Anatomy and Physiology Notes: Gastrointestinal-Hepatobillary System

This is an outlined lecture note on the Anatomy and Physiology of theGastrointestinal-Hepatobillary System. Some information are so compressed that some concepts are not explained in detail. If it is your first time to meet such information please refer to your textbook for further explanation of the concept. This review material requires a student to have a prior knowledge and good foundation of the subject matter for this only emphasizes important/ key information deemed important in understanding advanced concept in Pathophysiology and Medical Surgical Nursing.

Functions of the gastrointestinal system
- Process food substances.
- Absorb the products of digestion into the blood.
- Excrete unabsorbed materials.
- Provide an environment for microorganisms to synthesize nutrients, such as vitamin K.

 Mouth
- Contains the lips, cheeks, palate, tongue, teeth, salivary glands, muscles, and maxillary bones
- Saliva contains the amylase enzyme (ptyalin) that aids in digestion.

Esophagus
- Collapsible muscular tube about 10 inches long
- Carries food from the pharynx to the stomach


The stomach
- Contains the cardia, fundus, the body, and the pylorus
- Mucous glands are located in the mucosa and prevent autodigestion by providing an alkaline protective covering.
- The lower esophageal (cardiac) sphincter prevents reflux of gastric contents into the esophagus.
- The pyloric sphincter regulates the rate of stomach emptying into the small intestine.
- Hydrochloric acid kills microorganisms, breaks food into small particles, and provides a chemical environment that facilitates gastric enzyme activation.
- Pepsin is the chief coenzyme of gastric juice, which converts proteins into proteases and peptones.
- Intrinsic factor is necessary for the absorption of vitamin B12.
- Gastrin controls gastric acidity.

Small intestine
- The duodenum contains the openings of the bile and pancreatic ducts.
- The jejunum is about 8 feet long.
- The ileum is about 12 feet long.
- The small intestine terminates in the cecum.

Pancreatic intestinal juice enzymes
- Amylase digests starch to maltose.
- Maltase reduces maltose to monosaccharide glucose.
-  Lactase splits lactose into galactose and glucose.
- Sucrase reduces sucrose to fructose and glucose.
- Nucleases split nucleic acids to nucleotides.
-. Enterokinase activates trypsinogen to trypsin.


Large intestine
- About 5 feet long
- Absorbs water and eliminates wastes
- Intestinal bacteria play a vital role in the synthesis of some B vitamins and vitamin K.
- Colon: Includes the ascending, transverse, descending, and sigmoid colons and rectum
- The ileocecal valve prevents contents of the large intestine from entering the ileum.
- The anal sphincters control the anal canal.

Peritoneum: Lines the abdominal cavity and forms the mesentery that supports
the intestines and blood supply

Liver
-The largest gland in the body, weighing 3 to 4 lb.
-Contains Kupffer's cells, which remove bacteria in the portal venous blood
- Removes excess glucose and amino acids from the portal blood
- Synthesizes glucose, amino acids, and fats
- Aids in the digestion of fats, carbohydrates, and proteins
- Stores and filters blood (200 to 400 mL of blood stored)
- Stores vitamins A, D, and B and iron
- The liver secretes bile to emulsify fats (500 to 1000 mL of bile/day).
 Hepatic ducts
a. Deliver bile to the gallbladder via the cystic duct and to the
duodenum via the common bile duct.
b. The common bile duct opens into the duodenum, with the pancreatic duct at the ampulla of Vater.
c. The sphincter prevents the reflux of intestinal contents into the
common bile duct and pancreatic duct.

Gallbladder
-Stores and concentrates bile and contracts to force bile into the duodenum during the digestion of fats
- The cystic duct joins the hepatic duct to form the common bile duct.
- The sphincter of Oddi is located at the entrance to the duodenum.
- The presence of fatty materials in the duodenum stimulates the liberation of cholecystokinin, which causes contraction of the gallbladder and relaxation of the sphincter of Oddi.

Pancreas
Exocrine gland
- Secretes sodium bicarbonate to neutralize the acidity of the stomach contents that enter the duodenum
-. Pancreatic juices contain enzymes for digesting carbohydrates, fats, and proteins.
Endocrine gland
- Secretes glucagon to raise blood glucose levels and secretes somatostatin to exert a hypoglycemic effect
- The islets of Langerhans secrete insulin.
- Insulin is secreted into the bloodstream and is important for carbohydrate metabolism.

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