Dr. Mhawi 1 Digestive System 2 Flashcards
What are the 4 basic layers of the esophagus and GI tract
Mucosa
Submucosa
Muscularis (AKA muscularis externa)
two layers of smooth muscle
Serosa /adventitia
serosa is a mesothelium and underlying loose connective tissue
adventitia is found where the wall of the gut is attached to a structure
Alimentation means giving nourishment; hence the older alternative name of alimentary canal for gastrointestinal tract. This light micrograph depicts a cross section of the ileum. The four layers, namely, mucosa (M), submucosa (SM), muscularis externa (ME), and serosa (S) are visible. Muscularis externa subdivides into two layers, inner circular (IC) and and an outer longitudinal (OL). L, lumen.
What are the 3 components of the mucosa?
Epithelium and its underlying basal lamina
Lamina propria
Muscularis mucosae*
Muscularis mucosae is a layer of the mucosa which is unique for the gastrointestinal tract.
What are 3 functions of the mucosa epithelium?
Secretion:
Digestive enzymes
found in the apical (luminal) plasma membrane
Hormones
Mucous
Antibodies
-received from plasma cells found in the underlying lamina propria
Absorption of products of digestion
-absorption occurs in small and large intestine
Transportation of absorbed material to vascular system located in the lamina propria
What are the characteristics of the lamina propria in the mucosa?
Explain this image
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Since lymphatic vessels are the major route used by cancer cells to metastasize,
absence of these vessels in the mucosa of the large intestine is responsible for
the delay of the colon cancer metastasis ( = precancer cell; = cancer cell)
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What are the characteristics of the muscular mucosae and explain this image.
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Composed of two ill-defined layers of smooth muscles
forms boundary between mucosa and submucosa
Can produce movement of mucosa independent of movement of entire gut wall
Inset: cross section of the esophagus at low magnification. At this low magnification, muscularis mucosae is barely visible under the lining epithelium. The rectangular area is examined at higher magnification to reveal the mucosa which consists of epithelium (EP). Lamina propria (LP), and muscularis mucosae (MM). Submucosa (SM) appears under the mucosa.
What are the characteristics of the submucosa? Explain this image
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Consists of
moderately dense irregular connective tissue
larger blood vessels
Lymphatic vessels
Cross section of the colon. Submucosa contains blood (BV) and lymphatic (LV) vessels. M, mucosa; SM, submucosa; ME, muscularis externa.
what are the contents of the submucosa and explain the image.
Submucosa also contains nerve plexuses
Submucosal (Meissner’s) plexus
contains cell bodies of postganglionic (postsynaptic neurons of the parasympathetic division of the ANS
Controls intestinal gland secretion and movement of water and ions across the intestinal epithelium
Dashed line surrounds Meissner’s plexus in the submucosa of the alimentary canal. The plexus contains a chain of interconnected neurons. These neurons are described as postganglionic (or postsynaptic) neurons of the parasympathetic division of the autonomic nervous system.
Submucosa of the esophagus and initial part of duodenum contains ______
glands
Presence of these glands aids in identification of particular regions of gut
Submucosae (surrounded by the lines) of the esophagus (left) and duodenum (right) are characterized by the presence of the submucosal esophageal and duodenal (Brunner’s) glands, respectively.
What are the characteristics of the muscularis?
Consists of two concentric thick layers of smooth muscle.
I_nner_ layer forms tight spiral seen as a CIRCULAR LAYER
outer loose spiral described as a LONGITUDINAL layer
Undergoes waves of peristaltic contraction
Propel the gut contents toward the anus
Cross section of the duodenum. Muscularis externa (ME) is subdivided into inner circular (IC) and outer longitudinal (OL) layers. G, submucosal (Brunner’s) glands; M, mucosa; SM, submucosa.
What is located between the two muscle layers of the muscualris?
myenteric (Auerbach’s) plexus
contains cell bodies of postganglionic (postsynaptic) neurons of the parasympathetic division of the ANS
Controls GIT peristaltic motility
Cross section of the ileum. Between the inner circular (IC) and outer longitudinal (OL) layers of the muscularis externa (ME), myenteric (Auerbach’s) plexus is found (red rectangle). The plexus will be visible at higher magnification in the next slide.
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Explain this image
Myenteric (Auerbach’s) plexus located between the inner circular (IC) and outer longitudinal (OL) of the muscularis externa.
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Explain this image
Photomicrograph of an Auerbach’s plexus at higher magnification. Blue arrows indicate a group of parasympathetic postganglionic neurons (with large nuclei) surrounded by astrocyte-like enteric glial cells (black arrows) These neurons constitute the myenteric plexus located between 2 smooth muscle layers. The cell body of the parasympathetic preganglionic neurons are located in the dorsal motor nucleus of the vagus as well as in the sacral segments of the spinal cord. Note the red stained collagen fibers. Picrosirius-hematoxylin.
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What are the characteristics of the serosa?
Thin cover of simple squamous epithelium (mesothelium) and the underlying loose connective tissue, blood and lymphatic vesselsn
Serosa is continuous with the mesenteries
Thin flap of loose connective tissue covered by mesothelium on both sides
Support the intestine
Mesenteries are continuous with the peritoneum
Explain this image
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What are the characteristics of adventitia?
The part of the alimentary canal is covered by adventitia if it has no free surface
e.g., esophagus of the neck region
Adventitia is a layer of connective tissue that merges with the surrounding structures
Adventitia lacks mesothelium
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What are the layers in the esophagus?
Mucosa:
Epithelium non-keratinized stratified squamous
Lamina propria: loose connective tissue
Muscularis mucosae: composed of two ill-defined layers of smooth muscle
Mucosa forms longitudinal folds
Submucosa:
Contains esophageal glands proper
Cross section of the esophageal mucosa. The three layers of the mucosa are indicated. The submucosa appears at the lower third of the image . In this part of the esophageal wall, esophageal gland proper (G) is visible.
Explain the muscularis of the esophagus
upper 1/3 is striated muscle
Middle third striated and smooth muscle interwoven
Lower third Smooth muscle
Continuous with the rest of the gut
Photomicrograph of a cross section of the esophagus. Note the folding of the mucosa which creates irregular luminal profile.
Esophagus is covered by ______ in the neck and chest and by _____ in abdominal cavity
adventitia
serosa
What are the 2 types of esophageal glands and where are they found?
ESOPHAGEAL GLANDS PROPER
in submucosa, scattered throughout the length of the esophagus
ESOPHAGEAL CARDIAC GLANDS
in lamina propria of the mucosa, found in the cardiac region
What are the characteristics of esophageal glands proper and explain the image.
Occur in submucosa
Scattered throughout the length of esophagus; most in upper one half
Produce acidic mucus
Explain the image.
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Section of the esophageal gland proper. The secretory portion of the gland is located in the submucosa. The duct of the gland is penetrating the lamina propria and the stratified epithelium to escort the secretion into the esophageal lumen.
Explain the characteristics of esophageal cardiac glands and the image.
occur in l_amina propria_ of mucosa
Similar to cardiac glands of stomach
Present in terminal part of esophagus
Esoph. Cardiac glands produce neutral mucus
protect against regurgitated material
Esophageal cardiac glands (black arrows) are located in the lamina propria of the esophagus. Note the cardiac glands (green arrows) in the cardiac region of the stomach. Thick blue arrow points to the esophagogastric junction.
_____ is called the Z line in gross anatomy and is the most common site for esophageal carcinoma
Esophagogastric junction
Explain the characteristics of the stomach
Same organization as remaining gut
Mucosa, submucosa, muscularis, serosa
Inner surface has longitudinal folds called RUGAE
Poorly developed in upper stomach
more elaborate in lower part
Disappear when stomach is distended
Accommodate expansion
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Explain. this image.
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Cross section of one of the gastric folds (ruga). Note the four layers of the stomach wall namely, mucosa (M), submucosa (SM), muscularis externa, and serosa (Se). The mucosa and submucosa (asterisks) constitute the ruga. Thick arrows point to the three distinctive region of the mucosa. The most superficial region contains the gastric pits; the middle region contains the necks of the glands, and the deepest part of the mucosa contains the bottom of the gastric glands (stained heavily with hematoxylin).
What are the three histologically divided regions of the stomach?
cardia, fundus, pylorus
What are the characteristics of each part of the stomach?
CARDIA (cardiac region)
part near esophagus
contains c_ardiac glands_
FUNDUS (fundic region)
called the body
largest part
between cardia and pylorus
Contains f_undic glands AKA gastric glands_
PYLORUS (pyloric region)
part proximal to pyloric sphincter
contains pyloric glands
What are the 5 types of gastric secretions?
Explain the charcateristcis if gastric mucosa and the image.
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Epithelium is simple columnar
Called SURFACE MUCOUS CELLS
forms a continuous layer that lines the whole gastric lumen
Cells have a large apical deposit (cup) of mucin granules (see the TEM inset)
Mucus forms a thick gel-like coat on surface
Epithelium dips to form Gastric pits (black arrow)
Light micrograph of the stomach mucosa. The lumen of the stomach is lined by simple columnar epithelium which is comprised of surface mucous cells that secrete thick mucus. The carbohydrate-rich mucus is stained well with PAS stain. Lower inset: Electron micrograph of the simple columnar epithelium lining the stomach. Electron-dense mucin granules (arrow) are deposited above the nucleus of the cell.
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Explain the Image
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GASTRIC PITS or FOVEOLAE
Easily seen in SEM
Gastric pits lead into GASTRIC GLANDS
Long simple branch tubular
a) Top view SEM of the stomach lining reveals gastric pits (P) surrounded by polygonal apical ends of surface mucous cells (smiley face). (b) Side view SEM of the gastric pits and glands. The large bulging cells on these glands (indicated by the asterisk) are the parietal cells. Note also that this particular gland branches at its base (white arrows). The opening of one of the pits is indicated by the black arrow.
Explain this image of gastric glands
Present throughout gastric mucosa
Extend from bottom of the GASTRIC PITS to MUSCULARIS MUCOSAE
Produce gastric juice
What are the 5 cell types of the gastirc gland?
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MUCOUS NECK CELLS
PARIETAL CELLS (AKA oxyntic cells)
CHIEF CELLS
ENTEROENDOCRINE CELLS
Found in the gastric gland epithelium and scattered throughout the GIT
UNDIFFERENTIATED (stem) CELLS
located in upper neck region
give rise to mature cells listed above
Explain the image.
Fundic stomach. CC, chief cells; PC, parietal cells; L, lumen of the gland.
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Explain the image.
Fundic stomach. PAS stain for mucous. Note the large and round parietal cells (PC) and the dense granular chief cells (CC) at bases of glands. MM, muscularis mucosae.
Explain the image
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Parietal (oxyntic) cells are large round to triangular cells with eosinophilic cytoplasm and centrally located nucleus (thin arrows). Chief cells are located towards the base of the gland. They are recognized by their basically located nuclei and basophilic granular cytoplasm (thick arrows). MM, muscularis mucosae.
Explain the characteristics of mucous neck cells and the image.
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Located in neck region of the gastric glands
Shorter than surface mucous cell
Nucleus tends to be spherical rather than elongate
as in surface mucous cells
Secretes soluble mucus
compared to viscous surface mucus
Fundic stomach mucosa. PAS stain. Both surface mucous cells (top) and mucous neck cells, which are interspersed among the parietal cells in the neck region of the gland, are stained magenta. MM, muscularis mucosae.
Explain the characteristic of parietal chief cells.
AKA OXYNTIC CELLS
Secrete HCl and intrinsic factor
Most numerous in upper and middle region of the gland
Large cells
Appear round to triangular
Under the influence of gastrin hormone secreted by enteroendocrine cells (called G-cells)
Explain this image
Light micrograph of the fundus revealing many cell types of the gastric glands. The parietal cells (PC) appear, large in size and eosinophilic (bc lots of mitochondria) and their shape is round to triangular. Their nuclei are prominent, round, and centrally located. Chief cells (CC) are noticeable at the base of the glands. Their cytoplasm are filled with pepsinogen granules. Green arrows point to the mucous neck cells. Note that the cytoplasm of these cells looks empty due to the washing of the mucus away from the cytoplasm during the preparation of the tissue for histologic examination. MM, muscularis mucosae.
Explain this image
TEM of an inactive parietal cell. Note that the cytoplasm revealed many mitochondria (M) scattered among areas that are filled with membranes. These membranes are in the form of tubules and vesicles (tubulovesicular system; TV). The membranes of the tubulovesicular system contribute to the microvilli projecting into the lumen of the intracellular canalicular system formed when the cell becomes active (see next slide). MV, microvilli; N, nucleus.
Explain the intracellular system of parietal cells and the image
TEM of active parietal cell in gastric gland. The cytoplasm of the active cells reveals an intracellular canalicular system (C), which is a deep, trough-like invagination of the apical cell surface opening into the lumen (L). The luminal surface area of the intracellular canalicular system is further increased by numerous microvilli, which are contributed by the tubulovesicular system (see previous slide). Mitochondria are abundant.
Explain the tubulovesicular membrane system and this image
Composite diagram of a parietal cell, showing the ultrastructural differences between a resting cell (left) and an active cell (right). Note that the tubulovesicles (TV) in the cytoplasm of the resting cell fuse to form microvilli (MV) that fill up the intracellular canaliculi (IC) of active cell. G, Golgi complex; M, mitochondria.
Explain the characteristics and this image of chief cells
Typical protein-secreting cells
Occupy the basal portion of the gland
Cells easily identified by intense basophilia
Due to well-developed rER
Secrete:
pepsinogen as precursor of pepsin
a weak lipase
What are the two types of enteroendocrine cells?
Open type
- Directly contacts the lumen, Chemoreceptor, Samples the content of the GIT, When stimulated by the sample hormones are released basally into the lamina propria
Closed type
No direct contact with lumen, indirectly stimulated by the luminal content via neural and paracrine mechanism, secrete their hormones (basally)
Electron micrograph of “closed and open” enteroendocrine cells. tope: electron micrograph shows an example of the “opened” enteroendocrine cell. Note the microvilli at the free (luminal) end and the sub-nuclear cytoplasmic granules. bottom: This electron micrograph shows an example of the “closed” enteroendocrine cell. Arrowheads mark the boundary between the enteroendocrine cell and the adjacent epithelial cells. At its base, the enteroendocrine cell rests on the basal lamina (BL). This cell does not extend to the luminal surface. Numerous secretory vesicle (G) in the base of the cell are secreted in the direction of the arrows across the basal lamina and into the connective tissue (CT). En, endothelium of capillary; M, mitochondria; rER, rough endoplasmic reticulum; sER, smooth endoplasmic reticulum.
Explain the image.
The function is to regulate:
The peristaltic movement of the intestine
Secretion of digestive enzymes
Absorption of water and electrolytes
Light micrograph of enteroendocrine cells (arrows) stained with silver salts. The secretory granules has affinity to silver and chromium salts and appear black. MSC, mucous surface cell appear at the bottom of the gastric pits.
Explain this image and the characteristics of cardiac glands.
Limited to the cardiac region of the stomach
near esophageal orifice
Tubular glands
Tortuous
Composed of mainly mucous secreting cells
Mucus protects the esophagus from gastric acid
Photomicrograph of cardiac glands. This photomicrograph shows the esophagogastric junction. Note the presence of the stratified squamous epithelium of the esophagus in the upper right corner of the micrograph. The cardiac glands are tubular, somewhat tortuous. They are composed mainly of mucus-secreting cells similar in appearance to the cells of the esophageal glands. Mucous secretion reaches the lumen of the gastric pit via a short duct segment containing columnar cells.
Explain this image characteristic of pyloric glands.
Located between fundus and pylorus
Tubular glands
Coiled
Glands empty into d_eep and tortuous gastric pits_
n. hat occupy ½ the thickness of the mucosa
Secrete mucus
Pyloric gland (PG). Note the deep and tortuous (coiled) gastric pit (GP).
Explain the layers of the stomach muscularis.
Consist of three layers instead of two
Innermost: oblique
Middle: circular
Outermost: longitudinal
Explain the image and epithelial cell renewal
Immature cells at the bottom of the gastric pit (encircled) are responsible for the renewal of the lining of the gastric mucosa.
What are the characteristics of plicae circularies and explain the image
-valves of Kerckring
-permanent transverse folds that contain a core of submucosa
- Prominent in the jejunum
- Each fold circularly arranged
- extends around half to 2/3 of circumference of lumen
- Covered by villi
The internal surface of the small intestine is amplified to increase the effective surface area required for absorption. Upper panel: gross anatomical view of the plicae circularis (arrows). Lower panel: the plicae circularis are cut transversely for histological inspection. Each plica circularis has a core of dense connective tissue that extends from the submucosa. Note also that the plicae are covered by villi.
Compare and contrast plica circularises and ruga
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What are the characteristics of villi?
Gross anatomical structures
finger-like and leaf-like projections of mucosa into lumen
Covered by columnar cells
Core filled with l_amina propria_
Contain lacteal, smooth muscles, fenestrated blood vessels
What are the. characteristics of microvilli?
Microscopic structures
Cover the apical surface of the absorptive cells
are major amplification of luminal surface
each cell has several thousands
Explain the image.
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(a) SEM of the intestinal villi. Arrows indicate openings between bases of villi leading to the intestinal glands. (b) This three-dimensional diagram of the intestinal villi shows the continuity of the epithelium covering the villi with the epithelium lining the intestinal glands. Blood vessels and blind-ending lymphatic capillary (lacteal) are found in the core of the villi. Arrows point to the openings of the intestinal glands (crypts of Lieberkühn).
Explain the image
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Stars are place at the lamina propria where cells of diffuse lymphatic tissue are found. Deepest part of the mucosa, muscularis mucosae (MM), is made of two ill-defined layers.
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Explain the image.
Ileum; Peyer’s patches (pp) are good example of the lymphatic nodules.
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Explain the image
Ileum, monkey. The lymphatic nodules (LN) are partly within the mucosa of the ileum and extend into the submucosa (SM). ME, muscularis externa; V, villi.
Explain the image
Section through the intestinal glands. 1, enterocyte; 2, goblet cell; 3, enteroendocrine cell (close type); 4, enteroendocrine cell (open type); 5, Paneth cells. M cells are not represented in the micrograph.
What re the characteristics of enterocytes and explain the image.
Tall columnar cell
basal nucleus
Have well-developed microvilli on luminal surface
Absorptive
Upper panel: LM of the epithelium covering a villus of the small intestine. Enterocytes and goblet cells are visible. Lower panel: TEM of a part of the intestinal epithelium similar to the boxed area in the LM micrograph.
Explain the image
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Electron micrograph of epithelium of the small intestine. Abundant microvilli at the cell apex of the enterocytes can be seen to form the brush border. At the left are 2 lymphocytes (L) migrating in the epithelium. In the center is an enteroendocrine cell (E) with its basal secretory granules
Explain the image and characteristics of goblet cells.
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Increase in number
- from proximal to distal small intestine
Most numerous in terminal ileum
Mucus is water-soluble
Ileum. Note the increase in the number of goblet cells (stained with PAS).
Explain the image.
Goblet Cell.
Explain the characteristics and image of panteth cells.
Found in bases of intestinal glands
May be seen in colon as well
Contains large supranuclear secretory granules
very eosinophilic
refractile
granules permit identification of these cells
Lower panel: Light micrograph of the base of the intestinal glands (crypts of Lieberkuhn) in which Paneth cells (arrows) with their characteristic eosinophilic granules are visible.
Explain this image
Right panel: Photomicrograph of intestinal glands showing Paneth cells. This photomicrograph shows the base of intestinal glands in an H&E preparation. The gland on the right side of the micrograph is sectioned longitudinally; the circular cross-sectional profile of another gland is seen on the left side of the micrograph. Paneth cells are typically located in the base of the intestinal glands and are readily seen in the light microscope because of the intensive eosin staining of their vesicles. The lamina propria contains an abundance of plasma cells, lymphocytes, and other connective tissue cells. Note several lymphocytes in the epithelium of the gland (arrows). ×240. Inset. This high magnification of the area indicated by the rectangle shows the characteristic basophilic cytoplasm in the basal portion of the cell and large accumulations of intensely staining, eosinophilic, refractile secretory vesicles in the apical portion of the cell. An arginine-rich protein found in the vesicles is probably responsible for the intense eosinophilic reaction. ×680. Left panel: TEM image of a region similar to the boxed area in the inset of the right panel. Two Paneth cells surrounding a columnar cell at the base of the crypt of Lieberkuhn are indicated. Paneth cells are characterized by the presence in the cytoplasm of well-developed rough endoplasmic reticulum and apical large secretory granules.
Explain the characteristics of enteroendocrine cells.
Closed
Open
Hormone-containing granules are subnuclear
nCompare with Paneth cells (granules occupy supranuclear location)
Like those in stomach
Secrete into lamina propria
Explain the image
Electron micrograph of epithelium of the small intestine. Abundant microvilli at the cell apex can be seen to form the brush border. At the left are 2 lymphocytes migrating in the epithelium. In the center is an enteroendocrine cell (E) with its basal secretory granules.
Explain the image and function of M cells
take up sample from lumen of the intestine by endocytosis
vesicles transported basally
Sample is released by exocytosis to lymphocyte-rich underlying compartment
Therefore, M cells are antigen-transporting cells
They should not be defined as antigen-presenting cells
A, Electron micrograph of an M cell (M) located between two absorptive enterocytes and covering small nest of lymphocytes and macrophages. The thin cytoplasm of M cell facilitates a quick transportation of samples from the lumen of the intestine to the underlying lymphocytes and macrophages. B, interpretive schematic diagram.
What are the characteristics of the submucosa of the SI and explain the image.
Consists of
dense connective tissue
Conspicuous feature of duodenum is
submucosal glands (BRUNNER’S GLANDS)
Duodenum. M, mucosa; SM, submucosa; ME, muscularis externa. Note the presence of submucosal (Brunner’s) glands.
What are the characteristics of Brunners glans and explain the image.
Cells of Brunner’s glands have characteristics of both mucous and serous secretions
pH of secretions is 8.1-9.3
protects proximal small intestine
neutralizes acid from the stomach
creates optimal pH for enzymes
Duodenum. In this section the arrow points to one of Brunner’s glands piercing muscularis mucosae (MM) and opens into the intestinal gland (crypt of Lieberkühn).
Explain the image
Duodenum. In this field of view many Brunner’s glands (arrows) are penetrating mascularis mucosae to open into crypts of Lieberkühn.
Explain the image
Crosse section of the duodenum. Note that one of Brunner’s glands is piercing the muscularis mucosae by its duct (arrow) and opens into the intestinal (Lieberkühn) gland.
Explain the image
Cross section of the Duodenum. V, villi; Muc, mucosa; MM, muscularis mucosae; SubM, submucosa; ME, muscularis externa; BGl, Brunner’s glands; D, duct through which the glands open into the lumen of the duodenum; S, serosa.
How does cell renewal work in the SI
All mature cells in intestinal epithelium come from A SINGLE STEM CELL POPULATION
Stem cells localized at base of crypt
Regeneration of the epithelial lining of the stomach and small intestine. Note differences in the location of stem cells.
Explain some characteristics of cell renewal and the images of the SI.
Epithelial cells migrating from the base of the crypt onto the villus differentiate into:
Absorptive or goblet cells
Renewal time is 5-6 days
Enteroendocrine or Paneth cells
Renewal time 4 weeks
unidirectional, compare with stomach
Crypts of Lieberkuhn cut longitudinally (upper panel) and transversely (lower panel). In the upper panel dividing stem cells showing mitotic figures are shown just above Paneth cells. Note the supranuclear eosinophilic granules of Paneth cells and the presence of an enteroendocrine cell.
Explain the differences of the 4 histological layers of the large intestine and explain the image.
Mucosa is smooth (no plicae circularis, no villi)
Outer longitudinal layer of the muscularis externa (ME)
Modified to 3 equally spaced bands
Tenia coli
Cross section of the colon. The four layers that make up the wall of the colon are mucosa (Muc), Submucosa (SubM), Muscularis externa (ME) and serosa (S). Although these layers are the same as those in the small intestine, several differences are noted; namely, the absence of the plicae circularis, mucosa has no villi, and the muscularis externa is arranged in a distinctive manner. The outer longitudinal layer of the muscularis externa [ME(l)] is substantially thinner than the inner circular layer [ME(c)] and modified to three equally spaced bands called tenia coli (TC). BV, blood vessel.
Explain the image and characteristics of the colon mucosa.
Covered with simple columnar epithelium
Similar to those of the small intestine
Absorptive cells
absorb water and electrolytes
Contains numerous CRYPTS OF LIEBERKUHN
straight tubular glands, extend through full thickness of mucosa, Composed mostly of goblet cells
Photomicrograph of a section of large intestine with its various layers. Black arrows point to crypts of Lieberkuhn. Note the absence of villi. M, mucosa; SubM, submucosa; Me, muscularis externa; S, serosa (red arrow). Note that a lymphatic nodule (LN) extends from the lamina propria to the submucosa
Know the image
Explain the image
Cross section of the human colon. Note crypts of Lieberkuhn (the arrows point to their openings) and the absence of the villi (smooth surface).
explain the image and goblet cells of the mucosa.
Secrete mucus
Consists of highly glycosylated glycoproteins called mucins
Viscus
Physically imped microorganisms
Mucin is negatively charged
Binds positively charged defensins
Facilitates elimination of waste material
Highly magnified section of a large intestinal gland showing its absorptive and mucous goblet cells. Observe that the goblet cells are secreting and beginning to fill the lumen of the gland with its secretions. The microvilli in the absorptive cells (not visible in this section) participate in the process of water absorption. PT stain.
Explain the number of goblet cells and absorptive cells in the colon mucosa
Absorptive cells outnumber goblet; 4:1
Not apparent in histological sections
Absorptive cells are located more toward the lumen of the colon (arrows)
Goblet cells more toward the intestinal glands
Near rectum ratio is 1:1
Explain the lymphatic tissue and nodules of the lamina propria
Diffuse lymphatic tissue and large lymphatic nodules
lymphatic nodules distort regular spacing of crypts
and extend into submucosa
Reflects large number of microorganisms present in colon lumen
Section of the colon showing lymphatic nodule (LN) in the lamina propria.
_____ forms blind pouch distal to ileocecal valve
____ is a thin finger-like extension of the cecum
Cecum
is a thin finger-like extension of the cecum
Appendix (image)
Appendix is different in that it has a complete layer of the outer longitudinal muscle in the muscularis
true or False: there is a large amount of lymphatic nodules in the appendix
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true
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What are the characteristics of the rectum?
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What are the characteristics of the anal canal
Upper panel shows the histology of the transition of the epithelium from simple columnar that lines the rectum to stratified columnar epithelium to stratified squamous epithelium. Lower panel is endoscopic view of the anorectal junction. The transition of the epithelium from simple columnar epithelium (appears dark brown) to stratified squamous epithelium (appears light) is indicated by the arrows.
Explain the submucosa and muscular external characteristics of the anal canal
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