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► Med - Anatomy & Physiology > Physiology and Pharmacology of the Small and Large Intestine > Flashcards

Physiology and Pharmacology of the Small and Large Intestine Flashcards

1
Q

What is the longest part of the small intestine?

A

Ileum (3m)

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2
Q

What three substances does the small intestine recieve?

A
  1. Chyme from stomach
  2. Pancreatic juice from pancreas
  3. Bile from gallbladder
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3
Q

What substances does the small intestine secrete?

A

Succus entericus

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4
Q

What does the ileocaecal valve open in response to?

A

Proximal pressure and gastrin

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5
Q

What three parts of the small intestine increased its surface area?

A
  1. Circular folds (or Kerckring)
  2. Villi
  3. Microvilli
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6
Q

What is gastrin secreted from?

A

G cells of gastric antrum and duodenum

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7
Q

What is Cholecystokinin (CKK) secreted from?

A

I cells of duodenum and jejunum

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8
Q

Where is secretin secreted from?

A

S cells of duodenum

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9
Q

What is secreted from M cells of the duodenum and jejunum?

A

Motilin

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10
Q

What is an incretin from K cells of duodenum and jejunum?

A

Glucagon-like Insulinotropic Peptide (GIP aka, gastric inhibitory peptide)

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11
Q

What do incretins act on?

A

Beta-cells of pancreas to stimulate release of insulin

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12
Q

What is an incretin from L cells of the gut?

A

Glucagon-like peptide 1 (GLP-1)

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13
Q

What do all secretions of the small intestine: Gastrin, CCK, Secretin, Motilin, GIP, GLP-1 nad ghrelin all act on?

A

G-protein coupled receptors

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14
Q

Where is Ghrelin secreted from?

A

Gr cells of the gastric antrum, small intestine and pancrease

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15
Q

What 5 control mechanisms are there for succus entericus?

A
  1. Distension/irritation
  2. Gastrin
  3. cck
  4. Secretin
  5. Parasympathetic nerve activity (all enhance) and sympathetic nerve activity (decrease)
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16
Q

What two substances does succus entericus contain?

A

Mucus - for lubrication/protection (from goblet cells)

Aqueous salt - for enzymatic digestion (mostly from crypts of Lieberkuhn)

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17
Q

What involves Na+/K+ATPase, Na+/K+/2Cl-cotransporter and chloride channel (CFTR)?

A

Seretion of succus entericus

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18
Q

What is secreted at the crypts of Lieberkuhn?

A

Succus entericus

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19
Q

What involves alternating contraction and relaxation of segments of circular muscle?

A

Segmentation (mixing)

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20
Q

What is segmentation initiated by?

A

Small intestine pacemaker cells causing the BER which is continuous

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21
Q

What triggers segmentation in the empty ileum?

A

Gastrin from the stomach (gastroileal reflex)

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22
Q

Which has more segmentation contractions - ileum or duodenum?

A

Duodenum 12 per minute

Ileum 9 per minute

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23
Q

What enhances strength of segmentation and what decreases it?

A

Enhanced by parasympathetic activity and decreased by sympathetic activity

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24
Q

In peristalsis, what two activities occur in the interdigestive, or fasting, state?

A
  1. A few localised contractions

2. The migrating motor complex (MMC)

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25
Q

When does the MMC occur?

A

Between meals every 90-120 minutes

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26
Q

What is a strong peristaltic contraction passing the length of the intestine (stomach to ileocaecal valve)?

A

Migrating motor complex

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27
Q

What does the MMC clear and act as?

A

Clears small intestine of debris, mucus and sloughed epithelial cells between meals, “housekeeper”

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28
Q

What inhibits the MMC?

A

Feeding and vagal activity

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29
Q

What triggers the MMC and what two secretions inhibit it?

A

Motilin stimulates

Suppressed by Gastrin and CCK

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30
Q

What do macrolide antibiotics (erythromycin) mimic the effect of?

A

Motilin and may cause GI disturbances

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31
Q

What two substances are secreted from the endocrine pancreas and where are they secreted to?

A

Insulin and glugagon - secreted to blood

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32
Q

What cells of the exocrine pancreas secrete digestive enzymes?

A

Acinar cells

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33
Q

What cells in the exocrine pancreas secrete aqueous NaHCO3- solution?

A

Duct cells

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34
Q

What two substances secreted from the exocrine pancreas, make up pancreatic juice and are secreted to the duodenum collectively?

A

Digestive enzymes

Aqueous NaHCO3-

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35
Q

What enzymes can completely digest food in the absence of all other enzymes?

A

Pancreatic enzymes

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36
Q

What are the enzymes from acinar cells stored in?

A

Zymogen granules

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37
Q

What are the three classes of pancreatic enzymes?

A
  1. Proteases
  2. Amylases
  3. Lipases
38
Q

Name 3 proteases from the pancreas?

A
  1. Trypsinogen
  2. Chymotrypsinogen
  3. Procarboxypeptidase A and B
39
Q

Name an amylase from the pancreas?

A

Pancreatic amylase

40
Q

Name a lipase from the pancreas?

A

Pancreatic lipase

41
Q

What out of proteases, amylases and lipases are active and what are inactive?

A 
Active = amylases and lipases
Inactive = proteases
42
Q

What pancreatic enzyme joins with enterokinase from the duodenum to make trypsin?

A

Trypsinogen

43
Q

What enzyme is released from the duodenum (from mucosal cells) that influences pancreatic enzymes?

A

Enterokinase

44
Q

What does trypsin catalyse in the duodenum?

A

Chymotrypsinogen to chymotrypsin

45
Q

What does trypsin catalyse other than chymotrypsinogen to chymotrypsin in the duodenum?

A

Procarboxypeptidase A and B to Carboxypeptidase A and B

46
Q

What neutralises the acidic chyme entering the duodenum?

A

Alkaline HCO3-rich fluid from duct cells in the pancreas

47
Q

What is fluid secretion like in patients with CF?

A

Reduced (because of CFTR channel)

48
Q

What are the three phases in the control of pancreatic secretion?

A
  1. Cephalic
  2. Gastric
  3. Intestina;
49
Q

What mediates cephalic phase in control of pancreatic secretion?

A

Vagal stimulation of mainly the acinar cells

50
Q

How does control of the gastric phase work in control of pancreatic secretion?

A

Gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells

51
Q

What is the cycle of aqueous NaHCO3 solution neutralising acid in duodenal lumen?

A
  1. Increased secretion of aqueous NaHCO3 solution into duodenal lumen
  2. Neutralises acid in duodenal lumen
  3. Increased secretin release from S cells, secretin carried in blood to pancreatic duct cells
  4. Cycle repeats
52
Q

What is the cycle of increasing secretion of digestive enzymes into duodenal lumen to digest fat and protein in duodenal lumen?

A
  1. Increased secretion of digestive enzymes into duodenal lumen
  2. Digestion of fats and protein in duodenal lumen
  3. Increased CCK release from I cells, CCK carried in blood to pancreatic acinar cells
  4. Cycle repeats
53
Q

What is entry of ileocaecal material (indigestible residues, unabsorbed biliary components and unabsorbed fluid), permitted through the ileocaecal sphincter by?

A

Gastroileal reflex

54
Q

What three nervous control is the ileocaecal sphincter under?

A
  1. Vagus nerve
  2. Sympathetic nerves
  3. Enteric neurones
55
Q

What three substances does the large intestine absorb and secrete?

A

Absorbs H2O, Na+ and Cl-

Secretes K+, HCO3 and mucus

56
Q

What does HCO3 secreted from the large intestine do?

A

Neutralises acid produced by bacterial fermentation

57
Q

What happens to carbohydrate that is not absorbed by the small intestine?

A

It is fermented by colonic flora to short chain fatty acids

58
Q

What are faeces composed of?

A

Water, solids including cellulose, bacteria, bilirubin and salt

59
Q

What two functions takes place in the ascending and transverse colon?

A

Fluid reabsorption and bacterial fermentation

60
Q

What takes place in the descending colon to the sigmoid colon?

A

Final drying (desiccation) and storage

61
Q

What is the term for non-propulsive segemntation?

A

Haustration

62
Q

What are haustra?

A

Saccules caused by contraction of the circular muscle

63
Q

Where does haustration occur and what does it cause?

A

Occurs in proximal colon and causes orad movement

64
Q

In the colon, what is the outer longitudinal muscle layer comprised of?

A

Three bands, the taenia coli

65
Q

What two things does the gastrocolic response involve?

A

Gastrin and extrnisic nerve plexus

66
Q

What action of the large intestine is triggered by the gastrocolic response?

A

Mass movement - simultaneous contraction of large sections of the circular muscle of ascending and transverse colon

67
Q

What response does mass movement in the distal colon, propelling faeces into the rectum cause?

A

Defaecation reflex

68
Q

What happens after the rectum has filled with faecal matter?

A

Activation of rectal stretch receptors

69
Q

Once rectal stretch receptors have been activated, what two responses occur (both controlled by the pelvic nerve)?

A
  1. Activation of afferents to spinal cord

2. Activation of afferents to brain (urge to defaecate)

70
Q

Once afferents have been activated to the spinal cord, what becomes activated?

A

Parasympathetic efferents

71
Q

What do activation of parasympathetic efferents cause via the pelvic nerve?

A

Contraction of smooth muscle of colon and rectum - internal anal sphincter relaxes

72
Q

What is the rectospinteric reflex and what condition is it defective in?

A

Internal anal sphinter relaxation, defective in Hirschprung disease

73
Q

Once there has been activation of afferents to the brain (urge to defaecate) what occurs?

A

Altered firing rate in efferents to spinal cord

74
Q

What nerve does altered firing in efferents to spinal cord utilise to cause contraction or relaxation of skeletal msucle and the external skeletal sphincter?

A

Pudendal nerve

75
Q

What do colonic bacteria synthesise?

A

Vitamin K2 and free fatty acids (from carbohydrate) that are absorbed

76
Q

What does the presence of hard, dried faeces within the colon result from?

A

Delay in defaecation and enhanced absorption of H2O

77
Q

What is one cause of appendicitis?

A

Hardened, calcified, faecal matter within the appendix (appendicolths)

78
Q

What are purgatives?

A

Agents that cause purging, or cleansing of the bowels by promoting evaculation

79
Q

How do laxatives work?

A

Increase peristalsis and/or soften faeces causing,or assisting evacuation

80
Q

What are indigestible polysaccharide polymers that improve stool consistency and are slow acting?

A

Bulk laxatives

81
Q

Name a bulk laxative?

A

Methylcellulose

82
Q

What do bulk laxatives retain?

A

Water

83
Q

Name three stimulatn purgatives?

A
  1. Bisacodyl
  2. Sodium picosulfate
  3. Senna
84
Q

What type of laxative is senna?

A

Anthraquinone

85
Q

What side effect can stimulant purgatives give?

A

Abdominal cramping

86
Q

What along with faecal softening, do stimulant purgatives do?

A

Increase H2O and electrolyte secretion

Increase peristalsis

87
Q

What are poorly absorbed solutes that retain water, increase bulk and increase perstalsis?

A

Osmotic laxatives

88
Q

Name three osmotic laxatives?

A

Magnesium sulphate
Sodium citrate
Lactulose

89
Q

What drugs increase water and electrolyte secretion, increase perstalsis and faecal softening? They also have a detergent like action?

A

Faecal softeners

90
Q

Name two faecal softeners?

A

Docusate sodium - orally

Arachus oil - enema

91
Q

What are prolonged use of glucocorticoids for acute IBD attacks limited by?

A

Adrenal suppression

► Med - Anatomy & Physiology (130 decks)

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