Digestive System - Anatomy and Physiology II PDF

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Lecture notes of digestive system from Professor Hernandez Anatomy and Physiology II spring course. Received an A in the class....

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Chapter 24: Digestive System - Digestive System ● Called digestive tube, gastrointestinal tract (GI), alimentary canal ● Takes our food from the oral cavity to the rectum ● Food never leaves the track ● We release enzymes into the food to break it down ● Process food mechanically and chemically ● About 30 feet long (with no muscle tone) ● Begins in the mouth and finishes in the small intestine (finishes absorption) ● Digestive System Pathway ○ Oral cavity > esophagus > stomach > small intestine > large intestine > rectum > anus ● Accessory Digestive Organs ○ Never any food in these ○ Contribute digestive enzymes to the digestive tube ○ Deliver these enzymes at the small intestine ○ Pancreas ○ Liver ○ Gallbladder - Digestive System Process ● Ingestion ○ Taking food into the body ○ We start to chew and begin mechanical digestion ○ Mastication ■ Chewing ○ Bolus ■ Ball of food that gets pushed into the back of the mouth then to the pharynx ● Propulsion ○ Swallowing in the oropharynx then moves to the stomach ○ Done by smooth muscle tissue ○ Peristalsis ■ Involuntary process ■ Means by which food is propelled through digestive system ■ Series of wave-like contractions and relaxations through digestive tube ■ Contractions happen behind the food to move it along ■ Done in the stomach, small and large intestine ○ Churning ■ When the muscle layers of the stomach contract with air to make a growling sound

● Mechanical Digestion ○ Chewing in the mouth ○ Churning in the stomach ○ Segmentation in the small intestine ● Chemical Digestion ○ Enzymatic activity ○ Enzymes break down the food into small enough pieces to be absorbed by the digestive tract ○ Begins in the mouth ○ Saliva has salivary amylase (enzyme) to break down complex carbohydrates ■ Turns carbohydrates into simple sugars ○ Begins in the mouth and ends in the small intestine ● Absorption ○ In the small intestine, nutrients are absorbed into the body ○ By the time the food reaches the large intestine, water is reabsorbed ○ If not enough water is absorbed, diarrhea will occur ○ If too much water is absorbed then the feces will be hard to excrete: constipation ○ Lymphatic capillaries pick up excess nutrients to return to the body ● Defecation ○ Anything indigestible is turned to feces moved out through the anus - Membranes of the Digestive System ● Peritoneum Cavity ○ Cavity covering the digestive organs ○ Filled with fluid to cushion the organs and allow for frictionless movement ● Parietal Peritoneum ○ Lining cavity ● Visceral Peritoneum ○ Covering organ ● Greater Omentum ○ Union of visceral and parietal peritoneum ○ Act as natural girdle to the body, keeping the organs in place in the body ● Peritonitis ○ Bacterial infection or inflammation of the visceral and parietal peritoneum layers ○ Can be from a wound, burst appendix, or bleeding ulcer ○ Could spread to become body wide ○ Treated by antibiotics - Histology of the Alimentary Canal ● 4 layers from esophagus to anal canal ● Mucosa (Inner Layer) ○ Very moist, epithelial membrane

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Present from the mouth to the anus Functions for secretion, protection and absorption Provides lubricating area for the food to travel Epithelial Layer ■ Single layer of cell ■ Has goblet cells ○ Lamina Propria ■ Supportive ■ Loose connective tissue ■ Is able to absorb nutrients/materials through capillaries ○ Muscularis Mucosae ■ Smooth muscle tissue ● Submucosa ○ External to the mucosa ○ Strong ○ Submucosal Plexus ■ Grouping of nerves that supply submucosa layer ● Muscularis Layer ○ Where the bulk of all of our smooth muscle tissue is located ○ Where segmentation and peristalsis occur ○ Has sphincters ■ Valves along the digestive system ■ Only allow food to move further along ■ Holds food in the organs before they move to the next one ● Fats take the longest to digest (8-12 hours), then protein (7-8 hours), then carbohydrates (3-5 hours) ■ Weak ones results in acid reflux ○ Gastroesophageal Reflux Disorder ■ Backflow of food that has acidic contents in it ● Citrus fruit, dark sodas ■ Burning feeling ■ Washing up of acid ● Serosa (Outermost Layer) ○ Visceral peritoneum ○ Loose connective layer ○ Protective layer to organs ○ Has areolar connective tissue and epithelium - Anatomy of Digestive Organs ● Oral Cavity ○ Mouth ○ Digestion begins here

○ Extends from the lips to the oropharynx ○ Boundaries of the oral cavity ■ Cheeks ● Lateral boundaries ● Take part in chewing ■ Hard and Soft Palate ● Upper boundaries ■ Tongue ● Lower boundary ● Manipulates food, moves it over the teeth, mixes with saliva ● Organ of taste ● Forms the bolus and pushes it down the oropharynx ○ Lips ■ Hold food inside the oral cavity ■ Takes part in facial expression and speech ○ Salivary Glands ■ Located in various regions ■ Produce saliva ● Slightly acidic ● pH 6.3-6.8 ● 99.5% is water ● 0.5% is dissolved solute ● Has amylase (ptyalin) ○ Begins breaking down carbohydrates ● Food mixes with saliva to create a bolus ■ Exocrine glands (have a duct) ■ 3 pairs ■ Produces about 1L of saliva per day that flows into the mouth from the glands ■ Parotid Gland ● Next to the ear ■ Submandibular Gland ● In inner surface of mandible ■ Sublingual Gland ● Underneath the tongue ○ Teeth ■ Primary Set ● 20 deciduous (baby) teeth ■ Secondary Set ● 32 permanent teeth ● Have specific types of teeth here

● Incisor Teeth ○ Tear into the food with sharp, thin edges ■ Tooth Design ● Crown ○ Composed of enamel ○ Dentin begins here ● Neck ○ Area where tooth makes contact with gingiva ● Root ○ Has root canal and nerve tissue ○ Vascular ○ Palate ■ Hard Palate ● Anterior part ● Can feel it with your tongue ● Associated with the palatine bone ■ Soft Palate ● Posterior part ● Dips down into the uvula ● Pharynx ○ Serves the digestive and respiratory system ○ Passageway ○ Does not contain digestive enzymes ○ Aids in deglutition ■ Takes bolus and pulls it into the pharyngeal area to the esophagus ○ Moves upward when you swallow, causing epiglottis to cover trachea opening so food doesn't go down the trachea ● Esophagus ○ Straight transport tube from pharynx to stomach ○ No digestive enzymes ○ About 10 inches long and 1 inch in diameter ○ Posterior to the trachea ○ Smooth muscle expands as food moves down, muscles constrict behind the food and relaxes in the front ○ Food must go through lower esophageal sphincter to pass into the stomach ○ Gastroesophageal Reflux Disease (GERD) ■ When acid from the stomach flows back to the esophagus ■ Can change esophageal cells and can cause esophageal cancer ● Stomach ○ Has thick mucosal lining ○ Extends from esophagus to duodenum

○ Has cardiac and pyloric glands to produce mucus ○ Turns food into chyme ■ Acidic fluid in stomach that results from food mixing with gastric juices ○ Has fundus on top ■ Has fundic glands with different types of cells ● Chief cells (zymogenic) ○ Secretes and release pepsinogen ■ Protein digesting enzyme ■ Inactive form ■ Does not act upon digesting proteins right away ■ Moves up the stomach and when it hits the acidic part of the stomach (lumin), it turns into its active form, pepsin ○ Secretes gastric lipase ■ Fat digesting enzyme ● Parietal Cells ○ Secretes hydrochloric acid ■ When it is released in the stomach it separates into hydrogen and chlorine to break down food ■ Used to convert pepsinogen into pepsin ○ Secretes intrinsic factor ● Hormone - Producing G Cells ○ Produce gastrin ■ Takes part in protein digestive process ○ Cardia Area ■ Near the heart ○ Pylorus ■ Area that goes into the duodenum ○ Stomach Sphincters ■ Lower esophageal sphincter ● Entry to stomach ■ Pyloric sphincter ● Before entry into duodenum ○ Rugae ■ Folds inside the stomach ■ Folds break food apart when it is hit against the wall by stomach muscle contractions ■ Has gastric pits ● Has gastric glands on the bottom to produce gastric juice ○ 3 layers of muscle tissue ■ Longitudinal layer

● In all digestive organs ■ Circular layer ● In all digestive organs ■ Oblique layer ● Only in the stomach ○ Problems in the Stomach ■ Gastric ulcers ● H. pylori (helicobacter pylori) ○ Very resistant to gastric acid ○ Powerful in penetrating the mucosal lining ○ Causes opening in stomach lining ● Presence of nsaids (non-steroidal anti-inflammatory drugs) ○ Aspirin ○ Ibuprofen (advil) ○ Naproxen (aleve) ● Hypersecretion of stomach acid ● Treated by taking an antacid (tums) ○ Neutralizes the acids ○ Hydroxide ions connect to hydrogen (acidic) ions and convert them into water ● Treated by proton pump inhibitors ○ Hydrogen ions that prohibit secretion of acid by parietal cells ○ Protonix, nexium or tagamet ● Small Intestine ○ Longest segment of the digestive system ■ 20 feet long and 1 inch in diameter ○ Extends from the pyloric sphincter to the beginning of the large intestine ○ Divided into 3 sections ■ Duodenum ● Famous site for ulcers ● Stomach acid is shot onto this wall causing deterioration ■ Jejunum ■ Ileum ● Portion where small intestine ends and large intestine begins ○ Presence of villi ■ Finger like extensions ■ 4-5 million ■ Increase our absorption surface area ■ Composed of simple columnar epithelial tissue ■ Has capillary networks

■ Microvilli ● On edge of villi ● Give small intestine villi a fuzzy look (brush border appearance) ● Produce brush border enzymes ○ Enzymes digest proteins ■ Aminopeptidase ■ Dipeptidase ○ Enzymes digest carbohydrates ■ Maltase ● Digest maltose which is broken down into 2 molecules of glucose ■ Sucrase ● Works on sucrose, composed of glucose and fructose ■ Lactase ● Breaks down lactose, which is glucose and galactose ● Lactose Intolerant ○ Person has no lactase or person has low levels of lactase ■ Goblet Cells ● Mucous producing cells ■ Paneth Cells ● In between villi on the base surface ● Produce lysozyme ○ Goes after incoming bacteria ● Capable of phagocytosis ■ Enteroendocrine Cells ● Secrete secretin, cholecystokinin and enzymes ○ Lacteal ■ Takes up any escaped fluid in the area ● Pancreas ○ Accessory organ ○ Lies in the bend of stomach and small intestine ○ Pancreatic Duct (duct of Wirsung) ■ Allows pancreatic juices to flow into the duodenum of the small intestine ■ Ampulla of Vater ● Joining of common bile duct (liver) and duct of Wirsung (pancreatic duct) ● Allows one way flow of pancreatic juices to the small intestine by sphincter of Oddi

○ Has a dual function ■ Endocrine Gland ● Regulates blood-glucose levels ● Has islets of langerhans cells ○ Alpha cells ■ Secrete glucagon ● Converts glycogen in the liver to glucose ○ Beta Cells ■ Secrete insulin ● Takes excess glucose and turns it into glycogen ■ Exocrine Gland ● Involves acinar cells ● Produce digestive enzymes (pancreatic juices) ○ Clear fluid that contains water, enzymes and salt ○ Slightly alkaline ○ pH of 7.1-8.2 ○ Placed in the duodenum to inactive acids ● Produce ribonuclease and deoxyribonuclease ○ Break down nucleic acids ● Produces pancreatic amylase ○ Break down carbohydrates ● Produces pancreatic lipase ○ Breaks down fats ● Pancreatic protease ○ Can break down protein molecules ○ Inactive enzymes from the pancreas are released to turn into an active form ○ Converted over because of enterokinase ○ Trypsinogen converted to trypsin ■ This convergence allows other enzymes to turn to active form ■ Chymotrypsinogen to chymotrypsin ■ Procarboxypeptidase to carboxypeptidase ● Liver ○ Second largest organ ○ About 3lbs ○ Contains poison/toxin breakdown enzymes ■ NH2 can convert with H+ to get the toxic NH3 ■ Liver has enzymes that break NH3 down into urea ○ Liver Functions

■ Produces heparin (anticoagulant) ■ Destroys old RBC ● Stores excess hemoglobin ● Done by kupffer cells ● Hemoglobin pigment (bilirubin) is turned into bile pigment ■ Stores fat soluble vitamins ● Vitamins A, D, E and K ■ Stores minerals ● Iron and copper ■ Maintains blood glucose levels ● Turns excess glucose into glycogen ■ Produces bile ● Helps in the emulsification of fats ○ Liver Abnormalities ■ Hepatitis ● Can be caused by virus, drugs, chemicals and alcohol ● Named by certain virus that causes hepatitis ● Hepatitis A ○ Infectious hepatitis ○ Caused by fecal contamination ○ Caused by hepatitis virus A ● Hepatitis B ○ Caused by contaminated syringes and body fluids ■ Transfusion ■ Tears ■ Semen ○ Caused by hepatitis virus B ● Hepatitis C ○ Caused by hepatitis C ○ Can permanently damage the liver ○ Can cause liver cancer ■ Cirrhosis ● Scarred liver ● Hepatocytes are destroyed ● Caused by alcohol ■ Jaundice ● Liver cells are destroyed so they cannot break down our bodys bile ● Our skin and whites of eyes turn yellow ● Gallbladder ○ Pear shaped sacks that hangs from the liver ○ Functions to concentrate and store bile

○ Can release stored bile if the liver does not release enough ■ Releases it from down the cystic duct ■ Cystic duct merges with the common bile duct to merge with duodenum ○ Produces cholesterol due to the presence of bile ■ Gallstones ● Crystalized cholesterol ● Can be treated by being zapped or surgically removed ■ Can reduce cholesterol levels by the food we eat ○ We can live without a gallbladder, liver will take over the function ● Large Intestine ○ Has 2 ½ inch diameter and is 5 feet in length ○ Extends from the ilium to the anus ○ Cecum is technical first portion ○ Lots of water absorption occurs here ○ No nutrient absorption occurs ■ Amount of water determines the type of feces ○ Has ileocecal valve ■ Allows food from the small intestine to the large intestine ○ Haustra ■ Pouches/segments in the large intestine ■ Diverticulosis ● Weak, outpouches of the haustra, called diverticuli ● Can be infected, causing a fever ● Creates colon problems and stomach pain ● Diverticulitis ○ Infectious form of the condition ○ Large Intestine Pathway ■ Ascending Colon ● Upward portion ● Must pass through right colic (hepatic) flexure to get to transverse colon ■ Transverse Colon ● Across portion ● Must pass through left colic (spenic) flexure to get to descending colon ■ Descending Colon ● Downward portion ● We must pass through the sigmoid colon to get ot the rectum ○ Large Intestine Complications ■ Haustral Churning ● Strong contractions of the haustra of the large intestine

■ Mass Peristalsis ● Strong peristaltic waves over the large intestine ● Begin in the transverse colon ○ Colonoscopy ■ Examination of the large intestine ■ Can detect cancer, diverticulosis ■ Usually done after 50 years old ■ Colon must be cleared in order to examine it ○ Sigmoidoscopy ■ Examination of the sigmoid colon ● Rectum ○ Internal Anal Sphincter ■ Smooth muscle tissue ■ Involuntary ○ External Anal Sphincter ■ Skeletal muscle tissue ■ Voluntary ■ Has to develop in toddlers ■ Releases feces out of the body ● Anal ○ Defecation ■ Release of feces out of the body via the anus - Digestive Hormones ● Gastrin ○ Secreted by the stomach in response to food coming in ○ Once food is in the stomach, gastrin is released and then goes into the circulation and stimulates gastric juice production ○ Made in the pyloric area by G-Cells ○ Can be stimulated by alcohol ● Enterogastrone ○ Secreted by the duodenum in the response to secreting fat ○ Once fat is in the stomach, enterogastrone is released and then goes into the circulation then travels to the stomach wall ○ Goes to the stomach to inhibit stomach contraction ● Secretin ○ Secreted by duodenum in response to acid ○ Once acid is in the stomach, secretin is released and then goes into the circulation ○ Once it is in the circulation is goes to the pancreas and causes the pancreas to release bicarbonate enzymes to increase the pH to about 9, making it not acidic anymore ● Cholecystokinin

○ Secreted by the duodenum in response to fat ○ Once fat is in the duodenum, cholecystokinin is released and then goes into the circulation ○ This then targets the gallbladder, causing is to release bile to help digest the fats - Metabolism ● Food gives us energy which gives us ATP ● Occurs in the cytoplasm and the mitochondria ● Neurons and RBC use glucose for energy ● Cardiac, skeletal muscle tissue and liver use fatty acids for energy ● 1 glucose produces 36 ATP ● Glycolysis ○ Digestion of carbohydrates ○ Polysaccharides are broken down into monosaccharides ○ Some fats and proteins enter here ○ Occurs in the cytoplasm ● Krebs Cycle ○ Occurs in the mitochondria ● Electron Transport Chain ○ Nothing enters here ○ This is where we generate the ATP ○ Occurs in the mitochondria ● Lipolysis ○ Speeds up fat digestion because carbs are taken out ○ Glucose production results from carbohydrate digestion ○ Acetyl CoA begins to back/build up and increase because it cannot enter the krebs cycle fast enough ■ This causes the body to go into ketogenesis ● Causing our bodies to produce a lot of ketone bodies ○ This causes our bodies to go into a state of ketosis and acidosis ○ Acidosis drops our pH levels, causing danger ○ Serious acidosis can lead to a coma and death ● Deamination ○ Break down of proteins ○ Break down into the essential and non-essential amino acids ○ Non-essential ■ Body manufactures it for you ■ You don't have to take them it ○ Essential ■ Your body won't make them ■ You must take them in with the foods you eat

● Vitamins ○ Fat-soluble vitamins ■ Not enzymes, function as coenzymes ■ Allow enzymes to help reactions go forward ■ Organic molecules ■ Our bodies don’t make these so we have to take them in ■ We can manufacture vitamin D by being in the sunlight ● Made in the skin ■ We can manufacture vitamin K in the liver ■ Vitamin A, D, E, and K ■ Hypervitaminosis ● When we take an over abundance of these vitamins, affecting our liver ○ Water-soluble ■ Vitamins B and C ■ If you take too many of these they will be excreted in our urine ● Minerals ○ Inorganic substances ○ Can appear by themselves or with other ions ○ Constitute about 4% of the body ○ Seen in the skeleton ○ Calcium, phosphorus, sulfur, potassium, chlorine, sodium, magnesium and iron...