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Flashcards in 35 - GI System III Deck (116):
1

What four mechanisms does the stomach use to protect the mucosa from the harsh acidic environment?

1 - Presence of permanent layer of mucous
2 - Continuous secretion of mucous by epithelial cells
3 - Cell renewal by stem cells
4 - Alkaline tide

2

What is the alkaline tide?

- After a meal, parietal cells secrete HCl (acidic)
- Parietal cells then release bicarbonate into the blood stream
- Blood stream is more alkaline
- Alkaline blood is delivered to superficial epithelial cells
- Epithelial cells secrete bicarb into mucous layers
- Neutralization occurs

3

What happens when the protective mechanisms are breached?

Damage to the mucosa of the gastric lining

4

What happens when this damage penetrates into the submucosa?

Peptic ulcer

5

What is the difference between an ulcer and erosion?

Erosion occurs if the damage is confined to the mucosal layer and it has not penetrated into the submucosa

6

What is the junction between the stomach and the duodenum called?

Gastroduodenal junction

7

What is located at the gastroduodenal junction?

Pyloric sphincter

8

What is the pyloric sphincter?

A thickening in the muscularis externa
- Primarily the circular layer thickens
- The longitudinal layer somewhat thickens
- There is no oblique layer here

9

What is the primary function of the small intestine?

Increase the surface area for enzymatic degradation of nutrients as well as their absorption

10

What is the main structural modification that exists in the small intestine to increase functionality?

Plicae circulares
- Permanent folds of mucosa and submucosa
- Slow the movement of chyme
- Increase time for enzymatic degradation and absorption

11

What other structural modifications help to increase the function of the small intestine?

Villi and microvilli

12

Are plicae circulares permanent or do they come and go with increased chyme?

Permanent

13

How much do plicae circulares increase the surface area of the small intestine?

3 fold

14

Where are villi found?

Along the plicae circulares

15

What are villi?

Folds of the mucosa
- Superficial portion is columnar cells with goblet cells interspersed
- Core is lamina propria

16

How much do villi increase the surface area of the small intestine?

10 fold

17

What are microvilli?

Extensions of the villi
- Found along apical domain of columnar cells
- Form the brush or striated border of the small intestine

18

How much do microvilli increase the surface area of the small intestine?

20 fold

19

What is the overall increase in the surface area of the small intestine from plicae cirulares, villi and microvilli?

3 x 10 x 20 = 600 fold

20

What happens to the small intestine in a state of inflammation?

Villi can be damaged

21

What will a sensitivity to gluten result in?

Gluten enteropathy (celiac sprue disease)

22

What are the four histologic features of gluten enteropathy (celiac sprue)?

1 - Enterocytes (columnar cells) are disorganized
2 - Villus atrophy (no longer see villi)
3 - Crypt hyperplasia (intestinal gland proliferation)
4 - Inflammation of lamina propria

23

What is an esophageal stricture?

A narrowing of the lumen of the esophagus that results in difficulty swallowing solid foods (but not liquids)

24

What causes an esophageal stricture?

Regurgitation of stomach acid

25

What is Zollinger-Ellison syndrome?

- A gastrinoma is present (tumor of gastrin-producin cells)
- Causes proliferation of gastrin producing cells and therefore more gastrin
- Gastrin stimulates secretion of HCl

26

What is the gastrinoma triangle or Passaro's triangle?

A triangle in the abdomen where 90% of gastrinomas occur

27

Where is the gastrinoma triangle or Passaro's triangle?

Points
- Junction of cystic and common hepatic ducts
- Junction of parts 2 and 3 of the duodenum
- Junction of pancreatic head and neck

28

In the small intestine, what type of lymphocytes maintain surveillance of the gut?

T cells

29

Why is the gut always under a "controlled state of inflammation"?

Because there is constant immunologic challenges in the gut (lots of bacteria, microbes, etc.)

30

What happens when the gut is in a uncontrolled state of inflammation?

Inflammatory bowel disease

31

Where do lymphatic channels exist in the small intestine?

In the core of the villi (within the mucosal layer)

32

What are the channels of the lymphatic system called?

Lacteals

33

What is absorbed through the lacteals?

Fat

34

Where does to fat go after it is absorbed by the lacteals?

Into the larger lymphatic structures

35

How does the lymph move?

Contraction of smooth muscles in the lamina propria - they compress the lacteal and move the lymph from the lacteal into the lymphatic duct and then into the submucosa

36

What other immune system cells are found in the small intestine? What layer?

Plasma cells (secrete IgA) are found in the lamina propria

37

What are crypts of Lieberkuhn?

The points where the epithelium invaginates up into the lamina propria to form the intestinal glands

38

Where are stem cells of the intestinal glands located?

Deep in the gland at the base

Recall that in gastric glands of the stomach they were further up in the isthmus of the gland

39

What are Paneth cells?

A specialized cell population that is found at the bottom of the intestinal gland that secrete acidophilic granules

40

What do the granules of Paneth cells contain?

Lysozymes which are bacteriolytic

41

What are enteroendocrine cells?

Hormone secreting glands that secrete their product into the connective tissue of the lamina propria, NOT the lumen of the small intestine

42

Why are the hormones of the enteroendocrine cells secreted into the lamina propria?

So they can be picked up by the microcirculation and enter the greater circulation of the body

43

What type of epithelium will you find in the duodenum?

Simple columnar epithelium

44

What will you find in the submucosa of the duodenum?

Glands

45

What specific type of glands are a hallmark feature of the duodenum?

Brunner's glands

46

What do Brunner's glands secrete?

Alkaline mucus and human epidermal growth factor

47

What portion of the duodenum has more abundant Brunner's glands?

The proximal duodenum

48

Do Brunner's glands exist in the jejunum?

No - they are a signature feature of the duodenum

49

What does human epidermal growth factor stimulate?

Cell proliferation

It also inhibits acid secretion form the parietal cells

50

What other prominent cell type will you find in the duodenum?

Gobelt cells

51

Why is the duodenum named the duodenum?

It means "12" and is named because it is the length of 12 fingers

52

What is histologically remarkable about the jejunum relative to the other segments of the small intestine?

Nothing - no hallmark features, nothing remarkable

53

What type of epithelium will you find in the jejunum?

Simple columnar epithelium of goblet cells

54

What is different about the ileum?

It is flat - no plicae circulares

55

What is a prominent feature of the ileum?

The presence of lymphatic nodules in the submucosa called Peyer's patches

56

What is the function of M cells in the small intestine?

M cells are lymphocytes that are involved in immune surveillance

57

How do M cells function?

They pick up antigenic material, process it internally and transport it then deliver the antigen to lymphocytes

58

What antibodies do M cells deliver to?

IgA

59

How are IgA formed?

- B lymphocytes
- Plasma cells
- Release IgA
- IgA taken up by epithelium of gut tube
- IgA secreted into lumen to bind to antigen

60

Does the outer longitudinal layer of smooth muscle completely surround the large intestine?

No - Instead, three longitudinal bands of smooth muscle are found

61

What do we call the three longitudinal bands of smooth muscle found running along the large intestine?

Teniae coli

62

Does the presence of segmented smooth muscle (teniae coli) make the wall of the large intestine stronger or weaker?

Weaker

63

Is there teniae coli found in the rectum?

No

64

Why is it clinically important that there is no teniae coli in the rectum?

Surgeons use this as a landmark

65

The large intestine appears segmented. What are the segments called?

Haustra

66

Plicae semilunares are found in the large intestine. What are these?

Semilunar folds

67

What type of epithelial cells are found in the epithelium of the large intestine

Simple columnar epithelium

68

Does the large intestine have villi?

No

69

Is the brush border of the large intestine well developed or poorly developed?

Poorly developed - there are a few microvilli present, but not many

70

How abundant are goblet cells in the large intestine?

Very abundant

71

How dense are the crypts in the large intestine?

Very dense

Crypts are invaginations of epithelium into the lamina propria

72

How abundant are lymphatic vessels in the large intestine?

Depends on the layer
- Very poorly developed in lamina propria
- Much better developed in the submucosa

73

Which direction do lymphatic vessels spread out in the large intestine?

Radially (not longitudinally)

74

Is the radial orientation of the lymphatic vessels in the large intestine favorable or unfavorable from a clinical standpoint?

Favorable - it is easier to go in surgically when they are not longitudinally oriented

75

Are glands found abundantly in the large intestine?

Yes - you will see an increased intestinal gland density

76

How does the mucosa of the appendix appear?

Similar to the large intestine - no villi

77

In the appendix, which layer will be rich in lymphatic tissue?

Lamina propria

78

What layers does the muscularis externa have in the appendix?

An inner circular layer and an outer longitudinal layer

79

What other part of the GI tract does the muscularis externa of the appendix resemble?

Small intestine

80

What happens in appendicitis?

- Infection
- Ulcers in mucosal layer
- Hard mass of feces blocks the appendix
- Luminal pressure within the appendix increases

81

What accounts for the increased luminal pressure in appendicitis?

- Fecal material plugs the lumen of the appendix (remember it is just a tubular sac)
- Secretions from the appendix have no where to go
- Build up and cause pressure
- Compresses blood vessels in the appendix
- Tissue pressure exceeds blood pressure
- Blood vessels collapse
- Ischemia occurs
- Eventually necrosis occurs
- Appendicitis results

82

What is an alternative way to get appendicitis?

Infection

83

How do you know the difference between the two ways to get appendicitis?

If it is acquired by the alternative way, feces will not be blocking the appendix when they take it out

84

What layers of the muscularis externa exist in the rectum?

Complete circular layer and longitudinal layer

85

What are the three folds of the rectum called?

Transverse rectal folds or the "valves of Houston"

86

What are they called?

1 - Distal/inferior fold
2 - Middle fold
3 - Proximal/superior fold

87

What is the function of the three transverse rectal folds?

Support and suspend the fecal mass that is held in the rectum until defecation occurs

88

Can you identify these folds endoscopically?

Yes

89

What three wall layers exist in the transverse rectal folds?

Remember, AKA Valve of Houston
- Mucosa
- Submucosa
- Muscularis externa

90

What defines the anal canal?

It is the part that extends to the perianal skin and includes the skin around the anus

91

What is the landmark that divides the rectum from the anal canal?

Pectinate (dentate) line

92

What is the pectinate line of the anal canal?

The line that separates two different types of gut tube lining

93

What are the two types of gut tube lining that the pectinate line separates?

Above - gut tube lining derived from the hind gut (typical mucosa)

Below - gut tube lining derived from proectodeum

94

What type of innervation occurs above and below the pectinate line

Above - autonomic and NO pain sensation

Below - somatic

95

What lymphnodes exist below the pectinate line?

Inguinal nodes

96

Why is this clinically relevant that the inguinal nodes lie below the pectinate line?

Because if a patient has cancer below the pectinate line, the cancer will drain into the inguinal nodes

97

What are the layers of the anal canal before the pectinate line (proximal)?

- Epithelium
- Muscularis mucosae
- Submucosae

98

What type of epithelium is found in the anal canal before the pectinate line (proximal)?

Simple columnar epithelium with large population of goblet cells

99

What are the anal columns?

Ridges of the anal canal that project up into the lumen of the anus

100

What are the three anal columns that are highly distended known as?

Anal cushions

101

What are the three anal cushions?

- Left lateral
- Right anterior
- Right posterior

102

Why are the anal cushions names as they are?

Named for the anatomical position the anal cushions are in when the patient is supine

103

What is the clinical relevance of the three anal cushions?

This is where hemorrhoids develop

104

When the bottom of the anal columns come together, what do we call the base region?

The wall at the base of these structures is known as the anal valves

105

What are the depressions at the distal ends of the anal columns called?

Anal sinuses

106

What accumulates in the anal sinuses?

Glandular secretions

107

What happens when glands in the anal sinuses become infected?

Anorectal abscess

108

After the pectinate line (distal end), the epithelium begins to transition. What form(s) does it transition into?

- Simple columnar (around pectinate line)
- Stratified squamous non-keratinized
- Stratified squamous keratinized

109

When does the epithelium transition from simple columnar to stratified squamous non-keratinized?

At the intersphincteric groove (AKA white line of Hilton) which is a ring-like depression just below the pectinate line

110

What does the intersphincteric groove represent?

The border between the internal anal sphincter and external anal sphincter

111

What is an anorectal abscess?

- First, an anal sinus becomes plugged by gland secretions or fecal matter
- This leads to infection and inflammation
- Can spread to surrounding tissues
- Pockets of pus (abscesses) accumulate

112

How are anorectal abscesses named?

Based on their located

113

Where is the most common site of an anorectal abscess?

Perianal (40-50%)

114

What is a fistula in ano?

An anorectal abscess that develops into a tube which can then penetrate from the anal canal onto the skin of the perineum

115

How are fistulas in ano named?

Based on their location

116

What are the three locations you can find a fistula in ano? How common are they in each location?

- Intersphincteric (45%)
- Suprasphincteric (20%)
- Transsphincteric (30%)