Section 5

Question 1

What are the three segments of the small intestine?

Answer 1

The three segments of the small intestine are the duodenum, the jejunum, and the ileum.

The majority of digestion and absorption occurs in the small intestine.

Question 2

What is the term for motility in the small intestine?

Answer 2

The term for motility in the small intestine is segmentation.

Segmentation in the small intestine involves both mixing and slowly propelling the chyme.

Question 3

Describe the movement of segmentation in the small intestine.

Answer 3

Segmentation occurs through localized concentric contractions, which trap the chyme in relaxed areas, followed by relaxation of contracted areas and ring-like contractions in previously relaxed areas. This process allows thorough mixing and slow forward movement of the chyme.

Question 4

What initiates segmentation in the small intestine, and how is it regulated?

Answer 4

Segmentation in the small intestine is initiated by pacemaker cells generating a basic electrical rhythm (BER). Gastrin, secreted in response to chyme in the stomach, also contributes to segmentation.

The BER frequency is approximately 12 per minute in the duodenum and jejunum, and about 9 per minute in the terminal ileum.

Segmentation is enhanced by distention of the small intestine and extrinsic nerve activity, but it is absent between meals.

Question 5

What is the purpose of the migrating motility complex in the small intestine?

Answer 5

The migrating motility complex consists of weak peristaltic waves that occur when most of the meal has been absorbed. Its purpose is to move remnants of the previous meal, mucosal debris, and bacteria forward towards the colon.

Question 6

What is the purpose of the mucus secreted by the exocrine glands in the small intestine?

Answer 6

: The purpose of the mucus secreted by the exocrine glands in the small intestine is to provide lubrication, protection, and ample water for the hydrolytic reactions carried out by digestive enzymes.

Question 7

What are the three classes of membrane-bound enzymes found in the brush border of the small intestine?

Answer 7

The three classes of membrane-bound enzymes found in the brush border of the small intestine are enterokinases, disaccharidases, and aminopeptidases.

Question 8

How do disaccharidases contribute to digestion in the small intestine?

Answer 8

Disaccharidases complete carbohydrate digestion by hydrolyzing disaccharides (such as maltose, sucrose, and lactose) into monosaccharides.

Question 9

What clinical condition is associated with a deficiency in the disaccharidase lactase?

Answer 9

Lactose intolerance is associated with a deficiency in the disaccharidase lactase, leading to the inability to break down lactose. This condition can cause symptoms such as cramping and diarrhea due to excess fluids and gases in the intestine.

Question 10

What is the primary function of the small intestine?

Answer 10

The primary function of the small intestine is absorption, where almost all carbohydrates, proteins, fats, electrolytes, vitamins, and the majority of water are absorbed.

Question 11

Where does the majority of absorption occur in the small intestine?

Answer 11

The majority of absorption occurs in the duodenum and jejunum of the small intestine, with little absorption occurring in the ileum.

Question 12

How does the structure of the small intestine contribute to its high surface area?

Answer 12

The structure of the small intestine increases its surface area significantly:

• Circular folds in the inner surface increase the surface area three-fold.
• Villi, microscopic finger-like projections, further increase the surface area ten-fold.
  = Microvilli, hair-like projections on the epithelial cells of the villi (brush border), increase the surface area another twenty-fold.

Question 13

What is the absorptive capacity of the small intestine?

Answer 13

The absorptive capacity of the small intestine is much greater than the daily intake of nutrients, meaning that pretty much anything ingested will be absorbed.

Question 14

What are the three sources of exogenous proteins that need to be digested and absorbed in the small intestine?

Answer 14

1. Ingested proteins.
2. Proteins from epithelial mucosal cells that have been sloughed off.
3. Plasma proteins that normally leak from the capillaries into the digestive tract lumen.

Question 15

How are proteins broken down for absorption in the small intestine?

Answer 15

Regardless of the protein source, they are all broken down into individual amino acids and small peptides for absorption.

These are absorbed by secondary active transport, similar to glucose and galactose.

Small peptides are broken down by both the brush border aminopeptidases and intracellular peptidases.

Question 16

What happens to amino acids after absorption in the small intestine?

Answer 16

Amino acids move out across the basolateral membrane of the epithelial cells and into the blood for distribution to the rest of the body.

Question 17

How can sodium be absorbed in the small intestine?

Answer 17

Sodium can be absorbed both passively and actively. Chloride follows sodium due to the electrical gradient, and water follows sodium due to the osmotic gradient.

Question 18

Describe passive absorption of sodium in the small intestine.

Answer 18

In passive absorption, sodium moves down its electrochemical gradient into the interstitial fluid by passing between intestinal epithelial cells through leaky tight junctions.

Question 19

Explain active absorption of sodium in the small intestine.

Answer 19

Active absorption of sodium requires active transport. Sodium can pass through the luminal membrane either through sodium channels or co-transported with glucose or amino acids.

Once inside an epithelial cell, sodium is actively pumped out across the basolateral membrane into the interstitial fluid, from where it diffuses into the capillaries.

Question 20

How are carbohydrates absorbed in the small intestine?

Answer 20

All carbohydrates are absorbed as monosaccharides through active transport, either by sodium-monosaccharide cotransport or sodium-independent facilitated diffusion.

Question 21

Describe the absorption of galactose in the small intestine.

Answer 21

Galactose is absorbed through secondary active transport. Basolateral Na⁺-K⁺ pumps bring Na⁺ into epithelial cells, which is then used by cotransporters to bring galactose into the cell. Once concentrated inside, galactose moves down its concentration gradient across the basolateral membrane and into the blood.

Question 22

Explain the absorption of glucose in the small intestine.

Answer 22

Glucose is absorbed through secondary active transport similar to galactose. Basolateral Na⁺-K⁺ pumps bring Na⁺ into epithelial cells, which is then used by cotransporters to bring glucose into the cell. Once concentrated inside, glucose moves down its concentration gradient across the basolateral membrane and into the blood.

Question 23

How is fructose absorbed in the small intestine?

Answer 23

Fructose is absorbed last and is transported by facilitated diffusion.

Question 24

How are dietary fats absorbed in the small intestine?

Answer 24

1. Emulsification: Bile salts break down fats into smaller droplets.
2. Digestion: Pancreatic lipases break down triglycerides into monoglycerides and fatty acids.
3. Absorption: Monoglycerides and fatty acids diffuse from micelles into epithelial cells when they reach the luminal membrane of epithelial cells. The micelles return to the chyme to pick up more triglycerides.
4. Reabsorption: Bile salts are reabsorbed through active transport in the terminal ileum.
5. Processing: Inside epithelial cells, monoglycerides and fatty acids are reassembled into triglycerides.
6. Formation of Chylomicrons: Triglycerides combine with lipoproteins to form water-soluble chylomicrons (droplets).
7. Transport: Chylomicrons exit epithelial cells via exocytosis, enter the lymphatic system, and eventually reach the bloodstream.

Question 25

What is the role of iron in the body, and how is it absorbed in the small intestine?

Answer 25

Role: Iron is essential for the production of hemoglobin.

Absorption Factors: Absorption depends on iron state; ferrous iron (Fe2+) is more readily absorbed than ferric iron (Fe3+).

Absorption Process: Iron absorbed into small intestine epithelial cells can be immediately transferred to the blood for red blood cell production or stored as ferritin in the epithelial cell.

Use in Red Blood Cell Production: Iron transferred to the blood is bound to transferrin for delivery to the bone marrow.

Storage: Iron not immediately used is stored as ferritin within epithelial cells.

Secretion & Excretion: If iron levels within epithelial cells becomes too high, it is secreted into the intestinal lumen. Any ferritin is also dumped into the lumen when the epithelial cell is sloughed off within three days. All excess iron is excreted in the feces,

Question 26

What are the causes of diarrhea, and how does it impact the body?

Answer 26

Causes:
– Excessive small intestine motility: Often due to local irritation (bacterial, viral) or emotional stress, leading to inadequate water absorption.
– Excess of osmotically active particles: Examples include lactose intolerance, where undigested lactose draws water into the intestines.
– Toxins from microorganisms: Toxins like those from Vibrio cholerae can promote excessive fluid secretion by the intestinal mucosa.

Impact on the Body:
– Beneficial: Rapid emptying of the intestine aids in removing harmful materials.
– Detrimental: Excessive and prolonged diarrhea can lead to dehydration, loss of nutrients, and metabolic acidosis due to loss of bicarbonate (HCO3-).

Question 26

Which of the following enzymes are involved in the digestion of PROTEINS:

• chymotrypsin
• disaccharidase
• enterokinase
• trypsin
• lipase
• aminopeptidase
• carboxypeptidas
• amylase

Answer 26

Chymotrypsin
Enterokinase
Trypsin
Aminopeptidase
Carboxypeptidas

Question 27

Which of the following enzymes are involved in the digestion of CARBOHYDRATES:

• chymotrypsin
• disaccharidase
• enterokinase
• trypsin
• lipase
• aminopeptidase
• carboxypeptidas
• amylase

Answer 27

amylase and disaccharidase

Question 28

Which of the following enzymes are involved in the digestion of FATS:

• chymotrypsin
• disaccharidase
• enterokinase
• trypsin
• lipase
• aminopeptidase
• carboxypeptidas
• amylase

Answer 28

only lipase