GIT Physiology PDF

GIT Physiology Dr. Nermeen Bastawy Ass. Prof. of Physiology, Faculty of Medicine, Cairo University Clinical nutrition and Lactation specialist, Cairo University Hospitals Stimulus Food Nerve Chemical Food stimulates GIT by: Change pH Distention Breakdown products...

GIT Physiology Dr. Nermeen Bastawy Ass. Prof. of Physiology, Faculty of Medicine, Cairo University Clinical nutrition and Lactation specialist, Cairo University Hospitals Stimulus Food Nerve Chemical Food stimulates GIT by: Change pH Distention Breakdown products  Regulation of GIT (Nervous/Hormonal) ANS 1- Enteric NS (ENS) 2- Sympathetic NS 3- Parasympathetic NS (Vagus) Gastrocolic reflex Enterogastric reflex  Gastrocolic reflex It is a physiological reflex that controls the motility of the lower GIT following a meal. Enterogastric reflex It is a physiological reflex that controls the motility and emptying of the stomach  GIT Hormones Hormone Mechanism Of Secretion Action Gastrin - Vagal Stimulation ± Gastric secretion (HCL & ( From stomach) - Change pH ENZYMES) - Stomach distention ± Gastric motility - Digested food & proteins Growth of mucosa Contraction of LES Cholecystokinin - Distention Contraction of Gallbladder CCK (From Small - Change pH ± Pancreatic juice (Enzymes) Intestine) - Digested food products ↑ Motility of Small Intestine (Peptides, amino acids, fatty acids) Secretin ³ pH from acid chyme ± Pancreatic juice (HCO3) ( From Small Intestine) 2G Inhibits acid secretion Gastrin & Ghrelin > from stomach LES = lower esophageal sphincter Ghrelin is a hormone secreted from stomach, it ++ appetite  Mastication Drop of lower jaw by food Stretch of masseter muscle Elevation of jaw & crushing of food Reflex muscle contraction 1. Gastrin hormone is secreted from a.Esophagus b.Stomach c.Duodenum d.Pancreas  2. CCK hormone is secreted from a.Esophagus b.Small intestine c.Colon d.Pancreas 3. Contraction of LES is the action of: a.CCK b.Vagus nerve c.HCL d.Gastrin  4. Gastrocolic reflex : a.Is an abnormal reflex b.Stimulates evacuation of colon c.Inhibits large intestine motility d.Stimulates small intestine secretion 5. Stimulation of pancreatic juice rich in enzymes is the action of: a.CCK b.Acetyl choline c.Secretin d.Gastrin  Salivary Secretion 0.5-1.5 liters/day are secreted from salivary glands: ✓ Parotid: serous secretion Mandibular: mixed secretion ✓ Sublingual: mixed secretion seromucous ✓ Buccal glands: mucous secretion  Mechanism of Salivary Secretion The first stage involves the acini, which secrete a primary secretion that contains ptyalin and/or mucin in a solution of ions which shows no great difference from extracellular fluid As the primary secretion flows through the ducts, the ionic composition of the saliva is markedly modified by the following processes: (1) Sodium & chloride ions are reabsorbed, and potassium ions are secreted. Therefore, the sodium ion and chloride ion concentrations of the saliva are markedly reduced whereas the potassium ion concentration becomes increased during passage through the ducts. Aldosterone increases K+ conc. and reduces Na+ conc. of saliva (2) Bicarbonate ions (HCO3-) are secreted into the lumen of the duct. The ducts are relatively impermeable to water. Therefore, the saliva that reaches the mouth is hypotonic.  Salivary Secretion It is an Active process, and has 2 stages of secretion: 1st stage: 1ry secretion 2nd stage: 2ry secretion ✓ In Acini ✓ In Duct (Aldosterone) ✓ Isotonic ✓ Hypotonic High K & HCO3 During maximal salivation as a result of parasympathetic stimulation, Less NaCl the conc. of Na+, CI- and HCO3- in saliva increase, whereas the conc. of K+ decreases, because ductal modification of the saliva is markedly reduced by the rapid flow. Either way maximal salivation happened Or not HCO3 don't influenced  Innervation of salivary glands Stimulation of the parasympathetic nerve supply to the salivary glands causes profuse secretion of watery saliva Stimulation of the sympathetic nerve supply to the salivary glands causes vasoconstriction, and secretion of a small amount of saliva rich in organic - para > profuse Saliva secretion constituents. - sympathetic > less amount + high organic content  Nervous Regulation of salivary secretion Occurs through 2 types of Reflex Action: Conditional Reflex Unconditional Reflex Inborn reflex Acquired reflex need previous experience Presence of food ³ ++ taste Smelling, seeing, hearing, thinking ³ ++ buds → û salivary secretion Cerebral cortex³ û salivary secretion Parasympathetic efferent effects ▪  watery salivary secretion & vasodilatation Sympathetic efferent effects ▪  amount of saliva & vasoconstriction  Functions of Saliva 1. Articulation: Speech 2. Buffer: keep oral pH 7 3. Cleaning (antibodies IgA), & cooling 4. Dissolving, digestion (ptyalin =amylase),& (also known as salivary amylase) deglutition of food in 1ry secretion  Functions of Saliva 1. Taste sensation (Saliva acts as a solvent for the molecules that stimulate taste receptors) 2. Thirst sensation → water regulation 3. Teeth & mucosa protection  Xerostomia Dysfunction of salivary glands →Xerostomia (mouth dryness) What are the causes?  Swallowing (Deglutition) Oral (buccal) stage (voluntary) Pharyngeal stage Involuntary Esophageal stage  Buccal phase Tongue is elevated upwards and backwards against hard palate Bolus of food is rolled backwards to back of tongue. Bolus is forced to pharynx by contraction of mylohyoid muscle. Clinical applications: Tongue tie Hare lip (cleft lip) Cleft palate Pharyngeal Phase Upper/middle/lower  Pharyngeal phase Protective reflexes: "Protective Reflexes" refers to automatic, involuntary responses Nose: elevation of soft palate Mouth: elevation of tongue & contraction of mylohyoid Respiratory passage: Larynx: elevation of larynx to be covered by epiglottis Approximation of vocal cords Inhibition of respiration (apnea): The entire pharyngeal stage of swallowing on swallowing occurs in 1 to 2 seconds, respirations off interrupting respiration. The swallowing center specifically inhibits the respiratory center of the medulla during Soft palate elevates Tongue elevates this time, stopping respiration at any Larynx elevates point in its cycle to allow swallowing to Vocal cords approximate proceed. Respiration is inhibited if swallowing work in any time immediately inhibition to respiratory cycle in any points  Esophageal Phase peristaltic movement contraction & relaxation 2 types of esophageal peristalsis: click me 1. 1ry peristalsis - Initiated by swallowing as continuation of from pharyngeal contraction - Solids food takes 10 seconds to move from cervical region to the stomach 2. 2ry peristalsis - Occurs if 1ry peristalsis fail to push food to stomach → distention of esophagus by residual food (Retained bolus) result in →Stimulation of vagus & enteric nervous system (ENS)result in → esophageal contraction vagus nerve > ENS > (contraction & distention) esophagus  Receptive Relaxation of the Stomach As the esophageal peristaltic wave passes toward the stomach, a wave of relaxation, transmitted through myenteric inhibitory neurons → the entire stomach and the duodenum become relaxed as this wave reaches the lower end of the esophagus and thus they are prepared ahead of time to receive the food propelled down the esophagus during the swallowing act. in lower end Of esphagus > wave of relaxation from peristalsis > myentric inhibit > relaxation to entire stomach + duodenum  Lower Esophageal Sphincter (LES) Remains tonically contracted why Prevents reflux of gastric content into esophagus Tone of LES is affected by: ✓ acetylcholine , gastrin ² contraction of LES ✓ fat, tea, caffeine, chocolate ² relax LES If resting tone of lower esophageal sphincter is decreased, reflux of the gastric acid content into the esophagus (gastroesophageal reflux) will cause heart burn and esophagitis → ulceration and stricture of the esophagus due to scarring itis mean inflammation Reflux of acid into esophagus may be due to: (1) Food & drinks: Citrus juice, Tea and Coffee (2) Nervousness and stress (3) Smoking and some Drugs (4) Pregnancy Dysphagia : Difficulty of swallowing  VIP Disorders of LES It is failure of LES to relax during swallowing (abnormal high tone) → accumulation of food in the esophagus → dilatation. Or disorder in nerve in X ray it's S shape  Gastric Secretion gastric acid secretion is HCL 1500 - 2500 ml/day. -It is secreted by 3 types of glands: 1.Mucous glands 2.Oxyntic glands: contains oxyntic (parietal) cells that secret HCL 3.Pyloric glands Function of HCl: 1-Activation of pepsinogen into pepsin 2-It provides optimum pH for action of pepsin 3-Starts digestion of proteins into polypeptides 4-It initiates enterogastric reflex 5-Helps absorption of iron and calcium 6-It kills microorganisms 7- HCl in the duodenum ³ ++ secretin hormone ³ ü HCl secretion $ to secretin is low acidic chyme , action decrease gastric acid secretion (HCL) + pencarieic juice HCO3  Mechanism of Acid secretion Oxyntic (parietal) cell + H2O CA K+ chloride shift phenomena Alkaline Tide: as HCl is secreted, HCO3- is added to gastric venous blood 1- CO2 combines with water →H+ and HCO3- 2- HCO3- diffuse into the blood in exchange for chloride ions 3- Chloride ion is actively transported to the lumen 4- H-K ATPase (proton pump) moves H+ ions to the lumen  Stimuli of Gastric Acid secretion (Oxyntic cell) 3 stimuli of proton pump protein pump proton Pump (H+/K+) proton pump inhibitors (PPI): drugs used in treatment of GERD or peptic ulcer. They inhibit proton pump → decrease HCL secretion (Gastroesophageal Reflux Disease)  Control of Gastric Secretion 3 Phases of gastric secretion Nervous & Hormones Nervous only Ach. Gastrin Histamine CCK Secretin phase phase inhibitory phase Think, See or smell food → ++ Vagus Main Stimulus (2/3 of Enterogastric Reflex 5 senses GIT hormones nerve →± Gastric secretion (1/3) gastric secretion) (CCK & secretin) food in SI →  Stomach Motility Proximal unit Distal unit Structures Fundus & body Antrum & pylorus Functions Storage Motor Characters Receptive Contraction starts at mid relaxation great curvature TOWARDS the antrum The motor functions : SMS 1. Storage of food. 2. Mixing and partial digestion of food to form chyme. 3. Slow emptying of the chyme into the duodenum.  Factors affecting gastric emptying Consistency of food Liquid food is Pain → reflex Distension of Enterogastric Reflex evacuated faster inhibition of stomach, through GIT hormones than solids gastric nervous reflexes (CCK & secretin) emptying & gastrin → ± food in SI → Gastric emptying ³ Gastric emptying increase any Gastric i just slow it ? Disorders of gastric emptying It can cause heartburn, nausea, and vomiting most common Gastroparsis due to vagus nerve damage Common among diabetics  Gastric Mucosal barrier It is the mucosal defense mechanisms that protect the stomach against digestion, HCL and noxious agents. It is formed of : 1- The mucus-bicarbonate barrier: mucus cells secrete HCO3- and mucus ✓ The mucus is: insoluble (gel) and impermeable to H+ ions ✓ HCO3- neutralize any acid which may reach the mucosa 2- The tight junction between the cells prevents H+ back diffusion 3- The mucosal blood flow: provide nutrients & oxygen and disposal of any H+ permeating the get rid Of any H+ hack the mucosa mucosa 4- Prostaglandins (PGs): mucus secretion, blood flow & ↓ acid secretion  Peptic ulcer Def.: Breakdown of gastric mucosa barrier Stress high salt or sugar  Vomiting (Emesis) protective reflex: esophegal & Pharyngeal phase & vomiting Forceful evacuation of stomach contents through mouth Protective reflex Mechanism: Relaxation of stomach & LES Contraction of pyloric sphincter Contraction of diaphragm & abdominal muscles → squeeze the stomach  Causes and mechanism of Vomiting 7M Reflex VII M Mechanical stimulation of the posterior part of the tongue Irritation of the gastric mucosa Intestinal obstruction Visceral pain D,M, HAU + conditional reflex Central By stimulation of VOIMTING CENTER in medulla: - Drugs - Hypoxia, acidosis & uremia - Motion sickness: due to afferent from vestibular nuclei - Conditioned reflexes: nauseating smell, sickening sights Uremia is the buildup of waste products (like urea) in the blood Hypoxia refers to a condition where there is a deficiency of oxygen in the tissues, despite normal blood circulation  saliva secretien acini without duct Pancreas Endocrine: Exocrine: duct gland ductless gland (acini & ducts)  A. Pancreatic Enzymatic Secretion: Stimulated by CCK Pancreatic enzymes are secreted in inactive form to prevent autodigestion of pancreas. They are activated in the small intestine any enzyme secreted inactively to prevent digegestion cell itself  B. Pancreatic Aqueous Secretion Stimulated by secretin ▪ large volume (1000 ml/day) ▪ Poor in enzymes ▪ Rich in HCO3- Functions of HCO3- : 1. Neutralize acidity in duodenum neutralize acidity in gastric M barrier 2. Optimum pH for trypsin Optimum pH for pepsin HCL  Storage & Filtration glucose of Blood by bind to sulphas Storage Iron Vitamins: B12 & ADEK  Gastric acid secretion 1.5 > 2.5 Liver bile → 600-1200 ml/day Saliva: 0.5 >1.5 Pancreatic aqueous: 1L large → pH = 7.8 live bile : 600 > 1200 ml capacity Of GB is 20 > 60 contraction by CCK DAE the most important one in function is absorption bile salts. the most important one BBCP  Function of Bile Salts Help digestion of fat Help absorption of fat & fat soluble vitamins (ADEK) water repealing Emulsification Formation of micelles (FA + bile salts) Pancreatic Lipase  CHOLERETIC Vs CHOLAGOGUE increase bile salts formation Substance Choleretic ↑ BILE Bile salts SECRETION Substance CCK Cholagogue ++ GB increase bile salts contraction Vagus order to GB and secretion bile salts , not direct VIP "brings back" to prevent bile to bomb Prevent irritation of mucosa by acidic bile pH 7.8 FUNCTIONS OF SMALL INTESTINE F D A  Xerostomia Definition Dysphagia Causes Gastroparesis C/P Celiac disease Complications Short bowel syndrome