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What are the two main groups of the Digestion system?
- Alimentary Canal
- Accessory Digestive organs
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What is the function of the alimentary canal?
- Digest- Break down food to smaller fragments
- Absorb fragmented food into the blood
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What organs are included in the alimentary canal?
Mouth, pharynx, esophagus, stomach, sm intestines, lg intestines, anus
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What is the function of the accessory digestive organs?
Aid in digestion
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What are the accessory digestive organs?
teth, tongue, gall bladder, salivary glands, pancreas
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What are the 5 Digestive processes?
- Ingestion
- Propulsion
- Mechanical Digestion
- Chemical Digestion
- Absorption
- Defecation
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What is Ingestion?
taking food into the digestive tract, via mouth
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What is propulsion
- moving food through the alimentary canal
- Swallowing- Voluntary
- Peristalsis- IV, contracts and relaxe muscles in the walls to push food through the canal
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What is Mechanical digestion?
- prepares food for chemical digestion
- Chewing, mixing fodo with saliva, churning food in stomach, segmentation
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What is Segmentation?
Mixes food with digestive juices, increases rate of absoprtion
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What is Chemical digestion?
a series of processes that break down foods by enzymes secrete in the alimentary canals
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What is absoprtion?
Absoption of vitamins, minerals, and water from the alimentary canal to blood, mainly in the sm. intestine
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What is defecation?
elimination of indeigestible substances from the body
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What is included in Splancnic Circulation?
- The Celiac Trunk
- Mesenteric Vessels
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What is the Splancnic Circuit?
arteries that branch off of the celiac trunk to serve digestive organs and the hepatic portal circulation
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What is Hepatic Portal Circulation?
collects nutrient rich venous blood from digesive organs and brings it to the liver which collects and stores nutrients
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What are the 4 tunics of the alimentary canal?
- Mucosa
- Submucosa
- Muscularis Externa
- Serosa (adventitia)
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What is the function of the mucosa layer?
- Secrete mucus, digestive enzymes and hormons
- Absorb nutrients into blood
- Protect agains infection
- Made of Simple Columnar Epithelium
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What makes up the submucosa
Areolar CT, containg capillaries, lyphatic vessels, lymphatic follicles and nerve fibers
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What is the Muscularis Externa responsible for?
segmentation, peristalsis and forms sphincters
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What is the Serosa?
Visceral peritoneum
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What is the Parasympathetics affect on Gi activity? Parasympathetic?
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What is the function of the mouth?
Food ingestion
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What is the function of the teeth?
Masstication
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What is the function of the tongue?
Create Bolus, compacted food
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What doe the intrinsic and extrinsic muscles of the tongue do?
- Intrinsic- change shape of tongue
- Extrinsic- move tongue forward, side to side
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What are the 3 salivary glands?
Parotid, submandibular, sublingual
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Which Salivary glands are intrinsic?
Submandibular, sublingual
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What is the extrinsic salivary gland?
parotid gland
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What is the compostion of saliva/
97-99.5% water
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What defenses does the saliva contain?
- Ig A
- Lysozyme-antibacterial enzyme
- cyanid compound
- defensins
- Amylase- breaks down startch
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What is the purpose of the pharynx
Food passes through the oropharynx and laryngopharynx
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What is the purpose of the esophagus?
Pierces the diaphragm at the esophageal hiatus to join the stomach at the cardiac orific which is surrounded by the gastroesophageal sphincter
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What are the two phases of Deglutiiton (Swallowing)?
- Buccal Phase- voluntary, bolus is pushed into pharynx
- Pharyngeal Esophageal phase- Pharynx and esophagus, food is moved by peristalsis
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Where is the swallowing center located?
Pans/Medulla Oblongata
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What is Barett's esophagus?
when stomach juices reach the esophagus causes a change in the epithelium
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What is the function of the stomach?
initiates Chemical breakdown of Protein
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What is the mucosa of the stomach made of?
- Simple columnar epithelium with goblet cells
- Gastric pits > Gastric Glands
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What movement occurs in the stomach?
Segmentation
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What do Gastric pits contain?
Gastric Glands which secret gastric juices
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What are the cells of the gastric glands?
- Mucous neck Cells
- Parietal (Oxyntic) cells
- Chief (zymogenic) cells
- Enteroendocrine cells
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What do Mucous neck cells produce?
Avidic mucous
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What do Parietal (Oxyntic) cells produce?
- HCl and intrinsic factor
- HCl causes stomach's acidity
- Intrinsic factor- glycoprotein needed to absorb B-12
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What do Chief Cells produce?
- Pepsinogen (inactive pepsin), which is activated by HCl
- Pepsin is a protein digesting enzyme
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What do Enteroendocrine Cells produce?
- Histamine and Serotonin- act locally as paracrines
- Somatostatin- influences other digestive organs
- Gastrin- Stimulates HCl release
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What are the 3 phases of regulation of gastric secretion?
- Cephalic
- Gastric
- Intestinal
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What occurs during Cephalic phase?
- Occurs before food enters the stomach
- Activated by sight/smell/thought of food
- Stimulates the stomach to start secretions
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What occurs during the gastric phase?
- As food enters stomach, stretch receptors are stiulated, causes stomach glands to secrete
- Stimuli are Distension, peptides, low acidity
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What is the chemical stimulai for the Gastric Phase?
- Provided by caffeine, rising pH, partially digested proteins.
- Causes rise in pH > gastrin release > stimulate HCl > provides acidic condition
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What is HCl production stimulated by?
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What is the alkaline tide?
Blood leaving the stomach is more alkaline due to the stomach taking most of the HCl from the blood
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What are the two componenets of the Intestinal phase?
Excitatory and Inhibitory
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What occurs during the excitatory phase of the Intestinal phase?
- It's brief
- As partially digested food fills the Duodenum, Enteric gastrin is secreted to push food into the duodenum from the stomach
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What occurs during the inhibitory phases of the Intestinal phase?
- aka, enterogastric reflex
- When duodenum is filled with chyme, enterogastrones are released and they decrease gastric secretions and motility
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What are enterogastrones?
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What are the pacemakers of gastric motility?
Set the rhythm for the stomachs movements. Called cells of Cajal, AP is sent out 3x per minute
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How long does it take for the stomach is empty?
3-4 hours
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What are the plicae circularis?
folds of the mucosa and submucosa, causing food to spiral, dealrying transit time and mixing fodo with digestive enzymes
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What are villi?
- Finger- like rojections that absob fatty acids and monoglycerides.
- They contain Cripts of Lieberkuhn, which secrete intestinal juice
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What are microvillia
- projections that line the villia
- Contain Brush Border Enzymes, They absorb disaccharides, carbs, paptidases and protein
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What is the submucosa of the small intestine
- Ileum: Peyer's patches- prevent bacteria from entering the blood stream
- Duodenum: Brunner's Glands- secrete HCO3- mucus to neutralize acidic chyme from stomach
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What is the liver's digestive function?
To produce Bile
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What doe the bile salts travel in?
Enterohepatic Circulation, they are not eliminated, but recycled
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What do bile salts do?
- Emulsify fats
- facilitate fate and cholesterol absorption
- solubize cholesteral contained in bile
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What are Bile pigments?
Bilirubin converts to urobilinogen and sterocobilinogen
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What is the anatomy of a liver lobule?
- It is hexagonal
- Plates of hepatocytes
- Sinusoids
- Kupffer cells
- Triad
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What are hepatocytes?
liver plates, they make lines on the inside of the liver lobule
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What is located in the center of the liver lobule?
A Central Vein
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What is located on each corner of a liver lobule?
- A portal Triad:
- hepatic artery- supplies O2
- Hepatic Portal Vein- Venous blood with nutrients
- Bile Duct
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What is a liver sinusoid on a hepatocyte?
bring blood from the triad to the central vein
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What is the function of Kupffer cells?
remove Debris from the blood
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What is the function of the Gall Bladder?
Stores and concentrates bile
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What stimulates contraction of the gall bladder?
- Parasympathetic
- CCK: released by intestines when food enters duodenum, stimulates pancrease and relaxes sphincter of oddi
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What is the anatomy of the pancreas?
- Head, body, tail
- Hepatopancreatic duct
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What is the pH of pancreatic juice and why?
8.0, to neutralize the acidic chyme in the duodenum
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Describe pancreatic enzymes
They are inactive in the pancreas and are activated by duodenal enterokinases in the duodenum
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What regulates pancreatic secretions?
- Parasympathetic
- CCK- Stimulates pancreatic secretions
- Secretin- stimulated in response to HCl in intestines, targest cells to secrete HCO3-
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What is the acidic tide?
When the alkaline tide of the stomach becomes neutralized near the pancrease
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What is the movment of the Sm. Intestine?
Segmentation
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What is the gastroileal reflex?
Enhances segmentation of the ileum so food reaches the ileocecal valve
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How does Gastrin affect the ileocecal valve?
secreted by the stomach it increases the ileum's motility and relaxes the sphincter
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What is the function of the Lg Intestine
Absorb water from indigestible foods and then to eliminate them
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What is the function of bacterial flora?
- Ferment indigestible Carbs, which creates gas
- Synthesize B and K vitamins
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What is the movemtn of the Large intestine?
- Slow, short lived peristatlic contractions
- Haustral contractions
- mass movments
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Describe Haustral Contractions
slow segmenting movements that occur every 30 minutes
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Describe Mass movements
- long, slow powerful contractions that push feces into the rectum, occurs 3-4x per day right after a meal
- aka gastrocolic reflex
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Describe the defecation reflex
distension of the rectum sends an impulse to the CNS, which contracts the rectal walls, and relaxes the internal rectal sphincter
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