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Physiology of human organ systems > Digestive system > Flashcards

Digestive system Flashcards

1
Q

Gastrointestinal segmentation involves contraction of what?

A

circular and longitudinal muscles in short segments of intestine.

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2
Q

What does GI segmentation do?

A

Pushes bolus’ of food back and forth, with a small amount being pushed further down the gut.

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3
Q

What is the purpose of GI segmentation?

A

To mix the chyme with digestive juices and bring it into contact with absorbing surfaces.

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4
Q

Which muscles act as the pacemaker for GI segmentation?

A

Longitudinal muscles

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5
Q

What phenomenon determines the frequency of contractions?

A

The base electrical rhythm

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6
Q

What determines the strength of segmentation contraction?

A

The frequency of action potentials from the central nervous system.

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7
Q

Where does segmentation contraction receive their parasympathetic and sympathetic innervation from?

A 
Parasympathetic= Vagus and ENS
Sympathetic= ENS
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8
Q

What happens to the BER along the length of the gut, oral to anal end?

A

The BER decreases in strength.

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9
Q

What is the function of peristalsis?

A

To push bolus distally along the GI tract.

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10
Q

Where does the migrating motility complex begin and end?

A

The MMC begins at the gastric antrum and terminates at the iliocaecal junction.

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11
Q

What is the purpose of the MMC?

A

Prevent bacterial colonisation, move undigested food to the large intestine and move digested food onto absorbing surfaces.

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12
Q

Which hormone is involved in the MMC initiation?

A

Motilin

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13
Q

What can induce the MMC to start?

A

If the smooth muscle of the lumen is distended, the oral end contracts and the anal end relaxes, to push food.

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14
Q

Which neurone plexus mediates the MMC?

A

The myentric plexus.

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15
Q

Explain the gastroileal reflex?

A

when the bolus of food arrives at the ileocaecal junction, the distention causes the sphincter to open. When the bolus has entered the colon, distention of the colon will cause the cause the sphincter to close.

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16
Q

What do colonic bacteria digest/ferment undigested material into?

A

Vitamine K., Short chain fatty acids and various gases.

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17
Q

What is mass movement contraction?

A

The intense contraction of the colon to push a mass of faeces towards the rectum.

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18
Q

After the mass movement contraction has occurred, what induces the urge to defaecate?

A

Stretch receptors in the rectum sense the distension and cause the urge.

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19
Q

How does defaecation occur?

A

The rectum contracts and the internal and external sphincters relax.

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20
Q

Which nervous system controls defaecation?

A

Parasympathetic and somatic nerves.

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21
Q

What are the main functions of the stomach?

A

Sterilise the intake, begin protein digestion and secrete B12 intrinsic factor.

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22
Q

Which stomach functions occur in the body of the stomach?

A

Secretions and storage.

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23
Q

Which stomach functions occur in the antrum?

A

Mixing, grinding an secretion of gastrin.

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24
Q

What is the purpose of stomach rugae?

A

the wrinkles allow for expansion when full

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25
Q

What type of epithelium is found in the stomach?

A

Simple columnar cells.

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26
Q

What is the gateway to the gastric gland?

A

The gastric pit

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27
Q

What do gastric pits lead to?

A

The gastric glands.

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28
Q

Which three cells are found in the base of the gastric gland?

A

Parietal, Chief and G cells

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29
Q

Which two cells are found in the upper gastric gland and gastric pit?

A

Mucous neck cells and surface mucous cells.

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30
Q

What do Chief cells secrete and what is its purpose?

A

Pepsinogen- the inactive form of pepsin, which digests proteins.

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31
Q

What do Parietal cells secrete and what is its purpose?

A

HCl to activate the pepsinogen and to sterilise the stomach.

B12 intrinsic factor which allows for the absorption of B12 in the distal ileum.

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32
Q

What do G-cells secrete and what is its function?

A

Gastrin is a hormone involved in the control of digestion further down the tract.

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33
Q

How do parietal cells synthesise H+ ions?

A

CO2 diffuses into the cell and combines with water to form H2CO3. The hydrogen ion dissociates and enters the apical membrane of the stomach lumen.

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34
Q

How do Parietal cells get Cl-?

A

They pump HCO3- into the blood in exchange for CL-

35
Q

How do Cl- and H+ become HCl?

A

They are both pumped into the stomach of the lumen (with H+ exchanged for K+) and in water form aqueous HCl.

36
Q

Which receptor does gastrin bind to?

A

Parietal CCK-B receptors.

37
Q

By which pathway do does gastrin cause an increase in intracellular Ca2+?

A

Inositol bisphosphate pathway.

38
Q

What does an increase in intracellular Ca2+ result in?

A

Phosphorylates kinases to increased activity in the K+/H+ pump (increased formation of HCl)

39
Q

What do enterchromaffin cells secrete?

A

Histamine

40
Q

What does histamine bind to and what does it activate?

A

Parietal G-coupled H2 receptor which activates adenylase cyclase.

41
Q

Which reaction does parietal adenylase cyclase catalyse?

A

ATP to cAMP

42
Q

What does cAMP do in parietal cells?

A

Increases K+/H+ pump activity by phosphorylating kinases.

43
Q

What does the vagus nerve secrete and to which receptor does this bind to?

A

The vagus nerve secretes acetylcholine and this binds to muscarinic-3 receptors.

44
Q

What is the effect of Ach release on parietal cells?

A

Increase in intracellular Ca2+ and K+/H+ pump activity.

45
Q

What do prostaglandins do to parietal cells?

A

Deactivates the G-1 proteins to inhibit HCl production.

46
Q

What is the cephalic phase of gastric acid stimulation?

A

The ‘thought’ phase initiates the vagus nerve to stimulate acid production.

47
Q

What is the gastric phase of gastric acid stimulation?

A

Gastric distension invokes enteric and vagal reflexes to secrete more HCl.
Peptide presence induces gastrin cells to secrete gastrin, which is inhibited at low pH.

48
Q

What is the intestinal phase of gastric acid stimulation?

A

Acid in the duodenum stimulates the splanchnic reflex for s-cells to secrete secretin.
Fat in the duodenum causes the release of GIP.

49
Q

What do GIP and secretin both do?

A

Decreases the effectiveness of gastrin.

50
Q

What is the precursor of pepsin?

A

The zymogen pepsinogen is inactive.

51
Q

At which pH does pepsin become active?

A

Lower than 3.

52
Q

What is the role of mucous in the stomach?

A

Cytoprotective and mechanicoprotective role.

53
Q

What cannot occur if there is no B12 intrinsic factor?

A

B12 won’t be absorbed and this causes pernicious anaemia.

54
Q

What happens in pernicious anaemia?

A

RBC don’t fully mature and therefore don’t gain their biconcavity, vital for their function?

55
Q

How long can the body survive without intake of B12?

A

The liver has 3 years’ worth of stores, meaning that B12 deficiency doesn’t usually become symptomatic until then.

56
Q

How frequent are peristaltic waves?

A

Roughly 3 per minute?

57
Q

Which cells in the duodenum secrete HCO3-?

A

Submucosal brunners glands.

58
Q

What stimulates duodenal HCO3-?

A

Secretin and vagal/ENS reflexes

59
Q

What inhibits secretin in a -ve feedback loop?

A

Acid

60
Q

In terms of digestion, is the pancreas exocrine or endocrine?

A

Exocrine.

61
Q

By which structure does the common bile duct enter the duodenum, and where is it?

A

The sphincter of oddi is at the major papilla.

62
Q

How are zymogens activated when they exit the sphincter of oddi?

A

Enterocyte bound enterokinases, on the duodenal brush border, activate trypsinogen to trypsin. Trypsin activates other zymogens in the duodenum.

63
Q

How are zymogens stimulated to be secreted?

A

Secretin, amino acids and lipids stimulate CCK. CCK stimulates zymogen secretion.

64
Q

What is, and where are, hepatic portal triads?

A

A portal vein, systemic artery and a bile canaliculus are found on the edge of each corner of liver lobule.

65
Q

What is in the centre of a liver lobule?

A

A systemic vein

66
Q

What carries blood across a lobule?

A

Sinusoid capillaries.

67
Q

What are the main components of bile?

A

Bile acids, lecithin and cholesterol.

68
Q

What else may be found in bile, but in smaller concentrations?

A

Bilirubin and detoxified metals.

69
Q

What colour is bilirubin and what colour does it become?

A

It is yellow, giving yellow bile its colour. In the colon, it is digested by bacteria and become brown.

70
Q

How much of the bile salts need to be synthesised every day?

A

Around 0.5g because most of the bile salts can be recuperated and recycled from the ileum.

71
Q

What are bile salts synthesised from?

A

Cholesterol.

72
Q

What conjugates bile salts to acids?

A

Glycine or taurine residues.

73
Q

How does the gall bladder concentrate bile?

A

It pumps Na+ across the basal membrane and water follows it. This concentrates it.

74
Q

Where in the small intestine does most of the digestion take place?

A

Duodenum.

75
Q

What occurs 95% of the time in the jejunum

A

The absorption of nutrients.

76
Q

What does the ileum do?

A

Reabsorb NaCl (and therefore water) and concentrate the chyme.

77
Q

What do villus cells do?

A

Absorb: salt, water, amino acids, monosaccharides, lipids, minerals and vitamins.

78
Q

What do Crypt cells do?

A

Secrete Cl- and H2O

79
Q

How are amino acids transported into the epithelial cell?

A

Co-transported with sodium.

80
Q

How is sodium transported into the blood?

A

In an Na+/K+ antiporter

81
Q

How are lipids transported out of the lumen?

A

They diffuse cross the membrane into the villi lacteal, which drain into the lymphatic system.

82
Q

What are the layers of the alimentary canal?

A

Mucosa, submucosa, muscularis externa and serosa.

83
Q

The lamina propria, a layer of the mucosa, contains what?

A

Lymph and blood vessels

Physiology of human organ systems (5 decks)

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