Physiology of the Digestive System PDF

Physiology of the Digestive System Human Anatomy and Physiology II HUAP220 Objectives Define gastrointestinal tract and list its main functions Identify the nerve supply of the GIT and display the control mechanisms of GIT functions Describe each organ in GIT tract and mention...

Physiology of the Digestive System Human Anatomy and Physiology II HUAP220 Objectives Define gastrointestinal tract and list its main functions Identify the nerve supply of the GIT and display the control mechanisms of GIT functions Describe each organ in GIT tract and mention its function Objectives Interpret the causes of some common GIT disorders. Classify GIT hormones according to its location and function. Differentiate between different digestive enzymes. Human Anatomy and Physiology II HUAP220 Gastrointestinal Tract (GIT) *A long muscular tube of series of complex organs and glands, starting with the mouth ending with the anus, working together to digest food. (composed of alimentary canal and accessory organs) Main Functions of The GIT Breaking down the food into its basic forms (mechanically and chemically) to prepare it for the body use (Digestion) Absorption of digestive products Secretion of digestive juices Excretion of waste products Human Anatomy and Physiology II HUAP220 Nerve supply of the GIT 1) Intrinsic innervation (Enteric Nervous System) 2) Extrinsic innervation (Autonomic Nervous System) Anfaintic Intrinsic innervation (Enteric Nervous System) *There are two major networks of nerve (Nerve plexuses) in the wall of GIT. *Meissner's or submucosal nerve plexus regulates the exocrine and endocrine secretion of submucosal glands (Secretory function) *Auerbach's or myenteric nerve plexus regulates the peristaltic activity of the muscle layer (Motor function) Extrinsic innervation (Autonomic Nervous System) a) Parasympathetic innervation through vagus nerve and pelvic nerve Parasympathetic nerves are almost excitatory to the GIT (stimulate secretion and motility of GIT) a) Sympathetic innervation through T5 to L2 Sympathetic nerves are almost inhibitory to the GIT ( (inhibit secretion and motility of GIT) Human Anatomy and Physiology II HUAP220 Control of the GIT Functions Control of the GIT functions a) Nervous control 1) Local enteric reflexes, they pass to nerve plexus of the enteric nervous system 2) Ganglion reflexes, they pass to prevertebral ganglia Surfaces 3) Central reflexes, they pass to the CNS & Borders b) Hormonal control through GIT hormones GIT hormones are classified into now 4M my 1) Gastrin family: includes gastrin and cholecystokinin (CCK) 2) Secretin family: includes secretin, glucagon, Vasoactive intestinal peptide (VIP), gastric inhibitory peptide (GIP) smallintestaen 3) Others: includes motilin, somatostatin, neurotensin Human Anatomy and Physiology II HUAP220 Mouth (Oral Cavity) Mastication (Chewing) is rhythmic opening and closure of the mouth Functions of mastication: 1. It is essential for digestion of food by breaking large particles into small ones 2. It helps deglutition (swallowing) 3. It stimulates salivary secretion Surfaces 4. It stimulates taste buds that help in taste sensation & Borders Salivary glands There are 3 pairs of glands in the human being: 1) Parotid glands form 25% of saliva 2) Sublingual glands form 5% of saliva 3) Submandibular glands form 70% of saliva Human Anatomy and Physiology II i Ñ HUAP220 Composition & Functions of Saliva Composition of saliva: 1) Water: represents about 99.5% of salivary secretion 2) Solids: represents 0.5% of salivary secretion, which are subdivided into organic and inorganic a) The organic components are mainly mucin, ptyalin (salivary amylase), lysosomes and IgA. b) The inorganic components are mainly less Na, more K, Less Cl & more HCO3 compared to plasma. Functions of Saliva: FIFE 1. Articulation: It facilities speech through lubrication of the tongue and the buccal mucosa 2. Buffering: it maintains the pH at 7 of the mouth cavity constant by the buffers. At this pH the saliva is saturated with calcium, so teeth don’t lose calcium in oral cavity. 3. Cleaning: it mechanically clears and cleans the mouth cavity. 4. Digestion: it facilitates the digestion of CHO through salivary amylase enzyme (hydrolysis of starch into maltose and dextrin) 5. Excretion: it is a route of excretion of heavy metals as arsenic me 6. Facilitation of deglutition: it lubricates the food bolus making it easier to be swallowed. 7. H2O regulator: it is decreased on dehydration Human Anatomy and Physiology II HUAP220 Oral Cavity Diseases Salivary Gland diseases Mumps: inflammation of the salivary glands The Mumps virus Tumors: Salivary adenoma and Carcinoma adenoma Pharyngeal Diseases carcehond Tonsillitis: inflammation of the tonsils Viruses and Streptococcus pyogenes Pharyngitis: pharynx infection Respiratory tract infection Tonsils Diphtheria: pharynx infection Bacteria (Corynebacterium diphthriae) Thick covering in the back of the throat Human Anatomy and Physiology II HUAP220 Pharynx Food passes from the oral cavity to the pharynx (throat) 101 The soft palate at the top2of the mouth closes the nasal cavity (respiration is inhibited) so the food does not get into the nose The epiglottis (a flapw̅ like structure at the back of the throat) closes over the larynx making sure that the bolus passes into the oesophagus and not to the larynx and trachea. Human Anatomy and Physiology II HUAP220 Swallowing (Deglutition) It is the passage of food from the mouth to the stomach passing through the pharynx. It consists of 3 phases: Buccal phase (voluntary) talcarate Pharyngeal phase (Involuntary) Barenatal Esophageal phase (Involuntary) Human Anatomy and Physiology II HUAP220 Esophagus Esophagus Food takes about 4-8 sec. to pass Its walls contain smooth muscles that contract in a wave-like motion (peristalsis) Esophageal Sphincters (Upper UES & Lower LES) allow the passage of food downwards and prevent its backflow (regurgitation) Peristalsis It is a wave (ring) like motions (contraction behind the bolus and relaxation in front of the bolus) of the alimentary canal to push the food contents forward. Human Anatomy and Physiology II HUAP220 Esophageal Diseases Gastro-Esophageal Reflux Disease (GERD): it is the entry of the gastric contents into the lower end of esophagus due to incompetence of the lower esophageal GERD sphincter. Patients complains of heartburn. GERD is associated with >> increased intra-abdominal pressure (e.g. pregnancy and obesity) and low levels of the hormone gastrin (weak actions of the LES). Achalasia: a condition where there is failure of X -ray LES to relax on arrival of the bolus to the lower end of the esophagus resulting in massive dilatation of the esophagus above the LES (dysphagia / difficulty in swallowing) Human Anatomy and Physiology II HUAP220 Stomach General functions of the stomach: 1. Storage of food 6-8 hours. 2. Mechanical breakdown of food. 3. Digestion of the protein content of food by pepsin. 4. Sterilization of food by HCL and lysozyme. 5. Secretion of intrinsic factor which is essential for absorption of vit.B12 in terminal ileum, so patients with gastrectomy develop B12 deficiency anemia. X -ray 6. Absorption of iron (due to the acidic environment) , water 7. Regulation of the passage of the chyme to the duodenum through the pyloric sphincter Human Anatomy and Physiology II HUAP220 Gastric Secretion It has a volume of about 2.5-3 liters and a pH highly acidic of about 1. Constituents: GET 1) Gastric HCL (It is secreted from the Oxyntic or the parietal cells). 2) Enzymes e.g. Pepsinogen enzyme (it is secreted from the chief or peptic cells). 3) Mucous. 4) Intrinsic factor which is essential for vit B12 absorption (It is secreted from the Oxyntic or the parietal cells). Functions of gastric HCL: a) Sterilization of food (kills microorganism) b) stimulation of bile secretion c) Ionization of calcium so help its intestinal calcium absorption. d) Reduction of iron from ferric (Fe+3) into ferrous state (Fe+2) so help iron absorption in the duodenum and upper jejunum. e) Digestion of proteins through activation of pepsinogen into active pepsin. Human Anatomy and Physiology II HUAP220 Gastric Mucosal Barrier It prevents the autodigestion of the gastric mucosa by the acid and pepsin enzyme. It consists of the following: I 1. Tight junctions between gastric mucosal cells. 2. Presence of protective thick and alkaline mucous that covers the gastric mucosa. 3. Bicarbonate ions (HCO3) secretion. 4. Synthesis of prostaglandins. Gastrin Hormone (secreted by G cells in the antrum of the stomach). Functions: 1. Stimulation of gastric secretion. 2. Stimulation of gastric motility & growth and vascularity. 3. Stimulation of endocrine and exocrine pancreatic secretion. 4. Contraction of the lower part of the esophagus. Human Anatomy and Physiology II HUAP220 Gastric Diseases https://youtu.be/mRK6m8RicSM https://youtu.be/5RMeCgJn730 Gastritis means inflammation of the stomach. Causes Irritant drugs (non-steroidal anti inflammatory NSAIDs e.g. aspirin). Alcohol. Bacterial infection (Helicobacter pylori). Peptic ulcer means ulceration of the gastric mucosa by gastric juice due to disruption of the protective Gastric mucosal barrier. Causes 1) Stress, smoking, spicy food, alcohol for long time. 2) NSAIDs e.g. aspirin 3) Helicobacter pylori Human Anatomy and Physiology II HUAP220 Liver The largest and most important metabolic organ in the body. Functions: 1) Vascular Function (for storage and filtration of blood). 2) Metabolic Functions (Carbohydrate metabolism, Fat metabolism, Protein metabolism). 3) Secretion of bile. ADKe.g. K, iron, and 4) Storage (glycogen, fat soluble vitamins some water-soluble vitamins e.g. B12). 5) Detoxification of drugs and toxic substances (alcohol, microbial toxins, in-activation of some drugs) Human Anatomy and Physiology II HUAP220  Bile Composition of Bile 1- Water: 97.5% 2- Solids: 2.5% a) Organic constituents:2% : 1. Bile salts. 2. Bile pigments. 3. Cholesterol 4. Fatty acids 5. Lecithin b) Inorganic constituents 0.5% as: Na, K, Ca & HCO3. Blood Bile pigment (Bilirubin) Is a greenish yellow pigment Directio Is a metabolic product of hemoglobin Is excreted mostly in stool. n Functions of bile: 1. Neutralization of acid chyme 2. Digestion of lipids (by emulsification done by bile salts). 3. Absorption of lipids (by Micelle formation done by bile salts). 4. Excretion (bilirubin, cholesterol, some drugs, some dyes and some inorganic substances) Human Anatomy and Physiology II HUAP220 Jaundice (Icterus) Yellowish discoloration of the skin and whites of the eyes due to an increased level of BILLIRUBIN and deposition of Bile pigments. There are two types of bilirubin: Unconjugated (insoluble) = Indirect bilirubin Conjugated (soluble) = Direct bilirubin Human Anatomy and Physiology II HUAP220 Types of Jaundice Divided into three categories Prehepatic Hepatic Post-hepatic Human Anatomy and Physiology II HUAP220 Small Intestine Functions: 1. Onward movement of food contents (peristalsis) 2. Secretion of intestinal juice (Succus entericus: alkaline secretions >> water, mucus, and mineral salts) and hormones cholecystokinin (CCK) 3. Protection against infection by bacteria (solitary lymphatic follicles in the wall >> Peyer's patches) 4. Completion of the chemical digestion of food 5. Absorption of most nutrients Human Anatomy and Physiology II HUAP220 Motor Function of Small Intestine (Mixing and Propulsive movements) Mixing Propulsive M Movement ovement Human Anatomy and Physiology II HUAP220 Large Intestine Functions of large intestine 1. Defecation 2. Digestion of cellulose in animals. 3. Excretion of heavy metals as Mg and arsenic. 4. Absorption of water and electrolytes. 5. Synthesis of vitamins as K and vitamin B complex. 6. Secretion of mucous. 7. Storage of the fecal matter. Large intestinal bacteria * The Beneficial Bacteria: They synthesize vitamin K, histamine, biotin and folic acid. * The Non-Beneficial Bacteria: They consume vitamins C, B12 and choline and produce cholesterol also they produce histamine, tyramine and ammonia. The latter is absorbed by the liver clearing it from blood Human Anatomy and Physiology II HUAP220 Defecation It's the evacuation of the contents of the rectum and colon through the anal canal. Mechanism of defecation It is automatic reflex in animals and infants of human and become under control in adult human. 1) The autonomic spinal defecation Distension of the rectum —> stimulation of the stretch receptors in the rectal walls —> afferent impulses via the pelvic nerve to the sacral defecation center (S2, S3 & S4) —> Passage of the fecal matter inside the anal canal will stimulate more contractions of the wall of rectum and the pelvic floor with more relaxation of the external anal sphincter. Human Anatomy and Physiology II HUAP220 Defecation 2) The voluntary control via cerebral cortex If the conditions are not suitable for defecation to take place, then the cerebral cortex will inhibit the spinal defecation center. Common GIT Symptoms Diarrhea: The condition of having at least three loose or liquid bowel movements each day (leads to water and electrolytes loss) Constipation: Bowel movements that are infrequent or hard to pass Human Anatomy and Physiology II HUAP220 Intestinal Diseases Appendicitis: inflamed appendix presented with acute abdominal pain, treated with surgical removal (appendectomy) Inflammatory bowel disease (IBD): a) Crohn’s disease: chronic inflammatory condition involve the entire thickness of the gastrointestinal wall (diarrhea, abdominal pain, and weight loss) b) Ulcerative colitis: chronic inflammatory disease of the mucosa and submucosa of the colon and rectum (bloody diarrhea) Human Anatomy and Physiology II HUAP220 GIT Hormones GIT Hormone Location Stimuli for Release Function Gastrin LStomach and StPresence of peptides and amino Stimulates secretion of gastric acid (HCL) and intrinsic Duodenum acids in the gut factor from parietal cells Stimulates secretion of pepsinogen from chief cells Promotes gastric and intestinal motility and mucosal growth Increases LES constriction Cholecystokinin Duodenum Presence of fatty acids and amino - Stimulates gallbladder contractions (CCK) and Jejunum acids in the small intestine - Stimulates the release of pancreatic enzymes - Releases bile Secretin Duodenum Acidic PH in the lumen of small - Stimulates alkaline secretions (HCO3-) from the and Jejunum intestine pancreas and the bile ducts Motilin Throughout the Its secretion is associated - Increases gastric and intestinal motility and gut with fasting emptying Human Anatomy and Physiology II HUAP220 Digestive Enzymes Site of Production Site of Action Enzyme Substrate (Acts on) Product (Results of) Salivary glands Mouth Amylase Starch Maltose Disaccharide) Stomach cells Stomach Pepsin Protein Amino acids Liver Small intestine Bile salts Fat Fat droplets Pancreas Small intestine Amylase Starch Maltose Proteases Protein Amino acids Lipase Lipids Glycerol & fatty acids Small intestine Small intestine disaccharidases (eg. Maltase ) Maltose Glucose Peptidases Peptides Amino acids Human Anatomy and Physiology II HUAP220