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
What is the name of the condition that involves excess fat in faeces?
Steatorrhoea
Draw a diagram of the substances exchanged into/out of a duct cell in the pancreas
Diagram document
Draw the basic feedback loop that limits the acidity in the duodenum
Document
What is the digestive role of the liver?
Secretion of bile salts
Draw a map of the heart, the liver, the GI tract, and veins. What type of blood does the liver recieve from where?
How are hepatic lobules arranged?
- Hexagonal, with central vein in middle
- On each corner, branch of hepatic portal vein, hepatic artery, bile duct
Does blood move from inside to outside of hepatic lobule? How about bile?
Blood: Outside to inside
Bile: Inside to outside
Does blood move from inside to outside of hepatic lobule? How about bile?
Blood: Outside to inside
Bile: Inside to outside
What is the name of the specialised macrophages of the liver? What do they do
- Kupffer cells
- Break down old red blood cells
Describe the passage of bile from hepatic lobules
Hepatocytes -> bile canaliculus -> peripheral bile duct -> common bile duct
What are some components of bile?
How is bile concentrated in the gall bladder?
- Actively transports salt out
- Water following
- Volume decreases
What are gallstones?
(AKA Choleliths); are cystalline bodies that have precipitated from bile components (most made of cholesterol)
What sphincter connects to the ampulla of vater?
Sphincter of Oddi
Where does bile travel to get to the liver from the common bile duct?
Cystic duct
What is the diameter of a micelle? What comprises their hydrophilic components in the liver?
- 3-10nm
- Hydrophilic shell made of lecithin and bile salts
In terms of micelles, how do gallstones form? Therefore, how can it be treated?
- Fat-soluble cholesterol escapes core of micelle
- Microcrystals form
- Can be treated by ingesting bile salts
Where are bile salts recycled in the GI tract? How do they return to the liver? How much escapes to faeces?
- Reabsorbed in terminal ileum
- Return via hepatic portal system
- 5% escape to faeces
What are choleretics?
Factors that increase bile secretion
How can bile salt secretion be chemically stimulated
bile salts stimulate their own secretion when
returned to the liver during meal digestion
How can bile salt secretion be hormonally stimulated?
Secretin stimulates an aqueous NaHCO3 bile
secretion to neutralise chyme
How can bile salt secretion be neurally stimulated?
vagal stimulation of liver to increase bile flow
during cephalic phase plays a minor role
Is bilirubin involved in digestion
No. It is a waste product secreted in bile
How is bilirubin formed
Formed during the degradation of the heme (iron-containing) part of haemoglobin in RBCs
If bilirubin is a yellow pigment, how does it make faeces brown?
Modified by bacterial enzymes in the intestines
Why is urine yellow
Some bilirubin is reabsorbed and can be excreted in urine
What are three potential causes of jaundice?
- Obstruction
- Liver problems
- Haemolytic anemia, something wrong with blood
What is cirrhosis?
Active liver tissue is replaced by connective tissue
