chapter23-GI system

Question 1

which hormone that would help to counteract the effects of HCl in duodenum?

Answer 1

secretin stimulates the duct cells in the pancreas and liver to secrete a bicarbonate-rich solution that will bind hydrogen ions and increase the pH.

Question 2

The secretion in the large intestine consists of:

Answer 2

an alkaline mucus secretion of bicarbonate and potassium protects the large intestinal wall from acids produced by resident bacteria.

Question 3

Peristalsis

Answer 3

The major means of propelling food through the digestive tract.

Question 4

Saliva:

Answer 4

• contain carbohydrate-dissolving enzymes.
• moistens food and helps compact it into a bolus.
• dissolve food chemicals so that they can be tasted.
• clean the mouth.

Question 5

Characteristics of stomach:

Answer 5

• The stomach mucosa is folded into rugae.
• The stomach produces a double-layered coat of alkaline mucus.
• The stomach has three layers of muscle in the muscularis tunic.

Question 6

Lesser omentum

Answer 6

helps tether the stomach to the liver.

Question 7

pancreatic proteases:

Answer 7

protein-digesting enzymes produced by the pancreas in inactive forms, which are activated in the duodenum.

Question 8

Pancreatic proteases include:

Answer 8

typsinogen, which needs enteropeptidase to activate to trypsin, chemotrypsinogen, which needs trypsin to activate to chymotrypsin, procarboxypeptidase, which needs trypsin to activate to carboxypeptidase..

Question 9

Other pancreatic enzymes:

Answer 9

amylase, which digests carbohydrate. Lipases, which digests lipid. Nucleases, which digests nucleic acid.

Question 10

Brush border enzymes in small intestine to break down carbohydrate:

Answer 10

dextrinase, gluco-amylase, lactase, maltase, and sucrose.

Question 11

Path of carbohydrate absorption:

Answer 11

• Glucose and galactose are absorbed via cotransport with sodium ions.
• Fructose passes via facilitated diffusion.
• All monosaccharides leave the epithelial cells via facilitate diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

Question 12

Path of Protein absorption:

Answer 12

Amino acids are absorbed via cotransport with sodium ions.

• Some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cells.
• Infrequently, transcytosis of small peptides occurs.
• Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

Question 13

Path of fat absorption:

Answer 13

• Fatty acids and monoglycerides enter the intestinal cells via diffusion.
• Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells. The resulting chylomicrons are extruded by exocytosis.
• The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.
• Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.

Question 14

Path of nucleic acid absorption:

Answer 14

Units enter intestinal cells by active transport via membrane carriers.
- Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein.

Question 15

Protein digestion and absorption in the small intestine:

Answer 15

1. Proteins and protein fragments are digested to amino acids by pancreatic proteases, and by brush border enzymes of mucosal cells.
2. The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side.
3. The amino acids leave the villus epithelial cell be facilitated diffusion and enter the capillary via intercellular clefts.

Question 16

Emulsification, digestion, and absorption of fats:

Answer 16

1. Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets).
2. Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa.
3. Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons.
4. Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph.

Question 17

Enzymes in pancreatic juice:

Answer 17

Amylase, lipases, nucleases secreted in active form but require ions or bile for optimal activity.
Proteases secreted in inactive form.