8.4 The Small Intestine, Pancreas, Liver & Gallbladder Flashcards
Describe segmental activity of the small intestine in relation to meal timing
Between: slight/absent
Immediately after: vigorous
Why does chyme gradually move throughout the intestine due to segmentation?
Because the frequency of small intestine contraction decreases distally
Describe the gastroileal reflex
Ileal begins segmentation while empty in response to gastrin secreted by the stomach in the presence of chyme
How is the MMC controlled? Why doesn’t it occur during eating?
- Control by motilin: hormone secreted by endocrine cells of SI
- Inhibited by feeding
What causes the ileocaecal valve to close/open?
Open: ileal contents pushes valve open
Close: Colon contents pushes valve closed (why is is important to keep colon contents out?)
REMEMBER: IC VALVE IS A SPHINCTER
How much intestinal juice is secreted per day? What does it contain, and why?
- 1.5L/day
- Aqueous salt and mucus solution; lubricates, protects, and enables hydrolysis (NO ENZYMES IN INTESTINAL JUICE)
Describe the secretion of intestinal juice
Secreted from enterocytes. Contains enteropeptidase, which is the enzyme necessary for activating trypsin (and the following cascade of reactions)
What are the three levels of folding of the small intestine?
- Circular folds (3x)
- Villi (10x)
- Microvilli (20x)
Describe the structure of a villus
- Epithelial cells joined by tight junctions
- Have a luminal brush border with digestive enzymes
- Capillary network
- Central lacteal blind lymph vessel
Describe the actions of the crypts of liberkuhn
- Invaginations on each side of the villus, in which water and electroytes are secreted
- Mitotic activity of stem cells causes epithelial cells to migrate up toward tip and be shed into the lumen
- Antimicrobial cells are produced in the Paneth cells at the base of the pit
- Migration takes 3 days
What to paneth cells produce to safeguard stem cells?
- Lysozymes
- Defensins
Draw the process of digestion of carbohydrates, including relevant enzymes
Check diagram document
How do glucose and galactose enter the epithelial cells that line the small intestine
SGLT symporters; Na+ and energy dependent secondary active transport
How does fructose enter the epithelial cells that line the small intestine?
GLUT-5 Transporters
How do monosaccharides leave small intestine epithelial cells out of the stomach?
GLUT-2 Transporters
What enzymes work to break down proteins in the lumen of the SI? (precursors)
- Trypsinogen
- Chymotrypsinogen
- Procarboxypeptidase
Describe how absorbed monoglycerides and fatty acids enter lymphatic circulation
- Passively absorbed
- Reform triglycerides
- Coatted in lipoprotein from ER to form water-soluble chylomicrons
- Exocytosis
- Enter central lacteal (too big to pass through capilllaries)
True or false: the pancreas is derived from one tissue during embyronic development
False: endocrine and exocrine sections are derived from different tissues
True or false: the endocrine and exocrine regions of the pancreas have different functions but are under the same regulation
False: different functions, different regulation
The aqueous alkaline solution secreted from the ducts of the pancreas is rich in ___ which raises the pH, which is important for ____
Sodium bicarbonate. This is important for inactivating pepsin, which stops the duodenum from being digested.
Name three kinds of enzymes secreted from the acinar cells of the pancreas
- Proteolytic enzymes
- Pancreatic lipase
- Pancreatic amylase
List the three major pancreatic proteases
- Trypsinogen
- Chymotrypsinogen
- Procarboxypeptidase
Describe the activation of the three pancreatic proteases
- Enterokinase from epithelial cells converts trypsinogen to trypsin
- Trypsin converts chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase
Are pancreatic lipase and amylase secreted in active or inactive form? Why?
Active: no triglycerides or polysaccharides in acinar cells of pancreas
