GI System Histology Flashcards
1
Q
What are the layers of the mucosa in the GI tract?
A
- Epithelium
- Lamina propria - connective tissue, small blood vessels and lymphatics
- Muscularis mucosa (smooth muscle)
2
Q
What are the three principal functions of the GI mucosal layer?
A
- Secretion – provides lubrication, digestive enzymes, acidic and and alkaline fluids, and bile into the lumen of the GI tract
- Absorption – small molecules of food, water, electrolytes, vitamins, and recyclable products such as bile components and cholesterol into the blood and lymph of lamina propria
- Protection - serves as a barrier to noxious substances, antigens, and pathogenic organisms
3
Q
What are the principal functions of the submucosa of the GI tract?
A
provide blood and lymph vessels, nerve plexus, and occasional glands
4
Q
What are the principal functions of the inner circular layer of the muscularis externa of the GI tract?
A
compress and mix contents in the lumen
NOTE: Inner circular forms sphincters at specific locations along digestive tract!
5
Q
What are the principal functions of the outer longitudinal layer of the muscularis externa of the GI tract?
A
propels the contents by shortening the tube
6
Q
The muscularis externa of the GI tract is controlled by what?
A
enteric nervous system
7
Q
What does the mucosa of the esophagus consist of?
A
1) SS nonkeratinized epithelium
2) Thin lamina propria with cardiac glands (mucous) at upper and lower ends
3) GALT
4) esophageal glands
8
Q
What does the submucosa of the esophagus consist of?
A
mucus-secreting tubuloalveolar glands called esophageal glands proper
mucus provides protection to the mucosa layer
9
Q
What can be found between the inner circular and outer longitudinal fibers of the Muscularis externa in the esophagus?
A
Auerbach’s plexus
10
Q
The esophagus can be divided into three regions. What are these divisions based on?
A
the amount of skeletal and smooth muscle in the muscularis externa
11
Q
What is the muscle composition of the upper third of the esophagus?
A
all skeletal
12
Q
What is the muscle composition of the middle third of the esophagus?
A
mixture of skeletal and smooth
13
Q
What is the muscle composition of the lower third of the esophagus?
A
all smooth
14
Q
Skeletal to smooth muscle transition enables what?
A
voluntary control to involuntary control of swallowing
15
Q
What layer of the muscularis externa form upper and lower esophageal sphincters?
A
inner circular
16
Q
Incompetent inferior esophageal sphincter may cause what?
A
1) chronic heartburn and erosion of the mucosa or,
2) gastroesophageal reflux disease (GERD)
17
Q
What is the major function of the stomach and how does it accomplish this?
A
digestion. It does this by adding acidic fluid and mixing digested content into a chyme
18
Q
What are the layers of the mucosa of the stomach?
A
1) epithelium
2) lamina propria
3) muscularis mucosa (typically)
19
Q
What is the epithelium of the stomach made of?
A
simple columnar
20
Q
What does the lamina propria of the stomach contain?
A
CT, gastric glands, and lymphatic cells
21
Q
What are rugae?
A
large longitudinal gastric folds in the stomach (which disappear when the stomach is distended)
22
Q
What layer of the stomach forms the core of rugae?
A
submucosa
23
Q
What are the layers of the muscularis externa of the stomach?
A
3 layers- an inner oblique, middle circular, and outer longitudinal
24
Q
The plyoro-duodenal sphincter is formed from what?
A
the middle circular layer of the muscularis externa
25
Does the stomach have serosa or adventitia?
serosa (present on all stomach surfaces)
26
What can be seen in the simple columnar epithelial of the stomach?
surface mucous cells
27
What do surface mucous cells produce? Why?
alkaline mucous to protect stomach lining from acidic chyme
28
Invaginations of the stomach epithelium into the lamina propria are called what?
gastric pits
29
What cell types can be found in gastric glands?
1) stem cells
2) mucous neck cells
3) chief cells
4) parietal cells
5) enteroendocrine cells
30
What is the role of chief cells in gastric glands and what part of the gland are they primarily found in?
found in the deeper part of gland and secrete pepsinogen
31
What is the role of parietal cells in gastric glands and what part of the gland are they primarily found in?
most numerous in the upper part of the gland. They secrete HCl and intrinsic factor (which facilitates vitamin B12 absorption in the ileum)
32
What is the role of enteroendocrine cells in gastric glands and what part of the gland are they primarily found in?
all levels, secrete a variety of gastric hormones into the lamina propria
33
Where are stem cells found in gastric glands?
only in the isthmus region. Thus, cell division and regeneration is restricted to the isthmus region only.
34
What is the life span of:
a) surface mucous cells
b) parietal cells
c) enterendocrine cells
a) 3-5 days (thus, most new cells from the isthmus migrate up to this region)
b) 6 months
c) 3 months
35
What is the difference between rugae, mammillated folds, and gastric glands/pits?
rugae- contain mucosa and submucosa
mammillated folds- small elevations of mucosa only
gastric glands/pits- are not elevations, small holes
36
What are gastic ulcers?
erosions of stomach mucosa
37
Helicobacter pylori infection of the stomach causes which gastric ailments?
Cause of chronic gastritis, peptic ulcers, gastric carcinoma and gastric lymphoma
38
What part of the stomach are helicobacter pylori infections most common?
infection tend to concentrate in neck of gastric glands lined by mucus-secreting cells including the stem cells
39
T or F. Chronic injury and inflammation of
the neck region (site of proliferating gastric cells) caused by Helicobacter pylori gland infection is likely to accelerate proliferation of cells in gastric carcinoma in neck of the gastric
gland
T.
40
What is the main function of the small intestine?
- Absorption of nutrients is major function
| - Completion of digestion
41
What modifications does the intestinal wall exhibit to increase surface area for absorption?
1. plicae circulares (aka valves of Kerchring)- permanent transverse folds of the mucosa, increase surface area 3-fold
2. villi- finger-like projections of the mucosa – increase surface area 10-fold+
3. microvilli- on the surface of epithelial cells, form a striated (brush) border, increase surface area 100-fold+
42
Where are plicae circulares most common?
the jejunum
43
What is the core of plicae circulares composed of?
submucosa
44
The surface epithelium of intestinal villi has indentations that lead to glands named what?
Intestinal crypts or crypts of Lieberkuhn
45
What is Celiac disease?
People with celiac disease cannot tolerate gluten, a protein in wheat, rye, and barley. Gluten triggers immune system to damage or destroy villi.
46
Microvilli have a core made of what?
actin that allows for contraction/spreading of the microvilli
47
What is the epithelium in the small intestine?
simple columnar
48
What are the cell types present in the epithelium of the small intestine?
1) enterocytes
2) goblet cells
3) Paneth cells
4) M cells
5) enteroendocrine cells
6) intermediate cells (stem cells)
49
What is the role of enterocytes in the small intestine?
- the primary absorptive cell, found on the villi, the general surface and in the glands
- are attached to neighboring cells by tight junctions
- in the glands, the enterocytes also secrete water and electrolytes
50
Where are goblet cells found in the epithelium in the small intestine?
What do they contain?
- found on villi and in glands
| - apical part of cell contains mucinogen granules
51
What do Paneth cells do?
- Secretes lysozyme that digests bacterial cell walls and other antibacterial substances
- Can phagocytose certain bacteria and protozoa
- Paneth play significant role regulating bacteria in intestinal glands
52
What do M cells do in the small intestine?
have microfolds rather than microvilli
- are antigen-presenting cells, overlie lymphatic nodules
- endocytose microorganisms and macromolecules from intestinal lumen and discharge them into the underlying lymphatic tissue
53
What do enteroendocrine cells do?
secrete various peptide hormones
54
What do intermediate cells (stem cells) do?
- comprise most cells in the lower half of the gland
- intermediate between enterocyte and goblet
- can divide and form any of the epithelial cells
55
How often are:
a) absorptive and goblet cells renewed
b) paneth cells
a) every 5-6 days,
| b) about every 4 weeks
56
What are the contents of the lamina propria in the mucosa in the small intestine?
- is heavily infiltrated with lymphoid tissue – GALT.
| - Aggregation of lymph nodules, Peyer’s patches, (best developed in the ileum)
57
What is a lacteal?
each villus in the lamina propria of the small intestine contains a lymphatic capillary, called a lacteal, for absorption of fat
58
What are the layers of the muscularis mucosa in the small intestine?
- typical: inner circular, outer longitudinal
| - fibers extend into the villi to enable movement of villi
59
What are Brunner's glands (what is their role) and what parts of the small intestine have Brunner's glands?
What layer of the wall are they found in when present?
Duodenum contains Brunner’s glands in submucosa, secretes alkaline to buffer acid from the stomach entering duodenum
NOTE: The jejunum also has very few Brunner's glands,
60
Which parts of the small intestine has Peyer's patches?
Ileum. Neither the Jejunum or the duodenum have peer's patches
Peter’s patches are aggregations of lymph nodules
61
Does the small intestine have:
a) a submucosa
b) muscularis externa
c) serosa and avdentitia
yes to all three
Muscularis externa has inner circular and outer longitudinal orientation of muscle groups
62
What is the main function of the large intestine?
absorption of water and electrolytes and elimination of solid wastes and undigested food
63
What are the Teniae coli of the large intestine formed from?
three bands, created from the outer longitudinal layer of muscularis externa
64
What is the epithelium of the large intestine?
simple columnar
65
What kinds of cells does the epithelium of the large intestine contain?
same cell types as small intestine, except more goblet cells, no Paneth cells
66
Is the GALT well developed in the lamina propria of the large intestine?
yes.
NOTE: **there are no lymphatic vessels (hence slow metastasis of colon cancers)***
67
What are some main features of the appendix?
* has no teniae coli
* characterized by many lymph nodules in the propria, so large they encroach on the submucosa
* usually, much debris seen in the lumen
68
What 3 structures are named the portal triad.?
the proper hepatic artery, the common bile duct, and the portal vein
69
What is a portal vein?
a vessel that carries blood between two capillary beds.
Portal vein to the liver carries blood between capillaries of organs in the abdomen to sinusoids in the liver.
70
Is blood oxygenated in the portal vein or the proper hepatic artery?
the proper hepatic artery
71
What does a portal canal contain?
portal triad, lymphatic vessels, nerves, and CT
72
Where is blood from portal vein and hepatic arteries combined?
in sinusoids, which then flows into a venule, the central vein, which then flow to a sub lobular vein, and finally to the hepatic veins which empty into the IVC
73
What make up approximately 80% of cells in liver?
hepatocytes
74
What is the composition of hepatocytes?
Many are binucleated with large amount of heterchromatin, rER, sER, and Golgi units
make proteins, involved in storage, metabolism, and waste removal
they can regenerate
75
What is the role of Ito (stellate) cells in the liver?
stores vitamin A
76
What are the name of the macrophages responsible for removing bacteria and damaged red blood cells from blood?
Kupffer cells (they are located in the sinusoids)
77
What are sinusoids are lined with?
a thin fenestrated endothelium
78
Where is the perisinusoidal space (aka space of Disse) located in the liver?
between the fenestrated endothelium of sinusoids and hepatocytes
79
What is Bile produced by?
hepatocytes
80
What is the biliary pathway?
```
Canaliculi
Canal of Hering
Interlobular bile ducts
R or L Hepatic Duct
Common Hepatic Duct
Common Bile Duct
```
81
What components of bile are taken in to the intestine for reabsorption?
* Phospholipids (lecithin is an example) and cholesterol are metabolic substrates for other cells in the body.
* Bile salts (aka bile acids) act as emulsifying agents that aid in digestion and absorption of lipids from the gut and help to keep the cholesterol and phospholipids of the bile in solution.
* Electrolytes: Na+, K+, Ca2+, Cl-, HCO3-
82
What components of bile are taken in to the intestine for disposal?
Bile pigments, the end product of hemoglobin degradation from bilirubin.
83
What are the main functions of the gallbladder?
* Concentrates the bile and stores it during fasting.
* Secretion is stimulated by hormones from the small intestines.
Discharges bile into the cystic duct, then common bile duct, which carries it to the duodenum.
84
What is unique about the mucosa layer of the gallbladder?
has simple columnar epithelium but lacks a muscularis mucosae in mucosae layer
NOTE: Wall also lacks a submucosa
85
T or F. Muscularis externa of the gallbladder is
| irregularly arranged
T
86
How does the gallbladder concentrate bile?
achieved by removal of H2O.
• An osmotic gradient draws water from the lumen into the intercellular space between adjacent cells.
• Hydrostatic pressure forces water into lamina propria, and then into capillaries & venules.
87
What are gallstones and what are the types?
- Form when bile in the
gallbladder hardens into pieces of
stone-like material.
- Two types: cholesterol and
pigment stones
88
Is the pancreas an exocrine or an
| endocrine gland?
Both
89
What does the exocrine component of the pancreas do?
synthesizes and secretes enzymes and bicarbonate into ducts.
90
What does the endocrine component of the pancreas do?
synthesizes and secretes the hormones (insulin, glucagon, and the peptide, somatostatin) into the blood.
91
Where is the exocrine compartment of the pancreas located?
in the acinar pancreas
92
Where is the endocrine compartment of the pancreas located?
located in the islets of Langerhans
93
Describe the organization of the exocrine component of the pancreas
Structurally organized into acini (alveoli) - have serous cells.
Acini cells have zymogen granules, which are inactive digestive enzymes:
• proteolytic,amylolytic, lipases, and nucleolytic enzymes.
• Acini cells secrete into the duct system for transport to the intestines, where enzymes become active.
94
Describe the organization of the duct system of the exocrine component of the pancreas
• Pancreas acini secrete about 1 L/day.
• Within acini, centroacinar cells initiate intercalated ducts
– add water and bicarbonate to secretion
• The hierarchy of ducts is intercalated > intralobular > interlobular > main pancreatic duct!
95
What are intercalated ducts made of?
squamous cells
96
What are intralobular ducts made of?
Cuboidal or low columnar cells
97
What are interlobular ducts made of?
low columnar, lots of CT, located between lobules
