Chapter 26- Digestive System Review

List and explain general functional actives of the stomach?

-Ingested materials spend 2-6 hours here. Contains both mechanical and chemical digestion. Mechanically- It mixes the ingested food with secretions released from the stomach we all and mechanically digests the contents into a semifluid mass called CHYME. Chemical Digestion- of both protein and fat begins in the stomach, but absorption from it Is limited to small non polar molecules that in in contact with the mucosa of the stomach. -Serves as the holding bag for controlled release of partially ingested materials into small intestine,. where most chemical digestion and absorption may occur. -Most vital function- stomach release intrinsic factor. (which is required for the absorption of B12., which occurs the small intestine.

Describe the dedication reflex?

-Involuntary component in the elimination of feces. -Filling the rectum initiates the urge to defecatre. _stimulus results in transmission of nerve signals from receptors along sensory nuerons to the spinal cord. -In response, increase Neve signals are relayed along parasympathetic motor neurons -causes the sigmoid colon and rectum to contract and internal (involuntary) sphincter to relax. -Defecation involves both the valsalva maneuver and relaxation of the external anal sphincter.

Describe the accessory organs associated with the small intestine and the contributions of these secretions to digestion?

-Liver, Gallbladder and Pancras are accessory digestive Organs. Liver- Accessory digestive organ -Larget internal organ -Right upper quadrant of abdomen -Production of bile Is main function of liver . - CT capsule branches throughout organ, Forms septa (walls) that partition the liver into thousands of hepatic lobules (structural functional unit of the liver- hepatocytes) -Center of each lobule is central vein which drains the blood flow fro the lubule. Hepatic artery- transports oxygenated blood to the live Hepatic Portal Vein- carries deoxygenated blood from capillary beds of GI tract spleen pancreas.. (deliver 75% of blood to liver) Hepatic veins empty into inferior vena cava Function of Bile -Secreted by the liver -Contains water, bicarbonate ions, bile salts, and pigments cholesterol, lecithin, mucin. -Bile salts and lecithin help mechanically digest lipids. Gallbladder- saclike organ that stores, concentrates, and releases bile that the liver produces. -3 Tunics, inner mucosa, middle muscalris, and external serosa. -Mucosa with clods that allow for distention of wall. -Connected to common bile duct by cystic duct. -Sphincter valve controls flow of bile into and out of the gallbladder,. Pancreas- has both endocrine and exocrine functions Endocrine function- produces and secretes insulin and glucagon. Exocrine function- Produces pancreatic juice to assist with digestion activities. Acinar cells in pancreas produce and release digestive enzymes. Pancreatic juce- alkaline fluid containing mostly water, bicarbonate and mixture of digestive enzymes. -Pancreatic amylase to digest starch Pancreatic lipase for the digestion of triglycerides -Inactive proteases that when activated digest protein -Nuicleases for the digestion of nucleic acids (DNA and RNA)

How is the mucosa of the large intestine different from the mucosa of the small intestine?

-Mucosa of large intestine is lined by simple columnar epithelium with numerous goblet cells. -Unlike the small intestine the large intestine mucosa is smooth and lacks intestinal villi. Specilized structures of the large intestine is teniae coli they are thin longitudinal bundles of smooth muscle. -Theyu both have numerous intestinal glands that extend inward.

Describe the bacterial action that takes place in the large intestine?

-Numerous normal bacterial flora inhabit the large intestine . -Known as intestinal microbiota -They are responsible for the chemical breakdown of complex carbohydrates, proteins, and lipids that remain in the chyme after it has passed through the small intestine. -They produce carbon dioxide, H+ -Produce B vitamins and vitamin K which are then absorbed from the large intestine into the blood. -Feces is the final product -Feces is composed of water, salts, epithelial cells, bacteria and undigested material

Discuss the anatomy of the pharynx and esophagus and their complementary activities in the process of swallowing?

-Pharynx and Esophagus connect the oral cavity to the stomach. Anatomy of Pharynx (throat) -Funnel shaped muscular passageway. -Passageway for air and food -Three skeletal muscle pairs form the wall of the pharynx. Superior, Middle, and Inferior pharyngeal constrictors. Pharynx- Function in Swallowing -Oropharynx and laryngopharynx are lined with nonkeratinized stratified squamous epithelium that provides protection against abrasion associated with swallowing ingested materials. Anatomy of Esophagus -normally collapsed tubular passageway -begins at level of cricoid cartilage. Most of its length within the thoracic cavity. - Directly anterior to vertebral bodies. - Inferior region connecting to the stomach and passes through opening in diaphragm, called esophageal hiatus. -Last 1.5 cm in abdomen. Superior Esophageal Sphincter- closed during inhalation fo air. Inferior esophageal sphincter- not strong enough alone to prevent materials from regulating back into esophagus so diaphragm helps. Esophagus Histology- 4 LAYERS MUCOSA of esophagus lined with nonkeratinized stratified squamous epithelium. SUBMUCOSA thick with abundant elastic fibers, which permit dissension during swallowing. Numerous gland provide thick mucous. MUSCULARIS- Both skeletal and smooth muscle. Ensures that material moves rapidly out of pharynx. ADVENTITA/SEROSA

Explain Motility within the small intestine?

-Smooth muscle activity of the muscularis within the small intestine wall has three primary functions. -Mixing chyme with accessory gland secretions through segmentation through backward and forwarded motion -Moving the chyme continually against the brush border, -Propelling the contents through the small intestine toward the large intestine through peristalsis. -Segmentation is more prevalent early in the intestinal phase, mixes chyme, accessory gland secretions, and intestinal juice. Contractions- initiated by pacemaker cells and spread through muscuarlis via gap junctions. -Peristalsis is prevalent late in intestinal phase. -Initiated by motolin (released from duodenum) -Successive waves of contractions = migrating motility complex. -Repeats until all content is moved to the large intestine. -Moving chyme from small intestine to large intestine -Open valve so this can happen. -Gastroileal Reflex Ileum contracts Illeocecal sphincter relaxes (CCK helps cause this) and cecum relaxes. -Moves contents from ileum to cecum in response to food in stomach. -Illeocecal valve contracts to prevent back flow.

Describe the three phases of gastric regulation. Understand that gastric function is also impacted by intestinal processes.

-Stomach is a holding back for partially digested food until it is moved into the small intestine, where digestion is complete.d -Pacemaker cells in stomach are located within GI tract wall, and spontaneously depolarize. This establishes is basic rhythm for muscular contraction. Signals spreading though smooth muscle cells in the muscualris layer. The muscular contractions by the stomach wall are regulated by both nervous reflexes and hormones, which alter the force not the rate of contraction. -Organized in three phases, Cephalic, gastric (before meal), and intestinal phase (after meal) Cephalic Phase- Involves cephalic reflex- nervous system reflex initiated by thought, smell. sight, or taste of food. Nerve signals are sent to hypothalamus, which relays signals to medulla oblongata. Medula oblongata increases parasympathetic stimulation of stomach via vagus nerve which causes an increase in contractile force in the gastric wall, (increases motility) and secretory activity of the stomach glands. (growling of stomach) Gastric Phase- Involves processes that begins the bolus reaches the stomach. Regulated by both the nervous system via gastric reflex and also by endocrine system through the release of gastrin. Gastric reflex nervous system reflex initiated when food enters stomach. Barroreceptors in wall of stomach detect increased dissension of stomach wall, chemoreceptors detect presence of protein and increase in pH of stomach contents. (higher pH indicates presence of protein because proteins buffer h+ and increase pH) -Nerve signals relayed to the medulla oblongata ersilting in nerve signals relayed along motor neurons to stomach to cause same effects as cephalic reflex. An increase in both stomach motility and secretory activity of gastric cells. Hormones secreted during the Gastric Phase- Gastrin which increases force of stomach contractions and release of secretions, contracts pyloric sphincter. Intestinal Phase- Initiated by presence of acidic chyme in duodenum,. Receptors- chemoreceptors in intestinal wall detect acidic chyme or low ph in duodenum contents Sensory input- decreased nerve signals relayed to medulla oblongata. Medulla oblongata interstates sensory input -Motor output- decreased nerve signals relayed along vagus nerve to stomach Effector- stomach inhibited to decrease both its force fo contraction and release of secretions. -Lessens both motility and secretory activity of the stomach. Hormones secreted- CCK decreases the force of contraction in the stomach, Secretin-inhibits the release of stomach secretions.

Identify the mucosal adaptations of the small intestine as related to functions the small intestine?

-Villus is a small fingerlike projection of simple columnar epithelium and lamina proprietor of the mucosa. -Villi and circular folds increase the surface area of the epithelial lining through which nutrients are absorbed. -Villi are most numerous in the jejunum where must of the absorption takes place. -Each villus contains an arteriole, a rich blood capillary network, and a venule. - Most nutrients are absorbed into these blood capillaries. -Lacteal (lymphatic capillary_) within villus. Lacteal absorbs lipids and lipid soluble vitamins that are too large to be absorbed by the blood capillaries. -Microvilli microscopic extensions of the plasma membrane of the simple columnar epithelial cells lining the small intestine. -Microvilli further increase the surface area of the small intestine. -Microvilli form brush border which are embedded with various enzymes that complete the chemical digestion of most nutrients immediately after absorption. - Brush border enzymes are embedded within plasma membrane and are the required proteins for membrane transport for digested molecules. -Intestinal glands secrete intestinal juice,

Identify the six organs that make up the gastrointestinal tract?

1. Oral cavity (mouth) 2. Pharynx (throat) 3. Esophagus 4. Stomach 5. Small Intestine 6. Large Intestine -Entire length of GI tract is lined internally with a mucous membrane, within the lumen ( inner space ) of the GI tract, ingested food Is broken down into smaller components that can be absorbed along its length. The disassembly of molecules for absorption occurs within the lumen of the GI tract, and optimal digestion and absorption are dependent upon regulating and maintaining the environmental conditions within this space. OPESSL

List what organs are considered to be accessory organs or structures of the digestive system?

1. Salivary Gland 2. Liver 3. Pancreas -Produce secretions that empty into the lumen of the GI Tract. 4. Teeth 5. Tongue -Participates in chewing and swallowing of food. 6. Gallbladder -Concentrates and stores the secretions (bile) produced by the liver.

List and describe the four tunic of the GI wall. Be able to list going from outermost to innermost, or innermost to outermost.

4 Tunics Inner-Outermost Mucosa, Submucosa, Muscular, serosa/adventitia Mucosa- (Innermost) Consists of an epithelium, an underlying layer called the lamina proprietor, and a thin layer of muscuarlis mucosae. Epithelium- simple columnar epithelium (most of GI tract, stomach, small intestine, large intestine) allows for secretion and absorption. Portions of GI Tract such as esophagus are lined with nonkeratinized stratified squamous epithelium allowing for them to withstand abrasion. Underlying Lamina Propria consists of areolar CT that contains small blood and lymph vessels and fine small branches of nerves. Absorption occurs when sub are moved through the simple columnar epithelial cells the line the GI tract wall, absorbed into lymphatic cap located within lamina propia. Muscularis Mucosae- thin layer of smooth muscle. Contractions of this layer cause slight movements in mucosa to gently shake things up, which facilitates the release of secretion from mucosa into lumen, also increases contact of materials in lumen with epithelial layer of mucosa for more efficient absorption. Submucosa- areolar and dense irregular ct. Many blood vessels, lymph vessels, nerves, and glands within the submucosa. Fine branches of nerves extend into mucosa (submucosal nerve plexus) Areolar Ct has MALT, larger aggregates of lymphoid nodules in submucosa Calle dpeyer patches, Malt protects us from potentially harmful agents, prevent ingested microbes from crossing GI tract wall. Muscularis - Smooth muscle tissue. Inner Circular layer- contains muscle cells when contracted constrict layer of tube. This layer is thickened at several locations along the GI Tract to form a SPHINCTER. Smooth muscle relaxes-open, contracts-close. They controls movement of material into next section of go tract and prevent back flow. . Outer Longitudinal Layer- composed of muscle cells oriented lengthwise within the GI tract wall. Contraction shortens the tube. In-between these two layers of smooth muscle is fine brances of nerves and associated autonomic ganglia called the myenteric nerve plexus. Motor neurons in plexus control contractions of muscularis. FUNCTION- Motility, contraction of layers cause mixing and propulsion Mixing- backward/forward blends secretions with ingested material within the GI tract, occurs when mixing waves of stomach and segmentation by small intestine. Propulsion- DIRECTIONAL movement of materials through GI tract, occurs by peristalsis (contraction of the muscularis) within Gi tract wall that moves like a wave within Dif regions of GI TRACT. Perastalsis results in one way movement of the lumen contents from esophagus to the anus. Adventitia or Seroa- Outermost -Only intraperitoneal organs have a serosa as there outermost tunic.

List and describe the secretions that make up gastric juice and the cells they are secreted by?

5 types of secretory cells of the gastric epithelium (aid digestion) -4 produce gastric juice which is released into stomach lumen, fifth type secretes hormone Surface Mucous Cells- line the stomach lumen and extend into the gastric pits. -Continuously secrete an alkaline mucin onto the gastric surface. Mucin becomes hydrated, mucus layer coats epithelial lining. - Mucus layer helps prevent ulceration of stomach lining, and protects from gastric enzymes and high acidity. Mucous Neck Cells- immediately deep to the b base of the gastric pit and are interspersed among the parietal cells. -Release an acidic mucin - help maintain acidic conditions - both types of mucous cells help protect the stomach lining from abrasion and injury. Chief Cells- most numerous secretory cells within the gastric glands. Cells secrete packets of zygotes granules, which contain pepsinogen. (pepsinogen is the inactive precursor of the enzyme pepsin) Pepsin must be produced in this inactive form to prevent the destruction of chief cell proteins. pepsinogen is activated into pepsin following its release into the stomach. activated by low pH and active pepsin molecules already present in stomach. Pepsin chemically digests denatured proteins and smaller peptide fragments (oligopeptides) Produce gastric lipase. Partietal Cells - add two substances into the lumen of the stomach. Intrinsic Factor- (glycoprotein) Production and release of intrinsic factor is the only essential function of the stomach. Regulated for the absorption of b12 vitamin int he Ileum (last portion of small intestine). b12 is essential for the production of normal erythrocytes. (decrease in b12= anemia) Hydrochloric Acid- Hcl not formed within parietal cell, it would destroy the cell. Instead the parietal cells forms h+ and release both H+ and Cl- into stomach lumen. Hcl is responsible for the low ph of 1.2-2.5 in the stomach. -HCL denatures proteins, and facilitates chemical digestion. -HCl kills most microorganisms entering stomach.

List and describe the general functions of the digestive system?

6 Major Functions 1. Ingestion- First step in process of digesting and absorbing nutrients. occurs with the introduction of solid ad liquid nutrients into the oral cavity. 2. Motility- Voluntary (skeletal muscle) and involuntary (smooth muscle) muscular contractions for mixing and moving materials through GI tract. 3. Secretion is the process of producing and releasing substances that facilitate both digestion and the movement of contents in the GI Tract. Secretions are produced by salivary glands, liver, pancreas, and the wall of GI tract. 4. Digestion- breakdown of ingested food into smaller components that can ultimately be absorbed by the digestive tract. Mechanical Digestion- Mastification, chewing Mechanical breakdown of ingested material into smaller pieces, no change in chemical structure. Chemical Digestion- specific enzymes break down complex molecules into simpler ones so they can be absorbed. 5.Absorption- membrane transport of digested molecules, electrolytes, vitamins, and water across epithelial lining of Gi tract into blood or lymph. (SMALL INTESTINE) 6. Elimination- expulsion of indigestible components through anal canal, feces.

Provide the functions of the accessory organs of the digestive system and how they contribute to digestion.

Accessory digestive organs help in the breakdown of food. Teeth + Tongue- participate in the chewing and swallowing of food. Gallbladder- concentrates and stores secretions (BILE) that are produced by the liver. Salivary glands- saliva is secreted from salivary glands in response to food being present within the oral cavity. It is mixed with ingested materials to form a bolus. Saliva contains salivary amylase which is an enzyme that initiates the chemical digestion of starch aka amylose. Pancreas- creates enzymes helps breakdown food chemically Liver- Produces bile

Distinguish between accessory organs and those organs considered to be part of the digestive tract?

Accessory organs help in the breakdown of food, and are connected to the GI Tract and typically outgrowths from the tract. The organs that are part of the digestive tract form a continuous tube, that begins at the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestine, large intestine. Ends at the anus. Entire length of the GI tract is lined internally with a mucous membrane. -With in the lumen (space inside where blood flows through) of the Gi tract, ingested food is broken down into smaller components that can then be absorbed.. The disassembly of molecules for absorption occurs within the lumen of the GI tract and optimal digestion and absorption are dependent on regulation/maintaining environmental conditions in lumen.

List the major hormones and the organs they are produced by that regulate the process of digestion?

Circulating Hormones- released into the blood Gastrin- released from the stomach, this stimulates stomach motility and its release of digestive secretions (gastric secretions of paternal cells and chief cells) Secretin and Cholecytoskokinin CCK released from the small intestine, which inhibit stomach motility and the release of digestive secretions. Secretin: Stomach- inhibits stomach motility and gastric secretions Liver + Pancreas- stimulates secretion of HC03- CCK- Stomach inhibits stomach motility and gastric secretions Gall Bladder- stimulates release of bile Pancreas- stimulate release of enzyme rich pancreatic juice. Local Hormones- are released and influence adjacent cells. Histamine released from endocrine cells within stomach stimulates H+ release of from adjacent parietal cells. Other- Motilin- Small intestine- regulates migrating motility complex to move contents within lumen from the small intestine into the large intestine.

Describe the general function of the enteric nervous system and autonomic nervous system in the regulation of the digestive system?

Digestive processes are regulated by the nervous and endocrine systems. Enteric Nervous System- Sensory and motor neurons within submucosal and myenteric plexuses. From esophagus to anus. Innervates smooth muscle and glands of GI tract and coordinates rifles for the mixing and propulsion of materials. Autonomic Nervous System- Parasympathetic innervation promotes GI tract activity. Stimulates GI tract motility and release of secretions, and relates GI Tract sphincters. Sympathetic Innervation opposes GI tract activity. It inhibits Gi tract motility and release of secretions, Contract GI tract sphincters and vasoconstrictor blood vessels within the GI tract wall.

List the glands found in the small intestine and their secretions

Four types of secretory cells of the epithelium contribute to the process of digestion. -3 Types of these cells type produce intestinal juice Goblet Cells- W/in simple columnar epithelium produce mucin that when hydrated form mucus, which lubricates the intestinal lining. -These cells increase in # from the duodenum to ileum,. because more lubrication is required to digest materials. Digested are absorbed, undigested remain in lumen, Enteroendocrine Cells- Release hormones such as CCk and secretin into the blood. Paneth cells- located in the base of the intestinal crypts. Help with the function of the innate immune system by secreting lysozyme, help protect potentially harmful substances. Duodenal Submucosal Gland- Secretes a alkaline mucus. Protects the duodenum the acidic chyme entering the duodenum of the stomach.

Describe the control of gastric motility.

G Cells are enteroendocrine cells that are widely distributed in gastric glands. -Secrete gastric hormone (Stimulates stomach secretions and motility) Gastric motility consists of two primary functions,. Mixing the bolus to form chyme and emptying chyme form stomach to small intestine. Gastric Mixing- form of chemical digestion, changes the semi digested bolus into chyme. Contractions in stomachs thick muscularis layer churn and mx the bolus with the gastric secretions, leading to a reduction in the size of swallow particles. Gastric Emptying- Movement of acidic chyme from the stomach through he pyloric sphincter into the duodenum of the small intestine. -Pressure gradient moving contents toward pylorus - Gradient increasing force against pyloric sphincter - Sphincter opens, with entrance of small volume chyme - Sphincter closes with retropulsion (stomach contents are squeezed back toward stomach body) (So not everything is dumped at once) reverse flow of some contents back into the stomach.

What terms are used to describe the regional anatomy of the stomach?

Located in superior left abdominal quadrant, inferior to diaphragm. Composed of four Regions Carida- small, narrow, entry way into the stomach lumen from the esophagus. Fundus- dome shaped region lateral and superior to esophageal connection with the stomach. Fundus has both weaker muscular contractions and a higher pH in its lumen area than other regions of the stomach. Body- largest region of the stomach. Extends to the pylorus Pylorus- narrow funnel shaped terminal region of the stomach. Its opening into the duodenum of the small intestine is thick ring of circular smooth muscle called pyloric sphincter. Pyloric sphincter regulates the movement of material from the stomach into the small intestine.,

List the three regions of the small intestine?

Lower Gi Tract- small and large intestine. Small Intestine consists of three continuous regions -Small Intestine has 4 tunics mucosa, submucosa, muscularis, and serosa. -Duodenum -Forms first segment of small intestine. Originates in the pyloric sphincter which regulates movement of chyme from stomach into small intestine. -Jejunum -Middle region of the small intestine. Primary region of small intestine for nutrient reabsorption. (This is where the chemically digested contents that are received from the duodenum are moved from the small intestine lumen into either the blood or the lymph.) -Ileum -Last region of the small intestine. (Forms 3/5 of small intestine) Absorption of digested materials continues in the Ileum along with the absorption of bile salts.

Distinguish between mechanical and chemical digestion and provide examples of each?

Mechanical Digestion- Breaking down of ingested material into smaller pieces, without changing the chemical structure. Ex) Mixing and Chewing, Mastification teeth/tongue -mechanically reduces bulk to help with swelling and increased surface area to facilitate exposure to enzymes. Chemical Digestion- activity of specific enzymes to break down complex molecules into smaller ones so they can be absorbed. Ex) Bacteria within small intestine., salivary amalyase in oral cavity

Explain the process of mastication?

Mechanical digestion in the oral cavity is called mastication or chewing. -Mastication Center- Coordinated movement lips, tongue, cheeks, and jaws -Function: chewing the food is mechanically reduce its bulk into smaller particles to facilitate swallowing. -Mastication increases surface area to facilitate exposure to digestive enzymes. -Also promotes salivation to help moisten and soften food to form bolus. -Medications composed of small non polar molecules (nitroglycerin) can be placed under the gone where they pass through the epithelium by simple diffusion. Teeth collectively known as dentition.

Describe the structure and function of salivary glands and characteristics of saliva, as related to digestion. Understand which of the salivary glands produce the most saliva?

Salivary glands produce saliva, located within oral cavity (intrinsic salivary glands) and outside oral cavity (extrinsic salivary glands). Intrinsic Salivary glands are unicellular exocrine glands that continuously release relative ely small amounts of sec regions independent of the presence of food. Intrinsic salivary glands are the only glands that contain lingual lipase an enzyme that begins digestion of triglyceride. Extrinsic Salivary Glands- MOST SALIVA IS PRODUCED HERE. Multicellular exocrine glands outside the oral cavity. 3 pairs of multicellular salivary glands are located external to the oral cavity: parotid, submandibular, and sublingual glands. Parotid Savliary Gland- Largest salivary gland, (25-30% of saliva is produced here.) -Saliva is produced and then transported through the parotid duct to the oral cavity. (mumps infection of parotid glands. Submandibular Salivary Glands- PRODUCE MOST OF THE SALIVA -Submandibular duct opens from each gland to floor cavity. Sublingual Salivary Gland- Extends tiny ducts opening into inferior surface of cavity -Produces 2-3% of saliva. Saliva- 1-0-1.5 L secreted daily, most produced during mealtime. -Consists of 99.5% water and mix of solutes. -(Saliva is formed as water and electrolytes are filtered from plasma then through cells of salivary gland) Other components are added by cells of salivary glands such as Salivary amylase, mucin, lysozyme added. Function of Saliva- Moistens ingested food to help become BOLUS. -Saliva initiates the chemical breakdown of starch in the oral cavity because of the salivary amylase it contains. - food molecules dissolved here so taste receptors stimulated -Cleanses oral cavity structures -Antibacterial substances inhibit bacterial growth (lysozyme, IgA antibodies.

What processes contribute to digestive and account for functions of the digestive system?

Six main functions 1. Ingestion- introduction of solid and liquid nutrients into the oral cavity. (1st step in digesting and absorbing nutrients.) 2. Motility- Voluntary muscular contractions (skeletal system) and involuntary muscle contractions for mixing and moving materials through the GI tract. Function of muscularis 3. Secretion- process of producing and releasing fluid products facilitating digestion. Digestive enzymes, bile acid. 4. Digestion- the breakdown of ingested food into smaller structures that can be absorbed from the GI tract. Mechanical Digestion- material physically be broken down by chewing and mixing. (no change in chemical structure) Chemical Digestion- activity of specific enzymes to break down complex molecules into smaller molecules so they can be absorbed. 5. Absorption- membrane transport of digested molecules, electrolytes, vitamins, and water across the epithelial lining of the go tract into the blood or lymph. Absorption occurs primarily within the small intestine. 6. Elimination- is the expulsion of indigestible components through the anal canal.

Describe the swallowing reflex. All three Phases

Swallowing is the process of moving ingested materials from the oral cavity to the stomach. This happens in three phases- Voluntary phase, Pharyngeal phase, and esophageal phase. Voluntary Phase- Bolus of food (formed as ingested materials mix aka chewing with saliva) is pushed by tongue against hard palette and the moves towards oropharynx. Pharyngeal Phase- involuntary Arrival of bolus into entry way of oropharynx initiates the swelling reflex of pharyngeal phase. Soft palate and uvula close off nasopharynx and larynx elevates so epiglottis closes. Prevents ingested material from entering the trachea. -Bolus passes quickly and involuntarily through pharynx to esophagus,. -Contraction of pharyngeal sphincters decreases diameter of pharynx, causing a pressure difference forcing swallowed material from the pharynx to esophagus. Esophageal Phase- Involntary Soft palate, uvula and epiglottis return to starting position. Superior esophageal sphincter closes, bolus passes through esophagus to stomach. Superior and inferior esophageal sphincters are normally closed at rest. When bolus is swallowed sphincter relax to allow it to pass through esophagus, inferior esophageal sphincter contracts after passage of bolus helping prevent reflex of materials and fluids from the stomach into the esophagus.