Histology - Gastrointestinal Flashcards
What is the mouth lined by?
Stratified squamous non-keratinising epithelium. Different from the skin (stratified squamous keratinised epithelium)
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What are the 3 salivary glands?
Parotid, submandibular + sublingual gland
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What are the salivary glands lined by?
Secretory glandular epithelium as they need to secrete saliva + enzymes
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What is the oesophagus lined by?
Stratified squamous non-keratinised epithelium
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What glands does the oesophagus contain?
Submucosal glands
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What glands are found at the fundus of the stomach?
Gastric fundic mucosa = produce mucus
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What does gastric body mucosa contain?
Parietal cells = release hydrochloric acid and are source of intrinsic factor essential for absorption of vitamin B12
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What else does gastric body mucosa contain?
Chief cells = produce enzymes that start digestive process in stomach, e.g. pepsinogen, lipase
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Is gastric antral mucosa as specialised?
No. Still has glands that produce protective layer of mucin, but not hydrochloric acid etc.
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After the food has sat in the stomach, in reaches the intestines. What do the intestines do?
- Digest food
- Absorb food
- Absorb water
- Resist bugs
What are the intestines lined by?
- Cross sectionally, we have the lumen (where food is), then the mucosa (epithelial part = glandular epithelium). There are endocrine cells within this epithelium.
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In the intestines, what comes after the mucosa?
- Submucosa = connective tissue
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In the intestines, what comes after submucosa?
- Muscularis propria = all smooth muscle, contain ganglion cells (make the bowel move)
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What are the interstitial cells of Cajal?
- Found in muscular wall of intestine, pacemaker cells (ganglion cells make contractions, interstitial cells of Cajal pace this).
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In the intestine, what comes after muscularis proparia?
- Serosal surface (contains all the blood vessels)
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Image of layers of the bowel.
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All of the intestine contains glandular mucosa, but this is arranged differently. What is the basic architecture of glandular mucosa?
Crypts. At the bottom, you have stem cells. They produce transit cells, which are found further up. These transit cells eventually become columnar epithelial cells lining the gut
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Anatomy of small intestine.
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What does the duodenum do?
- Digests food (bile goes into duodenum, so there are digestive enzymes, bile salts etc.)
- Absorbs food
- Resists bugs
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What is the main way that the small intestine increases surface area?
Villi, covered in epithelium. Microvilli found on villi. This is to maximise absorption
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What is mucosa-associated lymphoid tissue (MALT)?
- Lymphocytes in the mucosa of the gut
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What do the jejunum and ileum do?
- Digest food
- Absorb food
- Resist bugs
- They have microvilli as well to maximise SA for absorption
In the appendix, what is the mucosa like?
Flat, no villi (absorption of food is more or less finished by the time it reaches the colon)
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Anatomy of the large intestine (colon).
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What does the colon do?
- Absorbs a bit of food
- Absorbs a bit of water
- Resists bugs
What is mucosa like in the colon?
Flat glandular mucosa, no villi
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The gut is a muscular tube. What is the general structure of the gut?
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What is the one exception to this general structure?
The stomach. The muscularis propria has a innermost oblique layer, a middle circular layers and an outermost longitudinal layer
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What is the tongue lined by?
Covered by stratified squamous non-keratinising epithelium on its ventral surface, but it is often heavily keratinised on its dorsal surface due to constant abrasion
The dorsum of the tongue is thrown into complex folds known as what?
Papillae. Filiform = most common, cover anterior 2/3. Fungiform = tip + sides of tongue, taste buds embedded in epithelium on lateral sides of these papillae. Circumvallate separate anterior 2/3 and posterior 1/3 of tongue’s surface, also contain taste buds
What is the epiglottis? What is it lined by?
- Forms boundary between oropharynx + laryngeal pharynx
- Most of its surface is covered by a stratified squamous epithelium although the lower part of its posterior surface has pseudostratified columnar ciliated epithelium (respiratory epithelium)
What is the oesophagus lined by? What type of muscle is there at the proximal and distal end?
Stratified squamous non-keratinised epithelium. Proximal end, outermost layer of muscle is composed mainly of skeletal muscle but at the distal end it is composed mostly of smooth muscle
What is the stomach lined by?
Simple columnar epithelium punctuated by gastric pits into which the gastric glands drain
What are the rectum and anal canal lined by?
- Rectum = simple columnar epithelium = similar to colon
- Anal canal lined mainly by stratified squamous epithelium that becomes keratinised at its distal end
Picture of parotid salivary gland.
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Picture of sublingual salivary gland.
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Picture of submandibular salivary gland.
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Picture of duodenum.
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Picture of jejunum.
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Picture of ileum.
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Picture of colon.
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What are the principle cells within the liver? How are they arranged?
Hepatocytes. Arranged in cords with intervening sinusoids
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Another histological feature to recognise in the liver are the portal tracts. What do these comprise? What is a third feature?
- Comprise branches of:
- Portal veins
- Hepatic artery
- Bile duct
- A third feature of the histology of the liver is the central veins
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By convention, we divide the liver into classic lobules. What is a classic lobule?
- Area drained by one central hepatic venule
- An artificial construct for understanding hepatic architecture
- Central vein surrounded by cords of hepatocytes. Corners of classic lobule contain portal tracts
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What is another way of thinking about the architecture of the liver? What is this based around?
- The acinus
- Diamond structure instead of hexagonal. Based around blood supply rather than drainage
What does the classic lobule mean for the hepatocytes?
- Means not all hepatocytes are equal as hepatocytes nearer portal tract will be more richly oxygenated (+ more glucose) than others (blood drains into central vein)
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What do hepatocytes contain? What do they produce?
- Principle functional cells of liver
- Abundant mitochondria
- Large central nuclei (small amount are binucleate)
- Produce bile
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What are the three surfaces of individual hepatocytes?
- Sinusoidal (70%) - permits exchange of material with blood (space of Disse)
- Canalicular (15%) - permits excretion of bile
- Intercellular (15%)
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What is the space of Disse?
- The area between hepatocytes + sinusoids
- Contains reticulin fibres + stem cells called stellate (Ito) cells
What are sinusoids? What do they contain?
- Highly specialised blood vessels
- Contains scattered Kupffer cells
- Allow hepatocytes to secrete + absorb efficiently
- Fenetrated + no basement membrane
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What are:
a) Stellate (Ito) cells
b) Kupffer cells?
a) pericytes within the space of Disse. Store lipids and vitamin A
b) tissue-bound macrophages located in the liver sinusoids
Hepatocytes synthesise bile. Where does this then drain? What are the bile ducts lined by?
- Canaliculi (inbetween hepatocytes), drains into bile ductules, fuse to form trabecular duct, fuse to form bile ducts
- Bile ducts lined by simple cuboidal-to-columnar epithelium
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If bile does not go straight to the duodenum, where is it stored? What is the function of this organ?
- Goes to gallbladder
- Gallbladder stores + concentrates (by absorbing water from bile) bile and expels bile via common bile duct into duodenum when stimulated
- Innermost surface is covered by a single layer of columnar epithelium that is folded and has microvilli
- Beneath the epithelial layer is a muscular layer that allows the gallbladder to contract to expel bile
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What is the microvilli in the epithelium of the gallbladder important for?
They help the gallbladder absorb water from bile to concentrate it
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What is the exocrine pancreas? What is surrounded by? What are the pancreatic epithelial cells arranged in?
- Comprises majority of pancreas
- Synthesises + secretes enzymes and bicarbonate-rich fluid into the duodenum to assist with digestion
- Surrounded by poorly defined fibrous capsule with septa dividing gland into lobules
- Epithelial cells arranged in acini
What is the shape of pancreatic acinar cells? What do they secrete?
- Exocrine
- Pyramidal shape
- Rich in RER
- Secrete zymogens
- Connected to an intercalated duct –> interlobular ducts (lined by cuboidal epithelium) –> main pancreatic duct (lined by columnar epithelium)
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Are the islets of Langerhans endocrine or exocrine? What cells producing pancreatic polypeptide are found in the islets of Langerhans?
- Endocrine
- PP cells found in islets of Langerhans + these produce pancreatic polypeptide
Picture of liver lobule.
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