L13 1502-2024-Intro GI-Esoph Lecture 13 PDF

1502 Introduction to GI & Esophagus Fall 2024 Lecture 13 Monday, Sept. 23: 9am Dr. Layla Al-Nakkash...

1502 Introduction to GI & Esophagus Fall 2024 Lecture 13 Monday, Sept. 23: 9am Dr. Layla Al-Nakkash [email protected] 1 © L. Al-Nakkash 2020  Learning Objectives 1. Identify basic functions of the GI system. 2. Identify structural differences & physiological roles of the GI tract wall. 3. Understand how digestive function is regulated. 4. Identify the basic structure & function of the oral cavity, and the role of teeth. 5. Saliva: discuss how saliva is produced. – Pathophysiology: xerostomia 6. Describe the phases and sphincters involved in swallowing. © L. Al-Nakkash 2024 2  Function of the Digestive System What is the primary function of the digestive system? – transfer nutrients/water/electrolytes from things we consume into the body’s internal environment. How does food become an energy source? – digested & biochemically broken down into smaller molecules. – absorbed from GI tract for cellular distribution. Digestive system – performs four digestive processes 1. M________ Motility 2. A________ Absorption 3. D________ Digestion 4. S________ Secretion 3 © L. Al-Nakkash 2024 1. Identify basic functions of the GI system.  Motility – Muscular contractions mix & move forward the contents of the GI tract. proximal distal – Smooth muscle in walls of GI tract exerts steady low level of contraction. What is this known as? tone proximal distal Propulsive – moves contents forward. – rate of propulsion depends on function of the specific area of GI tract. rapid transit region: Esophagus slow transit region: Small intestine Mixing – Medbullets.com – mix food with digestive juices/enzymes – exposes contents to surfaces of GI tract 1. Identify basic functions of the GI system. 4 © L. Al-Nakkash 2024 2. Identify structural differences & physiological roles of the GI tract wall.  Motility Contraction of smooth muscle in the walls of GI tract → Under what type of control?involuntary Motility at either end of GI tract involves skeletal muscle (chewing, swallowing & defecation) → Under what type of control? voluntary what type of motility? What type of motility? Peristalsis Segmentation Forward movement Mixing movement 1. Identify basic functions of the GI system. 2. Identify structural differences & physiological roles of the GI tract wall. 5 © L. Al-Nakkash 2024  Digestive Tract Wall Same general structure throughout. 4 major tissue layers. Outer longitudinal 2 muscle Muscularis externa Inner circular muscle Mucous membrane 4 Lamina propria Mucosa Muscularis mucosa Lumen Myenteric plexus 2 1 Serosa 3 Submucosa 3 Submucous plexus © L. Al-Nakkash 2024 2. Identify structural differences & physiological roles of the GI tract wall. 6  Factors involved in the Regulation of Digestive Function 1. Autonomous smooth muscle function Pacesetter cells – between longitudinal & circular smooth muscle. In myenteric plexus, muscularis externa layer Pacesetter cells: determine rate of rhythmic contractions. This will vary for different regions of GIT 2. Intrinsic nerve plexuses This is the: Myenteric & submucous plexus Enteric nervous system – located within length of GI wall. 7 © L. Al-Nakkash 2024 3. Understand how digestive function is regulated.  Neurotransmitters & Neuromodulators in Costanzo the Enteric Nervous System Acetylcholine (ACh) Cholinergic neurons Contraction of smooth muscle in wall Relaxation of sphincters ↑ Salivary secretion ↑ Gastric secretion ↑ Pancreatic secretion Norepinephrine (NE) Adrenergic neurons Relaxation of smooth muscle in wall Contraction of sphincters ↑ Salivary secretion Vasoactive Intestinal Peptide (VIP) Neurons of mucosa & smooth Relaxation of smooth muscle muscle ↑ Intestinal secretion ↑ Pancreatic secretion Gastrin-Releasing Peptide (GRP), Neurons of gastric mucosa ↑ Gastrin secretion or Bombesin Enkephalins (opiates) Neurons of mucosa & smooth Contraction of smooth muscle muscle ↓ Intestinal secretion Neuropeptide Y Neurons of mucosa & smooth Relaxation of smooth muscle muscle ↓ Intestinal secretion Substance P Cosecreted with ACh Contraction of smooth muscle ↑ Salivary secretion © L. Al-Nakkash 2024 3. Understand how digestive function is regulated. 8  Factors involved in the Regulation of Digestive Function 3. Extrinsic nerves Nerve fibers from both branches of the ANS influence motility and secretion SNS – – tend to slow GI tract secretion and motility. When would this system be activated? flight/fight response PNS – – tend to increase motility and secretion. © L. Al-Nakkash 2024 3. Understand how digestive function is regulated. 9  Factors involved in the Regulation of Digestive Function 4. GI peptides Contraction/relaxation of SM wall & sphincters. Secrete enzymes for digestion. Secretion of fluid & electrolytes – Either: hormones, paracrines, neurocrines ACh, CCK NE, Cholecystokinin, VIP Gastrin, secretin somatostatin Costanzo © L. Al-Nakkash 2024 3. Understand how digestive function is regulated. 10  Mouth Nasal passages Hard palate Soft palate Uvula Pharynx Epiglottis Bolus Esophagus Tongue Glottis at entrance Trachea of larynx © L. Al-Nakkash 2024 4. Identify the basic structure & function of the oral cavity, and the role of teeth. 11  Entry to GI tract via mouth/oral cavity Nasal passages Opening formed by lips (muscular) – 1 Hard palate Soft palate – Assist in guiding food in the 2 Uvula mouth 4 Pharynx – Important in speech Epiglottis Bolus 3 Esophagus Tongue Glottis at entrance Trachea of larynx 1 Palate – forms roof of oral cavity, separates mouth from nasal passages. Allows breathing & chewing to occur simultaneously. 2 Uvula – hangs down from palate – seals off nasal passage during swallowing. 3 Tongue – floor of cavity - voluntarily controlled skeletal muscle. Guides food during chewing, involved in speech, embedded with taste buds. 4 Pharynx – cavity at rear of throat – links mouth to esophagus. © L. Al-Nakkash 2024 4. Identify the basic structure & function of the oral cavity, and the role of teeth. 12  Teeth Role: Mastication/chewing – 1st step in digestion Malocclusion malocclusion occlusion Occlusion improper upper & lower teeth /abnormal contact fit together when of teeth jaws are closed which before after allows food to be ground/crushed between teeth. What are the major purposes of chewing: _______________________ Grind & mix food with Saliva Reflexly ↑ secretions _______________________ why? to prepare distal GIT for food (increase not only salivary secretions, but gastric, & pancreatic) © L. Al-Nakkash 2024 4. Identify the basic structure & function of the oral cavity, and the role of teeth. 13  Saliva – Produced by 3 pairs of Salivary glands located outside the oral cavity. – discharge saliva via ducts into the mouth. more aqueous more mucus-rich A mix of aqueous & mucin © L. Al-Nakkash 2024 14 5. Saliva: discuss how saliva is produced.  Saliva Saliva is composed of: Mostly H2O Some electrolytes Salivary proteins – Breaks polysaccharides into – amylase maltose (2 glucose units) What is the purpose – mucus of these? Facilitates swallowing – moistens food & provides lubrication Functions of Saliva: 1. solvent for molecules to stimulate taste buds 2. aids speech 3. keeps teeth & mouth clean 4. contains HCO3- buffers neutralize acids from food & from bacteria in mouth what will this help to prevent?Tooth decay © L. Al-Nakkash 2024 15 5. Saliva: discuss how saliva is produced.  Isotonic = same composition as plasma Contract to eject saliva Absorption of Na & Cl osmolarity low Secretion of K & HCO3 Costanzo Duct cells are H20 impermeable H20 is not absorbed → hypotonic saliva Absorption (Na & Cl) > Secretion (K & HCO3 ) Net absorption © L. Al-Nakkash 2024 5. Saliva: discuss how saliva is produced. 16  Salivary secretions- key points: 1. Composition modified as it flows from acini to ducts. 2. Ducts are relatively impermeable to H2O. 3. Na+ and Cl- are reabsorbed. 4. K+ and HCO3- are added. 5. Saliva is hypotonic. © L. Al-Nakkash 2024 17 5. Saliva: discuss how saliva is produced.  Stimulation of Salivary Secretion 1-2 L /day – volume varies depending on stimuli Salivary secretion stimulated by: Stimulation of SNS & PNS ↑ salivary secretion. PNS – watery, enzyme-rich (dominant normally) SNS – less volume, mucus-rich (active with stress) ANS regulated Cerebral cortex Other inputs NO HORMONES Salivary center Conditioned reflex Whose reflex? in medulla acquired Pavlov Pressure receptors Autonomic nerves Simple reflex and chemoreceptors in mouth Salivary glands Salivary secretions 18 © L. Al-Nakkash 2024 5. Saliva: discuss how saliva is produced.  Costanzo © L. Al-Nakkash 2024 19 5. Saliva: discuss how saliva is produced.  Xerostomia A pathology with ↓ saliva production Causes: staphylococcus/streptococcus – diseases: salivary gland infections or stones – medications –to treat hypertension & depression. Salivary stones Symptoms: – dry mouth, – difficulty chewing & swallowing, – ↑ dental caries. Treatments: – No alcohol/tobacco/caffeine – Sip more water – Take extra care of teeth. 5. Pathophysiology: xerostomia 20 © L. Al-Nakkash 2024  Swallowing UES Esophagus guarded at both ends by sphincters: Upper esophageal sphincter UES pharyngoesophageal sphincter Bolus Lower esophageal sphincter LES gastroesophageal sphincter If there is no esophageal peristalsis, the LES is closed. Why, what’s the purpose? This prevents gastric reflux - GERD Achalasia Tx If the LES fails to Surgery, esophageal relax during drugs to phase swallowing, then inhibit tone food does not Botox, Ca2+ LES channel enter stomach blockers 21 © L. Al-Nakkash 2024 6. Describe the phases and sphincters involved in swallowing.  Swallowing A sequentially programmed all or none reflex oral – Swallowing reflex Initiated - when a bolus of food is forced by phase tongue to rear of mouth to pharynx pharyngeal– Soft palate pulled upwards (prevents reflux of food –nasopharynx) phase – Vocal cords pull together, larynx moves forward & upward against