G7 Digestive System Manuscript PDF

Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ 16.1 Functions of the Digestive System Submucosa It is a thick layer of...

Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ 16.1 Functions of the Digestive System Submucosa It is a thick layer of loose connective The Digestive System with the tissue containing nerves, blood vessels, assistance of the circulatory system, is a and small glands. complex set of organs, glands, and above mucosa ducts that work together to transform food into nutrients for cells. Muscularis externa lies outside the submucosa 1. Ingestion and Mastication- Ingestion is Circular smooth muscle - inner layer the consumption of solid or liquid food, Longitudinal smooth muscle - outer usually through the mouth. Mastication layer is chewing. Serosa or Adventitia 2. Propulsion and Mixing- Propulsion is outermost layers the movement of food from one end of organs within the peritoneum have the digestive tract to the other. Mixing is serosa the movement of food back and forth in Adventitia which are organs that are the digestive tract. RETROPERITONEAL (behind the 3. Digestion and Secretion- Digestion is peritoneum) or no peritoneum attached the breakdown of large organic to it molecules to small organic molecules Enteric Nervous System that can be absorbed. Secretion is the It is a neural network in the gut that addition of liquid, enzymes, and mucus regulates digestion, including motility, to ingested food. secretion, and blood flow, independently 4. Absorption- Absorption is the of the brain and spinal cord. movement of molecules out of the Peritoneum digestive tract and into the blood or membrane lining the abdominal cavity lymphatic system. and covering abdominal organs, 5. Elimination- Elimination is the removal providing protection, support, and a of undigested material. frictionless surface for organ movement. Visceral Peritoneum - covers the 16.2 Anatomy and Histology of the Digestive organs System Parietal Peritoneum - lines the wall of the abdominal cavity. Digestive Tract (Gastrointestinal Tract) Peritonitis Oral cavity (mouth) Potentially life-threatening inflammation Pharynx (throat) of the peritoneal membranes. Esophagus Mesenteries Stomach are folds of the peritoneum that hold the Small intestine and Large intestine intestines in place and carry blood Anus vessels, nerves, and lymphatics to Specific Associated Organs: them. Salivary glands Mesentery proper Liver Connects the small intestine to the Pancreas posterior abdominal wall. Lesser omentum Fun Facts about the GI Tract Links the liver to the stomach and If you could stretch it out, it would duodenum. measure 30 feet (9 meters) Greater omentum Your body can move your food through Fatty layer covering and protecting the digestive system even while you are abdominal organs. standing on your head Omental bursa It is not connected to gravity because it Space behind the stomach for organ works with muscles. movement. The stomach has the ability to stretch Retroperitoneal and hold up to 4 pounds of food at one organs that have no mesenteries and lie time (almost 2 kgs) along the abdominal wall or organs located behind the peritoneum, partially covered by Consists of 4 major tunics or layers it. Mucosa (3 sub layers) Duodenum innermost tunic and secretes mucus Pancreas Mucous epithelium Ascending colon Lamina propria Descending colon Muscularis mucosa Rectum Kidneys  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ Adrenal glands Secondary teeth Urinary bladder Replacement for 20 primary teeth 16.3 Oral Cavity, Pharynx, and Esophagus Primary teeth Deciduous Oral Cavity Milk or baby teeth; lost during childhood Mouth Each tooth contains: three regions Two regions: (1) Vestibule: space - Crown: with one or more cusps (points) between the lips and cheeks and teeth; Most visible portion (2) Oral Cavity: inside the teeth and - Neck: small region between the crown houses the tongue and root (middle) Ingestion of liquid and solid foods. Largest region and anchors it in Lips the bone of the maxilla and mandible Muscular structures formed by - Root: covered with cementum orbicularis oris muscle Dentin Outer surfaces: keratinized stratified Living, cellular, calcified tissue formed in epithelium of the skin the bulk of the tooth Internal margin of the lips: moist Enamel stratified squamous epithelium The dentin is covered by extremely Reddish-pink color appearance dueq to hard, acellular substance; protect tooth thin, transparent epithelium against abrasion and acids produced by Cheeks bacteria Form the lateral walls of the cavity Nonliving and cannot repair itself Located within the cheeks: buccinator Cementum muscles Covered the dentin in the root Lips and cheeks are important in the Pulp Cavity process of mastication (chewing). Hollow space in the center of the tooth Mastication: mechanical digestion; Surrounded by dentin breaks down large food particles into Pulp smaller particles Filled material in the pulp cavity Hold the food in place Alveoli Help form words during the speech Teeth are held in place within the process pockets in the bone Tongue Covered by dense fibrous connective Large, muscular organ that occupies tissue and moist stratified squamous most of the oral cavity epithelium (gingiva or gums) Posterior part Periodontal ligaments Anterior two-thirds: covered by papillae, Secure the teeth in alveoli by contians taste buds embedding into the cementum Posterior one-third: devoid of papillae Dental Caries and few taste buds; contains large Tooth decay lymphatic tissue to form lingual tonsil Result of the breakdown of acids Holds the food in place during produced by bacteria mastication Periodontal disease Major role: Swallowing Inflammation and degeneration of the Major sensory organs for taste and periodontal ligaments, gingiva and major organs for speech alveolar bone Teeth Most common tooth loss in adults 32 teeth (normal adult) May occur in tooth, bone, surrounding Mandible (lower) and maxillae (upper) soft tissues 4 quadrants: May cause enlargement cervical lymph - Right upper nodes (all lymphatic drainage from the - Left upper face goes through these nodes) - Right lower - Left lower Dental professionals have developed a Each quadrant contains: “universal” numbering and lettering system for - 1 central convenience in identifying individual teeth. - 1 lateral incisor - 1 canine Palate - 1st and 2nd premolars Roof of the oral cavity - 1st, 2nd, 3rd molars (wisdom Separates the oral from nasal cavity tooth)—appear in late teens or twenties Prevents food from passing into nasal - cavity Permanent teeth  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ Consists of 2 parts: (1) hard and (2) soft Produce more serous than mucous palate secretions Hard palate: anterior part; contains Sublingual glands (below the tongue) bone Smallest of the three paired salivary Soft palate: posterior part; consists of glands skeletal muscle and connective tissue Produce primarily mucous secretions Uvula: posterior extension Lies below the mucous membrane of in Tonsils the floor of oral cavity Lateral posterior walls of the oral cavity, Each has 10-12 small ducts opening in nasophraynx and posterior surface of tongue Secretion: Regulated by autonomic nervous Salivary Glands system, with parasympathetic Scattered throughout the oral cavity stimulation being the most important Produces saliva Increase in response to a variety of Compound alveolar gland (like grapes) stimuli The mucous secretions of the - Tactile stimulation submandibular and sublingual contain a - Higher brain centers can large amount of mucin, a proteoglycan stimulate parasympathetic that gives a lubricating quality to the activity and thus increase the secretions of the salivary glands activity of or the sensation of Saliva hunger Mixture of serous (watery) and mucuos Sympathetic stimulation increases the fluids and has multiple roles. mucuos content of saliva Composed of fluid and proteins - When a person is frightened Functions: and the sympathetic division of - Helps keep the oral cavity moist the autonomic nervous system - Protective functions is stimulated, the person may - Begins the process of digestion have a dry mouth with thick - Prevents bacterial infections by mucus washing the oral cavity with a Mastication mildly antibacterial enzyme Food taken in the mouth is chewed by called lysozyme the teeth - Neutralizes pH, reduce harmful Incisors and canines: cut and tear the effects of bacterial acids on food tooth enamel Premolars and molars: crush and grind - Prevents the ulceration and Breaks large food particles into many infection of the oral mucosa and small ones, which have a much larger cavities formation total surface area than a few large Normal daily rate: 0.5 L to 1.5 L particles would have Serous part (parotid and Thru digestive enzymes, it increase the submandibular): contains digestive efficiency of digestion enzyme - salivary amylase, which Pharynx breaks down starch Throat - Breaks the covalent bonds Connects the mouth with the esophagus between glucose molecules in Consists of 3 parts: (1) nasopharynx, (2) starch and polysaccharides oropharynx and (3) laryngopharynx - Produces dissacharides: (2) and (3) carry the food into the maltose and isomaltose (sweet esophagus taste) Posterior walls of the oropharynx and - Thus, enhances sweet taste of laryngophraynx are formed by the food superior, middle and inferior pharyngeal Only about 5% of the total constrictor muscles. carbohydrates humans absorb are Esophagus digested in the mouth Muscular tube, lined with moist stratified squamous epithelium, that extends from (3) Three major pairs: the pharynx to the stomach Parotid glands (beside the ear) 25 cm’s long; lies anterior to the Largest of the salivary glands vertebrae and posterior to the trachea Serous glands located just anterior to within the mediastinum each ear Upper two-thirds: skeletal muscle in the Mumps: inflammation of the parotid wall gland caused by viral infection Middle third: mixture of skeletal and Submandibular glands (below the mandible) smooth muscle fibers  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ Lower one-third: smooth muscle; passes 1. An outer longitudinal layer through the diaphragm and ends at the 2. A middle circular layer stomach 3. An inner oblique layer Swallowing, which transports food from the pharynx to the stomach These muscular layers produce a churning Aid movement of food action in the stomach. Numerous mucous glands produce a The submucosa and mucosa of the thick, lubricating mucus that coats the stomach are arranged in large folds inner surface of the esophagus called rugae when the stomach is Swallowing empty. Deglutition These folds allow the mucosa and 3 phases: (1) Voluntary phase, (2) submucosa to stretch, and the folds paryngeal phase and (3) esophageal disappear as the stomach is filled. phase The stomach is lined with simple columnar epithelium. Voluntary phase The mucosal surface forms numerous A mass of food (bolus) is formed in the tubelike gastric pits, which are the mouth openings for the gastric glands. Tongue pushes the bolus against hard palate The epithelial cells of the stomach can be This forces the bolus toward the divided into five groups: posterior part of the mouth and into Surface mucous cells oropharynx which are found on the inner surface of Pharyngeal phase the stomach and lining the gastric pits. Controlled by reflex These cells produce mucus that coats Initiated when a blous of food stimulates and protects the stomach lining. receptors in the oropharynx to elevate Mucous neck cells the soft palate. Closing off the which produce mucus nasopharynx Parietal cells The pharynx elevates to receive the which produce hydrochloric acid and bolus from the mouth intrinsic factor The 3 pharyngeal constrictor muscles Endocrine cells then contract in succession, forcing the which produce regulatory hormones and food through the pharynx paracrine signal molecules Esophageal phase Chief cells Moving food from the pharynx to the which produce pepsinogen, a precursor stomach of the protein-digesting enzyme pepsin. Muscular contractions of the esophagus occur in :peristatic waves Secretion of the Stomach As food enters the stomach, the food 16.4 Stomach mixed with stomach secretions to become a semifluid mixture called The stomach is divided into four regions: chyme. Cardiac part the esophagus opens into the cardiac Stomach secretions from the gastric glands part of the stomach at the include four substances: gastroesophageal opening. Hydrochloric acid Fundus produces a pH of about 2.0 in the the part of the stomach to the left of the stomach. The acid kills microorganisms cardiac part and superior to the cardiac and activates the enzyme, pepsin. opening. Pepsin Body is converted from its inactive form, the largest part of the stomach, which called pepsinogen. Pepsin breaks turns to the right creating a greater covalent bonds of proteins to form curvature and a lesser curvature. smaller peptide chains. Pyloric part Mucus opens into the small intestine and is forms a thick layer, which lubricates the surrounded by the pyloric sphincter. epithelial cells of the stomach wall and Pyloric sphincter protects them from the damaging effect helps regulate the movement of gastric of the acidic chyme and pepsin. contents into the small intestine. Intrinsic factor 3 layers of Muscularis layers: binds with vitamin B12 and makes it more readily absorbed in the small intestine.  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ Heartburn Decreases gastric secretion or gastritis, is a painful or burning Strongly decreases gastric motility sensation in the chest usually Increases gallbladder contraction associated with an increase in gastric acid secretion and/or a backflush of Movement in the Stomach acidic chyme into the esophagus. Two types of stomach movement aid digestion and help move chyme through the digestive tract: Regulation of Stomach Secretions Mixing waves Approximately 2 L of gastric secretions Peristaltic waves are produced each day Both nervous and hormonal mechanism Mixing Waves regulate gastric secretions Relatively weak contractions result in Hormones produced by the stomach mixing waves, which thoroughly mix and intestine help regulate stomach ingested food with stomach secretions secretions to form chyme The more fluid part of the chyme is Regulation of stomach secretions can be divided pushed toward the pyloric sphincter, into three phases: whereas the more solid center of the Cephalic phase - can be viewed as “ chyme squeezes past the peristaltic get started” phase constriction back toward the body of the Gastric Phase - “ go for it” phase stomach. Intestinal Phase - “slow down” phase Peristaltic Waves Stronger contractions result in peristaltic Cephalic Phase waves, which force the chyme toward The cephalic phase is the brain phase of and through the pyloric sphincter. stomach secretion. It is controlled by the Again, the more fluid part of the chyme CNS. It begins even before the bolus of is pushed toward the pyloric region (blue food enters the stomach. arrows), whereas the more solid center Gastrin is a hormone that enters the of the chyme squeezes past the blood and is carried back to the peristaltic constriction back toward the stomach, where it stimulates additional body of the stomach secretory activity. Each peristaltic contraction is Histamine is both a paracrine chemical sufficiently strong to cause partial signal that acts locally and a hormone relaxation of the pyloric sphincter and to that enters the blood to stimulate gastric pump a few milliliters of chyme through gland secretory activity. Histamine is the the pyloric opening and into the most potent stimulator of hydrochloric duodenum. Increased motil-ity leads to acid secretion. increased emptying. Gastric Phase Peristaltic waves also occur when the The gastric phase of stomach secretion stomach is empty. produces the greatest volume of gastric These peristaltic waves are increased secretion. by low blood glucose levels and can Intestinal Phase create uncomfortable sensations called The intestinal phase of gastric secretion hunger pangs. inhibits gastric secretions Hunger Pangs The intestinal phase is controlled by the occur for about 2-3 minutes and can entrance of acidic chyme into the build in strength to a prolonged, or duodenum, which initiates both neural tetanic, contraction and hormonal mechanisms. Hunger pangs usually begin 12 to 24 hours after the previous meal Functions of the Major Digestive System If nothing is ingested, hunger pangs Hormones reach their maximum intensity within 3 Gastrin or 4 days and then become Gastric Gland progressively weaker. Increases gastric secretions Sometimes having hunger pangs is Secretin referred to as the stomach “growling.” Duodenum If the stomach empties too fast, the Decreases gastric secretion efficiency of digestion and absorption in Increases pancreatic and bile secretions the small intestine is reduced. However, high in bicarbonate ions if the rate of emptying is too slow, the Decreases gastric motility highly acidic contents of the stomach Cholecystokinin may damage the stomach wall. Duodenum Vomiting  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ is usually a protective mechanism against the ingestion of toxic or harmful The epithelial cells are located within substances. tubular glands of the mucosa, called Vomiting and associated nausea (feeling intestinal glands or crypts of Lieberkühn, likely to vomit) can result from irritation at the base of the villi. anywhere along the digestive tract Granular and endocrine cells are located in the bottom of the glands. The submucosa of the duodenum 16.5 Small Intestine contains mucous glands, called duodenal glands, which open into the Small Intestine base of the intestinal glands. The major function of the small intestine Lymphatic nodules are common along is the absorption of nutrients. the entire length of the digestive tract, major site of digestion and absorption of and clusters of lymphatic nodules, Peyer food, which are accomplished due to patches, are numerous in the ileum. presence of a large surface area. Ileocecal junction- the site where the ileum connects to the large intestin. The small intestine is about 6 meters long and consists of three parts: Secretions of the Small Intestine Duodenum Secretions from the mucosa of the small about 25 cm long intestine contain mainly mucus, ions, Jejunum and water is about 2.5 m long and makes up Most of the secretions entering the small two-fifth of the total length of the small intestine are produced by the intestinal intestine. mucosa, but the secretions of the liver Ileum and the pancreas also enter the small is about 3.5 m long and makes up intestine and play important roles in three-fifths of the small intestine digestion. The common bile duct from the liver and the The epithelial cells in the walls of the small pancreatic duct from the pancreas join and intestine have enzymes, bound to their free empty into the duodenum. surfaces. These enzyme group include: Peptidases The small intestine has three modifications that digest proteins. They break the peptide increases its surface area about 600-folds: bonds in proteins to form amino acids. Circular folds Disaccharides The mucosa and submucosa form a digest small sugars, specifically series of circular folds that run disaccharidases. break down perpendicular to the long axis of the disaccharides, such as maltose, into digestive tract monosaccharides, such as glucose. Villi Intestinal epithelium Tiny, fingerlike projections of the absorbs the resulting amino acids and mucosa form numerous villi, which are monosaccharides 0.5-1.5mm long. Within the loose Mucus connective tissue core of each villus are is produced by duodenal glands and by a blood capillary network and a goblet cells, which are dispersed lymphatic capillary called a lacteal throughout the epithelial lining of the Microvilli entire small intestine and within Most of the cells composing the surface intestinal glands. of the villi have numerous cytoplasmic extensions, called microvill. Movement in the Small intestine mixing and propulsion of chyme are the The mucosa of the small intestine is simple primary mechanical events that occur in columnar epithelium with four major cell types: the small intestine. Absorptive cells Peristaltic contractions - proceed which have microvilli, produce digestive along the length of the intestine for enzymes, and absorb digested food variable distances and cause the chyme Goblet cells to move along the small intestine which produce a protective mucus Segmental contractions - are Granular cells propagated for only short distances and which may help protect the intestinal mix intestinal contents epithelium from bacteria Endocrine cells which produce regulatory hormones.  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ 16.6 Liver and Pancreas Hepatic cords are strings of cells that radiate out from Liver the central vein of each lobule like the Liver is the largest internal organ of the spokes of a wheel. body and weighs about 1.36 kg (3 are composed of hepatocytes. pounds). Hepatocytes It is located in the right upper quadrant take up nutrients from the portal blood. of the abdomen, tucked against the functional cells of the liver. inferior surface of the diaphragm. Hepatic sinusoids The posterior surface of the liver is in are blood channels in the spaces contact with the right ribs 5-12. between the hepatic cords. are lined with a very thin, irregular Four Lobes of the Liver: squamous endothelium consisting of 1. RIGHT LOBE two cell populations: 2. LEFT LOBE 1.Extremely thin, sparse endothelial 3. CAUDATE LOBE cells 4. QUADRATE LOBE 2. Hepatic phagocytic cells Bile canaliculus The right and left lobes are separated by is a cleftlike lumen that lies between the a connective tissue septum, called the cells within each cord. falciform ligament. Bile The caudate and quadrate lobe are the produced the hepatocytes flows through two smallest lobes, that can be seen the bile canaliculi toward the hepatic from an inferior view. Also seen from the triad and exits the liver through the inferior view is the porta (gate), through hepatic ducts. which blood vessels, ducts, and nerves enter or exit the liver. Functions of the Liver Liver Two sources of blood is a large, reddish-brown organ located Hepatic artery on the right side of the abdomen. It delivers oxygenated blood to the liver, plays many essential roles, including which supplies liver cells with oxygen. detoxifying harmful substances, Hepatic portal vein producing proteins, storing energy, and carries blood that is oxygen poor but making bile. rich in absorbed nutrients and other Bile substances from the digestive tract to is important for digesting fats and it has the liver. a complex solution that contains: - Bile salts Hepatic Lobules - Bile pigments The liver is divided into hepatic lobules. - Cholesterol Hepatic lobules - are hexagon-shaped - Lipids regions surrounded by connective tissue - Lipid-soluble hormones septa and defined by a portal triad at - Lecithin (a mixture of phospholipids) each other and a central vein in the center of the lobule. Complex Solutions of Bile Bile salts Three structures of portal triads emulsify lipids, which is necessary for Hepatic portal vein subsequent digestion by lipase. main distinct source of rich blood supply Bile pigments of the kidney. are greenish- yellow to brown and give 1. Hepatic artery - also is main distinct feces their characteristic color. source of rich blood supply of the One common bile pigment is bilirubin, kidney. which results from the breakdown of 2. Hepatic duct - bile transport system. hemoglobin by hepatocytes. Gallstones Central veins may form if the amount of cholesterol the central vein collects the blood as it secreted by the liver becomes excessive leaves the lobule. and not able to be dissolved by the bile central veins of the lobules unite to form salts. hepatic veins, which exit the liver on its posterior and superior surfaces and Pancreas empty into the inferior vena cava. Pancreas is a complex organ composed of both endocrine and exocrine tissues that perform several functions.  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ It is Iocated retroperitoneal, posterior to the descending colon extends from the the stomach in the inferior part of the left left colic flexure to the pelvis, where it upper quadrant. becomes the sigmoid colon. It has a head near the midline of the The sigmoid colon forms an S-shaped body and a tail that extends to the left, tube that extends medially and then where it touches the spleen. inferiorly into the pelvic cavity and ends Endocrine - consists of pancreatic at the rectum. islets, or islets of Langerhans. The mucosal lining of the colon contains Islets cells - produce the hormones numerous straight, tubular glands called insulin and glucagon, which enter the crypts, which contain many blood. mucus-producing goblet cells. Exocrine - is a compound acinar gland. The longitudinal smooth muscle layer of Acini - produce digestive enzymes the colon does not completely envelop. the intestinal wall but forms three bands Functions of the Pancreas called teniae coli. Exocrine secretions Anal Canal include bicarbonate ions, which The external anal sphincter at the neutralize the acidic chyme that enters inferior end of the anal canal is formed the small intestine from the stomach. by skeletal muscle. Neutralized pH Hemorrhoids are enlarged or inflamed stops pepsin digestion. rectal, or hemorrhoidal, veins that required for the function of pancreatic supply the anal canal. Hemorrhoids may and small intestine enzymes. cause pain, itching, and/or bleeding prevents stomach acid from damaging around the anus. Treatments include the duodenum. increasing bulk (indigestible fiber) in the Pancreatic enzymes diet, taking sitz baths, and using are important in digesting all major hydrocortisone suppositories. Surgery classes of foods. may be necessary if the condition is without the pancreatic enzymes, lipids, extreme and does not respond to other proteins, and carbohydrates cannot be treatments. adequately digested. Functions of the Large Intestine The major protein - digesting enzymes are: Normally, 18–24 hours are required for Trypsin material to pass through the large Chymotrypsin intestine, in contrast to the 3–5 hours Carboxypeptidase required for chyme to move through the Pancreatic amylase small intestine. continues the polysaccharide digestion While in the colon, chyme is converted that began in the oral. to feces. The colon stores the feces until they are 16.7 Large Intestine eliminated by the process of defecation. Numerous microorganisms inhabit the Large Intestine colon. Large intestine is the portion of the Every 8–12 hours, large parts of the digestive tract extending from the colon undergo several strong ileocecal junction to the anus. contractions, called mass movements, It consists of four parts: which propel the colon contents a 1. Cecum considerable distance toward the anus. 2. Colon Feces distend the rectal wall and 3. Rectum stimulate the defecation reflex, which 4. Anal canal involves local and parasympathetic Colon reflexes. is about 1.5–1.8 m long and consists of Local reflexes cause weak contractions, four parts: the ascending colon, the whereas parasympathetic reflexes transverse colon, the descending colon, cause strong contractions and are and the sigmoid colon. normally responsible for most of the The ascending colon extends superiorly defecation reflex. from the cecum to the right colic flexure, The defecation reflex persists for only a near the liver, where it turns to the left. few minutes and quickly subsides. The transverse colon extends from the Defecation can be initiated by voluntary right colic flexure to the left colic flexure actions that stimulate a defecation reflex near the spleen, where the colon turns inferiorly;  Digestive System Manuscript Anatomy and Physiology with Pathophysiology ______________________________________________________________________ 16.8 Digestion, Absorption and Transport chymotrypsin, and carboxypeptidase into the small intestine in an inactive Digestion Process state. Digestion - Chemical and Mechanical In the small intestines, these enzymes breakdown of food. are activated. Absorption - Most Absorption occurs in In the small intestine, other enzymes the duodenum and jejunum, although termed peptidases, bound to the others occurs in the stomach and ileum. microvilli of the intestinal epithelium Transport -Moves food through digestive further break down small peptides into tract, includes swallowing and peristalis tripeptides. In the small intestine, other enzymes Carbohydrate Digestion termed peptidases, bound to the Polysaccharides turn into Disaccharides microvilli of the intestinal epithelium by the saliva and pancreatic amylase, further break down small peptides into then Disaccharides turn into tripeptides. Monosaccharides by breaking down monosaccharides by the Disaccharides Water and Mineral on the surface of the intestinal Water can move across the intestinal epithelium wall in either direction. Glucose is absorbed by the contransport The movement depends on osmotic with the Na+ into the intestinal pressures. epithelium. 99% of water entering intestine is Glucose is carried by the hepatic portal absorbed. vein to the liver and enters most cells by Minerals are actively transported across facilitated diffusion. wall of small intestine Lipid digestion Lipase is an enzyme that converts triglycerides into fatty acids and monoglycerides. Bile salts form micelles by enclosing fatty acids and monoglycerides within their outer shell. Micelles bind to intestinal epithelial cell plasma membranes, allowing fatty acids and monoglycerides to pass through simple diffusion into these cells. The intestinal epithelial cell converts fatty acids and monoglycerides into triglycerides. Proteins coat the triglycerides to form. chylomicrons, which move out of the intestinal epithelial cells by exocytosis. Chylomicrons enter the lacteals of the intestinal villi and are transported through the lymphatic system to the blood. Lipoprotein Digestion Lipids are packaged into lipoproteins to allow transport in the lymph and blood. Lipoproteins are molecules that are part water-soluble and part lipid-soluble. Since lymph and blood contain water and lipids are not water soluble, lipoproteins are necessary for transport. Lipoproteins include chylomicrons, low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Protein Digestion Pepsin is a protein-digesting enzyme secreted by the stomach. The pancreas secretes the protein-digesting enzymes trypsin,