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Digestive System


The digestive tract is also known as Alimentary Canal and gastrointestinal tract (GI tract)
What makes up the digestive tract? Mouth > Pharynx > Esophagus > Stomach > Small Intestine > Large Intestine
What is the function of the Alimentary Canal? Digestion and absorption
What are the accessory organs of the digestive canal? -Teeth -Gallbladder -Salivary Glands -Liver -Pancreas
What is the function of the accessory organs of the digestive system? To produce Secretions to aid in the process of digestion.
What are some examples of Secretions from the accessory organs of the digestive system? Saliva, bile, and digestive enzymes
What is Gastroenterology? The study of digestive tract and diagnosis and treatment of its diseases.
What is digestion? Physical and chemical breakdown of food to transform it into usable substances for cells.
Mechanical digestion (Phase I) Physically breaking down food into smaller pieces. -e.x. Chewing to contractions to churning (peristalsis) in stomach and S.I.
Chemical digestion (Phase II) *Still not absorbed! Digestive enzymes from salivary gland, stomach, pancreas, and S.I. -Break down food particles into nutrients (glucose, aa's, fatty acids)
Digestive Processes 1. Ingestion 2. Digestion a. Mechanical Digestion (chewing, churning, segmentation) b. Chemical Digestion (saliva, acid and enzymes) 3. Absorption 4. Elimination/Deification
What are the four tunics (Inner to Outer)? 1. Mucosa 2. Submucosa 3. Muscularis 4. Serosa
Mucosa -Three layers (epithelium, CT, thin muscle) -Areas of mechanical force and abrasion are stratified squamous epithelial -Areas of nutrient absorption are simple columnar epithelial w/ goblet cells
Submucosa Perfuse gut wall w/ blood; lymph nodules for immune function. Submucosal plexus of nerves.
Muscularis Longitudinal outer layer; circular inner layer. Myenteric plexus coordinates peristaltic contractions.
Serosa Visceral peritoneum contacts parietal peritoneum.
Enteric Nervous System Regulates digestive tract motility (movement), secretion, and blood flow. -Submucosal nerve plexus -Myenteric nerve plexus
Submucosal Nerve Plexus -Regulates the activity of glands and smooth muscle -A.K.A. Plexus of Meissner
Myenteric Nerve Plexus -Regulates motility - peristalsis of gut -A.K.A. Plexus of Auerbach
Peritoneum Thin membrane lining surface of organs in abdominal cavity.
Parietal peritoneum Lines inner wall of abdominal cavity. -Contains many pain receptors -Folds of parietal p. form the mesenteries
Visceral peritoneum Covers abdominal organs themselves
Peritoneal cavity -Potential space between the two peritoneum, containing lubricating fluid.
Pathological examples affection peritoneal cavity: Adhesions, peritonitis (life-threatening), ascites.
Mesentery Folds of peritoneum encasing the large and small intestines.
What are the functions of the mesentery? -Provides webbing blood, lymph and nerve support. -Attaches most of small and large intestines to posterior abdominal wall.
Mesocolon Connects duodenum and part of colon to posterior abdominal wall.
Greater omentum The largest fold of omentum and portion of the omentum that is suspended from the greater curvature of the stomach and covers the intestines like an apron. It dips in among the folds of the intestines and is attached to the transverse colon and mesocolon
What is the function of the Omentum? It contains fat, prevents friction and aids in localizing infections.
Lesser omentum The portion of the omentum that passes from the lesser curvature of the stomach to the transverse fissure of the liver.
Intraperitoneal Mesentery (serosa) encloses the abdominal organs on both sides, placing them within the peritoneal cavity.
Retroperitoneal Mesentery (serosa) covers only the ventral side of an organ; the dorsal side lies directly against the posterior abdominal wall so they are outside the peritoneal cavity. -Duodenum, most of the pancreas, kidneys.
Mouth Entryway to digestive tract and where digestion begins. -A.K.A. oral or buccal cavity -surrounded by lips, bordered by cheeks -Palate forms the roof of the mouth; tongue (muscle) is floor.
What are the structures of the mouth? -Tongue w/ lingual papillae (taste buds) -Lingual frenulum -Hard palate -Soft palate -Uvula -Palatine tonsil -Sublingual salivary gland -Submandibular salivary gland -Upper and lower lip -Teeth -Gingivae
What are the Major Oral Structures? -Tongue -Lingual Frenulum -Hard Palate -Soft Palate
Tongue Skeletal muscle covered by mucous membrane; repositions food during chewing. -Lingual papillae
What are Lingual Papillae? Taste bud projections (on the tongue).
Lingual Frenulum Anchors tongue to floor of mouth, which is ideal site for drug absorption d/t high numbers of superficial blood vessels.
Hard Palate Formed by maxillae and palatine bones; seperates mouth from nasal cavity.
Soft Palate
What are the functions of Saliva? 1. Cleans mouth 2. Moisten and dissolve food 3. Contains food dissolving + anti-bacterial enzymes
What glands produce Saliva? the Parotid, sublingual, and submandibular glands.
What is the composition of Saliva? -97-99.5% Water -Lysozyme -Mucin -Salivary Amylase and Lipase (starch and fat breakdown)
Parotid Gland -Anterior to the ear -Famously the site of swelling and inflammation due to mumps virus (paramyxovirus)
Submandibular Gland Empties into the mouth on either side of lingual frenulum
Sublingual Gland Drains through ducts on floor of mouth
What are the four different types of Teeth? -Incisors -Cuspids -Premolars -Molars
Incisors Sharp front teeth for biting into food
Cuspids (A.K.A. Canines) flank the incisors and have a pointed edge (cusp) to tear up food; piercing tough or fleshy foods.
Premolars (A.K.A. Bicuspids) Overall flatter shape with two rounded cusps useful for mashing foods.
Molars have several pointed cusps used to crush food (the third members of each set of three molars, top and bottom, are commonly referred to as wisdom teeth...)
Crown portion of tooth above gum line
Gingiva gum
Neck where root and crown of tooth meet
Root embedded tooth in alveolar socket of mandible
Enamel hard tissue covering crown of tooth; hardest substance in body
Dentin firm, yellow tissue; makes up bulk of tooth
Pulp Cavity mass of blood, nerves, and CT within tooth; fills root canals
Periodontal ligament keeps tooth in place
Cementum covers dentin of tooth in the root
Bolus mass of food, easy to swallow
What are the three regions of the Pharynx? 1. Nasopharynx 2. Oropharynx 3. Laryngopharynx
What is the pathway of food through the Pharynx? Food (as Bolus manipulated to back of oral cavity by tongue) moves through oropharynx and laryngopharynx to esophagus
Esophagus Connects pharynx to stomach. -posterior to trachea, penetrates diaphragm, enters stomach -glands in esophageal wall secrete mucous to lubricate passing food
Lower Esophageal Sphincter (LES) prevents back flow of food (GERD)
Peristalsis Muscular contractions that propel bolus (food) towards stomach. -muscular contractions triggered by entrance of bolus
Upper esophageal sphincter relaxation Allows the bolus to move from the laryngopharynx to the esophagus
Lower esophageal sphincter relaxation Allows the bolus to move from esophagus into the stomach and prevents chime from entering the esophagus
Mucus secretion (within esophagus) Lubricates the esophagus, allowing easy passage of the bolus
Mastication (a.k.a chewing) Cheeks and closed lips hols the food between the teeth, the tongue mixes the food with saliva to soften it, and the teeth cut and grind solid food.
Deglutition (a.k.a. swallowing) Food compacted by tongue into bolus. -Has three stages: Voluntary/Buccal phase, Pharyngeal phase, Esophageal phase.
What controls the pharyngeal phase and esophageal phase of deglutition(swallowing)? the Autonomic Nervous System controls
Where are most of the nutrients absorbed? the Intestine
What partially digests Proteins and small amounts of starch and fat? the Stomach
Rugae the folds inside the stomach.
Stomach Muscular tank designed to store food, break proteins, and churn food into Chyme.
What are the four main regions of the Stomach? Cardia, Fundus, Body, and Pylorus.
What are the two curves of the Stomach? Greater curvature and Lesser curvature.
What is the one sphincter within the stomach? Pyloric Sphincter
What are the four secretory cells of the Stomach? Muscus-neck cells, Parietal cells, Chief cells, Enteroendocrine cells.
What are the three gland areas of the Stomach? Cardia, Atrium and Body.
What are the three types of muscles of the Stomach? Longitudinal, circular and Oblique muscles which contact in 3 different directions.
Gastric Pits depressions in mucosa where glands secrete Gastric Juice
Mucous-neck cells mucus to protect lining and prevent autodigestion
Parietal Cells secrete hydrochloric acid to kill microbes and intrinsic factor to absorb vitamin B12
Chief Cells secrete pepsinogen, a digestive enzyme precursor (zymogen)-activated to pepsin to digest proteins
Enteroendocrine Cells make what secretions? -Gastrin -Cholecystokinin (CCK) -Somatostatin
Gastrin cause gastric glands to increase secretory activity (hydrochloric acid); secreted by G-cells
Cholecystokinin (CCK) increases action of secretin on liver as well as pancreas to increase bile and pancreas "juice"
Somatoastatin inhibits gastric secretions of all products and inhibits gastric motility and emptying
Peristaltic Contractions to move Chyme Chyme is either delivered in small amounts to the Duodenum or forced backward into the stomach for further mixing - total time is about 4 Hours following a typical meal.
What are the Three Phases of Stomach Secretions? 1. Cephalic Phase 2. Gastric Phase 3. Intestinal Phase
Cephalic Phase Brain control. Thinking, seeing or smelling food triggers neural impulse to brain. Vagus N. stimulates secretion of HCl and Pepsin. PNS signals stomach to release gastric juice + Gastrin.
Gastric Phase Food enters stomach. Stretching triggers nerve reflex to increase secretion of gastric juice + gastrin. Continued HCl and pepsin.
Intestinal Phase Chyme moves into Duodenum. Triggers nerve impulse to secrete hormones that Inhibit Gastric Secretion (stomach participation ends here when chyme hit pH below 2 or has lipids in it)
Vomiting Reverse Peristalsis! -Abdominal mm forcefully contract to push chyme out of stomach
What causes vomiting? -Overstretching, chemical irritants (alcohol, toxins), pain, fear, viruses, bad food -Emetic Center of medulla oblongata sends two types of impulses
What are the two impulses sent from the Emetic Center? -One to upper esophageal sphincter to open -One to esophagus and body of stomach to relax
What is an Anti-Emetic? A medicine that calms to stomach so as not to vomit.
Emetic means vomit
Small Intestine -Where most nutrient absorption and chemical digestion takes place -Approx. 20 ft. long
How does food move through the Small Intestine? Segmentation and Peristalsis
What are the three subdivisions of the Small Intestines? Duodenum, Jejunum and Ilieum
Ileocecal Sphincter transition between small and large intestine
Duodenum First 10'' of small intestine -where stomach HCl Is Neutralized and Pancreatic Enzymes begin digestion in earnest
Where are the most digestive processes of anywhere in the GI tract happen? duodenum
Where is the beginning and end of Duodenum? Pyloric Sphincter of stomach and end as abrupt downturn
What does the Duodenum receive? and from where? chyme from stomach, pancreatic juice from pancreas, and Bile from gallbladder
What is the function of (Duodenum Hormone) Secretin? -regulates Water Homeostatsis throughout body -Inhibits HCl secretion of parietal cells -stimulates Bicarbonate from pancreas -stimulates Bile from liver
What makes (Duodenum Hormone) Secretin? S-Cells of Duodenum
What inhibits (Duodenum Hormone) Secretin? H2 Antagonists, which reduce gastric acid secretion. (As a result, if the pH in the Duodenum increases above 4.5, Secretin cannot be released).
Jejunum 8' long small intestine, just after duodenum -wall is thick and muscular with rich blood supply (appears red due to blood supply)
Plicae the circular folds of the lining of the jejunum (Surface Area)
Villi - Jejunum projections on the plicae
Microvilli form the Brush Border (Nutrient Absorption)
Ilieum last 12' of small intestine -thinner than jejunum, less blood supply too
Peyer's Patches Clusters of lymphatic nodules only found in ilieum -the "tonsils of the intestine" -catch and destroy bacteria
Segmentation Ring-like contractions occurring in Digestive small intestine -one area relaxes, the next contracts, and so on, breaks up food and thoroughly mixes it with digestive juices
Peristalsis in small intestine After most nutrients have been absorbed, undigested residue must be moved out of body -Pacesetter cells -Successive waves ripple along, moving Waste towards exit
Circular folds (Plicae circulares) Slow progress of chyme and increase its contact with mucosa, increasing absorption through exposure
Villi (singular: villus) Cover top of circular folds like a carpet
Lacteal Lymph vessel in each villus (that transports fats to heart to be pumped out)
Intestinal crypts Pores at bases of villi; goblet cells secrete mucus. Site of regeneration.
Intestinal Mucosa Absorption Through Microvilli at the Brush Border
Function of Lacteals transport Fats from the small intestines to the thoracic duct for distribution throughout the body
How are non-fat Nutrients (Other Nutrients) transported? Where do they go? pass into bloodstream through capillaries and then Go To Liver
Liver Largest gland in the body
What is the function of the Liver? produces & secretes Bile stores & releases Glucose produces Proteins involved in blood coagulation Stores absorbed productions of digestion(carbs, fats, vits, and iron) -Detoxifies poisons to make them less toxic & more easily eliminated from the body
What are the four lobes of the Liver? 1. Right Lobe 2. Left Lobe 3. Quadrate Lobe (gallbladder side) 4. Caudate Lobe (near IVC)
Falciform Ligament Seperates lobes; anchors liver to abdominal wall
Hepatic Artery
Hepatic Portal Vein Deoxy, nutrient-rich blood from digestive system coming to liver for cleaning
Liver Lobules Functional Units of the Liver
Hepatocytes Liver cells which are arranged into lobules
Lobules -Hexagonal-shaped functional unit of the liver -Drained by a venule in its center, called a Central Vein.
Portal Triad (Lobule) 1 Arteriole-a branch of hepatic artery entering the liver 2 Venule- a branch of the hepatic portal vein entering the liver 3 Bile Duct-branch of the bile duct leaving the liver (also contains Lymphatic Vessels and Vagus Nerve (parasympathetic) fibres)
Blood Flow through Liver Nutrient-rich oxygen poor blood enters lobule via small branch of Portal Vein -each lobule receives nutrient-rich venous blood from intestines Oxygen rich blood enters via small branch of Hepatic Artery -each lobule receives oxy blood from celiac trunk
Kupffer Cells of liver phagocytize bacteria, dead RBCs, debris out
Central Vein of liver carries the processed blood to Hepatic Vein them IVC
What is the function of Sinusoids? Blood filter -Nutrients removed (amino acids, iron, glucose, vitamins) -Toxins, hormones, and drugs removed -Clotting factors added (albumin, angiotensin, glucose)
Bile -Salt secreted by liver -Emulsifies (breaks down) large fat droplets (dietary fats) in the small intestines so that Pancreatic Lipase can break fat down further
Where is bile concentrated and stored? the Gallbladder (until ready to be released into duodenum)
What is Bile made up of? mostly water, small amount if Bile Salts and Bilirubin
How does Bile reach the duodenum? flows down through Common Bile Duct
What is caused by a backup of Bile in tissues? Jaundice
How does the liver secrete Bile? through Right and Left Hepatic Ducts.
Where does overflow bile travel to collect in gallbladder? Cystic Duct
What hormone calls bile to come? cholecystokinin (CCK)
The Ampulla of Vater controls bile from the common bile duct as it merges with pancreatic duct
Sphincter of Oddi controls the flow of Both bile and pancreatic juice into the duodenum
Pancreas Large gland behind the stomach -Head resting on duodenum, tail below spleen and above L kidney -Endocrine and exocrine gland -Pancreatic islets of Langerhans secrete insulin + glucagon
Pancreatic Juice Exocrine Function -digestive enzymes in an alkaline fluid secreted to duodenum
Acinar Cells secrete digestive enzymes for pancreas
Epithelial Cells of pancreas secrete bicarbonate to neutralize HCl chyme
How does the pancreas send its secretions to the duodenum? Join common bile duct at ampulla and enter duodenum via sphincter of Oddi
Cholecystokinin (CCK) for pancreas AA & Fatty Acids in Chyme stimulates duodenum to release CCK CCK causes gallbladder to contract forcing bile into bile duct & the release of pancreatic enzymes The hepatopancreatic sphincter(of Oddi)relaxes to allow bile & pancreatic juice into duodenum
What is are sugars? poly-, di- and monosaccharides
What chemical digestion of carbohydrates happens in mouth? salivary glands secrete salivary amylase
What chemical digestion of carbohydrates happens in mouth? Low pH inactivates amylase but 1/2 starch digested
What chemical digestion of carbohydrates happens in the small intestine? chyme mixes with Pancreatic Amylase and resumes starch digestion
What chemical digestion of carbohydrates happens on the Villi level of intestines? chyme sloshes against Brush Border so enzymes in Microvilli can bind to sugars = Contact Digestion
What is the final step of chemical digestion of carbohydrates? Glucose is absorbed
What must be broken down to turn Proteins into Amino Acids? Peptide Bonds
What is used in the stomach and small intestines to digest proteins? Proteases
What is used in the stomach to hydrolyze peptide bonds?
What chemical digestion of proteins happens to chyme in the duodenum? pepsin is inactivated. Pancreas releases Trypsin and Chymotrypsin to resume bond breaking.
What chemical digestion of proteins happens on the Villi level? Brush Border of microvilli has enzymes called Peptidases break remaining a.a. chains
What is the final step of chemical digestion of proteins? Amino Acids are absorbed into bloodstream
How do fats enter the duodenum? congealed mass of fat gobules
How are fats be chemically broken down? must be emulsified
What emulsifies fats into small droplets? Lecithin and Bile Salts
What is the main fat busting enzyme in the duodenum? And what does it break fat down into? Pancreatic Lipase; result in fatty acids and glycerol.
As a result of chemical digestion of fats, what is absorbed directly at the Brush Border? Short chain F.a.'s and Glycerol
What must long chain and monoglycerides be converted to? and how are they absorbed? Triglycerides; enter Lacteal of Villi and travel in Lymph system to blood.
What happens in the large intestine? Water is reabsorbed at large intestines, leaving feces behind.
What are Haustra? Pouches along large intestine where smooth mm tone increased.
What is Mass Movement? Contractions of Haustra move waste along every 30 min.
Appendicitis Blockage of fecal material in appendix; must be removed stat.
What three vitamins are produced in the large intestine? 1. Vitamin K (fat soluble) 2. Biotin (water soluble) 3. Vitamin B5 (water soluble)
Vitamin K (fat soluble) Required by liver for synthesizing four Clotting Factors, including prothrombin
Biotin (water soluble) Important in glucose metabolism
Vitamin B5 (water soluble) Required in manufacture of steroid hormones and some neurotransmitters
Pathway of Large Intestine Ileocecal Valve and Cecum (Appendix) > Ascending Colon > Transverse Colon > Descending Colon > Sigmoid Colon > Rectum > Anal Canal > Anus
Created by: Meaagggannn



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