Cadaver dissection videos http anatomy med umich educourseinfovi

Cadaver dissection videos • http: //anatomy. med. umich. edu/courseinfo/vi deo_index. html – Gastrointestinal: http: //anatomy. med. umich. edu/gastrointestinal_ system/peritoneum_vid. html 24 -1

The Digestive System • Mouth---bite, chew, swallow • Pharynx and esophagus---transport • Stomach----mechanical disruption; absorption of water & alcohol • Small intestine--chemical & mechanical digestion & absorption • Large intestine----absorb electrolytes & vitamins (B and K) • Rectum and anus---defecation 24 -2

Layers of the GI Tract 1. Mucosal layer 2. Submucosal layer 3. Muscularis layer 4. Serosa layer 24 -3

Mucosa • • • Epithelium – stratified squamous (in mouth, esophagus & anus) = tough – simple columnar in the rest • secretes enzymes and absorbs nutrients • specialized cells (goblet) secrete mucous onto cell surfaces • enteroendocrine cells---secrete hormones controlling organ function Connective tissue = Lamina propria – thin layer of loose connective tissue – contains BV and lymphatic tissue Muscularis mucosae---thin layer of smooth muscle – causes folds to form in mucosal layer – increases local movements – movements increase absorption with exposure to “new” nutrients 24 -4

Submucosa • Loose connective tissue – containing BV, glands and lymphatic tissue • Meissner’s plexus – parasympathetic – results in • vasoconstriction • local movement by muscularis mucosa smooth muscle 24 -5

Muscularis • Skeletal muscle = voluntary control – in mouth, pharynx, upper esophagus and anus – control over swallowing and defecation • Smooth muscle = involuntary control – inner circular fibers & outer longitudinal fibers – mixes, crushes & propels food along by peristalsis • Auerbach’s plexus (myenteric) – both parasympathetic & sympathetic innervation of circular and longitudinal smooth muscle layers 24 -6

Serosa • a serous membrane consists of a thin layer of connective tissue covered with simple squamous epithelium • known as the Peritoneum • Covers all organs and walls of cavities not open to the outside of the body – Portion covering organs = visceral layer – Portion forming the cavity wall = parietal layer • Secretes a watery, serous fluid • also forms the mesenteries of the GI tract

Peritoneum • Surrounds the Peritoneal cavity – potential space containing a bit of serous fluid – Contains most of the digestive organs • a sheet of serosa forms the peritoneal cavity = parietal peritoneum • Organs are covered with visceral peritoneum

The 4 Mesenteries • the serosa also forms connections from the parietal peritoneum to several organs in the cavity = Mesenteries • 4 kinds: • Mesentery Proper– connects small intestines to the parietal peritoneum Mesocolon – connects the large intestine (colon) to the parietal peritoneum • Lesser omentum • Greater omentum: 4 sheets of peritoneum surrounding fat deposits

The path of food: oral cavity/teeth/salivary glands oropharynx/epiglottis esophagus stomach small intestine: duodenum small intestine: jejunum small intestine: ileum large intestine: ascending colon large intestine: transverse colon large intestine: descending colon sigmoid colon rectum anus 24 -10

Two types of Digestion • Chemical • Mechanical 24 -11

Mouth • Oral cavity proper – roof = hard, soft palate and uvula – floor = geniohyoid, mylohyoid – contains the tongue – walls (lips and cheeks) = cheeks contain buccinator muscle that keeps food between upper & lower teeth – Vestibule = area between cheeks and teeth • Lined with an oral mucosa (stratified squamous epithelium & lamina propria) – Lining of the cheeks = buccal mucosa – Lining of the maxilla and mandible = alveolar mucosa (gingiva) • Oral cavity landmarks: lingual frenulum, 2 labial frenula, uvula

Oral cavity • Oral cavity ends as an arch of skeletal muscle = Palatoglossal muscle • extends from palate down to tongue • middle of the arch is the landmark known as the uvula • elevates the soft palate when we swallow – Closes off the nasopharynx and directs food into the oropharynx • behind the arch = palatine tonsil

Tongue • A muscular structure covered with oral mucosa • tongue is attached to hyoid bone, mandible, hard palate and styloid process • Two groups of muscles • 1. Intrinsic muscles – Change the shape of the tongue – Organized as transverse muscles, longitudinal and vertical muscles • 2. Extrinsic muscles – move the tongue in the oral cavity – Styloglossus, palatoglossus & hyoglossus – Geniohyoid & genioglossus

Tubal tonsil Intrinsic Muscle of tongue Genioglossus Geniohyoid Mylohyoid Lingual tonsil Epiglottis Vocal cords

Salivary Glands • Parotid gland below your ear and over the masseter • Submandibular gland is under lower edge of mandible • Sublingual gland is deep to the tongue in floor of mouth • All have ducts that empty into the oral cavity (exocrine glands) – Parotid duct open up near maxillary pre-molars – The submandibular and sublingual glands share the same duct – opens on either side of lingual frenulum

Salivary Glands • Classified either as: serous or mixed • Serous glands - cells secrete a watery fluid – e. g. parotid • Mixed glands secrete both mucus and a serous fluid – e. g. submandibular & sublingual Sublingual gland

Saliva • • • Wets food for easier swallowing – forms the bolus Dissolves food for tasting Bicarbonate ions buffer acidic foods Helps build stronger enamel Chemical digestion begins with salivary enzymes salivary amylase & lingual lipase – – • • Salivary amylase made by parotid gland – carbohydrate digestion Lingual lipase made by submucosa of tongue – fat digestion Also contains lysozyme - helps destroy bacteria Protects mouth from infection with its rinsing action

• Parotid gland secretes the enzyme Salivary amylase • Submucosa layer of the tongue secretes Lingual lipase Parotid Sublingual Submandibular

Salivation • Parasympathetic nerves - Increase salivation – sight, smell, sounds, memory of food, tongue stimulation---rock in mouth – cerebral cortex signals the salivatory nuclei in brainstem – carried by parasympathetic nerves = CN 7 & 9 • Sympathetic nerves - Stop salivation – dry mouth when you are afraid – sympathetic nerves

Teeth: -grinding, tearing and shearing of food -two main divisions: crown and root -crown: above gum-line/gingiva -covered with a layer of enamel -root: below the gum-line -embedded in the alveolar socket of the jaw -root is secured in the alveolar socket by two tissues: cementum & periodontal membrane/ligament -neck – where crown and root meet -gingiva should form a tight a seal at this area -crown and root of tooth is formed of a calcified connective tissue called dentin -dentin, enamel and cementum – made of calcium phosphate very similar to bone = hydroxyapatite 24 -21

Teeth: -inside of the tooth is filled with pulp -pulp – tissue rich in nerves/blood vessels -nerves and BVs enter at the bottom of the root - through the apical foramen -travel through root canals to enter the pulp cavity -pulp cavity – site of the pulp (blood vessels, nerves and lymphatics)

Primary and Secondary Dentition -primary: 20 teeth starting at 6 months -secondary/adult: between 6 and 12 years = 32 teeth 8 incisors 4 canines (cuspids) 8 premolars (bicuspids) 12 molars (tricupids) ** third pair of molars (wisdom teeth) may not erupt -impacted 24 -23

Pharynx • Funnel-shaped tube extending from internal nares to the esophagus (posteriorly) and larynx (anteriorly) • Skeletal muscle lined by mucous membrane • Divided into three regions Tubal tonsil Nasopharynx Intrinsic Muscle of tongue Geniohyoid Oropharynx Mylohyoid Laryngopharynx Lingual tonsil Epiglottis Vocal cords

Deglutition: Swallowing • Deglutition or swallowing is facilitated by saliva and mucus – starts when bolus is pushed into the oropharynx – sensory nerves send signals to deglutition center in medulla oblongata

Deglutition: Swallowing • Voluntary phase---tongue pushes food to back of oral cavity & into oropharynx – Can still prevent swallowing and return food to the oral cavity • Involuntary phase----pharyngeal stage – – – breathing stops & airways are closed soft palate & uvula are lifted to close off nasopharynx vocal cords close epiglottis is bent over airway as larynx is lifted controlled by autonomic nervous system

Deglutition: Swallowing • Peristalsis pushes food down esophagus – circular fibers contract behind bolus to narrow esophagus – longitudinal fibers contract in front of bolus to shorten length of esophagus in front of food • • Travel time is 4 -8 seconds for solids and 1 sec for liquids Lower esophageal sphincter relaxes as food approaches the stomach

Esophagus • • • Collapsed muscular tube In front of vertebrae Posterior to trachea Posterior to the heart Pierces the diaphragm at the hiatus – Site for hiatal hernia or diaphragmatic hernia • Mucosa = stratified squamous • Submucosa = contains large mucous glands • Muscularis = upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth – upper & lower esophageal sphincters are prominent rings of circular muscle

Thoracic Aorta Esophagus Diaphragm Liver

Gastroesophageal Reflex Disease • If lower esophageal sphincter fails to open – distension of esophagus feels like chest pain or heart attack • If lower esophageal sphincter fails to close – stomach acids enter esophagus & cause heartburn (GERD) – for a weak sphincter---don't eat a large meal and lay down in front of TV – smoking and alcohol make the sphincter relax worsening the situation • Control the symptoms by avoiding – coffee, chocolate, tomatoes, fatty foods, onions & mint – take Tagamet HB or Pepcid AC 60 minutes before eating – neutralize existing stomach acids with Tums

Anatomy of Stomach • Size of a large sausage when empty – Capable of expansion • Mucosa forms rugae – folds in the mucosa caused by contraction of the m. mucosae – Folds = rugae • Muscularis – three layers of smooth muscle – longitudinal – circular – oblique

Anatomy of Stomach • Anatomy of stomach – – – Starts with Lower esophageal sphincter Cardiac region Fundus of stomach Body of stomach Pyloric region --starts to narrow as it approaches the pyloric sphincter - Greater curvature - Lesser curvature • Bolus of food enters and mixes with gastric juice Chyme • Stomach empties as small squirts of chyme leave the stomach through the pyloric valve/sphincter

Anatomy of Stomach FUNDUS UR AT CU RV SS ER BODY LE Starts with Lower esophageal sphincter Cardiac region Fundus of stomach Body of stomach Pyloric region --starts to narrow at the pyloric sphincter - Greater curvature - Lesser curvature E – – – RE TU PYLORIC REGION A RV R TE A RE PANCREAS G DUODENUM CU

Mucosa of the Stomach • simple columnar epithelium with embedded mucus cells • forms columns = gastric glands that open into the stomach lumen through gastric pits

Gastric Glands of the Mucosa • • • Chief cells secrete pepsinogen (inactive protease) into the stomach which will become pepsin (active protease) – for protein digestion Parietal cells secrete H+ and Cl- ions into the stomach – become Hydrochloric acid HCl converts pepsinogen into pepsin = protein digestion Intrinsic factor - secreted by parietal cells – absorption of vitamin B 12 for RBC production Gastrin hormone – secreted by G cells • Increases gastric juice production, gastric motility and increase gastric emptying

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Anatomy of the Small Intestine • 20 feet long----1 inch in diameter • Large surface area for absorption • 3 parts – duodenum---10 inches – jejunum---8 feet – ileum---12 feet • ends at ileocecal valve

Small Intestine • Mucosa forms ridges – plicae circularis • • permanent ½ inch tall folds in the mucosa not found in lower ileum cannot stretch out like rugae in stomach do increase the surface area of the SI mucosa

Small Intestine • The plicae circularis is covered with finger-like projections of mucosa – villi • • • 1 Millimeter tall Covered with absorptive epithelial cells (mucosa) Core is lamina propria of mucosal layer Contains arterioles, capillaries and venules PLUS lacteals (lymphatic capillaries)

Small Intestine • The epithelial covering of the villus = absorptive cells • Absorptive cells possess microvilli – Found on the apical surface of absorptive cells – Gives the villus the appearance of a brush border

Intestinal Villus • Absorptive cells -project their microvilli into the lumen of the SI -absorb amino acids, nucleosides and saccharides from food • Epithelial cells at the bottom of the villus = Intestinal gland – production of brush-border enzymes • brush-border enzymes are “stuck” onto the microvilli of absorptive cells – sucrase, maltase, lactase: disacharides monosaccarides – aminopeptidase, dipeptidase: smalle peptides amino acids

Intestinal Villus • Submucosal layer has duodenal glands secretes alkaline mucus • Goblet cells – mucus production • Enteroendocrine cells – Found within the intestinal glands – Secrete three hormones – secretin – cholecystokinin – gastric inhibitory peptide • Paneth cells – secretes lysozyme – kills bacteria

Where will the absorbed nutrients go? 24 -43

Large Intestine • 5 feet long by 2½ inches in diameter • Ascending & descending colon • Cecum & appendix • Transverse colon • Sigmoid colon • Rectum • Anal canal & Anus • Ascending & descending colon are retroperitoneal (not in the peritoneal cavity) • Ileum connects to the ascending colon at the ileocecal valve/sphincter • Cecum found below this sphincter

Large Intestine • Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx • Anal canal = last 1 inch of GI tract – ends as the anus – internal anal sphincter----smooth muscle & involuntary – external anal sphincter----skeletal muscle & voluntary control

Lesser Omentum Liver Stomach Gallbladder Transverse Colon Ascending Colon Small Intestine Descending Colon Mesentery of Small Intestine

Histology of Large Intestine • Muscular layer – internal circular layer is normal – outer longitudinal muscle can be seen from the outside • taeniae coli = shorter bands • Permanent contractions of these bands puckers the LI into pouches called haustra (also called diverticula) • epiploic appendages • Serosa = visceral peritoneum 24 -47

Histology of Large Intestine • Mucosa is a smooth tube with no villi – Contains many intestinal glands made up of simple columnar absorptive cells & goblet cells – absorptive cells absorb water – goblet cells secrete mucus • NO HUMAN DIGESTIVE ENZYMES MADE!!!! • Submucosal & mucosa contain lymphatic nodules

Defecation • Reflex moves feces into rectum • Stretch receptors signal to the sacral spinal cord • Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter • External sphincter is voluntarily controlled 24 -49

Anatomy of the Pancreas • • 5" long by 1" thick Head found in the C-shaped curve of duodenum; tail located next to spleen Main pancreatic duct opens into duodenum as major duodenal papilla Major duodenal papilla connects to hepatopancreatic ampulla (Ampulla of Vater) – union of pancreatic duct and common bile duct • Accessory duct opens into duodenum as minor duodenal papilla

Pancreatic Juice • • Pancreatic acinar cells form clusters called acini They make pancreatic juice 1 + 1/2 Quarts/day at p. H of 7. 1 to 8. 2 Contains water, digestive enzymes & sodium bicarbonate

Pancreatic Juice • Digestive enzymes: from exocrine acinar cell clusters – – pancreatic amylase (carbohydrates) disaccharides pancreatic lipase (fats) 4 proteases (protein degradation) small peptides Ribonuclease & deoxyribonuclease - digest nucleic acids nucleotides • Products of pancreatic juice are then broken down by brush-border enzymes

The 4 Proteases Enterokinase (intestines) – trypsinogen--Trypsinogen Trypsin activated by enterokinase (a brush border enzyme) Trypsin – chymotrypsinogen---- Chymotrypsinogen Chymotrypsin activated by trypsin – procarboxypeptidaseactivated by trypsin – proelastase--Trypsin Proelastase Elastase activated by trypsin Procarboxypeptidase Trypsin Carboxypeptidase

Anatomy of the Liver and Gallbladder • Liver – – weighs 3 lbs. below diaphragm right lobe larger gallbladder on right lobe – size causes right kidney to be lower than left • Gallbladder – fundus, body & neck • • • Digestive function of Liver = production of Bile Digestive function of Gallbladder = storage of excess bile Bile release is stimulated by the presence of fat in the duodenum

Flow of Bile • • • Bile capillaries of liver collect bile from hepatocytes Right and Left Hepatic ducts connect to form Common Hepatic Duct Cystic duct extends from neck of gallbladder common hepatic duct joins the cystic duct to form Common Bile Duct Common bile duct & pancreatic duct unite to form the Ampulla of Vater

Right & Left Hepatic Ducts Common Hepatic Duct Pancreatic Duct Gallbladder Cystic Duct Ampulla of Vater Common Bile Duct 24 -56

Blood Supply to the Liver • Hepatic portal vein – nutrient rich blood from stomach, spleen & intestines – splenic vein + superior mesenteric vein + inferior mesenteric vein • Hepatic artery branches off the Common hepatic artery (from the celiac trunk) Hepatic Portal Vein Common Bile Duct Splenic Vein Superior Mesenteric Vein Inferior Mesenteric Vein 24 -57

• Lined with simple columnar epithelium • No submucosa • Three layers of smooth muscle just like the stomach • for the storage of Bile • role in the absorption of fats • Fat stimulates CCK production by SI which stimulates contraction of the gallbladder and the release of bile Gallbladder

Types of Digestion • Mechanical – mouth, stomach, SI, LI • Chemical – mouth, stomach, SI

Chemical Digestion of Carbs • Mouth---salivary amylase • Esophagus & stomach---no digestion • Duodenum----pancreatic amylase • Brush border enzymes (maltase, sucrase & lactase) act on disaccharides – these enzymes produce the monosaccharides fructose, glucose & galactose – lactose intolerance (no enzyme; bacteria ferment sugar)--gas & diarrhea

Chemical Digestion of Proteins • Mouth – no digestion • Stomach – HCl denatures or unfolds proteins – pepsin turns proteins into peptides • Pancreas – 4 Proteases --split peptides into smaller peptides and dipeptides • Intestines: brush border enzymes – aminopeptidase & dipeptidase- produce amino acids – split off amino acid at amino end of a peptide (aminopeptidase) or split dipeptides into individual amino acids (dipeptidase)

Chemical Digestion of Lipids • • Mouth----lingual lipase Stomach – no digestion Small intestine – pancreatic lipase---splits triglycerides into 2 fatty acids & a monoglyceride (glycerol + one fatty acid) – emulsification by bile micelles that are absorbed into the absorptive cell – No fat degrading enzyme found in brush border enzymes fats are reassembled in the absorptive cell and transported into the lacteal combined with proteins (chylomicrons) – Return to the bloodstream via lymphatic connection to the subclavian veins

Chemical Digestion of Nucleic Acids • Pancreatic juice contains 2 nucleases – ribonuclease which digests RNA nucleotides – deoxyribonuclease which digests DNA nucleotides • Nucleotides are further digested by brush border enzymes (nucleosidase and phosphatase) – The phosphatase removes the phosphate group from the nucleotide – The nucleosidase breaks up the pentose sugar and the nitrogenous base 24 -63

Absorption & Feces Formation in the Large Intestine • food has now been in the GI tract for 3 to 10 hours • solid or semisolid due to water reaborption = feces • feces – water, salts, sloughed-off epithelial cells, bacteria, products of bacterial decomposition, unabsorbed and undigested materials • 90% of all water absorption takes place in the SI – 10% in the LI • but the LI is very important in maintaining water balance • also absorbs some electrolytes---Na+ and Cl- and vitamins • dietary fiber = indigestible plant carbohydrates (cellulose, lignin and pectin) • soluble fiber – dissolves in water (beans, barley, broccoli, prunes, apples and citrus) – forms a gel that slows the passage of materials through the colon – also helps to lower blood cholesterol – binds to bile salts to prevent their reabsorption – liver must make more cholesterol to make more bile salts – takes this cholesterol from the blood • insoluble fiber – woody or structural parts of the plant (skins of fruits and vegetables, coatings around bran and corn) – passes though the colon relatively unchanged 24 -64

Absorption of Water • 9 liters of fluid dumped into GI tract each day • Small intestine reabsorbs 8 liters • Large intestine reabsorbs 90% of that last liter • Absorption is by osmosis through cell walls into vascular capillaries inside villi 24 -65

Liver Functions--Carbohydrate Metabolism • Turn proteins into glucose • Turn triglycerides into glucose • Turn excess glucose into glycogen & store in the liver • Turn glycogen back into glucose as needed Liver Functions --Lipid Metabolism • Synthesize cholesterol • Synthesize lipoproteins----HDL and LDL (used to transport fatty acids in bloodstream) • Stores some fat • Breaks down some fatty acids Liver Functions--Protein Metabolism • Deamination = removes NH 2 (amine group) from amino acids • Converts resulting toxic ammonia (NH 3) into urea for excretion by the kidney • Synthesizes plasma proteins utilized in the clotting mechanism and immune system • Convert one amino acid into another 24 -66

Other Liver Functions • Detoxifies the blood by removing or altering drugs & hormones (thyroid & estrogen) • Releases bile salts help digestion by emulsification • Stores fat soluble vitamins-----A, B 12, D, E, K • Stores iron and copper • Phagocytizes worn out blood cells & bacteria • Activates vitamin D (the skin can also do this with 1 hr of sunlight a week) 24 -67

Bile Production • One quart of bile/day is secreted by the liver – yellow-green in color & p. H 7. 6 to 8. 6 • Components – water & cholesterol – bile salts = Na & K salts of bile acids – bile pigments (bilirubin) from hemoglobin molecule