Histology Of Gastrointestinal Tract 2 Flashcards
Describe the gastro-duodenal junction
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
What are the peptic ulcers?
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
What are the complications of the cgronic peptic ulceration ?
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
What are small intestines?
Longest component of digestive tract measuring over 6 meters long.
– Principalsitefordigestion& absorption
– Receives:
• Chymefromstomach
• Enzymes from pancreas and microvilli of enterocytes
• Bile from liver
What are the cell specializations of the small intestines?
Tissue & cell specializations increase surface area
- Plicae circularis (PC)
- Villi (V)
- Microvilli (Mv
What are the regions of the small intestines?
Duodenum
Ileum
Jejunum
Describe the mucisa and submucosa of the small intestine
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
Describe the muscularis externa and serosa/adventitia of the small intestine
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
Describe plicae circulares or circular folds
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
Describe the villi
– 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
Describe the microvilli Of the small intestine
– 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
Describe the crypts of Lieberkuhn of the intestinal glands
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
What are enterocyte cells?
• Simple columnar cells which are primarily:
absorptive cells which renew every 4-6 days
• They also have secretory function – Producedigestiveenzymes
– Secreteswaterandelectrolytes
Describe the specialization of enterocyte cells
– 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
Describe goblet cells of tye smaall intestines
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
Describe the paneth cells
Paneth cells are found in base of intestinal glands
• Renewed every 4 weeks
• Intensely acidophilic apical secretory vesicles
What are the functions of the paneth cells?
– 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
What are the enteroendocrine cells?
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
Where are most active regulators of GI physiology released?
In the smmall intestine
- CCK
- Secretin
- GIP
- Motilin
Describe the structure of M cells
• Epithelial cells that cover Peyer’s patches and large lymphatic nodules
– Microfold cells
– Modified enterocytes
– Coverenlargedlymphaticnodules
• Microfolds on apical surface rather than microvilli
What are the functions of M cells?
• Antigen-transporting cells
– Take up microorganisms & macromolecules
from lumen
– Transport vesicles to basolateral cell membrane
– Discharge vesicle contents into intercellular space
– Processedsubstancesinteractwithcellsof GALT
What are the distinguishing characteristics of the duodenum?
Distinguishing characteristics
– Submucosal (Brunner’s) glands which secrete an alkaline mucus that neutralizes acidic chime
What are the general characteristics of the dupdenum?
• 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
What are the distinguishing characteristics of the jejunum?
- ~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
What is the ileum?
- 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
What are the distinguishing features of peyers patches?
- 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
What is malabsorption syndrome?
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
What is celiac disease?
- 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
What is seen in a microscopic level in celiac disease?
Microscopic:
– Increased lymphocytes and plasma cells in lamina propria
– IncreaseIntraepithelial lymphocytes and plasma cells
How is celiac disease diagnosed?
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%)
What is Crohn’s disease?
- 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
Describe the parts of the large intestine
Parts or the large intestine include: – Colon • Ascending • Transverse • Descending • Sigmoid
– Cecum & vermiform appendix
– Rectum
– Anal canal
What are the distinguishing features of the large intestine?
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
Describe mucosa in large intestine
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
Describe the muscularis externa of the large intestines
• 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
What is the appendix?
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
explain the clinical significance colonic adenomatous polyps-adenomas
Slow growing Intraepithelial neoplasm
• Dysplastic epithelium may form glands or villous
processes which defines the type.
• Usually asymptomatic but may present with occult bleeding
What are the 3 types of colonic adenomatous polyps-adenomas?
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
What is the rectum?
Distaldilatedportionof alimental canal
– Anatomic transverse folds
– Mucosa is same as colon
• Intestinal glands (Crypts of Lieberkühn)
• Abundantgobletcells
– Muscularisexterna
• Noteniacoli-> continuous outer longitudinal layer
– Adventitia
What is anal canal?
Most distal portion of the gastrointestinal tract
Anal glands which extend into the submucosa & sometimes muscularis externa
Gradual transition through 3 zones
- Colorectal zone (CRZ)
• Upper 1/3
• Simple columnar epithelium - Anal transition zone (ATZ)
• Middle 1/3
• Transition between simple columnar of rectal mucosa to stratified squamous of perianal skin - Squamous zone (SQZ)
• Lower 1/3
• Stratified squamous keratinized epitheliu
Describe the congenital megacolon (Hirschsprung disease)
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
What does the tongue look like(buds)?
What do filifirm abd fungiform look like?
How are foliage and circumvillate buds look like?
How are taste buds shaped?
What are the layers 9f the esophagus?
What are the layers of the stomach?
Contrast the cardiac and pyloric region?
Describe the funding region
Contrast mucous cells
Contrast parietal (oxynitic cells)
What do chief cells do?
What are enteroendocrine?
