Unit 8 - GI Structure and Function Flashcards
What are the 6 main functions of the GI system?
- Ingestion
- Mastication (chewing)
- Deglutition (swallowing)
- Digestion
- Absorption
- Defecation
What does the liver secrete?
Bile
What is the function of the gallbladder?
Storage of bile
What is the function of the large intestine?
Dehydration and compaction of indigestible materials
What is the function of the stomach?
Chemical breakdown of ingested material
What is the digestive function of the pancreas?
Secretes digestive enzymes
What is the function of the small intestine?
Enzymatic digestion and absorption of water, organic substances, vitamins and ions
What is the mesentery?
Fold of tissue that attaches the organs to the body wall
- supplies intestines with blood vessels, lymph and nerves
What can happen if the mesentery are too long?
Twisting
- cut off blood supply to the intestines (close or compress blood vessels)
What are the 5 main layers of the GI tract?
- Peritoneum
- Smooth muscle
- Submucosa
- Mucosa
- Lumen
How much saliva is secreted into the oral cavity each day?
1 - 1.5 litres of saliva
What are the 5 functions of saliva?
- Amylase - digest starch
- Lingual lipase - digests fat (in the stomach)
- Mucus - aids in swallowing
- Lysozyme - kills bacteria
- Immunoglobulin A - inhibits bacterial growth
If someone has a tumor of the salivary glands (aka … less saliva), what can you expect/project?
- Infections in the mouth (less lysozyme and immunoglobulin A)
- Difficulty tasting (less starch digestion)
- Difficulty swallowing (less mucus)
What are the two phases of swallowing?
- Buccal phase (makes a bolus - voluntary)
2. Pharyngeal and esophageal phase (bolus pushed down esophagus - involuntary)
What prevents food from entering the lungs?
Epiglottis
What does the esophagus pass through to enter the stomach?
Esophageal hiatus in the diaphragm
If the lower esophageal sphicter is loose, what can happen?
Acid reflux
What do the longitudinal, circular, and oblique muscle layers of the stomach do?
Help mix up ingested food
In the stomach, what is the function of mucus cells?
Produce mucus
- prevents erosion of gastric mucosa
What do chief cells in the stomach produce (2)?
- Pepsinogen
2. Chymosin
What do parietal cells in the stomach produce (2)?
- HCl (Hydrocholoric acid)
2. Intrinsic factor
Why is intrinsic factor important? What can it lead to if you are deficient in intrinsic factor?
Helps with absorption of vitamin B12
- if you are deficient, could lead to pernicious anemia
How much gastric juice do we produce a day?
2-3 litres
What happens if there is a lot of gastric secretion on an empty stomach?
Ulceration
How is H+ pumped into the stomach?
By H+K+ATPase
- antiporter uses ATP to pump H+ into stomach and K+ out
What are the three phases of gastric secretion?
- Cephalic phase (gastric secretions at thought of food)
- Gastric phase (digestive enzymes)
- Intestinal phase (secretion of bicarbonate and more enzymes)
How can we control gastric acidity?
- Disabling H+K+ATPase
- Proton pump inhibitors (pantaproazole, ometraprazole, -zole family)
- Antacids
What is the rebound effect of antacids?
If you use too many antacids, your body will compensate and produce MORE acid to balance out
What are the functions of hydrochloric acid (4)?
- Activates enymes (pepsin and lingual lipase)
- Breaks up connective tissue and plant cell walls
- Converts ingested Fe+3 to Fe+2 (used for hemoglobin synthesis)
- Destroys ingested bacteria and pathogens
What happens to bacterial growth in the stomach if HCl is decreased?
Overgrowth
How is pepsin activated in the stomach?
- Parietal cells release HCl.
- Chief cells release pepsinogen.
- HCl converts pepsinogen to pepsin
What does the pancreas secrete (4)?
- HCO3-
- Proteases
- Lipases
- Amylases
At what pH does pancreatic enzymes work best?
pH 8
- therefore, pancreatic juice contains sodium bicarbonate
How much pancreatic juice is secreted everyday?
1500 mL
Where is CCK released from?
Duodenum
What stimulates the release of CCK?
In response to arrival of acid and fat
- causes contraction of gallbladder (release of bile), secretion of pancreatic enzymes, relaxation of hepatopancreatic sphincter
Where is secretin released from?
Duodenum
What stimulates the release of secretin?
In response to arrival of acidic chyme
- stimulates all ducts to secrete more bicarbonate
How are carbohydrates digested?
- Salivary amylase (in the mouth)
- Pancreatic amylase (in duodenum)
- Brush border enzymes (in duodenum, jejunum and ileum)
What happens if there are insufficient secretion of digestive enzymes?
Incomplete absorption
What breaks down fat?
- Bile (emulsifies fats)
- Pancreatic lipase
Where is the majority of water absorbed in the digestive tract?
8L in the small intestine
- 0.8L in the large intestine
What is the function of the large intestine?
Compaction of fecal matter
- squeezes out remaining water
What are the pockets of large intestine called?
Haustra
What happens if there is inflammation in the large intestine?
Stool is of small volume (not being compacted properly)
- still results in diarrhea
- stool will be covered in mucus
What is the role of Peyer’s patches in the large intestine?
Lymphatic nodules that defend the large intestine
Why do you not see Peyer’s patches close to the stomach?
Because they are not needed
- stomach acid effectively kills off bacteria
- once bicarbonate is added to digested material, then peyer’s patches are needed
What are the functions of bowel motility (3)?
- Mixes chyme with intestinal juice, bile and pancreatic juice
- Churns chyme to increase contact with mucosa for absorption and digestion
- Moves residue towards large intestine
What are the three types of bowel motility?
- Segmentation
- Peristalsis
- Mass movements
What is segmentation? Where does it occur?
- random ringlike constrictions
- mixes and churns intestinal contents
- occurs 12 times per min in duodenum
What is peristalsis?
Wave-like contraction beginning in duodenum
- push chyme along for 2 hours
How many mass movements do we have a day?
1-3
What is the transit time through the small intestine?
2-4 hours
How quickly does content move through the large intestine?
5 - 10 cm per hour
What stimulates defacation?
Stretching of the rectum
- intrinsic defecation reflex causes muscularis to contract and internal sphincter to relax
True or False:
Defacation reflex involves parasympathetic nerves
True
True or False:
Defacation occurs only if external anal sphincter is voluntarily relaxed
True
True or False:
Men have longer GI tracts than women
False
- females have longer GI tracts than males
- we don’t know why
Describe the steps involved in the neural control of defacation
- Filling of the rectum
- Reflex contraction of rectum and relaxation of internal anal sphincter
- Voluntary relaxation of external sphincter
