26 - Digestive System 3 - Digestion - 202402.pdf

Digestive System 3 Dr. Simon Wells [email protected] Adapted from a lecture produced by Dr. Bronwen Mayo at UniSA Lecture Focus: Digestive system 3 Learning outcomes: Liver Histology Metabolism Bile function Ga...

Digestive System 3 Dr. Simon Wells [email protected] Adapted from a lecture produced by Dr. Bronwen Mayo at UniSA Lecture Focus: Digestive system 3 Learning outcomes: Liver Histology Metabolism Bile function Gallbladder Bile: storage, concentration & release Small Intestine Overview Digestion of carbohydrates, lipids & proteins Absorption Large Intestine Histology Function Digestion Readings: Chapter 24, Martini, Nath & Bartholomew, Fundamentals of Anatomy & Physiology, 2018 (11th Edition). PART 1: Liver 3  Liver Heaviest glandular organ in body (1.5kg) Metabolic and synthetic functions 4 lobes CORONARY ligament layering Porta hepatis doorway of liver hepatic portal vein- from stomach; job bring food molecules after digestion artery - supply nutrient and o2 from heart chemicals stored for liver acts as a guarda nd chceks everthing absobed; lipid filter bascially digestion  Liver Portal vein delivers nutrient rich blood from intestines to the liver. This blood passes through liver lobules (filters). Hepatocytes monitor and alter components of the blood.  Liver Lobes consist of functional units (lobules). In lobules Hepatocytes arranged around sinusoids and central vein Adjust levels of circulating nutrients Blood passes through sinusoids and drains into central vein Stellate macrophages (Kupffer cells) dr. kupffer discovered that big eater Phagocytic – engulf pathogens, cell debris and damaged RBCs Hepatic artery comes from left side of heart that Delivers oxygenated blood Hepatic portal circulation food weighing blood absorbed from small intestine Delivers nutrient rich blood from intestines Bile secreted into bile canaliculi and moves to gallbladder liver cells produce bile that is secreted  Liver Lobules red- arterial blood from left side of heart veins- blue part that brings food molecules from digestive sytems food from small intestine from blue part into drains and across central veins and dump up into exception function of stellate green bile canaculi (starlight)macrophage moves hepotocytes fiil in and pull things in and excarbate  Liver Function Metabolic regulation store carbo and throw out Carbohydrate, Lipid & Protein metabolism Waste removal from digestive system and unncessary Store vitamins and minerals after the process of ingestion Process drugs (inactivation) Haematological regulation regulating quality of blood Removal of bacteria (and old RBC & WBC) and antigen presentation Make plasma proteins albumin( most comman blood protein( bulk flow in capillaries Removal of hormones and antibodies or else blood will clot up Activation of vitamin D Removal or storage of toxins lexample is of mercury Bile production produces and sents into duodenum Synthesis and secretion of bile into duodenum Excrete bilirubin metabolic output of breakdwon of RBCs Liver failure – build up of hormones and toxins 10 % FUNCTION BUT STILL KEEP GOING UP PART 2: Bile & Gallbladder 9 Gallbladder Small pear-shaped, muscular sac Stores bile collects biles from liver and moves into bile duct and it can bifarcate into storage or into duodenum doesnt holdup can dehydrate and is bad as it can cause gall stones Concentrates bile Water absorbed, bile salts and solutes concentrated Releases bile into duodenum Under stimulation of CCK  Bile Contains: water, ions, bile salts, bilirubin and cholesterol links to bile salts Digestion of lipids because it is emphathalic Not water soluble which means hydrophilic and Mechanical processing in stomach creates large drops hydrophobic which can containing lipids enzyme remains at the interate with lipds and water, bile Pancreatic lipase is not lipid soluble surface and eat up through the surface and cholestrol can assist w lipid Interacts only at surface of lipid dropletand cannot enter the digestion surface Bile salts break droplets apart (emulsification) Increases surface area exposed to enzymatic attack Creates tiny emulsion droplets coated with bile salts Promote absorption of the lipids by epithelium small intestine droplets coated w bile salts epithelial cells  summarizer of Gallbladder CCK- GALL BLADDER MOVEMENT CHOLE(BILE, GALL)/ CYST( BLADDER) / KININ (MOVEMENT) OPEN SPHINCTER AND ALLOW BILE TO COME INTO SMALL INTESTINE Figure: 24-19d, pg 959, Martini, Nath & Bartholomew, Fundamentals of Anatomy & Physiology, 2018 (11th Edition).  Gallstones mainly due to dehydration Solidified cholesterol and bile saltswhich can crystalize into a large stone 80-90% are cholesterol gallstones Liver secretes bile abnormally saturated with cholesterol Excess crystallizes Forms stones stored in gallbladder or cystic duct Can also form due to low levels of bile acids and bile lecithin Epidemiology – 5 Fs Female after removing gall Fair baldder , liver continues to produce bile which is Forty taken into smaller amounts into the small Fertile intestine, and not Fat consume fatty meals PART 3: Small Intestinal Digestion & Absorption 14  Digestive Enzymes Digestive enzymes Salivary glands Stomach Pancreas Brush border enzymes microvilli Classes Carbohydrases (amylases) Break bonds between simple sugars (carbohydrates) Proteases/Peptidases Break bonds between amino acids (proteins) Lipases Separate fatty acids from glycerides (lipids) Nucleases Break nucleotides into sugars, Phosphates and Nitrogenous bases  Carbohydrate Digestion Oral cavity Carbohydrates are highly Salivary amylase polar. Enter and exit denatured by hcl intestinal cells by: Chemical digestion halts Facilitated diffusion Stomach as amylase destroyed by 2 active transport/co- the stomach transport Small Pancreatic amylase & Intestine brush border enzymes like glucose and Absorption fructose Monosaccharides are small Capillaries enough to move into the capillaries  Protein Digestion Amino acids are highly Oral cavity Chewing polar. Enter and exit intestinal cells by: Facilitated diffusion HCl denatures proteins + Stomach Pepsinogen pepsin 2 active transport/co- fall apart and strings transport of amino acids pepsin chews away amino aids Small Pancreatic proteases & Intestine brush border enzymes Absorption need active transport to move into the capillaries Amino acids are small Capillaries enough to move into the capillaries  Lipid Digestion Oral Lipids are hydrophobic so cavity Lingual lipase can freely diffuse into denatured by hcl intestinal cells goes from Chemical digestion halts lumen into Stomach as lipase destroyed by cell through the stomach lipids cant diffusion travel in water so enterocytes Small Bile salts & convert into Pancreatic lipase monotry intestine into trigly into chymlo Absorption capillaries dont They are assembled into accept lipids but Lacteals lacteals let them chylomicrons which are too enter due to big holes and w large to enter capillaries > exocytois out of cell must enter lacteals  Lipid Absorption Hydrophobic lipids do not travel well in blood Intestinal cells create triglycerides that are then packaged into chylomicrons, that can travel in blood Chylomicrons are too big to fit into capillaries so are taken in by lacteals endo& exocyt osis green thing is the lacteal Digestion Overview q. detail pathway of lipids from food to absorption PART 4: Large Intestine 21  Large Intestine litle bit of absorption ; mainly producing feaces 1.5m long Ileocaecal sphincter to anus goes from ileum to join ceacum and to the anus Tonic contraction of 3 longitudinal muscles outer layer twitched into ribbons os m 2 layers (teniae coli) to form pouches (haustra) Aids in mechanical digestion Mixing chambers Segmentation Serosa Teardrop shaped sacs of fat (omental little globes appendices) of fat  Large Intestine 3 main divisions Caecum Ileocecal valve Appendix acroos Colon going down Ascending food from ceacum to colon Transverse going upwards Descending Sigmoid Rectum pouch finger like projection ; more likey to die  Mucosa/Glands in LI No villi or circular folds in mucosa Haustra instead – expansible pouches bulging out haustra Mucosa Epithelial cells Water and ion absorption Goblet cells comes down to fat Mucus secretion for the lubrication and to let min damage of epithelial cells Organised into crypts (intestinal glands) Mucosa/Glands in LI white are mucous cells; capacity of producing mucous for lubrication pores which are intestinal crips that can gown (remnescent of ruage, longitudinal is a ribbon  Large Intestine Functions Reabsorption of water (Production of feaces) Compaction of intestinal contents into feces Absorption of important vitamins produced by bacteria (microbiome) Breakdown of some remaining products for removal Storage of fecal material prior to defecation  Digestion in the Large Intestine Mechanical digestion (motility): Peristalsis slower than SI smaller intestine Movement from the caecum to the transverse colon can be hours just up the acsneding colon Allows for increased reabsorption of water can take hours Haustral churning (segmentation) Initiated by distension of haustra as chyme enters LI Mass movement rush to push faecal towrds the exits Strong peristaltic wave beginning in transverse colon that drives controlled by automic system contents into rectum Occurs during or immediately after meal when food enters stomach Causes defecation reflex iniates  Digestion in the Large Intestine Chemical digestion Final stage of digestion occurs through activity of bacteria Produces gases and other by-products Vitamin K, biotin, pantothenic acid Organic waste products Short chain fatty acids Toxins Bacteria produce necessary enzymes that humans don’t have genetic capacity to produce. Able to digest complex polysaccharides (indigestible carbohydrates)  Defecation reflex pooping force and stretch inside rectum causes the feeling of defaceting stimulate activity to propel end of sigmoid colon rectum snd anus anus ahs 2 ring muscle that is involuntary which material are hormonal neural moving in that controls has stretch receptors which expands rectum  Diarrhoea Passage of highly fluid faecal matter ↑ frequency and ↑ fluidity of feces Results in rapid dehydration and metabolic acidosis Loss of nutrient material Less time in colon = less water reabsorbed = DEHYDRATION  Diarrhoea - Causes Exposure to damaging agents, e.g. radiation Excessive intestinal motility Substances move through faster → less water absorption Excessive osmotically active particles Will draw water out of cells into intestinal contents Toxins E.g. Vibrio cholera Excessive secretion by SI, can lose 10L fluid/day  Stories to tell: possible exam concepts Tell us about the liver What are the main functions of the liver? What is the role of bile in the digestive system? Tell us about the gallbladder What are the main functions of the gallbladder? Tell us about the small intestine functions What are the classes of digestive enzymes? Can you describe the main steps involved in the digestion and absorption of nutrients? Carbohydrates Proteins Lipids Tell us about the large intestine How does the large intestines structure differ from the small intestine? What are the main functions of the large intestine? What happens to stimulate and complete the defecation reflex?