Digestion, absorption and nutrition (guyton Ch. 65)

Question 1

The chemistry of digestion is simple because, in the case of all three major types of food, the same basic process is involved. What is this process called?

Answer 1

Hydrolysis

Question 2

Initial digestion of carbohydrates is catalyzed by what digestive enzyme secreted mainly by the parotid gland

Answer 2

Ptyalin (alpha-amylase)

Question 3

Salivary amylase is inhibited in the stomach because…..

Answer 3

Amylase is inhibited in acidic medium (Ph

Question 4

Carbohydrates are almost totally converted into _____ before passing beyond the ______

Answer 4

Maltose and/or other very small glucose polymers; duodenum or upper jejunum

Question 5

Hydrolysis of disaccharides and small glucose polymers into monosaccharides is catalyzed by what enzymes?

Answer 5

Intestinal epithelial enzymes (lactase, sucrase, maltase, and a-dextrinase located in the enterocytes)

Question 6

Peptic enzyme of the stomach, is most active at a pH of ____ and is inactive at a pH above about _____

Answer 6

2.0 to 3.0; 5.0

Question 7

These gastric glands secrete hydrochloric acid in large amounts

Answer 7

Parietal cells

Question 8

True or false

In protein digestion, pepsin is the enzyme that catalyzes the majority of total protein digestion to produce amino acids

Answer 8

False

**pepsin only initiates the process of digestion and contributes to only 10-20% of the total protein digestion

Question 9

It is an albuminoid type of protein that is affected little by other digestive enzyme

Answer 9

Collagen

Question 10

Collagen is digested by what enzyme?

Answer 10

Pepsin

Question 11

What is the site of most protein digestion?

Answer 11

Upper small intestine (duodenum and jejunum)

**under the influence of proteolytic enzymes from pancreatic secretion

Question 12

Enzymes that split protein molecule into small polypeptides

Answer 12

Trypsin and chymotrypsin

Question 13

Enzymes that cleave individual amino acids from the carboxyl ends of the polypeptides

Answer 13

Carboxypeptidase

Question 14

True or false
Only a small percentage of the proteins are digested all the way to their constituent amino acids by the pancreatic juices. Most remain as dipeptides and tripeptides

Answer 14

true

** This is because carboxypeptidases can only cleave BASIC and NEUTRAL amino acid

Question 15

The last digestive stage of the proteins in the intestinal lumen is achieved by _____

Answer 15

Enterocytes

Question 16

True or false
Dipeptides and tripeptides are not easily transported through the microvillar membrane to the interior of the enterocytes

Answer 16

False

• *amino acid, dipeptides and tripeptides are all easily transported through the interior of the enterocytes
• *inside the cytosol of the enterocyte are multiple other peptidases that are specific for the remaining types of linkages between amino acids

Question 17

A small amount of triglycerides is digested in the stomach by _____

Answer 17

Lingual lipase

Question 18

The first step in fat digestion is physically to break the fat globules into very small sizes so that the water-soluble digestive enzymes can act on the globule surfaces. This step is called

Answer 18

Emulsification

Question 19

Most of the emulsification occurs in the ____under the influence of _____

Answer 19

Duodenum; Bile

Question 20

Bile salts, when in high enough concentration in water, have the propensity to form what structures?

Answer 20

Micelles

Question 21

The stomach is a poor absorptive area of the gastrointestinal tract for these 2 reasons

Answer 21

It lacks the typical villus type of absorptive membrane and also because the junctions between the epithelial cells are tight junctions

Question 22

Folds of kerckring increase surface are by ____. Villi increase surface are by _____. Microvilli increase surface are by _____

Answer 22

3-fold, 10-fold, 20-fold (total area of almost 250 m2)

Question 23

Water is transported through the intestinal membrane entirely by _____

Answer 23

Diffusion

Question 24

Secreted by the cortices of the adrenal glands to enhance sodium absorption

Answer 24

Aldosterone

Question 25

PASSIVE absorption of chloride ion occurs in ____

Answer 25

The duodenum and jejunum

Question 26

Sodium ion absorption through the BASOLATERAL MEMBRANE into the BLOOD occurs through what mechanism? As opposed to chloride ion absorption in the DUODENUM and JEJUNUM ______

Answer 26

Sodium – active transport; Chloride ion – diffusion

Question 27

Sodium ion absorption from the GUT LUMEN into the CELL INTERIOR

Answer 27

Facilitated diffusion

Question 28

What ion is secreted in the gut lumen in exchange for sodium ion absorption?

Answer 28

Hydrogen ions

Question 29

What is the “active absorption of bicarbonate ions”?

Answer 29

When sodium ions are absorbed, moderate amounts of hydrogen ions are secreted into the lumen of the gut in exchange for some of the sodium. These hydrogen ions in turn combine with the bicarbonate ions to form carbonic acid (H2CO3), which then dissociates to form water and carbon dioxide. The water remains as part of the chyme in the intestines, but the carbon dioxide is readily absorbed into the blood and subsequently expired through the lungs

Question 30

In the ILEUM and LARGE INTESTINE, ACTIVE absorption of chloride ion occurs in exchange for what ion?

Answer 30

Bicarbonate – this is important in the large intestine to neutralize acidic products of intestinal bacteria

Question 31

Factors controlling calcium absorption in the blood

Answer 31

Parathyroid hormone secretion and Vitamin D

Question 32

Glucose is absorbed through what process

Answer 32

Sodium co-transport mechanism (SGLT1)