Difference between GI Tract and Accessory Organs

• Accessory organs are salivary glands (submandibular, parotid, and sublingual), liver, gallbladder (stores bile), pancreas, teeth, tongue
• GI tract is the muscular digestive tube that winds through the body, extending from the mouth to the anus

Major Function

• Break food down into pieces small enough to be absorbed into the circulatory system
• Eliminate what cannot be broken down

Mechanical Digestion Vs Chemical Digestion

• Cut food up small. Mechanical digestion involves the teeth (chewing), stomach (churning) and small intestine (segmentation)
  
  • Segmentation: nonadjacent segments of alimentary tract organs alternatively contract and relax, moving food forward and backward
• Chemical Digestion involves chemicals (enzymes), stomach, small intestine (many come from pancreas), mouth (saliva)

Peristalsis: adjacent segments of alimentary tract organs alternatively contract and relax moving food along the tract distally.

Food travels from oral cavity -> pharynx-> esophagus -> stomach-> small intestine -> large intestine -> anus

Mesentery: double layered peritoneum that stores fat, provides place for nerves and blood vessels to "hang out", and holds organs in place

• Mesentery proper: within the jejunum & ileum
• Mesocolon: within the transverse and sigmoid colon
• Lesser omentum: from the liver to the lesser curvature of the stomach
• Greater omentum: stores fat. has the ability to wrap around and enclose an infected area or inflamed organ (ex appendix)

Intraperitoneal: surrounded by the peritoneal cavity

• liver, stomach, ileum, jejunum, sigmoid colon and transverse colon
  
  

Retroperitoneal: outside the peritoneum against the posterior abdominal wall

• ascending and descending colon, pancreas, rectum, duodenum ( almost all of it)

• Parietal cells/glands: secretes hydrochloric acid and intrinsic factor that is used to absorb vitamin B12. Vitamin B12 produces erythrocytes
• Chief cells/gland: secrete acid and pepsinogen. Pepsin is the enzyme used to breakdown protein.

Sphincters:

• Cardiac sphincter prevents reflux of acid into the esophagus
• Pyloric sphincter regulates the amount of chyme moving on into the small intestine

Rugae of stomach increase storage capacity and increase surface area

Structures:

• Duodenal glands that secrete alkaline mucous to neutralize the acidic stomach
• intestinal glands: secrete a watery intestinal juice
• Peyer patches - collection of lymphocytes

• Ileocecal valve prevents content from moving backwards

Teniae coli, haustra, and epiploic appendages

• Teniae coli: 3 strips of longitudinal muscle
• Haustra: contract and pull colon into pouches (sacs)
• Epiploic appendages - has fat

Liver Function

• remove toxins from the blood
• process fat and amino acids
• produce blood proteins: albumin, fibrinogen, globulin
• making bile - stores some vitamins
• stores glucose as glycogen
  
  

Hepatic Portal System

• Most nutrients absorbed by the intestine pass through the liver which serves as a filter that can remove potentially harmful xenobiotics before they get into the systemic circulation
• Portal circulation is heart -> arteries to digestive system-> capillaries-> hepatic portal vein-> capillaries of liver -> hepatic vein -> inferior vena cava -> heart

Pancreatic Acini Function

• exocrine part of gland that produces bicarbonate which is an alkaline substance that neutralizes acid in stomach and secretes 22 + enzymes that enter the duodenum