38 Questions
What is the direction of transport in active transport?
From a higher concentration to a lower one
What is the source of energy for active transport in glucose absorption?
Hydrolysis of ATP
What is the role of sodium ions in active transport?
To transport glucose against its concentration gradient
What is the condition characterized by the inability to digest lactose due to lactase deficiency?
Lactose intolerance
What is the characteristic of congenital lactose intolerance?
There is a complete absence or deficiency of lactase enzyme
What is the site of glucose and galactose absorption?
Intestine
What type of bonds are cleaved during the digestion of lipids?
Ester bonds
Which enzyme is responsible for digesting lipids in the stomach?
Gastric lipase
What is the pH range for the intestinal phase of protein digestion?
pH 1.8-3.5
What is the primary function of lingual lipase?
To digest lipids
What type of amino acids are found at the carboxylic end?
Aromatic amino acids
Which hormone stimulates the release of bile acid from the gallbladder?
Cholecystokinin
What is the function of microvilli?
To increase the surface area for absorption
What is the name of the enzyme that digests COO end of proteins?
Carboxypeptidase
What is the main function of pancreatic juice?
To neutralize stomach acid
What happens to the pyloric part's contractility during the intestinal phase?
It reduces to reduce the stomach's emptying
What is the primary function of trypsin?
To digest proteins at the N terminus
Which cell type secretes gastric lipase?
Chief cells
What is the primary ingested lipid form?
Triacylglycerol (TAG)
What is the primary function of gastric inhibitory polypeptide?
To inhibit gastric acid secretion
What is the main source of carbohydrates?
Plants
What is the process that occurs before lipids are digested in the small intestine?
Emulsification
What is the universal fuel for human cells?
Glucose
What is the primary function of the parasympathetic nervous system in digestion?
To stimulate digestive enzyme secretion
What is the primary site of carbohydrate digestion?
Mouth and small intestine
What is the condition where the immune system attacks the tissues when eating gluten?
Celiac disease
What is the function of salivary α-amylase in the mouth?
To initiate the hydrolysis of starch
What happens to carbohydrate digestion in the stomach?
It halts temporarily
What is the result of α-amylase action on dietary starch in the mouth?
It breaks down starch into dextrins
What is the function of the enterogastric reflex in the digestion process?
To reduce the stomach's emptying
What is the function of intestinal gastrin?
Stimulates the production of gastric juice
What is the function of phospholipase A2 (PLA2)?
Hydrolyzes phospholipids into fatty acids and lysophospholipids
What is the function of pancreatic lipase?
Hydrolyzes triglycerides into fatty acids and glycerol
What surrounds the small fat droplet?
Bile salts and phospholipids
What is the function of co-lipase?
Activates pancreatic lipase
What percentage of bile salts recycle through the enterohepatic cycle?
94%
What is the function of chemoreceptors at the duodenum?
Inhibit the PSNS and stimulate the SNS
What is the function of the lymphatic vessel?
Transports lipids from the digestive system to the bloodstream
Study Notes
Digestion and Absorption of Carbohydrates
- Carbohydrates are the major source of energy for humans
- Glucose is the universal fuel for human cells
- The principal sites of carbohydrate digestion are the mouth and small intestine
- Dietary carbohydrates consist of:
- Polysaccharides (starch, glycogen, and cellulose)
- Disaccharides (sucrose, maltose, and lactose)
- Monosaccharides (glucose and fructose)
- Monosaccharides do not require digestion prior to absorption, whereas disaccharides and polysaccharides must be hydrolyzed to simple sugars before absorption
- Digestion in the mouth:
- Salivary glands secrete α-amylase (ptyalin), which initiates the hydrolysis of starch
- α-amylase breaks some α-(1 → 4) bonds, hydrolyzing starch into dextrins
- Digestion in the stomach:
- Carbohydrate digestion temporarily halts in the stomach due to the high acidity that inactivates salivary α-amylase
- Active transport:
- The transport of glucose and galactose across the brush-border membrane of mucosal cells occurs by an active transport process that requires energy
- Sodium-dependent glucose transporter (SGLT-1) binds both glucose and Na+ at separate sites and transports them through the plasma membrane of the intestinal cell
Digestion and Absorption of Proteins
- Proteins are hydrolyzed into smaller peptides and amino acids through the action of various enzymes
- Proteolytic enzymes are produced in the stomach and small intestine
- Digestion in the stomach:
- Gastric amylase and gastric lipase hydrolyze carbohydrates and lipids, respectively
- Digestion in the small intestine:
- Pancreatic juice containing proteases (trypsin, chymotrypsin, and carboxypeptidases) and amylase hydrolyze proteins and carbohydrates, respectively
- Brush-border enzymes (peptidases and carbohydrases) further hydrolyze peptides and sugars
Digestion and Absorption of Lipids
- Dietary lipids consist of triacylglycerols (TAG), cholesterol esters, and phospholipids
- Digestion of lipids occurs mainly in the small intestine
- Emulsification of lipids by bile salts and phospholipids enhances the surface area for enzymatic digestion
- Pancreatic lipase hydrolyzes TAG into fatty acids and glycerol
- Colipase binds to lipase and substrate, enhancing enzymatic activity
- The products of lipid digestion are absorbed into the intestinal cells and re-esterified into TAG, which are then transported to the lymphatic system as chylomicrons
Regulation of Digestion and Absorption
- The digestive process is regulated by hormones and nervous system signals
- The enteric nervous system (ENS) and the central nervous system (CNS) interact to regulate digestion and absorption
- Hormones such as gastrin, cholecystokinin (CCK), secretin, and gastric inhibitory peptide (GIP) play key roles in regulating digestive processes
This quiz covers the physiological processes involved in digestion, including the cephalic, gastric, and intestinal phases, and their effects on stomach emptying.
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