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Year 2- GIT > Small Intestine Structure and Function > Flashcards

Small Intestine Structure and Function Flashcards

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1
Q

What is the average length of the small intestine?

A

6 metres

->called the small intestine due to small diameter, not length!

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2
Q

Name the three parts of the small intestine.

A

Duodenum
Jejunum
Ileum

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3
Q

What is the shortest part of the small intesttine?

A

Duodenum, about 25 cm long

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4
Q

What is the function of the duodenum?

A

-Gastric acid neutralisation as is the first part that the stomach contents will meet after leaving the stomach.
-Digestion.
-Iron absorption.

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5
Q

How is gastric acid neutralised?

A

By bicarbonate

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6
Q

Where does bicarbonate come from?

A

Duodenum
Pancreatic juice
Bile

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7
Q

How does the duodenum play a role in digestion?

A

Digestive enzymes come from the pancreatic juices and bile which help with the breakdown of fats

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8
Q

Why is it important, it terms of the digestion of fat, to have bile and pancreatic juice?

A

Bile creates an emulsion which is critical to allow fats to be digested and broken down

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9
Q

How long is the jejunum?

A

Approx. 2.5m long

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10
Q

What is the main function of the jehunum?

A

Nutrient absorption- 95% of nutrients are absorbed in the jejunum

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11
Q

How long is the ileum?

A

Approx. 3.5m

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12
Q

What is the main function of the ileum?

A

Absorption of sodium chloride and water to dehydrate the chyme

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13
Q

Why is it important to dehydrate the chyme?

A

So it’s more solid when entering the large intestine and can be removed from the body as faeces

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14
Q

How is the absorptive surface area of the small intestine enhanced?

A

Villi, folds

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15
Q

What are the layers of the small intestine?

A

Mucosa
Submucosa
Muscularis
Serosa

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16
Q

What are the two muscle layers in the small intestine?

A

Circular muscle
Longitudal muscleq

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17
Q

What do the folds in the small intestine allow for?

A

Mixing of the chyme

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18
Q

Where does absorption usually happen in the small intestine?

A

Villi

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19
Q

What are the capillaries of the villi called?

A

Lacteal

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20
Q

What do the lacteal allow for?

A

Assists with fat absorption

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21
Q

What are the roles of the goblet cells on the surface of the villi?

A

Secrete mucus

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22
Q

What are the roles of crypt ducts on the villi?

A

-Secrete water into the lumen of the small intestine
-Also contain stem cells so can help w the regeneration of intestinal epithelial cells.

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23
Q

There is a continuous turnover of epithelial cells of the small intestine. How long is the lifespan of an epithelial cell in the small intestine?

A

3-5 days

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24
Q

What happens to the epithelial cells when they die?

A

Can be used as nutrients as made of proteins
Removed from body in faeces

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25
Q

Why will there be many side effects to the GIT is a patient is having chemo?

A

Chemo targets rapidly growing and dividing cells, which the epithelial cells of the GIT are

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26
Q

What type of epithelium are the epithelial cells of the small intesine?

A

Columnar epithelium

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27
Q

How much more surface area does having the folds in the small intestine give it?

A

3x greater surface area

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28
Q

How much more surface area does having the villi in the small intestine give it?

A

30x greater surface area

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29
Q

How much more surface area does having the microvilli in the small intestine give it?

A

600x greater surface area

30
Q

What is the difference between villi and microvilli?

A

Villi are the larger projections on the surface of the small intestine, microvilli are small projections on the villi of the small intestine

31
Q

What form of fat do lacteals absorb?

A

Chylomicrons

32
Q

Which cells form the villi?

A

Villus cells

33
Q

What can villus cells absorb?

A

Sodium chloride
Monosaccharides (glucose, galactose, fructose)
Amino acids
Peptides
Fats
Vitamins
Minerals
Water

34
Q

RECAP- briefly describe how the sodium coupled active transport works in the small intestine.

A

Secondary active transport as NaK pump too
NaK pump-> 3 Na out, 2 K in, electrochemical gradient for sodium inside cells meaning it transports into lumen of cells.

Sodium transport is co-transport as glucose or amino acid gets transported into the cell at the same time thanks to the sodium coupled receptor

35
Q

How much water does the small intestine produce in a day?

A

Approx. 1500ml

36
Q

Where does the water secretion come from in the small intestine?

A

Epithelial cells lining crypts of Lieberkuhn

37
Q

Why is water important in the small intestine?

A

Keeps material in a liquid state until the ileum
Promotes mixing with digestive enzymes

38
Q

Describe the transport of chlorine into the lumen.

A

-Comes from blood through the basolateral membrane via sodium potassium chloride channel.
-2 Cl, 1 Na, 1 K get transported into the cell simultaneously.
-Use of NaK pump to keep the cycle of Na out of cell and K into cell.
-Chlorine accumulates and eventually goes through brush border membrane and into lumen of small intestine.

39
Q

How does chlorine get through the brush border membrane?

A

Via CFTR

40
Q

What is CFTR?

A

Cystic fibrosis transmembrane conductance regulator

41
Q

What do CFTR do?

A

Helps move chlorine outside the crypt epithelial and this moves water indirectly.

42
Q

What happens if there are genetic changes in the CFTR?

A

Individuals will be born w cystic fibrosis

43
Q

What activates the CFTR channel?

A

Enzyme called adenylate cylase.

44
Q

What does adenylate cyclase do?

A

Converts ATP to cyclic AMP

45
Q

What are the two types of intestinal motility?

A

Segmentation
Peristalsis

46
Q

When is segmentation common?

A

During meals

47
Q

What is the main function of segmentation?

A

To mix and digest food

48
Q

How does the chyme move during segmentation?

A

Continuous contraction and relaxation of the small intestine

49
Q

How is segmentation generated?

A

Contractions caused by depolarisation generated by pacemaker cells.
This produces action potentials which make contraction.

50
Q

Which cells initiate depolarisation for contractions of segmentation and where are they found?

A

Pacemaker cells found in longitudal muscle

51
Q

What does the intestinal basic electrical rhythm (BER) do?

A

Produces oscillations in membrane potential which exceeds the threshold which produces an action potential, causing contraction.

52
Q

What determines the strength of contraction?

A

The frequency of action potentials

53
Q

As the chyme moves from the intestine towards the rectum, what happens to the BER?

A

Decreases further down the system

54
Q

Which nervous system increase strength of contraction of the small intestine?

A

Parasympathetic NS

55
Q

Which nervous system decrease strength of contraction of the small intestine?

A

Sympathetic NS

56
Q

Why is there no effect of the autonomic NS on the BER?

A

Self controlled by pacemaker cells in the longitudal muscle

57
Q

What does peristalsis do?

A

Helps move the chyme towards the large intestine

58
Q

What controls peristalsis?

A

Migrating motility complex (MMC)

59
Q

When does MMC stop?

A

When food arrives in the stomach, segmentation begins at this point

60
Q

What does MMC act to do in the process of peristalsis?

A

Move undigested material to large intestine.
Prevent bacterial colonisation of small intestine.

61
Q

What is involved in the initiation of MMC?

A

Motilin, a type of hormone

62
Q

What happens to the size of the small intestine when chyme reaches it?

A

Causes distension and size of small intestine will increase

63
Q

What happens to the muscle on the oral side of the bolus?

A

Contracts

64
Q

What happens to the muscle on the anal side of the bolus?

A

It relaxes

65
Q

What is the difference between bolus and chyme?

A

Chyme is food that has been mixed with gastric juice
Bolus is food which has been mixed w saliva

66
Q

How is the contraction and relaxation of the small intestine (to move the food from one end to the other) mediated?

A

By neurones in the myenteric plexus

67
Q

When there is gastric emptying, what happens in the ileum?

A

Increase in segmentation activity in the ileum

68
Q

What opens when there is an increase in segmentation activity in the ileum?

A

Opening of ileocecal valve

69
Q

What does the ileocecal valve/sphincter do?

A

Controls entry of chyme into large intestine

70
Q

After distension of the colon, what happens to the ileocecal valve?

A

It closes to prevent backflow

71
Q
A

Year 2- GIT (37 decks)

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