GI Histology Flashcards
1
Q
What does the digestive system consist of?
A
The tract extends from the mouth (oral cavity) to the anus, as well as the digestive organs emptying into this tract, primarily the salivary glands, liver, gall bladder and pancreas.
2
Q
What are the four main layers of the GI tract wall?
A
Mucosa, submucosa, muscularis, and serosa/adventitia.
3
Q
What is the mucosa consist of?
A
An epithelial lining (stratified squamous or columnar), an underlying lamina propria of loose connective tissue rich in blood vessels, lymphatics, lymphocytes and small glands.
A smooth muscle layer called muscularis mucosae separates the mucosa from the submucosa and allows local movement of mucosa.
4
Q
What is the thin layer of smooth muscle that separates mucosa from submucosa called?
A
The muscularis mucosae.
5
Q
What does the submucosa contain?
A
It is a fibroelastic loose connective tissue. It contains larger blood vessels and lymphatics, often glands and an important network of nerves and ganglia of the autonomic nervous system.
6
Q
What does the muscularis contain?
A
It consists of smooth muscle with inner circular and outer longitudinal orientations.
Between the layers is a network of nerves known as the myenteric (auerbach’s plexus).
7
Q
What does contraction of the muscularis do?
A
It mixes and propels the luminal contents forward (peristalsis). This contraction is coordinated by the myenteric plexus.
8
Q
What is contraction of the muscularis coordinated by?
A
The myenteric plexus.
9
Q
What is the adventitia or serosa?
A
Connective tissue surrounding the muscularis externa.
10
Q
When facing the peritoneal cavity (distal esophagus, stomach, jejunum, ileum and parts of the large intestine) what is the adventitia encased in?
A
A thin layer of simple squamous epithelium known as mesothelium.
11
Q
When mesothelium forms the outermost layer of the gut, what is the combined connective tissue and mesothelium referred to?
A
Serosa
12
Q
What is serosa?
A
When mesothelium forms the outermost layer of the gut, it is the combined connective tissue and mesothelium
13
Q
What is the function of serosa?
A
It allows adjacent portions of the GI to come in contact and be able to slide over each other with minimal abrasion.
14
Q
Where in the abdomen is there not serosa?
A
Some areas of the non-peritonealized or retroperitoneal surfaces (such as the thoracic esophagus, duodenum, and ascending and descending colon).
15
Q
In areas devoid or serosa what is the only tissue present?
A
connective tissue.
16
Q
What is the esophagus and what does it extend between?
A
It is a muscular organ the extends between the pharynx and the stomach (mostly within the thoracic cavity).
17
Q
What is the lumen of the esophagus lined by?
A
Mucosa that is a thick nonkeratinized stratified squamous epithelium able to withstand abrasion.
18
Q
What does the lamina propria contain in the esophagus?
A
Lymphocytes (seen as clusters of dark purple staining in H and E sections).
19
Q
What does the mucosa epithelium overly (2 things) in the esophagus?
A
Lamina propria and a variably thick muscularis mucosa composed of smooth muscle cells.
20
Q
Describe the submucosa in the esophagus?
A
Mucus secreting gland may be found in the submucosa known as esophageal glands.
21
Q
What do the submucosal veins do in the distal 8 cm of the esophagus?
A
They anastomose with branches of the portal vein.
22
Q
what is the muscularis externa made up of in the esophagus?
A
The proximal one third is skeletal muscle, the middle one third is a mix of skeletal and smooth, and the distal one third is smooth muscle.
23
Q
Describe the adventitia/serosa in the esophagus?
A
It is the outermost layer of the thoracic portion of the esophagus. it is a loose connective tissue that blends the surrounding tissues.
24
Q
What is the serosa of the esophagus?
A
After passing through the diaphragm, mesotheliym covers the connective tissue (adventitia). The connective tissue plus the mesothelium layer is referred to as serosa.
25
What are the four main functions of the stomach?
1. continued digestion of carbohydrates initiated by salvilary enzyme amylase
2. The addition of an acidic fluid to the ingested food and mixing its contents into a viscous mass called chyme by the churning activity of the muscularis.
3. Continued digestion of triglycerides initiated by pancreatic enzyme lipase
4. Initial digestion of proteins with enzyme pepsin.
26
What regions can the stomach be subdivided into?
The fundus, the cardia, the body and the pyloric antrum.
27
Describe the mucosa of the stomach.
It is a simple columnar epitheliym consisting entirely of mucus-secreting cells. The epithelium forms invaginations into the underlying lamina propria giving rise to the gastric glands.
28
Where are branching gastric glands? What do they do?
They are in the fundus of the stomach. They open into gastric pits which empty their contents into the lumen of the stomach.
29
What are the 5 cell types within the gastric glands?
1. Regenerative cells/Stem cells.
2. Mucous cells
3. parietal cells
4. chief cells
5. Enteroendocrine cells
30
Describe regenerative cells/stem cells of the gastric glands
Undifferentiated cells that give rise to the other cell types in the glands and the gastric pits.
31
Describe the mucous cells in the gastric glands?
They line the lumen of the gastric pits and secrete a thick, adherent, and highly viscous protective mucous that is rich in bicarbonate ions.
32
Describe parietal cells in the gastric glands?
They are predominant in the upper segment of the gastric gland and produce hydrochloric acid, important for the conversion of pepsinogen to pepsin, and intrinsic factor which is essential for the absorption of Vitamin B12.
33
What do parietal cells produce?
hydrochloric acid, important for the conversion of pepsinogen to pepsin, and intrinsic factor which is essential for the absorption of Vitamin B12.
34
What do chief cells in the gastric glands do?
They secrete inactive proenzyme pepsinogen.
Pepsinogen is released into the lumen of the gland and converted in the acidic environment of the stomach to pepsin, a proteolytic enzyme capable of digesting most proteins.
35
What do enteroendocrine cells in the gastric glands do?
They secrete hormones that have effects on gut motility (serotonin) and HCl secretion (gastrin).
36
What do gastric glands in the cardia and pyloric regions of the stomach primarily consist of?
Mucus cells and a few enteroendocrine cells.
37
What does the submucosa of the stomach consist of?
A loose connective tissue with coarse collagen bundles.
38
What is the increased thickness of the submucosa in the stomach responsible for?
rugae of the mucosa. (a series of ridges).
39
What nerve supply is found in the submucosa of the stomach?
Meissner's plexus
40
What are the layers of the stomach muscularis?
Three layers of smooth muscle including and inner oblique, middle circular and outer longitudinal/
41
What plexus is present in the stomach muscularis and where?
Auerbach's/myenetric plexus is present in the outer ttwo layers (middle circular and outer longitudinal layers).
42
What is the outer mesothelium of the stomach called?
The serosal layer
43
What are the three regions of the small intestine?
The duodenum, jejunum, and the ilium
44
What is the function of the small intestine?
It continues digestion of chyme from stomach using pancreatic enzymes and liver bile and absorbs nutrients.
45
The small intestine contains all the usual layer (mucosa, submucosa, muscularis, and serosa). Where are it's unique features associated with?
Mucosal and submucosal layers.
46
What are the circular folds called in the luminal surface of the small intestine? What do they contain
Plica circulares. They contain villi
47
What are the plica ciculares and villi function?
They increase the luminal surface area necessary for absorption of nutrients from the digested food.
48
What does the mucosa of the small inestine include?
A simple columnar epithelium joined by extensive tight junctions.
Several cell types are present: enterocytes, globlet cells, paneth cells, enteroendocrine cells, stem cells
49
What are enterocytes
absorptive cells
50
What are goblet cells
mucus-secreting cells
51
What are paneth cells
lysozyme secreting cells
52
What are enteroendocrine cells
hormone sercreting cells
53
What is the function of stem cells in the mucosa of the small intestine?
Replace enterocytes and goblet cells every 3-5 days.
54
What are the enterocytes in the small intestine covered with? Why
They are covered with microvilli to increase the absoptive area.
55
What do enterocytes do?
They absorb Carbohydrates, proteins, lipids, vitamins, Calcium, Iron from the lumen and transport them into the blood or lymph.
56
What are carbohydrates digested into?
Monosaccharides, they are transported to the portal blood.
57
What are proteins digested to?
Amino acids, dipeptides and tripeptides. Further digestion may occur and then amino acids are transported to the portal blood.
58
What are triglycerides digested into?
They are emulsified by bile salts and digested to fatty acids and monoacylglycerols.
Long chain fatty acids are packaged as chylomicrons that enter the lacteal in the center of the vilus.
Short and medium chain fatty acids enter enterocytes directly and delivered to the portal blood.
59
Where do long chain fatty acids go?
Long chain fatty acids are packaged as chylomicrons that enter the lacteal in the center of the vilus.
60
Where do short and medium chain fatty acids go?
Short and medium chain fatty acids enter enterocytes directly and delivered to the portal blood.
61
Where does water soluble vitamin B12 go?
its absorbed in the ileum and requires intrinsic factor.
62
What does calcium require for absorption?
Vitamin D
63
Where are paneth cells found?
The base of the crypt
64
Do goblet cells increase or decreate in number further in the GI tract?
Increase to meet the need for increased lubrication of luminal contents.
65
How do goblet cells appear in H and E sections?
Clear
66
What is the intestinal galnd or crypts of lieberkuhn?
The epithelium at the base of the vili invaginates into the lamina propria to form short intestinal gland or crypts.
67
What color are paneth cells in an H and E stain?
an orange red color
68
Why do paneth cells stain an orange red color?
Due to the presence of numerous cytoplasmic granules filled with lysosome (an antibacterial substance), tumor necrosis factor (proinflammatory factor) and defensins (anti-bacterial and antiparasitic).
69
What is the function of paneth cells?
They synthesize and secrete substantial quantities of antimicrobial peptides and proteins as well as factors that help sustain and modulate the epithelial stem and progenitor cells that cohabitate in the crypts and rejuvinate the small intestinal epithelium.
70
What does dysfunction of paneth cell biology contribute to?
The pathogenesis of chronic inflammatory bowel disease.
71
What are the factors that enterendocrine cells secrete in the small intestine?
Cholecystokinin, secretin, gastric inhibitory peptide, and glucagon like peptide.
72
What is cholecystokinin?
It is secreted in response to small peptides, amino acids, or fatty acids in the gut lumen.
It stimulates secretion from pancreatic acinar cells and release of bile from gallbladder.
73
What is secretin made in response to? What does it stimulate?
Secretin is made in response to H+ and fatty acids in the gut lumen. It stimulates release of HCO3 from pancreas and biliary tract of liver.
74
What is gastric inhibitory peptide made in response to? What does it stimulate?
Released in response to glucose, amino acids and fatty acids in the gut lumen. Stimulates insulin secretion and inhibits glucagon secretion.
75
Where are brunner's glands found? What are they?
They are only found in the submucosa of the duodenum adjacent to the stomach.
They secrete alkaline mucus via ducts that empty into the bases of the crypts to help neutralize the acidic contents of the stomach entering the small intestine.
76
In what part of the intestine can lymphocytes be found?
In the lamina propria.
77
Where will the highest concentrations of lymphocytes be present?
In the ileum as individuals cells or as groups of lymphoid nodules referred to as peyer's patches.
78
What are groups of lymphoid nodules referred to as?
Peyer's patches or gut associated lympoid tissue (GALT)
79
Where can components of the enteric nervous system be found in the small intestine?
In the muscularis region.
80
Where does the myenteric plexus originate from in the small intestine?
It originates from neural crest cells and formbs between the inner and outer layers of smooth muscle.
81
What is the function of the large intestine?
It absorbs about 4/5 of the water, salt, and chlorine from the fluid presented to it from the ileum. It concentrates it and solidifies it to form feces.
82
Are there folds in the mucosa of the large intestine?
No, except for the rectum.
83
Are there vili in the mucosa of the large intestine?
No
84
What does the mucosa of the large intestine consist of?
A simple columnar epithlial cells which regularly invaginate to form tubular intestinal glands.
Dispersed enteroendocrine cells may also be found within the mucosal epithelium.
85
What are the majority of surface cells and cells of the glands in the mucosa of the large intestine?
Goblet cells.
86
Where can undiferentiated stem cells in the mucosa of the large intestine be found?
They are present within the bases of the glands and migrate upward to form the other cell types.
87
Describe the muscularis of the large intestine?
It has inner longitudinal and outer circular layers but differs from the small instestine with fibers of the outer layer gathered into 3 separate longitudinal bands called teniae coli.
88
What are teniae coli.
They are found in the muscularis of the large intestine. They are fibers of the outer layer gathered into 3 separate longitudinal bands.
89
What are intraperitoneal portions of the colon covered by?
A serosa which is characterized by a small. pendulous portuberances of adpiose called appendix epiploica.
90
What is appendix epiploica?
small, pendulous protuberances of adipose tissue
91
What is the appendix?
It is a small blind ended diverticulum of the cecum with layers similar to those of the large intestine.
92
What are characteristic histological features of the appendix?
The accumulations of lymphoid tissue present within the lamina propria.
93
What are the organs associated with the digestive tract?
major salivary glands, pancreas, liver ,and gallbladder. Products of these organs facilitate transport and digestion of food within the gastrointestinal tract.
94
What are the main functions of the salivary glands?
To moisten and lubricate ingested food and oral mucosa, to initiate the digestion of carbohydrates and lipids with amylase and lipase.
95
What does the pancreas do?
It secretes digestive enzymes that act in the small intestine and hormones important for the metabolism of the absorbed nutrients.
96
Where is bile stored and made?
It is made in the liver but stored in the gallbladder.
97
What does the liver do?
It plays a major role in carbohydrate and protein metabolism, inactivates many toxic substances and drugs, and synthesizes most plasma proteins and factors needed for blood coagulation.
98
Is the pancrease exocrine or an endocrine gland?
Both it produces both digestive enzymes and hormones.
99
Describe the histology of the exocrine pancreas
The exocrine portion makes up 80% of the organ. It consists of numerous acinar cells aggregated into lobules that can be seen grossly.
100
What do acinar cells look like?
They are large, pyramida shaped cells with a single nucleus.
| The nucleus lies close to the base of the cell that rests on the basal laminae.
101
Where are centroacinar cells located?
Located in the center of the acinus.
102
What do centroacinar cells look like?
They have a pale nucleus and form the smallest ducts of the gland.
103
How are ancinar cell secretions regulated
Merocrine secretion of proenzymes by the ancinar cells is regulated by secretin and cholecystokinin from the enteroendocrine cells of the duodenum and jejunum as well as stimulation from the vagus nerve.
104
What does gastric acid in the intestinal lumen stimulate?
It stimulates secretin release
105
What does secretin do?
It causes acini and ductal cells to add water and bicarbonate to fluid, making it alkaline, rich in electrolytes and poor in enzyme activity. This fluid neutralizes the chyme so that the pancreatic enzymes can function at optimal neutral pH
106
What do long chain fatty acids, gastric acid and some essential amino acids in the gut stimulate?
The release of cholecystokinin. This hormone promotes secretion of an enzyme-rich (but less abundant) fluid.
107
What are islets of langerhans?
Lightly stained cells, only seen histologically. The endocrine portion of the pancreas in found in aggregates of these lightly stained cells (islets of langerhans).
108
What is the product of cell type Alpha (A) of endocrine pancreas?
The product is glucagon
109
What is the function of cell type Alpha (A) of endocrine pancreas?
It increases blood glucose, gluconeogenesis, glycogenolysis. (product is glucagon)
110
What is the product of cell type beta (B) of endocrine pancreas?
Insulin
111
What is the function of cell type beta (B) of endocrine pancreas?
Promotes decrease of blood glucose, stimulates storage of glucose as glycogen
112
What is the function of cell type delta (D) of endocrine pancreas?
Inhibits the secretion of glucagon and insulin
| product somatostatin
113
What is the product of cell type delta (D) of endocrine pancreas?
Somatostatin.
114
What is the liver parenchyma organized into?
Hepatic lobules that are roughly hexagonal in shape
115
What is the center of a hepatic lobule characterized by?
It is indicated by the presence of the efferent central vein. The central vein is surrounded by hepatocytes and arranged radially in plates or cords.
116
What is at the periphery of the heaptic lobule?
Portal triads containing a branch of the hepatic artery, portal vein and bile duct (with lymphatics and nerves).
117
What are the lobules 3 functional zones?
Centrilobular (zone III), midlobular (Zone II) and peripheral (Zone I)
118
How does blood flow in the heaptic lobule?
From the periphery to the center .
119
What do hepatocytes near portal areas rely on (aerobic or anaerobic metabolism).
They rely on aerobic metabolism and are often more active in protein synthesis.
120
What do hepatocytes near the central areas (zone 3) rely on (are they exposed to higher or lower concentrations of nutrients and oxygen)?
They are exposed to lower concentrations of nutrients and oxygen. They are involved with detoxification and glycogen metabolism.
121
How does bile produced in hepatocytes flow?
Into the bile canaliculi that eventually connect to small bile ducts in the portal triads. The bile flow progresses in the opposite of blood, from the center of the lobule to its periphery.
122
What is the liver parenchyma?
It is primarily composed of hepatocytes arranged into plates or cords, and they are the functional cell of the hepatic lobule.
123
What is between the anastomosing plates of hepatocytes of a hepatic lobule?
The vascular sinusoids that emerge from the peripheral branches of the portal vein and hepatic artery and converge on the lobule's central vein.
124
What type of blood flows in the hepatic sinusoids?
Portal venous blood and hepatic arterial blood mixes in the irregular hepatic sinusoids that are lined by fenenstrated endothelial cells that allow the plasma easily move into the space of disse and interact with hepatocyte.
125
What does direct contact between hepatocytes and plasma do?
It facilitates the most key hepatocyte functions that involve uptake and release of nutrients, proteins, and potential toxins.
126
Where are phagocytic kupffer cells found?
Within the sinusoids.
127
What do phagocytic kupffer cells do?
They are important in phagocytosis of aged red blood cells, bacteria or other debris in the portal blood.
128
Where are the Ito cells found?
In the space of dISSE
129
what do the Ito cells do?
They store vitamin A and other fat-soluble vitamins.
130
Where is the gallbladder?
It is a pear-shaped organ that occupies an area on the posterior aspect of the right lobe of the liver.
131
What is the gallbladder composed of? What is its function?
It is a blindly ending fundus. It has a central body and a narrow neck.
It concentrates, stores and releases bile. Approximately 1000 ml of bile flows into the gallbladder daily from the liver and after concentration about 30-50 ml is stored.
132
What does the gallbladder contain and lack histologically?
It has a surface epithelium, a lamina propria, muscularis and adventitia.
It lacks a muscularis mucosae and submucosa.
133
What are the luminal folds of the gallbladder lined with?
A single layer of simple columnar epithelium.
134
What are the epithelial cells capable of in the gallbladder?
Secreting small amounts of mucus. They alos have an active sodium-transporting mechanism necessary for concentration of bile.
135
What is contraction of the gallbladder induced by?
It is induced by cholecystokinin, a hormone produced by enteroendocrine cells of the small intestine. Cholecystokinin is released in response to the presence of dietary fats in the small intestine.
136
What is the function of salivary glands?
Secretion of enzymes that aid in digestion and moistening of food.
137
What are the major salivary glands?
Parotid, submandibular, and sublingual.
138
How are salivary glands classified?
According to their function and location, as well as their predominance of either serous or mucous acini.
139
What does the gland structure of the salivary gland consist of?
Connective tissue stroma of blood vessels, nerve, lymphatics and ducts.
The gland is surrounded by a connective tissue capsule.
140
How are lobes created in the salivary gland?
Septa extend from the capsule into the gland and create lobes, and then futher divide into smaller lobules.
141
What do the acini of the salivary gland contain?
They may contain serous cells, mucous cells or a combination of both.
142
What do the serous and mucous cells do in the acini of the salivary gland?
The serous cell secrete enzymes and other proteins, while the mucous cells secrete mucins that provide lubricating properties to the saliva.
143
Where are myoepithelial cells in salivary glands?
They lie between the epithelial cells and basal lamina of the acini.
144
What do myoepithelial cells do?
They are flat and have long cytoplasmic processes that aid in contraction.
145
What does the duct system of the salivary gland do?
It transports the saliva from the gland to the oral cavity and modifies its ionic composition by reabsorbing Na+ and Cl- making it more hypotonic.
146
What is the first segment out of the acini of the salivary gland?
The intercalated duct. It is lined with squamous or low cuboidal epithelium.
147
What do the intercalated ducts of the salivary gland empty into?
They empty into the striated or interlobular ducts taht are located in the connective tissue septae that subsequently lead into the main excretory duct system.
148
Describe the histology of the parotid gland (of the salivary gland).
Serous acini consists of pear-shaped groups of epithelial cells surrounded by a distinct basement membrane. The epithelial cells have a dense cytoplasm and a basal nucleus. The acini have a central lumen into which secretions flow from the epithelial cells
149
Describe the sublingual gland.
Mucous acini have an abundant cytoplasm filled with clear mucus. The cells are pyramidal with flatten basal nuceli.
150
Describe the sumandibular gland
Mixed acini can be characterized by a crescent-shaped formation of serous cells capping a mucous acinus (serous demilune) or by a mixed pattern of serous and mucous acini.
151
How is secretion of the salivary gland stimulated?
The autonomic nervous system.
152
Wen does parasympathetic secretion of the salivary happen?
In response to the taste or smell of food. it promotes vasodilation and copious watery secretion.
153
What does sympathetic stimulation of the salivary gland do?
It produces a small amount of viscous saliva.
154
Where can bruner's glands be found
In the submucosa of the duodenum
155
Where will the highest concentration of lmphocytes be present?
In the lamina propria of the ileum. Found in groups of lymphoid nodules referred to as peyer's patches or gut associated lympohoid tissue
156
What are acinar cells regulated by?
Secretin and CCK
157
Where is the plica circularis and the vili found?
In the mucosa layer of the small intestine
158
What areas are devoid of serosa? What do they have instead?
The retroperitoneal surfaces are devoid of serosa: the thoracic esophagus, duodenm and ascending and descending colon. They only have connective tissue present called adventitia.
159
What does the entereoendocrine cells of the gastric gland secrete?
Serotonin (controls gut motility)
| Gastrin (controls HCl secretion)
160
What is characteristic of the submucosa of the stomach?
It is responsible for the rugae of the stomach.
161
what is the difference in function of zone 1 and zone 3 of the hepatic lobule (what do each do)?
Zone 1 relies on aerobic metabolism and is often more active in protein synthesis.
Zone 3 is exposed to lower oxygen concentrations of nutrients and oxygen and are more involved with detoxification and glycogen metabolism.
