Digestive System
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258 Terms
Digestive systme consists of…
GI tract (essentially a tube) and three accessory digestive organs.
The three accessory digestive organs
Salivary glands, liver, and pancreas.
The GI tract (tube) consists of the following anatomical parts
Esophagus, stomach, small intestine, large intestine, rectum, and anus.
The GI tract… and … breaks down food.
Mechanically and chemically
The broken down food by GI tract can be absorbed through…
The intestinal wall and transported by the blood and lymph for the cells of tthe body.
Liver releases…
Bile into the small intestine.
Pancreas release…
Pancreatic enzymes into the small intestine.
… and … provide unidirectional movement of food.
Pyloric and ileocecal sphincters
There are … of salivary glands
3 pairs
Salivart glands are…
Compound tubuloalveolar glands.
Salivary glands contain…
Serous/mucous cells
Saliva pH
7
… move food through the esophagus.
Peristaltic contractions
Stomach turns food into…
Chyme, secretes HCl and pepsinogen.
The mucosa of stomach has…
Gastric folds, gastric pits and gastric glands.
ONLY… undergo PARTIAL digestion
Proteins
Stomach pH
1-1.5
Small intestine
Main site of digestion and absoprtion.
Small intetsine is characterized by…
Great length, great surface area plicae, villi, and microvilli on the epithelial cells.
Substances for small intestines are absorbed into…
The blood and into the central lacteal.
Small intestine pH
8
Motility
One way food movement
Secretion
Exocrine and Endocrine
Digestion
Breakdown into smaller subunits
Absorption
Passage of end products into the blood/lymph
Elimination
Defecation
ANS innervates…
The entire GI tract
Saliva pH
7
Stomach pH
1.5
Small intestine pH
8
Histology of the Digestive Tract
Mucosa
Squamous Epithelium
Mucosal Folds
Exocrine Glands
Villi
Muscularis Mucosae
Squamous Epithelium
Cells are shed and replaced every 2-3 days
Histology of the Digestive Tract
Submucose
Submucosal plexus
Ganglions - part of the enteric system
Histology of the Digestive Tract
Muscularis Externa
Circular inner
Longitudinal outer
Myenteric plexus (ganglions Auerbach plexus)
Histology of the Digestive Tract
Serosa/Adventia
Food enters the…through…
Alimnetary tract through the mouth
Mouth resists the…
Abrasion by food fragments
The tongue is…
Mucosa-covered skeletal muscle
There are three pairs of salivary glands
Parotid gland
Submandibular gland
Sublingual gland
Salivary glands are compound…
Tubuloalveolar glands
Salivary glands contain…
Serous/mucous cells
Saliva rate
1500ml/24 hrs
Salivary secretion
0.5 ml/min (base rate)
Can increase by 10 times - 5mL/min (sucking on a lemon)
Salivary secretion is regulated by…
The salivary center in the medulla oblongata
Saliva is also important for…
Speech articulation and in dental health
Saliva production is under control of…
Parasympathetic nervous system
Saliva is chracterized by…
Low Osmotic pressure
< 300 mOsm
Saliva composition
Water
95%
Saliva composition
Electrolytes
Na+ > Cl- > HCO3- > K+
Saliva composition
Proteins
Salivary alpha-amylase (ptyalin) enzyme
Mucin
Salivary alpha-amylase (ptyalin) enzyme produced by…
Parotid glands
Mucin produced by…
Sublingual and submandibular glands responsible for viscosity
Saliva composition
Antimicrobial agents
IgA
Lysozyme
Lactoferrin
Proline
Lysozyme
Enzyme destroys some bacteria (Staphylycoccus)
Lactoferrin
Iron binding protein-inhibits microbial growth
Proline
Rich proteins
Add in tooth enamel formation/antimicrobial effects
Saliva composition
Other agents
Epidermal growth factor
Blood group substances
Saliva Composition
Wastes
Urea
Uric Acid
Salivary amylase starts the process of…
Polysaccharides digestion
Salivary amylase breaks starch into…
Molecules of dissaccharide maltose
Maltose
A carbohydrate formed from two molecules of glucose
In the stomach, salivary amylase is inactivated by…
The low pH
pH=1
It is not clear if…
There is any role for amylase in vivo
An alternative explanation
Amylase helps to “keep the mouth clean”
Swallowing center inhibits…
Respiratory center
Uvula elevates to…
Orevent food from entering nasal passages
Position of the tongue prevents…
Food from entering the mouth
Epiglottis is pressed over…
Closed glottis to prevent food entering airways
Swallowing
Oral phase
The tongue forms a food bolus and pushes it into the laryngopharynx
Swallowing
Pharyngeal phase
The palate, tongue, vocal cords, and epiglottis block the oral and nasal cavities and airway while pharyngeal constrictors push the bolus into the esophagus
Esophagus
Peristaltic contractions move food into the stomach
Esophagus length
25cm long
Upper 1/3 of esophagus
Skeletal muscles
Middle 1/3 of esophagus
Skeletal + Smooth muscles
Last 1/3 of esophagus
Smooth muscles
Upper Esophageal Sphincter
Prevents air entrance to the esophagus
Bolus movement
2-4 cm/s
Traverses the esophagus in 6-10 seconds
Esophagus pressure
> 100 mmHg
Bolus passes through…
The lower esophageal sphincter
Sphincter tone is regulated by…
Ach, nitric oxide (NO), and vasoactive intestinal peptide
Mechanism of Peristalsis
Contraction of…
Circular muscle behind bolus
Mechanism of Peristalsis
Contraction of…
Longitudinal muscles ahead of bolus
Mechanism of Peristalsis
Contraction of …
Circular muscle-propel bolus
Mechanism of Peristalsis
First pressure wave
Primary peristalsis
Mechanism of Peristalsis
Repetitive waves
Secondary peristalsis
Stomach turns…
Food into chyme
Stomach secretes…
HCl and Pepsinogen.
Mucosa of stomach has…
Gastric folds, gastric pits, and gastric glands.
ONLY… undergo … digestion
ONLY Proteins undergo Partial digestion
Stomach has a … structure
Distensible structure
Relaxation mediated by vagal nerves - Ach, NO, and VIP
Stomach stores…
Food (1.5L)
Stomach ONLY initiates…
Protein digestion
Stomach kills…
Bacteria
Stomach moves food into…
The small intestine
Gastric secretion from the gastric pits
1500 mL/hour
Goblet cells
Mucus (alkaline)
Parietal cells
HCl (Ach, gastrin, histamine-stimuli)
Chief cells
Pepsinogen (Ach, gastrin, histamine - stimuli)
Argentaffin cells
Serotonin, Histamine - stimuli for parietal cells/chief cells
G-cells
Gastrin (stimuli for parietal cells/chief cells)