Histology Flashcards
how is the oral cavity, oropharynx and laryngopharynx covered?
- is the covering generally keratinised?
by stratified squamous epithelium
- generally NOTT keratinised
how is the nasal cavity and nasopharynx covered?
by respiratory epithelium
what is the anterior 2/3rd of the tongue covered by?
stratified squamous epithelium
describe where it is thick and thin on the anterior 2/3rd of tongue?
thin on ventral surface
thick & with papillae on dorsal surface
what is the posterior 1/3rd covered by?
smooth stratified squamous epithelium
describe if the posterior 1/3rd of the tongue covering with papillae.
except for circumvallate papillae, lacks papillae but does have substantial lymphoid aggregates in sub-mucosa
what does the pharynx include?
= a ring of lymphoid tissue composed of palatine tonsils, lingual tonsils, tubal tonsils and pharyngeal tonsils (adenoids)
from oesophagus to anal canal, what is the digestive tract composed of? (4 major layers) starting from lumen and going out
and what do these layers contain?
- mucosa
= epithelium
= lamina propria
= musculaire mucosa - suubmucosa
= loose connective tissue - musculares externa
= 2 thick layers smooth muscle; an inner circular and outer longitudinal layer - serosa or adventista
= outer layer of connective tissue that either suspends the digestive tract or attaches it to other organs
what indicates an oesophagus on a microscope ?
= submucosa glands in middle
= and band of our mucosa later of stratified squamous epithelium
what is gastro-oesophageal junction?
= abrupt transition from stratified squamous epithelium of oesophagus to simple columnar epithelium of cardia of stomach
what is the surface view of the stomach?
= one relatively fast surface, but with holes in it = gastric pits
what are gastric pits?
holes that can be seen from a surface view of the stomach
what are at the bottom of gastric pits?
1-7 gastric glands
what are gastric pis lined by?
surface mucous cells.
Yes or No.
Are cells of the gastric gland evenly distributed?
No - they are not evenly distributed
what does the isthmus of the stomach contain?
= mostly parietal cells and stem cells.
what does the neck of the stomach mostly contain?
= neck mucous cells and partial cells
what does the fundus (base) of the stomach contain?
= mostly chief cells with a few parietal cells and entero-ednocrinecells (called neuroendocrine cells)
what are chief cells in gastric glands?
digestive enzyme secreting cells.
what are parietal cells in gastric glands?
hydrochloric acid producing cells.
what are the 3 different regions of mucosa in the stomach and describe each?
1) cardia
= deep gastric pits that branch into loosely packed, tortuous glands.
2) body
= shallow gastric pits with long straight gastric glands
3) pylorus
= deep gastric pits with branched coiled gastric glands at a higher density than in cardia
why is the muscularis external of stomach unusual?
= in areas it contains an additional layer
describe the additional layer of muscularis externna of stomach and what does this layer aid?
= layer is oblique to usually circular and longitudinal muscle layer and its located internal to the circular layer.
+ this layer aids churning action of stomach
what is the gastro-duodenal junction?
an abrupt transition from stomach mucosa to duodenal mucosa.
- inner, circular layer of smooth muscle is markedly thickened to form the pyloric sphincter (PS)
what would the surface view of the small intestine show?
= finger like projections, the VILLI, and between the bases of adjacent villi are pits frilling downwards, the crypts of Leiberkuhn
what are the crypts of Leiberkuhn?
= the pits in between the bases of adjacent vili hat drill downwards that can be seen from the surface view of the small intestine
describe the length of the small intestine?
what are the 3 distinct segments of the small intestine?
- coiled tube about 5m long
1) duodenum - 25cm long
2) jejunum - 2m long
3) ileum - 2.75m long
what does the duodenum contain?
burner’s glands in submucosa
what segment of the small intestine contains the tallest villi?
jejunum.
- located on permanent circular folds of mucuosa and submucosa, the place circulars
- lymphoid follicles infrequent
what is the ileum characterised by?
shorter villi and aggregation of lymphoid follicles Calle Peyer’s patches found in sub-mucosa and often extending into lamina propria
what are the 5 cells of the small intestine epithelium?
1) enterocytes
2) goblet cells
3) paneth cells
4) enteeroexndocrine cells
5) stem cells
what do enterocytes contain?
must numberous cells
- they are tall columnar cells with a birch border
= principle absorptive cells
what do goblet cells produce and why do they produce this?
mucin to protect epithelium and lubricate passage of of material
where are paneth cells found?
and what is their function?
at base of crypts of Lieberkuhun
= defensive function and a role in regulating bacterial flora (secret lysozyme and definitions)
what do enter-endocrine cells produce?
hormones contributing to control of secretions and motility (e.g. CCK, gastrin, vasoactive intestinal peptide)
where are stem cells found and why do they divide?
= found at base of crypts of Lieberkuhun
- divide to replenish epithelium
what does then duodenum of small intestine receive?
= receives acidic, partly digested semi-fluid material called chyme from stomach
why does the duodenum of small intestine differ from other regions of GI below the oesophagus?
as it has glands located within sub-mucosa
what are the glands located in the duodenum called?
and when these glands re stimulate what happens?
Brunner’s glands.
- when stimulated by presence of chyme they produce a thin, alkaline mucous to neutralise the chyme
What is there a substantial amount of in the ileum of small intestine?
lynhmhpod tissue associated with gut (hence it is ‘gut associated lymphoid tissue’ = GALT)
- much of this consist of scattered lymphocytes, but areas of relatively large aggregations of lymphoid tissue exist, particular in ileum = Peyers Patches
what are Peyers patches?
areas of relatively large aggregations of lymphoid tissue in ileum
what could you forgive the large intestine for and why?
the stomach as it also has holes called colonic glands
what are the 2 principle types of cells in the large intestine epithelium?
1) absorptive cells
= for removal of salts and thus water
2) goblet cells
= for secretion of mucus to lubricate colon
how are these 2 Principe cells in large intestine epithelium arranged?
= in straight, tubular glands, referred to as crypts, that extend down to muscular mucosae
Yes or No.
In the large intestine, is the outer longitudinal smooth muscle distinct?
- describe this layer.
Yes.
- it is not continuous, but is found in 3 muscular strips called teniae coli.
what is the appendix?
= a blind ending hollow extension of cecum.
describe the structure of the appendix?
= similar to rest of colon, but crypts are far less abundant and there is typically a circular arrangement of lymphoid tissue in sub-mucosa and often lamina propria
- lymphoid tissue tends to decline with age
what are rectoanal junction?
= distinct junction between mucosa of rectum and non-keratinised stratified squamous epithelium of anal canal.
- the long anal canal is then continuous with keratinised stratified squamous epithelium of surrounding skin
what nervous system controls the digestive tract?
= enteric nervous system.
(same number of neurones as spinal cord).
receives inputs from ASN, but is capable of co-ordinating gut motility locally.
describe the plexus network of the ENS?
= Inter-connected network of fibres that has 2 plexus;
1) submucosa
2) myenteric
- inter-connected network of fibres that is the muscle layer of muscular external controlling gut motility
where do most of the neurones in ENS live?
= live in groups, usually outside the brain and spinal cord called GANGLION
what are ganglion?
group of nerve cells living outside brain and spinal cord
what is the 2nd network of neurones found in sub-mucosa called?
= sub-mucosal plexus
controls muscle of the muscularis mucosae and helps regulate secretion in epithelium
LIVER, PANCREAS & GALL BLADDER
LIVER, PANCREAS & GALL BLADDER
what do the liver and pancreas develop as?
an outgrowth of the gut
what is the parenchyma of liver and pancreas composed of?
= glandular epithelial cells
what are the functions of the liver?
1) oxidise triglycerides to produce energy
2) synthesise plasma lipoproteins
3) synthesise cholesterol
4) convert carbohydrates & proteins into fatty acids & triglycerides
5) regulate blood glucose concentration by glycogenesis, glycogenolysis and gluconeogenesis.
6) Synthesize plasma proteins (albumin, clotting factors, etc.)
7) Detoxification of metabolic waste products
8) Detoxification of toxins and drugs
9) Storage of glycogen, some vitamins and iron
10) Synthesis and secretion of bile (exocrine gland)
what is the liver covered by?
a collagenous connective tissue capsule, which is covered by a layer of mesothelial cells (simple squamous epithelium) derived from peritoneum
what is the liver made up of?
segments called lobules.
describe the shape and venous supply of each lobule in the segments of liver?
= hexagonal and has a branch of the hepatic vein called centrolobular vein (or central vein) at its centre and portal triads at each corner
what does the human liver NOT have that the pig liver does?
= doesn’t have clear connective tissue septa between lobules
what are 3 branches of vessels of the portal triad which enter at the porta hepatis?
1) hepatic portal vein
2) hepatic artery
3) bile ducts (a branch of the conduit which leaves liver at portal hepatis)
‘portal triad’
in simplified form, what 3 things does the portal tract include?
1) hepatic portal vein
2) hepatic artery
3) bile duct
what is the bile ductile lined by?
= Simple cuboidal cells called cholangiocytes
what do the portal tracts also typically include?
= lymphatic vessels
what are the main cells of the liver called?
hepatocytes
what are hepatocytes?
= polyhedral epithelial cells that appear in sections to be cords of liver cells but in fact are plates or sheets of cells with spaces in between for blood to flow through
what are the blood channels in hepatocytes called?
= sinusoids
how is the liver organised?
and what are the 2 main types of lobules?
= the lobule
1) classic hepatic lobule
2) hepatic acinus
how are sinusoids lined?
= by epithelial cells and there is a narrow space between these lining cells and hepatocytes.
what is the space between lining cells in sinusoids and hepatocytes called?
and what projects into the space?
= Space of Disse (perisinusoidal space)
- microvilli of hepatocytes project into the space
what is the endothelial lining of sinusoids like?
= fenestrated so liquid component of blood generally has free access to hepatocytes, but blood cells don’t
what are the portal tracts of liver accompanied by?
= collagenous connective tissue
what is the parenchyma of the liver supported by?
= reticular fibres (type III collagen), along with some Type I collagen that is found in space of Disse
where are hepatic stellate cells found?
= found scattered in space of Disse.
what are hepatic satellite cells?
what do hepatic satellite cells do in pathological conditions (e.g. cirrhosis)?
- modified fibroblasts and make connective tissue.
- also stored Vit A within fat droplets in their cytoplasm.
- they transform into myofibroblasts & produce scar tissue in liver
what are macrophages of sinusoids called and what do they do?
= Kupffer cells.
- they remove particular matter from blood and help move worn out blood cells.
what is bile?
= an alkaline solution containing water, ions, phospholipids, bilirubin and bile slats.
what is bilirubin?
= a pigment which result from breakdown of heamoglobin in spleen, and when excreted in bile, is principle cause of brown colour of faeces.
why are bile slats necessary?
= for emulsification of fats in digestive tract.
- Primary bile that is produced by hepatocytes is modified in several ways(e.g. addition of bicarbonate ions and H20) by cholangiocytes, the cells that line biliary tree.
Yes or No.
do all hepatocytes produce bile?
YES.
all hepatocytes produce bile.
where does bile flow via?
via bile canaliculi towards bile ducts in portal tracts and then to hepatic ducts.
describe bile canaliculi?
= small channels formed by tight junctions in cell membranes of adjacent hepatocytes.
what is the gall bladder and what is it lined by?
a muscle sac
- lined by simple columnar epithelium backed up by lamina propria of loose connective tissue rich in blood vessels and lymphatic vessels, a coat of smooth muscle and a outer collagenous layer of adventitia.
what does the gall bladder do?
- sotres bile
- has a folded mucosa when empty = this flattens when distended
- modifies the bile stored within it
About 20-30% of volume of bile arriving from liver is removed by gall bladder.
True or False.
FLASE
about 80-90%
how is the volume of bile arriving from liver removed by gall bladder?
- actively pumping Na and Cl ions from bile into spaces between adjacent epithelial cells
- water then flows due to increase in osmotic pressure in these spaces, which becomes distended with fluid when gall bladder is actively concentrating bile.
- water is carried away, largely by lymphatic vessels of lamina propria
what is the gall bladder stimulated to do?
to contract and deliver bile to duodenum, both under nervous control and via release of hormone cholecystokinin by endocrine cells of duodenum when fatty food enters i.
what is the gall bladder lined by?
= tall columnar epithelial cells with a brush border
what is cholecystitis affecting gall bladder?
inflammation of gall bladder
- gallstones have obstructed cystic duct leading to expansion of gall bladder, thickening muscle layers and inflammation
why is the pancreas unusual?
as it has an exocrine and endocrine gland
what does the exocrine gland produce?
about a litre of digestive juices containing proteases to break down proteins and lipase to break down lipids, nucleases to breakdown DNA/RNA and amylase to break down start each day
= these enter the duodenum via pancreatic duct
what does the endocrine gland consist of?
of small scattered islands of tissue called ISLETS OF LANGERHANS, producing number of hormones including insulin and glycogen
what does the exocrine portion of pancreas resemble on a microscope?
= parotid gland, with numerous serous acini and ducts
- the cells re very basophilic as they contain large amounts of RER
in exocrine pancreas what are the enzymes produced as?
= inactive proenzymes.
- once pancreatic secretion arrives in duodenum an enteropeptidase converts inactive proteolytic enzyme trypsinogen into active form trypsin
- this begins a cascade resulting in activation of other enzymes
what does the pancreas have?
a thin connective tissue capsule that is continuous with connective tissue septa that divides the gland into lobules
unlike in other acinus glands, e.g. parotid, where do the smallest ducts in pancreas called intercalated ducts start?
they DONT start where the acinus ends, but rather extend into the acinus
what are centroacinar cell?
the duct cells that are within the acini
- their nuclei and cytoplasm do not stain as intensely as secretary cells.
what do the main pancreatic ducts join?
join the common bile ducts and opens into the duodenum on a papillae: the hepatopancreatic ampulla (of Vater)
