1- Gi histology Flashcards
what is the dorsal and ventral surface of tongue?
dorsal - top of tongue
ventral - underneath (bottom) of tongue
dorsal does mean back and ventral front
what cells cover the oral cavity, oropharynx and laryngopharynx?
stratified squamous epithelium (not keratinized)
what cells cover nasal cavity and nasopharynx?
respiratory epithelium = pseudostratified columnar epithelium, ciliated with goblet cells non-keratinised
what is trick to remember when keratinised or not?
moist = non-keratinised
what cells compose the anterior part of tongue? (top 2/3)
stratified squamous epithelium, thin on ventral surface, thick + with papillae on dorsal surface (think about how top of tongue is rough)
what cells compose the posterior part of tongue? (bottom 1/3)
covered by smooth stratified squamous epithelium which except for circumvallate papillae, lacks papillae but does have substantial lymphoid aggregates in submucosa
= no papillae, collection of lymphocytes (tonsil)
what are papillae?
bumps on tongue - there are different kinds (circumvallate, fungiform, foliate, filiform)
what are circumvallate papillae?
most common →has inner + outer wall with gaps that serous glands secrete into = what keeps tongue moist. have taste buds (modified epithelial cells that are present in between lining on the tongue)
what are fungiform papillae?
not in centre but along border of tongue. no outer + inner wall - they also contain taste buds
what are foliate papillae?
also at border, not too prominent in humans but do exist, also have taste buds
what are filiform papillae?
across whole dorsal surface of tongue, lined by stratified columnar epithelium, will get keratinised layer (why you feel roughness when run tongue over hard palate). no taste buds
what are palatine tonsils, lingual tonsils, tubal tonsils and pharyngeal tonsils composed of?
ring of lymphoid tissues
what are adenoids?
a mass of enlarged lymphatic tissue = pharyngeal tonsils (in nasal cavity), not prominent later in life but prominent in children (can block children if enlarged)
how many lymphocytes are a folic and how many lymphocytes are lymphatic nodules?
1 lymphocyte = folic
collection of lymphocytes = lymphatic nodules
what are tonsillar crypts?
gaps in between - in palatine tonsils (big ones you think of)
= they are lined with stratified squamous epithelium and the lymphatic follicles
what are the 4 layers of cells from inside to outside in oesophagus to large intestine?
- mucosa - contains 3 layers (together are mucosa)
- submucosa - layer of connective tissue (dense irregular)
- muscularis externa - thicker smooth muscle, 2 layers
- serosa or adventitia - outer layer of connective tissue that either suspends the digestive tract or attaches it to other organs
*serosa not connective tissue = simple squamous epithelium (mesothelium)
what are the 3 layers of mucosa (which is 1st layer from oesophagus to large intestine)?
from inside to out:
1. lining epithelium = stratified columnar epithelium (non-keratinized)
2. layer of connective tissues, lamina propria
3. layer of smooth muscle, muscularis mucosa (inner circular layer and outer longitudinal layer)
what is characteristic features of oesophagus and duodenum submucosa?
contains glands
*in other structures, glands are in lamina propria
what is sudden change in cells from oesophagus to cardia of stomach?
Abrupt transition from stratified squamous epithelium of oesophagus to the simple columnar epithelium of the cardia of the stomach
what are layers of stomach?
stomach epithelium (has gastric pits + glands) , mucosa, submucosa, muscularis externa
what are gastric pits?
surface dip inside - gastric glands (there are 1-7 inside gastric pit)
what are cells of gastric glands?
simple tubular glands that contain different unevenly distributed cells
- isthmus mostly has parietal + stem cells
- neck is mostly neck mucous cells + parietal cells
- fundus (base) is mostly chief cells, with a few parietal cells + enteroendocrine cells
what is function of chief cells?
make pepsinogen - digestive enzyme secreting cell
what is function of parietal cell?
hydrochloric acid producing cell
what are different regions of stomach?
oesophagus going into cardia then fundus is main bit then pylorus end but before duodenum
what is rugae?
wrinkles on stomach lining
what is mucosa like in cardia region of stomach (bit of stomach straight after oesophagus enters)?
Deep gastric pits that branch into loosely packed, tortuous glands
what is mucosa like in fundus region of stomach (main body of stomach)?
Shallow gastric pits with long straight gastric glands
what is mucosa like in pylorus region of stomach (bit of stomach straight before duodenum)?
Deep gastric pits with branched, coiled gastric glands at a higher density than in the cardia
what is unusual about muscularis externa in stomach?
unusual in that in areas it contains an additional layer = oblique muscle layer
- it is in between circular + longitudinal = contracts in twisting fashion, helping mixing and churning of food and gastric juices in the stomach, helping digestion
what is important change in stomach mucosa to duodenal mucosa?
= the inner circular layer of smooth muscle is thickened to form pyloric sphincter = helps control flow of gastric emptying
what lining epithelium in mucosa of stomach?
simple columnar
what are crypts of lieberkuhn?
intestinal glands in small intestine
what is on surface of small intestine?
villi
what is histologically distinct about duodenum?
contains Brunner’s glands in the submucosa
what is histologically distinct in jejunum?
Tallest villi, located on permanent circular folds (the plicae circularis) of the mucosa and submucosa
Lymphoid follicles infrequent (clusters of lymphoid tissue that contain immune cells)
what is histologically distinct in ileum?
Characterized by shorter villi and aggregations of lymphoid follicles called Peyer’s patches found in the submucosa and often extending into the lamina propria.
what are villi on small intestine composed of?
lined by simple columnar epithelium, in between are small cells (goblet cells which are unicellular glands, not much in small intestine but do get in between lining)
what are enterocytes?
The most numerous cells, they are tall columnar cells with a brush border and are the principle absorptive cell.
what is goblet cells function?
Produce mucin to protect epithelium and lubricate passage of material
what are paneth cells?
Found at the base of the crypts of Lieberkuhn, they have a defensive function and have a role in regulating bacterial flora (secrete lysozyme and defensins)
what are entero endocrine cells function?
Produce hormones that contribute to the control of secretion and motility (e.g. gastrin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP))
where are stem cells found in small intestine?
Found at the base of the crypts of Lieberkuhn, they divide to replenish epithelium
what is purpose of microvilli?
cytoplasmic projections from enterocytes - increase surface area for absorption →why called brush border
what glands are found in submucosa of duodenum?
brunners gland
what are brunners glands?
when stimulated by the presence of chyme they produce a thin, alkaline mucous to neutralise the chyme
(chyme is acidic, partly digested semi-fluid material from stomach)
what are plicae circularis?
permanent circular folds with fingerlike projections (villi) - they’re not just folds of mucosa but also contain submucosa
*the villi project upwards and at their base tubular crypts of lieberkuhn burrow down
what are peyer’s patches?
a lot of lymphatic nodules in ileum
= lots of lymphoid tissue in gut but large aggregations are peyer’s patches
what cells compose large intestine?
lining of epithelial still simple columnar and have abundant goblet cells (no microvilli as no absorption)
what is ratio of columnar cells to goblet cells in large intestine and rectum?
large intestine = 4 columnar cells:1 goblet cell
rectum = 1 columnar cell:1 goblet cell
what is distinct about muscles in large intestine?
the outer, longitudinal smooth muscle is distinct as not continuous but found in 3 muscular strips called teniae coli
what part of GI tract has a lot of lymphatic nodules?
appendix
what is appendix location?
blind-ending hollow extension of the cecum
what is structure of appendix?
similar to the rest of the colon, but the crypts are far less abundant and there is typically a circular arrangement of lymphoid tissue in the submucosa and often the lamina propria - a lot of lymphatic nodules
The lymphoid tissue tends to decline with age
what is components of rectoanal junction?
distinct junction between mucosa of rectum and non-keratinized stratified squamous epithelium of anal canal
the long anal canal is then continuous with keratinized stratified epithelium of surrounding skin
what is protective mucosa?
non-keratinized stratified squamous epithelium
(oral cavity, pharynx, oesophagus, anal canal)
what is secretory mucosa?
simple columnar epithelium with extensive tubular glands
(stomach)
what is absorptive mucosa?
simple columnar epithelium with cilli + tubular glands
(small intestine)
what is protective + absorptive mucosa?
simple columnar epithelium with tubular glands
(large intestine)
what is the nervous system of digestive tract?
enteric nervous system = receives input from autonomic nervous system but is capable of coordinating gut motility locally
where are 2 plexus of enteric nervous system?
one in submucosa (submucosal) and one in between muscle layers of muscularis externa (myenteric)
what does submucosal plexus of nerves of enteric nervous system control?
controls the muscle of muscularis mucosae and also helps regulate secretion in epithelium
what does myenteric plexus of enteric nervous system control?
gut motility
what is considered largest gland in body?
liver
what is omentum?
peritoneum for connecting stomach to other organs?
what is the liver composed of?
collagenous connective tissue capsule, which is in turn covered by a layer of mesothelial cells (simple squamous epithelium) derived from peritoneum
what is structure of liver?
several segments called lobules (hexagonal shape) - each lobule has hepatic vein called centrolobular vein at centre
- at each edge of lobule, their are portal triads
what are components of portal triad?
hepatic portal vein, hepatic artery + bile duct
what are the names of main liver cells?
hepatocytes - they’re not isolated from each other, they have lamina that radiate from central toward periphery
what are sinusoids in liver?
= thin walled blood vessels lined by epithelium, they have perisinusoidal space
blood channels formed by hepatocytes making sheets of cells
what is the other name of perisinusoidal space and is there anything inside?
called space of Disse and microvilli of the hepatocytes project into the space (also some type I collagen)
- also hepatic stellate cells are scattered
what does the endothelium of sinusoids being fenestrated mean?
means the liquid component of the blood generally has free access to the hepatocytes, but the blood cells do not
what are reticular fibres?
type III collagen that supports the parenchyma of the liver (along with some type I collagen found in space of disse)
what are hepatic stellate cells/ito cells?
modified fibroblasts that make connective tissue and store vitamin A within fat droplets in their cytoplasm
= they’re found in space of disse
what can happen to hepatic stellate cells in some pathological conditions like cirrhosis?
they transform into myofibroblasts and produce scar tissue in liver
what are kupffer cells?
resident macrophages that are scattered within sinusoids = they remove particulate matter from blood and help remove worn out RBCs
where is bile production in liver?
All hepatocytes produce bile. Bile flows via bile canaliculi toward the bile ducts in the portal tracts and thence to the hepatic ducts
what forms bile canaliculi?
tight junctions in cell membranes of adjacent hepatocytes
what is the gal bladder?
muscular sac that stores bile and modifies the bile stored in it
what is components of gal bladder?
- lined by simple columnar epithelium backed by a lamina propria of loose connective tissue rich in blood vessels and lymphatic vessels, a coat of smooth muscle and an outer collagenous layer of adventitia
- Has a folded mucosa when empty – this flattens when distended
what is cholecystitis?
inflammation of the gall bladder
what is cell components of pancreas?
thin connective tissue capsule that is continuous with connect tissue septa that divide gland into lobules
exocrine part - looks like parotid glands as numerous serous acini and ducts. The cells are very basophilic because they contain large amounts of RER
endocrine part - consists of small, scattered islands of tissue called islets of Langerhans (make up 1%-2%)
what is function of islets of langerhans on pancreas?
produce a number of hormones including insulin and glucagon
where are intercalated ducts in pancreas?
they are smallest ducts in pancreas in acinar glands that extend into acinus = called centroacinar cells
are acinar gland cells only in pancreas?
no - they are common and found in other places
what parts of cells of pancreas or basophilic and what parts are eosinophilic?
basal part = basophilic (as extensive RER)
apical part = eosinophilic (due to zymogen granules)
what are centroacinar cells?
specialized cells found at the center of the acini, where they connect with the intercalated ducts = play a role in transporting the digestive enzymes produced by the acinar cells into the duct system
what is function of main pancreatic duct and where does it drain?
= carries digestive enzymes produced by the acinar cells to the duodenum, where they aid in digestion.
The main pancreatic duct typically joins the common bile duct (which carries bile from the liver and gallbladder) and together they open into the duodenum.
what is the point where main pancreatic duct joins the common bile duct?
= called the hepatopancreatic ampulla, also known as the ampulla of Vater.
