Gastrointestinal Tract Flashcards
What lines the oral cavity and oropharynx
Stratified squamous non-keratinising epithelium
- protective layer
Oral cancer
Squamous cell carcinoma
Can excise them operatively
Responsive to readily and chemotherapy
Role of salivary glands
Produce saliva
Produce enzymes
Role of oral cavity
Receive food
Chew food
Lining of salivary gland
Secretory glandular epithelium
Secretory glandular epithelium
Lots of cytoplasm containing granules
Sjorgren’s syndrome
Autoimmune disease of salivary glands
No saliva production
Dry tongue
Function of oesophagus
Swallows food
Muscles in oesophagus walls
Circular and longtitudinal layers of muscle
Coordinate contractions to push food down into stomach
Lining of oesophagus above thoracic diaphragm
Stratified Squamous non-keratinising epithelium
Underneath is a thin lamina propria and narrow muscularis mucosa of smooth muscle
Oesophageal submucous glands (secrete mucus that lubricates food as it is swallowed)
4 parts of stomach
Cardia
Fundus
Body
Pylorus
2 ends of stomach
Oesophagus—> cardiac sphincter
Pyloric sphincter—> duodenum
Function of stomach
Digestion of food
Gastric fundic mucosa
Located in fundus of stomach
Produce mucus
Role of mucus in the stomach
Layer of mucin on inner lining buffers between the acid of the lumen of the stomach and the epithelium
Gastric body mucosa
Located in body of stomach
Contains:
parietal cells that produce hydrochloric acid
Chief cells that produce pepsinogen and lipase
Parietal cells
Produce hydrochloric acid
Rich in the enzyme carbonic anhydrase
Source of intrinsic factor essential for the absorption of vitamin B12
Occur mostly in upper parts of the glands, close to the gastric pits
Chief cells
Produce pepsinogen and lipase (digestive enzymes)
Suffix -ogen
Inactive form of enzyme
Pepsinogen
Produced and secreted by chief cells
Broken down by stomach acid into pepsin
Gastric antral mucosa
Glands which produce mucin
Helicobacter pylori
Lives in mucin of stomach
Causes inflammation and ulcers
Structure of intestines- 4 layers
Lumen —> mucosa —> submucosa —> muscularis propria—> serosal surface
What epithelium lines the small and large intestine
Glandular epithelium containing endocrine cells
Submucosa of intestines
Loose connective tissue
Contains glands and lymphoid tissue
Loose collagen and blood vessels
Muscularis propria
Smooth muscle
Controlled by autonomic nervous system
Ganglion cells sit between circular and longitudinal muscle layers
Hirschsprung’s disease
A congenital absence of ganglion cells at the bottom of the intestine, rectum and colon
Interstitial cells of Cajal
Located in muscular wall of bowel
Pacemaker cells of muscle contraction
Can form tumours
Gastrointestinal stromal tumours
Caused by interstitial cells of Cajal
Mutation in C-kit gene
Commonly benign
Serosal surface
Simple squamous epithelium
Contains blood supply of gut
Mesentry
Attaches bowel to posterior abdominal wall
What covers the gut in the peritoneal cavity
Mesothelial cells
Crypts
U-shaped long columns
Transit cells at top
Potential stem cells
Stem cells
Paneth cells
3 parts of small intestine
Duodenum
Jejunum
Ileum
Name of large intestine
Colon
Anatomy of duodenum
Joined to pyloric end of stomach
C shaped
Pancreatic duct and common bile duct enters
Stuck to retroperitoneum
Ampulla of vater
Entrance of pancreatic duct into duodenum
Jejunum
Coils of small bowel as attached to flexible mesentry
Function of duodenum
Digests food
Absorbs food
Resists bugs
Anatomy of small intestine
Villi
Crypts (producing new cells to form villi) in between villi
Lymphocytes
Villi
Finger-like projections of small intestine covered in epithelium to increase surface area
Have microvilli on surface
Mucosa-associated lymphoid tissue (MALT)
Release lymphocytes in the gut
Giardia lambila
Protozoanal bugs cover mucosa and prevent absorption of nutrients
Leads to diarrhoea, weight loss, tiredness and malnutrition
Coeliac disease
Allergy to gliadin (gluten) in wheat
Loss of villi (villous atrophy)
Crypt hyperplasia (larger than normal)
Lymphocytes react with gliadin- killing cells of duodenal epithelium
Malabsorption
Role of Jejunum and ileum
Digest food
Absorb food
Resist bugs
Jejunum and ileum
Villi and micorvilli
Caecum
Joins ileum and large intestine
Appendix
Projects from caecum
Role unsure
Lining of appendix and colon
No villi
Flat glandular mucosal surface
Function of colon
Primarily absorbs water
Absorbs food
Resists bugs
4 parts of colon
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Hepatic flexure
Point where colon bends near liver
Ascending ——> transverse
Splenic flexure
Transverse—> descending
Ulcerative colitis
Inflammation of the colon
Only affects the mucosa
Sharp distinction between normal and diseased tissue
Lamina propria
Loose fibrous connective tissue
Gut as a muscular tube
Exception stomach
Lumen
Epithelium on a basement membrane
Lamina propria
Muscularis mucosae
Submucosa
Muscularis propria (inner circular layer and outer longitudinal layer)
Adventitia
(Serosa)
Stomach walls
Epithelium on a basement membrane
Lamina propria
Muscularis mucosae
Submucosa
Muscularis propria (innermost oblique layer, middle circular layer, outermost longitudinal layer)
Adventitia
Serosa
3 layers of stomach muscularis propria
Innermost oblique layer
Middle circular layer
Outermost longitudinal layer
Where does the oral cavity extend from
Lips to palatoglossal folds
What is the outlet of the oropharynx protected by
Ring of lymphoid tissue (palatine and lingual tonsils)
What do the salivary glands secrete
Saliva that contains enzymes and lubricants that aid the passage and digestion of ailments
Secrete bacteriostatic agents and products that protect and promote the growth of the mucosal lining of the GI tract
3 pairs of salivary glands
Parotid
Submandibular
Sublingual
Mucosal covering of the lip
Stratified squamous epithelium
keratinising ——> non-keratinising at margin of skin to mouth
Ventral surface of tongue
Stratified squamous non-keratinising epithelium
Dorsal surface of tongue
Stratified squamous keratinising epithelium due to constant abrasion of this surface
Papillae
Located on dorsum of the tongue
Tall, pointed filiform papillae are most common and cover whole anterior 2/3 of tongue
Less numerous mushroom shaped fungi form papillae are found on tip and sides of tongue
Pale-staining taste buds embedded in epithelium on lateral sides of these papillae
V-shaped row of dome-shaped circumvallate papillae separate the anterior 2/3 and posterior 1/3 of tongue - also bear taste buds
What separates the anterior 2/3 and posterior 1/3 of tongue
A v-shaped row of dome-shaped circumvallate papillae
Bear taste buds
Where are mushroom shaped fungiform papillae located
Tip and sides of tongue
Where are tall, pointed filiform papillae located
Whole of anterior 2/3 of tongue
Parotid salivary glands
Produce a watery enzyme-rich secretion (serous secretion) rich in alpha amylase that digests starch
Lie anterior to the ear on both sides of the face and enter the mouth via ducts adjacent to the 1st upper molar teeth
Contain lymph nodes
Acini
Spherical clumps of serous gland cells in parotid gland
Parotid gland secretory cells
All serous
Pyramidal in shape
Spherical nucleus
Cytoplasm full of rER and apex of cell contains prominent secretion granules
What do the parotid acini drain into
Ducts lined by a simple cuboidal epithelium that may become stratified at the distal end
Sublingual salivary glands
Lie beneath the tongue and discharge their secretions into the floor of the mouth by a series of ducts either side of the frenulum of the tongue
Structure of sublingual glands
Branched tubular-acinar glands
Produce a sticky mucus-rich secretion that helps to lubricate the mouth and bolus of food
Secretory cells appear swollen - filled with pale staining mucus granules
Oval nucleus is squashed to base of the cell
What do the sublingual tubular-acinar drain into
Ducts lined by simple or stratified cuboidal epithelium
(Cells appear pinker)
Orbicularis oris muscle
Ring of muscle that surrounds the mouth
Major constituent of secretion of the sublingual gland
High molecular weight mucopolysaccharide
Absorbs large amounts of water so are very good lubricants
Serous Demi-lunes
Half-moon shaped clusters of serous cells that lie at the closed ends of the branched mucus-secreting tubules that make up part of the submandibular gland
Submandibular salivary glands
Well-defined globular glands
Lie subcutaneously below the mandible, either side of the tongue
Discharge by a pair of ducts in to the frenulum of the tongue
Frenulum of the tongue
small fold of mucous membrane extending from the floor of the mouth to the midline of the underside of the human tongue
Structure of submandibular glands
Branched tubulo-acinar type
Often interspersed with fat
Display 2 types of secretory cells:
1. Pale staining mucus-producing cells
2. Darker staining enzyme producing serous cells
Serous cells form acini or lie at the closed ends of the tubules forming Demi-lunes
What do submandibular glands produce
A mixed secretion, part mucus and part an enzyme-rich secretion
Sources of epidermal growth factor that promotes growth of epithelium in GI tract
Parotid and submandibular glands
Epiglottis structure
Covered by a stratified squamous epithelium
Posterior surface = pseudo stratified columnar ciliates epithelium (respiratory epithelium)
Internally:
Plate of elastic cartilage
Submucosa often contains lymph nodules and salivary glands
3 components of mucosa
- a lining epithelium that is often folded
- a layer of connective tissue (lamina propria) that often contains lymphoid tissue
- muscularis mucosa= a ring of smooth muscle
Meissner’s plexus
A rich plexus of nerves part of the enteric nervous system in the submucosa of the gut tube
Regulates the mucosa and processes of absorption and secretion
Auerbach’s plexus
Nerves of the enteric nervous plexus between two layers of muscle in muscularis propria
Regulates much of the contractile activity of the gut
Lining of oesophagus below thoracic diaphragm
Simple columnar epithelium
Can become the site of pathological change
Thicker muscle layer
Submucosa of oesophagus
Contains sero-mucous glands whose secretions lubricate the oesophagus
At distal end = contains many large, thin-walled veins (may become the site of oesophageal varicosities)
Muscularis externa of oesophagus
Composed mainly of skeletal muscle
At distal end - mostly composed of smooth muscle
Rugae
Visible longtitudinal folds of mucosa in stomach
Lining of stomach
simple columnar epithelium punctuated by gastric pits into which the gastric glands drain
Muscularis propria of stomach layers
3- additional oblique layer of fibres closest to the mucosa that helps to churn up the food within the stomach
Gastric glands of 4 sections of stomach
fundus and body show very similar histological structure particularly with respects to their gastric glands.
The cardia and pylorus have a different histological appearance.
mucosa of the stomach contains many tubular glands within its mucosa. These fill the lamina propria and discharge their secretions into gastric pits that communicate with the lumen of the stomach.
Mucus neck cells
provide a lubricatory, acid-resistant mucus
Types of gastric glands in fundus and body of stomach
Mucus neck cells
Parietal cells
Chief cells
Types of gastric glands in cardiac and pylorus of stomach
Mucus neck cells
Varicosities
occur when your veins become enlarged, dilated, and overfilled with blood. Varicose veins typically appear swollen and raised, and have a bluish-purple or red color.
Site of oesophageal varicosities
Submucosal layer at distal end of oesophagus
Gastric pits
Several tall straight or branched glands open into each gastric pit
Purpose of elastic tissue in stomach
Cause collapse of the stomach on emptying
Helps prevent the perforation of the stomach wall by sharp fragments of bone (particularly well-developed in carnivores)
Normal pH of gastric juice
2
Structure of parietal cells
Globular shape
Stain bright pink with H&E
Surface deeply invaginated to form intracellular canaliculi
Contain many mitochondria
Structure of chief cells
Pyramidal shape
Occupy deeper parts of the gastric glands
Part of cytoplasm stains blue with H&E
Cells contain secretion granules
For which tissue constituent does pepsin have an affinity
It digests proteins but has a particular affinity for collagen
-facilitates break down of meat by attacking the connective tissue between the muscle fibres
Pyloric region gastric glands
Shorter than those of the body or fundus
Coiled rather than straight
Mainly mucus neck cells
Contains:
- isolated cells that produce gastrin and a bombesin-like peptide
- endocrine cells that produce serotonin, somatostatin and vasoactive intestinal peptide (VIP) = regulate breakdown and delivery of foodstuffs to the duodenum
What do the endocrine cells in the gastric glands of the pyloric region of the stomach produce and why
Serotonin, somatostatin and vasoactive intestinal peptide (VIP)
- regulate breakdown and delivery of foodstuffs to the duodenum that occurs during the digestion process
Plicae circulares
Circular folds of the lining of the intestines
Increase surface area available for absorption
Where are Plicae circulares most numerous
Jejunum
Where are Plicae circulares least numerous
Distal part of colon
Lining of villi
Simple columnar epithelium with 2 main cell types:
1. Enterocytes - absorptive cells
2. Goblet cells- mucus secreting cells
What do villi contain
In its core - a small arteriole, a thin walled venule and a blind-ended lymphatic (lacteal)
Smooth muscle cells that rhythmically shorten the villus, milking the blood and lymph from the villus
Role of venules and lacteals in villus
Carry absorbed nutrients to the liver
Crypts of Lieberkühn
Straight tubular glands between the villi of the intestine
Contain a stem cell population
Newly formed cells migrate from the crypts in to the surface of the villi and are eventually sloughed off from the tips
Enterocytes
Absorptive cells in villi of intestines
Each cell possesses around 300 microvilli
Have specific receptor complexes that allow the uptake of certain immunoglobulins that subsequently form part if the system of passive immunity - most active in neonate in response to immunoglobulins in mother’s first milk (colostrum) but declines in significance within a few months
How long is the process of stem cells —> being sloughed off villi
5 days
Microvilli
Surface covered in well-developed glycocalyx that acts as a filter and as an anchorage for exo-enzymes
Most nutrients absorbed by this pathway
Stains intensely by Periodic Acid Schiff (PAS) due to high concentration of hexose sugars in glycocalyx
Length of duodenum
12 inches (30 cm)
Structure of duodenum
Relatively smooth lining with few plicae circulares
Villi are broad-leaf structures
Relatively few goblet cells
Submucosa filled by Brunner’s gland
Brunner’s glands
Mucous secreting cells in duodenum- alkaline secretion helps to neutralise the chyme emerging from the stomach
Which of the 2 layers of the muscularis extema is thicker
The inner circular layer is 4 or 5 times thicker than the outer longitudinal layer
Paneth cells
Differentiated cells found at the bottom of the crypts and villi
Secrete lysozyme - play an important role in regulating bacterial flora of the gut as it breaks down bacterial cell walls
Bright pink-staining granules
Structure of Jejunum
Close packed plicae circulares
Long and narrow villi
Relatively short crypts
Many goblet cells present
Lymph nodes present in the Lamina propria
Variable in thickness submucosa - very loose
Structure of the ileum
Less tightly packed plicae circulares
Shorter villi
Goblet cells increase in numbers towards distal end
Peyer’s patches in submucosa
Peyer’s patches
Large patches of lymphoid tissue present in the submucosa of the ileum
Vermiform appendix
Arises from the caecum
Lined by simple columnar epithelium with goblet cells
No villi
Only a few rudimentary crypts
Lamina propria and submucosa filled with lymphoid tissue (amount declines with age)
No muscularis mucosa
Muscularis externa - 2 layers of smooth muscle
Taenia coli originate at base of appendix and run whole length of large intestine
Lining of colon
No intestinal villi
Mucosa consists of close packed crypts that mainly contain Enterocytes and goblet cells
Lamina propria restricted in volume due to packed nature of crypts
Prominent muscularis mucosa
Mucosa and submucosa have lymph nodules embedded within them as part of GALT system
Muscularis externa = thickened inner circular layer and taenia coli
Taenia coli
3 longtitudinal bands of smooth muscle that compose outer layer of colon muscularis externa
Lining of rectum
Simple columnar epithelium
Lining of anal canal
Stratified squamous epithelium that becomes keratinising at its distal end
Submucosa contains fat and prominent internal plexus of veins (anal varicosities)
Smooth muscle of Muscularis externa is thickened to form internal anal sphincter
Surrounded by striated muscle of external anal sphincter
Where is the striated muscle of the external anal sphincter derived from
Pelvic bowl
Peri-anal skin
Contains hair follicles and modified sebaceous glands
Where are sweet taste buds located on tongue
Mainly at the tip
Where are salty taste buds located on tongue
Either side towards the front of the tongue
Where are sour taste buds located on tongue
Either side towards the back of the tongue
Where are bitter taste buds located on tongue
Across the whole back of the tongue
Where are immunoglobulins in parotid saliva produced
Plasma cells resident in the gland produce immunoglobulin A (IgA)
Are discharged in the saliva where they combine with proteinaceous secretory pieces also produced by the glands
Function of immunoglobulins in parotid saliva
Complexes are protected from digestion which allows the IgAs to reach the intestine unmodified
Dental plaque
Calcified deposit rich in dead or dying oral bacteria and food debris
Striated duct
Part of the duct of the parotid gland
Result of deep invaginations of the basal plasmalemma of the cells and large elongated mitochondria that lie perpendicularly between them
Capable of secretion and reabsorption of water and ions from the saliva
Do salivary enzymes continue to function in the stomach
Have a neutral pH optima so are inactivated by the acid environment of the stomach
In bolus of food, enzymes are shielded from gastric juices so continue to act until bolus is dispersed
Function of gastrin
Promotes the secretion of HCl by the parietal cells in the body and fundus of the stomach
Which cells secrete gastrin
Endocrine secreting cells in pyloric region of stomach and duodenum
2 parts of intrinsic innervation of gut
Auerbach’s plexus
Meissner’s plexus
What lines most of the mouth
Stratified squamous non-keratinising epithelium over a loose fibrous connective tissue storms
Where are the circumvallate papillae
Between anterior 2/3 and posterior 1/3 tongue
Function of filiform papillae
Roughen surface of the tongue- aids mastication
Unique structure of posterior 1/3 of tongue
Epithelium overlies a lymphoid infiltrate (part of Waldeyer’s ring)
- blue layer when stained with H&E
In which gland are all acini serous
Parotid
In which glands are acini mostly mucous
Sublingual gland
Buccal glands
Lingual glands
Are mucous or serous acini dark staining
Serous
What feature confirms oesophageal origin of cells
Squamous lined ducts in lamina propria
What type of acini cells are in submandibular gland
Both serous and mucous acini
Which two parts of stomach are histologically the same
Gastric body and gastric fundus
Features of gastric antrum
Long crypts that branch
Lined by mucous-secreting cells
Lack parietal cells
What percentage of the thickness of the antrum and pylorus is superficial zone of the mucosa
More than half
What percentage of the thickness of the cardia is superficial zone of the mucosa
50%
What do parietal cells secrete
Intrinsic factor
HCl
Features of lining of small intestine
Crypts and villi
What do Brunner’s glands secrete
Bicarbonate-rich alkaline secretion
Where are Brunner’s glands found
Duodenum
Which cells lie below epithelium in ileum
Lymphoid cells (MALT) - Peyer’s patch
How to tell difference between appendix and colon
Lymphoid tissue in appendix
Which part of GI tract does not have villi
Appendix
Colon
Which cells lie below epithelium in duodenum
Brunner’s glands
Where is Auerbach’s plexus
Muscularis propria
Where is Meissener’s plexus
Submucosa of gut tube
Colorectal histology
Same whole length from caecum —> rectum
