Why a Digestive System ? Kingdom Animalia Heterotrophism

Digestive System General Function The digestive system is responsible for the … Intake and breakdown of complex foods into two categories: Useable materials (nutrients) Non-useable materials (wastes)

Six Major Digestive Processes INGESTION PROPULSION MECHANICAL DIGESTION CHEMICAL DIGESTION ABSORPTION (of nutrients) DEFECATION (of wastes)

GI Accessory Tract Organs Oral Cavity Esophagus Stomach Small Intestine Large Intestine Anus Teeth Tongue Gall Bladder Glands Liver Pancreas Salivary

GI Tract and Accessory Organs

Digestive Processes of the Oral Cavity INGESTION MECHANICAL DIGESTION CHEMICAL DIGESTION

Oral Cavity Borders: Anterior  Lips Lateral  Cheeks Superior  Palate (Hard/soft) Inferior  Tongue Tongue: Accessory Organ for: mixing, taste buds ***

THE ESOPHAGUS carries bolus from oral cavity to stomach. PERISTALSIS the automatic, involuntary, continuous propulsion of food through the GI tract.

P E R I S T A L S I S

Functional Anatomy cont PART II The STOMACH

Digestive Processes of the Stomach Storage tank Chemical digestion of proteins Mechanical digestion Bolus  Chyme Volume— 50 ml  4 liters Rugae allow for expansion Enervated by ANS

Gastric Sphincters Cardiac Sphincter Pyloric Sphincter Functions: Regulates/controls propulsion of food into/out of the stomach

Cardiac sphincter Pyloric sphincter

PART III SMALL INTESTINE ACCESSORY STRUCTURES LIVER GALL BLADDER PANCREAS

Small Intestine Three Regions: Duodenum Jejunum Ileum ~1 ft ~8 ft

Digestive Processes of the Small Intestine CHEMICAL DIGESTION OF… CARBOHYDRATES PROTEINS LIPIDS NUTRIENT ABSORPTION!!

Microscopic Anatomy of the Small Intestine Mucosa Circular folds (“plicae circulares”) Slow propulsion of chyme Villi Finger-like projections w/ capillaries in center Microvilli Small projections of cells that absorb nutrients (aka absorptive cells)

Before Nutrient Absorption occurs… CHEMICAL DIGESTION MUST BE COMPLETED IN THE SMALL INTESTINE THROUGH ENZYMATIC ACTIVITY!

But There’s a Problem… THE SMALL INTESTINE LACKS CELLS THAT PRODUCE/SECRETE DIGESTIVE ENZYMES!

Accessory Structures to the Rescue

LIVER Largest internal organ of the body Over 500 metabolic functions Digestive Function: Produces BILE for chemical digestion of LIPIDS

GALL BLADDER Small sac embedded in liver Stores bile produced by liver

PANCREAS Embedded within outer duodenum Produces PANCREATIC JUICE containing: Secretes PJ into duodenum via common bile duct amylases proteases lipases Nucleases

PART IV THE LARGE INTESTINE (aka COLON)

Digestive Processes of the Large Intestine ABSORPTION OF: WATER VITAMINS PRODUCTION OF VITAMIN K E. coli; bacterial flora PROPULSION OF FECES FOR DEFECATION