Module 21 Digestive System

Question 1

What are the four things that happen once you eat something?

Answer 1

1. Digestion: mechanical and chemical break down of food
2. Absorption: movement of food from GI tract into ECF
3. Secretion: enzymes and hormones are secreted by cells to aid with digestion
4. Motility: Smooth muscle helps get digested food through the GI tract

Question 2

Digestion and motility take place in the lumen of the digestive tract?

Answer 2

True

Question 3

Absorption of food only occurs if the food passes through the wall of the digestive tract and the fluid into the bloodstream?

Answer 3

True

Question 4

The walls of the digestive tract contain cells that secrete?

Answer 4

True

Question 5

What organs/parts are involved in the gastrointestinal tract?

Answer 5

1. Mouth
2. Pharynx
3. Esophagus
4. Stomach
5. Small intestine
6. Large intestine (colon)
7. Rectum
8. Anus

Question 6

Name all the accessory glands

Answer 6

1. Salivary glands
2. Liver glands
3. Gallbladder
4. Pancreas

Question 7

Motility in the GI tract is regulated by

A) Parasympathetic nervous system

B) Somatic motor system

C) Local control from neurons within the intestinal walls

D) Angiotensin II (via vasoconstriction)

Answer 7

The parasympathetic nervous system and local control from neurons within the intestinal walls.

Question 8

What are the layers of the GI tract and what are their functions?

Answer 8

1. Epithelial Layer: layer of cells that controls exchange between the internal and external environment
2. Smooth muscles arranged in alternating patterns to conduct peristalsis to push bolus forward.
3. Enteric Nervous System: Nerves in the GI tract that are on the muscle layer

Question 9

Does motility every end in the gastrointestinal tract?

Answer 9

No, motility occurs from the mouth all the way to the rectum.

Question 10

Where does secretion take place?

Answer 10

It occurs in the stomach, small intestine and ends in the colon.

Question 11

Where does absorption take place?

Answer 11

In the small intestine and and in the colon.

Question 12

What regulates digestion locally?

Answer 12

The enteric nervous system which is part of the peripheral nervous system contains sensory, motor, and interneurons to regulate digestion locally.

Question 13

What also regulates digestion?

Answer 13

The automatic nervous system (parasympathetic nervous system) which promotes motility and secretion.

Question 14

What does the mouth do? What is in the saliva?

Answer 14

Salivary glands: enzymes to break down starch
Water: to moisten and dissolve food
Mucous Production: to lubricate foods
Lysosomes: to kill bacteria
Bicarbonate: to neutralize sour foods

Question 15

What does amylase break down starch into?

Answer 15

maltose (disaccharide) and short polysaccharides.

Question 16

Where does the food go after mechanical and partial chemical digestion in the mouth?

Answer 16

Travels down the esophagus passing through the sphincters into the stomach.

Question 17

What do sphincters do?

Answer 17

They prevent stomach acid from entering into the esophagus and small intestine.

Question 18

Stomach as a storage place for food?

Answer 18

Yes the stomach slowly releases food into the small intestine for absorption.

Question 19

What does the stomach secrete?

Answer 19

It secretes acid to help break down food. It can break down proteins via the enzyme pepsin and acid HCl.

Question 20

What are the three functions of stomach acid?

Answer 20

The low pH kills pathogens, it activates pepsinogen to be (pepsin) and it denatures food proteins.

Question 21

what does the active form of pepsinogen do? It’s activated by the low pH into pepsin.

Answer 21

Pepsin will break down the food proteins into smaller peptides that will enter the small intestine.

Question 22

What do epithelium cells secrete in the stomach?

Answer 22

H+ ions to generate a low pH environment and pepsinogen

Question 23

What is the partially digested food called?

Answer 23

It’s called chyme

Question 24

After food leaves the stomach what parts of the small intestine does it hit and what occurs there?

Answer 24

1. Duodenum: site of most digestion due to release of pancreatic enzymes and bile from liver
2. Jejunum: site of most absorption
   3.

Question 25

What makes the small intestine good for absorption?

Answer 25

Villi extensions or folds in the intestinal walls that increase the surface area. The villi is the large structure.

Question 26

What are the components of the villi?

Answer 26

1. Enterocytes cover the villi and they have microvilli on them
2. Capillaries/Lacteal part of the lymphatic system
3. Capillaries which are for fat absorption

Question 27

Exocrine function of the pancreas

Answer 27

Lies under stomach and releases fluids and enzymes into the duodenum via the pancreatic duct. (HCO3- will neutralize the acid coming from the stomach)

Question 28

What enzymes does the pancreas release?

Answer 28

1. Pancreatic Amylase: continues digestion of starches
2. Lipase: digest fats
3. Proteases: digest proteins

Question 29

We have broken down the starches into maltose so far; but the body favors glucose. What happens next?

Answer 29

In the small intestine the enterocytes which contain the microvilli will release enzymes to break down the maltose into a glucose monomer which is the only form that can be absorbed into the cells.

Question 30

The enzyme maltase on the microvilli will convert maltose into glucose. What happens next?

Answer 30

Glucose can enter the enterocyte via a pump and then exits into the interstitial fluid and into the blood.

Question 31

Digestion and absorption of proteins

Answer 31

This continues in the duodenum of the small intestine. Pancreas secretes proteases in the inactive form called zymogens. Activate once they enter the duodenum.

Question 32

Trypsinogen (inactive form)

Answer 32

Enzyme in the brush border will activate trypsinogen to trypsin. Trypsin turns on other zymogens. They all break down food peptides into individual amino acids. Amino acids are absorbed by enterocytes using transporters.

Question 33

What travels to the liver?

Answer 33

1. Amino acids
2. Sugars
   The liver will remove harmful toxins and other unknown chemicals before circulating in the systemic circulatory system. Enzymes in liver destroy toxins.

Question 34

Describe how carbohydrates are digested

Answer 34

1. Carbohydrate digestion begins in the mouth with salivary amylase which breaks down starch.
2. Continues digestion in the luman of the duodenum with pancreatic amylase.
3. Maltase will break down maltose/small polysaccharides into glucose monomers.
4. Glucose will be actively transported into the enterocytes due to the Na+ gradient.
5. Glucose enters the capillaries via ATP

Question 35

Describe how proteins are digested in the small intestine?

Answer 35

1. Stomach breaks down the proteins into smaller amino acids via pepsin.
2. Pancreas releases trypsinogen into the duodenum which is converted to trypsin by a brush border enzyme.
3. Trypsin activates the other zymogens that were released by the pancreas.
4. Together they all are active proteases that break down amino acids further.
5. Amino acids enter the blood stream after crossing the enterocytes and head to the liver.

Question 36

Describe how fat is digested and absorbed?

Answer 36

1. Digestion begins in the mouth and stomach since some lipases are present.
2. Digestion continues in the small intestine
3. Bile (made in liver and released by gallbladder) breaks down fats via emulsification so that the triglycerides are more accessible to the lipases.
4. Pancreatic lipases break them down into monoglycerides/fatty acids (a.k.a micelles) to enter the enterocytes.
5. These fats recombine with cholesterol/proteins to form chylomicrons which leave the cell and enter the lymphatic system (lacteal exit).