Propulsive Movements and Mixing of Food PDF

• Oral Dygestion & Deglutition • Propulsion and Mixing • Of Food in the Alimentary Tract Dr. Arzu Temizyürek Ingestion of food is simply voluntarily taking food into the digestive tract through the oral cavity. Ingestion of Food • The amount of food that a person ingests is determined principa...

• Oral Dygestion & Deglutition • Propulsion and Mixing • Of Food in the Alimentary Tract Dr. Arzu Temizyürek Ingestion of food is simply voluntarily taking food into the digestive tract through the oral cavity. Ingestion of Food • The amount of food that a person ingests is determined principally by intrinsic desire for food called hunger. • The type of food that a person preferentially seeks is determined by appetite. Digestive Processes: • Ingestion • Mechanical digestion Mixing by gastric juices • Chemical digestion enzyme – in the chyme • Propulsion • Deglutition (swallowing) Digestive Processes: Mouth  Mechanical digestion  Chewing = mastication  Food mixed with saliva  Shaped into a bolus  Chemical digestion – salivary amylase breaks down and converts polysaccharides (starches) to disaccharides (maltose) and monosaccharides (glucose) [no enzymatic action with cellulose which is also a polymer of glucose]  Bolus: ball of food or liquid to be swallowed Ptyalin (a-amylase) Starch Maltose -Small polymers of glucose Only 5 % of starch is hydrolyzed in the mouth Mechanical digestion (chewing-mastication) Teeth •Anterior teeth (incisors) for cutting •Posterior teeth (molars) for grinding tongue chewing muscles Mastication is both voluntary and partly reflexive Ingestion of Food Mastication (Chewing) Chewing muscles are innervated by CN-V (5th cranial nerve). • • • • Masseter Temporalis Lateral Pterygoid Medial Pterygoid Chewing process is controlled by nuclei in the brain stem. Stimulation of taste centers in the brain stem and Hypothalamus rhythmical chewing movements Ingestion of Food Mastication (Chewing) a. Most of the chewing process is caused by a chewing reflex 1. Food enters mouth reflex inhibition of the muscles and lower jaw drops open 2. Opening of lower jaw initiates a stretch reflex in chewing muscles 3. Stretch reflex causes contraction of these muscles and mouth closes b. Chewing is important for the digestion of all foods, but especially fruits and raw vegetables (cellulose) c. Increases the surface area for the action of digestive enzymes the rate of digestion is dependent on the total surface area exposed to the digestive secretions Ingestion of Food Swallowing (Deglutition) Moving bolus from mouth to stomach • Facilitated by saliva, mucous secretions • Involves tongue mouth, pharynx, esophagus • Three phases 1. Buccal stage - voluntary 2. Pharyngeal stage – involuntary, 3. Esophageal stage – involuntary The reflex is initiated by touch receptors in the pharynx (back of the throat) as the bolus of food is pushed to the back of the mouth. Physiology of Deglutition (Swallowing) 1. Buccal phase Voluntary Moves bolus to oropharynx Bolus of food Tongue Pharynx Epiglottis Glottis Trachea 1 Upper esophageal sphincter is contracted. During the buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins. Physiology of Deglutition (Swallowing) 2. Pharyngeal phase • Involuntary • Receptors in oropharynx stimulate medulla and pons to: 1. Block mouth with tongue 2. Block nasopharynx with soft palate 3. Raise larynx to seal epiglottis, blocking airways 4. Relax upper esophageal sphincter • Bolus is moved through pharynx into esophagus  The motor impulses from the swallowing center to the pharynx and upper esophagus that cause swallowing are transmitted successively by the 5th, 9th, 10th, and 12th cranial nerves and even a few of the superior cervical nerves. Uvula Bolus Epiglottis Esophagus 2 The uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. Physiology of Deglutition (Swallowing) 3. Esophageal stage • • • • • Upper esophageal sphincter closes Gastroesophageal sphincter opens Esophagus controls involuntary peristaltic movement Epiglottis reopens Bolus moves from esophagus to stomach Bolus 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry. Esophagus ➢connects the pharynx to the stomach. • The upper esophageal sphincter; controls the movement of food from the pharynx into the esophagus. • The upper 2/3 of the esophagus consists of both smooth and skeletal muscle fibers → peristalsis • secretions from the esophageal mucosa lubricate the esophagus and food. • Food passes from the esophagus into the stomach at the lower esophageal sphincter (gastroesophageal or cardiac sphincter); - sphincters contract → closing the tube - sphincters relax → opening the tube and food pass into the stomach and then contracts to prevent stomach acids from backing up into the esophagus The musculature of the pharyngeal wall and upper third of the esophagus is striated muscle Therefore the peristaltic waves in these regions are controlled by skeletal nerve impulses from the glossopharyngeal and vagus nerves. In the lower two thirds of the esophagus, the musculature is smooth muscle this portion of the esophagus is also strongly controlled by the vagus nerves that act through connections with the esophageal myenteric nervous system. Esophagus Peristalsis • Involuntary, rhythmic contraction of muscularis - primary peristalsis: continuation of the wave that begins in the pharynx (8-10 sec) - secondary peristalsis: results from the distention of the esophagus itself • Controlled by medullary centers • A movement activity: inner circular layer of smooth muscle contracts behind bolus to push it forward; outer longitudinal muscle contracts to pull esophagus wall up Representing the enteric circuitry underlying the peristaltic reflex.  The circumferential and longitudinal muscle layers of the intestines behave in a stereotypical pattern during peristaltic propulsion. Saliva secretion and function Salivary Glands • The principal glands of salivation are: 1. Parotid glands 2. Submandibular (Submaxillary) glands 3. Sublingual glands 4. Smaller glands in mucosa of tongue, palate, etc. Daily secretion of saliva normally ranges between 800 and 1500 milliliters. Saliva secretion and function Salivary Glands • The principal glands of salivation are: 1. Parotid glands serous 2. Submandibular (Submaxillary) glands serous/mucus 3. 4. Sublingual glands serous/mucus Buccal glands - Smaller glands in mucosa of tongue, palate, etc. mucus Saliva secretion  Daily secretion of saliva - 800-1500 mL/day (average value of 1000 mL) - pH = 6-7  Saliva contains two types of protein secretion: 1. serous secretion; - contains water, ions and enzymes such as ptyalin (an αamylase) ➢ Parotid, Submandibular and Sublingual glands 2. mucous secretion; - contains mucin ( to lubricate and protect surface ) ➢ Submandibular and Sublingual glands Secretion of Saliva Secretion of Ions in Saliva • Saliva contains large quantities of potassium and bicarbonate ions - the submandibular gland contains acini and salivary ducts. • Acini secrete a primary secretion containing ptyalin or mucin in a solution of ions • Ductal epithelium secretes the bicarbonate ion into the lumen Composition of saliva Functions of Saliva 1. 2. 3. 4. 5. 6. It moistens food It begins digestion It adjusts salt appetite The flow of saliva helps wash away pathogenic bacteria and food. It contains antibodies Saliva contains several factors that destroy bacteria such as thiocyanate ions, antibodies, lactoferrin which chelates iron necessary for bacterial growth and proteolytic enzymes such as lysozyme which is: i. active against bacterial walls ii. helps thiocyanate ions in entering bacterial wall where they become bactericidal. Secretion of Saliva Nervous Regulation of Salivary Secretion 1. Controlled mainly by parasympathetic pathways 2. Salivation can be stimulated or inhibited by signals coming from higher brain centers 3. Salivation can occur in response to reflexes in the stomach and upper small intestines 4. Sympathetic stimulation can increase salivation a small amount 5. the blood supply to the glands affects salivary secretion because secretion always requires adequate nutrients from the blood  https://www.youtube.com/watch?v=YQm5RCz9Pxc MOTOR FUNCTIONS OF THE STOMACH 1) 2) 3) Storage of food Mixing of food with gastric secretions → chyme Emptying of food into the small intestine MOTOR FUNCTIONS OF THE STOMACH Physiologically (1) the “orad” portion (2) the“caudad”portion Anatomically (1) the body (2) the antrum STORAGE FUNCTION OF THE STOMACH Entrance of food into the stomach Stomach stretching → “vagovagal reflex” from the stomach to the brain stem & then back to the stomach Muscular tone of gastric wall is decreased the wall bulges → more food accomodates Bulges outward Completely relaxed stomach accomodates 0.8-1.5 liters food MIXING AND PROPULSION OF FOOD BASIC ELECTRICAL RHYTHM OF THE STOMACH WALL • Gastric glands secretes the digestive juices contact with stored food • Weak peristaltic constrictor waves (mixing waves) begin in the mid- to upper portions of the stomach Wall • These waves are basic electrical rhythm, initiated by the gut wall • Intense constrictor waves provides powerful peristaltic action potential (driven constrictor rings) MIXING AND PROPULSION OF FOOD • peristaltic wave approaches the pylorus, • the pyloric muscle contracts, which further impedes emptying through the pylorus. • antral contents are squeezed upstream toward the body of the stomach the moving peristaltic constrictive ring + upstream squeezing action retropulsion The bolus is mixed with gastric juice to form chyme. After food is mixed with the stomach secretions, the resulting mixture that passes down the gut is called chyme. • degree of fluidity depends on the amount of food, water, and stomach secretions - pasty Another type of intense contraction Hunger contractions • Rhythmic peristaltic contractions of the stomach after the stomach has been empty for several hours • Most intense in young, healthy people who have high degrees of gastrointestinal tonus • increased by the person’s having lower than normal levels of blood sugar • Hunger pangs : mild pain in the pit of the stomach Sometimes your stomach’s growl pierces the silence Why Does Your Stomach Growl When You’re Hungry? STOMACH EMPTYING - Intense antral peristaltic contractions during emptying - Peristaltic wave forces up to several milliliters of chyme into the duodenum → pyloric pump - Pyloric sphincter- usually open enough for water and other fluids to empty but not for chyme until it is the right consistency Stomach Regulation of stomach emptying The rate at which the stomach empties is dependent on signals from both the stomach and the duodenum 1. Gastric factors that promote emptying - increased food volume - stretching of the stomach wall - effect of gastrin- causes secretion of gastric juice; enhances the activity of the pyloric pump Small volume → weaker contractions Large volume → stronger contractions Stomach Powerful Duodenal Factors that Inhibit Stomach Emptying If the volume of chyme in the duodenum becomes too much a. Inhibitory effect of enterogastric nervous reflexes from the duodenum; mediated by three routes: 1. Directly from the duodenum to the stomach through the enteric nervous system 2. Through extrinsic nerves 3. Through the vagus nerve All three inhibit the pyloric pump and increase the tone of the pyloric sphincter Stomach Powerful Duodenal Factors that Inhibit Stomach Emptying b. Types of factors that can initiate enterogastric inhibitory reflexes: The enterogastric inhibitory reflexes are especially sensitive to the presence of irritants and acids in the duodenal chyme 1. Degree of distension of the duodenum 2. Irritation of the duodenal mucosa 3. Degree of acidity of the duodenal chyme (pH<3.5 to 4) 4. Degree of osmolality of the chyme 5. Presence of breakdown products of proteins and fats in the chyme Stomach Powerful Duodenal Factors that Inhibit Stomach Emptying c. Hormonal feedback from the duodenum inhibits gastric emptying 1. 2. 3. jej u Cholecystokinin (CCK jej ) n jejunum u u jej Secretin duodenal mucosa n m gastric inhibitory peptide (GIP) un upper small u m Glucose-dependent insulinotropic u peptide m intestine Summary of the Control of Stomach Emptying ❖ Emptying of the stomach is controlled only to a moderate degree by stomach factors ❖ The more important control of stomach emptying resides in inhibitory feedback signals from the duodenum Movements of the Small Intestine 1. mixing contractions 2. propulsive contractions Movements of the Small Intestine Major Contractions (Segmentation Contractions) Segmentation movements of the small intestine Movements of the Small Intestine • Major Contractions (Segmentation Contractions) 1. Contractions “chop” the chyme 2-3 per minute but can be as high as 12 per minute 2. Frequency is determined by the electrical slow waves in the intestinal wall Can be blocked by atropin Movements of the Small Intestine • Propulsive Movements 1. Peristalsis in the small intestine-normally weak and die out after 3-5 cm, rarely travel farther than 10 cm 2. Control of peristalsis by nervous and hormonal agents (i.e. gastrin, Cholesistokinin (CCK), insulin, motilin, serotonin). 3. Conversely, secretin and glucagon inhibit small intestine motility Function is to cause progression and the spreading out of the chyme Movements of the Small Intestine • Propulsive Effect of the Segmentation Movements 1. Peristaltic rush- intense irritation of the mucosa, as occurs in infectious diarrhea, can cause rapid and powerful peristalsis Movements of the Small Intestine Function of the Ileocecal Valve • prevents backflow of cecal contents Function of the Ileocecal sphincter • after a meal emptying of ileal contents into the cecum • Feedback Control of the Ileocecal Sphincter delays emptying The degree of contraction of the ileocecal sphincter and the intensity of peristalsis in the terminal ileum are controlled significantly by reflexes from the cecum. Fig. 63.4 Emptying of the ileocecal valve Movements of the Colon The principal functions of the colon (1) Absorption of water and electrolytes from the chyme to form solid feces (2) Storage of fecal matter until it can be expelled. The proximal half of the colon absorbtion The distal half storage Movements of the Colon • Mixing Movements-Haustrations ❑ Combined contractions of the circular and longitudinal strips of muscle cause the unstimulated portion of the large intestine to bulge outward into baglike sacs called haustrations. ❑ Much of the propulsion in the cecum and ascending colon results from the slow but persistent haustral contractions. • Propulsive Movements-Mass Movements ❑ From the cecum to the sigmoid, mass movements can, for many minutes at a time, take over the propulsive role Movements of the Colon •Initiation of Mass Movements by Gastrocolic and Duodenocolic Reflexes The appearance of mass movements after meals is facilitated by gastrocolic and duodenocolic reflexes. • These reflexes result from distention of the stomach and duodenum • Irritation in the colon can also initiate intense mass movements Fig. 63.5 Absorptive and storage functions of the large intestine Movements of the Colon • Defecation and Defecation Reflexes When a mass movement forces feces into the rectum • Reflex contraction of the rectum • Relaxation of the anal sphincters. Composed of smooth muscle Fig. 63.6 Afferent and efferent pathways of the parasympathetic mechanism for enhancing the defecation reflex Composed of striated muscle Defecation Reflexes The external sphincter is controlled by nerve fibers in the pudendal nerve • voluntary • conscious Somatic nervous system The external sphincter is usually kept continuously constricted unless conscious signals inhibit the constriction. Defecation Reflexes 1. Intrinsic reflex mediated by the local enteric nervous system in the rectal wall • Feces enter the rectum, • distention of the rectal wall • afferent signals • initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing feces toward the anus. peristaltic wave approaches the anus, the internal anal sphincter is relaxed if the external anal sphincter is also consciously, voluntarily relaxed at the same time, defecation occurs.