion happens.
• Small intestine hold two functions:
• Break down of carbohydrates by amylases, proteins by peptidases and fats by lipases.
• Absorption of monosaccharides, amino acids, fatty acids and glycerol (by microvilli)
• Nutrients are absorbed in the small intestine through active transport and diffusion.

Large Intestine

• Includes the colon, rectum, and anus.
• No Digestion occurs.
• Absorption of some nutrients happens here.
• Absorption of water, minerals & vitamins occurs here.
• Cellulose and undigested bacterial fragments are stored here.
• Rectum at the end removes compact solids from the colon

Accessory Organs

• Includes the liver and the pancreas
• The glands in the Pancreas secrete bicarbonate (a base) and digestive enzymes.
• Bicarbonate neutralizes the acidity in the small intestine, enabling its enzymes to digest nutrients.
• The pancreas makes insulin.
• The Liver produces and secretes bile into the small intestine.
• Bile is stored in the gallbladder, and contains bile salts that makes fats soluble
• Blood from stomach and small intestine is directed to the liver.
• When glucose levels are high, glucose is converted to glycogen.
• When glucose levels are low, the liver breaks down glycogen

Food Path

• Food moves from the mouth, to the esophagus, to the stomach, to the small intestine, to the large intestine, to the rectum/anus.

The digestive system converts food into essential nutrients through ingestion, secretion, mixing, digestion, absorption, and excretion. Key components include the gastrointestinal tract, pancreas, gallbladder, liver and other.