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Alimentary System > Small Intestine Structure and Function > Flashcards

Small Intestine Structure and Function Flashcards

1
Q

What is the length of the small intestine?

A

About 6m

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2
Q

What does the small intestine consist of?

A

Duodenum

Jejunum

Ileum

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3
Q

How long is the duodenum?

A

25cm long

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4
Q

What are some functions of the duodenum?

A

Gastric acid neutralisation

Digestion

Iron absorption

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5
Q

How long is the jejunum?

A

2.5m long (2/5 of total length)

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6
Q

What are some functions of the jejunum?

A

Nutrient absorption

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7
Q

What percentage of nutrient absorption occurs in the jejunum?

A

95%

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8
Q

How long is the ileum?

A

3.5m (3/5 total length)

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9
Q

What is the function of the ileum?

A

NaCl/H2O absorption

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10
Q

What is the absorptive surface of the small intestine enhanced by?

A

Folds, villi and microvilli

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11
Q

What are the circular folds of the small intestine called?

A

Plicae

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12
Q

What is the relative surface area increase of the small intestine due to plicae?

A

3

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13
Q

What is the relative surface area increase of the small intestine due to villi?

A

30

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14
Q

What is the relative surface area increase of the small intestine due to microvilli?

A

600

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15
Q

What is the classification of the epithelium in the small intestine?

A

Simple columnar

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16
Q

What does villus cells absorb?

A

NaCl

Monosaccharides

Amino acids

Peptides

Fats

Vitamins

Minerals

Water

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17
Q

What are the functions of crypt cells?

A

Secrete Cl and water

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18
Q

How much water does the small intestine secrete everyday?

A

1500ml

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19
Q

Where does the water that the small intestine secretes come from?

A

Epithelial cells lining the crypts of Lieberkuhn

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20
Q

How does the small intestine secrete water passively?

A

Osmotically as a consequence of secreting Cl into the lumen of the gut

21
Q

Why is H2O secretion important for normal digestive processes?

A

Maintains luminal contents in liquid state

Promotes mixing of nutrients with digestive enzymes

Aids nutrient presentation to absorbing surface

Dilutes and washes away potentially injurious substances

22
Q

What happens to H2O secreted by crypts?

A

Normally reabsorbed by villi

23
Q

What are the 2 distinct kinds of movements that makes up intestinal motility?

A

Segmentation

Perstalsis

24
Q

What is segmentation?

A

Contraction of the circular muscles in the digestive tract

25
Q

What is perstalsis?

A

Contraction of the longitudinal muscles in the digestive tract

26
Q

When is segmentation most common?

A

During a meal

27
Q

What is the function of segmentation?

A

Alterations between contraction and relaxation of short intestinal segments moves chyme up and down into adjacent areas of relaxation

Provides thorough mixing of contents with digestive enzymes

Brings chyme into contact with absorbing surface

28
Q

How long does each cycle of segmentation last?

A

A few seconds

29
Q

Explain the mechanism of segmentation contractions?

A

1) Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer
2) Intestinal basic rhythm (BER) produces oscillations in membrane potential
3) Reaches threshold which generates an action potential
4) Causes contraction

30
Q

What is BER?

A

Basic electrical rhythm

31
Q

What determins the strength of contraction for segmentation?

A

Action potential frequency

32
Q

What is frequency of segmentation determined by?

A

BER

33
Q

How does BER change as chyme moves down the intestine to the rectum?

A

Decreases

34
Q

What supplies the innervation for segmentation?

A

Parasympathetic (vagus) increases contraction strength

Sympathetic decreases contraction strength

35
Q

Does the autonomic nervous system have an effect on BER?

A

No

36
Q

What effect does the parasympathetic nervous system have on segmentation?

A

Increases contraction strength

37
Q

What effect does the sympathetic nervous system have on BER?

A

Decreases contraction strength

38
Q

What does segmentation cause?

A

Slow migration of chyme towards large intestine (more chyme is pushed towards it than away from it)

39
Q

What occurs following absorption of nutrients in terms of segmentation and peristalsis?

A

Segmentation stops and peristalsis begins

40
Q

What are the pattern of contractions that creates peristalsis known as?

A

Migrating motility complex (MMC)

41
Q

Explain the mechanism of peristalsis?

A

1) Starts in gastric antrum
2) As one MMC ends at the terminal ileum another begins

42
Q

Where does peristalsis begin and end?

A

Begins at the antrum of the stomach and ends at the terminal ileum

43
Q

How does the arrival of food into the stomach impact segmentation and peristalsis?

A

Causes cessation of MMC and initiation of segmentation

44
Q

What is the function of peristalsis?

A

Move undigested material into large intestine

Limit bacterial colonisation of small intestine

45
Q

What is a hormone involved in the initiation of MMC?

A

Motilin

46
Q

What happens when intestinal smooth muscle is distended such as due to chyme?

A

Muscle on oral side contracts

Muscle on anal side relaxes

Bolus is moved into area of relaxation towards colon

47
Q

What is the bolus moving towards the colon mediated by?

A

Enteric nervous system

48
Q

Explain the mechanism of the gastroileal reflex?

A

1) Gastric emptying causes increase in segmentation activity in ileum
2) Opening of ileocaecal valve (sphincter)
3) Distention of colon
4) Reflex contraction of ileocaecal sphincter (prevents backflux into small intestine)

49
Q

What reflex controls chyme entering the large intestine?

A

Gastroileal reflex

Alimentary System (41 decks)

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