The Functional Anatomy and Histology of the Gastrointestinal Tract Including the Liver and the Pancreas PDF MBS 232 2020

The Functional Anatomy and Histology of the Gastrointestinal Tract Including the Liver and the Pancreas MBS 232 Dr KB Makhathini 2020  Digestive System Provides fuel for body cells’ functioning Two gro...

The Functional Anatomy and Histology of the Gastrointestinal Tract Including the Liver and the Pancreas MBS 232 Dr KB Makhathini 2020  Digestive System Provides fuel for body cells’ functioning Two groups of organs 1. Alimentary canal (gastrointestinal or GI tract) Digests and absorbs food Mouth, pharynx, esophagus, stomach, small intestine, and large intestine 2. Accessory digestive organs Teeth, tongue, gallbladder Digestive glands – Salivary glands – Liver – pancreas 2  Parotid gland Mouth (oral cavity) Sublingual gland Salivary Tongue Submandibular glands gland Esophagus Pharynx Stomach Pancreas Liver (Spleen) Gallbladder Transverse colon Duodenum Descending colon Small Jejunum Ascending colon intestine Ileum Cecum Large Sigmoid colon intestine Rectum Vermiform appendix Anus Anal canal 3 Six Functions of the Digestive System 1. Ingestion – Occurs when food and drink enter mouth 2. Mechanical processing – Crushing of solid food to make it easier to move along the digestive tract – Increases surface area for enzymes to work – Process begins in oral cavity with teeth and tongue 3. Chemical processing – Chemical breakdown of food to absorbable size 4  Six Functions of the Digestive System 4. ​Secretion – Release of water, acids, enzymes, and buffers into lumen of digestive tract 5. ​Absorption – Movement of small organic molecules, electrolytes, and water across digestive epithelium and into interstitial fluid of digestive tract 6. ​Excretion (defecation) – Elimination of waste products from digestive tract – Products are ejected as feces in process called defecation 5 Ingestion Food Mechanical digestion Pharynx Chewing (mouth) Esophagus Churning (stomach) Propulsion Segmentation Swallowing (small intestine) (oropharynx) Chemical Peristalsis digestion Stomach (esophagus, stomach, small intestine, large intestine) Absorption Lymph vessel Small intestine Large Blood intestine vessel Mainly H2O Feces Defecation Anus 6  Digestive Tract Lining Plays defensive role for the body Protects surrounding tissues from: – Corrosive effects of digestive acids and enzymes – Physical abrasion – Bacteria that are ingested or live in digestive tract 7 Four Histological Layers of the GI Tract 1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa 8  Mucosa Mucous membrane that forms the inner lining of the digestive tract Consists of: – Mucosal epithelium – Underlying layer of areolar tissue called the lamina propria – Muscle layer called the muscularis mucosae Smooth muscle that helps move mucosa 9  Mucosal Epithelia Stratified squamous in high physical stress organs – Oral cavity, pharynx, esophagus, anus Rest is simple columnar with surface modifications Ducts of secretory glands open to surface of epithelium Circular folds and villi increase surface area for absorption 10  Submucosa Layer of dense irregular connective tissue Binds mucosa to muscularis externa Contains blood vessels and lymphatics Outer margin contains: – Parasympathetic neurons and sensory neurons – Submucosal plexus Neural network that can function without CNS Regulates secretion and motility 11  Muscularis Externa Band of smooth muscle arranged in: – Inner circular and outer longitudinal layer Function to mix and propel materials Myenteric plexus between layers of muscle – Contains parasympathetic ganglia, sensory neurons, interneurons, and sympathetic postganglionic fibers – Parasympathetic stimulation increases activity – Sympathetic stimulation decreases activity 12  Serosa and Adventitia Serosa – Serous membrane covering muscularis externa along GI tract enclosed by peritoneum – Also called the visceral peritoneum – Continuous with the parietal peritoneum, which lines inner surfaces of body wall Adventitia – Layer covering muscularis externa of regions where there is no serosa Examples: oral cavity, pharynx, esophagus, and rectum – Attaches GI tract to adjacent structures 13  Mesenteries Double sheets of serous membrane (parietal and visceral peritoneum) Suspend portions of digestive tract Provide pathways for blood vessels, lymphatics, and nerves Help organize and stabilize attached organs 14 Structure of the Digestive Tract 15 16  The Oral Cavity Also called the buccal cavity Part of digestive tract that receives food Lined by oral mucosa – Stratified squamous epithelium Contains tongue, teeth, and gingivae, or gums – Gingivae are ridges of oral mucosae surrounding base of teeth 17  Functions of the Oral Cavity Senses food before swallowing Mechanically processes food Lubricates food with saliva and mucus Begins enzymatic digestion of carbohydrates and lipids 18  Oral Cavity Boundaries Lateral walls formed by cheeks – Supported by pads of fat and buccinator muscle Anterior boundary – Labia, or lips, are continuous with cheek – Vestibule is space between cheeks (or lips) and teeth Roof formed by hard palate and soft palate Floor dominated by tongue – Free edge of tongue is attached to floor with lingual frenulum Imaginary line dividing oral cavity from oropharynx – Extends between base of tongue and uvula 19 The Oral Cavity 20  The Tongue Manipulates food within oral cavity – Mechanically compresses, abrades, distorts material – Assists in chewing and preparing food for swallowing – Provides sensory analysis of touch, temperature, and taste Lingual tonsils – Paired lymphoid nodules at base of tongue – Help resist infection 21  Tongue Functions include – Repositioning and mixing food during chewing – Formation of the bolus – Initiation of swallowing, speech, and taste Intrinsic muscles change the shape of the tongue Extrinsic muscles alter the tongue’s position Lingual frenulum: attachment to the floor of the mouth 22  Tongue Surface bears papillae 1. Filiform—whitish, give the tongue roughness and provide friction 2. Fungiform—reddish, scattered over the tongue 3. Circumvallate (vallate)—V-shaped row in back of tongue These three house taste buds 4. Foliate—on the lateral aspects of the posterior tongue Terminal sulcus marks the division between – Body: anterior 2/3 residing in the oral cavity – Root: posterior third residing in the oropharynx 23  Palate Hard palate: palatine bones and palatine processes of the maxillae – Slightly corrugated to help create friction against the tongue Soft palate: fold formed mostly of skeletal muscle – Closes off the nasopharynx during swallowing – Uvula projects downward from its free edge 24 Epiglottis Palatopharyngeal arch Palatine tonsil Lingual tonsil Palatoglossal arch Terminal sulcus Foliate papillae Circumvallate papilla Midline groove of tongue Dorsum of tongue Fungiform papilla Filiform papilla 25  The Salivary Glands Three pairs of glands that secrete into oral cavity 1. Parotid salivary glands On each side of oral cavity between mandible and skin Parotid duct empties into vestibule at level of second upper molar 2. Sublingual salivary glands Under mucous membrane on floor of mouth Numerous sublingual ducts open on either side of lingual frenulum 3. Submandibular salivary glands In floor of the mouth along inner surfaces of mandible Ducts open into mouth behind teeth on either side of lingual frenulum 26 The Salivary Glands 27  Saliva Amount and Contents About 1.0–1.5 liters produced each day – During eating, production increases to about 7 mL per minute – Regulated by autonomic nervous system Composition – 99.4 percent water – Mucins, ions, buffers, waste products, metabolites, and enzymes Mucins absorb water and form mucus 28  Functions of Saliva 1. Water lubricates mouth and dissolves chemicals 2. Mucus reduces friction and makes swallowing easier 3. Buffers keep pH near 7.0 and prevent buildup of acids produced by bacteria 4. Salivary antibodies (IgA) and lysozyme help control bacterial levels 5. Salivary amylase (an enzyme) begins chemical digestion of starches (complex carbohydrates) – Produced primarily by parotid salivary gland 29  The Teeth Perform chewing, or mastication Parts of a tooth – Neck is boundary between root and crown – Enamel layer covers crown Hardest biologically manufactured substance Requires Ca2+, phosphates, and vitamin D3 for formation – Dentin makes up most of tooth – Pulp cavity receives blood vessels and nerves through root canals – Periodontal ligament, with cementum, binds to bone in tooth socket, or alveolus 30 Teeth: Structural Components and Dental Succession 31  Tooth Decay Generally result of bacterial action Bacteria produce matrix, trapping food particles – Creates deposits called dental plaque – Plaque can calcify and form hard layer of tartar, or dental calculus 32  Types of Teeth Incisors – Blade-shaped teeth at front of mouth – Used for clipping or cutting Cuspids, or canines – Sharp ridgeline and pointed tip – Used for tearing or slashing Bicuspids, or premolars, and molars – Have flattened crowns with ridges – Used for crushing, mashing, and grinding 33 Incisors Incisors Central (6–8 mo) Central (7 yr) Lateral (8 yr) Lateral (8–10 mo) Canine (eyetooth) Canine (eyetooth) (11 yr) (16–20 mo) Premolars Molars (bicuspids) First molar First premolar (10–15 mo) Deciduous (11 yr) Second molar (milk) teeth Second premolar (about 2 yr) (12–13 yr) Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar Permanent (wisdom tooth) teeth (17–25 yr) 34  Dental Formulas A shorthand way of indicating the number and relative position of teeth – Ratio of upper to lower teeth for one-half of the mouth – Primary: 2I,1C, 2M – Permanent: 2I,1C, 2PM, 3M 35  Dental Succession Two sets of teeth form during development Deciduous teeth are first to appear – Also called primary, baby, or milk teeth – Usually 20 in number – Periodontal ligaments and roots erode during eruption (emergence) of adult teeth Secondary dentition, or permanent dentition – Usually 32 in number – Third molars, or wisdom teeth, are last to come in 36  The Pharynx Commonly called the throat Serves as common passageway for food, liquid, and air Food passes through oropharynx and laryngopharynx to esophagus Mucosa is stratified squamous epithelium Lamina propria contains mucous glands and tonsils Pharyngeal muscles cooperate with oral cavity and esophageal muscles for swallowing 37  The Esophagus Muscular tube (25cm long and 2cm wide) that acts as passageway from pharynx to stomach Located posterior to trachea Enters abdominal cavity through esophageal hiatus in diaphragm – Diaphragmatic, or hiatal, hernia involves movement of abdominal organs upward through the esophageal hiatus Lined with stratified squamous epithelium Circular muscles at either end form upper and lower esophageal sphincters 38  Lips and Cheeks Contain orbicularis oris and buccinator muscles Vestibule: recess internal to lips and cheeks, external to teeth and gums Oral cavity lies within the teeth and gums Labial frenulum: median attachment of each lip to the gum 39  Upper lip Gingivae (gums) Superior labial Palatine raphe frenulum Palatoglossal arch Hard palate Soft palate Palatopharyngeal arch Uvula Posterior wall Palatine tonsil of oropharynx Tongue Sublingual fold Lingual frenulum with openings of sublingual ducts Opening of submandibular duct Gingivae (gums) Vestibule Inferior labial Lower lip frenulum Anterior view 40  The Stomach Four primary functions 1. Temporary storage of ingested food 2. Mechanical breakdown of ingested food 3. Chemical digestion by acids and enzymes 4. Production of intrinsic factor needed for vitamin B12 absorption Chyme is mixture of food and gastric secretions 41  Regions of the Stomach J-shaped organ with four main regions 1. Cardia Where the esophagus connects 2. Fundus Bulge of stomach superior to cardia 3. Body Large area between fundus and curve of the J 4. Pylorus Most distal portion Connects stomach to small intestine Pyloric sphincter regulates flow of chyme into small intestine 42  Internal Features of the Stomach Rugae – Folds of mucosa – Show prominently when stomach is empty – Flatten out with stomach distention – Stomach can expand to accommodate up to 1.0–1.5 liters Muscularis externa – Has circular, longitudinal, and third oblique layer – Extra layer strengthens stomach wall and assists in mixing and churning chyme 43 The Anatomy of the Stomach 44  Mesenteries Associated with the Stomach Greater omentum – Very large peritoneal pouch – Extends from greater curvature of stomach down over abdominal viscera Lesser omentum – Smaller peritoneal pouch – Extends from lesser curvature of stomach to liver 45  The Gastric Wall Lined by simple columnar epithelium with numerous mucous cells Mucous epithelium secretes alkaline mucus that protects epithelium Gastric pits – Shallow depressions that open to gastric surface – Mucous cells at base, or neck, undergo active mitosis, replacing mucosal cells every three to seven days Gastric glands – Located in fundus, body, and pylorus – Connected to gastric pits – Cells produce 1.5 liters/day of gastric juice 46  The Gastric Gland Cells Parietal cells secrete: – Intrinsic factor for vitamin B12 absorption – Hydrochloric acid (HCl) Lowers pH of gastric juice to 1.5–2.0 Kills microorganisms and activates enzymes Chief cells secrete: – Pepsinogen, activated by HCl, which is converted into proteolytic enzyme, pepsin – In infants, also secrete rennin and gastric lipase that are important in digestion of milk 47 The Anatomy of the Stomach 48 Stomach Histology Rugae: Folds in stomach when empty Gastric pits: Openings for gastric glands – Contain cells Surface mucous cells: Mucus Mucous neck cells: Mucus Parietal cells: Hydrochloric acid and intrinsic factor Chief cells: Pepsinogen Endocrine cells: Regulatory hormones 24-49 Small Intestine Site of greatest amount of digestion and absorption Divisions – Duodenum – Jejunum – Ileum: Peyer’s patches or lymph nodules Modifications – Circular folds or plicae circulares, villi, lacteal, microvilli Cells of mucosa – Absorptive, goblet, granular, endocrine 24-50  Small Intestine Secretions Mucus – Protects against digestive enzymes and stomach acids Digestive enzymes – Disaccharidases: Break down disaccharides to monosaccharides – Peptidases: Hydrolyze peptide bonds – Nucleases: Break down nucleic acids Duodenal glands – Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa 51 Duodenum and Pancreas 52 Duodenum Anatomy and Histology 53  Functions of the Liver Bile production – Salts emulsify fats, contain pigments as bilirubin Storage – Glycogen, fat, vitamins, copper and iron Nutrient interconversion Detoxification – Hepatocytes remove ammonia and convert to urea Phagocytosis – Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria Synthesis – Albumins, fibrinogen, globulins, heparin, clotting factors 54 Liver Lobes – Major: Left and right – Minor: Caudate and quadrate Ducts – Common hepatic – Cystic From gallbladder – Common bile Joins pancreatic duct at hepatopancreatic ampulla 24-55 Duct System 56  Gallbladder Bile is stored and concentrated Stimulated by cholecystokinin and vegal stimulation Dumps into small intestine Production of gallstones possible – Drastic dieting with rapid weight loss 57  Pancreas Anatomy Secretions – Endocrine – Pancreatic juice (exocrine) Pancreatic islets produce Trypsin insulin and glucagon Chymotrypsin – Exocrine Carboxypeptidase Acini produce digestive Pancreatic amylase enzymes Pancreatic lipases – Regions: Head, body, tail Enzymes that reduce DNA and ribonucleic acid 58 The Pancreas 59  Large Intestine Extends from ileocecal junction to anus Consists of cecum, colon, rectum, anal canal Movements sluggish (18-24 hours) 24-60  Large Intestine Cecum – Blind sac, vermiform appendix attached Colon – Ascending, transverse, descending, sigmoid Rectum – Straight muscular tube Anal canal – Internal anal sphincter (smooth muscle) – External anal sphincter (skeletal muscle) – Hemorrhoids: Vein enlargement or inflammation 61 Histology of Large Intestines 62 The Digestion and Absorption of Carbohydrates, Fats and Proteins MBS 232 Dr KB Makhathini 2020  Introduction Balanced diets include all ingredients needed to maintain homeostasis – Carbohydrates, proteins, lipids Broken down into absorbable forms by enzymes – Process called hydrolysis Used by cells to generate ATP or build complex carbohydrates, proteins, lipids – Water, electrolytes (minerals), vitamins No processing, but require special transport mechanisms  Carbohydrate Digestion and Absorption Begins in mouth during mastication – Salivary amylase breaks down complex carbohydrates into di- or trisaccharides Pancreatic amylase continues process Brush border enzymes on intestinal microvilli complete breakdown into monosaccharides Monosaccharides absorbed through facilitated diffusion or cotransport Transported into capillaries by diffusion  Carbohydrates Consist of starches, glycogen, sucrose, lactose, glucose, fructose Polysaccharides broken down to monosaccharides Monosaccharides taken up by active transport or facilitated diffusion and carried to liver Glucose is transported to cells requiring energy – Insulin influences rate of transport  Chemical Digestion and Absorption of Carbohydrates Digestive enzymes – Salivary amylase – Pancreatic amylase – Brush border enzymes Dextrinase Glucoamylase Lactase Maltase Sucrase  Salivary and Pancreatic enzymes Enzymes: Salivary amylase and Pancreatic alpha amylase PH 6.7 – 7.5 Begins in mouth during mastication mixed with salivary amylase (parotid and submandibular salivary gland) Breaks down starches (complex carbohydrates) into disaccharides (2 simples sugars) and trisaccharides Salivary amylase continues (1-2h) until stomach acids renders the enzyme inactive  Pancreatic phase Duodenum: remaining carbohydrates are digested by pancreatic alpha amylase. No disaccharides, trisaccharides produced through digestion Any in the food is further digested.  Carbohydrates: Duodenal phase – brush border Disaccharides and tri-saccharides broken down into mono- saccharides by the brush border enzymes of the intestinal microvilli Enzyme, – Maltase: Split bond between 2 glucose molecules of Maltose – Sucrase: Breaks sucrose into glucose and fructose – Lactase: Breaks Lactose into glucose and galactose  Carbohydrate digestion Lactose (milk) – NB in infancy and childhood Lactose intolerant – Intestinal mucosa stops producing lactase  Absorption of Monosaccaharides Intestinal epithelium – Diffusion Passive or facilitated – Co-transport Difference: – Facilitated Diffusion: 1 molecule/ion across membrane No ATP NOT if opposing gradient – Co-transport: >1 molecule Down the concentration gradient for at least 1 Expend ATP – maintain homeostasis (Na+ in – out) Carbohydrates  Digestion and Absorption of Lipids Lipid molecules contain carbon, hydrogen, and oxygen – In different proportions than carbohydrates Triglycerides are the most abundant lipid in the body Lipid Catabolism (also called lipolysis) – Breaks lipids down into pieces that can be Converted to pyruvic acid Channeled directly into TCA cycle – Hydrolysis splits triglyceride into component parts One molecule of glycerol Three fatty acid molecules  Digestion and Absorption of Lipids Cells require lipids – To maintain plasma membranes Steroid hormones must reach target cells in many different tissues Solubility – Most lipids are not soluble in water Special transport mechanisms carry lipids from one region of body to another Circulating Lipids – Most lipids circulate through bloodstream as lipoproteins – Free fatty acids are a small percentage of total circulating lipids Digestion and Absorption of Lipids Involves lingual lipase from glands under tongue and pancreatic lipase from pancreas Triglycerides enter duodenum in large fat droplets – Bile salts emulsify droplets – Pancreatic lipase breaks apart triglycerides Digestion and Absorption of Lipids Triglycerides are broken into fatty acids and monoglycerides – These combine with bile salts to form micelles Micelles diffuse into epithelial cells and are converted into triglycerides – Coated with proteins to form chylomicrons – Secreted by exocytosis into interstitial fluids – Absorbed into lacteals (lymphatic vessels – small intestine) and transported through lymphatic system to left subclavian vein Digestion and Absorption of Lipids Free Fatty Acids – Come from catabolized adipose tissue – Are an important energy source During periods of starvation When glucose supplies are limited – Liver cells, cardiac muscle cells, skeletal muscle fibers, and so forth Metabolize free fatty acids  Free Fatty Acids (FFAs) Are lipids Can diffuse easily across plasma membranes In blood, are generally bound to albumin (most abundant plasma protein) Sources of FFAs in blood – Fatty acids not used in synthesis of triglycerides diffuse out of intestinal epithelium into blood – Fatty acids diffuse out of lipid stores (in liver and adipose tissue) when triglycerides are broken down  Lipoproteins Are lipid–protein complexes Contain large insoluble glycerides and cholesterol Five classes of lipoproteins – Chylomicrons – Very low-density lipoproteins (VLDLs) – Intermediate-density lipoproteins (IDLs) – Low-density lipoproteins (LDLs) “ Bad cholesterol” deposited in arterial plaques – High-density lipoproteins (HDLs) “Good cholesterol” transports cholesterol to liver  Fat globule 1 Large fat globules are emulsified Bile salts (physically broken up into smaller fat droplets) by bile salts in the duodenum. 2 Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate Fat droplets with bile salts to form micelles which coated with “ferry” them to the intestinal mucosa. bile salts Micelles made up of fatty acids, monoglycerides, and bile salts 3 Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons. 4 Chylomicrons are extruded from the Epithelial epithelial cells by exocytosis. The cells of chylomicrons enter lacteals. They are Lacteal small carried away from the intestine by lymph. intestine Digestion and Absorption of Lipids Fat digestion Enzyme(s) Site of Foodstuff and source action Path of absorption Unemulsified Fatty acids and monoglycerides fats enter the intestinal cells via Emulsification by Small diffusion. the detergent intestine Fatty acids and monoglycerides action of bile are recombined to form salts ducted triglycerides and then in from the liver combined with other lipids and proteins within the cells, and the resulting chylomicrons are Pancreatic Small extruded by exocytosis. lipases intestine The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the Monoglycerides Glycerol thoracic duct. and fatty acids and Some short-chain fatty acids fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein. Digestion and Absorption of Lipids  Digestion and Absorption of Proteins The body synthesizes 100,000 to 140,000 proteins – Each with different form, function, and structure All proteins are built from the 20 amino acids Cellular proteins are recycled in cytosol – Peptide bonds are broken – Free amino acids are used in new proteins When glucose and lipid reserves are inadequate, liver cells – Break down internal proteins – Absorb additional amino acids from blood Amino acids are deaminated – Carbon chains broken down to provide ATP  Digestion and Absorption of Proteins Amino Acid Catabolism – Removal of amino group by transamination or deamination Requires coenzyme derivative of vitamin B6 (pyridoxine) Transamination – Attaches amino group of amino acid To keto acid – Converts keto acid into amino acid That leaves mitochondrion and enters cytosol Available for protein synthesis  Digestion and Absorption of Proteins Deamination – Prepares amino acid for breakdown in TCA cycle – Removes amino group and hydrogen atom Reaction generates ammonium ion Chemical Digestion and Absorption of Nucleic Acids Enzymes – Pancreatic ribonuclease and deoxyribonuclease Absorption – Active transport Transported to liver via hepatic portal vein  Chemical Digestion and Absorption of Proteins Enzymes: pepsin in the stomach Pancreatic proteases – Trypsin, chymotrypsin, and carboxypeptidase Brush border enzymes – Aminopeptidases, carboxypeptidases, and dipeptidases Absorption of amino acids is coupled to active transport of Na+  Lumen of Amino acids of protein fragments intestine Brush border enzymes Apical membrane (microvilli) Pancreatic proteases 1 Proteins and protein fragments Na+ are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxy- peptidase), and by brush border Na+ Absorptive enzymes (carboxypeptidase, epithelial aminopeptidase, and dipeptidase) cell of mucosal cells. 2 The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side (transcytosis). Amino acid carrier 3 The amino acids leave the villus epithelial cell by facilitated Active transport Capillary diffusion and enter the capillary Passive transport via intercellular clefts. Protein digestion Enzyme(s) Site of Foodstuff and source action Path of absorption Protein Amino acids are absorbed Pepsin by cotransport with (stomach glands) Stomach sodium ions. in presence Some dipeptides and Large polypeptides of HCl tripeptides are absorbed Pancreatic via cotransport with H++ Small enzymes and hydrolyzed to amino intestine Small polypeptides, (trypsin, chymotrypsin, acids within the cells. small peptides carboxypeptidase) Amino acids leave the Brush border epithelial cells by Small enzymes facilitated diffusion, enter Amino acids intestine (aminopeptidase, the capillary blood in the (some dipeptides carboxypeptidase, villi, and are transported and tripeptides) and dipeptidase) to the liver via the hepatic portal vein. Absorption of Minerals and Vitamins MBS 232 Dr KB Makhathini 2020 1  Vitamins Vitamins are organic molecules essential to metabolic reactions. Function as coenzymes in enzymatic reactions. Two groups: – Fat-soluble vitamins: Dissolves in lipids. A, D, E, and K. – Water-soluble vitamins: Dissolves in water. B vitamins and C. 2 Vitamins 3 Vitamin Absorption and Storage 4  Vitamin Absorption and Storage  Water-soluble vitamins Absorbed with water and enter directly into the blood stream. Most absorbed in the duodenum and jejunum. Most are not stored in the body. Excess intake excreted through the urine. Important to consume adequate amounts daily. Dietary excesses can be harmful. 5 Absorbing Vitamins 6  Absorption of Vitamins Fat-soluble vitamins: A, D, E, and K – Absorbed in micelles along with lipids. – Vitamin K also produced in colon by bacteria. Water-soluble vitamins: B vitamins and C – All but B12 are easily absorbed by digestive epithelium. B12 requires intrinsic factor (protein secreted by parietal cells of stomach) for absorption. – Bacteria in gut are also source of water-soluble vitamins. 7  Water-Soluble Fat-Soluble Vitamins Vitamins Absorbed in the Small Intestine Small Intestine Hydrophobic or Hydrophilic Hydrophobic Hydrophilic Absorbed into the Blood Lymph Stored in the body Not Generally Yes Can build up and Not Generally Yes become toxic Need to consume Yes No daily 8  Absorption of Vitamins Bacteria in colon make three key vitamins 1. Vitamin K: Needed for production of clotting factors. 2. Biotin: Essential for glucose metabolism. 3. Vitamin B5 (pantothenic acid): Required for synthesis of neurotransmitters and steroid hormones. 9  Absorption of Vitamins In small intestine: – Fat-soluble vitamins (A, D, E, and K) are carried by micelles and then diffuse into absorptive cells. – Water-soluble vitamins (vitamin C and B vitamins) are absorbed by diffusion or by passive or active transporters. – Vitamin B12 binds with intrinsic factor, and is absorbed by endocytosis (ileum). 10  Absorption of Vitamins In large intestine: - Vitamin K and B vitamins from bacterial metabolism are absorbed. 11  Fat-Soluble Vitamins Vitamins A, D, E, and K. Vitamins A, E, and K absorbed from the digestive tract along with lipid contents of micelles. Vitamin D3 can be synthesized by skin exposed to sunlight. Can be stored easily in cells. Body contains significant reserves. 12 Fat-Soluble Vitamins 13  Vitamin A absorption Capability for the de novo synthesis of compounds with vitamin A activity is limited to plants and microorganisms. Higher animals must obtain vitamin A from the diet, either as the preformed vitamin or as a pro-vitamin carotenoids such as ß-carotene. In the intestinal mucosa, carotene is converted (via two enzymatic steps) to retinol. The major dietary forms of preformed vitamin A are long- chain fatty acids (contains >12 C atoms) of retinol esters. 14  Vitamin A absorption Retinol esters (RE) must be hydrolyzed prior to intestinal absorption. Hydrolysis of the esters can be catalyzed both by enzymes secreted by the pancreas into the intestinal lumen and by those associated directly with intestinal cells. Following the hydrolysis of dietary REs, the free retinol is then taken up by the mucosal cell, where it is re-esterified with long-chain, mainly saturated fatty acids by the enzyme lecithin: retinol acyltransferase (LRAT), which is membrane bound. 15  Vitamin A absorption The resulting REs are incorporated with other neutral lipid esters (i.e., triacylglycerols and cholesteryl esters) into chylomicrons and absorbed via the lymphatics. In the vascular compartment, much of the chylomicron triacylglycerol is hydrolyzed by lipoprotein lipase in extrahepatic tissues, resulting in the production of a “chylomicron remnant” that contains most of the newly absorbed REs. 16  Vitamin A absorption Under conditions of adequate vitamin A nutriture, the liver is the main site of vitamin A storage, with more than 95% of the total neutral retinoid being present as REs, predominately retinyl palmitate and stearate. Although chylomicron remnants (and the REs they contain) initially are taken up exclusively by the hepatocytes in liver, the REs are then transferred largely to the perisinusoidal stellate cells. In both cell types the REs are stored in cytoplasmic lipid droplets along with other neutral lipids. 17  Vitamin A Vitamin E – prevents the oxidation of vitamin A (antioxidant). Bile is essential for fat soluble vitamin absorption. Released form the liver – transported by retinol binding protein (RBP). 18 Fat-Soluble Vitamins 19  Water-Soluble Vitamins Most are components of coenzymes. Easily absorbed from digestive tract. Excess readily excreted in urine. 20 Water-soluble Vitamins 21 Water-Soluble Vitamins 22  Hypovitaminosis and Hypervitaminosis Hypovitaminosis, or vitamin deficiency disease: – Rarely occurs with fat-soluble vitamins since they are easily stored. – Intestinal bacteria help prevent deficiency. Produce five of nine water-soluble vitamins and vitamin K. Hypervitaminosis: – Occurs when dietary intake exceeds ability to store, use, or excrete vitamin. – Most often involves fat-soluble vitamins. – Only occurs with water-soluble vitamins if person is taken in large doses of vitamin supplements. 23  Electrolyte Absorption Mostly along the length of small intestine. Iron and calcium are absorbed in duodenum. – Na+ is coupled with absorption of glucose and amino acids. – Ionic iron is stored in mucosal cells with ferritin. – K+ diffuses in response to osmotic gradients. – Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH). 24  Minerals Inorganic ions released by dissociation of electrolytes. Important for three reasons: 1. Ions such as Na+ and Cl– determine osmotic concentration of body fluids. 2. Various ions needed in physiological processes, such as: maintaining membrane potential, muscle contraction, generating action potentials, buffers, etc. 3. Ions function as cofactors in enzymatic reactions. 25  Potassium (K+) Simple diffusion. Water absorption – rise – increase in luminal K+ concentration. Diarrhoea – loss of K+. 26  Calcium (Ca+) Absorption strongly controlled by reflexes – changes in plasma calcium. Regulation is mediated by Vitamin D. Decreases in plasma calcium – increases active Vitamin D. Enhancement of calcium active transport across intestinal epithelium. 27  Fe; Fe2+; Fe3+ Ferrous (Fe2+) and to a lessor extent ferric (Fe3+) are actively transported into the intestinal epithelium. Incorporated into Ferritin. Transported out of enterocyte by ferroportin (Hepcidin – mediated). Hepcidin is a protein which is a key regulator of the entry of iron into the circulation in mammals. Released into bloodstream and bound to transferrin. Controlled by body stores. 28 Minerals 29  Water Daily requirement averages 2500 mL/day (roughly 40 mL/kg body weight). – May need more or less based on activity and body temperature. – Most obtained through consumed food and water. – Small amount produced in mitochondria by electron transport system: Called metabolic water. Accounts for about 300 mL of water per day. 30  Water Absorption 95% is absorbed in the small intestine by osmosis. Net osmosis occurs whenever a concentration gradient is established by active transport of solutes. Water uptake is coupled with solute uptake. 31 Water and Ions Water: – Can move in either direction across wall of small intestine depending on osmotic gradients. Ions: – Sodium, potassium, calcium, magnesium, phosphate are actively transported. 32  Malabsorption of Nutrients Causes – Anything that interferes with delivery of bile or pancreatic juice. – Damaged intestinal mucosa (e.g., bacterial infection). 33  Malabsorption of Nutrients Gluten-sensitive enteropathy (celiac disease): – Gluten damages the intestinal villi and brush border. – Treated by eliminating gluten from the diet (all grains but rice and corn). 34 Digestive System Age-Related Changes Division rate of epithelial stem cells declines: – More susceptible to damage by abrasion, acids, enzymes. – Peptic ulcers more likely. Smooth muscle tone decreases: – Slows rate of peristalsis, leads to constipation. – Straining leads to hemorrhoids. – Weakening muscular sphincters can lead to more frequent “heartburn”. Cumulative damage becomes apparent: – Tooth loss due to dental caries (“cavities”) or gingivitis. – Cirrhosis or other liver disease. 35 Digestive System Age-Related Changes Increase in cancer rate: – Rates of colon and stomach cancers rise with age. – Oral, esophageal, pharyngeal cancers more common in smokers. Dehydration: – Osmoreceptor sensitivity declines. Aging of other systems affects digestive tract: – Loss in bone mass and calcium can lead to tooth loss. – Loss of taste and olfactory sensations changes diets. 36 Control of GIT secretion and GIT movements, and the flux of GIT content analward MBS 232 Dr KB Makhathini  GI tract regulatory mechanisms 1. Mechanoreceptors and chemoreceptors – Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion – Initiate reflexes that  Activate or inhibit digestive glands  Stimulate smooth muscle to mix and move lumen contents 2  GI tract regulatory mechanisms 2. Intrinsic and extrinsic controls – Enteric nerve plexuses (gut brain) initiate short reflexes in response to stimuli in the GI tract – Long reflexes in response to stimuli inside or outside the GI tract involve CNS centers and autonomic nerves – Hormones from cells in the stomach and small intestine stimulate target cells in the same or different organs 3  External stimuli (sight, smell, taste, Central nervous system thought of food) and extrinsic autonomic nerves Long reflexes Afferent impulses Efferent impulses Internal Chemoreceptors, Local (intrinsic) Effectors: (GI tract) osmoreceptors, or nerve plexus Smooth muscle stimuli mechanoreceptors (“gut brain”) or glands Short reflexes Response: Gastrointestinal Change in wall (site of short contractile or reflexes) secretory activity Lumen of the alimentary canal 4  Salivary Glands Extrinsic salivary glands (parotid, submandibular, and sublingual) Intrinsic (buccal) salivary glands are scattered in the oral mucosa Secretion (saliva) – Cleanses the mouth – Moistens and dissolves food chemicals – Aids in bolus formation – Contains enzymes that begin the breakdown of starch 5 Tongue Teeth Parotid Ducts of gland sublingual gland Parotid duct Masseter muscle Frenulum of tongue Body of Sublingual mandible (cut) gland Posterior belly Mylohyoid of digastric muscle (cut) muscle Submandibular Anterior belly of Submandibular duct digastric muscle gland Mucous Serous cells (a) cells forming (b) demilunes 6 Figure 23.9  Composition of Saliva There are three salivary glands Secreted by serous and mucous cells 97–99.5% water, slightly acidic solution containing – Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3– – Salivary amylase and lingual lipase – Mucin – Metabolic wastes—urea and uric acid – Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms 7  Control of Salivary Secretions By autonomic nervous system – Parasympathetic and sympathetic innervation Parasympathetic accelerates secretion by all salivary glands Salivatory nuclei of medulla oblongata influenced by: – Other brain stem nuclei – Activities of higher centers 8  Control of Salivation Intrinsic glands continuously keep the mouth moist Extrinsic salivary glands produce secretions when – Ingested food stimulates chemoreceptors and mechanoreceptors in the mouth – Salivatory nuclei in the brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia) 9  Swallowing Also called deglutition – Complex process – Can be initiated voluntarily or involuntarily – Proceeds automatically once begun – Tongue forms food into bolus, or small mass Compression of bolus against hard palate initiates swallowing process 10  Three Phases involved in the process of swallowing (deglutition) 1. Buccal phase – Voluntary phase – Movement of bolus into back of oral cavity and into oropharynx – Soft palate closes over nasopharynx 2. Pharyngeal phase – Epiglottis folds over larynx – Food and liquid are directed past closed glottis – Uvula and soft palate block nasopharynx 3. Esophageal phase – Bolus is pushed into esophagus and toward stomach – Pharyngeal and esophageal phases are 11 involuntary due to swallowing reflex  Movement of Digestive Materials Pacesetter cells in smooth muscle of digestive tract trigger contraction Peristalsis – Involuntary contraction and relaxation of intestinal smooth muscles that propels foods forward – Waves of contraction initiated by circular layer, followed by longitudinal layer – Propels bolus (food mass) down tract Segmentation – A mixing action with no propulsion 12  The Stomach Four primary functions 1. Temporary storage of ingested food 2. Mechanical breakdown of ingested food 3. Chemical digestion by acids and enzymes 4. Production of intrinsic factor needed for vitamin B12 absorption Chyme is mixture of food and gastric secretions 13  Regulation of Gastric Activity Production of acid and enzymes – Controlled by central nervous system – Regulated by reflexes involving stomach wall – Regulated by hormones of digestive tract Involves three overlapping phases 1. Cephalic phase 2. Gastric phase 3. Intestinal phase 14  Cephalic Phase Triggered by sight, smell, taste, thought of food Prepares stomach to receive food Parasympathetic stimulation of gastric cells increases production of gastric juice – Rates up to 500 mL/hour Generally only lasts short period 15 Regulation of Gastric Activity 16  Gastric Phase Begins when food enters stomach Stretch reflexes increase myenteric stimulation of mixing waves Submucosal plexus – Stimulates parietal and chief cells – Stimulates G cells to produce gastrin – Results in rapid increase in gastric juice production Phase may continue for several hours 17 Regulation of Gastric Activity 18  Intestinal Phase Begins when chyme enters small intestine Mostly inhibitory controls, slowing gastric emptying – Enterogastric reflex inhibits gastrin production – Intestinal hormones secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP) reduce gastric activity Ensures efficient intestinal functions – Secretion, digestion, and absorption 19 Regulation of Gastric Activity 20  Digestion in the Stomach Pepsin initiates protein digestion to small peptides Salivary amylase will digest carbohydrates until pH falls below 4.5 – Generally active for one to two hours after a meal No nutrients are absorbed in the stomach – Mucosa covered in alkaline mucus – Epithelial cells lack transport mechanisms – Gastric lining is impermeable to water – Digestion is incomplete, nutrients are still complex 21  Intestinal Movements Weak peristaltic contractions move chyme toward jejunum – Local reflexes not under CNS control Gastroenteric reflex – Initiated by distention of stomach – Increases glandular secretion and peristaltic contractions along length of small intestine – Empties duodenum Gastroileal reflex – Triggered by gastrin – Relaxes ileocecal valve – Material pushed from ileum into large intestine 22  From Intestinal Movements mouth (a) Peristalsis: Adjacent segments of (b) Segmentation: Nonadjacent segments alimentary tract organs alternately contract of alimentary tract organs alternately and relax, which moves food along the tract contract and relax, moving the food distally. forward then backward. Food mixing and slow food propulsion occurs. 23  Coordination of Secretion and Absorption Neural and Hormonal Mechanisms – Coordinate activities of digestive glands – Regulatory mechanisms center around duodenum Where acids are neutralized and enzymes added Neural Mechanisms of the CNS – Prepare digestive tract for activity (parasympathetic innervation) – Inhibit gastrointestinal activity (sympathetic innervation) – Coordinate movement of materials along digestive tract (the enterogastric, gastroenteric, and gastroileal reflexes) – Motor neuron synapses in digestive tract release neurotransmitters 24  Intestinal Secretions Intestinal juice produced at rate of about 1.8 liters/day Moistens intestinal contents Helps buffer acids Provides liquid environment for intestinal contents Composed mostly of water from mucosa – Moves into lumen by osmosis Rest is secreted by intestinal glands – Stimulated by touch and stretch receptors in intestinal wall – Also respond to signals in cephalic phase 25  Six Hormones of Duodenal Enteroendocrine Cells Coordinate digestive functions – Gastrin – Secretin – Cholecystokinin (CCK) – Gastric inhibitory peptide (GIP) – Vasoactive intestinal peptide (VIP) – Enterocrinin 26  Intestinal Hormones Intestinal tract secretes peptide hormones with multiple effects – In several regions of digestive tract – In accessory glandular organs Gastrin released in response to incompletely digested proteins – Promotes stomach motility – Stimulates production of acid and enzymes Secretin released in response to acidic chyme – Increases secretion of bile and buffers by liver and pancreas Cholecystokinin (CCK) released in response to high-fat chyme – In pancreas, increases enzyme production – In gallbladder, causes the ejection of bile 27  Intestinal Hormones cont. Gastric inhibitory peptide (GIP) released in response to high- fat and high-glucose chyme – Inhibits gastric activity – Causes release of insulin Vasoactive Intestinal Peptide (VIP) – Stimulates secretion of intestinal glands – Dilates regional capillaries – Inhibits acid production in stomach Enterocrinin – Is released when chyme enters small intestine – Stimulates mucin production by submucosal glands of duodenum 28 29 Activities of Major Digestive Tract Hormones 30  Digestion in the Small Intestine Most important digestive processes are completed in small intestine Final products of digestion absorbed here Most enzymes and buffers come from pancreas and liver – Small intestine enzymes produced by brush border cells 31  Control of Pancreatic Secretions About 1000 mL of pancreatic juice secreted each day Regulated by hormones – Secretin released from duodenum in response to presence of acidic chyme entering from stomach Triggers pancreas to release watery, alkaline (pH 7.5–8.8) fluid One of primary buffers in fluid is sodium bicarbonate Increases pH of chyme to optimal pH for digestive enzymes – Cholecystokinin (CCK) stimulates production and release of pancreatic enzymes 32  Pancreatic Enzymes Classified by substances they help break down – Carbohydrases (general term) digest sugars and starches Pancreatic amylase breaks down carbohydrates – Pancreatic lipase breaks down lipids, or fats – Nucleases break down nucleic acids – Pancreatic proteases break down proteins Make up 70 percent of total pancreatic enzyme production Examples: trypsin, chymotrypsin, carboxypeptidase Secreted as inactive proenzymes and activated after reaching small intestine 33  Metabolic Regulation by the Liver Liver has primary role in regulating composition of circulating blood Blood flows from absorptive areas of digestive tract through liver where hepatocytes: – Extract nutrients and toxins from blood Store and synthesize nutrient molecules Fat-soluble vitamins (A, D, E, and K) are stored – Monitor and adjust circulating levels of organic nutrients High blood glucose triggers synthesis of glycogen Low blood glucose triggers breakdown of glycogen and release of glucose 34 Hematological Regulation by the Liver Largest blood reservoir in the body – Receives about 25 percent of cardiac output Phagocytic Kupffer cells remove old or damaged RBCs, debris, and pathogens from blood Hepatocytes synthesize plasma proteins – Determine osmotic pressure of plasma – Function as nutrient transporters – Key elements of clotting and complement cascades 35  Movement in Large Intestines Mass movements – Common after meals Local reflexes in enteric plexus – Gastrocolic: Initiated by stomach – Duodenocolic: Initiated by duodenum Defecation reflex – Distension of the rectal wall by feces Defecation – Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration 36 Movements of the Large Intestine Gastroileal and gastroenteric reflexes move material into cecum Transit time through large intestine very slow – Allows for water reabsorption Mass movements – Powerful peristaltic contractions – Occur a few times per day – Triggered by distention of stomach and duodenum – Forces feces into rectum, producing urge to defecate 37  Secretions of Large Intestine Mucus provides protection – Parasympathetic stimulation increases rate of goblet cell secretion Pumps – Exchange of bicarbonate ions for chloride ions – Exchange of sodium ions for hydrogen ions Bacterial actions produce gases called flatus 38  Two Positive Feedback Loops Short reflex Triggers peristaltic contractions in rectum Long reflex Coordinated by sacral parasympathetic system Stimulates mass movements 39  Defecation Reflex Involves two positive feedback loops 1. Shorter loop Stretch receptors in rectal walls stimulate local peristalsis Moves feces toward anus, distends rectum 2. Longer loop Stretch receptors stimulate parasympathetic reflex in sacral spinal cord Stimulate increasing peristalsis and increased distention in rectum 40  Defecation Reflex Rectal Stretch Receptors – Also trigger two reflexes important to voluntary control of defecation A long reflex – Mediated by parasympathetic innervation in pelvic nerves – Causes relaxation of internal anal sphincter A somatic reflex – Motor commands carried by pudendal nerves – Stimulates contraction of external anal sphincter (skeletal muscle) 41  Defecation Process Internal anal sphincter relaxes involuntarily Conscious relaxation of external sphincter required for defecation Other conscious actions help force fecal material into rectum – Tensing abdominal muscles or elevating intra-abdominal pressure – Valsalva maneuver Attempting to forcibly exhale with a closed glottis Repeated bouts of straining to defecate permanently distends veins in the anal canal, producing hemorrhoids 42 Defecation Reflex 43  Control of Digestive Functions (Local, Neural and hormonal) Local Factors – Prostaglandins, histamine, and other chemicals released into interstitial fluid May affect adjacent cells within small segment of digestive tract – Coordinate response to changing conditions For example, variations in local pH, chemical, or physical stimuli – Affect only a portion of tract 44  Control of Digestive Functions (Local, Neural and hormonal) Neural Mechanisms – Control Movement of materials along digestive tract Secretory functions – Motor neurons Control smooth muscle contraction and glandular secretion Located in myenteric plexus 45  Control of Digestive Functions (Local, Neural and hormonal) Neural Mechanisms – Short reflexes Are responsible for local reflexes Control small segments of digestive tract Operate entirely outside of CNS control – Sensory neurons – Motor neurons – Interneurons 46  Control of Digestive Functions (Local, Neural and hormonal) Neural Mechanisms – Long reflexes Higher level control of digestive and glandular activities Control large-scale peristaltic waves Involve interneurons and motor neurons in CNS May involve parasympathetic motor fibers that synapse in the myenteric plexus – Glossopharyngeal, vagus, or pelvic nerves 47  Control of Digestive Functions (Local, Neural and hormonal) Hormonal Mechanisms – At least 18 peptide hormones that affect: Most aspects of digestive function Activities of other systems – Are produced by enteroendocrine cells in digestive tract – Reach target organs after distribution in bloodstream 48 49  The effect of short bowl syndrome on GIT function, and the health of an individual. MBS 232 Dr KB Makhathini 2020  Small Intestine Healthy and intact GIT is essential for maintenance of health. GIT digests and absorbs nutrients. Small intestine is completely formed by 20 weeks of gestation. Most intestinal growth prior to birth occurs in the third trimester. Before 27 weeks of gestation, the average length of the small intestine is 115 cm. 2  Small Intestine This length increases to approximately 250 cm with a diameter of 1.5 cm after 35 weeks of gestation. The mucosal surface area increases with age: – Infants have 950 cm2 – Adults have 7500 cm2 3  Small Intestine Nutrients, vitamin B12, calcium, iron, and bile acids are absorbed through the cells of the intestinal lining. The mucus covers the surface of the mucosa cells and acts as a trap to hold nutrients in contact with the cell surface. The mucus also acts as a bacterial barrier. The most crucial factor is the length of the intestine. The removal of the stomach, jejunum, or colon is better tolerated than removal of the ileum. 4  Short bowl syndrome Definitions: – Malabsorpative state that may require massive resection of the small intestine – Inadequate intestine to maintain normal nutrition by eating. – State of malabsorption and malnutrition that occurs following massive anatomical or functional loss of the small intestine. 5  Short bowl syndrome Average length of the small bowel is: – Neonatal 250-300cm in length – Adult 750-800cm in length 50% or more of the small bowel resected is considered short bowel syndrome Infants have more favorable long term prognosis outcomes, over adult prognosis outcomes 6  Etiology The majority of SBS involves anatomical loss of segments of the small intestine caused by surgical resection. Functional loss, is a state of decreased motility and resultant decreased absorption. 7  Etiology SBS can be congenital or acquired Congenital causes of SBS include: – Intestinal atresia (complete intestinal obstruction / blockage) – Gastroschisis (congenital defect) – Omphalocele (congenital defect) – Hirschsprung’s disease (involves the large intestine - defecation difficulty) Acquired causes of SBS include: – Necrotizing Enterocolitis (NEC) (damage to the inner lining of the small or large intestine – bacterial infection) – Mid-Gut volvulus (intestinal twisting) – Ischemic injury (diminished or absent blood flow) – Crohn’s disease (IBD) – Radiation enteritis (inflammation of the small or large intestine – radiation treatment) 8  Pathophysiology Markedly decreased mucosal surface area due to resection. Loss of trophic hormones. Loss of peptide hormones that regulate motility. Abnormal transit. Malabsorption of protein, fat, carbohydrate, vitamins, electrolytes, and trace elements, depending on site of resected intestine. 9 5 Types of Small Bowel Resections 1. Duodenal Resection 2. Jejunal Resection 3. Ileal Resection 4. Loss of the ileocecal valve 5. Colon 10  Duodenal Resection Resection of the Duodenum results in the following deficits: Protein, Carbohydrates, fat malabsorption Calcium, Magnesium, Iron, Folate malabsorption Fat soluble vitamin deficiencies 11  Jejunum Resection Jejunum is the site of absorption of most nutrients and minerals, such as calcium, magnesium, and iron. With removal of the jejunum, there is loss of some of the enzymes that break down carbohydrates, which decreases carbohydrate absorption. Unfortunately, bacteria can use these unabsorbed carbohydrates and produce lactic acid. The absorption of the increased lactic acid can lead to increased acid in the bloodstream. 12  Jejunum Resection Fat and protein digestion may be reduced if the jejunum is resected. Calcium and magnesium loss is also increased Jejunum resection can cause: – Carbohydrate malabsorption – Water soluble vitamin deficiencies 13  Ileum Resection Carbohydrate, protein, fluid, and electrolytes are also absorbed in the ileum. The ileum is the principal source of absorption of bile salts; vitamin B12; and the fat- soluble vitamins A, D, E, and K. Removal of most of the ileum results in vitamin B12 and fat- soluble vitamin deficiencies and diarrhea. Diarrhea is from both the large volume of fluid passed into the colon, and the unabsorbed bile salts can cause the colon to release water. 14  Ileum Resection Loss of these bile salts can also result in a decrease in fat absorption since the bile salts help the intestine to absorb fats. The ileocecal valve slows the progress of intestinal fluids into the colon. It also increases the pressure gradient between the ileum and the colon to prevent the colon fluids with high concentrations of bacteria from moving back up into the small intestine. 15  Loss of Ileocecal Valve Ileocecal Valve or ICV is the filter between the small and large bowel, located at the end of the ileum. Patients without an ICV are more at risk of: – Bacterial Overgrowth or Small Bowel Bacterial Overgrowth (SIBO) Allows bacteria to reflux from the colon back into the ileum, Which can result in infection, acidosis, or behavioral changes – Rapid transit time that exacerbates malabsorption Loss of ICV may result in rapid transit from the small intestine to large intestine, which can limit the time for adequate absorption to occur. Rapid transit results in chronic diarrhea, which at times is watery or non- formed. For patients with no ICV chronic diarrhea is their normal cycle. 16  Colon Resection Colon is the site of absorption of fluid and sodium and the excretion of potassium and bicarbonate. Removal of the large intestine has minimal effect on digestion and absorption. In SBS, the presence of the colon is of importance because it increases the absorption of fluids and electrolytes and decreases diarrhea 17 3 Phases of Short Bowel Syndrome 1. Active Phase 2. Adaptation Phase 3. Maintenance Phase 18  Active Phase Starts immediately after bowel resection and lasts 1-3 months Output is greater than 5 liters per day – This includes ostomy output if patient has an ostomy (artificially created via a stoma) – provide examples of ostomies. Life threatening dehydration and electrolyte imbalances Extremely poor absorption of all nutrients Reliant solely on parenteral (intravenous tube) and enteral (feeding tubes) nutritional feeds for adequate nutrition 19  Adaptation Phase Begins 12-24 hours after resection and lasts up to 1-2 years 90% adaptation occurs during this phase Villus hyperplasia and increased crypt depth occurs resulting in increased absorptive area Nutrition is essential for adaptation and should be started as soon as possible Parenteral nutrition (intravenous) is essential throughout this period. 20  Maintenance phase Absorptive capacity is at a maximum at this phase Patients start to become more educated about their condition – Start playing a bigger role in their healthcare. – Intestinal Rehab is a TEAM effort and not just “doctor’s orders”. – Come prepared with ideas, options, and questions about how to best benefit with or manage SBS. In order to achieve the best results, the patient and the physician, nutrition specialist and gastroenterologist must be able to listen to each other, and consider new treatment options or therapies. 21 Diagnosing Short Bowel Syndrome Multiple different ways for diagnosis of SBS include: – Lab studies (blood tests, fecal-fat test) – Microbiology – Radiology – Nutrition – Surgical – Computerised tomography (CT) scan 22  Surgical Care Small Bowel Resections Line Placement/Replacements Gastrostomy Tube Placement/Replacements (endoscopy) Non-Transplant Procedures – Serial Transverse Enteroplasty (STEP) (intestinal cuts) – Bianchi Procedure (longitudinal incision to the intestine) Small Intestinal Transplantation – Isolated Small Bowel Transplant – Multivisceral Transplant (Stomach, Small, Large, Colon, Liver) 23