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Systems: Alimentary AB > Small Intestine Structure and Function > Flashcards

Small Intestine Structure and Function Flashcards

1
Q

How long is the small intestine?

A

Roughly 6m

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2
Q

What are the 3 components of the small intestine and their lengths?

A
  • Duodenum 25cm
  • Jejunum 2.5m
  • Ileum 3.5m
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3
Q

What takes place in the duodenum?

A
  • Gastric acid neutralisation
  • Digestion
  • Iron absorption
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4
Q

What takes place in the jejunum?

A

95% of nutrient absorption

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5
Q

What takes place in the ileum?

A

NaCL and H2O absorption leading to chime dehydration

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6
Q

How is the absorptive area of the small intestine enhanced?

A
  • Folds
  • Villi
  • Microvilli
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7
Q

What does a villus cell absorb?

A
  • NaCl
  • Monosaccharides
  • Amino acids
  • Peptides
  • Fats
  • Vitamins
  • Minerals
  • Water
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8
Q

What do crypt cells secrete?

A
  • Cl

- H2O

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9
Q

Describe the Na coupled secondary active transport that takes place at the villi.

A
  • Cooperative transport means that Na enters alongside glucose/galactose/amino acids/nucleosides
  • Na is then pumped into the blood while K is pumped in.
  • Another transporter pumps K into the blood
  • Meanwhile a transporter pumps glucose/glactose/amino acids/nucleoside into the blood
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10
Q

How much water does the small intestine secrete each day?

A

1500ml

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11
Q

Where does H2O secretion come from?

A

Epithelial cells lining crypts of Lieberkuhm

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12
Q

How is H2O secreted?

A

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

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13
Q

Why is H2O important for normal digestion?

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
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14
Q

What normally happens to H2O secreted by crypts?

A

Reabsorbed by villi

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15
Q

Slide 9

A

Slide 9

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16
Q

What are the 2 distinct types of movement within the intestine?

A
  • Segmentation

- Peristalsis

17
Q

When is segmentation most common?

A

During a meal

18
Q

What is segmentation?

A

Contraction and relaxation of short intestinal segments

19
Q

Describe the process of segmentation.

A
  • Contraction moves chyme into adjacent areas of relaxation
  • Relaxed areas then contract and push chyme back
  • Provides thorough mixing of contents with digestive enzymes
  • Brings chyme into contact with absorbing surface
20
Q

How is segmentation generated?

A

-Initiated by depolarisation generated by pacemaker cells in longitudinal muscle layer

21
Q

What does the intestinal basic electrical rhythm produce?

A
  • Oscillations in the membrane potential
  • Meets threshold
  • Initiates action potential
  • Leads to contraction
22
Q

What determines the strength of contraction?

A

Action potential frequency

23
Q

What is the frequency of segmentation determined by?

A

BER

24
Q

What happens to BER as it moves down the intestine to the rectum?

A

Decreases

25
Q

What does segmentation produce?

A

Slow migration of chyme towards large intestine (more chyme pushed down that up)

26
Q

How does the parasympathetic system affect segmentation?

A

Via the vagus increases contraction

27
Q

How does the sympathetic system affect segmentation?

A

Decreases contraction

28
Q

How does the autonomic nervous system affect BER?

A

No effect

29
Q

When does peristalsis occur?

A

Following absorption of nutrients, segmentation stops and peristalsis starts

30
Q

What is the migrating motility complex?

A

Pattern of peristaltic activity travelling down small intestine ( starts in gastric antum)
-As one MMC enda another begins

31
Q

What causes cessation of MMC?

A

Food arriving in the stomach which causes initiation of segmentation

32
Q

What does MMC act to do?

A
  • Move undigested material into large intestine

- Limit bacterial colonisation of small intestine

33
Q

What is involved in the initiation of MMC?

A

Hormone motilin

34
Q

Law of Intestine

If intestinal smooth muscle is distended:

A
  • Muscle on oral side of bolus contracts
  • Muscle on anal side of bolus relaxes
  • Bolus is moved into area of relaxation towards colon
  • Mediated by neurones in myenteric plexus

Systems: Alimentary AB (37 decks)

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