Download Gastrointestinal System I Part I (Tongue, Esophagus

Oliver Stroeh, [email protected]
Gastrointestinal System I Ð Part I
(Tongue, Esophagus, Stomach)
Tongue
O bundles of skeletal muscle arranged in three planes
o arranged at right angles to one another
o allow for flexibility & precise movement (needed for speech, digestion, swallowing)
o arrangement unique to tongue
O 3 types of papillae cover anterior portion of tongue
o filiform papillae
§ most numerous
§ slender projections w/ posteriorly slanted keratinised tip
§ gives tongue its raspy texture – allows tongue to carry solids & liquids to back of
mouth
§ only papillae with NO TASTE BUDS
o fungiform papillae
§ mushroom-shaped
§ more numerous near tongue tip
§ taste buds present within stratified squamous epithelium of papillae
o circumvallate papillae
§ large, dome-shaped structures separating anterior 2/3rds of tongue from posterior
1/3rd – “circumvallate are near the palate”
§ each papilla surrounded by moat-like invagination lined with stratified squamous
epithelium
• this epithelium contains numerous taste buds & openings of ducts of von
Ebner’s glands (lingual salivary glands)
• serous secretions flush away food bits to allow taste buds to “respond to
changing stimuli”
O taste buds
o present on fungiform & circumvallate papillae
o appear as oval, pale-staining bodies that extend through thickness of epithelium
o taste pore – opening onto epithelial surface at apex of taste bud
o contain three main cell types
§ neuroepithelial cells
§ supporting cells
§ basal cells
Basic Structure of GI Tract
O four layers of tissue (from lumen, outwards)
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o
o
o
o
mucosa
§ epithelium & basement membrane
§ lamina propria – contains glands, vessels that receive absorbed substances,
immune system elements
§ muscularis mucosa – smooth muscle (arranged as inner circular and outer
longitudinal layer
submucosa
§ dense, irregularly arranged connective tissue
§ contains some glands, larger blood vessels, lymphatic vessels & nerve plexuses
(e.g. Meissner’s plexus)
muscularis externa
§ two concentric & relatively thick layers of muscle
• inner layer = circularly oriented – mixes contents
• outer layer = longitudinally oriented – move contents along (peristalsis)
§ Auerbach’s myenteric plexus – rests in the thin connective tissue layer that lies
between the two muscle layers
serosa & adventitia
§ serosa = serous membrane consisting of mesothelium & connective tissue; the
most superficial layer of those portions of the digestive tract that are suspended
in peritoneal cavity
§ adventitia = the loose connective tissue that attaches those portions of the
digestive tract that do not possess a serosa to the wall of the abdominal cavity
Esophagus
O usually lined all along with non-keratinized stratified squamous epithelium
O structural notables
o mucosa – muscularis mucosa is unusually thick in proximal esophagus to aid in
swallowing
o submucosa – along with muscularis mucosa, forms longitudinal folds that dilate & flatten
out to accommodate food as it passes down esophagus
o muscularis externa – differs from rest of digestive tract
§ upper third = STRIATED muscle (continuation of muscle of oropharynx)
§ middle third = interwoven striated & smooth muscle
§ distal third = smooth muscle
O junction of esophagus & stomach
o abrupt transition of epithelium from stratified squamous non-keratinized epithelium
(esophagus) to simple columnar (stomach)
§ esophagus transports food → needs barrier (stratified epithelium)
§ stomach mixes & partially digests food w/ gastric secretions → do not need
barrier, need secretions (simple columnar epithelium)
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Stomach
O simple columnar epithelium
O structural notables
o inner surface of empty stomach has longitudinal folds (rugae)
§ they do not alter total surface area, but accommodate expansion/filling of
stomach
o presence of gastric pits in mucosal surface, into which gastric glands empty
o gastric submucosa – contains submucosal (Meissner’s) plexus
o gastric muscularis externa
§ traditionally (hard to see as such) described as consisting of…
• outer longitudinal layer
• middle circular layer
• inner oblique layer
§ myenteric (Auerbach’s) plexus present between muscle layers
O gastric secretions
o three main types of secretory cells in stomach
§ mucous-secreting cells
• surface mucous cells – the epithelial cells that line the surface & the
gastric pits
o have basal nuclei
o mucinogen granules – on lumenal side & appear washed out in
H&E stains; can be stained with PAS
• mucous neck cells – the epithelial cells that line the neck region (the
deeper continuation of the gastric pit) of the gastric glands
§ shorter than surface mucous cells
§ have considerably less mucinogen (vs. surface m.c.)
§ have more spherical nuclei (vs. surface m.c.)
§ parietal cells
• large pyramidal or spherical cells wedged between other cells of gastric
glands
• cytoplasm stains intensely with eosin
• central, spherical nucleus
• acidophilic cytoplasm due to numerous mitochondria
• secrete…
o HCl – promotes acid hydrolysis of substrates & converts
pepsinogen to pepsin
o Intrinsic Factor (IF) – necessary for vitamin B12 absorption in
more distal portions of GI tract
§ chief (zymogen) cells
• secrete enzymes, especially pepsinogen (inactive precursor of pepsin)
• basal pole – lots of rER – basophilic
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• EM shows lots of membrane-bound granules
O junction of stomach & duodenum
o muscularis externa thickens to form pyloric sphincter
o comparison between stomach & duodenum:
Stomach
Duodenum
appears as flat surface w/ pits
appears as surface w/ large folds
(plicae circulares)
mostly mucus-secreting cells
mostly absorptive cells w/ interspersed
goblet cells (secrete mucous, too)
Brunner’s glands in submucosa
Things Stressed on Last Year’s Exam
O the transitional zones between different parts of GI tract (esophagus, stomach, duodenum, etc.)
O the histology & function of unique cells & glands
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GI System: Small Intestine and Large Intestine
SMALL INTESTINE (ROSS, 453)
The lining of the small intestine is specialized to maximize the absorptive surface area:
1) Plicae Circularis: “circular folds” with a core of submucosa
2) Villi: finger-like mucosal projections with a core of lamina propria
3) Microvilli: “brush border” surface on enterocytes with a core of actin filaments
From the lumen outward, there are 4 concentric coats that characterize much of the digestive system:
I.
Mucosa
II.
Submucosa (contains dense CT, blood vessels, Meissner’s Plexus, and duodenal
Brunner’s glands)
III.
Muscularis Externa (2 smooth muscle layers: inner circular and outer longitudinal,
with Auerbach’s Plexus in between the 2 layers)
IV.
Adventitia/Serosa (loose CT layer)
The Mucosa has barrier, secretory, and absorptive functions. Its 3 components are:
A. Epithelium
B. Lamina Propria
C. Muscularis Mucosae
A. The mature cellular components of the Epithelium include:
1. Enterocytes absorptive cells that are tall and columnar with basal nucleii
- have thousands of microvilli on apical surface that stain pink with PAS
- digestive enzymes located in the glycocalyx of the microvilli complete the
breakdown of most sugars and proteins
- have junctional complexes and terminal web (#102)
2. Goblet Cells PAS positive mucus producing cells interspersed among enterocytes
- appear “empty” because mucus is washed out
3. Paneth Cells - located at bottoms of intestinal glands (Crypts of Lieberkuhn) between villi (#37)
- function to regulate bacterial flora of the gut by secreting lysozymes
- have basally basophilic cytoplasm and apically acidophilic granules
4. Enteroendocrine cells - secrete hormones: GIP, CCK, Secretin
- appear “spindle-like” with silver stain (#102)
- also located in the stomach
5. M Cells - more squamous epithelial cell type that overlie Peyer’s Patches
- possess microfolds rather than microvilli on surface
- function to transport antigens from lumen to the underlying lymphoid tissue, enabling
the mounting of an immune response
B. Lamina Propria - comprised of loose, cellular connective tissue
contains lymph nodules and immune cells (lymphocytes, macrophages, etc.)
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forms the core of villi that project into the intestinal lumen
also contains lacteals (endothelial-lined lymphatic channels) within the villi that
uptake lipid droplets
C. Muscularis Mucosae - boundary between mucosa and submucosa
- two thin layers of smooth muscle (inner circular for segmentation and outer
longitudinal for peristalsis)
Large Intestine (Ross, 464)
Functions: reabsorption and elimination.
The same four concentric layers present in the small intestine are also present in the large intestine
(mucosa, submucosa, muscularis externa, adventitia/serosa).
Mucosa contains straight, tubular intestinal glands consisting of simple columnar cpithelium.
Distinguishing features include:
a) absence of plicae circularis and villi
b) more numerous goblet cells
Rectum and Anal Canal (#48)
- junction shows abrupt transition from simple columnar to stratified squamous
epithelium
- intestinal glands also end abruptly at junction
- muscularis mucosae disappears at about the level of rectoanal margin
- inner circular layer of muscularis externa thickens to form internal anal sphincter
- submucosa of anal canal has plexus of hemorrhoidal vessels that, when dilated, bulge
inward yielding internal hemorrhoids
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Erika Yoo
ejy2001
LIVER
Lobules
There are three different schemes set up to divide the liver into functional units:
1. Classic Lobule – a hexagon with a central vein in the middle and portal triad (hepatic artery,
portal vein, bile duct) at boundary points.
2. Portal Lobule – connects 3 adjacent central veins into a triangle; it follows bile drainage
3. Liver acinus – diamond shaped and bordered by 2 central veins and portal triads.
**Check out Ross fig. 17.3 on p.500 for a drawing of these.**
BLOOD FLOW
The liver receives a dual blood supply:
• 75% from the portal vein – it is the largest component of portal tract, with a thin wall and
often irregular shape
• 25% from the hepatic artery – which appears small in the portal tract with a relatively thick
wall
Those vessels eventually divide into interlobular vessels, which are the vessels of the portal
triad. From there, the interlobular vessels send blood into the liver sinusoids, which bathe the
hepatocytes. Blood from the sinusoids drains toward the central veins; the central veins merge to
form the hepatic vein, which dumps into the inferior vena cava:
Portal vein + hepatic artery à interlobular vessels à liver sinusoids à central vein à hepatic
vein à IVC
Bile ducts
• Bile ducts can be identified by the simple cuboidal or columnar epithelium that forms the
lumen.
• The bile produced by hepatocytes is secreted into canaliculi. The canaliculi form a ring
about the hepatocytes and form a network that drain into the canals of Hering.
• The canals of Hering look like little clear dots between the lateral membranes of adjacent
hepatocytes. They drain into the bile ducts of the portal canals.
• The flow of bile is in the opposite direction of that of blood
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OTHER COMPONENTS
Kupffer cells – macrophages that can be seen in the sinusoids. They clean out debris like senile
RBC’s and often look like they are occluding the sinusoid.
• If you see a big cell with lots of cytoplasm in the sinusoid, think Kupffer cell!
• If you see a cell with a nucleus poking into the sinusoid and the cytoplasm stretched
out on the lumen, it’s probably an endothelial cell of the sinusoid…
Space of Disse – The endothelium of the sinusoid is fenestrated, allowing the Space of Disse to
emerge, where the exchange of materials between blood and hepatocytes occurs. (See Ross fig
17.7)
Space of Moll – Lymph originates in the perisinusoidal space, flows backward, in the space of
Disse, toward the lymphatic channel in the portal triad. When it reaches the triad, the space of
Disse is continuous with the periportal Space of Moll. This is between the stroma of the portal
canal and the outermost hepatocytes.
Hepatocytes – large cells, often with two nuclei. They have abundant rER, mitochondria, and
large deposits of glycogen that can be seen with PAS.
Pancreas (exocrine):
The exocrine pancreas dumps into the duodenum a whole lot of enzymes necessary for digestion.
Examples are trypsinogen, pepsinogen, amylase, lipase, deoxyribonuclease, etc. The acini start
production of their enzymes in response to cholecystokinin (CCK). All this enzymatic activity
makes the pancreas a serous gland. In fact, it is a purely serous gland that’s tricky to tell apart
from the parotid gland. There are a few things to look for to help you discern the difference:
1) You may be able to see Islets of Langerhans (the endocrine part of the pancreas which
produces insulin and glucagon—you’ll get to it later) that appear as clusters of palestaining cells surrounded by the regular exocrine pancreatic acini. They are most dense
in the tail of the pancreas.
2) You should see centroacinar cells. Centroacinar cells are really just the beginning of the
intercalated duct that have pushed their way inside the acinus. The’re low, cuboidal
epithelial cells, and they usually stain paler than the acinar cells themselves. The
intercalated duct secretes HCO3- and water in response to secretin.
3) You probably won’t be able to see striated ducts, but you can see interlobular or
excretory ducts that are large and prominent. If you do see striated ducts, think parotid
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and not pancreas. The pancreatic juices flow from the interlobular duct into the
pancreatic duct and from there to the ampulla of vater.
nn2005
pab2003
KIDNEY
I.
Introduction
A. divisions
1. each kidney contains 8-18 lubes
2. each lobe includes the outer cortex and inner medulla
3. collecting ducts in the inner medulla come together to form the renal papilla
4. renal papilla “empty” into the calyces
5. calyces come together to form the renal pelvis
6. the renal pelvis is the dilated proximal part of the ureter
B. vasculature
renal artery → interlobar arteries → arcuate arteries → interlobular arteries →
afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries & vasa
recta
II.
Nephron
- functional unit of the kidney
- millions of nephrons exist in each kidney lobe
- each nephron contains the renal corpsucle & renal tubules
III.
Renal Corpuscle
A. structure:
- glomerulus: vascular tuft arising from afferent arteriole
- vascular pole: contains the entrance of the afferent arteriole & the exit of the
efferent arteriole
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podocytes: epithelial cells that invest the glomerulus; form the visceral layer of
Bowman’s capsule
Bowman’s capsule: continuous of with the proximal convoluted tubule
Bowman’s space: the space between the visceral (podocytes) and parietal layers
of Bowman’s space
urinary pole: the area where Bowman’s space becomes the proximal convoluted
tubuele
mesangium: supporting tissue of the renal corpuscle
- mesangial cells: have smooth muscle and phagocytic properties
- mesangial matrix: secretes by the mesangial cells
B. function:
- flitration of plasma
- plasma flowing in the glomerular capillaries is filtered into Bowman’s space
through the filtration barrier
- capillary endothelium: large fenestrations
- glomerular basment membrane: collagen IV; negatively charted proteoglycans
keep the negatively charged proteins in the capillaries and out of the filtrate
- podocytes: visceral layer of Bowman’s capsule has filtration slits between
podocyte processes
IV.
Renal Tubules
A. function:
- reabsoprtion of molecules from the filtrate
- secretion of excretory products from blood into the filtrate
B. proximal convoluted tubule
- most abundant in the cortex
- reabsorbs ~75% of filtrate
- cuboidal epithelium: strongly eosinophilic with very prominent brush border
(strong PAS stain)
- high concentration of mitochondria (stain with iron hematoxylin)
- high concentration of lysosomes (stain with acid phosphatase)
C. loop of Henle
1. thick descending segment
- looks like the proximal convoluted tubule
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2. thin segment
- simple sqaumous epithelium
3. thick ascending segment
- looks like the distal convoluted tubule
- water impermeable = diluting segment because the filtrate becomes
increasingly dilute as it goes through this segment
D. distal convoluted tubule
- cuboidal epithelium
- seen adjacent to proximal tubulues
- NOTE: the distal tubules do NOT have a brush border and thus are differentiated
from the proximal tubules
- fewer intracellular organs (stain less eosinophilic)
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