Kaplan Ch. 9 - The Digestive System Flashcards
State the pathway that food takes in the digestive tract.
Oral cavity —> pharynx —> esophagus —> stomach —> small intestine —> large intestine (colon) —> rectum —> anus
What role does the oral cavity play in digestion?
1) mechanical digestion (masticulation) —> increase surface area to volume ratio to give more access for chemical digestion later
2) starts chemical digestion with enzymes in saliva
3 subdivisions of pharynx?
What causes choking?
Nasopharynx
Oropharynx
Laryngopharynx
Failure of epiglottis to block larynx from food, food enters larynx.
Describe the composition of the esophagus.
What parts of the nervous system control the esophagus?
The top is made of skeletal muscle, the bottom is made of smooth muscle, the middle is a mix of both
Too enervated by somatic NS (voluntary) bottom enervated by autonomic NS (involuntary)
Peristalsis and emesis
Peristalsis is rhythmic contraction of smooth muscle that propels food down digestive tract.
Emesis = vomiting, reversal of peristalsis, causes by chemicals, infection, cognitive processes
What two sphincters are there in the esophagus?
Upper esophageal sphincter (oropharynx), bolus enters esophagus from mouth
Lower esophageal sphincter (cardiac sphincter), bolus leaves esophagus to stomach
What are the 2 kinda of glands in the stomach and where are they located?
Gastric glands (located in the fungus and the body)
Pyloric glands (located in the pylorus and the antrum)
What is the name for the folded lining of the stomach?
Rugae
Describe the environment of the stomach in general.
Stomach uses HCl and enzymes to digest food, highly acidic, has thick mucosa to protect itself from being digested by its own environment
Gastric glands:
1) respond to signals from _____?
2) what are the 3 different cell types of gastric glands and what are their functions?
1) vagus nerve of parasympathetic NS
2) a) mucous cells (produce bicarbonate rich mucous to protect stomach walls)
b) chief cells (secrete pepsinogen = zymogen or inactive protein that is later cleaved to become enzyme pepsinogen)
c) parietal cells (secrete hydrogen ions in form of HCl to cleave pepsinogen to pepsin, which cleaves amino acids near aromatic residues)
What is the significance of the acidic environment of the stomach?
- needed for stomach enzymes to function
- kills most harmful bacteria
- chemical digestion (denature proteins, break bonds)
What cells do pyloric glands secrete? What is the function of these cells?
G - cells : secrete gastric (peptide hormone) that induces parietal cells to secrete more HCl, also signals stomach to contract to mix contents
Chyme
Acidic, semi fluid mixture that is the result of digestion in the stomach
Is the stomach responsible for absorption?
No - very few compounds are dissolved directly from the stomach. Absorption primarily responsibility of small intestine.
What are the 3 segments of the small intestine?
Duodenum
Jejunum
Ileum
Duodenum:
1) what is it’s main responsibility?
2) what does the passage of chyme into the duodenum cause?
1) majority of chemical digestion
2) release of brush border enzymes (disaccharidases and peptidases) that break down carbohydrates and proteins into smaller components that are absorbable
Flatulence
If you lack disaccharidase, then you don’t break down the carbohydrate but bacteria in the intestines may be able to instead which produces methane gas as a byproduct
Undefeated sugars also pull water into stool resulting in diarrhea
Enteropeptidases
Activated trypsinogen to trypsin (pancreatic protease)
What is secretin?
What are it’s functions? (3)
Secretin is a peptide hormone that is secreted by the duodenum
It causes pancreatic enzymes to be released into the duodenum
It regulates pH by reducing HCl (antagonist to gastrin) secretion from parietal cells
Slows motility through tract to allow for increased digestive time (enterogastrone)
Cholecystokinin (CCK):
1) when is it secreted?
2) what is it?
3) what are it’s functions
1) when chyme passes into duodenum
2) peptide hormone
3) release of pancreatic juices and bile and also promotes satiety in the brain
Bile
Fluid composed of bile salts, pigment, and cholesterol
Bile salts
Amphiphilic molecules derived from cholesterol, emulsify fats in small intestine into micelles allowing an environment for lipases to act
Pancreatic juices
Mixture of several enzymes in a bicarbonate alkaline solution. Bicarbonate is present to neutralize the acidic chyme and enzymes present to digest all 3 major types of macromolecules
Acinar cells
Make up bulk of pancreas, produce pancreatic juices
