51 Questions
How do monoglycerides and free fatty acids leave micelles inside the epithelial cells?
By facilitated diffusion
What is the fate of triglycerides inside epithelial cells?
They are re-synthesized from monoglycerides and fatty acids
How do chylomicrons leave the epithelial cells after being formed?
By exocytosis
By what process do amino acids exit the epithelial cells at the basal membrane?
Facilitated diffusion
How are small peptides absorbed into epithelial cells?
Through active transport
What happens to the small peptides once they are absorbed into the epithelial cells?
They are broken down into amino acids by intracellular peptidases
How are fats able to diffuse through the luminal membrane after being broken down into micelles?
Via simple facilitated diffusion
What triggers cholecystokinin (CCK) to be released?
Fat
Which cells in the pancreas does cholecystokinin (CCK) stimulate?
Acinar cells
What enzyme activates trypsinogen in the pancreas?
Enteropeptidase
How are disaccharides broken down in the small intestine for absorption?
By disaccharidases
How are glucose and lactose absorbed into epithelial cells in the small intestine?
Secondary active transport with Na+
Which mechanism is responsible for fructose entering epithelial cells in the small intestine?
Facilitated diffusion by Glut-5
How do glucose, galactose, and fructose exit epithelial cells in the small intestine?
Facilitated diffusion via Glut-2
What is the function of exocrine secretions of the pancreas?
Release proteolytic enzymes and pancreatic amylase
During the oesophageal stage of swallowing, what happens to the gastroesophageal sphincter?
It relaxes to allow bolus entry into the stomach
What role does the epiglottis play during swallowing?
Prevents food from entering the trachea
Which enzyme is responsible for breaking down peptide linkages in the small intestine?
Chymotrypsinogen
What triggers the release of secretin in the digestive system?
Acidic chyme entering the duodenum
Which of the following is a voluntary action in the swallowing process?
Pushing bolus to pharynx with tongue
What prevents food from entering the nasal passage during swallowing?
Elevation of ovula
What initiates impulses to the salivary centre in the medulla during the simple reflex of saliva production?
Chemoreceptors and pressure receptors in the oral cavity
What causes salvation in the conditioned reflex of saliva production?
Thinking, seeing, or smelling food
Which type of nerves are innervated to stimulate the salivary glands and promote saliva production?
Autonomic nerves
Which gland is responsible for producing watery saliva when stimulated by the parasympathetic nervous system?
Parotid gland
Which division of the autonomic nervous system controls saliva production and increases the production of thick mucus saliva?
Sympathetic division
What triggers the reflex for swallowing?
Pressure receptors in the pharynx
Which part of the brain is responsible for controlling the swallowing process?
Medulla
Which type of saliva does the sympathetic nervous system increase production of?
'Thick mucus' saliva
What initiates impulses via afferent nerves to the salivary center in the medulla during the simple reflex of saliva production?
Chemoreceptors and pressure receptors in throat
How are amino acids absorbed into epithelial cells?
Via Na+ symporters
What is the mechanism by which small peptides are absorbed by epithelial cells?
Via H+ symporter
How do triglycerides leave epithelial cells?
Via exocytosis
What is the fate of chylomicrons after leaving the basal membrane?
Enters the lymphatic system
How do monoglycerides and free fatty acids enter epithelial cells?
Via passive diffusion
What is the role of pancreatic lipase in fat absorption?
To breakdown fats into micelles
Which cells in the pancreas produce cholecystokinin (CCK)?
I cells
How are disaccharides broken down in the small intestine for absorption?
By disaccharidases
What triggers the release of secretin in the digestive system?
Acidic chyme in the duodenum
How do glucose, galactose, and fructose exit epithelial cells in the small intestine?
Via facilitated diffusion
Amino acids are absorbed into epithelial cells via K+ symporters.
False
Small peptides are broken down into amino acids by intracellular lipases.
False
Glucose exits epithelial cells in the small intestine via active transport.
False
Bile salts breakdown fats into chylomicrons inside epithelial cells.
False
The water-soluble chylomicrons exit epithelial cells via exocytosis.
True
Names of the proteolytic enzymes in inactive and active form.
inactive= trypsinogen, procarboxypeptidase and chymotrypsinogen. active= trypsin, carboxypeptidase and chymotrypsin.
what activates trypsinogen and from where?
enteropeptidase from small intestine
2 pancreatic hormonal secretions
secretin and cholecystokinin
what type of nerve regulates digestive functions?
extrinsic nerves. it is dual innervated by both sympathetic and parasympathetic nerves
what autonomic nerve regulates digestion and how?
Parasympathetic it stimulates digestive secretion it increases blood flow relaxation of sphincters.
what cells secrete secretin?
S cells
Study Notes
Swallowing
- 3 stages of swallowing: oral/oropharyngeal stage, oesophageal stage, and gastric stage
- Involved 31 pair of muscles
- Voluntary swallowing is initiated by pushing the tongue against the hard palate
- The bolus is pushed to the back of the pharynx, and the ovula is elevated to seal off the nasal passage
- Food is prevented from entering the trachea by elevation of the larynx and closure of vocal folds (glottis and epiglottis)
Exocrine Secretions of Pancreatic Juice
- Pancreatic juice is a watery alkaline solution (sodium bicarbonate) produced by duct cells
- Proteolytic enzymes are produced by acinar cells and released in inactive form
- Enzymes are activated by enzymes in duodenal membrane in small intestine
- Trypsinogen, chymotryspinogen, and procarboxypeptidase are activated to trypsin, chymotrypsin, and carboxypeptidase
- Each different type of proteolytic enzyme attacks different peptide linkages
Protein Reabsorption
- Amino acids are absorbed into epithelial cells via Na+ symporters
- Amino acid symporters are selective for different amino acids
- Some small peptides are also absorbed by H+ symporter and broken down into amino acids by intracellular peptidases
- Amino acids exit the cell at basal membrane passively via carriers (facilitated diffusion) and enter the blood via simple diffusion
Fat Absorption
- Pancreatic lipase and bile salts break down fats into micelles
- Micelles passively diffuse through membrane, and monoglycerides and free fatty acids leave the micelles and passively diffuse through the luminal membrane
- Inside epithelial cells, monoglycerides and fatty acids are re-synthesised into triglycerides
- Triglycerides aggregate coated with lipoprotein from the ER to form water-soluble chylomicrons
- Chylomicrons leave the basal membrane via exocytosis and enter the lymphatic system, unable to cross the basement membrane of the capillaries
Carbohydrate Reabsorption
- Carbohydrates are normally found in the form of disaccharides such as maltose, sucrose, and lactose
- Disaccharides are broken down into absorbable monosaccharides units of glucose, galactose, and fructose
- Glucose and lactose are absorbed into epithelial cells by symport with Na+ (SGLT = sodium glucose transporters)
- SGLT is energy-dependent secondary active transport located on the luminal membrane
- Fructose enters the cell passively by facilitated diffusion by a Glut-5
- Glucose, galactose, and fructose exit the cell at basal membrane by passive facilitated diffusion via Glut-2 and enter the blood via simple diffusion
Absorption in Small Intestines
- Special hair-like projections on the luminal surface of the small intestine = microvilli form the brush border
- Microvilli contain 3 types of membrane-spanning proteins that function as membrane-bound enzymes
- Enteropeptidase activates pancreatic proteolytic enzyme called trypsinogen
- Disaccharidases break down disaccharides into monosaccharides
- Aminopeptidases hydrolyse small peptide fragments into amino acids
- These hair-like projections are constantly being replaced due to the harsh environment and are sensitive to cancer treatment
Test your knowledge on the stimulation of duct cells to produce sodium bicarbonate, the role of cholecystokinin in triggering enzyme production, the absorption in small intestines, and the function of microvilli in the digestive system.
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