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Second Year Systems > Small Intestine Structure and Function > Flashcards

Small Intestine Structure and Function Flashcards

1
Q

What is the length of the duodenum, jejunum and ileum?

A

Duodenum - 25cm long

Jejunum - 2.5 m long

ileum - 3.5 m long

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2
Q

What is the function of the duodenum, jejunum and the ileum?

A

Duodenum - gastric acid neutralisation, digestion, iron absorption

Jejunum - Nutrient absorption 95%

Ileum - •NaCl/H2O absorption - chyme dehydration

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3
Q

Why is the jejunum usually flat?

A

Because it is usually empty

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4
Q

How much water does the ileum absorb each day?

A

Around 9 litres, 2200ml is lost in faeces each day

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5
Q

What is the name given to the circular folds that are present in the small intestine?

A

Plicae circularis

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6
Q

What is the function of the plicae?

A

Increase surface area but also create a swirling motion when food is being mixed

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7
Q

Where do the stem cells arise from?

A

The crypt of Lieberkuhn

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8
Q

What structure in the villi is responsible for removing the products of fat digestion?

A

The lacteal

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9
Q

What are the three mechanisms for increasing surface area in the small intestine?

A
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10
Q

What do the villus cells absorb?

A
  • NaCl
  • Monosaccharides
  • Amino acids
  • Peptides
  • Fats
  • Vitamins
  • Minerals
  • Water
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11
Q

What do crypt cells secrete?

A

Cl and water

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12
Q

How is glucose absorbed?

A
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13
Q

What is the purpose of the leaky potssium channel?

A

Prevents the cell from depolarizing - keeps inward drive for sodium

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14
Q

Why is H2O secretion of the intestines described as passive?

A

Epithelial cells lining the crypt of Lieberkuhn actively secrete chloride into the intestinal lumen - consequent movement of water

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15
Q

Why is H2O secretion important for normal digestive process?

A

A - Maintains lumenal contents in liquid state

B - Promotes mixing of nutrients with digestive enzymes

C - Aids nutrient presentation to absorbing surface

D - Dilutes and washes away potentially injurious substances

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16
Q

What is the transporter required to bring chlorine into the epithelial cell of the crypt of Lieberkuhn?

A

Sodium potassium chloride co transporter - transports potassium chloride and sodium (2 chloride and one of each (K and Na)

17
Q

What is the name of the Chloride transporter on the lumenal side of the epithelial cell?

A

CFTR - Cystic Fibrosis Transmembrane Conductance Regulator - activated by the indirect action of adenylate cyclase

18
Q

What are the two distinct types of intestinal motility?

A

Segmentation and peristalsis

19
Q

Describe the process of segmentation

A
  • Most common during meal
  • Contraction and relaxation of short intestinal segments
  • Contraction (few seconds) moves chyme (up & down) 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

Slightly faster contraction at the proximal portion of the small intestine results in a net migration of chyme down the small intestine

20
Q

What causes segmentation?

A

Generated by pacemaker cells in the longitudinal muscle layer.

Intestinal basic rhythm produces oscillations

Frequency of segmentation is determined by BER

21
Q

What changes the strength in contraction?

A

The action potential frequency

22
Q

When does peristalsis happen?

A

Following absorption of nutrients: segmentation stops and peristalsis starts

23
Q

What is the migrating motility complex?
MMC

A
  • Pattern of peristaltic activity travelling down small intestine (starts in gastric antrum)
  • As one MMC ends (terminal ileum) another begins
  • Arrival of food in stomach - cessation of MMC and initiation of segmentation
24
Q

What is the effect of the MMC?

A

Moves undigested material into the large intestine

Limits the bacterial colonisation of small intestine

Undigested food includes the likes of cellulose
bacteria in the large intestine ok but not the small intestine.

25
Q

What is motilin?

A

A hormone involved in initiation of MMC

Motilin levels in the blood rise when nutrient levels in the lumen fall below a certain level

26
Q

Explain how a bolus moves down the intestine

A

When the intestinal smooth muscle becomes distended:

Muscle on the oral side contracts

Muscle on the anal side relaxes

Bolus moves to the area of relaxation (towards colon)

27
Q

What mediates peristalsis?

A

Neuorones in the myenteric plexus

28
Q

What is the gastroileal reflex?

A

Contraction of the ileocaecal sphincter when chyme enters the large colon, as a result of distension of the large bowel

29
Q

What is the purpose of the gastroileal reflex?

A

Prevents backflux into the ileum

Second Year Systems (21 decks)

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