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Questions and Answers
What is the form of iron that is absorbed into intestinal cells?
What is the form of iron that is absorbed into intestinal cells?
- Fe2+ (ferrous) (correct)
- Transferrin
- Ferritin
- Fe3+ (ferric)
What happens to excess iron that is not absorbed into the blood?
What happens to excess iron that is not absorbed into the blood?
- It is sloughed off as cell debris.
- It is excreted in feces.
- It is stored in the liver.
- It is converted to ferritin. (correct)
What initiates the formation of water-soluble chylomicrons in fat absorption?
What initiates the formation of water-soluble chylomicrons in fat absorption?
- Coating with apoproteins (correct)
- Diffusion through cell membrane
- Fusion with lysosomes
- Exocytosis of amino acids
In the process of iron absorption, what is the role of transferrin?
In the process of iron absorption, what is the role of transferrin?
Where is iron primarily absorbed in the gastrointestinal tract?
Where is iron primarily absorbed in the gastrointestinal tract?
What does the coating of chylomicrons with apoproteins facilitate?
What does the coating of chylomicrons with apoproteins facilitate?
Which form of iron is not absorbable and cannot be taken up by intestinal cells?
Which form of iron is not absorbable and cannot be taken up by intestinal cells?
What is the main consequence of sloughing off intestinal epithelial cells?
What is the main consequence of sloughing off intestinal epithelial cells?
Which statement about the effects of PNS and SNS on SI contraction is correct?
Which statement about the effects of PNS and SNS on SI contraction is correct?
How do the rates of segmentation differ between the duodenum and ileum?
How do the rates of segmentation differ between the duodenum and ileum?
What is the role of the ileocecal sphincter when pressure is applied on the cecal side?
What is the role of the ileocecal sphincter when pressure is applied on the cecal side?
Where are dietary disaccharides primarily broken down?
Where are dietary disaccharides primarily broken down?
What mechanism is required for the absorption of single amino acids in the small intestine?
What mechanism is required for the absorption of single amino acids in the small intestine?
What initial processes lead to the formation of disaccharides in carbohydrate absorption?
What initial processes lead to the formation of disaccharides in carbohydrate absorption?
Which type of transport is primarily involved when glucose and galactose are absorbed into the epithelial cells?
Which type of transport is primarily involved when glucose and galactose are absorbed into the epithelial cells?
What type of transport allows for the absorption of fructose in the carbohydrate absorption process?
What type of transport allows for the absorption of fructose in the carbohydrate absorption process?
Which enzymes are responsible for converting disaccharides into monosaccharides in carbohydrate absorption?
Which enzymes are responsible for converting disaccharides into monosaccharides in carbohydrate absorption?
How is sodium involved in the process of carbohydrate absorption?
How is sodium involved in the process of carbohydrate absorption?
What is the final destination of absorbed monosaccharides after passing through the intestinal epithelial cells?
What is the final destination of absorbed monosaccharides after passing through the intestinal epithelial cells?
What role does facilitated diffusion play in carbohydrate absorption?
What role does facilitated diffusion play in carbohydrate absorption?
Which type of carbohydrates can be first broken down by salivary amylase?
Which type of carbohydrates can be first broken down by salivary amylase?
What is the primary function of cotransport in carbohydrate absorption?
What is the primary function of cotransport in carbohydrate absorption?
Which of the following describes the process that requires energy during carbohydrate absorption?
Which of the following describes the process that requires energy during carbohydrate absorption?
What is another name for enterokinase?
What is another name for enterokinase?
Which enzyme is produced from the activation of trypsinogen?
Which enzyme is produced from the activation of trypsinogen?
Which of the following correctly describes amino acids transport?
Which of the following correctly describes amino acids transport?
What type of transport mechanism is used for di- and tripeptides absorption?
What type of transport mechanism is used for di- and tripeptides absorption?
What role do brush border membrane enzymes (BBE) have in oligopeptide digestion?
What role do brush border membrane enzymes (BBE) have in oligopeptide digestion?
Which enzyme completes protein digestion by hydrolyzing small peptide fragments?
Which enzyme completes protein digestion by hydrolyzing small peptide fragments?
Which enzyme is NOT involved in the initial stages of protein digestion?
Which enzyme is NOT involved in the initial stages of protein digestion?
How do small peptides get absorbed in the intestinal cells?
How do small peptides get absorbed in the intestinal cells?
What is the primary function of carboxypeptidase in protein digestion?
What is the primary function of carboxypeptidase in protein digestion?
What is the primary mechanism for the absorption of amino acids in the intestine?
What is the primary mechanism for the absorption of amino acids in the intestine?
What is the primary function of segmentation in the small intestine?
What is the primary function of segmentation in the small intestine?
What initiates segmentation contractions in the small intestine?
What initiates segmentation contractions in the small intestine?
Which segment of the small intestine exhibits faster segmentation contractions?
Which segment of the small intestine exhibits faster segmentation contractions?
What role does the gastroileal reflex play in the small intestine?
What role does the gastroileal reflex play in the small intestine?
How often do migrating motility complexes occur in the small intestine?
How often do migrating motility complexes occur in the small intestine?
What is the main activity of migrating motility complexes?
What is the main activity of migrating motility complexes?
The segmentation contractions in the small intestine primarily occur between which types of muscle layers?
The segmentation contractions in the small intestine primarily occur between which types of muscle layers?
What triggers the increase in segmentation contractions in the duodenum?
What triggers the increase in segmentation contractions in the duodenum?
What is the expected duration for contents to move through the small intestine?
What is the expected duration for contents to move through the small intestine?
What occurs to segmentation contractions when a new meal is introduced?
What occurs to segmentation contractions when a new meal is introduced?
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Study Notes
Small Intestinal Motility
- Segmentation is the primary form of motility during meal digestion, mixing and slowly propelling chyme
- Segmentation is driven by oscillating contractions of the circular smooth muscle layer along the length of the intestine
- Segmentation is characterized by contracted segments alternating with relaxed areas where chyme is located
- The rate of segmentation contractions is higher in the duodenum than the ileum (proximal faster than distal)
- Migrating Motility Complex (MMC): occurs when most of the meal is absorbed, and segmentation contractions stop
- The MMC is a repetitive, peristaltic wave that occurs every 1.5 hours and is more of a clean-up type motility
- The MMC is initiated by small intestinal pacesetter cells within the GIT walls
- The duodenum segments are stimulated by local distension, while the ileum segments are stimulated by gastrin. This is known as the gastroileal reflex.
- Chyme in the stomach is the major stimulus for gastrin release
Carbohydrate Absorption
- Dietary carbohydrates (starch, glycogen, lactose, sucrose) are broken down into monosaccharides (glucose, galactose, fructose) in the small intestine
- Salivary amylase begins the breakdown of polysaccharides in the mouth, while pancreatic amylase continues the process in the small intestine
- Disaccharides are broken down into monosaccharides by brush border membrane enzymes (maltase, lactase, sucrase)
- Monosaccharides are absorbed into the small intestinal epithelial cells through active transport (glucose, galactose) and facilitated diffusion (fructose)
- Glucose and galactose are absorbed by sodium-dependent active transport
- Fructose is absorbed by facilitated diffusion
Protein Digestion & Absorption
- Proteins are digested into smaller peptides by pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase)
- Brush border membrane enzymes (aminopeptidases) complete protein digestion by breaking down small peptide fragments into amino acids
- Amino acids are absorbed into the small intestinal epithelial cells by sodium-dependent active transport
- Di and tripeptides are absorbed by H+-dependent cotransporters
- Oligopeptides require further breakdown by brush border membrane enzymes before absorption
Fat Absorption
- Dietary fat is converted into chylomicrons
- Chylomicrons are assembled within intestinal cells
- Lipid droplets (TG) are coated with apoproteins in the gut
- Chylomicrons are exocytosed from the small intestine into the lymphatic system
Brush Border Membrane Enzymes
- Enterokinase (enteropeptidase): Activates pancreatic trypsinogen to produce trypsin, chymotrypsin, and carboxypeptidase
- Aminopeptidases: Complete protein digestion
- These enzymes are crucial for the final stages of digestion and efficient absorption of nutrients
Iron Absorption
- Ferrous iron (Fe2+) is absorbed in the small intestine
- Ferric iron (Fe3+) is not absorbed
- Dietary iron is absorbed into small intestinal epithelial cells
- Some absorbed iron is stored in the cell as ferritin, and some is transported into the blood
- Iron in the blood is bound to transferrin, a protein that transports iron throughout the body
True/False Statements
- False: The rate of duodenum and ileum segmentation is not the same. The duodenum's segmentation rate is higher than the ileum's (12/min vs. 9/min).
- False: The ileocecal sphincter does not contract more with pressure on the cecal side. It normally contracts to prevent backflow of bacteria-laden colonic contents into the small intestine.
- True: Dietary disaccharides are broken down at the brush border membrane (BBM) by brush border enzymes (BBEs).
- False: Pancreatic amylase also aids in the digestion of polysaccharides, not just salivary amylase.
- True: Single amino acid absorption requires sodium-dependent active transport, while di- and tripeptides utilize H+-dependent cotransport.
- True: In small intestinal epithelial cells, monoglycerides (MGs) and free fatty acids (FFAs) re-esterify to form triglycerides (TGs).
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