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BSC216 week of 3/21 notes

by: Alexandra

BSC216 week of 3/21 notes 216

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Digestive System
Human Anatomy and Physiology II Lecture
Jason Pienaar
Class Notes
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This 16 page Class Notes was uploaded by Alexandra on Thursday March 24, 2016. The Class Notes belongs to 216 at University of Alabama - Tuscaloosa taught by Jason Pienaar in Winter 2016. Since its upload, it has received 20 views. For similar materials see Human Anatomy and Physiology II Lecture in Biological Sciences at University of Alabama - Tuscaloosa.

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Date Created: 03/24/16
Digestive system Explain the basic anatomy, organization, functions, and regulation of the digestive system  Alimentary canal organs (Gastrointestinal or digestive tract) o Oral cavity o Pharynx o Esophagus o Stomach o Large intestine o Small intestine  Accessory organs o Teeth & tongue o Salivary glands o Liver o Gall bladder o Pancreas  Functions o Ingestion: of food o Secretion: of saliva, mucus, enzymes, acid & hormones to aid digestion o Propulsion: of food from one organ to another o Digestion: mechanical and chemical breakdown of food o Absorption: of water, electrolytes, vitamins and nutrients o Defecation: of unused foods and metabolic waste  Digestive regulation overview o Digestive system motility  Swallowing, churning, peristalsis, defecation o Skeletal muscle  Swallowing & defecation  Oral cavity  Pharynx  Superior portion of esophagus  Last portion of large intestine o Smooth muscle  Churning & peristalsis  Rest of esophagus  Stomach  Small intestine  Most of the large intestine o Regulation: ANS and Endocrine  Parasympathetic division stimulates (long reflexes)  Sympathetic division inhibits (long reflexes)  Enteric nervous system (short reflexes)  Numerous hormones and paracrine signals regulate digestion Describe the histological structure and function of each of the four alimentary canal layers  Serosa/adventitia o Serosa  For organs in peritoneal cavity  Simple squamous & loose CT o Adventitia  For organs outside peritoneal cavity  Dense irregular CT  Muscalaris externa o Longitudinal layer o Myenteric plexus o Circular layer  Submucose o Dense irregular CT o Submucosal plexus  Cluster of enteric nerves o Blood & lymphatic vessels o Submucosal gland  Mucosa o Muscularis mucosae  2 this layers of smooth muscle inner circular, outer longitudinal o Lamina propria  Loose CT  Houses blood, lymphatic vessels, MALT & glands o Epithelium  Simple columnar (stomach to end of large intestine)  Numerous goblet cells  Regenerative epithelium cells o Lumen Discuss the structure and function of the oral cavity, teeth and tongue  Oral cavity o Teeth, tongue and salivary glands turned chewed food into a bolus  Teeth  Tongue o Skeletal muscle covered by a layer of stratified squamous epithelium o Attached to floor of oral cavity by lingual frenulum o Papillae  Filiform: keratinized stratified squamous epithelium  Circumvallate, fungiform, foliate: taste buds Describe the structure and function of the salivary glands  2 secretory acinar cells o Serous cells  Water based fluid with enzymes and solutes  Aid in digestion o Mucus cells  Mucus  Keeps mouth moist  Glands o Parotid glands  Serous cells only  25-30% o Submandibular glands  Mostly serous some mucus cells  65-70% o Sublingual glands  Mostly mucus cells, some serous  5%  Saliva & salivation (water, electrolytes (Na+, Cl-, K+), mucus) o Salivary amylase  Breaks large polysaccharides into smaller sugars o Lysozyme  Perforates bacterial cell membranes o Secretory IgA  Mediates pathogen destruction o Bicarbonate ions  Neutralizes stomach acid regurgitated into esophagus o Salivation  Salivary gland secretion – parasympathetic reflex arc starting with smell or taste of food Describe the structure and function of the pharynx  Oropharynx & laryngeal pharynx o Stratified squamous epithelium o Palatine & lingual tonsils o Primary function to propel food bolus into esophagus o Upper, middle, and lower pharyngeal constrictors Describe the structure and function of the esophagus  Esophagus o Upper esophageal sphincter o Stratified squamous epithelium o Esophageal glands in mucosa and submucosa secrete mucus o Gastroesophageal sphincter Describe the process of deglutition (swallowing) 1. Voluntary phase a. Tongue pushes bolus against hard palate & towards oropharynx 2. Pharyngeal phase a. Bolus enters oropharynx b. Soft palate seals of nasopharynx c. Epiglottis seals of larynx d. Pharyngeal constrictor muscles activated by swallowing reflex arc 3. Esophageal phase a. Upper esophageal sphincter relaxes b. Enteric neurons stimulate esophageal muscle contraction c. Peristaltic waves move bolus towards stomach Describe the gross anatomy and histology of the stomach Same 4 tissue layers as rest of canal but muscularis external and mucosa are slightly modified  Muscularis externa o Additional layer of smooth oblique muscle, aids in churning  Mucosa o Gastric pit o Gastric gland  Goblet cells  Mucus neck cells  Secrete acidic mucus  (endocrine & exocrine cells)  Parietal cells  Secrete HCl o Low pH activates perinogen & destroys pathogens  Secrete intrinsic factor  (B12 absorption)  Chief cells  Secrete pepsinogen  Enteroendocrine cells  Secrete gastrin & other hormones Describe the secretory, propulsive and digestive functions of the stomach  Secretion o Gastric glands  Hormones  HCl  Mucus  Pepsinogen  Propulsion o Receptive function  Receptive relaxation: gastroesophageal sphincter and fundus smooth muscle relax (mediated by medulla & vagus nerve) o Churning function  Peristaltic contractions propel small portion of chime not duodenum, rest propelled back into stomach and churned (mediated by gastric pacemaker cells) o Emptying function  Rate of flow into duodenum depends on composition of chime  High stretch, low pH, high (lipid) or (solute) delay gastric emptying  Digestion o Chemical  Pepsin  Initiates peptide bond hydrolysis in stomach (protein digestion) o Mechanical  Churning aids mechanical breakdown and mixing of chyme Explain why HCl is secreted in the stomach and how HCl secretion is regulated Describe the structures of the duodenum, jejunum and ileum  Duodenum o 25 cm length o Major duodenal papilla  Secretions from gall bladder and pancreas o Submucosa contains Brunner’s glands  Secrete alkaline mucus  Jejunum o 2.5 m length o Situated within peritoneal cavity o Most active in chemical digestion& absorption  Ileum o 3.6 m length o Terminates in cecum of large intestine Discuss the histology and motility of the small intestine with regards to its function Three types of folds in increase abortive surface area 400-600x  Histology o Circular folds  Both mucosa and submucosa increase surface area  Slow down chime o Villi  Mucosa only  Simple columnar epithelium  Goblet cells  Lacteal  Capillaries  Intestinal crypts  Enteroendocrine cell o Microvilli  From a brush border on enterocytes  Brush border associated with sucrose, maltase, lactase & peptidases  Motility o Fasting  Migrating motor complex  Slow rhythmic contractions  2 hrs to move residual food from duodenum to ileocecal valve  controlled by the ENS & hormone motilin o Eating  Peristalsis  Alternating contractions of circular and longitudinal muscle  Propels chime through the intestine  Segmentation  Contraction of circular muscle only  Mixes chime with intestinal & pancreatic enzymes, mechanical digestion Describe the gross and microscopic anatomy of the large intestine  Histology o No villi or microvilli o Numerous goblet cells in mucosa  Fucntions o Propulsion and defecation of undigested fecal matter o Water and electrolyte absorption o 10x as many bacteria in large intestine as all human cells  Produce vitamin K  Metabolize undigested materials  Deter harmful bacterial growth  Stimulate immune system Discuss the defecation reflex and conscious control of defecation Digestive System (II) Describe the gross and microscopic structures of the pancreas, liver and gall bladder and explain their role in digestion  Pancreas o Acinar cells  Modified cuboidal epithelial cells o Pancreatic acini  Acinar & duct cells secrete pancreatic juice o Pancreatic Juice  Water  Bicarbonate ions  Digestive enzymes  Pancreatic amylase  Trypsinogen  trypsin  Other protease precursors  active forms  Liver o Falciform ligament  Separates right and left lobe  Fold of visceral peritoneum o Round ligament  Remnant of umbilical vein o Porta hepatis (indentation allowing veins and arteries to enter liver)  Hepatic portal vein  Nutrient rich  Deoxygenated blood to liver  Hepatic artery  Oxygenated blood to liver  Common hepatic duct o Histology  Liver lobule  Hexagonal shape  Central vein  At the corners o Hepatic arteriole o Portal venule o Bile duct  Blood flows from hepatic arterioles and portal venules  through sinusoids  to central vein (drains to vena cava) o Function (in Digestion)  Bile production  Water, electrolytes, & organic components (bile salts)  Required for lipid digestion & absorption o Bile salts emulsify lipids  Mechanism by which liver excretes wastes that kidneys cannot o Cholesterol, waste products (bilirubin) & toxins  Nutrient metabolism  Carbohydrates and proteins delivered by hepatic portal vein  Lipids by hepatic arteries o Glycogen, plasma, and clotting proteins etc.  Detoxification & Excretion  Bilirubin, dietary toxins (e.g. alcohol), various drugs  Gall Bladder o Indent in right lobe of liver o Common bile duct o Next to quadrate lobe of liver o Beneath caudate lobe of liver o Flow  Bile flows from hepatocytes  through bile canaliculi  to bile ducts (drain to common hepatic duct) o Function  Concentrated and stores bile  Releases it into duodenum How are pancreatic and biliary secretions regulated?  Parasympathetic (vagus nerve) and hormonal secretion o Secretin binds to duct cells and cholecystokinin (CCK) to Acinar cells  Stimulates pancreatic juice and bicarbonate ion secretion o Duodenal cells release secretin and cholecystokinin (CCK) into blood stream when lipids, acids and partially digested proteins are detected o Bile salts and secretin trigger the release of more concentrated bile  (positive feedback) o Cholecystokinin causes contraction of the gall bladder  Releases concentrated bile How does enzymatic hydrolysis differ from mechanical digestion of nutrients and where does each process occur  Mechanical o Physical break down of food into smaller particles  Mastication in mouth  Churning in stomach  Segmentation in sm. intestine  Emulsification by bile salts in sm. intestine  Chemical o Breaking of different chemical bonds in different nutrients (hydrolysis through specific enzymes) ((active in sm. intestine)  Proteins  Peptide bonds o Pepsin  Active in stomach o Trypsin o Chymotrypsin o Carboxypeptidase  Carbohydrates  Glycosidic bonds o Salivary amylase  Active in mouth & esophagus o Pancreatic amylase o Lactase o Maltase o Sucrose  Lipids  Ester bonds o Pancreatic lipase  Nucleic acids  Phosphodiester bonds o nucleases How are carbohydrates, proteins, lipids and nucleic acids digested and absorbed?  Small intestine lumen o Carbohydrates, lipids, proteins and nucleic acids chemically digested into their monomers (or oligomers)  Enterocytes o Most nutrient molecules are transported into the enterocytes with protein transporters o Typically cotransport or facilitated diffusion o Most nutrient molecules transported into the interstitial fluid with protein transporters o Molecules enter intestinal capillaries (or lacteals) between or through endothelial cells  Type o Carbohydrates  Salivary amylase  Inactivated in stomach  Pancreatic amylase  Results in oligosaccharides  Sucrose, maltase, lactase  Active on brush border of sm. intestine  Results in monosaccharides  Glucose & Galactose need to move against concentration gradient through enterocytes  Na+/Glucose cotransporter  Fructose crosses via facilitated diffusion o Proteins  Pepsin  Activated in stomach  Results in oligopeptides and some free amino acids  Inactivated in sm. intestine  Trypsin  Chymotrypsin  Carboxypeptidase  Various brush border peptidases  Active in lumen and on brush border of sm. intestine  Na+/oligopeptide/AA cotransporter o Nucleic acids  Pancreatic Nucleases  Active in sm. intestine  Result in nucleotides  Brush border nucleases  Result in free ribose, phosphate and nitrogenous base  Primary & Secondary transport o Lipids  Hydrophobic so tend to form large globules in solution  Mastication & churning break up globules in mouth and stomach  Gastric lipase begins chemical digestion (1 fatty acid removed)  Segmentation breaks up globules in sm. intestine  Bile salts o Amphiphilic o Can surround lipids (hydrophobic part) and keep them separate and dissolved in water (hydrophilic part) – emulsification in sm. intestine  Pancreatic lipase continues chemical digestion (1-2 fatty acids removed)  bile salts remain associated with digested fatty acids & monoglycerides to keep them emulsified


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