Gastro-intestinal Motilities PDF

23 M.k. handout Tasneem Jarwan MOHAMMED KHATATBEH  Gastro-intestinal Motilities Mixing and movements of food along the GI tract: Mastication (chewing): Chewing results in a grinding action on food, breaking it down into smaller particles. This process occurs through the ac...

23 M.k. handout Tasneem Jarwan MOHAMMED KHATATBEH  Gastro-intestinal Motilities Mixing and movements of food along the GI tract: Mastication (chewing): Chewing results in a grinding action on food, breaking it down into smaller particles. This process occurs through the activation of the chewing reflex. Centers in the hypothalamus and cerebral cortex are stimulated by smell and taste, triggering the chewing of food in the mouth.(Voluntary, but has more of reflex behavior) The initiation of the chewing reflex begins with muscle stretching, caused by the drop of the lower jaw when a food bolus is present in the mouth. This stretching leads to a rebound of the lower jaw through the activation of the stretch reflex. In the mouth, alongside the grinding action of chewing, mixing is facilitated by the movements of the tongue.(Mixing of food with saliva and grinding) ___________________________________________________________________ Deglutition (Swallowing): →initiated voluntarily→ Continuing as involuntary reflex Two Stages of Deglutition: 1. Voluntary Stage: ¤ The tongue presses food upward and backward against the soft palate. ¤ This movement squeezes the food bolus into the pharynx. 2. Involuntary Stages: Reflexes initiated by the presence of food in the pharynx result in the following: ¤ Contraction of the pharynx. ¤ Esophageal peristalsis, inducing the movement of the bolus along the esophagus. ¤ In these reflexes, swallowing receptors located in the pharyngeal mucosa and swallowing centers in the brain are involved. The involuntary stage is further subdivided into: a. Pharyngeal Stage Duration: Approximately 2 seconds. Key Events: ➔ Respiration is interrupted. ➔ The soft palate is pulled upward to close the posterior nares. ➔ The larynx is pulled upward and anteriorly, resulting in the closure of the epiglottis. ➔ The upper esophageal sphincter (pharyngo-esophageal sphincter) relaxes, and the esophageal opening enlarges. ➔ These events force the bolus into the esophagus. b. Esophageal Stage Conducts the bolus along the esophagus to the stomach. Types of Contractions by Esophageal Muscle: i. Primary Peristaltic Contractions 1) Continuation of the contractions initiated in the pharynx. 2) Conduct the bolus through the esophagus. 3) The wave of contractions travels along the esophagus in approximately 8-10 seconds. ii. Secondary Peristalsis 1) Intrinsic reflexes (within the myenteric plexus) and extrinsic reflexes (via afferent and efferent vagus fibers). 2) Triggered by esophageal distension caused by retained food or when the primary reflex fails to move the bolus. Notes: ☆ Muscle Composition: The pharynx and upper third of the esophagus consist of striated muscle, controlled by the glossopharyngeal nerve. The lower third is composed of smooth muscle, controlled by: →Extrinsic control via the vagus nerve. ➔ Intrinsic control via the myenteric nervous system. Peristaltic Wave: ◇ Ends with the relaxation of the gastroesophageal sphincter (lower esophageal sphincter) and receptive relaxation of the stomach. ◇ Mechanism of Relaxation: → Activation of inhibitory neurons in the lower part of the esophagus. ➔ These neurons inhibit tonic contraction of the sphincter and facilitate stomach relaxation. Pathological Conditions: 1. Achalasia: Caused by the failure of the myenteric plexus to relax the sphincter. 2. Esophageal Reflux: Occurs when the gastroesophageal sphincter system fails, allowing gastric contents to return to the esophagus. Additional Protection: The gastroesophageal sphincter has a valve-like closure at the distal end of the esophagus to prevent reflux. ____________________________________________ Gastric Motilities: The motor activities of the stomach: ☆ Primary Function: Storage of Food The stomach can dilate from a capacity of 50 ml to 1000 ml. This dilation begins with receptive relaxation, mediated by the vago-vagal reflex, which decreases muscular tone upon food entering the stomach. Gastric Secretions and Mixing: The stomach secretes 2000 ml/day of secretions that, when mixed with ingested food, form chyme. Mixing Waves (Peristaltic Constrictive Waves): → Motor activity mixes secretions with food. →Occur at a frequency of 3/min in the mid-portion of the stomach, moving toward the antrum. →Frequency is determined by the Basic Electrical Rhythm (BER) of gastric smooth muscle.  Constrictive Rings: → As contractions approach the antrum, they become more intense and form constrictive rings. →At the pylorus, these waves constrict the pyloric sphincter, impeding chyme emptying into the duodenum. Retropulsion: →Food is ground and tossed back and forth between the antrum and the body of the stomach. →This process ensures thorough mixing and grinding of food into chyme. _______________________________________________________________ Gastric Emptying Small Chyme Passage: ❖ Only small amounts of fluid-consistency chyme pass through the pyloric sphincter into the duodenum. ❖ About 20% of the time, peristaltic contractions intensify, increasing antral pressure and forcing several milliliters of chyme into the duodenum. Pyloric Pump: ❖ The process responsible for gastric emptying. ___________________________________________________________ Pylorus as a Functional Structure: ➔ The pylorus is a small opening between the stomach and duodenum, guarded by smooth muscle cells forming the pyloric sphincter. ➔ The sphincter maintains tonic contraction, allowing only fluids to pass into the duodenum. ➔ Solid food particles cannot pass until they are thoroughly mixed and ground into fluid-consistency chyme. ________________________________________________________________ Hunger Contractions Occur when the stomach is empty and last for several hours. Characterized by rhythmical peristaltic contractions lasting 2-3 minutes each. These contractions are linked to blood glucose levels and increase as glucose levels drop. Neural and Hormonal Control of Gastric Emptying: Stimulation of Gastric Emptying: 1. Filling of the Stomach: Activates myenteric reflexes, increasing the pyloric pump’s activity and reducing the tone of the pyloric sphincter. 2. Gastrin: Hormone secreted by the antral mucosa. Mildly stimulates peristaltic activity, enhancing the pyloric pump. Inhibition of Gastric Emptying 1. Entero-Gastric Reflexes: →Triggered by the passage of chyme into the duodenum, which decreases pH. →Initiates reflexes at three levels: ➔ ENS (Enteric Nervous System). ➔ Prevertebral Ganglia. ➔ Vago-Vagal Reflexes: Signals through the vagus nerve inhibit excitatory vagal signals to the stomach. →Effects: Decrease antral propulsive contractions. Increase the tone of the pyloric sphincter. 2. Hormonal Feedback from the Duodenum: Cholecystokinin (CCK): 1)Secreted by the jejunum.2)Stimulated by fat in chyme. Gastric Inhibitory Peptide (GIP): 1)Released from specialized cells in the upper small intestine. 2)Stimulated by fat and carbohydrates in chyme. Secretin: Stimulated by acid in the duodenum. __________________________________________________ Intestinal movements: Site of most digestion and absorption: duodenum and jejunum Types of GI Movements: 1. Propulsive (Peristalsis) Movement: Ensures the movement of chyme toward the anus (analward) at an appropriate rate. 2. Mixing (Segmentation) Movements: Mixes food with gastrointestinal (GI) secretions to aid digestion and absorption. ____________________________________________________________ Propulsive Movements: ♧ Mechanism of Peristalsis: ▪︎ Movements of food along the GI tract are driven by peristaltic contractions. ▪︎ Peristalsis involves: 1. Contractile Ring: Circular muscle contracts above the distended segment. 2. Receptive Relaxation: Circular muscle relaxes below the distended segment. 3. Longitudinal Muscle Shortening:Rhythmic shortening of the longitudinal muscle layer. ♧ Peristaltic Reflex: ➔ Initiated by local reflexes caused by gut distension. ➔ Contractile rings form 2-3 cm above the distended part, moving chyme forward. ➔ The resulting analward movement of chyme is referred to as the “law of the gut”. ♧ Functions of Peristalsis: ➔ Main Role: Propels chyme in the caudal direction. ➔ Additional Role: Mixes food and spreads chyme along the intestine, aiding nutrient absorption. Neural Control of Peristalsis: ☆Role of the Enteric Nervous System (ENS): The ENS provides a complex neural network controlling GI movements and the rate of chyme movement. Orad Extension : →Excitatory neurons extend upward. Caudad Extension : →Inhibitory neurons extend downward. ENS Integrity: →A functional ENS is essential for effective peristalsis. →The congenital absence or the decreased activity of the enteric nervous system may depress or weaken the peristaltic reflexes and decrease the effectiveness of peristalsis to move the chyme in analward direction. ☆ Mucosal Stimulation : → Peristaltic contractions can also be triggered by mucosal stimulation, as seen in peristaltic rush (rapid, powerful contractions). ☆Parasympathetic Nervous System: → Modulates peristaltic activity by influencing neural networks and smooth muscle cell function. ___________________________________________________________________________________________________________ Hormonal Control of GI Motility: After meals many hormones are secreted during phases of food processing.Certain hormones affect intestinal motility: ➔ Enhance Motility: Gastrin, CCK, Serotonin. ➔ Inhibit Motility: Secretin, Glucagon. ___________________________________________________________________________________________________________ Mixing Movements:The mixing of food with secretions in the GI tract ♤ Mechanism of Mixing: ➔ Circular smooth muscle contractions create segmentations: alternating contractions and relaxations. ➔ These segmentations mix chyme with secretions and help spread it within the intestine. ♤ Frequency of Segmentations: ~ Determined by Basic Electrical Rhythm (BER) or slow waves of smooth muscle cells. ~ Maximum Frequency: ➔ 12/minute in the upper intestine (duodenum and jejunum). ➔ 8/minute in the terminal ileum. ♤ Functions of Segmentations: ▪︎ Main Role: Mixes chyme with secretions. ▪︎ Additional Role: Provides slight propulsive movement in the analward direction. _________________________________________________________________ Other Types of Intestinal Contractions 1. Peristaltic Rush: (Remove harmeful agents) ➔ Powerful and rapid peristaltic contractions along the small intestine. ➔ Triggered by mucosal irritation and/or intestinal distension. 2. Migrating Motor Complex (MMC): A type of motor activity that occurs during inter-digestive periods. Starts in the distal part of the stomach and continues along the entire small intestine. Phases of MMC Contractions: ➔ Phase 1: Slow waves appear as electrical activity without associated contractions. ➔ Phase 2: Some slow waves are followed by contractions (e.g., one slow wave followed by contraction, with 1-5 waves not followed by contractions). ➔ Phase 3: Lasts 5-15 minutes, during which all slow waves are followed by contractions. Function: Sweeps intestinal contents during the period between meals. Control Mechanisms: ➔ Hormonal: Motilin is believed to play a role. ➔ Neural: Regulated by the nervous system. ‫‪3. Movements Caused by the Activity of Muscularis Mucosa:‬‬ ‫)‪(Spreading chyme over the mucosa‬‬ ‫‪1) Responsible for shortening and elongating mucosal folds.‬‬ ‫‪2) Facilitates the absorptive process by the intestinal mucosa.‬‬ ‫‪3) Contractions are influenced by the activity of the enteric nervous system.‬‬ ‫األمعاء بتشتغل زي مصنع صغير‪ ،‬شغلها األساسي إنها تخلط األكل وتمشيه لتكمل عملية الهضم و االمتصاص ‪.‬‬ ‫عندها أنواع مختلفة من الحركات‪ ،‬وكل وحدة لها وقتها وطريقتها‪ ،‬وبعضها بيصير لحاله وبعضها متزامن ‪.‬‬ ‫‪.1‬الحركة العادية (الخلط) ‪:mixing‬‬ ‫األمعاء بتعمل تقلصات صغيرة زي تقطيع‪ ،‬بتخلط األكل مع السوائل اللي فيها عشان يسهل امتصاص العناصر‬ ‫الغذائية‪.‬هاي الحركات بتصير بشكل متزامن مع الحركات الثانية‪ ،‬ألنها بتحافظ على الخلط خالل الدفع‪.‬‬ ‫‪.2‬الحركة الدافعة (االندفاع) ‪:Propulsive‬‬ ‫لما األكل يتحرك باتجاه فتحة اإلخراج‪ ،‬األمعاء بتعمل تقلصات قوية اسمها الحركة التمعجية‪.‬هاي التقلصات زي‬ ‫موجة بتدفع األكل ليتحرك لقدام‪.‬هاي الحركات ممكن تتزامن مع الخلط بس بطريقة مرتبة عشان ما توقف دفع‬ ‫األكل‪.‬‬ ‫‪.3‬االندفاع السريع (التموج السريع) ‪:Propulsive rush‬‬ ‫إذا كان في تهيج أو انتفاخ باألمعاء‪ ،‬بتصير تقلصات قوية وسريعة‪ ،‬وهاي اسمها اندفاع تموجي سريع‪.‬هاي‬ ‫الحركات بتصير لحالها وقت الضرورة‪ ،‬زي لما يكون في حاجة سريعة إلفراغ األمعاء‪.‬‬ ‫‪.4‬الحركة بين الوجبات (الحركة المهاجرة) )‪:Migrating Motor Complex (MMC‬‬ ‫بين الوجبات‪ ،‬األمعاء ما بتظل ساكتة‪ ،‬بتعمل حركات تنظيف‪.‬بتبدأ من المعدة وتمر بكل األمعاء عشان تنظف‬ ‫الفضالت‪.‬هاي الحركات بتصير لحالها لما المعدة واألمعاء تكون فاضية‪.‬‬ ‫‪.5‬حركة العضالت الصغيرة (العضلة المخاطية)‪:Muscularis Mucosa‬‬ ‫في طبقة داخلية باألمعاء اسمها العضلة المخاطية‪ ،‬بتعمل حركات قصيرة وطويلة عشان تساعد بامتصاص األكل‬ ‫بشكل أحسن‪.‬هاي الحركات ممكن تصير بشكل مستقل‪ ،‬لكنها بتكون مستمرة طوال الوقت‪.‬‬ ‫كل هاي الحركات بتنظمها أعصاب وهرمونات‪ ،‬وبعضها بيشتغل مع بعض عشان الهضم واالمتصاص يكونوا‬ ‫بأفضل صورة‪ ،‬وبعضها بيشتغل لحاله حسب الحاجة‪.‬‬ Movements of the Colon: 1. Haustration Contractions ☆Description: →Similar to segmentation contractions of the small intestine. →Represented as rhythmic contraction and relaxation of the circular layer of colonic smooth muscle, spanning about 2.5 cm. →Each contraction lasts for 30-60 seconds. ☆Mechanism: Longitudinal muscle strips (teniae coli) are involved, causing the haustral appearance of the colon. ☆Functions: →Spreads colonic contents over the mucosa to aid in water and electrolyte absorption. →Provides a propulsive effect, moving fecal material slowly from the cecum and ascending colon into the transverse colon. 2. Propulsive Movements (Mass Contractions) ¤ Description: ➔ Series of powerful contractions occurring 1-3 times/day, lasting 10-30 minutes each. ➔ Most common in the first hour after breakfast. ¤ Mechanism: ➔ Begin with constrictive rings at the transverse colon. ➔ Followed by the contraction of about 20 cm or more distal to the constrictive ring. ➔ Each contraction lasts 30 seconds, followed by 2-3 minutes of relaxation before the next wave begins. ¤ Facilitators: ➔ Gastrocolic and duodenocolic reflexes, conducted through the autonomic nervous system. ➔ Colon irritation (e.g., ulcerative colitis) can also increase mass movements. ¤ Effect: ➔ Moves feces from the transverse colon to the sigmoid colon. ➔ Forces feces into the rectum, potentially initiating the defecation reflex. Defecation: Reflexes Preceding Defecation 1. Intrinsic Reflexes: Triggered by rectal distension. Signals travel through the myenteric plexus (ENS), causing: ➔ Increased contractions in the descending colon, sigmoid, and rectum. This reflex is weak and insufficient to cause defecation on its own. 2. Extrinsic Reflexes (Parasympathetic Defecation Reflex): ▪︎ Triggered by rectal and sigmoid distension. ▪︎ Increases parasympathetic signals, causing: ➔ Stronger contractions in the descending colon, sigmoid, and rectum. ➔ Relaxation of the internal anal sphincter. ▪︎ These reflexes are involuntary. Voluntary Act of Defecation : After reflexes, defecation occurs only as a voluntary act involving: ➔ Relaxation of the external anal sphincter (under voluntary control). ➔ Increased abdominal pressure: 1) Achieved by closing the glottis and contracting abdominal wall muscles. 2) This pulls the pelvic floor downward on the anal ring, relaxing it and evacuating feces..  ‫األمعاء الغليظة (القولون) بتشتغل زي محطة نهائية بتنظم حركة الفضالت‪.‬عندها نوعين من الحركات‪:‬‬ ‫‪.1‬حركة التقطيع (هاوستريشن)‪:‬‬ ‫القولون بعمل تقلصات صغيرة زي تقطيع‪ ،‬بتاخد وقت بين ‪ 30‬لـ ‪ 60‬ثانية‪ ،‬وبتساعد بخلط الفضالت مع جدار القولون‬ ‫عشان يمتص المي واألمالح‪.‬هاي الحركة كمان بتساعد تحرك الفضالت شوي شوي من بداية القولون لحد المنطقة‬ ‫العرضية‪.‬هاي العملية بتشتغل لحالها وبتكون مستمرة بهدوء عشان تجهز الفضالت للحركة القوية‪.‬‬ ‫‪.2‬الحركة القوية ‪:‬‬ ‫هاي التقلصات قوية وبتيجي ‪ 3-1‬مرات باليوم‪ ،‬غالبا ً بعد الفطور‪ ،‬وبتاخد ‪ 30-10‬دقيقة‪.‬بتبدأ من القولون العرضي‬ ‫وبتدفع الفضالت بقوة باتجاه السيني والمستقيم‪.‬هاي الحركة بتشتغل لحالها‪ ،‬ومش متزامنة مع حركة التقطيع‪ ،‬ألنها‬ ‫بتركز على دفع الفضالت بدل الخلط‪.‬‬ ‫عملية اإلخراج (التبرز)‪:‬‬ ‫لما الفضالت توصل للمستقيم‪ ،‬الجسم بعمل ردود فعل تلقائية (غير إرادية)‪ ،‬زي إنه يزيد تقلصات العضالت الداخلية‬ ‫ويرخي العضلة الداخلية للشرج‪.‬بس عشان نخرج الفضالت‪ ،‬الزم نقرر إراديا ً ونرخي العضلة الخارجية للشرج‪.‬كمان‬ ‫بنزيد الضغط بالبطن عن طريق شد عضالت البطن وإغالق الحنجرة‪ ،‬وهاي الحركات كلها بتصير متزامنة عشان تساعد‬ ‫على إخراج الفضالت بشكل طبيعي‪.‬‬ ‫إغالق الحنجرة هون المقصود فيها الحركة اللي بنسويها لما نحاول نزيد الضغط داخل البطن‪.‬الفكرة إنك بتحبس النفس‬ ‫وتشد عضالت البطن‪ ،‬وبتسكر الحنجرة (عبر إغالق األحبال الصوتية) عشان الهواء ما يطلع من الرئتين‪.‬هاي الحركة‬ ‫بتزيد الضغط داخل تجويف البطن‪ ،‬وبتساعد على دفع الفضالت لخارج الجسم‪.‬فـ "إغالق الحنجرة" هون مش بمعنى إنه‬ ‫الحنجرة بتسكر بالكامل‪ ،‬لكن بمعنى إنك تمنع خروج النفس مؤقتًا عشان تساعد العضالت الداخلية‪.‬‬ ‫صورة مسربة للدراسة بعد ال ‪midterm‬‬ ‫______________________________________________________________________________‬ ‫تمت كتابة هذا الشيت صدقة جارية عن روح والدة زميلنا عمرو رائد من دفعة تيجان‬ ‫️‬ ‫دعواتكم لها بالرحمة والمغفرة‬ ‫😊 ‪Thanks‬‬