BS161 Anatomy and Physiology 2024/25 Digestive System Lecture Notes PDF

BS161 Anatomy and Physiology 2024/25 Lecture 9: Digestive System Dr Angela Pine [email protected] 1  Week 4 Module Feedback Survey Response to module feedba...

BS161 Anatomy and Physiology 2024/25 Lecture 9: Digestive System Dr Angela Pine [email protected] 1  Week 4 Module Feedback Survey Response to module feedback  Intellectually stimulated & challenged: 88%, 3% not… it gets harder!  Know how to contact us: 83%, 17% unsure? [email protected], [email protected] OR join Slack….  Know how you will be assessed: 80%, 9% do not… I’ve posted about this on Slack today. Any questions contact me.  Feel part of a community: 38%, 53% unsure, 9% do not… Join Slack, message the community and chat… arrange meet ups…  Apply learning: 84%, 14% unsure? You can apply learning in assessment and practicals (we haven’t had any yet!).  Resources are good: 91%, 9% unsure... Explore Mastering A&P!  Organised: 77%, 12% unsure, 5% say it is not… I’ve updated Slack to include links to Moodle. Moodle is where all the information you need is. Slide  Slack Channel The BS161 Community Slide 3  Practicals and Assessment ATTENDENCE IN ALL LABS IS COMPULSORY- YOU WILL GET ZERO FOR THE ASSESSMENT IF YOU DO NOT ATTEND THE ASSOCIATED LAB PRACTICAL DATE OF PRACTICAL ASSESSMENT TYPE DEADLINE 1. Organs dissection- Week 5: 10% timed moodle quiz Moodle quiz closes STEM LAB 2.1 Lab group 1 – Tuesday (2- Tuesday 5th Nov, 5pm) 10am (Week 6) (60 min to complete once started) Lab group 2 - Wed (9:30-12:30) 2. Bone tissue and Week 6: 10% moodle quiz 2 Moodle quizzes to complete case studies All students – FRI (2-5pm) and submit before the end of the IT Lab L IT Lab session. 3. Muscle tissue and Week 8: 10% moodle quiz 2 Moodle quizzes to complete case studies IT Lab L All students – TUES and submit before the end of the (2-5pm) IT Lab session. 4. Week 9: (5 lab groups 60% DAI submitted online via 10am Tues 3rd December (Week Cardiovascular Mon/Tues – please FASER 10) function SC LAB 1.14 check your timetable and (part of sports centre) come to your allocated session) 5. Online continuous n/a 10% from 3 weekly quizzes- see See table below for each quiz assessment: table below deadline Mastering A&P 4 Slide  An Introduction to the Digestive System Learning Objectives  14. Describe the structure of the alimentary canal and organs of the GI system.  15. Describe the basic functions of the GI system and the processes of digestion, absorption and elimination.  28. Describe the underlying pathology of a named disease in each of the body systems (respiratory, cardiovascular, renal/urogenital, digestive, musculoskeletal, nervous and endocrine/reproductive) Slide  The Small Intestine  Consists of 3 sections - Plays key role in digestion and absorption of nutrients - 90 percent of nutrient absorption occurs in the small intestine 1. The Duodenum - The segment of small intestine closest to stomach - 25 cm (10 in.) long - “Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver - Functions of the duodenum: - To receive chyme from stomach - To neutralize acids before they can damage the absorptive surfaces of the small intestine (Brunner’s glands- secrete alkaline substances) Slide  The Small Intestine 2. The Jejunum - Is the middle segment of small intestine - 2.5 meters (8.2 ft) long - Is the location of most chemical digestion and nutrient absorption- by diffusion AND active transport - Has few plicae circulares and small villi 3. The Ileum - The final segment of small intestine - 3.5 meters (11.48 ft) long - Ends at the ileocecal valve - A sphincter that controls flow of material from the ileum into the cecum of the large intestine Slide  Segments of the Small Intestine 1-Duodenum (blue) 2-Jejunum (purple) 3-Ileum (pink) Large intestine Rectum a The positions of the duodenum, jejunum, and ileum Figure 24-16a Segments of the Intestine. Slide  Histology of the Small Intestine 1. Circular folds (plicae circulares) Transverse folds in intestinal lining Circular Are permanent features folds Do not disappear when small intestine fills 2. Intestinal villi A series of fingerlike projections in mucosa of small intestine Gross anatomy of the jejunum Covered by simple columnar epithelium b A representative view of 3. Covered with microvilli the jejunum Circular fold Villi These 3 features increase surface area from 33m2 to 20,000m2- 600 fold a A single circular fold and multiple villi Slide  Histology of the Small Intestine Intestinal glands (Crypts of Lieberkühn) Villi Intestinal Lymphoid Lacteal Mucous cells between crypt nodule columnar epithelial cells Layers of the Small Intestine Submucosal Which eject mucins Mucosa artery and vein onto intestinal surfaces Lymphatic Muscularis vessel mucosae Submucosal Openings from Submucosa plexus intestinal glands to Circular layer of smooth intestinal lumen at Muscularis muscle bases of villi externa Myenteric plexus Serosa Longitudinal layer of smooth muscle b The organization of the intestinal wall Slide  Within the Small Intestine In addition to intestinal glands; Duodenal glands - Also called submucosal glands or Brunner’s glands - Produce copious quantities of alkaline mucus for when chyme arrives from stomach - protects epithelium from acidic environment  Intestinal Secretions - Watery intestinal juice - 1.8 liters per day enter intestinal lumen mostly by osmosis, flowing out of the mucosa (or from intestinal glands) - Moistens chyme and assists in buffering acids - Keeps digestive enzymes and products of digestion in solution Slide  Pancreas Lies posterior to stomach Extending from duodenum toward spleen Is bound to posterior wall of abdominal cavity Is wrapped in thin, connective tissue capsule 15cm long, weighs about 80g Common Pancreatic Lobules Tail of bile duct duct pancreas 1. Head: Broad Body of Accessory -In loop of duodenum pancreatic pancreas duct 2. Body: Slender Head of Duodenal pancreas -Extends toward spleen papilla Duodenum 3. Tail: Short and rounded a The gross anatomy of the pancreas. The head of the pancreas is tucked in to a C-shaped curve of the duodenum that begins at the pylorus of the stomach. Slide  The Pancreas: Histological Organization Organized into Lobules - Are separated by connective tissue partitions (septa) - Contain blood vessels and tributaries of pancreatic ducts - In each lobule: - Ducts branch repeatedly - End in blind pockets (pancreatic acini) - Pancreatic acini: exocrine (produces enzymes) - Blind pockets - Are lined with simple cuboidal epithelium (99% of pancreatic cells) - Pancreatic islets: endocrine (produces hormones) - Endocrine tissues of pancreas - Scattered (1% of pancreatic cells) Slide  Structure and functions of the Pancreas Pancreatic duct Exocrine cells: Connective tissue septum Acinar cells and epithelial cells of duct system secrete pancreatic Exocrine cells in juice pancreatic acini Endocrine cells in pancreatic islet Endocrine cells of the pancreatic islets Secrete insulin and glucagon into bloodstream b Diagram of the cellular (Hormonal function will be covered later in ‘endocrine system’) Figure 24-18b The Pancreas. organization of the pancreas. Slide  Physiology of the Pancreas - 1000 mL pancreatic juice produced per day (exocrine secretions) - Secretion controlled by hormones from duodenum - Contain pancreatic enzymes including - Pancreatic alpha-amylase - Pancreatic lipase - Nucleases - Proteolytic enzymes Slide  Enzymes of the Pancreas 1. Pancreatic Alpha-Amylase - A carbohydrase, breaks down starches, similar to salivary amylase 2. Pancreatic Lipase - Breaks down complex lipids, releases products (e.g., fatty acids) that are easily absorbed 3. Nucleases - breaks down nucleic acids 4. Proteolytic Enzymes -Break certain proteins apart; Proteases break large protein complexes - Peptidases break small peptides into amino acids - 70 percent of all pancreatic enzyme production secreted as inactive pro-enzymes; activated after reaching small intestine (prevents autolysis) - For example, trypsinogen is converted into trypsin- cleaves peptide bonds in peptides>amino acids Slide  The Liver - Is the largest visceral organ (1.5 kg; 3.3 lb) - Located in the abdominal cavity - Performs essential metabolic and synthetic functions Coronary ligament  Anatomy of the Liver - Wrapped in tough fibrous capsule Right lobe Left lobe - Covered by visceral peritoneum Falciform - Divided into lobes ligament Round ligament Gallbladder b The anterior surface of the liver Slide  Coronary Left hepatic vein ligament Inferior vena cava Left lobe Caudate lobe Porta Hepatis Hepatic portal vein Hepatic artery proper Right lobe Common bile duct Quadrate lobe Gallbladder c The posterior surface of the liver Figure 24-19c The Anatomy of the Liver. Slide  The Liver- hepatic blood supply - 1/3 is arterial blood from hepatic artery proper - 2/3 is venous blood from hepatic portal vein, originating at: - Esophagus - Stomach - Small intestine - Most of large intestine - This blood contains all of the nutrients to be detoxified/absorbed/used by cells Slide  Histological organisation of the Liver Consists of Liver lobules - The basic functional units of the liver - Each lobe is divided by connective tissue - About 100,000 liver lobules - 1 mm diameter each - Hexagonal in cross section - With six portal areas (portal triads) - One at each corner of lobule Slide  Structure of the Liver A Portal Area/Hepatic Triad - Contains three structures 1. Branch of hepatic portal vein (blue) 2. Branch of hepatic artery proper (red) 3. Small branch of bile duct (green) 1 mm Interlobular Bile Branch of Bile Figure 24-20a Liver Histology. septum duct hepatic portal vein Portal area ductules a A diagrammatic view of liver structure, showing relationships among lobules Slide  Hepatocytes (beige cells) - Function is to adjust circulating Sinusoid Central levels of nutrients Hepatocytes vein Kupffer cells - Through selective absorption Bile and secretion Portal Area canaliculi Bile duct Branch of hepatic - In a liver lobule, they form a portal vein Branch of hepatic series of irregular plates artery proper b A single liver lobule and its cellular components arranged like wheel spokes Slide  Histology of the Liver - Many Kupffer cells (pink) are located in sinusoidal lining/central veins Immune cells that destroy old, worn out cells or pathogens - As blood flows through sinusoids: - Hepatocytes absorb solutes from plasma and secrete materials such as plasma proteins Sinusoid Central Hepatocytes vein Kupffer  The Bile Duct System cells - Liver secretes bile fluid and bile salts made from Bile canaliculi cholesterol Portal Area Bile duct - Into a network of narrow channels Branch of hepaticportal vein Branch of hepaticartery proper (bile canaliculi-green channels) b A single liver lobule and its cellular components Slide  Ducts of the Liver 1. Right and Left Hepatic Ducts - Collect bile from all bile ducts of liver lobes Round ligament Left hepatic duct Right hepatic duct - Unite to form common hepatic duct that Left hepatic Cystic duct artery leaves the liver, and joins up with the Gallbladde Common hepatic duct Fundusr Cut edge of lesser Body omentum 2. The cystic duct, which comes from the Neck Common bile duct Hepatic portal vein gallbladder, to form Common hepatic artery Liver 3. The common bile duct, which penetrates Duodenu Right gastric artery m wall of duodenum and meets pancreatic duct at duodenal ampulla Stomac h Pancrea s Slide  Functions of the Liver 1. Metabolic regulation 2. Haematological regulation 3. Bile production Slide  1. Metabolic regulation of the Liver The liver regulates: - Composition of circulating blood, nutrient metabolism, waste product removal, nutrient storage, drug inactivation  Composition of Circulating Blood - All blood leaving absorptive surfaces of digestive tract >Enters hepatic portal system >Flows into the liver - Liver cells extract nutrients or toxins from blood >Before they reach systemic circulation through hepatic veins >Liver removes and stores excess nutrients Slide  2. Haematological regulation of the Liver - The liver contains the largest blood reservoir in the body - Receives 25 percent of cardiac output Functions of Haematological Regulation - Phagocytosis and antigen presentation - Synthesis of plasma proteins - Removal of circulating hormones, antibodies, toxins - Synthesis and secretion of bile Slide  3. Bile production in the Liver The Functions of Bile - Dietary lipids are not water soluble - Mechanical processing in stomach creates large drops containing lipids - Pancreatic lipase is not lipid soluble - Interacts only at surface of lipid droplet - Bile salts break droplets apart (emulsification) - Increases surface area exposed to enzymatic attack - Creates tiny emulsion droplets coated with bile salts Slide  The Gallbladder 1 Is a hollow, pear-shaped, muscular sac The liver Stores and concentrates bile prior to excretion into small secretes bile intestine continuously— 2 about 1 Releases bile into duodenum, but only under stimulation Bile becomes more liter per day. of intestinal hormone cholecystokinin (CCK) in the concentrated the longer it remains in stomach the gallbladder. Full gallbladder contains 40–70 mL bile Liver Bile composition gradually changes in gallbladder Water is absorbed Bile salts and solutes become concentrated Duodenum 3 CCK The release of CCK by the 4 duodenum triggers dilation In the lumen of of the hepatopancreatic the digestive tract, sphincter and contraction Lipid bile salts break of the gallbladder. This ejects droplet the lipid droplets bile into the duodenum apart by emulsification. through the duodenal ampulla. d Physiology of the gallbladder. Figure 24-21d The Anatomy and Physiology of the Gallbladder and Bile Ducts. Slide  The Large Intestine Structure: - Is horseshoe shaped - Extends from end of ileum to anus - Lies inferior to stomach and liver - Also called large bowel - Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide Function: - Reabsorption of water - Compaction of intestinal contents into feces - Absorption of important vitamins produced by bacteria - Storage of fecal material prior to defecation Slide  Parts of the Large Intestine 1. Cecum The pouchlike first portion - Receives material arriving from the ileum - Stores materials and begins compaction - Also Appendix- a slender, hollow appendage about 9 cm (3.6 in.) long - Is dominated by lymphoid nodules (a lymphoid organ) 2. Colon The largest portion 3. Rectum The last 15 cm (6 in.) of digestive tract Slide  The Large Intestine- Colon - Has a larger diameter and thinner wall than small intestine - The wall of the colon forms a series of pouches (haustra) - Haustra permit expansion and elongation of colon Four Regions of the Colon: 1. Ascending colon - Begins at superior border of cecum - Ascends along right lateral and posterior wall of peritoneal cavity 2. Transverse colon - Crosses abdomen from right to left; turns at left colic flexure (splenic flexure) 3. Descending colon - Proceeds inferiorly along left side to the iliac fossa (inner surface of left ilium) 4. Sigmoid colon - Is an S-shaped segment, about 15 cm (6 in.) long - Starts at sigmoid flexure - Lies posterior to urinary bladder - Empties into rectum Slide Figure 24-24a The Large Intestine. Aorta Splenic vein Hepatic portal vein Superior mesenteric artery Right colic Superior Inferior mesenteric vein (hepatic) mesenteric vein flexure Inferior vena cava Left colic (splenic) flexure Greater omentum (cut) Transverse colon Descending colon Left colic vein Middle colic artery and vein Inferior Right colic mesenteric artery and vein artery Left colic artery Ascending colon Haustra Omental appendices Intestinal arteries and veins Ileum Rectal Ileocecal valve artery Sigmoid arteries Cecum and veins Appendix Teniae coli Sigmoid flexure Sigmoid colon a The gross anatomy and regions of the large intestine Rectum Slide  The Large Intestine- rectum - Forms last 15 cm (6 in.) of digestive tract - Is an expandable organ for temporary storage of faeces - Movement of faecal material into rectum triggers urge to defecate  The Anal Canal - Is the last portion of the rectum  Anal Sphincters - Internal anal sphincter - Circular muscle layer, not under voluntary control - External anal sphincter - A ring of skeletal muscle fibers, under voluntary control Slide Figure 24-24c The Large Intestine. Rectum Anal canal Anal columns Internal anal sphincter External anal sphincter Anus c The rectum and anus Slide  Histology of the Large Intestine - Lacks villi - Abundance of mucous cells - Presence of distinctive intestinal glands - Are deeper than glands of small intestine - Are dominated by mucous cells - Does not produce enzymes - Provides lubrication for fecal material - Simple columnar epithelium- absorption function (mainly water) Slide Figure 24-25a The Mucosa and Glands of the Colon. Teniae coli Omental appendices Haustrum Aggregated Simple lymphoid columnar nodule epithelium Layers of the Large Intestine Mucous cells Mucosa Intestinal crypt Muscularis mucosae Muscularis mucosae Submucosa Submucosa Muscularis externa Circular layer Longitudinal layer (teniae coli) Serosa a Diagrammatic view of the colon wall Slide  Physiology of the Large Intestine - Less than 10 percent of nutrient absorption occurs in large intestine - Prepares fecal material for ejection from the body  Absorption in the Large Intestine - Reabsorption of water - Reabsorption of bile salts - In the cecum - Transported in blood to liver - Absorption of vitamins produced by bacteria - Absorption of organic wastes Slide  Vitamin production in the Large Intestine Three Vitamins Produced by normal bacteria in the Large Intestine 1. Vitamin K (fat soluble) - Required by liver for synthesizing four clotting factors, including prothrombin 2. Biotin (water soluble) - Important in glucose metabolism 3. Vitamin B5 (pantothenic acid) (water soluble) - Required in manufacture of steroid hormones and some neurotransmitters Slide  In summary: digestion  The Processing and Absorption of Nutrients - Breaks down physical structure of food - Disassembles component molecules - Molecules released into bloodstream are: - Absorbed by cells - Broken down to provide energy for ATP synthesis - Or used to synthesize carbohydrates, proteins, and lipids Slide  Digestion  Digestive Enzymes - Are secreted by: - Salivary glands, Tongue, Stomach, Pancreas - Break molecular bonds in large organic molecules - Carbohydrates, proteins, lipids, and nucleic acids - In a process called hydrolysis - Are divided into classes by targets - Carbohydrases break bonds between simple sugars - Proteases break bonds between amino acids - Lipases separate fatty acids from glycerides - Nucleases break nucleic acids into bases and sugars Slide Table 24-1 Digestive Enzymes and Their Functions Slide  Digestive Dietary Input Secretions Water absorption Food and drink Saliva 2000 mL 1500 mL - Cells cannot actively absorb or Gastric secretions secrete water 1500 mL 5000 mL Liver (bile) 1000 mL Pancreas (pancreatic juice) 1000 mL - All movement of water across lining Water Reabsorption 9000 mL Intestinal secretions of digestive tract occurs through Small intestine 2000 mL reabsorbs 7800 mL passive water flow down osmotic 1200 mL gradients Colonic mucous Colon reabsorbs secretions 1400 200 mL 1250 mL mL 150 mL lost in feces Slide  Ion regulation - Osmosis does not distinguish among solutes - Determined only by total concentration of solutes - To maintain homeostasis: - Concentrations of specific ions must be regulated - Sodium ions - Calcium ions - Potassium ions - Cations (magnesium, iron) - Anions (chloride, iodide, bicarbonate, and nitrate) - Phosphate and sulfate ions Slide  Pathology of the digestive system  Colorectal cancer- 4th most common cancer in men and women (after breast/prostate, lung)  Around 43,000 new cases per year in the UK  55 year olds now invited for one-off bowel scope screening  Then screening for blood in stool (FOB) samples now offered to all 60-74 year olds in the UK  Also those at higher risk (family history, polyps, IBD)  Colonoscopy then offered, further surgery if needed  If identified and treated early enough, survival rate after 5 years can be 92% Cancer Research UK, 2022 Slide 26% 54% Preventable Causes Hereditary 20% Other Cancer Research UK, 2022 Slide  Quiz time!  Now go to PollEv.com/angelapine275 Slide