DIGESTIVE SYSTEM

Phases of the Regulation of Stomach Secretions

1) Cephalic Phase 2) Gastric Phase 3) Intestinal Phase

Groups of Epithelial Cells in the Stomach

1) Surface mucous cells; produce mucus, located on surface line of gastric pit. 2) Mucous neck cells; produce mucus. 3) Parietal cells; produce hydrochloric acid(most things die in contact w this) and intrinsic factor(important in the absorption of B12). 4) Chief(zymogenic) cells; produce pepsinogen; pepsin is the enzyme involved in the reaction that will break down protein. 5) Endocrine cells; produce regulatory hormones.

Trypsinogen, Chymotrpsinogen, & Procarboxypeptidase

3 Enzymes released from the pancreas and into the small intestine in inactive forms. The Enzyme Enteropeptidase(enterokinase), produced by the small intestine activates trypsinogen to trypsin. Trypsin in turn activates Chymotrpsinogen to chymotrpsin and procarboxypeptidase to carboxypeptidase.

Deglutition; Swallowing

3 Separate Phases; Voluntary Phase, Pharyngeal Phase, Esophageal Phase

Small Intestines

6m long; Site at which the greatest amount of digestion and absorption occur. Most of the digestive enzymes that enter the small intestine come from the pancreas. Enzymatic digestion and absorption of water, organic substrates, vitamins and ions.

Bilirubin

A Bile pigment that results from the breakdown of hemoglobin.

Voluntary Phase of Deglutition

A Bolus of food is formed in the mouth and pushed by the tongue against the hard palate, forcing the bolus toward the posterior part of the mouth and into the Oropharynx.

Tongue

A Large Muscular Organ covered by moist stratified squamous epithelium that occupies most of the Oral Cavity when the mouth is closed. Sensory Organ for taste. Its major attachment in the oral cavity is through its posterior part. The Anterior portion is relatively free and is attached to the floor of the mouth by a thin fold of tissue called the frenulum. (Contain Lingual Glands)

Digestive Tract

A tube extending from the mouth to the anus and its accessory organs through which food passes during the process of being digested. These include the mouth, esophagus, pharynx, salivary glands, stomach, pancreas, small intestine, liver, gallbladder, large intestine, rectum, and anus. Each segment is specialized to assist moving contents from the oral end to the anul end.

Chemical Digestion

Accomplished by Digestive Enzymes that are secreted along the digestive tract

Pancreatic Lipase

An enzyme produced by the pancreas and released into the duodenum. Facilitates the majority of triglyceride(Fat) digestion in the small intestine.

Submandibular Glands

Are Mixed glands with more serous then mucous secretion, can be felt as a soft lump along the inferior border of the posterior half of the mandible.

Intrinsic Muscles of the Tongue

Are largely responsible for changing the shape of the tongue, such as flattening and elevating the tongue during drinking and swallowing.

Parotid Glands

Are the largest salivary glands; serous glands, which produce mostly watery saliva and are located just anterior to the ear on each side of the head.

Sublingual Glands

Are the smallest of the three large paired salivary glands. Are mixed glands whose secretion is primarily mucous secretion,

Secretion

As food moves through the digestive tract, secretions are added to lubricate, liquify, and digest bolus.

Segments of the Large Intestines

Cecum, Ascending colon, Transverse Colon, Descending Colon, Sigmoid Colon, Rectum; joins the anal canal, which ends at the anus ; the inferior termination of the digestive tract.

Pharynx

Consists of 3 parts; Nasopharynx; Normally only the oropharynx and the laryngopharynx propel materials into the esophagus.

Large Intestine

Dehydration and Compaction of indigestible materials in preparation for elimination; Is the last section of the digestive tract; Absorbs water and salts and concentrates undigested food into feces.

Digestive System

Delivers the Nutrients to many cells of the Body. It provides the body with water, electrolytes and other nutrients.

Enzymes in Microvilli in the Small Intestine

Disaccharides, which break disaccharides down to monosaccharides; Peptidases, which hydrolyze the peptide bonds between small amino acid chains; Nucleases, which break down nucleic acids.

Segments of the small intestine

Duodenum; 1st segment 12 inch long Jejunum; 2nd segment, 2/5th's of total length of the intestines; small glands exist along its length and it is a major site of absorption. ileum; 3rd segment; 3/5th's of length, similar to jejunum, except there are fewer digestive enzymes and more mucous secreted and less absorption occurs.

Pancreatic Amylase

Enzyme in pancreatic juice that breaks down carbohydrates. Converts polysaccharides into monosaccharides. Is secreted in its Active Form.

Pancreas

Exocrine secretions of the pancreas are called pancreatic juice and have 2 major components. Aqueous (neutralize chyme) and enzymatic (acinar cells). The pancreatic juice is produced in the pancreas and then delivered through pancreatic ducts to the small intestine, where it functions in digestion.

Cheeks

Form the Lateral Walls of the oral cavity, they consist of an interior lining of moist stratified epithelium. Help to manipulate food within the mouth and hold food in place while the teeth crush or tear it. (Contain Buccal Glands)

Functions of the Stomach

Functions Primarily as a storage and mixing chamber for the chyme, which is a semi fluid mixed with digested food and stomach secretions. Although some digestion and absorption occur here it is not its major functions.

Hormones that Regulate Stomach Secretions

Gastrin, Secretin, Gastric-inhibitory polypeptide, Cholecytokinn

Pharyngeal Phase of Deglutition

Involuntary;2nd phase of swallowing Is a reflex that is initiated by stimulation of tactile receptors in the area of the oropharynx. Involves the elevation of the larynx, reflection of the epiglottis, and closure of the glottis. These movements of the Larynx prevent food from passing through the opening to the Larynx.

Mechanical Digestion

Involves Mastification and mixing of Food

Intrinsic Factor

Is a Glycoprotein that binds with vitamin B12 and makes the vitamin more readily absorbed in the ilium.

Rectum

Is a straight, muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal.

Colon

Is about 1.5-18m long and consists of 4 parts. The Ascending Colon; The Transverse Colon; The Descending Colon; The Sigmoid Colon.

Esophagus

Is about 25mm long; Extends from the Pharynx to the stomach and Transports foods from the pharynx to the stomach; has thick walls consisting of the 4 tunics similar to the digestive tract; mucosa, submucosa, muscularis , serosa. Difference is that it consists of skeletal muscle in the superior part and smooth muscle in the inferior part. Mucosal lining is moist stratified squamous epithelium.

Stomach

Is an enlarged segment of the digestive tract in the left superior part of the abdomen. Chemical Breakdown of materials via acid and enzymes; mechanical processing through muscular contractions.

Appendicitis

Is an inflammation of the Vermiform appendix and usually occurs bc of obstruction of the appendix, secretions from the appendix can not pass the obstruction and accumulate causing enlargement and pain. Symptoms include abdominal pain, specifically in the lower portion of the abdomen, slight fever, loss of appetite, constipation, diarrhea, nausea and vomiting. If appendix bursts it can be life threatening.

The intramural plexus

Is important in the control of movement and secretion; consists of both Myenteric Plexus(Aurbach's) and the Submucosal plexus(Meissners)

Cecum

Is the 1st portion of the large intestine. Where the large and small intestine meet. Attached to the Cecum is a small bind tube about 9cm long called the vermiform appendix.

Elimination

Is the Process by which the waste products of digestion are removed from the body. Occurs primarily in the large intestines.

Digestion

Is the breakdown of organic molecules into their component parts; Carbohydrates into monosaccharides, Proteins into amino acids, Triacylglycerols into fatty acids and glycerol.

Duodenum

Is the first portion of the small intestines. The liver and the pancreas are associated with this. Is Simple Columnar Epithelium w 4 major cell types. 1) Absorptive cells; have microvilli, which produce digestive enzymes and absorb digestive food. 2) Goblet cells; produce protective mucus. 3) Granular cells; help protect the intestinal epithelium from bacteria. 4) Endocrine cells; produce regulatory hormones.

Mouth; Oral Cavity

Is the first section of the digestive tract. Is surrounded by the lips, cheeks, teeth and palate and it contains the tongue.

Body of Stomach

Is the largest part of the stomach. which turns to the right and creates a greater curvature and lesser curvature.

Absorption

Is the movement of molecules out of the Digestive tract and into the circulation or into the Lymphatic System

Uvula

Latin for a little grape; projection hanging from the soft palate. Purpose of this is to prevent food from going down the nasopharynx, where it can come out of your nose.

Oral Cavity; Mouth

Lined with moist stratified squamous epithelium; Divided into two regions; Vestibule and Oral Cavity Proper.

Hepatocytes

Liver cells that can remove sugar from the blood and store it in the form of glycogen, they can also store fat, vitamins A, B12, D, E,K, copper and iron. Remove ammonia from the circulation and covert it to urea, which is secreted into circulation and then eliminated by the kidneys in urine.

Surface Mucous Cells and Mucous Neck Cells

Located in the Stomach. Secreted a viscous and alkaline mucus that covers the surface of the epithelial cells and forms a layer of 1-1.5mm thick. The thick layer of mucus lubricates and protects the epithelial cells of the stomach wall from the damaging effects of the acidic chyme and pepsin.

Stomach Secretions

Mucus, Hydrochloric Acid, Gastrin, Intrinsic Factor, Pepsinogen

Lips; Labia

Muscular folds covered internally by mucosa and externally by stratified squamous epithelium. Are important in the process of mastication and speech. Help to manipulate food within the mouth and hold food in place while the teeth crush or tear it. (Contain Labial Glands)

Emulsification

Occurs by the action of bile salts, which are part of bile. Bile emulsifies fats so that the pancreatic lipase has greater access to the triglyceride molecules and may more effectively chemically digest the fat.

Serosa (Adventitia)

Outermost layer of surrounding connective tissue and simple squamous epithelium.

Fondus

Part of Stomach located left to the Cardiac Region

Liver

Performs important digestive and excretory functions, stores and processes nutrients, synthesizes new molecules and detoxifies harmful chemicals. Produces and secretes about 600ml-1000ml of bile each day.

Bile

Produced and secreted by the Liver. Contains no digestive enzymes but plays a role in digestion by diluting and neutralizing stomach acid and by emulsifying fats. The ph of chyme is too low for normal function of pancreatic enzymes. Bile helps to neutralize the acidic chyme and bring the ph up to a level at which the pancreatic can function. Bile salts can emulsify fats. Most bile salts are reabsorbed in the ileum and carried in the blood back to the liver where they stimulate further bile secretion.

Proteolytic Enzymes

Produced in pancreas by acinar cells and released into the small intestine. They digest proteins and are secreted in inactive forms. Major Proteolytic Enzymes are; Trypsin, Chymotrypsin, Carboxypeptidase.

Acinar Cells

Produces the enzymatic component of the pancreatic juice, which is important in digestion of all major classes of food.

Hydrochloric Acid

Produces the low ph of the stomach, which is normally between 1 and 3. Has a minor digestive effect on ingested food. Main function is to kill bacterias that are ingested. The low ph also denatures many proteins and it provides the proper ph environment for the function of pepsin.

Extrinsic Muscles of the Tongue

Protrude and contract the tongue, move it from side to side, and change its shape.

Pylorus

Region of stomach which joins the small intestine-the opening is called the pyloric opening

Cardiac Region of Stomach Cardiac Sphincter

Regions of stomach that surround the cardiac opening

Peristalsis

Responsible for moving material through most of the digestive tract. Muscular contractions occur in peristaltic waves.

Mucus

Secreted along the Entire Digestive Tract, lubricates the foods and the lining of the digestive tract; protects epithelial cells of the Digestive tract from; Mechanical Abrasion, the damaging effects of acid in the stomach and the digestive enzymes of the digestive tract.

Pepsinogen

Secreted by the Stomach. Is the Inactive form of the protein digesting enzyme pepsin. Is secreted by the chief cells within the gastric glands.

Saliva

Secreted of a rate of about 1-1.5L/day. Serous part of the saliva contains a digestive enzyme called salivary amylase, which breaks down the covalent bonds between glucose molecules in starch and other polysaccharides to produce disaccharides, maltose and isomaltose. Saliva prevents bacterial infection in the mouth by washing the oral cavity and contains substances such as lysozyme, which has antibacterial action and Immunoglobulin A, which helps prevent bacterial infection.

Parietal Cells

Secretes Intrinsic Factor and a concentrated solution of hydrochloric acid.

Salivary Glands

Secretion of Lubricating Fluid containing enzymes that breakdown carbohydrates. Are Accessory Organs of the oral Cavity.

Stomach Histology

Serosa; outermost layer, consists of inner connective tissue and an outer layer of simple squamous epithelium Muscularis; 3 layers, Outer- longitudinal, middle-circular, inner-oblique layer, Rugae; allows stomach to descend and stretch. Creates large folds when empty and stretches when full. Stomach is lined with Simple Columnar Epithelium

Jejunum and Ileum

Similar in structure to duodenum except there is a gradual decrease in diameter of small intestine, thickness of intestinal wall and circular folds and less villi. Are the major sites of nutrient absorption. Lymph nodes called Pyers patches are numerous in the Ilium.

Mechanism of Digestive System

Specialized to Ingest Food; Propel it through the Digestive Tract and absorb water, electrolytes and other nutrients from the lumen of the GastroIntestinal Tract. Once useful substances are absorbed they are transported through the circulatory System to cells, where they are used. Undigested matter from the food is removed through the digestive tract and eliminated through the Anus.

Gallbladder

Storage and Concentration of Bile that is secreted by the liver. It can store 40-70ml of bile. Shortly after a meal, the gallbladder contracts in response to stimulation of cholecystokinin and dumps large amounts of bile into the small intestine.

Deglutition

Swallowing; moves mouthfulls of food and liquids, called a bolus from the oral cavity into the esophagus.

Esophageal Phase Of Deglutition

Takes about 5-8 seconds and is responsible for moving the food from the pharynx and to the stomach. Muscular contractions in the wall of the esophagus occur in peristaltic waves.

Cephalic Phase

The 1st Phase in the regulation of gastric secretions. Phase of gastric activity in which the stomach responds to the mere sight, smell, taste, or thought of food by stimulating gastric secretion.

Gastric Phase

The 2nd Phase in the Regulation of gastric Secretions. The greatest volume of gastric secretions is produced, which is initiated by the presence of food in the stomach. The primary stimuli are distention of the stomach and the presence of amino acids and peptides in the stomach.

Intestinal Phase

The 3rd phase of gastric secretions where there is an activation of the receptors in the small intestines by the chyme that moves into the duodenum. Now hormones will be released that will inhibit gastric emptying and a slow down of secretions so that the chyme doesn't dump into the duodenum too fast

Muscles of Mastification

The Temporalis, Masseter and Medial pterygoids all close the jaw and the Lateral Pterygoids opens it.

Teeth of Mastification

The anterior teeth, the incisors and the canines primarily cut and tear the food, whereas the premolars molars primarily crush and grind it.

Mucosa

The innermost Tunic consists of 3 Layers; Inner Mucous Epithelium, Loose Connective Tissue called Lamina Propria, An outer thin muscle layer, muscularis

Ingestion

The introduction of a solid or liquid food into the stomach. The normal route of Ingestion is through the Oral Cavity.

Anal Canal

The last 2/3rd's of the digestive tract. Begins at the inferior end of the rectum and ends at the anus.

Propulsion

The movement of food from one end of the digestive tract to the other. The total time for food to travel the length of the digestive tract is about 24-36 hours. Each segment of the digestive tract is specialized to assist in moving its content to the oral to the anul end.

Gastroesophageal Opening of Stomach

The opening from the esophagus into the stomach

Transportation

The process by which absorbed molecules are distributed throughout the body; this distribution can occur either directly by way of circulation or indirectly by first entering the lymphatic system and then passing the circulatory system.

Mastification

The process by which food taken into the mouth is chewed by the teeth. Breaks down large food particles into many smaller particles, which have a larger surface area. Increases the efficiency of digestion bc digestive enzymes digest food molecules only on the surface of the particles.

Regulation

The processes of propulsion, secretion, absorption, and elimination are regulated by the nervous and hormonal mechanisms.

Gastric Inhibitory Hormone and Cholecystokinin

The release of these two hormones is through the fatty acids and lipids in the Duodenum and the Proximal Jejunum.

Salivary Glands

The secretion from all of the glands helps keep the oral cavity moist and begins the process of digestion. Saliva is a combination of serous fluids and mucus.

Vestibule

The space between the lips or cheeks and alveolar processes, which contain the teeth.

Submucosa

Thick Connective Tissue Layer containing nerves, blood vessels, and small glands that lie beneath the mucosa. Also consists of the Submucosal plexus(Meissner's); network of unmyelinated nerve fibers and ganglion cells.

Palate

Very important in the swallowing process; prevents food from passing into the nasal cavity; Consists of two parts; Hard Palate; Anterior boney part and Soft Palate; the posterior non boney part, which consists of skeletal muscle and connective tissue;

Oral Cavity; Teeth, Tongue

Where Chemical and Mechanical Digestion begins. Chemical is the moistening and mixing with salivary secretions.

The Muscularis Layer

consists of an inner layer of circular smooth muscle and an outer layer of longitidinal smooth muscle. And the myenteric plexus, which consists of nerve fibers and parasympathetic cell bodies.

Layers of Digestive Tube

mucosa, submucosa, muscularis externa, serosa