Small Intestine Structure and Function

Question 1

What are the three parts of the small intestine and their roles?

Answer 1

Duodenum - Gastric acid neutralisation, digestion * iron absorption (25cm)
Jejunum - Nutrient absorption (2.5m)
Ileum - NaCl/H2O absorption leading to chyme dehydration (3.5m)

Question 2

How is the absorptive surface increased?

Answer 2

Microvilli found on top of the epithelial cells of the villi

Question 3

Where are crypts found, what are they lined with and what is found at the bottom of them?

Answer 3

At the bottom of villi
Younger epithelial cells which are primarily involved in secretion
Stem cells

Question 4

Where are hydrogen ions held?

Answer 4

Within the mucus layer

Question 5

What does the villous cell absorb?

Answer 5

NaCl
Monosaccharides
Amino acids
Peptides
Fats
Vitamins
Minerals 
Water

Question 6

What do crypt cells secrete?

Answer 6

Chloride ions

Water

Question 7

Where does water secretion come from and how does it occur?

Answer 7

Epithelial cells lining the crypts of Lieberkuhn

Secreted passively as consequence of the active secretion of chloride from the intestinal lumen

Question 8

Why is water important in digestion?

Answer 8

Maintains luminal contents in liquid state
Promotes nutrient mixing
Aids nutrient presentation
Dilutes/washes away potential harmful substances

Question 9

What happens to water after it is secreted?

Answer 9

Usually reabsorbed by the villi

Question 10

What are the two types of movement in the GI tract?

Answer 10

Peristalsis

Segmentation

Question 11

When is segmentation most common and what is it the contraction of?

Answer 11

During a meal
The short circular intestinal segments
Longitudinal segments remain relaxed the whole time

Question 12

What area contracts?

Answer 12

That which was relaxed as the other part was contracted to provide a thorough mixing of contents with digestive enzymes

Question 13

What does segmentation bring the chyme into contact with and where does it propel it?

Answer 13

The absorbing surface

Towards the large intestine

Question 14

How is the generation of contractions initiated?

Answer 14

Depolarisation of pacemaker cells in the longitudinal muscle layer causing the BER to produce oscillation in the membrane potential

Question 15

Does the BER increase or decreased as it moves down the intestine towards the rectum?

Answer 15

Decreases

Question 16

How do sympathetic and parasympathetic signals affect contraction?

Answer 16

Sympathetic decreases contraction

Parasympathetic increases contraction

Question 17

How does the autonomic nervous system affect the BER?

Answer 17

It has no effect

Question 18

Following the absorption of nutrients what stops and what starts?

Answer 18

Segmentation stops and peristalsis starts

Question 19

What is the Migrating Motility Complex (MMC)?

Answer 19

Pattern of peristaltic activity travelling down the small intestine and as one MMC ends, another begins

Question 20

What is the aim of MMC?

Answer 20

To move undigested material into the large intestine

Limit bacterial colonisation of of small intestine

Question 21

What will happen if cellulose remains in your gut for too long?

Answer 21

Bacteria will colonise there

No bacteria wanted in the small intestine

Question 22

What area of the lumen does the bolus always move into?

Answer 22

The relaxed muscle on the anal side

Question 23

What does gastric emptying lead to with respect to the ileum?

Answer 23

An increase in segmentation activity

Question 24

What sphincter allows the entry of the chyme into the large intestine causing distension?

Answer 24

Ileocaecal valve

Question 25

What is the large intestine in terms of chyme and faeces?

Answer 25

It is a one way process