Digestive System 4

Question 1

What is Segmentation in the Small Intestine?

Answer 1

Alternating areas of contraction and relaxation that creates a Backward/forward motion (“massaging chyme”)

Question 2

What does segmentation allow for in the Small Intestine? (4)

Answer 2

1. Mechanical Digestion - Physical Breakdown
2. Assists in mixing chyme with Chemical Digestive Enzymes, promoting chemical digestion
3. Brings the chyme in contact with the Absorptive Surfaces of the digestive tract, enhancing the Absorption of nutrients
4. Propulsive Motility - The strength of segmentation is often greater in the early segments of the small intestine compared to the later segment

Question 3

What is the Rate and Regulation of segmentation (number per minute)?

Answer 3

Parasympathetic and Gastrin: Parasympathetic stimulation and the hormone gastrin increase the rate of segmentation.

Sympathetic:
Sympathetic stimulation decreases the rate of segmentation.

Question 4

What is Intestinal juice?

Answer 4

Collective name for:

• Accessory contributions – added at duodenum from pancreas, liver, gallbladder.
• Gastric emptying – stomach into duodenum.
• Intestinal secretions along small intestine – water and mucus

Question 5

Small intestine:

Answer 5

• Final digestion to absorbable size.
• 90% of absorption (10% in large intestine and stomach).
• Typically ~3 – 5 hours in small intestine

Question 6

What Breaks down Disaccharides to monosaccharides? (glucose, galactose, fructose)

Answer 6

brush border enzymes on apical membrane

Question 7

What Breaks Down Sucrose?

Answer 7

Sucrose is broken into glucose and fructose by sucrase

Question 8

What Breaks down Lactose?

Answer 8

Lactose is broken down to glucose and galactose by lactase

(lactase limited – lactose intolerance)

Question 9

What Breaks down Maltose?

Answer 9

Maltose is broken down to glucose and glucose by maltase

Question 10

How do Monosaccarhides Cross the Apical Membrane and the Basolateral Membrane?

Answer 10

• Facilitated diffusion glucose transporter or GLUT (fructose).
• Secondary active transporter involving sodium (glucose or galactose).
• All cross basolateral membrane by facilitated diffusion GLUTs

Question 11

What is Transported through the Apical Membrane by Primary Active Transport? (ignore)

Answer 11

Fructose via GLUT

glucose transporter

Question 12

What is Transported through the Apical Membrane by Secondary Active Transport?

Answer 12

Glucose and Galactose cotransported with Sodium (Na+)

Question 13

What Happenes to CHO in the Small Intestine?

Answer 13

Most CHO digested/absorbed within proximal 20% of small intestine.

Some CHO indigestible – soluble and insoluble fiber.

Question 14

How many different Glucose Transporters are in Humans?

Answer 14

14 different GLUT in humans.

Question 15

How are small peptides broken to individual AAs?

Answer 15

small peptides (made up of 2 – 3 amino acids; AAs) are broken down by brush border enzymes on apical membrane

Question 16

How do Small Peptides and Amino Acids Cross the Apical Membrane?

Answer 16

Small peptides (ones not broken down by brush border enzymes) cross by Secondary Active Transporter involving H+.

Individual AAs by Secondary Active Transporter involving sodium.

both cotransprort into intestinal epithilial cell

Question 17

What happens to Small Peptides and Amino Acids once they cross the Apical Membrane and are now in the Intestinal Epithalial Cell?

Answer 17

• Small peptides that crossed apical membrane intact are broken down to individual AAs by peptidases inside cell.
• All cross basolateral by facilitated diffusion amino acid transporters.

Question 18

How many Amino Acids and Amino Acid Transporters in Humans?

Answer 18

20 AAs with different amino acid transporters (~10 in humans)

Question 19

What needs to happen to fats before they can be absorbed?

Answer 19

“Pre-treatment” or emulsification

• Pieces of triglycerides from globule are coated in bile
  salts and phospholipids converting large fat globules
  into smaller emulsification droplets

Question 20

Nature of Bile Salts and Phospholipids:

Answer 20

Bile salts and phospholipids have a unique structure with a polar (hydrophilic or water-loving) side and a nonpolar (hydrophobic or fat-loving) side

Question 21

How do the Bile Salts and Tryglycerides arrange themselves during Emulsification? Why?

Answer 21

Bile salts and phospholipids surround triglyceride molecules with their polar sides facing outward.

This arrangement makes the triglycerides more water-soluble. The polar side interacts with water, while the nonpolar side interacts with the fat

The polar surface of the emulsified triglyceride droplets faces outward, creating a repulsion between droplets. This prevents them from coalescing back into larger fat globules.

Question 22

Why is Emulsification considered a One-Way process?

Answer 22

Emulsification is considered a one-way process, as it prevents the reaggregation of fat molecules into larger masses.

Question 23

How does Emulsification help Pancreatic Lipase?

Answer 23

The emulsification process exposes a greater surface area of the triglyceride droplets.

This increased surface area facilitates the action of pancreatic lipase, an enzyme that breaks down triglycerides into monoglycerides (glycerol bound to one fatty acid) and two separate fatty acids

Question 24

What breaks down triglycerides into monoglyceride?

Answer 24

pancreatic lipase

Question 25

How do Monoglycerides and fatty acids cross apical membrane?

Answer 25

Simple Diffusion

Question 26

fat absorbed w/ and w/o emulsion:

Answer 26

Without emulsion:

• 49 – 51% fat absorbed.

With emulsion:

• 96 – 98% fat absorbed

Question 27

How are Micelle’s formed?

Answer 27

Micelles are formed by the combination of bile salts, monoglycerides, and fatty acids.

Bile salts surround monoglycerides and fatty acids with their polar (hydrophilic) side facing outward, creating a small spherical structure

Micelles are similar to emulsification droplets, but they are smaller in size.

Question 28

What is the Purpose of Micelle?

Answer 28

Micelles serve as a temporary stage where monoglycerides and fatty acids are kept in a controlled environment before they can diffuse across the apical membrane of absorptive cells.

Question 29

Migration of Micelle:

Answer 29

Micelles tend to migrate toward the apical membrane of absorptive cells.

This migration brings monoglycerides and fatty acids in close contact with the absorptive surface of the cell, facilitating their diffusion across the membrane

Question 30

What is Chylomicron?

Answer 30

Chylomicron (lipoprotein for transport):

• Once abspobed inside epithelial cell monoglycerides and fatty acids reform triglycerides.
• Further combine with phospholipids and cholesterol to form chylomicron.
• Cell organizes them inside a vesicle (sac).

Question 31

What is Exocytosis?

Answer 31

Exocytosis:

• Vesicle fuses will basolateral membrane.
• Membrane opens up and releases chylomicrons into interstitial fluid.

Question 32

What is Migrating myoelectric complex (MMC)?

Answer 32

The Migrating Motor Complex (MMC) is a cyclical pattern of electrical and mechanical activity that occurs in the smooth muscle of the gastrointestinal tract, particularly in the stomach and small intestine during the fasting state. It is responsible for clearing undigested food, bacteria, and debris from the digestive system between meals

Question 33

What happens when MMC takes over?

Answer 33

MMC:

• Form of peristalsis that begins in stomach antrum.
• Travels a short distance (~60 cm) and stops.
• Next peristalsis starts roughly where last ended; it too travels a short distance then stops.
• Pattern continues with peristalsis starting roughly where previous peristalsis ended; travelling a short distance before stopping.
• These short peristaltic waves will migrate down small intestine in a series of steps; taking ~2 hours to reach large intestine.

Question 34

What Happenes at the end of the Ileum during MMC?

Answer 34

• At end of ileum, if chyme still in small intestine, will return back to stomach antrum and start again.
• Motility – propulsive to “sweep” remaining material along so minimal left in small intestine (aids in preventing bacterial growth).
• Some evidence exercise helps simulate.