Physiology of Digestion

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Questions and Answers

What is the direction of transport in active transport?

Against the concentration gradient, but without energy

In the same direction as the concentration gradient

From a higher concentration to a lower one (correct)

From a lower concentration to a higher one

What is the source of energy for active transport in glucose absorption?

Sodium pump

Breakdown of glucose

Hydrolysis of ATP (correct)

Glycogenesis

What is the role of sodium ions in active transport?

To transport glucose down its concentration gradient

To bind to the transport protein

To transport glucose against its concentration gradient (correct)

To provide energy for active transport

What is the condition characterized by the inability to digest lactose due to lactase deficiency?

Lactose intolerance Signup and view all the answers

What is the characteristic of congenital lactose intolerance?

There is a complete absence or deficiency of lactase enzyme Signup and view all the answers

What is the site of glucose and galactose absorption?

Intestine Signup and view all the answers

What type of bonds are cleaved during the digestion of lipids?

Ester bonds Signup and view all the answers

Which enzyme is responsible for digesting lipids in the stomach?

Gastric lipase Signup and view all the answers

What is the pH range for the intestinal phase of protein digestion?

pH 1.8-3.5 Signup and view all the answers

What is the primary function of lingual lipase?

To digest lipids Signup and view all the answers

What type of amino acids are found at the carboxylic end?

Aromatic amino acids Signup and view all the answers

Which hormone stimulates the release of bile acid from the gallbladder?

Cholecystokinin Signup and view all the answers

What is the function of microvilli?

To increase the surface area for absorption Signup and view all the answers

What is the name of the enzyme that digests COO end of proteins?

Carboxypeptidase Signup and view all the answers

What is the main function of pancreatic juice?

To neutralize stomach acid Signup and view all the answers

What happens to the pyloric part's contractility during the intestinal phase?

It reduces to reduce the stomach's emptying Signup and view all the answers

What is the primary function of trypsin?

To digest proteins at the N terminus Signup and view all the answers

Which cell type secretes gastric lipase?

Chief cells Signup and view all the answers

What is the primary ingested lipid form?

Triacylglycerol (TAG) Signup and view all the answers

What is the primary function of gastric inhibitory polypeptide?

To inhibit gastric acid secretion Signup and view all the answers

What is the main source of carbohydrates?

Plants Signup and view all the answers

What is the process that occurs before lipids are digested in the small intestine?

Emulsification Signup and view all the answers

What is the universal fuel for human cells?

Glucose Signup and view all the answers

What is the primary function of the parasympathetic nervous system in digestion?

To stimulate digestive enzyme secretion Signup and view all the answers

What is the primary site of carbohydrate digestion?

Mouth and small intestine Signup and view all the answers

What is the condition where the immune system attacks the tissues when eating gluten?

Celiac disease Signup and view all the answers

What is the function of salivary α-amylase in the mouth?

To initiate the hydrolysis of starch Signup and view all the answers

What happens to carbohydrate digestion in the stomach?

It halts temporarily Signup and view all the answers

What is the result of α-amylase action on dietary starch in the mouth?

It breaks down starch into dextrins Signup and view all the answers

What is the function of the enterogastric reflex in the digestion process?

To reduce the stomach's emptying Signup and view all the answers

What is the function of intestinal gastrin?

Stimulates the production of gastric juice Signup and view all the answers

What is the function of phospholipase A2 (PLA2)?

Hydrolyzes phospholipids into fatty acids and lysophospholipids Signup and view all the answers

What is the function of pancreatic lipase?

Hydrolyzes triglycerides into fatty acids and glycerol Signup and view all the answers

What surrounds the small fat droplet?

Bile salts and phospholipids Signup and view all the answers

What is the function of co-lipase?

Activates pancreatic lipase Signup and view all the answers

What percentage of bile salts recycle through the enterohepatic cycle?

94% Signup and view all the answers

What is the function of chemoreceptors at the duodenum?

Inhibit the PSNS and stimulate the SNS Signup and view all the answers

What is the function of the lymphatic vessel?

Transports lipids from the digestive system to the bloodstream Signup and view all the answers

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

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Description

This quiz covers the physiological processes involved in digestion, including the cephalic, gastric, and intestinal phases, and their effects on stomach emptying.