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Physiology. Gastrointestinal Physiology. > The Small Intestine. > Flashcards

The Small Intestine. Flashcards

1
Q

What 2 major processes occur in the small intestine?

A

Digestion and absorption.

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2
Q

What are the 4 major functions of the small intestine?

A

To further propel chyme through the intestine.

To buffer acidic chyme.

To further digest acidic chyme.

To absorb micronutrients, water and electrolytes.

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3
Q

What 2 modes of contraction are carried out by the small intestine?

A

Persitalsis.

Mixing.

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4
Q

What prevents the flow of chyme into the large intestine from the small intestine?

A

The ileocecal sphincter.

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5
Q

What are the small projections that project off the wall of the small intestine known as?

A

Intestinal villi.

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6
Q

What is the function of the intestinal villi?

A

They increase the surface area of the intestine and aid with absorption.

They also secrete digestive enzymes.

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7
Q

What is found in between each intestinal villi?

A

A crypt of lieberkuhm.

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8
Q

What is found in the crypts of lieberkuhn?

A

Different cells at different levels with stem cells at the bottom.

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9
Q

What happens to the stem cells at the bottom of the crypts of Lieberkuhn?

A

They differentiate into the cells that are located at the lowest level of the crypt.

They are then pushed upwards by more developing cells.

As they are pushed up they turn into cells that are found at the higher levels of the crypt.

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10
Q

Is there a very high turnover of cells in the crypts of Lieberkuhn?

A

Yes, they are replaced roughly every 5 days.

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11
Q

What is the order of cells found in the crypt of Lieberkuhn from youngest to oldest?

A

Intestinal stem cells.

Paneth cells.

Transit amplifying cells.

Goblet cells.

Enteroendocrine cells.

Enterocytes.

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12
Q

What are the secretory cells of the crypts of Lieberkuhn?

A

The enterocytes.

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13
Q

What age are the secretory cells that are found in the crypts of Lieberkuhn?

A

The young enterocytes.

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14
Q

Where are the enterocytes located on the intestinal villi?

A

At the end of the intestinal villi.

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15
Q

What is the function of the young enterocytes of the intestinal villi?

A

They secrete intestinal fluid into the lumen.

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16
Q

What is the function of intestinal fluid that is secreted by the young enterocytes of the intestinal villi?

A

Cl- is secreted into the gut lumen.

Na+ follows the gradient into the lumen and water follows.

The water dilutes the chyme.

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17
Q

What cells are the absorptive cells of the intestinal villi?

A

The mature enterocytes.

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18
Q

What is the function of the mature enterocytes of the intestinal villi?

A

They develop microvilli called a brush border membrane and this contains digestive enzymes and absorptive mechanisms.

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19
Q

What will break down the partially digested macromolecules in the chyme of the small intestine?

A

BBM enzymes.

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20
Q

What disorder can affect the young enterocytes of the intestinal villi?

A

Diarrhoea as this leads to more water secretion into the intestine.

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21
Q

What is the difference between luminal and membranous digestion in the small intestine?

A

Luminal digestion occurs is due to enzymes that were released in the mouth and stomach.

Membranous digestion is due to BBM enzymes.

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22
Q

What enzymes carry out hydrolysis in the small intestine?

A

Enzymes from the luminal phase of digestion.

Enzymes from the membranous phase of digestion.

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23
Q

Bile salts and B12 are absorbed in what part of the small intestine?

A

In the ileum.

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24
Q

How are starch and glycogen broken down in the luminal phase of digestion?

A

Amylase breaks large polysaccharides down into oligopeptides etc.

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25
Q

How are starch and glycogen broken down in the membranous phase of digestion?

A

Oligosaccharides are broken into monosaccharides.

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26
Q

What part of a carbohydrate can be absorbed?

A

Monosaccharides.

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27
Q

How are disaccharides broken down in the luminal phase of digestion?

A

BBM enzymes lactase and sucrase will break them down.

Sucrose is broken into glucose and fructose.

Lactose is broken into glucose and galactose.

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28
Q

What are 2 examples of common dietary disaccharides?

A

Sucrose.

Lactose.

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29
Q

What happens to lactose in lactose intolerant people?

A

It cannot be digested in the small intestine and it is fermented by bacteria in the large intestine.

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30
Q

What mechanism allows for monosaccharides to be absorbed?

A

Secondary active transport involving sodium.

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31
Q

What is the only monosaccharide to be absorbed by diffusion?

A

Fructose.

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32
Q

How are monosaccharides absorbed by secondary active transport?

A

Sodium and glucose will be absorbed into the cell together.

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33
Q

How do monosaccharides leave enteric cells after they have entered via secondary active transport?

A

They diffuse into the blood.

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34
Q

Can structural carbohydrates be digested by enzymes?

A

No, they must be broken down by bacteria in the large intestine.

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35
Q

What must proteins be converted into for absorption to occur?

A

Individual amino acids.

Di-peptides.

Tri-peptides.

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36
Q

What occurs during the luminal phase of protein digestion?

A

HCl activates pepsin.

Pepsin breaks proteins to polypeptides.

Pancreatic proteolytic enzymes break down polypeptides into oligopeptides.

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37
Q

What occurs during the membranous phase of protein digestion?

A

Peptidase breaks oligopeptides.

38
Q

How are proteins absorbed into the epithelial cells?

A

Via secondary active transport in con-junction with sodium.

39
Q

What is necessary for proteins to be absorbed via secondary active transport?

A

A gradient of hydrogen ions.

40
Q

How does hydrogen help with the absorption of proteins?

A

Hydrogen is removed from the cell and sodium enters the cell.

As hydrogen re-enters the cell there is enough energy to allow the peptides to enter the cell.

41
Q

How can amino acids enter the blood from the endothelial cells?

A

Via diffusion.

42
Q

How can di and tri-peptides enter the blood from the endothelial cells?

A

Via a sodium potassium exchanger.

43
Q

What is one of the few intact proteins that can be absorbed without being broken down?

A

Colostrum.

44
Q

What inhibits many of the transporters that are responsible for nutrient absorption?

A

Enterotoxins e.g. in diarrhoea except for the sodium glucose transporter.

45
Q

What are the only nutrients that are absorbed during diarrhoea?

A

Glucose and fructose.

46
Q

Are any BBM enzymes released for fat absorption?

A

No.

47
Q

How are fats absorbed into the enteric cells?

A

Via diffusion.

48
Q

How do fats leave the enterocytes and enter the blood?

A

They form chylomicrons and then leave the cell and enter the blood.

49
Q

What can lead to maldigestion and malabsorption of fats?

A

Disorders with the liver or pancreas.

50
Q

What happens to the water that is secreted into the small intestine?

A

It is re-absorbed.

51
Q

Water will generally follow what electron?

A

Sodium.

52
Q

How is water re-absorbed in the small intestine?

A

Sodium is absorbed in conjunction with glucose and proteins and the water follows the sodium.

53
Q

How much water is absorbed from chyme in the small intestine?

A

Around 80-90%.

54
Q

How is bicarbonate reabsorbed in the small intestine?

A

The epithelial cells will secrete chlorine ions in exchange for bicarbonate.

55
Q

What ion is sodium usually absorbed in conjunction with?

A

Cl-.

56
Q

How is potassium reabsorbed in the small intestine?

A

Via diffusion.

57
Q

What is diarrhoea?

A

Softer than normal poo which contains a lot of water.

58
Q

What are the 3 types of diarrhoea?

A

Malabsorptive.

Osmotic.

Hypersecretory.

59
Q

What causes malabsorptive diarrhoea?

A

Loss of absorptive cells in the small intestine.

Very little absorption occurs.

60
Q

How does malabsorptive diarrhoea occur?

A

The unabsorbed nutrients suck water into the intestine and this is pushed through the GI tract.

61
Q

What can inhibit many sodium co-transporters?

A

Toxins.

62
Q

What virus causes breakdown of microvilli?

A

Parvovirus?

63
Q

What are the 2 most common causes of diarrhoea?

A

Inflammation and viral infections.

64
Q

What causes osmotic diarrhoea?

A

Accumulation of partially digested ingesta due to an enzyme deficiency.

Intake of non-absorbable compounds.

65
Q

How does osmotic diarrhoea occur?

A

The unabsorbed nutrients suck water into the intestine and this is pushed through the GI tract.

66
Q

What causes hypersecretory diarrhoea?

A

Toxins.

Inflammatory mediatiors.

Mucosal irritants.

Parasympathetic stimulation.

67
Q

How does hypersecretory diarrhoea occur?

A

Toxins cause secretory cells to secrete more water into the lumen.

68
Q

What are the 4 major consequences of diarrhoea?

A

Fluid loss.

Bicarbonate loss.

Intestinal defects.

Potassium loss.

69
Q

How does fluid loss caused by diarrhoea affect the body?

A

Hypovolemia.

Low blood pressure.

Hypoxia.

70
Q

How does bicarbonate loss caused by diarrhoea affect the body?

A

Metabolic acidosis.

Tissue damage.

71
Q

How do intestinal defects caused by diarrhoea affect the body?

A

Loss of intestinal barrier.

Septicemia.

72
Q

How does potassium loss caused by diarrhoea affect the body?

A

Hypokalemia.

Loss of membrane potential.

Hyperpolarisation of cells.

73
Q

What are the 4 basic functions of the large intestine?

A

Propulsion of chyme towards rectum.

Absorption of water an electrolytes.

Microbial fermentation.

Storage and expulsion of faeces.

74
Q

What causes the ileocecal sphincter to open?

A

The gastro ileal reflex.

75
Q

What 2 modes of motility occur in the large intestine?

A

Segmentation/mixing.

Peristalsis.

76
Q

Are there villi in the large intestine?

A

Yes.

These will absorb water, vitamins and some fermentation products.

77
Q

What hormone regulates absorption in the large intestine?

A

Aldosterone.

78
Q

What can lead to diarrhoea in the large intestine?

A

Intense irritation such as colitis.

79
Q

What are the 2 reflexes that are involved in defecation?

A

The myenteric reflex.

The parasympathetic reflex.

80
Q

What are the steps of defecation that are governed by the myenteric plexus?

A

Movement of faeces from colon to rectum stimulates the myenteric plexus.

Internal sphincter relaxes.

Defecation occurs.

81
Q

What nerves stimulate the parasympathetic reflex?

A

Pelvic nerves.

82
Q

What are the steps of defecation that are governed by the parasympathetic reflex?

A

Rectum distension.

Intensified peristalsis.

Defecation.

83
Q

How can the defecation reflexes be blocked?

A

By voluntary constriction of the external sphincter and puborectal muscles.

84
Q

What nerve stimulates the external sphincter and puborectal muscles?

A

The pudendal nerve.

85
Q

What are the effects of pelvic nerve damage?

A

Constipation.

86
Q

What are the effects of pudendal nerve damage?

A

Faecal incontinence.

87
Q

Which of the 2 defecation reflexes cannot be controlled?

A

The parasympathetic reflex.

88
Q

What makes defecation a voluntary process?

A

Our ability to control the external anal sphincter.

89
Q

What sphincter cannot be opened if the pelvic nerve is damaged?

A

The internal anal sphincter.

90
Q

What sphincter cannot be opened if the pudendal nerve is damaged?

A

The external anal sphincter.

Physiology. Gastrointestinal Physiology. (6 decks)

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