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67 Cards in this Set

  • Front
  • Back
What is the structure of the GI tract musculature and , from superficial to deep?
Muscularis externa
What two layers compose the muscularis externa and what are their functions?
Outer longitudinal muscle; shortens length of the tube

Inner circular muscle; squeezes things through
What's another name for the parietal peritoneum?
serosa which is superficial to the muscularis externa
What is the submucosa?
A relatively thick layer of connective tissue deep to the muscularis externa
What function does mesentery serve?
Acts as a conduit for blood vessels, nerves, and lymphatic vessels
What are the two types of motility movements and what are they called?
Propulsive is peristalsis

Mixing is segmentation contractions
What are the major movements in the gut and what do they do?
Segmentation Contractions; they move intermittently to chop up and mix its contents
What do carbs have to be broken down into to be absorbed?
What breaks down Polysaccharides?
What steps do proteins go through during digestion?
The amino acid chains are broken into peptide fragments which are broken down by aminopeptidase into their constituent amino acids
What is a triglyceride?
Three fatty acids on a sugar backbone
Where does digestion start?
In the mouth
What secretions are found in the mouth and what are their functions?
Amylase - breaks down carbs


Lysozyme - breaks down bacterial cell walls
What type of muscle contraction is swallowing? What aids it and how?
Peristalsis. Mucus; by providing lubrication
What secretions are there in the stomach? What type of digestion occurs?
Intrinsic factor

Carb continues, protein begins
What are the pancreatic digestive enzymes?
What kind of motility is there in the small intestine? What are the secretions?

Mucus, pancreatic, and liver (bile)
What kind of motility does the large intestine have? What does it absorb?
Mass movements

Salt & water
What are the 3 non-digestive functions of the GI tract?

fluid/electrolyte balance (Small Intestine reabsorbs up to 9-11 liters/day)

What is GALT?
Gut Associated Lymph

Lymphocytes and mast cells located in between
epithelial cells and in the lamina Propria (underlying connective tissue)
Where does everything absorbed in the gut go and why?
To the Kupffer cells of the liver; so that they can phagocytize any pathogens
What is the enteric nervous system?
Postganglionic fibers of the parasympathetic
nervous system that innervate the gut (extension of ParaNS)

Has the same # of nerves as spinal cord
What are the two major networks of the ENS?
Myenteric Plexus

Submucosal Plexus
Where is the Myenteric Plexus located and what does it do?
Between the inner and outer muscles; it controls motility
Where is the submucosal plexus and what does it do? What does it influence indirectly and how? What kind of neurons does it contain?
Deep to the muscles; controls secretion & absorption

It also indirectly influences motility by stimulating or inhibiting the myenteric plexus

What is the purpose and location of the pharyngoesophageal and gastroesophageal sphincters?
To minimize the amount of air swallowed; in the neck

To prevent gastric reflux; directly above the stomach
Where does most mixing occur and why?
Antrum; because it is the most muscular portion of the stomach.
What are the three divisions of the stomach, from inferior to superior?
Pyloric gland area, oxyntic mucosa, & fundus
What are the folds of the stomach called?
What causes motility in the stomach and in which direction does it go? What makes the neurons more excitable?
The myenteric plexus fires action potentials in the pace setter cells

It goes down

Presence of food and GI hormones
What is the function of the deep invaginations known as gastric pits?
Protects the stomach from HCl, as it's filled by high pH mucus
What is contained in the gastric pits of the oxyntic mucosa?
Gastric exocrine and paracrine glands which release alkaline mucus, pepsinogen from the chief cells, HCl and Intrinsic factor from the parietal cells, and Histamine from the ECL cells, which is a paracrine gland
What functions do the secretions of the oxyntic mucosal glands perform?
Pepsinogen is the inactive form of pepsin which is activated by high acidity

Intrinsic factor is essential for B12 binding, which then gets absorbed in SI by receptor-mediated endocytosis

Histamine causes local paracrine action to produce HCl
What form are proteolytic enzymes released as in most cases and why?
inactive forms; if they were released as active forms, they'd digest the cells that create them
What are the two types of Pyloric Gland Area (PGA) endocrine glands, what do they secrete, and what are their functions?
G cells release gastrin, which enhances gastric secretion, motility (in stomach and all along GI tract)

D cells release somatostatin which slow down motility
What are the 4 phases of gastric secretion, in order?
Interdigestive Phase
Cephalic Phase
Gastric Phase
Intestinal Phase
What cues the Cephalic Phase?
What happens in the first mechanism of the cephalic phase?
Food is sensed, vagal nerve stimulated which stimulates the ENS, which produce pepsinogen and HCl.
What happens in the second mechanism of the cephalic phase?
Vagal nerve stimulation activates G cells which release gastrin from PGA, stimulates the oxyntic glands, releasing histamine, which releases the HCl and pepsin
What are the strongest stimulators of the Gastric Phase?
Protein, caffeine, EtOH, and distention
What do the strong stimulators in the Gastric Phase cause?
Stimulation of the ENS via detection of food, which releases ACh to the oxyntic area which causes chief cells to release Pepsinogen and also stimulates the Parietal cells, along with Gastrin to release HCl
What signals the intestinal phase and what happens during it?
Strongest signal is food in the duodenum, as well as pH decrease. This stimulates the D cells to release Somatostatin which inhibits the Parietal Cells, G Cells, and ECL cells.
Where is protein digested in the stomach?
Where does salivary amylase carb digestion occur?
In fundus and body
What is gastric emptying dependent on?
strength of Antral peristalsis
What's the strongest signal that stops the gastric phase?
Lipids in the duodenum
What are the two responses to gastric emptying?
Enterogastric reflex (neural)

enterogastrones (hormonal; released from duodenal mucosal cells)
What does the enterogastrone Cholecystokinin (CCK) do?
Inhibits gastric emptying

Increases pancreatic secretion

Increases bile secretion
What does the enterogastrone Secretin do?
Inhibits gastric emptying

Decreases gastric acid secretion

Increases pancreatic secretion of HCO-3
How are pancreatic digestive enzymes packaged and what do they do?
In Zymogens which contain the enzymes necessary to break down all 3 categories of food (peptidases, amylases, and lipase)
What do pancreatic Acinar cells
secrete digestive
(amylase, lipase, proteolytics)
What do pancreatic Duct cells do?
release aq NaHCO3 sol
What is the endocrine portion of the pancreas called and what does it release?
(Islets of Langerhans)

Hormones(insulin, glucagon)
What do the inactive pancreatic Proteolytic enzymes start or end with?
end in –gen or begin with pro-
What does enterokinase do?
activates trypsinogen to trypsin which activates the other two proteolytic enzymes
What is the process of bile release and storage?
Bile is produced from cholesterol in the liver, then passed down common bile duct which is then stored in gallblader if can’t get into duodenum (if food not present);

CCK causes contraction in gallblader and relaxes Spinchter of Oddi (if food in duodenum) which then allows bile to emulsify fat;
What is the strongest stimulation for the liver to produce new bile and what is that process called?
return of bile salts to liver

enterohepatic circulation (positive feedback loop)
How does bile help in fat digestion and absorption?
Bile breaks up big lipid droplets, emulsify, then lipase comes in and breaks triglycerides into free fatty acids and monoglycerides, which are then carried in packages called micelles, which is crucial for FFA and monoglycerides for absorption
What three influences control Bile secrection?
1) Chemical - Cholerectics
2) Hormonal - Secretin
3) Neural - Vagal Stimulation
What are the 3 segs of the SI?


Primary motility in the small intestine is:
What determines the intensity of segmentation contractions in the SI?
degree on distension

presence of gastrin

extrinsic nerve activity (ie. Vagal input)
Brush border membrane contains three categories
of membrane-bound digestive enzymes which are:
1) Enterokinases
2) Disaccharidases
3) Aminopeptidases
Where does fat go in the villi of the SI?
Central lacteal, which is lymphatic tissue
Where is the ileocecal valve?
The junction between the SI and LI
How often do mass movements occur? What kind of movement is it? What stimulates it?
3-4 times a day (usually after meals)


gastrocolic reflex - via Gastrin
How are water and salt absorbed in LI?
Sodium is actively transported

Chloride crosses passively down its electrical gradient.

Water absorbed via osmosis