BAI GIANG HE TIEU HOA

Gastrointestinal/digestive system Objectives: - Functions of the digestive system -Basics of food digestion process: hydrolysis reactions of food molecules -Structures and components of digestive system -General structure of the wall of gastrointestinal tract -Digestion in the mouth -Digestion and absorption in the stomach -Digestion and absorption in the small intestine - Secretion and motility of the GI tracts Why we need a digestive system ? Biosynthesis Digestion • Cells need nutrients for its structure and energy for it activities • Foods are macromolecules which can not be directly absorbed by cells Digestion is a process containing hydrolysis reactions of food molecules enzyme • Polysaccharide +H2O > monosaccharides enzyme • Protein + H2O -–> amino acids enzyme • Triglyceride + H2O > Glycerol + fatty acids Factors and activities occurring in the digestive system accelerate hydrolysis reactions of food molecules • Mechanical activities: mastication/chewing, mixing, motility of intestines and stomach • Secretion • Emulsification • Enzyme catalyzation • Acidic pH environment of the gastric juice • Body temperature • Hormonal and neural regulation Components of human digestive system • gastrointestinal (GI) tract: mouth -> anus (9m): oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine • Accessory digestive organs - Teeth, tongue -Salivary glands -Exocrine pancreas - Billiary system (liver and gallbladder) Fundamental Physiology 4e Sherwood, 2012 General structure of the gastrointestinal wall: layers of tissues • Mucosa (enterocytes) • Submucosa • Muscularis externa • Serosa/adventitia http://www.easynotecards.com/uploads/358/22/593ab409_13673075871 8000_00000007.jpg Digestive and absorption processes in the gastrointestinal tract –Secretion –Motility –Digestion –Absorption Digestion in the mouth is minimal; no absorption of nutrients occurs • Mechanical digestion: chewing by teeth and movement of tongue to grind and break food into smaller pieces to facilitate swallowing and to increase the food surface area on which salivary enzymes will act • Chemical digestion occurs only with polysaccharides: amylase polysaccharides + H2O  disaccharides Saliva • secreted under the control of sympathetic and parasympathetic stimulations • Secreted continuously by major pairs of salivary glands: to liters / day • Saliva contents : 99.5% H2O’ 0.5% electrolytes and protein: amylase, and lysozyme, mucus • facilitates swallowing by moistening food particles • Antibacterial by lysozymes • serves as a solvent for molecules that stimulate the taste buds Saliva aids speech by facilitating movements of the lips and tongue (tuyến mang tai) (tuyến hàm) (Tuyến lưỡi) • • Keeps the mouth and teeth clean • Saliva is rich in bicarbonate buffers, which neutralize acids in food Swallowing: the process of moving food from the mouth through the esophagus into the stomach - oropharyngeal stage Human Physiology 12e, S.Fox, 2011 sec Secretion in the small intestine • Intestinal juice: mucus, electrolytes, H2O, enzymes • Bile: bile salts, cholesterol, bilirulin: Emulsification of fat, neutralize acidic chyme from stomach • Pancreatic juice: – Na+, K+, HCO3-: neutralize acidic chyme from stomach – Enzymes (20): • Amylase • Trypsin, chymotrypsin, carboxypeptidase • Pancreatic amylase • Lipase Small - intestine Mucosa • • • • • • circular folds (3x) villus-villi (10x) Microvilli (20x) Absorptive cells Goblet cells: mucus Paneth cells: antibacterial molecules (lysozyme and antimicrobial peptides) • Endocrine cells: hormones • intestinal crypts (crypts of Lieberkühn) • stem cells at the base of intestinal crypts • intestinal epithelium is renewed every four to five days trypsinogen Enterokinase trypsin Chymotrypsinogen Chymotrypsin Procarboxypeptidase Carboxypeptidase Chemical digestion in the small intestine Pancreatic enzymes: Trypsin, chymotrypsin, carboxypeptidase Proteins/peptids: Intestinal juice : aminopeptidase, Amino acids Iminopeptidase, tripeptidase, Dipeptidase Emulsification of fat by bile salts Chemical digestion in the small intestine • Lipids: Monoglycerit, Fatty acid, glycerol – Lipids Lipase Phospholipase Phosphat + diglycerit – Phospholipids cholesterolesterase Fatty acid, glycerol – Cholesterol • Glucids Pancreatic Amylase – Saccharose – Lactose Saccharase Lactase Maltose maltase Glucose Glucose + Fructose Glucose + Galactose Regulation of secretions in the small intestine, pancreas, gallblader HCl Pancreas: H2O, NaHCO3 Duodenum mucosa Secretin liver: bile juice (H2O, HCO3-) Intestine: intestinal juice Duodenum mucosa Cholecystokinin (Pancreozymin) Pancreas: enzymes gallbladder: ejection of bile into the duodenum intestine: intestinal juice Amino acid, fatty acids •Parasympathetic nervous stimulation: increased intestinal, pancreatic, intestinal jui • Sympathetic stimulation, morphin: inhibit… Digestive products of nutrients • Carbohydrates glucose, fructose, galactose • Lipids – Fatty acids, monoglycerides – Cholesterol, phospholipid • Proteins – Amino acids Absorption of glucose cotransport Active transport http://fig.cox.miami.edu/~cmallery/150/memb/sf40x12c.jpg diffusion Absorption of Fatty acids and monoglycerides Lipoproteins and plasma cholesterol • lipoproteins are complex of lipids and proteins to transport lipids in the blood •Plasma lipoproteins are classified based on the density of protein contained in them – Very low density lipoprotein (VLDL) – Low density lipoprotein (LDL) – bad cholesterol –Low density lipoprotein (HDL) contents Phospholipid (%) Triacylglycerol (%) Cholesterol (%) Protein (%) 90 Lipoprotein mật độ thấp (VLDL) 18 60 14 Lipoprotein mật độ thấp (LDL) 20 10 45 25 Lipoprotein mật độ cao (HDL) 30 20 45 Lipoproteins Chylomỉcon Absorption of H2O • 9L H2O/day: from ingested food and digestive juices – 92% H20 is absorbed in the small intestine – 6-7% is absorbed in the large intestine • Osmosis – H20 is absorbed followed the absorption of other nutrients Absorption of ions • Na+,K+, Mg2+: active transport • Ca 2+ : active transport under the control of Vit.D, PTH, calcitonin • Cl-: – Passive transport following the transportation of Na+: duodenum – Active transport: ileum [...]... over the fundus -> body -> the antrum -> pyloric sphincter • peristaltic contractions in the fundus and the body are weak -> Gastric storage takes place in the body of the stomach • Gastric mixing takes place in the antrum of the stomach Gastric emptying Human Physiology 12e, S.Fox, 2011 • Factors in the duodenum and others control gastric emptying • fat, acid, hypertonicity, and distension in the duodenum... food through the esophagus to the stomach: 5-9 sec Human Physiology 12e, S.Fox, 2011 5 to 9 seconds • Peristalsis: ringlike contractions of the circular smooth muscle of the esophagus • The pharyngoesophageal sphincter keeps air from entering the digestive tract during breathing • The gastroesophageal sphincter prevents reflux of gastric contents • Choking • Heartburn http://nutritionforthemodernstudent.wordpress.com/anatomy-andphysiology-of-the-digestive-system/... final form, thus exposing more of the peptide bonds for enzymatic attack • HCl kills most of the microorganisms ingested with food • The gastric mucosal barrier protects the stomach lining from gastric secretions Human Physiology 12e, S.Fox, 2011 Gastritis and Peptic Ulcers • The layer of mucus containing alkaline bicarbonate (HCO 3 −) protects epithelial surface of the stomach from damage caused by... erosions of the mucosa of the stomach or duodenum (Peptic ulcers) • Cause of Peptic ulcers: – Excessive gastric acid secretion (by Excessive gastrin secretion ->ulcers of the duodenum) – Reduce the barriers of the gastric mucosa (gastric ulcer) – Helicobacter pylori infection (2005 Nobel Prize) – Anti prostaglandin (e.g aspirin, as prostaglandin stimulate mucus and HCO3- secretion of the gastric mucosa)... Absorption in the small intestine Small intestine • The small intestine is the site where most digestion and absorption take place • Small intestine – Longest part of the digestive tract (3-6m), divided into 3 segments: • Duodenum (tá tràng ,20-25cm) • Jejunum (2/5) (hỗng tràng) • ileum (3/5) (hồi tràng) • Bile and pancreatic juice are secreted into the duodenum facilitating digestion in the small intestine... no absorption occurs in the stomach (exception to alcohol and aspirin) Fundamental Physiology 4e Sherwood, 2012 Acidic environment in the stomach and the gastric mucosal barrier • HCl activates the enzyme precursor pepsinogen to an active enzyme, pepsin, and provides an acid environment optimal for pepsin action • HCl denatures protein; that is, it uncoils proteins from their highly folded final... distension in the duodenum can slow the rate of gastric emptying by neural or hormonal responses • Emotions can alter gastric motility by acting through the autonomic nerves Human Physiology 12e, S.Fox, 2011 Digestion in the stomach • Carbohydrate digestion continues in the body of the stomach by salivary amylase until amylase is inactivated by HCl • Protein digestion begins in the antrum HCl pepsinogen -... peptides) • Endocrine cells: hormones • intestinal crypts (crypts of Lieberkühn) • stem cells at the base of intestinal crypts • intestinal epithelium is renewed every four to five days trypsinogen Enterokinase trypsin Chymotrypsinogen Chymotrypsin Procarboxypeptidase Carboxypeptidase Chemical digestion in the small intestine Pancreatic enzymes: Trypsin, chymotrypsin, carboxypeptidase Proteins/peptids:... by bile salts Chemical digestion in the small intestine • Lipids: Monoglycerit, Fatty acid, glycerol – Lipids Lipase Phospholipase Phosphat + diglycerit – Phospholipids cholesterolesterase Fatty acid, glycerol – Cholesterol • Glucids Pancreatic Amylase – Saccharose – Lactose Saccharase Lactase Maltose maltase Glucose Glucose + Fructose Glucose + Galactose Regulation of secretions in the small intestine,... Intestine: intestinal juice Duodenum mucosa Cholecystokinin (Pancreozymin) Pancreas: enzymes gallbladder: ejection of bile into the duodenum intestine: intestinal juice Amino acid, fatty acids •Parasympathetic nervous stimulation: increased intestinal, pancreatic, intestinal jui • Sympathetic stimulation, morphin: inhibit… Digestive products of nutrients • Carbohydrates glucose, fructose, galactose • Lipids