The Digestive System alimentary canal Overall Function Digestion

The Digestive System “alimentary canal”

Overall Function Digestion is the chemical and physical breakdown of food into a form usable by cells.

Organs of Digestive System MAJOR ORGANS • Mouth • Oropharynx • Esophagus • Stomach • Small intestine • Large intestine • Rectum ACCESSORY ORGANS • salivary glands • Tongue • Teeth • Liver • Gallbladder • Pancreas • Vermiform appendix

Digestive Tract Also known as alimentary canal or gastrointestinal (GI) tract. It forms a tube that separates from digesting food from the body’s internal cavity.

Layers of GI tract Mucosa – Inner layer of the lumen (open space) Submucosa – Made of connective tissue, glands, blood vessels and nerves Muscularis – Surrounds submucosa, smooth muscle that contains nerves that form part of the intramural plexus Serosa – Outermost layer made of connective tissue

The Mouth • Lips – When closed form the oral fissure • Cheeks – Formed by muscle and adipose tissue • Hard & soft palate – Uvula suspends from soft palate • Tongue – Muscle movements aid in mastication

The Mouth

Salivary Glands • Pairs include parotids, submandibular, and sublingual • Secrete ~1 L of saliva per day • Buccal glands in the mucosa lining produces a small amount of saliva

The Teeth • Three main parts – Crown – Neck – Root • Deciduous teeth(20) are baby teeth • Permanent teeth(32) show up from 6 -13 yrs

The Pharynx • Deglutition is the act of swallowing a bolus, rounded mass of food and saliva from the mouth to the stomach.

The Esophagus • • • ~10 inches longs Sits posterior to trachea and heart It is normally flatted in resting state • Each end is guarded be a sphincter – Upper esophageal (UES) – Lower (cardiac) esophageal (LES) • Esophageal hiatus is opening in diaphragm where esophagus passes – When enlarged can lead to hiatal hernia GERD- gastro esophageal reflux disorder, severe acid reflux and indigestion caused by weakened LES.

The Stomach • Located directly below the diaphragm • Normally holds 1 -1. 5 L • 3 parts Esophageal hiatis – Fundus (upper left) – Body (central) – Pyloris (lower) • 2 sphincter – LES(cardiac) – Pyloric fundus body pyloris

The Stomach • Gastric Mucosa, lining of the stomach contain many folds called rugae and depression called gastric pits • Cells in the stomach produce HCL and intrinsic factor • Intrinsic factor binds to B 12 molecules keeping them from being broken down so they can be absorbed in the sm. Intestines

The Stomach • Gastric muscles, muscularis, is made of longitudinal, circular and oblique layers. This gives it strong grinding power.

The Stomach Overall Functions • Secrete gastric juices and intrinsic factor • Store partially digested food • Churn food with digestive juices and move it into duodenun • Limited absorption, alcohol, some H 2 O and some fats • Release hormones that regulate digestive functions • Destroy pathogenic bacteria

The Small Intestine • ~6 m in length • 3 parts – Duodenum- first section, shaped like a C – Jejunum- 2. 5 m, begins with abrupt turn – Ileium- last 3. 5 m • Small projections called villi line the sm. Intestine. – Each contain an arteriole, venuole and lacteal • Microvilli present on the villi increase the surface area of intestinal wall

The Small Intestine • Secretion of digestive enzymes and absorption occur in small intestine • Small pockets at the base of the villi, called crypts, contain cells that reproduce rapidly • These cells push up and constantly replace older cells that are shed

Large Intestine • 1. 5 -1. 8 m • 3 parts – Cecum- first 5 -8 cm – Colon • • Ascending Transverse Descending Sigmoid (s-shaped) – Rectum 17 -20 cm • Anal canal has folds with a vein and artery • Hemorrhoids are enlargement of those veins – Anus is made up of two sphincters

The Large Intestines

Accessory Structures • Vermiform appendix- thought to hold beneficial flora • Peritoneum- serous membrane that lines abdominal cavity • Mesentery- fan shaped part of peritoneum which attaches to small intestine • Omentum- attached to greater curvature of the stomach and is laced with fat deposits

The Liver • Weighs ~1. 5 kg • Made of two lobes – Left lobe is smaller – Right lobe has 4 parts • Liver is made of small units called hepatic lobules

The Liver • Blood enters the lobules from the hepatic portal system to be “cleaned” • The liver: – Destroys old RBCS, bacteria – Vitamins and nutrients are metabolized – Toxins are absorbed and detoxified – Bile formed collects in small bile ducts

Bile Ducts • The right and left bile ducts emerge from under the liver to form the common hepatic duct • The common hepatic duct joins with the cystic duct (gallbladder) to form the common bile duct • Common bile duct empties into the duodenum

Function of the Liver • Detoxify substancealcohol, medicines • Bile production • Metabolize fats, proteins and carbohydrates • Store substances. Fe, vitamins A, B 12, D • Bile salt released by liver aid in absorption of fats

Gall Bladder • Main function is to store and concentrate bile • Contain tiny folds of rugae that contract to secrete bile during digestion • Jaudice is caused by a buildup of bile in the blood • Cholelithiasis is the formation of gallstones

Pancreas • Fish shaped textured organ that is exocrine and endocrine gland • Rests below stomach on top of duodenum • Exocrine portion secrete digestive enzymes that collect in the pancreatic duct, that joins the common bile duct • Endocrine islets cells secrete insulin and glucagon directly into the blood