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Digestion And Metabolism > Histology Of Gastrointestinal Tract 2 > Flashcards

Histology Of Gastrointestinal Tract 2 Flashcards

1
Q

Describe the gastro-duodenal junction

A

The stomach transitions to the first part of the duodenum at the gastroduodenal junction.

Note changes to each of the layers :
•Mucosa→appearance of finger shaped villi

  • Submucosa→appearance of Brunner’s glands (mucous)
  • Muscularis externa→disappearance of innermost oblique layer and return to typical 2 layers of muscles
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2
Q

What are the peptic ulcers?

A

Crater-like lesion in areas exposed to gastric juices: Stomach ( gastric ulcer) or Duodenum (duodenal ulcer)

Common causes:
– Infection by H. Pylori: secretes urease and proteases which (I) break down mucus (II) creates an alkaline environment which stimulates gastrin→increase acid/pepsin
– Tobacco smoking
– Nonsteroidal anti-inflammatory medications – inhibit
prostaglandins
– Zollinger Ellison syndrome: gastrinoma

  • All of the above factors result in loss of mucosal protection or increase in acid secretion leading to inflammation
  • Inflamed mucous membrane may become necrotic, leaving a sore or ulcer
  • Classically ulcers are observed with a crater filled with necrotic tissue, fibrosis and scar tissue from the body’s attempt to heal
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3
Q

What are the complications of the cgronic peptic ulceration ?

A

Ulcers may extend deeper if left untended, penetrating submucosa, muscularis externa and serosa leading to serious illness

Major complications include :
– Bleeding: erosion of vessels at the base of an ulcer
– Perforation
– Peritonitis secondary to perforation
– Macrocytic(pernicious)anemiadue to loss of functional gastric mucosa→ especially fundic ulcers

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4
Q

What are small intestines?

A

Longest component of digestive tract measuring over 6 meters long.
– Principalsitefordigestion& absorption

– Receives:
• Chymefromstomach
• Enzymes from pancreas and microvilli of enterocytes
• Bile from liver

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5
Q

What are the cell specializations of the small intestines?

A

Tissue & cell specializations increase surface area

  1. Plicae circularis (PC)
  2. Villi (V)
  3. Microvilli (Mv
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6
Q

What are the regions of the small intestines?

A

Duodenum

Ileum

Jejunum

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7
Q

Describe the mucisa and submucosa of the small intestine

A

Mucosa:
– Simplecolumnarepithelium
– Lamina propria contains Gut Associated
Lymphatic Tissue (GALT)
– Muscularis mucosae: 2 thin layers, inner circular and outer longitudinal
– Villi–evaginationsoftheepithelium and lamina propria
– Intestinal glands or Crypts of Lieberkühn – invaginations of the epithelium into the lamina propria

Submucosa
– Dense connective tissue
– Submucosal(Meissner’s)plexus
– CircularfoldsorPlicaecircularis(PC)– permanent evaginations of the submucosa

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8
Q

Describe the muscularis externa and serosa/adventitia of the small intestine

A

Muscularis externa
• 2 muscle layers: Inner circular (CM) and outer longitudinal (LM) with myenteric (Auerbach’s) plexus. Segmentation contraction of CM mobilize chyme.
• Both CM and LM are involved in peristaltic contraction

Serosa /Adventitia
• Mainly serosa except 2nd, 3rd and 4th parts of duodenum

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9
Q

Describe plicae circulares or circular folds

A

Plicae Circulares or circular folds
– Also referred to as Valves of Kerckring

– Permanent transverse folds of the
submucosa

– Most numerous in distal duodenum and jejunum

– Reduced in size and frequency in ileum

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10
Q

Describe the villi

A

– Finger-like & leaf-like projections of the mucosa • 0.5-1.5mm
– Simple columnar epithelium

– Core of lamina propria contains central lacteals
• Blind-ended lymphatic capillary
• Accompanied by smooth muscle
• Absorption of lipid

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11
Q

Describe the microvilli Of the small intestine

A

– Feature of enterocytes
– Major increase in luminal surface area
– Eachcellpossessesseveralthousand microvilli (Mv)
– Give the cells a striated border (SB) in the light microscope
• Brushborder

– Glycocalyx(G)
– Insert into terminal web (T

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12
Q

Describe the crypts of Lieberkuhn of the intestinal glands

A

Crypts of Lieberkühn

– Invagination of epithelium into the lamina propria
– Simple columnar epithelium continuous with
epithelium of villi

– Extend from muscularis mucosae to open unto lumen at base of villi
– Simple tubular glands
– Surrounded by lamina propria

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13
Q

What are enterocyte cells?

A

• Simple columnar cells which are primarily:
absorptive cells which renew every 4-6 days

• They also have secretory function – Producedigestiveenzymes
– Secreteswaterandelectrolytes

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14
Q

Describe the specialization of enterocyte cells

A

– Microvilli→Form the striated border which contains terminal digestive enzymes

– Tight junctions→Allows selective absorption across the plasma membrane

– Lateral plication→Increase lateral surface area

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15
Q

Describe goblet cells of tye smaall intestines

A

Goblet cells are unicellular mucus secreting cells
– Renewed every 4-6days
– Mucinogen granules accumulate in the apical cytoplasm
– Increase in number from duodenum to colon

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16
Q

Describe the paneth cells

A

Paneth cells are found in base of intestinal glands
• Renewed every 4 weeks
• Intensely acidophilic apical secretory vesicles

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17
Q

What are the functions of the paneth cells?

A

– Lysozyme
• Antibacterial enzyme
• Digests cell walls of certain groups of bacteria

– α-defensins
• Microbicidal peptides

  • Basophilic basal cytoplasm
  • Regulate normal bacterial flora in small intestine
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18
Q

What are the enteroendocrine cells?

A

Similar to those seen in the stomach
– Closed cells concentrated in lower portion of
intestinal gland
– Open cells found at all levels

  • Found at the base of the crypts
  • Renewed every 60-90 days
  • Produce some of the same peptide hormones as stomach
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19
Q

Where are most active regulators of GI physiology released?

A

In the smmall intestine

  • CCK
  • Secretin
  • GIP
  • Motilin
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20
Q

Describe the structure of M cells

A

• Epithelial cells that cover Peyer’s patches and large lymphatic nodules
– Microfold cells
– Modified enterocytes
– Coverenlargedlymphaticnodules

• Microfolds on apical surface rather than microvilli

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21
Q

What are the functions of M cells?

A

• Antigen-transporting cells
– Take up microorganisms & macromolecules
from lumen
– Transport vesicles to basolateral cell membrane
– Discharge vesicle contents into intercellular space
– Processedsubstancesinteractwithcellsof GALT

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22
Q

What are the distinguishing characteristics of the duodenum?

A

Distinguishing characteristics

– Submucosal (Brunner’s) glands which secrete an alkaline mucus that neutralizes acidic chime

23
Q

What are the general characteristics of the dupdenum?

A

• At ~25 cm it is the shortest & widest part

• Begins at gastroduodenal junction and ends at
duodenojejunal junction

• Duodenal cap (1st part) is exposed to gastric juices→duodenal peptic ulcer

24
Q

What are the distinguishing characteristics of the jejunum?

A
  • ~2.5 m long and site of most of the absorption
  • Begins at duodeno-jejunal junction
• Distinguishing characteristics
– Numerous plicae circularis→Feathery appearance in contrasted radiographs
– Longprominentvilli
– Increase in goblet cells
– No submucosal glands
25
Q

What is the ileum?

A
  • Terminal part of the small intestine where absorption of Vitamin B12 and any remaining nutrients take place
  • Lumen is smaller with small plicae versus jejunum
  • Increase in Paneth and goblet cells

• Thickening of muscularis mucosae and
externa at the terminal part form the ileocecal valve

26
Q

What are the distinguishing features of peyers patches?

A
  • Well developed lymphoid aggregates which form part of GALT which extends between mucosa and submucosa
  • Associated with M-cells (previously described)
  • Polio virus and Salmonella ( typhoid fever) targets PP
27
Q

What is malabsorption syndrome?

A

Diseases of the gastrointestinal tract which results in abnormal absorption of on or more nutrients

• Causes
– Mucosal damage :
• Celiacdisease
• Tropical Sprue
• Vitamin B12 malabsorption

– Enzyme deficiency
• Disaccharidasedeficiency(ex. Lactose)
• Pancreatic insufficiency

– Infection
– Structural ( short intestine)
– Crohn’s disease

• Signs and symptoms specific to the nutrient/s affected

28
Q

What is celiac disease?

A
  • Gluten sensitive enteropathy
  • Autoimmune mediated intolerance to Gliadin (a glycoprotein found in gluten)
  • There is marked inflammation of mainly distal duodenum and proximal jejunum

• Mucosa appears flattened due to:
– Atrophyofvilli
– Hyperplasia of crypts

29
Q

What is seen in a microscopic level in celiac disease?

A

Microscopic:
– Increased lymphocytes and plasma cells in lamina propria
– IncreaseIntraepithelial lymphocytes and plasma cells

30
Q

How is celiac disease diagnosed?

A

Diagnosis:
• IgA antibodies for transglutaminase and endomysium and
deamidated glaidin peptide

  • Mucosal changes can revert to normal with a gluten free diet
  • May lead to malignancy ( 10-15%)
31
Q

What is Crohn’s disease?

A
  • Ulcer formation of mainly small intestine especially the terminal ileum however may affect the large intestine, and upper GI
  • Malabsorption accompanied by crampy abdominal pain
  • Long fissure-like ulcers with normal mucosa in between
  • Underlying inflammation give a “cobblestone” appearance
  • Patchy distribution of ulcers (skip lesions)

• Non caeseating Granuloma formation
with Giant cells+

  • Ulceration frequently extends through all layers of the wall producing fistulas
  • Fibrosis from chronic inflammation results in strictures→obstruct
32
Q

Describe the parts of the large intestine

A 
Parts or the large intestine include:
– Colon
• Ascending
• Transverse 
• Descending 
• Sigmoid

– Cecum & vermiform appendix
– Rectum
– Anal canal

33
Q

What are the distinguishing features of the large intestine?

A 
Distinguishing features:
Taenia coli (TC)
• 3 thickened bands of the outer longitudinal muscularis externa layer

-Haustra coli (HC)
• Visible sacculations between TC
• External surface of cecum and colon

-Omental appendices (OA)
• Small fatty projections of the serosa
• Outer surface of colon

34
Q

Describe mucosa in large intestine

A

Smooth” surface (no villi)
Numerous intestinal glands (crypts of Lieberkühn)

Principal functions
– Reabsorption of water & electrolytes
– Elimination of waste

• Epithelium
– Simple columnar
• No Paneth cells
• Abundant goblet cells

• Lamina propria contains GALT
• Muscularis mucosae
– Inner circular
– Outer longitudinal

35
Q

Describe the muscularis externa of the large intestines

A

• Found in ascending, transverse, descending and sigmoid colon, cecum
• Inner circular layer
• Outer longitudinal layer
– Teniae coli (TC)
• Prominent longitudinal bands of longitudinal muscle

• Myenteric (Auerbach’s) plexus

36
Q

What is the appendix?

A

The appendix is a thin, finger-like extension of the cecum
• Tenia coli ends at base of appendix→ quick identification during appendectomy
• Distinguishing characteristic
– Numerous lymphatic nodules that
extend into submucosa

• Appendicitis ( refer to anatomy for clinical features).
– Results from blockage of opening to the cecum
• Scarring, thick mucus or stool

37
Q

explain the clinical significance colonic adenomatous polyps-adenomas

A

Slow growing Intraepithelial neoplasm

• Dysplastic epithelium may form glands or villous
processes which defines the type.

• Usually asymptomatic but may present with occult bleeding

38
Q

What are the 3 types of colonic adenomatous polyps-adenomas?

A

Three types
– Tubular (most common) – dysplastic epithelium arranged in branched tubular glands connected to the mucosa by a stalk. Less malignant potential

– Villous (rare) - fingerlike villous appearance

– Tubulovillous – intermediate features

39
Q

What is the rectum?

A

Distaldilatedportionof alimental canal
– Anatomic transverse folds

– Mucosa is same as colon
• Intestinal glands (Crypts of Lieberkühn)
• Abundantgobletcells

– Muscularisexterna
• Noteniacoli-> continuous outer longitudinal layer

– Adventitia

40
Q

What is anal canal?

A

Most distal portion of the gastrointestinal tract
Anal glands which extend into the submucosa & sometimes muscularis externa
Gradual transition through 3 zones

  1. Colorectal zone (CRZ)
    • Upper 1/3
    • Simple columnar epithelium
  2. Anal transition zone (ATZ)
    • Middle 1/3
    • Transition between simple columnar of rectal mucosa to stratified squamous of perianal skin
  3. Squamous zone (SQZ)
    • Lower 1/3
    • Stratified squamous keratinized epitheliu
41
Q

Describe the congenital megacolon (Hirschsprung disease)

A

Autonomic ganglia are derived from neural crest cells therefore deficient migration of neural crest cells results→failure of development of myenteric plexus in the distal alimentary canal

  • Decreased peristaltic movements of the affected region gut→ functional obstruction
  • Dilated colonic segment proximal to the aganglionic reg
42
Q

What does the tongue look like(buds)?

A
43
Q

What do filifirm abd fungiform look like?

A
44
Q

How are foliage and circumvillate buds look like?

A
45
Q

How are taste buds shaped?

A
46
Q

What are the layers 9f the esophagus?

A
47
Q

What are the layers of the stomach?

A
48
Q

Contrast the cardiac and pyloric region?

A
49
Q

Describe the funding region

A
50
Q

Contrast mucous cells

A
51
Q

Contrast parietal (oxynitic cells)

A
52
Q

What do chief cells do?

A
53
Q

What are enteroendocrine?

A

Digestion And Metabolism (57 decks)

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