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The process of breaking down food groups into molecules that are small enough to be utilized by the cells of the body
Digestion
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Overview of GI tract Functions:
Mouth---bite, chew, swallow
Ingestion
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Overview of GI tract Functions:
Pharynx and esophagus
Propulsion
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Overview of GI tract Functions:
Stomach
- -mechanical & chemical disruption
- -absorption of water & alcohol
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Overview of GI tract Functions:
absorbs electrolytes & vitamins (B and K)
Large intestine
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Overview of GI tract Function
--defecation
Rectum & Anus
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Where is the peritoneum serous membrane found?
abdominal cavity
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Covers organs
Visceral layer of peritoneum
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Lines the walls of body cavity
Parietal layer of Peritoneum
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Potential space containing a bit of serous fluid
Peritoneal cavity
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What are the 4 layers of the GI Tract?
- 1. Mucosal layer- epithelium, lamina propria and muscularis mucosa
- 2. Submucosal layer- connective tissue and submucosal plexus
- 3. Muscularis layer- smooth muscle and myenteric plexus
- 4. Serosa layer –visceral peritoneu
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Contains buccinator muscle that keeps food between upper & lower teeth
Lips & Cheeks
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Area between cheeks and teeth
Vestibule
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-the roof = hard, soft palate and uvula
-the floor= the tongue
Oral cavity proper
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Pharyngeal Arches consists of __ muscles
2
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– extends from palate to tongue
– forms the first arch
– posterior limit of the mouth
Palatoglossal arch
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– extends from palate to pharyngeal wall
– forms the second arch
– between: palatine tonsil
Palatopharyngeal arch
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• Parotid below your ear and over the masseter
• Submandibular is under lower edge of mandible
• Sublingual is deep to the tongue in floor of mouth
• All have ducts that empty into the oral cavity
Salivary Glands
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•Wet food for easier swallowing
• Dissolves food for activation of taste receptors
• Bicarbonate ions buffer acidic foods
Saliva
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Chemical digestion of starch begins with _______ (salivary amylase) and _____ (lingual lipase)
enzyme; fats
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Composition & Functions of Saliva:
Helps destroy bacteria
Enzyme (lysozyme)
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Protects mouth from infection with its rinsing action---1 to 1.5 l/day
Saliva
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What are the 5 structures of a tooth?
- • Crown
- • Neck
- • Roots
- • Pulp cavity (contains connective tissue, blood vessels, nerves and lymphatic vessels)
- • Root canal
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Composition of Teeth:
– hardest substance in body
– rich in calcium salts (calcium phosphate and carbonate)
Enamel
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Composition of Teeth:
– calcified connective tissue (harder than bone-more calcium salts)
Dentin
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Composition of Teeth:
– bone-like
– periodontal ligament (fibrous connective tissue) connects cementum to bone socket
Cementum
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Dentition:
– 20 teeth that start erupting at 6 months
– 1 new pair of teeth per month
Primary or baby teeth
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Dentition:
– 32 teeth that erupt between 6 and 12 years of age
– differing structures indicate function
Permanent teeth
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What teeth for:
for biting
Incisors
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What teeth for:
Tearing
Canines or cuspids
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What teeth for:
Crushing & grinding food
Premolars & molars
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What teeth:
Third set of molars may impact (no room)
Wisdom teeth
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-Funnel-shaped tube extending from internal nares to the esophagus (posteriorly) and larynx (anteriorly)
-Skeletal muscle lined by mucous membran
Pharynx
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Deglutition or swallowing is facilitated by _____ and ______
saliva; mucus
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Physiology of the Esophagus - Swallowing
--tongue pushes food to back of oral cavity
Voluntary phase
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Physiology of the Esophagus - Swallowing
---pharyngeal stage
Voluntary phase
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– 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 lifte
Involuntary phase----pharyngeal stage
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• Collapsed muscular tube
• In front of vertebrae
• Posterior to trachea
• Posterior to the heart
• Pierces the diaphragm at hiatus
Esophagus
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Histology of the Esophagus
Mucosa is composed of which type of tissue?
stratified squamous cells
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Histology of the Esophagus
large mucous glands
Submucosa
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Histology of the Esophagus
Upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth
Muscularis
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Upper esophageal sphincter prominent circular muscle, lower sphincter is narrowing of lumen, physiological
Muscularis
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Histology of the Esophagus:
connective tissue blending with surrounding connective tissue--no peritoneum
Adventitia
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Size of the stomach when empty
Large sausage
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Stomach stretches due to _______
Rugae
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What are the 3 parts of the stomach?
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Which part of the stomach starts to narrow as approaches pyloric sphincter
pylorus
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Empties as small squirts of ________leave the stomach through the pyloric valv
chyme
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Secrete pepsinogen and gastric lipase (fat digestion)
Chief (zymogenic) cells
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Secrete HCL –converts pepsinogen to pepsin (protein digestion) and intrinsic factor- absorption of vitamin B12 for RBC production
Parietal cells
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Secrete Gastrin hormone (g cell)- release more gastric juice, increase gastric motility, relax pyloric sphincter, constrict esophageal sphincter preventing entry
G cells
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Three layers of smooth muscle--outer longitudinal, middle circular & inner oblique
Muscularis
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Permits greater churning & mixing of food with gastric juice
Muscularis
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Chemical Digestion:
– HCl denatures (unfolds) protein molecules
– HCl transforms pepsinogen into pepsin that breaks peptides bonds between certain amino acid
Protein digestion begins
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Chemical Digestion:
– gastric lipase splits the triglycerides in milk fat
Fat digestion continues
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Chemical Digestion:
Kills microbes in food
HCl
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Protect stomach walls from being digested with 1-3mm thick layer of mucous (aspirin inhibits mucous formation)
Mucous cells
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What is absorbed by the stomach?
- • Some water
- • Electrolytes
- • Some drugs (especially aspirin) & alcohol
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3 meters long----2.5cm in diameter
Large surface area for majority of absorption
Small Intestine
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What are the 3 parts of the small intestine?
- – duodenum
- – jejunum
- – ileum (ends at ileocecal valve)
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