Digestive+System

** Should have 2 images, and missing quiz! **


Structure and Function Upper Digestive System
 * Esophagus: The esophagus is a muscular tube connecting the throat. The esophagus is about 8 inches long, and is lined by moist pink tissue called mucosa. Just before entering the stomach, the esophagus passes through the diaphragm.


 * stomach: The stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives food from the esophagus.

Lower Digestive System]
 * Duodenum : The duodenum is the shortest part of the small intestine, where most chemical digestion takes place
 * Bowel or IIntestine
 * jejunum: connecting the Duodenum to the Ileum. It contains the plicae circulares, and villi
 * Ileum: Has villi, where all soluble molecules are absorbed into the blood.
 * Pancreas: secretes pancreatic fluid to help to further break down the carbohydrates, proteins, and lipids (fats)
 * Gallbladder: aids mainly in fat Digestion and concentrates Biles produced by the liver


 * Large intestine: Has three parts:
 * Cecum: The Vermiform appendix is attached to the Cecum).
 * Colon: The main function of the Colon is to absorb water, but it also contains bacteria that produce beneficial vitamins like Vitamin K
 * Rectum:The rectum intestinum acts as a temporary storage site for feces
 * Anus: The human anus [|[2] ] is the opening of the rectum

HERE'S A VIDEO!

[]

Regulation of the Digestive System automatic activity autonomic nerves hormones parasympathetic: rest and digest sympathetic: fight and flight enteric nervous system: intrinsic nervous system in GI system __ Autonomic Branch __ ­ parasympathetic ­ motility, open valves __ Effect on GI system __ ­ sympathetic ¯ motility, close valves Three Phases in Control of Gasric Function

__ Cephalic Phase __ : Stomach responds to the mere sight, smell, taste, or thought of food Regulation by the vagus nerve: lasts approximately 30 minutes. Activation of the vagus nerve:
 * indirectly causes the parietal cells to secrete HCl
 * directly stimulates chief cells to secreate pepsinogen to digest proteins

__ Gastric Phase : __ Stimulated by distension of the stomach (i.e. amount of chyme) chemical nature of the chyme
 * The goal of this phase is to release acid and proteolytic enzymes into the stomach.

__ Feedback loops __


 * A positive feedback loop occurs in which peptides cause acid and pepsinogen to be released and this in turn causes more peptides in the stomach
 * A negative feedback loop occurs in which the low pH of the stomach inhibits gastrin secretion by the G cells which results in less acid secretion.

__ Stimulus for gastric phase: __ peptides (particularly phenylalanine and tyrptophan) stimulate pepsinogen and acid secretion glucose and fats do not stimulate acid secretion. __ Intestinal phase: __ duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes

__ Control of Intestine __
 * Chyme in duodenum stimulates
 * gastric inhibition
 * pancreatic secretion
 * bile secretion

Enzymes/Hormones

Digestion is the chemical breakdown of large food molecules into smaller molecules that can be used by cells. The breakdown occurs when specific enzymes are mixed with the food. Salivary amylase breaks starch down to maltose. Mucins lubricate and help hold chewed food together in a clump called a bolus. Gastric glands within the stomach produce secretions called **gastric juice**. Hydrochloric acid converts pepsinogen to pepsin which breaks down proteins to peptides. It also dissolves food and kills microorganisms. Mucousprotects the stomach from HCl and pepsin. Seeing, smelling, tasting, or thinking about food can result in the secretion of gastric juice. The duodenum is the first part of the small intestine. The pancreas acts as an exocrine gland by producing **//pancreatic juice//** which empties into the small intestine via a duct. The pancreas also acts as an endocrine gland to produce insulin. Pancreatic juice contains sodium bicarbonate which neutralizes the acidic material from the stomach. The presence of food in the stomach stimulates stretch receptors which relay this information to the medulla oblongata. The medulla stimulates endocrine cells in the stomach to secrete the hormone **//gastrin//** into the circulatory system. Gastrin stimulates the stomach to secrete gastric juice. This pathway of information is summarized below. It stimulates the pancreas to produce sodium bicarbonate, which neutralizes the acidic chyme. It also stimulates the liver to secrete bile.
 * Enzymes involved in Digestion **
 * __ Stomach __****__ Enzymes __**
 * Gastric juice **
 * // Pepsinogen //** is converted to pepsin, which digests proteins. Pepsinogen production is stimulated by the presence of gastrin in the blood.
 * // Gastrin //** is a hormone that stimulates the stomach to secrete gastric juice.
 * __ Duodenum __**
 * __ Pancreas __**
 * Pancreatic Juice **
 * __ Hormones Involved in Digestion __**
 * Gastrin **

Communication

The digestive system is controlled by the enteric nervous system. It oversees every aspect of digestion. The ENS is en extension of the central nervous system. It is embedded in all 30 feet of the digestive tract.

The Brain

The brain communicates with the digestive system through the autonomic nervous system, which controls the body's vital functions. Parasympathetic nerves pass tyour o and from the base of the brain through the vagus nerve from the upper digestive tract or the sacral nerves from the colon. The gut and brain use their shared neurotransmitters, including acetylcholine and serotonin, to transmit information back and forth by way of the sympathetic and parasympathetic nerves.

This is why you stop eating when you are full. The nerve ending of the ENS tell your brain the food level.