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The Alimentary Canal > Small Intestine Structure and Function > Flashcards

Small Intestine Structure and Function Flashcards

1
Q

What length is the small intestine?

A

Around 6 metres - 4.5 to 9 metres

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2
Q

Describe the duodenum

A

Is 25cm long
Gastric acid neutralisation, digestion and iron absorption

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3
Q

Describe the jejunum

A

Is 2.5m long
Does 95% of the nutrient absorption

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4
Q

Describe the ileum

A

3.5m long
NaCl/H2O absorption which gives chyme dehydration

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5
Q

What increases the surface area of the small intestine?

A

Folds, villi and microvilli

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6
Q

How much does folds, villi and microvilli increase the relative surface area?

A

Folds - 3
Villi - 30
Microvilli - 600

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7
Q

Describe the structure of the villi

A

Simple columnar epithelium
Lacteal - takes up product of fat digestion
Capillary network
Goblet cells
Crypt of Lieberkuhn

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8
Q

What does the villus cell absorb?

A

NaCl
Monosaccharides
Amino acids
Peptides
Fats
Vitamins
Minerals and Water

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9
Q

What does does a crypt cell secrete?

A

Cl and Water

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10
Q

What is the difference between a crypt cell and a villus cell?

A

Villus cell absorbs
Crypt cell secretes

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11
Q

Describe Na coupled secondary active transport

A

Na enters cell along with ex. glucose, galactose, amino acids or nucleosides
Promotes water transport
Na leaves basolateral membrane by NaK pump as K is recycled

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12
Q

How much intestinal fluid does the small intestine secrete in a day?

A

1500ml of H2O

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13
Q

How is H2O secreted from crypts of Lieberkuhn?

A

Passively as a consequence of active secretion of chloride into intestinal lumen

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14
Q

Why is H2O secretion important for normal digestive process?

A

Maintains lumenal contents in liquid state
Promotes mixing of digestive enzymes and nutrients
Aids nutrient presentation to absorbing surface
Dilutes and washes away injurious substances

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15
Q

What happens normally to the H2O secreted by crypts?

A

Reabsorbed by villi

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16
Q

Describe the transport of Cl across the small intestine into lumen

A

Cl needs K and Na to cross basal membrane
When in cell creates an even more negative environment so Cl leaves cell into lumen - promoting water secretion

17
Q

Explain the CFTR

A

Adenylate cyclase converts ATP into cAMP
Which activated PKA causing the release of Cl

18
Q

What are the 2 distinct types of movement in the small intestine?

A

Segmentation
Peristalsis

19
Q

Describe segmentation

A

Contraction and relaxation of short intestinal segments
The contraction moves chyme into adjacent areas of relaxation
Relaxed areas then contract

20
Q

What is the function of segmentation in intestinal motility?

A

Provides thorough mixing of contents with digestive enzymes
Brings chyme into contact with absorbing surface

21
Q

How is segmentation contraction initiated?

A

By depolarisation generated by pacemaker cells in longitudinal muscle layer

22
Q

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

A

Produces oscillations in membrane potential causing threshold to be met - firing AP
Then causing contraction

23
Q

What is the frequency of segmentation determined by?

A

BER

24
Q

Does BER increase or decrease when moving down intestine?

A

Decreases towards rectum

25
Q

Is segmentation slow or fast?

A

Slow migration of chyme towards large intestine

26
Q

Describe the parasympathetic innervation on segmentation

A

Vagus nerve causes increased contraction

27
Q

Describe sympathetic innervation on segmentation

A

Descreases contraction

28
Q

Does autonomic nerves effect BER

A

No effect

29
Q

When does peristalsis start?

A

Following absorption of nutrients - segmentation stops

30
Q

Explain migrating motility complex (MMC)

A

Pattern of peristaltic activity travelling down the small intestine
As one MMC ends then another begins

31
Q

What does arrival of food in stomach do to the MMC?

A

Causes cessation of MMC and initiation of segmentation

32
Q

What is the purpose of the MMC?

A

Move undigested material into large intestine
Limit bacterial colonisation of small intestine

33
Q

Describe the hormone Motilin

A

Released when nutrient levels in small intestine are gone
Initiates MMC

34
Q

According to the law of intestine what happens if smooth muscle is distended?

A

Muscle on oral side of bolus contracts and on anal side it relaxes
Bolus is moved to area of relaxation towards the colon

35
Q

What is peristalsis mediated by?

A

Neurones in the myenteric plexus

36
Q

Explain the gastroileal reflex

A

Opening of ileocaecal valve/sphincter
Causes entry of chyme into large intestine
Distention of colon
Reflex contraction of ileocaecal sphincter

37
Q

What does gastric emptying cause?

A

Segmentation activity in ileum

The Alimentary Canal (33 decks)

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