GIT Physiology PDF

GASTRO- INTESTINAL PHYSIOLOGY (GIT) PSL 214 0 DIGESTIVE (GIT) SYSTEM FUNCTIONS: 1) MOTILITY (M) 2) SECRETION (S) is 3) DIGESTION (D) 4) ABSORPTION...

GASTRO- INTESTINAL PHYSIOLOGY (GIT) PSL 214 0 DIGESTIVE (GIT) SYSTEM FUNCTIONS: 1) MOTILITY (M) 2) SECRETION (S) is 3) DIGESTION (D) 4) ABSORPTION (A) Go DIGESTIVE SYSTEM: SUMMARY OF FUNCTIONS I e 0  FUNCTIONAL ANATOMY OF GIT WALL STRUCTURE FUNCTION 1. MUCOSA Secretion, Absorption, Protection HIT in Two g SUBMUCOSA Blood vessels and lymphatics. connective tissue= Allows stretch of GIT wall. The MUSCULOSA (longitudinal & circular layers) FMotility SEROSA Attachment, Lubrication, prevents 0 friction Fist STRUCTURE OF GI LONGITUDINAL SECTION: WALL retain TAG Our 0 STRUCTURE OF WALL OF STOMACH 0  REGULATION OF GIT FUNCTION By: 1. Neural regulation we 2. Hormonal regulation (GIT hormones) side NERVOUS REGULATION Extrinsic (Autonomic) Nerves *Parasympathetic nerves (acetylcholine) t a ee I f Stimulate motility and secretion Inhibit (relax) sphincters I C noradrenaline mid *Sympathetic nerves (adrenaline) Inhibit motility and secretion Stimulate (contract) sphincter 0  B. INTRINSIC NERVE PLEXUS Network of neurons only inside the GIT system is 69 1. Myenteric Plexus: Between longitudinal and circular muscle layers. Mainly Controls motility by release of: 1. Acetylcholine ↑ motility was 2. Serotonin 1. Nitric oxide ↓ motility www 2. VIP 2. Submucosal Plexus: In the submucosa layer o * Controls secretion and blood flow * The 2 plexuses are interconnected and are influenced by extrinsic nerves (Autonomic). statwTI 0  HORMONAL REGULATION Many hormones from endocrine cells in stomach & small intestine (See Table) 0  GASTROINTESTINAL HORMONES III SECRETED STIMULUS HORMONE BY FOR RELEASE ACTIONS G cells in 1. Protein in stomach. 1. Stimulates parietal cells (HCl) stomach 2. Vagal stimulation 2. Stimulates Chief cells (Pepsinogen). Gastrin 3. ↑ Gastric motility 1. ↓Gastric emptying & gastric secretion Duodenum Acid in duodenum 2. ↑Secretion of pancreatic bicarbonate Secretin 8 3. ↑ Secretion of bile (Liver) rich in bicarbonate 1. ↓Gastric emptying & gastric secretion CCK Duodenum Lipid in duodenum 2. ↑Secretion of pancreatic enzymes 3. ↑ Contraction of gallbladder 1. Lipid/acid in 1. ↓Gastric emptying & gastric secretion Duodenum duodenum. 2. ↑ Secretion of insulin from pancreas GIP E 2. Stretch of duodenum CCK = Cholecystokinin 0 GIP = Gastric Inhibitory Peptide  GIT MOTILITY 3 Main Types: Peristalsis, Segmentation, Tonic contractions Peristalsis Contraction behind and Elation relaxation in front of bolus. contgation Wi djsde.ITSegmentation bolus Stationary contractions 3 0 Tonic contractions Weak, sustained contractions Awww gi 0 1  SWALLOWING Occurs in the oral cavity, pharynx and esophagus. 8 31 Idlib 14 Moves bolus of food into the stomach mainly by peristalsis. 3 Phases: 7111 1. Oral Phase (Voluntary): Bolus moves by tongue into Oropharynx 411,1 2. Pharyngeal phase (Involuntary): Moves bolus into esophagus 3. Esophageal phase (Involuntary): Moves bolus into stomach. Consists of Primary and Secondary peristalsis 0 SWALLOWING – 3 PHASES ORAL PHASE Voluntary Bolus touches hard palate → Swallowing reflex Swallowing center: Medulla PHARYNGEAL PHASE Involuntary 1) Close the Openings into nose and trachea 2) inhibit Respiration Esophageal PHASE Involuntary Primary peristalsis: entry of bolus to the 8 esophagus Secondary peristalsis: remains of the bolus in the esophagus Upper & Lower esophageal sphincters – closed when no swallowing 0  Lower Esophageal Sphincter Lower (LES) & Upper (UES) esophageal sphincters are always closed except during swallowing. III ↑ Abdominal pressure may push stomach contents back into esophagus (Reflux). (Reflux esophagitis) Heartburn: Ii.IE Was Acid irritates the esophagus → Patient feels burning sensation in chest above the heart region. wins Is 0  GIT secretions and digestion: in the Mouth :MOUTH - SALIVA him I Water (99%); Bicarbonate; Mucus; Amylase; Lipase; Lysozyme. OH is Functions: Polysaciaride 1- Digestion: Initiates starch digestion: saliva contains the enzyme amylase which begin to digest dietary starch into maltose. J Disaccaride 2- Mucus: Protection, Lubrication → Swallowing 3- Lysozyme: Kill bacteria Boys 4- Facilitate: Taste, Speech t.is Absorption: None 0  Control of salivary secretion Simple Reflex : Food in mouth → reflex = ↑ secretion. ow Conditioned Reflex : OW Thinking, smelling nice food → reflex = ↑ secretion What increases salivary secretion? 1. Parasymp: large volumes of Watery saliva rich in enzymes. 2. Symp (severe stress): small volumes of saliva Thick saliva rich in mucus. 0 we  Stomach Functions 1. Motility: *1) Storage of food: Proximal stomach * 2) Gastric emptying: Distal stomach A) emptying is fastest for Carbohydrate > Protein > Fat B) emptying is Inhibited by Events in Duodenum: a. Stretch b. Presence of fat c. Presence of proteins d. High osmolarity e. Decreased pH (increased H+ 2. SECRETION: The Stomach secretes Gastric Juice 0  The Stomach: gastric glands The gastric mucosa Contains gastric glands opening into the lumen The glands consist of: 1. Parietal cells: Secrete HCl and intrinsic factor 2. Chief cells: Secrete Pepsin 3. Mucous cells: secrete mucous 4. Enterochromafin-like cells: secrete histamine 5. G cells: secrete the hormone Gastrin  Secretions of the gastric glands ( Gastric Juice **) CELL STIMULUS FUNCTIONS Alkaline ** Goblet cells Stretch Protects the mucosa. Mucus Mucus cells Pepsinogen ** Chief cells ACh, Gastrin. Activated to pepsin by HCl. Digest protein → peptides HCl ** Parietal cells ACh, Gastrin,. Activates pepsinogen Histamine. Breaks down connective tissue & Bacteria. Denatures proteins Intrinsic Factor Parietal cells Needed for Vit B12 absorption ** Gastrin G cells ACh Stimulates Parietal, Chief & Protein ECL cells Somatostatin D cells Acid Inhibits Parietal, Chief, G & ECL cells. 0  GASTRIC JUICE Control of gastric secretion: Occurs in three phases 1. Cephalic Phase (30%): Before food inters the stomach Smelling, tasting, thinking of food → Vagal stimulation → ↑ ACh and↑ Gastrin → ↑ HCl and ↑ Pepsinogen. 2. Gastric Phase: >60%: Food in stomach → Vagal stimulation and Intrinsic nerves → ↑ Ach ,↑ Gastrin and ↑ Histamine Note: ↑↑↑ Gastric acid (pH