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An elderly, male patient with stomach cancer had a feeding tube inserted…

- - - - Palate: forms roof of mouth and has two parts
        
        Hard palate: formed by palatine bones and palatine process. Mucosa is slightly corrugated to help create friction
        
        Soft Palate: formed by mostly skeletal muscle and closes off nasopharynx during swallowing
      - Salivary Glands: cleanses the mouth, dissolves food chemicals for taste, moistens food for compaction and begins breakdown of starch for amylase.
        
        Major Salivary Glands: located outside oral cavity
        
        Parotoid: anterior to ear and external to master muscle
        
        Submandibular: medial to body of mandible
        
        Sublingual: anterior to submandibular gland under tongue
        
        Minor Salivary Glands: scattered throughout oral cavity
        
        2 types of secretory cells:
        
        Serous Cells: produce watery secretions, enzymes, ions and bits of mucin
        
        Mucous Cells: produce mucus which lubricates oral cavity and hydrates foodstuff
    - - Allows passage of food, fluids and air.
      - Lined with stratified squamous epithelium with mucus producing glands.
      - External muscle layers consist of two skeletal muscle layers.
      - Inner layer of muscle runs longitudinally while outer pharyngeal constrictors encircle wall of pharynx
    - - Gastroesophageal sphincter: surrounds cardiac orifice. Keeps orifice closed when food is not being swallowed.
        
        Esophageal mucosa contains stratified squamous epithelium which changes to columnar at stomach.
        
        Submucosa has mucus secreting esophageal glands that aid in food passage. Also contains adventitia instead of serosa.
    - - Gross Anatomy
        
        Cardial region: surrounds cardiac orifice
        
        Fundus: dome shaped region beneath diaphragm
        
        Body: mid portion
        
        pyloric region: terminates in pylorus which is continuous with duodenum through pyloric valve
        
        Greater Curvature: convex lateral surface of stomach
        
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      - Microscopic Anatomy
        
        Stomach wall contains all 4 tunics but muscular and mucosa are modified.
        
        Muscular has extra third layer which is called oblique.
        
        Smooth muscle allows stomach to not only churn, mix and move chyme but also to physically break it down into smaller fragments.
        
        Mucosa consists of simple columnar epithelium entirely composed of mucous cells.
        
        Secrete coat of alkaline mucus that traps bicarbonate rich fluid layer beneath it.
        
        Dotted with gastric pits which lead into gastric glands that produce gastric juice.
        
        Types of gastric gland cells
        
        Parietal: secrete hydrochloric acid, denatures proteins, activates pepsin, breaks down plant cell walls and kills many bacteria.
        
        Required for absorption of b12 in small intestines
        
        Chief cells: secrete pepsinogen, inactive enzyme that is activated by pepsin by hydrochloric acid and pepsin itself.
        
        Enteroendocrine: secrete chemical messengers. Some are paracrine (histamine) while others are hormones (gastrin)
        
        Mucosal barrier: protects stomach from harsh conditions and is created by three factors
        
        Thick layer of bicarbonate rich mucus.
        
        Tight junctions between epithelial cells prevent juice from seeping underneath.
        
        Damaged epithelial cells are quickly replaced by division of stem cells
    - - Duodenum: mostly retroperitoneal, curves around head of pancreas
        
        Ileum: attached posteriorly by mesentery; joins large intestine at ileocecal valve
        
        Jejunum: attached posteriorly by mesentery
      - Structural modifications for absorption:
        
        Length and surface area is increased for nutrient absorption.
        
        Circular folds: permanent folds that force chyme to slowly spiral through lumen, allowing more time for absorption
        
        Villi: fingerlike projections of mucosa with core containing dense capillary bed and lymphatic capillary called lacteal for absorption
        
        Microville: contain membrane bound enzymes called brush border enzymes which are used for final digestion of proteins, carbohydrates and nucleic acids.
      - Small intestine wall histology
        
        Intestinal crypts: tubular glands scattered between villi
        
        Enterocyctes: make up bulk of epithelium
        
        In ville: absorb nutrients and electrolytes, brush border enzymes bound to plasma membrane
        
        In crypts: produce intestinal juice, watery mixture of mucus that acts as carrier fluid for absorbing nutrients from chyme
        
        Goblet cells: mucus secreting cells
        
        Enteroendorcien cells: source of enetrogastrones and secretin
        
        Paneth cells: secrete antimicrobial agents(defensins and lysozyme)
        
        Mucosa associated lymphoid tissue (MALT) protects against microorganisms
        
        Peyer's patches located in the mucosa of the ileum and extend into the submucosa
        
        Duodenal glands: in submucosa of the duodenum and secrete alkaline mucus to neutralize acidic chyme
    - - Teniae Coli: three bands of longitudinal smooth muscle in the muscularis
        
        Haustra: rocketlike sacs caused by tone of teniae coli
      - Subdivisions
        
        Cecum: first part of large intestines
        
        Appendix: contains masses of lymphoid tissue; bacterial storehouse
        
        Colon: regions are retroperitoneal
        
        Ascending Transverse and Descending colon: travels up right side, across and down left side of abdominal cavity
        
        Sigmoid colon: s-shaped portion that travels through pelvis
        
        Rectum: three rectal valves stop feces from being passed with gas
        
        Anal canal: last segment that opens to body exterior at anus
        
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      - Microscopic Anatomy
        
        Contains thicker mucosa made up of simple columnar epithelium
        
        Except in anal canal where it becomes stratified squamous epithelium
        
        Contains abundant deep crypts with many mucus producing goblet cells
  - - - Mastication: process of chewing that tears and grinds food into smaller fragments
        
        Incisors: chisel shape for cutting
        
        Canines: fanlike that tear or pierce
        
        Premolars: broad crowns with rounded cusps used to grind or crush
        
        Molars: broad crowns and rounded cusps. These are the best grinders
      - Each tooth has 2 major regions:
        
        Roots: portion embedded in jawbone
        
        Crown: exposed part above gums. Covered by enamel which is heavily mineralized with calcium salts and hydroxyapatite crystals
    - - Filiform Papillae: gives tongue roughness to provide friction. Only one that doesn't contain taste buds
    - - Consists of four primary lobes which are right, left caudate and quadrate
        
        Falcifrom ligament: separates larger right and smaller left lobes. suspends liver from diaphragm and anterior abdominal wall
        
        Round Ligament: remnant of fetal umbilical vein along with free edge of falciform ligament
        
        Blood enters through hepatic artery and hepatic portal vein which enters at porta hepatis
        
        Ducts transporting bile include common hepatic duct leaving the liver which unites with cystic duct from gallbladder to form the bile duct
      - Microscopic anatomy of liver
        
        Liver lobules: hexagonal structural and functional units
        
        Composed of plates of hepatocytes that filter and process nutrient rich blood
        
        Portal triad: in each corner of lubule
        
        Branch of hepatic portal vein that brings nutrient rich blood from intestines
        
        Bile duct: receives bile from bile canaliculi
        
        Branch of hepatic artery that supplies oxygen
        
        Liver Sinusoids: leaky capillaries located between hepatic plates
        
        Blood from both hepatic portal vein and hepatic artery proper percolates from triad regions through sinusoid and empties into central vein.
    - - Exocrine function: secrete pancreatic juice via duct
        
        Acini: clusters of secretory cells that produce zymogen granules contains proenzymes
        
        Endocrine: secrete insulin and glucagon by pancreatic islet cells
      - Composition of pancreatic juice
        
        Alkaline solution to neutralize acidic chyme coming from stomach
        
        Protease (for proteins) which is secreted in inactive form
        
        amylase (carbs)
        
        Lipase (lipids)
        
        Nuclease (for nucleic acids)
- - - - Two phases of deglutition
        
        Buccal phase: voluntary contraction of tongue. pushes the food bolus into the oropharynx
        
        Pharyngeal-esophageal phase: involuntary phase controlled by the swallowing center in the brain
        
        Once food enters pharynx, respiration is momentarily prohibited
        
        Talking or inhaling while swallowing can short circuit these protective mechanisms
  - - - HCl denatures proteins by unfolding amino acid chain so it is more accessible to enzyme
        
        Pepsin carries out enzymatic digestion of proteins
    - - Carries out mechanical breakdown of food
        
        Lipid soluble alcohol, aspirin, and other drugs are absorbed into blood.
    - - Required absorption go B12
        
        B12 needed to mature red blood cells
        
        Lack of intrinsic factor causes pernicious anemia
        
        Treated with B12 injections
  - - - Bile salts: cholesterol derivatives; functioning fat emulsification and absorption
        
        Bilirubin: pigment formed from heme; broken down by bacteria in intestines to stercobilin
    - - Returned to liver via hepatic portal blood where it is used in new bile
        
        95% of secreted bile salts are recycled each time
  - - - Chyme entering duodenum is usually hypertonic; chyme delivery has to be slow to prevent osmotic loss of water from blood.
        
        Low PH of chyme os adjusted upward
        
        Chyme is mixed with bile and pancreatic juice to continue digestion.
        
        Enterogastric reflex and entergastrones control movement of food into duodenum to prevent it from being overwhelmed
    - - After meal segmentation is most common motion. Mixes chyme with pancreatic and brush border enzymes and bile
        
        Between meals peristaltic waves are initiated every 90-120 minutes
        
        Meal remnants, bacteria and debris are moved toward large intestines
        
        Ileocecal valve opens and admits chyme into large intestines when force of segmentation and motility in ileum increase
        
        ileocecal valve closes when chyme exerts backward pressure
  - - - Major function of large intestines is propulsion of feces to anus and defecation.
        
        Digestion: some remaining food residues are digested by gut bacteria
        
        Mass movements: slow, powerful peristaltic waves
        
        Gastrocolic reflex: initiated by presence of food in stomach and amount of fiber increase strength of contraction
    - - Parasympathetic signals stimulate contraction of sigmoid colon and rectum relaxation of internal anal sphincter.
        
        Conscious control allow relaxation of external anal sphincter band muscle of rectum contract to expel feces
        
        Assisted by valsalva's maneuver: closing of glottis, contraction of diaphragm and abdominal wall muscles cause an increase in intra- abdominal pressure
  - - - Propulsion: voluntary buccal phase of deglutition ignited by tongue, propels food into pharynx
        
        Mechanical Breakdown: mastication by teeth and mixing movement by tongue
        
        Digestion: salivary amylase in saliva, produced bu salivary glands begins digestion of starch
- - - - Starch and disaccharides are broken down into oligosaccharides and disaccharides; begins in mouth with salivary amylase.
        
        Then broken down into lactose, maltose and sucrose.
        
        Final break down into monosaccharides (glucose, fructose and galactose)
  - - - Broken into:
        
        Small peptides
        
        Amino acid monomers
        
        Large/ small polypeptides
        
        Some dipeptides and tripeptides
    - - Converted at a PH of 1.5-2.5 because it becomes inactive in high PH of duodenum
  - - - Emulsification: triglycerides and their break down products are insoluble in water
        
        Digestion: pancreatic lipase breaks down fat into three fatty acids and monoglycerides
        
        Micelle formation: products from digestion become coated with bile salts
        
        Diffusion: lipid products leave micelles and cross epithelial membrane via diffusion
        
        Lipid products are converted back to triglycerides and enter lymphatic lacteal
        
        Eventually emptied into venous blood at thoracic duct
        
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  - - - Pancreatic nuclease hydrolyze nucleic acid to nucleotide monomer.
        
        Brush border enzymes break nucleotides down into three nitrogenous bases, pentose sugar and phosphate ions.
- - - - Proteins: breaks oligopeptides and dipeptides into amino acids
      - Carbohydrates: further breaks them into lactose, maltose and sucrose then finally into monosaccharides