GIT Flashcards
The GI Tract consists of
Mouth (oral cavity) Oesophagus Stomach Small intestine (duodenim, jejunum, ileum) Large intestine (colon, caecum) Rectum Anus
Lip Skin
: keratinized stratified squamous epithelium. Contains hair follicles, sebaceous glands, sweat glands.
Lip Vermilion Border
Very thin keratinized epithelium. Contains dilated venules and veins, but lacks salivary glands.
Lip Oral Mucosa
Most-surface, covered by nonkeratinized stratified squamous epithelium. Labial salivary glands in submucosa.
Oral Mucosa
thick stratified squamous epithelium, supported by a lamina propria
In mobile areas, such as the soft palate, underside of the tongue, floor of the mouth, and mucosal surfaces of the cheeks and lips, the epithelium is not keratinised, although in some places it may be parakeratinized.
• In other areas, such as the gums (gingivae), hard palate, and most of the upper surface of the tongue, the epithelium is keratinised and, in some areas, parakeratinized.
• Underneath the oral mucosa, there is a tough collagenous submucosal layer, with accessory salivary glands, except where the oral mucosa lies over bone, where the submucosa is thin.
Tongue Dorsal Surface
Lingual Muscles: Striated • Extrinsic
• Intrinsic
Sulcus Terminalis
• V-shaped depression which divides tongue into anterior 2/3 and 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
Lingual Papillae Filliform
Small and Conical • Lined by keratinized stratified squamous epithelium • No taste buds • Mechanical function
Lingual Papillae Fungiform
Fungiform
• Mushroom shaped
• Prominent on tip of tongue
• Lined by stratified squamous epithelium
• Taste buds in the epithelium on dorsal surface
Lingual Papillae Foliate
- Found on the lateral edges of tongue • Parallel rows separated by deep clefts • Taste buds
- Rudimentary in human
Lingual Papillae Circumvallate
8 to 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
Taste Buds
Composition: • Taste pore • Three types of cells: • 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
Teeth Odontoblasts
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.
Teeth Ameloblasts
Tall columnar secretory cells from ectodermal origin near surface tooth
Produce enamel.
Enamel - 96% mineralised, hydroxyapatite the primary mineral, does not contain collagen.
Ameloblasts die when the tooth erupts
Parotid Glands Acini
Pure serous gland
• Only serous cells (protein-secreting) in acini.
• Serous cells produce e.g. Amylase (carbohydrates)
• Amylase stored apical in acidophilic secretory granules
• Granules also contain peroxidase, lysozyme, cystatins
Parotid Glands Ducts
Secretory acini – Intercalated ducts – Intralobular or Striated ducts – Interlobular ducts – Major ducts
• The parotid gland has the longest intercalated ducts
• Myoepithelial cells around acini
Submandibular Glands Acini
Mixed gland
• Mostly pure serous acini, but also groups of mixed acini
among the pure serous acini.
• Serous cells (protein-secreting) are filled with prominent, purplish-staining zymogen granules.
• Mucous cells (mucin-secreting) are pale-staining with abundant clear cytoplasm. Arranged in duct-like structures, capped by so-called serous demilumes.
Submandibular glands Ducts
Intercalated ducts are short, but present; striated ducts are long and clearly evident.
Sublingual glands Acini
Mixed gland
ID
• Gland consist mostly of mucous acini capped with serous demilumes. The mucin-secreting cells predominate, with far less protein-secreting cells
Sublingual glands ducts
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.
M S
Oesophagus
- ~25cm long muscular tube
- Connects pharynx to stomach
- Function as a conduit for the bolus of food from the mouth
- Lumen normally collapsed with longitudinal folds
Oesophagus Mucosa
Epithelium • Stratified squamous non keratinized epithelium • Protects from mechanical and chemical injury • Lamina Propria • Connective tissue containing diffuse lymphatic tissue and lymphatic nodules • Eosophageal Cardiac Glands (NOT shown) • Present mainly in terminal part of esophagus • Produces neutral mucus which protects from regurgitated gastric contents • Muscularis Mucosae • Single layer of longitudinal muscle
Oesophagus Submucosa
Dense irregular connective tissue
• Large blood and lymphatic vessels
• Submucosal Plexus (Meissner’s plexus)
• Eosophageal Glands Proper:
• Scattered throughout the length • Produces slightly acidic mucous • Lubricates the lumen
• Excretory duct: (green arrow) lined by stratified squamous epithelium
Oesophagus Muscularis external
Typical two layers: inner circular and outer longitudinal • Upper third: striated • Middle third: striated and smooth • Lower third: smooth • Myenteric plexus (Auerbach’s plexus)
Serosa and Adventitia
- Above the diaphragm
- Fixed to adjacent structure by adventitia
- Below the diaphragm
- Serosa continuous with that of the stomach
Oesophagus Junction
Mucosa undergoes an abrupt transition
Epithelium→ Stratified squamous to simple columnar epithelium
Lamina propria→ Esophageal cardiac glands replaced by cardiac glands of stomach
Muscularis mucosa→ Two layers of smooth muscles arranged as inner circular and outer longitudinal
Submucosa→ Esophageal proper glands to NO glands in the submucosa
Muscularis externa→ Inner oblique layer
Stomach
Histologically divided into 3 regions based on the type of glands
Cardiac region (cardia)
• Near oesophageal orifice
• Contains cardiac glands
Fundic region (fundus)
• Situated between cardia and pylorus
• Contains fundic (gastric) glands
Pyloric region (pylorus)
• Distal, funnel-shaped region proximal to pyloric sphincter
• Contains pyloric glands
Stomach Mucosa
Gastric pits or foveolae
• Gastric glands
• Extend from muscularis mucosae
• Empty into gastric pits
Stomach Epithelium
- Lines gastric pits
* Simple columnar epithelium • Surface mucus cells
Stomach Lamina Propria
• Loose connective tissue • Surrounds gastric glands
Stomach Muscularis Mucosae
Inner circular and outer longitudinal
Stomach Submucosa
Dense connective tissue
• Lymphatics, blood vessels and submucosal plexus
Stomach Muscularis Externa
- Three 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
Stomach Serosa
Continuous with that of duodenum
Stomach Fundus Region
Short pits • Lined by surface mucus cells Long glands • Simple branched tubular glands • 2-4 glands empty into one gastric pit • Three parts • Isthmus • Neck • Fundus (base) Cell types • Mucous neck cells • Parietal cells • Chief cells • Enteroendocrine cells • Stem cells • Found in isthmus of gland
Fundic Gland Secretions
• Cells produce gastric juice • 2 L/day • 4 major components 3. Mucus • Protective coating for the stomach – Physiological barrier » Neutral to alkaline pH: bicarbonate – Physical barrier Intrinsic factor • Essential for B12 absorption in the distal ileum 1. Hydrochloric acid (HCl) • Produced by parietal cells • Gives gastric juice low pH • < 1.0 to 2.0 • Converts inactive pepsinogen into pepsin • Kills most bacteria Pepsin • Produced by chief cells • Potent proteolytic enzyme • Hydrolyzes proteins into small peptides • Converted from pepsinogen
Mucous Cells
Surface mucus cells • Secretes thick viscous mucus that adheres to epitheliumprotects from acidity of gastric juice • Lines gastric pits • Elongated nucleus • Large apical cup of mucinogen granules takes up most of cytoplasm 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
Parietal (Oxyntic) Cells
- SecreteHClandIntrinsicfactor
- Foundthroughoutglandbutconcentratedinneck
- Largemonoorbinucleatedcells
- Eosinophilicdueto+++mitochondria
- Extensiveintracellularcanalicularsystemthat communicates with lumen of gland
- Stimulatedbygastrin
Chief Cells
Located at the base of gland
• Typical protein-secreting cell
• Abundant rER
• Gives cells basophilic appearance • Apical zymogen granules
Secretions
1. Pepsinogen Converted to pepsin by low pH
(proteolytic enzyme) 2. Secretes weak lipase
Enteroendocrine Cells
Secretes hormones into the lamina propria
• Found throughout the gland
• More prevalent in the base
• Typically appear clear with H & E stain
• 2 general cell types • Closed
• Do not reach the lumen • Open
• Exposed to lumen
• Serve as primary chemoreceptors
• Gastrin secreting cells are concentrated in the pyloric antrum
Gastroduodenal Junction
•Mucosa – appearance of finger shaped villi •Submucosa – appearance of Brunner’s glands (mucous) •Muscularis - Only 2 layers of muscles
Small Intestine
Longest component of digestive tract measuring over 6 meters long. • Principal site for digestion & absorption • Receives: • Chyme from stomach and • enzymes from pancreas and microvilli of enterocytes • Bile from liver • 3 regions 1. Duodenum 2. Jejunum 3. Ileum • Tissue & cell specializations increase surface area 1. Plicae circularis (PC) 2. Villi (V) 3. Microvilli (Mv) Small Intestine
SI Mucosa
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
SI Submucosa
Dense connective tissue
• Submucosal (Meissner’s) plexus
• Circular folds or Plicae circularis (PC)
• Duodenal submucosal glands
SI 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
SI Serosa/ Adventitia
• Mainly serosa except 2nd, 3rd and 4th parts of duodenum
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
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
Intestinal Gland
Crypts of Lieberkühn • Simple tubular glands • Extend from muscularis mucosae to open unto lumen at base of villi • Continuous with epithelium of villi • Surrounded by lamina propria
Enterocytes SI
Simple columnar epitheliocytes which are Primarily absorptive cells which renew every 4-6 days
• They also have secretory function
• Produce digestive enzymes
• Secretes water and electrolytes
Specialization:
• MicrovilliForm the striated border which contains terminal digestive enzymes
• Tight junctionsAllows selective absorption across the plasma membrane
• Lateral plicationIncrease lateral surface area
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
Paneth Cells
Paneth cells are found in base of intestinal glands
• Renewed every 4 weeks
• Intensely acidophilic apical secretory vesicles • 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
SI Enteroendocrine
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
• Most active regulators of GI physiology released in the small intestine
• CCK
• Secretin • GIP
• Motilin
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
• 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
Large Intestine
Colon • Ascending • Transverse • Descending • Sigmoid • Cecum & vermiform appendix • Rectum • Anal canal
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 Large Intestine • • Colon • Ascending • Transverse • Descending • Sigmoid • Cecum & vermiform appendix • Rectum • Anal canal
LI Mucosa
• • • Mucosa “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
LI Muscularis Externa
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
Colon: Longitudinal section through tenia coli (trichrome)
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
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
Recto anal junction
• Internal anal sphincter – Thickened inner circular layer of the muscularis externa • External anal sphincter – Striated muscle of the pelvis
Pathology-associated with Gastrointestinal Tract
Barrett’s oesophagus (metaplasia)
Gastric and duodenal ulcer (H. Pylori) Celiac disease (gluten, autoimmune) Crohn’s Disease (inflammation, ulcerations) Adenocarcinoma (polyps)
Hirschsprung’s Disease (megacolon) Oesophageal varices & Haemorrhoids
