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DIGESTIVE SYSTEM
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I. Introduction A. Organs of the Digestive System 1. Alimentary Canal
mouth to the anus in between is the alimentary canal 24-48 hours
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Food is digested in the duodenum becomes nutrients, nutrients are absorbed (jejunum and ileum) to the bloodstream
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4 major types of organic compounds
1. carbohydrates = monosaccharides 2. lipids (fats) = fatty acids 3. proteins = amino acids 4. nucleic acids = nucleotides
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2 types of glands in the Body
1. Endocrine glands = secretes hormones in the body ex. Thyroid gland = thyroxine hormone 2. Endocrine glands = secretes a chemical substance into a duct (tube) ex. Salivary glands
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Salivary Glands
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Glands Parotid gland Submandibular
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Glands Sublingual Submandibular
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Pharyngeal tonsil Palatine tonsil
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Salivary gland
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Salivary gland
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Tongue Taste buds
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2. Accessory Exocrine Glands
A. secretes enzymes and other substances into the alimentary canal 1. salivary glands 2. liver (bile) 3. gall bladder 4. pancreas
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Ingestion = food = digestion = food residues (cellulose) + nutrients = absorption = egestion
4. egestion (defecation)
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Exocrine glands – parotid, submandibular, sublingual glands
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Parotid gland – located just in front and below (antero-inferior) the ears * Mumps: viral infection
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C. Overall Embryological Development of the Digestive System
1. during the 4th week - the mouth and anus develop, forming a continuous tube (the alimentary canal) 2. during the 5th week a. the yolk sac constricts off from the mid-gut b. endodermal buds begin to develop from the alimentary canal, and project into the surrounding mesoderm at certain locations
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Regions of the Alimentary Canal
A. Divisions: Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine (Colon), Anus B. Mouth
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1. Oral Cavity A. Lips (1) superior labial frenulum (“bridle”) (2) inferior labial frenulum B. Cheeks ** Buccinator Muscles C. Gingivas (gums) – consists of the oral mucosa (non-keratinizing epidermis and underlying dermis)
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Teeth
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Occlusal surface of the crown = the portion of the crown that contacts opposing teeth
Cusps – the elevations present on the occlusal surface of the crown
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Root – the inferior portion of the tooth that is embedded in the alveolar process of the maxilla or mandible (which is covered by periosteum, called the periodontal membrane) Neck – the constricted region between the crown and the root of the tooth
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Tooth fills into a socket called an alveolar process
Tooth is filled into a socket In between the teeth and alveolar process is the (dento-alveolar) joint – Gomphosis Periodontal membrane – around the tooth
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Crown i. anatomical crown = the superior portion of the tooth that is covered by enamel Ii. clinical crown – that portion of the anatomical crown visible above the gingiva
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A. Incisors – front teeth, one root
i. chisel-shaped teeth used for biting ii. Crown is chisel-shaped iii. There is one root
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B. canines (cuspids) – pointed teeth, very prominent in dogs
i. pointed teeth used for tearing ii. crown has 1 cusp iii. there is one root
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C. Premolars (bicuspids) – 2 cusps in each tooth
i. broad teeth used for grinding ii. crown has 2 cusps iii. there is 1 or 2 roots
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D. Molars (multicuspids) – multiple elevations
i. broad teeth used for grinding and crushing ii. crown has 3-5 cusps iii. there is 2-3 roots
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Permanent Teeth a. begins to erupt at about 6 years of age B. dental formula I, C, P, M = in each quadrant 2, 1, 2, 3 x 4 = 32 teeth 3rd molar is the wisdom tooth The last 8 set of permanent molars are called wisdom teeth
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Deciduous (Milk) Teeth
A. begins to erupt about 6 months of age B. dental formula I, C, P, M 2, 1, 0, 2 x 4 = 20 teeth
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Endodontics – dental specialization focusing on the inner tissue of the teeth called the pulp.
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Sensory neuron for the upper and lower teeth Dentists inject anesthetic into the trigeminal nerve
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Diseases of the Teeth A. dental caries (cavities) – holes in the enamel caused by acids produced by bacteria B. gingivitis C. (pyorrhea) Periodontitis – infection of the alveolar socket D. impacted wisdom tooth
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Periodontitis
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Tongue = lingual 1. functions: A. mastication
B. deglutition – swallowing C. speaking = study of languages is linguistics D. taste buds (chemoreceptors) = chemoreceptors = sensory receptors sensitive to chemicals
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Sensory Neurons Sweet = activated by sugars, chemicals that can also activate sweet receptors are artificial sweeteners Sour = activated by acids like citric acid (oranges, lemons, grapefruit, plain yogurt) Salty = salts (NaCl) is a metal and a non-metal Bitter = aspirin (KCl) Umami (Savory, meaty, brothy) = activated by amino acids (MSG) – monosodium glutamate = derived from glutamic acid (an amino acid
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Taste buds tell us whether there are sugar, salts, bitter
Bitter maybe toxic or poisonous Taste buds inform us what is in our food
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Three tonsils 1. palatine tonsils (“tonsilitis/tonsilectomy)
2. lingual tonsil 3. pharyngeal tonsil (nasopharynx)
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Microscopic Anatomy of the GI Tract The GI tract consists of a tube that extends from the mouth to the anus. It has four tissue layers (tunics):
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Gastroesophageal Junction
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Histology of The Stomach Wall
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Histology of the Small Intestine (Duodenum)
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Intestinal Villus
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Histology of Selected GI Tract Organs
A. The Pancreas – Gross View
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The Liver Gross View of the Liver
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Liver – Microscopic Anatomy
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Gross Anatomy of the GI Tract
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The Mouth
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The Esophagus
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The Stomach
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Pharyngeal constrictor muscles
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Inside tonsils: Macrophages and Lymphocytes (WBCs) = antibodies (proteins, immunoglobulins) = inactivate foreign agents
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Salivay gland = parotid gland = largest among the salivery glands below the ear
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Submandibular Salivary Glands
Located within the lower jaw (mandible) The duct opens just beside the lingual frenulum
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Esophagus 1. a 10-inch long muscular tube that extends from the laryngo-pharynx down to the stomach 2. the bolus of food moves down the esophagus by a peristaltic wave of contraction (and by gravity) Food is ushered down the digestive sytem by peristaltic contractions of circular muscles that proceed downward, forcing the food along in front of them.
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The vertebral column is the yardstick for locating organs
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Histological appearance of the alimentary canal:
A. the mucosa 1. epithelial lining 2. lamina propria 3. muscularis mucosa B. the submucosa C. the muscularis D. the serosa
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The Stomach 1. the stomach is a J-shaped muscular organ located in the left upper quadrant of the abdominal cavity
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Appendix – right lower quadrant
Liver – biggest organ in the body not counting the skin
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Gastro-esophageal (Cardiac) sphincter – circular/ring- shaped muscle
Palatine rugae – ridges in the mouth Sphincters/valves = function is to always allow one-way flow
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A. gastro-esophageal (“cardiac”) sphincter (valve)
B. fundus of stomach C. body of stomach D. pylorus of stomach E. pyloric-sphincter (valve) – allows what is in the stomach to go into the duodenum and prevent it from going back
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Greater curvature attach the fatty membrane called greater omentum
Greater omentum – hanging from the stomach which you have to lift up to see the intestine - protects/cushions the stomach from any blow to the abdomen
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Functions of the greater omentum
1. cushions underlying viscera 2. protects underlying viscera from the spread of infection 3. stores fat – in part explains belly fat, because the greater omentum is fat
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Histology of the digestive system
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Lesser omentum – not as fatty or big, still protective in nature
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3 divisions of the stomach
1. body – middle part of the stomach 2. pylorus – last part of the stomach 3. fundus – top part of the stomach * gastric rugae – prominent folds of the mucosal lining
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The stomach functions to churn, mix and hold the partially digested food called chyme
A. gastric glands located in the lamina propria of the mucosa, secretes gastric juice 1. HCl (parietal cells) – kills bacteria 2. pepsinogen (chief or principal cells) a. pepsinogen (inactive) = HCL = pepsin (active) (an enzyme) * gen (inactive) = no gen (active) fibrinogen = fibrin b. protein (polypeptide) = pepsin = short peptide chains * a peptide is 3 or 4 amino acids each
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Very little digestion or absorption in the stomach
Main job of the stomach is to hold food as well as churn or grind the food The walls of the stomach filled with gastric glands that secrete gastric juice
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Chyme = food that is churned or mixed up
- it is called vomit if it is outside our body - it is just food mixed with gastric juice Gastric juice = HCl and pepsinogen
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Substances normally absorbed in the stomach
1. water 2. monosaccharides – honey (lots of simple sugars or monosaccharides) 3. alcohol – warm feeling in the stomach 4. aspirin – may irritate the wall of the stomach
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The contents of the stomach are normally emptied within 1-4 hours
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Disorders associated with the stomach
A. Gastric Irritation B. Esophagitis (“heartburn”, gastric reflux) - “GERD” (Gastro-Esophageal Reflux Disease) * Esophagus is right behind the heart * Eat a large pizza plus lots of beer at midnight then sleep C. Gastric Ulcer (Sore)
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Majority of gastric ulcers were caused by Helicobacter pylori
D. Gastritis – inflammation of the stomach E. Flatulence (“gas”) – carbonated drinks, swallow air, - burp or flatulence
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Gas formed in the stomach comes out of the mouth = belch/burp
Gas formed in the small and large intestine = flatulence - these are the gases produced by bacteria breaking down food residues in the large intestine
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F. Cancer of the stomach = surgically remove the whole stomach
- *obese* G. Pyloric stenosis (Constriction) – congenital condition, common
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Pyloric stenosis – more common among boys than girls
Boys – 1 in 200 births Girls – 1 in 1000 births - if the baby keeps burping out all the milk and the baby is losing weight, you call a pediatrician and they will most likely think pyloric stenosis and do surgery
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Vomiting (heaves) = valsalva maneuver – tightening of the abdominal muscles to expel something (vomiting, defecate, expel baby) The gastro-esophageal sphincter does not close effectively unlike the pyloric sphincter in order for vomiting to occur
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Acid/Peptic Disease The stomach produces hydrochloric acid, with a pH of about 3 The main purpose of this acidic secretion is to sterilize food as it enters the body
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In certain situations, this acid can do damage to:
Esophagus Stomach Duodenum
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Acid/Peptic Disease The stomach produces mucous that lines the stomach and protects the stomach from the acid Sometimes the stomach does not produce enough of this protective mucous
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Acid/Peptic Disease Sometimes the stomach does not produce enough of this protective mucous, this can be caused by: STRESS!
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If more stomach acid is produced than what the protective mucous lining can handle, the result can be: - gastritis - errosions – preulcers - ulcers (peptic ulcer disease, PUD)
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Picture of Gastrointestinal Tract
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Stomach errosion
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Stomach errosion
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Acid/Peptic Disease Sometimes the stomach acid is refluxed into the esophagus Gastro Esophageal Reflux Disease (GERD)
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Acid/Peptic Disease If GERD is severe enough, it can change the lining of the esophagus: - esophagitis - errosions - strictures - Barrett’s Esophagitis – precancerous
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Esophageal Stricture
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Acid/Peptic Disease Sometimes excess stomach acid production can lead to ulcers of the duodenum as well
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Gastrointestinal tract (GI tract)
Mouth: Internal: nonkeratinized stratified squamous epithelium Middle: buccinator muscles, bone
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2. pharynx: skeletal muscle; nonkeratinized stratified squamous epithelium
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3. esophagus: a. nonkeratinized stratified squamous epithelium b. skeletal (superior); smooth muscle (inferior)
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4. esophagus to anal canal Deep to superficial
Mucosa Epithelium: touches food Nsse – protection Simple columnar (stomach/intestines)– secretion/absorption exocrine cells (mucus) endocrine cells (hormones) Lamina propria (conn.)- blood/lymph vessels Smooth muscle – makes folds
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Submucosa Binds mucosa to muscularis Blood/lymph vessels/neurons
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Muscularis Skeletal muscle until middle esophagus (swallowing); external anal sphincter Smooth muscle Inner: circular fibers Outer: longitudinal fibers
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Serosa: connective and simple squamous epithelium (reduce friction)
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ACCESSORY ORGANS
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pancreas Small clusters of glandular epithelial
99%: called acini (exocrine function – secrete pancreatic juice for digestion) 1%: called pancreatic islets (endocrine function)
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liver Consists of many lobules
Contains epithelial cells called hepatocytes arranged irregularly around a central vein. Capillaries, called sinusoids, are highly present and contain fixed phagocytes (to removed WBCs and RBC, bacteria, etc)
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gallbladder Mucosa is simple columnar epithelium
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