Gastrointestinal Tract (plus Diseases) Flashcards
1
Q
What does the gastrointestinal tract consist of?
A
- mouth (oral cavity)
- oesophagus
- stomach
- small intestine (duodenum, jejunum, ileum)
- large intestine (colon, caecum)
- rectum
- anus
2
Q
What does the lip consist of?
A
- skin
- oral mucosa
- vermilion border
3
Q
Oral mucosa
A
- thick stratified squamous
epithelium, supported by a lamina propria - soft palate, underside of tongue, floor of mouth and mucosal surfaces: not keratinised, some may be parakeratinised
- gums, hard palate, most upper surface of tongue: keratinised, some may be parakeratinised
4
Q
Underneath the oral mucosa
A
- tough collagenous submucosal layer with accessory salivary glands
- thin submucosa where it lies over bone
5
Q
Tongue - dorsal surface
A
- Lingual Muscles (Striated): Extrinsic and Intrinsic
- Sulcus Terminalis
- V-shaped depression, divides tongue into anterior 2/3 + posterior 1/3. Foramen caecum at its apex.
- Lingual papillae on the anterior 2/3: Filiform, Fungiform, Circumvallate, Foliate
- Taste buds associated with select papillae
6
Q
Filiform of lingual papillae
A
- Small and Conical
- Lined by keratinized stratified squamous epithelium
- No taste buds
- Mechanical function
7
Q
Fungiform of lingual papillae
A
- Mushroom shaped
- Prominent on tip of tongue
- Lined by stratified squamous epithelium
- Taste buds in the epithelium on dorsal surface
8
Q
Foliate of lingual papillae
A
- Found on the lateral edges of tongue
- Parallel rows separated by deep clefts
- Taste buds
- Rudimentary in human
9
Q
Circumvallate of lingual papillae
A
- 8-12 large and dome shaped found anterior to
sulcus terminalis - Surrounded by a moat-like invagination which receives ducts of serous Von Ebner’s glands
- Taste buds in epithelium of lateral surface
10
Q
Taste buds
A
- extend through the entire thickness of epithelium and detect taste stimulating particles from food
11
Q
Composition of taste buds
A
- Taste pore
- Sensory neuroepithelial cells: synapse with afferent neurons (CN VII, IX, X), microvilli on apical surface, express 1 class of receptor protein, turnover ~ 10 days
- Supporting cells: microvilli on apical surface, turnover ~ 10 days
- Basal cells: stem cells
12
Q
Teeth
A
- main areas: crown and root
- odontoblasts
- ameloblasts
13
Q
Odontoblasts
A
- tall columnar secretory cells near pulp cavity
- produce dentine, which is laid down and then calcified
- dentine: 90% type I collagen, 70% wet weight hydroxyapatite
14
Q
Ameloblasts
A
- tall columnar secretory cells from ectodermal origin near surface tooth
- produce enamel
- enamel: 96% mineralised, hydroxyapatite the primary mineral, doesn’t contain collagen
- they die when the tooth erupts
15
Q
Salivary glands
A
- 3 major pairs of salivary glands and many minor glands
- Parotid glands on the inside of the cheeks
- Submandibular glands at the floor of the mouth
- Sublingual glands under the tongue
16
Q
Acini in parotid glands
A
- pure serous glands
- Only serous cells (protein-secreting)
- pure serous cells produce e.g. Amylase (carbohydrates)
- Amylase stored apical in acidophilic secretory granules
- Granules also contain peroxidase, lysozyme, cystatins
17
Q
Ducts in parotid glands
A
- secretory acini - intercalated ducts - intralobular or striated ducts - interlobular ducts - major ducts
- parotid gland has longest intercalated ducts
- myoepithelial cells around acini
18
Q
Acini in submandibular glands
A
- Mixed gland
- Mostly pure serous acini, but also groups of mixed acini among the pure serous acini
- Serous cells are filled with prominent, purplish-staining zymogen granules
- Mucous cells (mucin-secreting) are pale-staining w/abundant clear cytoplasm. Arranged in duct-like structures, capped by so-called serous demilumes
19
Q
Ducts in submandibular glands
A
- Intercalated ducts are short, but present; striated ducts are long and clearly evident
20
Q
Acini in sublingual glands
A
- Mixed gland
- Gland consist mostly of mucous acini capped with serous demilumes
- The mucin-secreting cells predominate, with far less protein-secreting cells
21
Q
Ducts in sublingual glands
A
- Short intercalated and striated ducts, but are few in
number - Long excretory ducts: Multiple sublingual ducts empty directly into the floor of the oral cavity, near to or with the submandibular ducts
22
Q
Gross structure of oesophagus
A
- ~25cm long muscular tube
- Connects pharynx to stomach
- Function: conduit for the bolus of food from the mouth
- Lumen normally collapsed with longitudinal folds
23
Q
Epithelium in oesophagus
A
- stratified squamous non keratinised
- protects from mechanical and chemical injury
24
Q
Lamina propria of oesophagus
A
- connective tissue containing diffuse lymphatic tissue and lymphatic nodules
- Oesophageal Cardiac Glands: mainly in terminal part, produces neutral mucus which protects from regurgitated gastric contents
25
Muscularis mucosae of oesophagus
- single layer of longitudinal muscle
26
Submucosa of oesophagus
- Dense irregular connective tissue
- Large blood and lymphatic vessels
- Submucosal Plexus (Meissner’s plexus)
- Oesophageal Glands Proper: scattered throughout the length, produces slightly acidic mucous, lubricates the lumen, excretory duct lined by stratified squamous epithelium
27
Muscularis externa of oesophagus
- typical 2 layers, inner circular and outer longitudinal
- upper 3rd: striated
- middle 3rd: striated and smooth
- lower 3rd: smooth
- myenteric plexus (Auerbach's plexus)
28
Serosa and Adventitia
- above diaphragm: fixed to adjacent structure by adventitia
| - below diaphragm: serosa continuous w/that of the stomach
29
Oesophagogastric Junction
- mucosa undergoes an abrupt transition
- epithelium: stratified squamous to simple columnar
- lamina propria: oesophageal cardiac glands replaced by cardiac glands of stomach
- muscularis mucosa: 2 layers of smooth muscles arranged as inner circular and outer longitudinal
- submucosa: oesophageal proper glands to NO glands
- muscularis externa: inner oblique layer
30
Stomach
- 3 region based on type of glands
- cardiac region: near oesophageal orifice, contains cardiac glands
- fundic region: situated between cardia and pylorus, contains fundic glands
- pyloric region: distal, funnel-shaped region proximal to pyloric sphincter, contains pyloric glands
31
Mucosa of stomach
- gastric pits or foveolae
| - gastric glands: extend from muscularis mucosae, empty into gastric pits
32
Epithelium on stomach
- lines gastric pits
- simple columnar epithelium
- surface mucus cells
33
Lamina propria on stomach
- loose connective tissue
| - surrounds gastric glands
34
Muscularis mucosae on stomach
- inner circular and outer longitudinal
35
Submucosa on stomach
- dense connective tissue
| - lymphatics, blood vessels and submucosal plexus
36
Muscularis externa of stomach
- 3 layers of muscle: innermost oblique, middle circular: thickens to form the
pyloric sphincter, outer longitudinal
- Functions: to mix stomach contents (chyme) and force the partially digested food into the small intestines
37
Serosa of stomach
- Continuous with that of duodenum
38
Cardiac region of stomach
```
- Relatively short pits & short
glands
- Tubular with occasional
branching
- Cells: mucous-secreting, enteroendocrine
```
39
Pyloric region of stomach
```
- Relatively long pits and short
glands
- Branched, coiled, tubular with wide lumen
- Mucus cells secrete a viscous mucus
- Enteroendocrine
```
40
Fundic region of stomach
- short pits: lined by surface mucus cells
- long glands: simple branched tubular glands, 2-4 glands empty into one gastric pit, 3 parts: isthmus, neck, fundus
- Cell types: mucous neck cells, parietal cells, chief cells, enteroendocrine cells, stem cells
41
Hydrochloric acid (fundic gland secretion)
- produced by parietal cells
- Gives gastric juice low pH: < 1.0 to 2.0
- Converts inactive pepsinogen into pepsin
- Kills most bacteria
42
Pepsin (fundic acid secretion)
- Produced by chief cells
- Potent proteolytic enzyme
- Hydrolyzes proteins into
small peptides
- Converted from pepsinogen
43
Mucus (fundic acid secretion)
- Protective coating for the
stomach
- physiological barrier: neutral to alkaline pH: bicarbonate
- physical barrier
44
Intrinsic factor (fundic acid secretion)
- essential for B12 absorption in the distal ileum
45
Surface mucus cells
- Secretes thick viscous mucus that adheres
to epithelium - protects from acidity of gastric juice
- Lines gastric pits
- Elongated nucleus
- Large apical cup of mucinogen granules takes up most of cytoplasm
46
Mucus neck cells
- Located in neck of gland
- Secretes soluble mucous that helps transports gastric secretion to lumen
- Smaller than SMC
- Less mucinogen in apical cytoplasm
- Spherical nucleus
47
Parietal (oxyntic) cells
- Secrete HCl and Intrinsic factor
- Found throughout gland but concentrated in neck
- Large mono or binucleated cells
- Eosinophilic due to +++mitochondria
- Extensive intracellular canalicular system that
communicates with lumen of gland
- Stimulated by gastrin
48
Chief cells
- Located at the base of gland
- Typical protein-secreting cell: Abundant rER (Gives cells basophilic appearance), Apical zymogen granules
- Secretions: Pepsinogen converted to pepsin by low pH (proteolytic enzyme), secretes weak lipase
49
Enteroendocrine cells
- secretes hormones into lamina propria
- found throughout the gland: more prevalent in the base
- Close cells: don't reach lumen
- Open cells: exposed lumen, serve as primary chemoreceptors
- Gastrin secreting cells are concentrated in pyloric antrum
50
Gastro-duodenal junction
- mucosa: appearance of finger shaped villi
- submucosa: appearance of Brunner's glands (mucous)
- muscularis: only 2 layers of muscles
51
Small intenstine
- longest component of digestive tract
- principal site for digestion and absorption
- receives chyme from stomach, enzymes from pancreas, microvilli of enterocytes, bile from liver
52
Mucosa of small intestine
- Simple columnar epithelium
- Lamina propria contains Gut Associated Lymphatic Tissue
(GALT)- ex. Peyer’s patches in ileum
- Muscularis mucosae (MM)2 thin layers: Inner circular and
outer longitudinal
- Villi
- Intestinal glands or Crypts of Lieberkühn
53
Submucosa of small intestine
- dense connective tissue
- submucosal (Meissner's) plexus
- circular folds or Plicae circularis
- duodenal submucosal glands
54
Muscularis externa of small intestine
- 2 muscle layers: inner circular and outer longitudinal with myenteric plexus
- both are involved in peristaltic contraction
55
Serosa/Adventitia
- mainly serosa except 2nd, 3rd and 4th parts of duodenum
56
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
57
Villi
- Finger-like & leaf-like mucosal projections: 0.5-1.5 mm
- Lamina propria contains central lacteals: blind-ended lymphatic capillary, accompanied by smooth muscle, absorption of lipids
58
Crypts of Lieberkuhn
- Simple tubular glands
- Extend from muscularis mucosae to open unto
lumen at base of villi
- Continuous with epithelium of villi
- Surrounded by lamina propria
59
Enterocytes
- Simple columnar epitheliocytes which are primarily absorptive, renew every 4-6 days
- They also have secretory function: produce digestive enzymes, secretes water and electrolytes
- 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
60
Goblet cells
- Goblet cells are unicellular mucous secreting cells
- Renewed every 4-6 days
- Mucinogen granules accumulate in the apical cytoplasm
- Increase in number from duodenum to colon
61
Paneth cells
- found ib base of intestinal glands
- renewed every 4 weeks
- intensely acidophilic apical secretory vesicles
- lysozyme: antibac enzyme, digest cell walls of certain groups of bacteria
- alpha-defensins: microbicidal peptides
- basophilic basal cytoplasm
- regulate normal bacterial flora in small intestine
62
Enteroendocrine cells
- Closed cells concentrated in lower portion of intestinal
gland
- Open cells found at all levels
- Found at base of the crypts
- Renew every 60-90 days
- Produce some of the same peptide hormones as stomach
- Most active regulators of GI physiology released in the small intestine: CCK, secretin, GIP, motilin
63
M cells
- Epithelial cells that cover Peyer’s patches and large lymphatic nodules
- Microfold cells
- Modified enterocytes
- Cover enlarged lymphatic nodules
- Microfolds on apical surface rather than microvilli
- Antigen-transporting cells
64
What makes M cells antigen-transporting cells?
- Take up microorganisms & macromolecules from lumen
- Transport vesicles to basolateral cell membrane
- Discharge vesicle contents into intercellular space
- Processed substances interact with cells of GALT
65
Parts of large intestine
- Colon: ascending, transverse, descending, sigmoid
- Cecum & vermiform appendix
- Rectum
- Anal canal
66
Characteristic features of large intestine
- 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
67
Mucosa of large intestine
- “Smooth” surface
- Numerous, straight, tubular, 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
68
Muscularis externa of large intestine
- 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
69
Appendix
- 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: results from blockage of opening to
the cecum, scarring, thick mucus or stool
70
Rectum
- Distal dilated portion of
alimental canal
- Anatomic transverse folds
- Mucosa is same as colon: intestinal glands (Crypts
of Lieberkühn), abundant goblet cells
• Muscularis externa: No tenia coli - continuous outer longitudinal layer
- Adventitia
71
Recto anal junction
- Internal anal sphincter – thickened inner circular layer
of the muscularis externa
- External anal sphincter – Striated muscle of the pelvis
72
Barrett's oesophagus (metaplasia)
- Heartburn: burning sensation felt behind the breastbone (sometimes in neck and throat)
- Caused by stomach acid refluxing up into oesophagus
- At lower end of oesophagus where it enters the stomach: Lower Oesophageal Sphincter, should remain tightly closed, except to allow food and liquid to pass into the stomach, heartburn occurs when the LES opens at the wrong
73
Gastroesophageal Reflux Disease (GERD)
- heartburn severe or
occurs frequently over a long period of time
- if untreated, constant acid irritation to lining of the oesophagus, and complications can occur
- 1 in 10 with GERD are found to have Barrett's oesophagus some of which may lead to invasive adenocarcinoma of the
oesophagus
74
Gastric and duodenal ulcer
- H. Pylori secretes urease and proteases: break down mucus, creates an alkaline
environment) - stimulates
gastrin - increase acid/pepsin
- causes chronic gastritis, exposing the surface to the effects of pepsin and acid.
- Irritated and inflamed membrane becomes necrotic, leaving a hole.
- HCl secretion is under nerve and hormonal control, stressful situations can trigger ulcers.
75
Coeliac disease
- gluten sensitive enteropathy
- autoimmune mediated intolerance to Gliadin
- marked inflammation of mainly distal duodenum and proximal jejunum
- mucosa appears flattened due to villi atrophy and crypts hyperplasia
- increased lymphocytes and plasma cells in lamina propria
76
Diagnosis of coeliac disease
- IgA antibodies for transglutaminase and endomysium and deamidated gliadin peptide
- mucosal changes can revert to normal w/ gluten free diet
- may lead to malignancy (10-15%)
77
Crohn's disease
- Ulcer formation of terminal ileum in SI as well as LI, and
upper GI
- Malabsorption accompanied by crampy abdominal pain
- Long fissure-like ulcers with normal mucosa in between
- “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 - obstruction
78
Hirschsprung's disease
- Congenital disorder of the colon
- Incomplete migration of cells from neural crest into large colon
- Absence of ganglia nerve cells (Auerbach and Meissner plexus)
- Variable length but seldom >30 cm
- That section of colon is essentially paralyzed
- Chronic constipation
- Diagnosis (Barium enema (mainstay), rectal biopsy (only certain)
- Pull-through surgery
79
Oesophageal varices
- Extremely dilated submucosal veins
- Lower 3rd of oesophagus
- Cause: mostly liver cirrhosis (alcohol)
- risk of bleeding increases with pressure in portal vein (portal hypertension)
- Variceal haemorrhage carries a high mortality/recurrence
80
Haemorrhoids
- Dilations of the submucosal veins
- Any pathology with increased pelvic pressure
- Secondary to portal hypertension
- Chronic constipation
- Internal (painless), external (very painful)
- Bleeding, thrombosis, infection
