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What are the two main groups of the Digestion system?
- Alimentary Canal
- Accessory Digestive organs
What is the function of the alimentary canal?
- Digest- Break down food to smaller fragments
- Absorb fragmented food into the blood
What organs are included in the alimentary canal?
Mouth, pharynx, esophagus, stomach, sm intestines, lg intestines, anus
What is the function of the accessory digestive organs?
Aid in digestion
What are the accessory digestive organs?
teth, tongue, gall bladder, salivary glands, pancreas
What are the 5 Digestive processes?
- Mechanical Digestion
- Chemical Digestion
What is Ingestion?
taking food into the digestive tract, via mouth
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
What is Mechanical digestion?
- prepares food for chemical digestion
- Chewing, mixing fodo with saliva, churning food in stomach, segmentation
What is Segmentation?
Mixes food with digestive juices, increases rate of absoprtion
What is Chemical digestion?
a series of processes that break down foods by enzymes secrete in the alimentary canals
What is absoprtion?
Absoption of vitamins, minerals, and water from the alimentary canal to blood, mainly in the sm. intestine
What is defecation?
elimination of indeigestible substances from the body
What is included in Splancnic Circulation?
- The Celiac Trunk
- Mesenteric Vessels
What is the Splancnic Circuit?
arteries that branch off of the celiac trunk to serve digestive organs and the hepatic portal circulation
What is Hepatic Portal Circulation?
collects nutrient rich venous blood from digesive organs and brings it to the liver which collects and stores nutrients
What are the 4 tunics of the alimentary canal?
- Muscularis Externa
- Serosa (adventitia)
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
What makes up the submucosa
Areolar CT, containg capillaries, lyphatic vessels, lymphatic follicles and nerve fibers
What is the Muscularis Externa responsible for?
segmentation, peristalsis and forms sphincters
What is the Serosa?
What is the Parasympathetics affect on Gi activity? Parasympathetic?
What is the function of the mouth?
What is the function of the teeth?
What is the function of the tongue?
Create Bolus, compacted food
What doe the intrinsic and extrinsic muscles of the tongue do?
- Intrinsic- change shape of tongue
- Extrinsic- move tongue forward, side to side
What are the 3 salivary glands?
Parotid, submandibular, sublingual
Which Salivary glands are intrinsic?
What is the extrinsic salivary gland?
What is the compostion of saliva/
What defenses does the saliva contain?
- Ig A
- Lysozyme-antibacterial enzyme
- cyanid compound
- Amylase- breaks down startch
What is the purpose of the pharynx
Food passes through the oropharynx and laryngopharynx
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
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
Where is the swallowing center located?
What is Barett's esophagus?
when stomach juices reach the esophagus causes a change in the epithelium
What is the function of the stomach?
initiates Chemical breakdown of Protein
What is the mucosa of the stomach made of?
- Simple columnar epithelium with goblet cells
- Gastric pits > Gastric Glands
What movement occurs in the stomach?
What do Gastric pits contain?
Gastric Glands which secret gastric juices
What are the cells of the gastric glands?
- Mucous neck Cells
- Parietal (Oxyntic) cells
- Chief (zymogenic) cells
- Enteroendocrine cells
What do Mucous neck cells produce?
What do Parietal (Oxyntic) cells produce?
- HCl and intrinsic factor
- HCl causes stomach's acidity
- Intrinsic factor- glycoprotein needed to absorb B-12
What do Chief Cells produce?
- Pepsinogen (inactive pepsin), which is activated by HCl
- Pepsin is a protein digesting enzyme
What do Enteroendocrine Cells produce?
- Histamine and Serotonin- act locally as paracrines
- Somatostatin- influences other digestive organs
- Gastrin- Stimulates HCl release
What are the 3 phases of regulation of gastric secretion?
What occurs during Cephalic phase?
- Occurs before food enters the stomach
- Activated by sight/smell/thought of food
- Stimulates the stomach to start secretions
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
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
What is HCl production stimulated by?
What is the alkaline tide?
Blood leaving the stomach is more alkaline due to the stomach taking most of the HCl from the blood
What are the two componenets of the Intestinal phase?
Excitatory and Inhibitory
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
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
What are enterogastrones?
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
How long does it take for the stomach is empty?
What are the plicae circularis?
folds of the mucosa and submucosa, causing food to spiral, dealrying transit time and mixing fodo with digestive enzymes
What are villi?
- Finger- like rojections that absob fatty acids and monoglycerides.
- They contain Cripts of Lieberkuhn, which secrete intestinal juice
What are microvillia
- projections that line the villia
- Contain Brush Border Enzymes, They absorb disaccharides, carbs, paptidases and protein
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
What is the liver's digestive function?
To produce Bile
What doe the bile salts travel in?
Enterohepatic Circulation, they are not eliminated, but recycled
What do bile salts do?
- Emulsify fats
- facilitate fate and cholesterol absorption
- solubize cholesteral contained in bile
What are Bile pigments?
Bilirubin converts to urobilinogen and sterocobilinogen
What is the anatomy of a liver lobule?
- It is hexagonal
- Plates of hepatocytes
- Kupffer cells
What are hepatocytes?
liver plates, they make lines on the inside of the liver lobule
What is located in the center of the liver lobule?
A Central Vein
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
What is a liver sinusoid on a hepatocyte?
bring blood from the triad to the central vein
What is the function of Kupffer cells?
remove Debris from the blood
What is the function of the Gall Bladder?
Stores and concentrates bile
What stimulates contraction of the gall bladder?
- CCK: released by intestines when food enters duodenum, stimulates pancrease and relaxes sphincter of oddi
What is the anatomy of the pancreas?
- Head, body, tail
- Hepatopancreatic duct
What is the pH of pancreatic juice and why?
8.0, to neutralize the acidic chyme in the duodenum
Describe pancreatic enzymes
They are inactive in the pancreas and are activated by duodenal enterokinases in the duodenum
What regulates pancreatic secretions?
- CCK- Stimulates pancreatic secretions
- Secretin- stimulated in response to HCl in intestines, targest cells to secrete HCO3-
What is the acidic tide?
When the alkaline tide of the stomach becomes neutralized near the pancrease
What is the movment of the Sm. Intestine?
What is the gastroileal reflex?
Enhances segmentation of the ileum so food reaches the ileocecal valve
How does Gastrin affect the ileocecal valve?
secreted by the stomach it increases the ileum's motility and relaxes the sphincter
What is the function of the Lg Intestine
Absorb water from indigestible foods and then to eliminate them
What is the function of bacterial flora?
- Ferment indigestible Carbs, which creates gas
- Synthesize B and K vitamins
What is the movemtn of the Large intestine?
- Slow, short lived peristatlic contractions
- Haustral contractions
- mass movments
Describe Haustral Contractions
slow segmenting movements that occur every 30 minutes
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
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