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What are glands?
Specialized epithelial cells designed to produce secretory products
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What are some types of glands in the GI tract?
- Simple surfae glands
- Tubular glands
- complex tubular and acinar glands
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Name some stimuli that promote secretion in the GI tract
- Presence of food in the GI tract
- Chemical irritation
- Distention of the gut wall
- Enteric nervous system stimulation
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How does the ANS affect secretion?
- Parasympathetics - Increase
- Sympathetics - Decrease
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How does the Enteric Nervous System affect GI secretion?
- Controls secretory function at local level without higher CNS input
- Sensory nerves of the ENS promote reflexive increase in mucus, digestive enzymes and hormone secretion
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What are the three basic stimuli that excite sensory nerves of the ENS?
- Mechanical stimulation/presence of food
- Chemical irritation in the gut
- Distention of the gut wall
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Parasmpathetics control what?
Primarily controls secretion from salivary, esophageal, gastric, duodenal, pancreatic and distal colon glands
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Sympathetics control what?
- Decreased pancreatic secretion, decreased blood flow to GI tract
- Increase in salivary secretion
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What are the two main types of GI secretions?
- Serous - composed of mainly water and electrolytes
- Protein (mucus) - composed of enzymes for nutrient digestion and mucus
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What are two types of secretions?
- Primary secretions - initial secretory product developed by acinar cells
- Secondary secretions - Primary secretory product is modified by cells that line the ducts of the glands
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What is mucus?
- Major secretory product that is secreted in all portions of the GI tract
- Composed of water, electrolytes, and glycoproteins
- The chemical properties of mucus allows it to serve as a protectant and lubricant within the GI tract
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What are two main important properties of mucus?
- "Stickiness" allows it to adhere to food particles and to the lining cells of the GI tract
- Coats the GI wall and serves as a protectant
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Name 3 types of salivary glands
- Parotid gland
- Submandibular gland
- Sublingual gland
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What are some functions of saliva?
- Lubricate food and maintain neutral pH
- Amylase enzyme to begin digestion of carbohydrates
- Protects mucosa of the oral cavity
- Aids in taste, speech, and prevention of oral infections
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What are the main components of primary secretions?
Water, electrolytes, and ptyalin as an isotonic solution
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What is the main function of secondary secretion?
Reabsorption of NaCl from the ducts and addition of K+ and HCO3- into the ducts
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What are some stimulators of saliva production?
- Taste stimuli
- Tactile stimuli in the oral cavity
- Smell of food
- Stomach irritation
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Name the gastric glands and what they release
- Mucus/HCO3 - mucous neck cells
- HCl (acd) - parietal cells
- Intrinsic factor - parietal cells
- Pepsinogen % lipase - chief cells
- Gastrin - G cells
- Somatostatin - D cells
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What does HCl create a low pH for?
- Conversion of pepsinogen to pepsin
- Enhanced protein digestion
- Preventing bacterial growth
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What does pepsinogen do?
When converted to pepsin, aids in protein digestion
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What is Intrinsic Factor for?
Necessary for Vitamin B12 absorption in the ileum
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What does the hormone Gastrin do?
- Stimulates acid secretion
- Gastric distention
- Presence of protein digestion products
- Parasympathetic stimulation (vagus nerve)
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Histatime does what?
- Increase acid secretion
- Local inflammation
- Parasympathetic stimulation
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Somatostatin (hormone) is in charge of what?
Inhibits gastrin and acid secretion
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Acetylcholine from ENS stimulates what?
Acid secretion
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what does the parasympathetic nervous system stimulate?
Enteric neuron activity, and secretion of acid, gastrin, histamine, pepsinogen
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Gastrin and Histamine increase what?
H+
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Somatostatin inhibits what?
Gastrin and H+
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What is the Cephalic phase?
- Sight, smell, taste or thought of food activates vagal reflex
- Stimulates secretion of acid, gastrin and pepsinogen
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What is the Gastric phase?
- Food entering the stomach stimulates vagus nerve and ENS
- Stimulates acid & gastrin secretion
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What is the Intestinal phase?
- Presence of food ain the duodenum stimulates release of:
- Somatostatin, Cholecstokinin, secretin, gastric inhibitory peptide
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Small intestine mainly secretes what?
mucus, water, and electrolytes (Cl-, HCO3-)
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What else does the intestinal mucosa secrete?
Secretin and CCK
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Local mechanisms of the ENS control what?
Intestinal secretions
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Large intestine mainly secretes what?
mucus, HCO3-, under local enteric control
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What are the Islets of Langerhands in charge of?
- Insulin, Somatostatin, Glucagon
- Control of blood glucose levels and energy production from carbohydrates
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What is the exocrine function of the pancreas?
- Secretion fo water, electrolytes
- Lipases
- Pancreatic amylase
- Proteases (trypsin, secreted as trypsinogen)
- DNase, RNase
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How do parasympathetics affect pancreatic secretion?
Stimulate exocrine secretion via enteric neurons
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How do sympathetics afect pancreatic secretion?
- Inhibit exocrine secretion via enteric neurons
- Also reduces blood flow
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What are some hormonal controls of pancreatic secretion?
- Secretin - Stimulate water and bicarbonate release
- CCK - Stimulates secretion fo digestive enzymes
- Pancreatic polypeptide - inhibits secretion of digestive enzymes (negative feedback)
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What is the Cephalic phase of Pancreatic Secretion?
Sight, smell, taste of food stimulates pancreate exocrine secretion
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What is the Gastric Phase of Pancreatic Secretion?
Gastric distention stimualtes pancreatic exocrine secretion
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What is the Intestinal Phase of Pancreatic Secretion?
- Small intestine distention, presence of food products stimulate pancreatic exocrine secretion
- CCK and secretin also responsible for secretion of pancreatic digestive enzymes
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What is Bile?
- Necessary for digestion of lipids
- Synthysized in liver, stored in gall bladder
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What does bile contain?
- Bile acids (salts)
- Bile pigments (bilirubin)
- Cholesterol & phospholipids
- Ions & water
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Where do most absorbed fats go through?
Lymphatics to reach the circulation
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What does the Gall Bladder do?
- Stores bile produced in the liver
- Concentrates organic component of bile by removing water and ions
- Contracts to eject bile into the duodenum (through the sphincter of Oddi)(CCK stimulates contraction)
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What are some facts about the Biliary System?
- Bile acids/salts are re-circulated to the liver for re-use
- Bile is absorbed in the ileum
- Moves through the portal circulation to reach the liver
- Bile acids are easily recycled and prevent excess demand for newly synthesized bile
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What does the presence of a bolus stimulate?
- Gastro colic reflex
- H+, gastrin, histamine, mucus, HCO3-, intrinsic factor
- Stimulation of pancreatic secretions
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Describe Gastric Emptying
- Stimulates Duodenal secretions (secretin, CCK)
- Stimulates pancreatic secretion (digestive enzymes)
- Stimulates bile release (gall bladder)
- Inhibits gastric motility and emptying
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How often does the gastric and intestinal tract contract?
Every 90 min to "clean out"
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