Tutorial Workbook 1017MSC T3 2023 Module 5 Gastrointestinal System

2 Module 5: Gastrointestinal System 5.1: Functional anatomy of the GIT Label the following diagrams. Salivary Glands Parotid gland Sublingual gland Submandibular gland Pharynx Stomach Pancreas Spleen Large intestine Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anal Canal Anus Ileum Jejunum Duodenum Small intestine Gallbladder Liver Oesophagus Tongue Mouth (oral cavity) Soft palate Palatoglossal arch Hard palate Oral Cavity Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid Bone Laryngopharynx Oesophagus Uvula

5 4) Serosa (outermost layer) connective tissue for protection. 6. How does GIT activity change with the following: Sympathetic dominance Inhibits gut activity; especially secretary activity. First synapse at outlying ganglia, allowing for widespread effect, so reduction in blood flow occurs along entire gut (mostly post-ganglionic sympathetic neurons on GIT) Parasympathetic dominance Stimulates gut activity, especially motility. Increased blood flow and activity of the gut stimulation results in localised effects (preganglionic neurons, close to target). 7. Explain the long and short reflexes involved in routine digestion and absorption in the GIT. Mechanoreceptors and chemoreceptors throughout the wall dot eh gastrointestinal tract monitor the structural and chemical conditions within the lumen in order to maintain the perfect environment for digestion and absorption. This stimulates bot intrinsic and extrinsic control mechanisms. The short reflex acts within the enteric nerve plexus (the gut brain) to the wall of GI tract: myenteric and submucosal nerve plexi. The long reflexes involve autonomic nerves, responding to external stimuli such as sight, smell and taste. Visceral afferent are processed in the CNS. Visceral efferent then act on the local intrinsic nerve plexus in the GIT. These reflexes influence contractions of smooth muscle and endocrine gland activity in the GIT. The stomach and small intestine also have hormone-secreting cells that release hormones to elicit secretion or contraction (e.g. gastrin, secretin, cholecystokinin). 8. Outline the structure and function of the Enteric Nervous System, including its subdivisions. The gut brain (short reflexes) located entirely in the wall of the GIT. - the inhouse or intrinsic nerve supply of the GIT. Can operate autonomously – 100 million neurons.

8 e) between the ileum and the caecum

11 i) Mucous lining ii) Bicarbonate iii) Damaged mucosal cells are rapidly replaced (3-6 days) iv) Tight junctions between mucosal cells v) Buffering capacity of food 5. Critical thinking: What causes a gastric ulcer ? What is the treatment for the most common cause? Casued by excess acid or low mucus secretion Acid resistance Helicobacter pylori bacteria most common cause – burrow through mucous and destroy mucosal layer. If mucous barrier is breached, inflammation will occur causing gastritis. Persistent damage/inflammation causes gastric ulcers. Symptoms – epigastric pain (1-3 hours) after meal Treatment: Antibiotics. 6. Answer the following questions about mucous and its role in the GIT. i) Which cell or tissue types produce mucous a) in the stomach Mucous neck cell b) in the small intestine Goblet cell, Brunner’s gland (Duodenal glands) ii) What are the special properties of mucous? Made up of glycoproteins, polysaccharides, electrolytes, water. Coats and protects against mechanical and chemical damage to the single-cell epithelial layer of the gut wall. Very resistant to digestive enzymes and acid. Very adherent to sides of the gut and to food particles. Lamina slip: layers can slide over each other easily, while being hard to pull apart. 7. Describe how chyme content of the duodenum affects stomach contractile activity and emptying . Speed of gastric emptying is dictated by duodenal content. Carbohydrate-rich foods move through to the duodenum quickly.

14 2. List the 5 major cell types found in the mucosal epithelium of the small intestine , their secretions and their function . Name of cell Secretion Function 1 Enterocytes N/A Absorption 2 Enteroendocrine (I cells) Cholecystokinin Gallbladder contraction, Hepatopancreatic Sphincter relaxtion, Release of pancreatic enzymes from acinar cells 3 Enteroendocrine (S Cells) Secretin Bile secretion Release of bicarbonate-rich fluid from pancreas duct cells 4 Goblet Mucous Protects the epithelium from luminal content 5 Paneth Defensin Anti-microbial peptide 3. Name the 3 anatomical divisions of the small intestine i) Duodenum ii) Jejunum iii) Ileum 4. What is the purpose of the circular folds in the lumen of the small intestine? Transverse folds that increase surface area for absorption x3 Slows the passage of the partly digested luminal contents along the intestines. 5. What is lactose intolerance ? What are the implications? Lactose is the primary carbohydrate (disaccharides) in milk (milk sugar). Lactose is hydrolysed by the enzyme lactase into monosaccharides = Glucose + Galactose. If the intestinal mucosa stops producing Lactase -> Lactose intolerance causes unpleasant digestive problems. - Flatulence - Abdominal Pain (from holding in gas) - Diarrhoea Undigested disaccharides remain in the intestinal lumen, creating osmotic gradients that prevent water absorption, and pull water into the lumen -> diarrhoea.

17 8. Describe the chemical denaturing and digestion of proteins , and the absorption of the digested products. 1)Pancreatic amylase breaks down starch and glycogen into oligosaccharides and disaccharides 2)Brush border enzymes break oligosaccharides and disaccharides into monosaccharides 3)Monosaccharides (glucose and galactose) are cotransported across the apical membrane of the absorptive epithelial cell. This active transport. Uses the Na+ concentration gradient established by the Na+ -K+ ATPase (pump) in the basolateral membrane 4)Monosaccharides exit across the basolateral membrane by facilitated diffusion and enter the capillary via intercellular clefts.

20 5.4: Pancreatic and Hepatic functions 1. Label the following diagrams. Liver Right and left hepatic ducts Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Tall of pancreas Main pancreatic duct and sphincter Head of pancreas Jejunum Hepatopancreatic ampulla and sphincter Major duodenal papilla Duodenum Cystic Duct Mucosa with folds Gallbladder Interlobular veins (to hepatic vein) Central vein Bile canaliculi Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Bile duct Portal venule Portal arteriole Portal triad Stellate macrophages in sinusoid walls Portal veins Plates of hepatocytes Sinusoids Lobule Central vein Connective tissue septum

21 2. Explain why the hepatic portal system is so unique and the role it plays in digestion. It takes venous blood to another organ – the liver. Arterial blood passes through two capillary beds before entering the venous system. First fenestrated capillaries in the GIT and then sinusoidal capillaries in the liver. The hepatic portal system conveys venous blood (rich in absorbed nutrients) from the digestive system to the liver for filtering and processing. Residual venous blood is rained from the liver via the hepatic veins and empties into the inferior vena cava. 3. Name 4 primary roles played by the liver i) Metabolism: glucose metabolism, synthesis of lipids, metabolism of proteins, detoxification. ii) Storage: fat soluble vitamins and iron. iii) Filtration: Kupffer cells (Stellate macrophages) eliminate bacteria and debris. iv) Secretion: Bilirubin from degradation of haeme unit (yellow urine) and conversion to stercobilin by gut bacteria (brown faeces), bile (for breakdown of fats) 4. The liver secretes ______________. a) bile b) proteolytic enzymes c) enzymes to lyse carbohydrates d) enzymes to break up fat e) all of the above 5. The functional unit of the liver is the a) bile duct b) portal triad c) lobule d) portal arteriole 6. All of the following are bile constituents except _______________________. a) bile salts b) bicarbonate

22 c) cholesterol d) urea 7. The pancreas has both exocrine and endocrine functions. The exocrine role of the pancreas is regulated by acinar cells which produce digestive enzymes and duct cells which produce bicarbonate + H2o. These two products combine to form digestive or pancreatic juice , used for digestion in the duodenum. The endocrine function involves the secretion of glucagon from Alpha (A) cells and insulin from Beta (B) cells in the pancreatic islets of Langerhans. 8. List 4 pancreatic enzymes and their targets for digestion . Pancreatic Enzyme Break down product Protease Proteins – Amino Acids Amylase Carbohydrates - Monosaccharides Lipase Fats – Monoglycerides + Free Fatty Acids Nuclease Nucleic Acids 9. Pancreatic protease: What protective mechanism prevents the pancreas from digesting itself? Include in your answer the name of the enzyme responsible for activation of the precursors, and where it is located and activation takes place. Pancreatic enzymes are secreted as inactive precursors. Pancreatic enzymes include: protease (proteins), amylase (starch), lipase (fat) and nuclease (nucleic acids). The inactive pancreatic protease (protein enzymes) are: trypsinogen, chymotrypsinogen and procarboxypeptidase. Trypsinogen is activated in the duodenum by enterokinase – enzyme bound to membrane of duodenal cells – active form is Trypsin.

23 Trypsin then activates Chymotrypsinogen and Procarboxpeptidase to their active forms Chymotrypson and Carboxpeptidase respectively. The storage and secretion of the inactive precursors ensures that there is no digestion of the acinar and ductal cells of the pancreas. 10. Enterogastrones are hormones that influence GIT function by acting on the pancreas and the liver. Name the 2 key enterogastrones, and the cell that secretes them. i) Secretin ii) Cholecystokinin iii) Duodenal enteroendocrine cells 5.5: Large intestine function and secretions Liver Gallbladder Lesser Omentum Stomach Duodenum Transverse colon Small intestine Cecum Urinary bladder

24 1. Digestion & absorption: What are major roles played by the large intestine ? Motility: short, haustral contractions, powerful mass movements Defaecation Stores unabsorbed waste Harvest vitamins (B and K) made by gut bacteria Reclaims most of the water and some electrolytes from indigestible foods 2. What is the importance of the millions of bacteria that inhabit the large intestine? Bacterial Flora - Metabolise mucin - Ferment indigestible carbohydrates (cellulose) - Generate or synthesise vitamins – B complex and K needed for clotting 3. Describe the 2 types of movements of the large intestine. i) Haustral contractions: slow, short, segmenting, uncoordinated movements ~ every 25 minutes Greater omentum Transverse colon Transverse mesocolon Descending colon Jejunum Mesentery Sigmoid mesocolon Sigmoid colon Ileum

25 ii) Mass Movements – giant migrating contractions, intense prolonged peristaltic contraction not seen elsewhere in the GIT, 3-4 times daily after eating. 4. What increases motility of the ilium? Hormone Gastrin – released from the stomach Gastroileal reflex – long neural reflex triggered by stomach activity Also relax the ileocaecal sphincter. 5. What is appendicitis and why does it occur? Appendix becomes blocked and inflamed, often by stool, a foreign body or cancer. Appendix also swells in response to any infection in the body. 6. What stimulates the defaecation reflex ? Distension of the rectum on filling. As the walls of the rectum distend due to filling, mechanoreceptors fire, stimulating desire to defecate.

26 REFLECTION 1. What area do I feel most confident with? Why? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ 2. What area needs improvement? How can I make this improvement? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ Have you completed your Gastrointestinal System checklist?