Digestive System Chapter 18

Muscularis

2 or 3 layers of smooth muscle in the GI tract, responsible for movement, motility. It is responsible for segmental contractions and peristaltic movement through the GI tract.

Urobilinogen

A SUBSTANCE FORMED WHEN BACTERIA IN THE DIGESTIVE TRACT BREAKS DOWN BILIRUBIN. SMALL % IS EXCRETED IN THE URINE AND IS INCREASED IN LIVER DISEASE. UROBILINOGEN GIVES COLOR TO FECES

Cecum

A U-shaped pouch at the proximal end of the large intestine, Blind pouch, posterior end of small intestine. , connected to the junction of the small and large intestines. Absorb fluids and salts

Appendix

A small, fingerlike extension of the vertebrate cecum; contains a mass of white blood cells that contribute to immunity.

Bile

A substance produced by the liver that breaks up fat particles. The liver makes 250-1500 ml of bile per day. Composed of Bile pigment, bile salts, phospholipids, cholesterol, inorganic ions.

Bolus

A term used to describe food after it has been chewed and mixed with saliva

Bile Salts

An example of an emulsifier, From Gallbladder Aids in digestion, Lipids that break down fats in small intestine. Made from bile acids conjugated with glycine of taurine. Derived from cholesterol.

Cardiac Region of Stomach

An imaginary horizontal line drawn through the cardiac region divides the stomach into an upper fundus and lower body which together compose the 2/3 of the stomach

Digestion of Fats

As fat enters the small intestine bile is secreted from the gallbladder into the small intestine. Bile is produced by the liver and stored in the gallbladder. Bile disperses fat into small fat droplets. Pancreatic enzymes break fat into 2 separate fatty acids and a monoglyceride. Fat digestion occurs at the surface of the droplets through the enzymatic action of pancreatic lipase which is aided in its action by a protein called colipase that coats the emulsification of droplets and anchors the lipase enzyme to them.

Intestinal Microbiota

Bacteria residing in the intestine, primarily the colon. They produce significant amounts of vitamin K and folic acid, which is absorbed in the large intestine. Microorganisms are present in relatively small numbers in the stomach and proximal portion of the small intestine. In the colon the intestinal microbiota are comprised mostly of anaerobic bacterial species.

Pharyngeal Phase

Bolus comes in contact with sensory receptors around the pharynx and the posterior pharyngeal wall, initiating the involuntary swallowing reflex. Receptors in the posterior portion of the oral cavity and oropharynx stimulate the pharyngeal phase of the swallowing reflex.

Digestion

Breakdown of food substances into simpler forms that can be absorbed and used

Digestion of carbohydrates

Carbohydrate digestion begins in the mouth through the action of salivary amylase. Amylase breaks down complex carbohydrates into smaller fragments, producing a mixture primarily composed of disaccharides & trisaccharides. Most carbs are ingested as starch.

Sections of the Large Intestine

Cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, and anal canal.

Digestion of proteins

Digestion of proteins begins in the stomach, Proteins are converted to amino acids, which are usually converted back into the proteins that the body requires. Some amino acids are broken down via glycolysis or the krebs cycle, while others are converted into Acetyl CoA

Peptic Ulcer

Erosions of the mucosa of the stomach or duodenum that penetrate through the muscalaris layer. Zollinger-Ellison syndrome ulcers of the duodenum are produced by excessive gastric acid secretion is response to very high levels of the hormone gastrin., -open sore in the lining of the stomach esophagus or upper small intestine

Ileum

Final segment of the small intestine; fine tune oraganic absorption (B12,iron,etc) picks up/absorbs any nutrients not already absorbed. Empties into the large intestine

Duodenum

First part of the small intestine. The first 20-30 cm extending from the pyloric sphincter.

Rugae

Folds, Elevations or ridges, as in stomach mucosa. The openings of the stomach lumen are called gastric pits. The cells that line the folds secrete various products into the stomach; these cells form the exocrine gastric glands.

Ingestion

Food intake

Layers of the Gastrointestinal Tract

From the esophagus to the anal canal is compsed of four layers, or tunics. Each tunic contains a dominant tissue type that performs specific functions in the digestive process. Mucosa, submucosa, Muscularis, Serosa.

Mucosa

Inner layer of the alimentary canal which is lined with epithelium attached to connective tissue; it protects tissues of the canal and carries on secretion and absorption. t is the absorptive and major secretory layer.

Peristalsis

Involuntary waves of muscle contraction that keep food moving along in one direction through the digestive system.

Stomach

J-shaped and most distensible part of the GI tract. Continuous with the esophagus superiorly and empties into the duodenum of the small intestine inferiorly.

Liver

Largest Internal Organ. Hepatocytes form hepatic plates. The plates are separated from each other by large capillary spaces called sinusoids. Immediately beneath the diaphragm, mostly on the right side. Kubffer cells are also in the sinusoids. Hepatic damage due to alcohol or viral hepatitis causes liver fibrosis that can lead to cirrhosis of the liver.

Swallowing Center

Located in medulla. When stimulated, reflex activates in appropriate sequence the muscles involved in swallowing. Most complex process in body. , Interacting neurons in the medulla oblongata that coordinate the pattern of contractions required for swallowing.

Jejunum

Middle portion of the small intestine, Attaches anteriorly to the duodenum, Absorbs carbohydrates and proteins

Segmentation

Movement of food through the gastrointestinal tract

Enterochromaffine-Like Cells

Nueroendocrine type (paracine) cells, part of gastric gland. They are activated by circulating gastrin and parasympathetic nerves (vagus). They release histamine which stimulates parietal cells.

Substances absorbed in Stomach Wall

Only commonly ingested substances that can be absorbed across the stomach wall are alcohol and asprin. Absorption occurs as a result of the lipid solubility of molecules. Aspirin and NSAIDS can promote damage to the gastric mucosa and cause bleeding, and must be avoided in people with gastric ulcers.

Phases of Deglutition

Oral, Phyaesophagus.ryngeal, Esphageal. Swallowing is a complex activity that requires the coordinated contractions of 25 pairs of muscles in the mouth, pharynx, larynx and esophagus.

Serosa

Outer connective tissue covering, secretes serous fluid to lubricate and prevent friction between digestive organs and surrounding tissue. Also provides support., Most superficial layer of alimentary canal

Chyme

Partially digested, semiliquid food mixed with digestive enzymes and acids in the stomach.

Oral Phase

Phase of the deglutition process in which the bolus is compressed against the hard palate and into the pharynx, Begins when the tongue elevates against the alveolar ridge, moving the bolus posteriorly, and ends with the onset of the pharyngeal swallow. The muscles of the mouth and tongue mix the food with saliva and create a bolus or food that the tongue muscles move toward the oropharynx.

Emulsification

Physical process of breaking up large fat globules into smaller globules, thereby increasing the surface area that enzymes can use to digest the fat.

Mucous Neck Cells

Produce mucus which protects the internal lining of the stomach mucosa from HCL and enzymes

Portal System

Products of digestion absorbed in intestines are delivered to the liver via the hepatic portal vein. Veins from the pancreas, gallbladder, stomach, omentum, and spleen also join with the hepatic portal vein. After circulation through liver capillaries, the blood leaves via the hepatic vein to join regular venous circulation.

Digestion of Starches

Require prolonged digestion to be broken down into simple sugars, maltose in the small intestine comes from digestion of starches. Occurs mainly in the duodenum as a result of the action of pancreatic amylase.

G Cells

Responsible for the release of Gastrin; enters circulation and travels to stomach where it stimulates parietal cell to secrete HCL; stimulates pepsinogen secretion

Parietal Cells

Secret hydrochloric acid (HCI)

Chief Cells/Zymogenic Cells

Secrets pepsinogen, an inactive form of the protein-digesting enzyme pepsin.

Esophageal Phase

Swallow Phase, food goes down esophagus and into stomach, phase of swallowing that is initiated by stretch receptors in esophagus, peristalsis moves the food to stomach

Storage and elimination

Temporary storage and subsequent elimination of indegistible food molecules.

Submucosa

The layer of connective tissue directly under the mucosa of an open body cavity., A layer of the human digestive system that contains nerves, blood vessels, and lymph nodes, - composed of Areolar and Dense Irregular Connective Tissue; amounts vary depending on the specific region of the GI tract. Provides nerves supply to the muscularis mucosae of the small and large intestine.

Digestive Tract

The organs through which food passes during the process of being digested. These include the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. The digestive tract is open at both ends and is continuous with the environment

Mastication

The process of chewing

Secretion

The secretion of useful substances from a cell, either into the blood (endocrine secretin) or into a cavity or onto the body surface (exocrine secretion). Secretion increases the rate at which substances can be removed from the body.

Immune Barrier

The simple columnar epithelium that lines the intestine, with its tight junctions between cells, provides a physical barrier to the penetration of pathological organisms and their toxins.

Motility

This refers to the movemen tof food through digestive trace through the processes of Ingestion, Mastication, Deglutition, Peristalsis and Segmentation.

Absorption

This refers to the passage of digested end-products into the blood or lymph.

Sections of the Small Intestine

duodenum, jejunum, ileum

Absorption of Water

function of large intestine. Occurs passively as a result of the osmotic gradient created by the active transport of ions. The epithelial cells of the intestinal mucosa are joined together. The secretion of water by the mucosa of the arge intestine occurs by osmosis as a result of the transport of Sodium and Chlorine out of the epithelial cells into the intestinal lumen.

Digestive Tract Functions

ingestion, digestion & absorption of nutrients & elimination of wastes. Motility, Secretion, Digestion, Absorption, Storage and elimation, Immune Barrier

Pyloric Region

part of the stomach closest to the small intestine, terminal portion of the stomach that extends between the body and duodenum. Begins at the antrum and ends at the pyloric sphincter.

D Cells

produce somatostatin. regulates other islet cells.

Endocrine Secretions

released into the surrounding interstial fluid and blood; hormones (ex, thyroid and pituitary gland secretions). The stomach and small intestine secret a number of hormones that help to regulate the digestive system.

Function of the Stomach

stores food and regulates entry into small intestine, initiate the digestion of proteins, to kill bacteria with the strong acidity of gastric juice and to move the food into the small intestine as a pasty material called chyme

Gallbladder Functions

stores/concentrates bile from the liver; contracts and secretes bile into the common bile duct to the duodenum. Sac like organ attached in the inferior surface of the liver.

Deglutition

the act of swallowing

Ascending Colon

the part of the large intestine that ascends from the cecum to the transverse colon, Chyme travels upward in this part of the large intestine

Exocrine Secretions

travel by the way of ducts before reaching their target organs, body cavities or body surfaces. Include mucus,sweat,saliva,and digestive enzymes. Water, hydrochloric acid, bicarbonate and many digestive enzymes are secreted into the lumen of the gastrointestinal tract.