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GINME > Week 1: GI Histology > Flashcards

Week 1: GI Histology Flashcards

1
Q

Identify

A
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2
Q

The mucosa consists of

A
  • consists of an epithelial lining (stratified squamous or columnar) an underlying lamina propria of loose connective tissue rich in blood vessels, lymphatics, lymphocytes and often containing small glands
  • and a thin layer of smooth muscle called the muscularis mucosae separating the mucosa from the submucosa and allowing local movements of the mucosa
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3
Q

The mucosa is also frequently called

A

a mucous membrane

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4
Q

Digestive accessory organs that empty into the GI tract

A
  • salivary glands
  • liver
  • gall bladder
  • pancreas
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5
Q

Layers of the GI tract

A
  • mucosa
  • submucosa
  • muscularis
  • serosa/adventitia
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6
Q

Mucosa structure

A

the mucosa consists of an epithelial lining (stratified or columnar) an underlying lamina propria of loose connective tissue rich in blood vessels, lymphatics, lymphocytes, and often containing small glands and a thin layer of smooth muscle called the muscularis mucosae separating the mucosa from the submucosa and allowing local movements of the mucosa

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7
Q

Submucosa structure

A

this layer is under the mucosa and is fibroelastic loose connective tissue

this layer contains larger blood vessels and lymphatics, often glands and an important network of nerves and ganglia belonging to the Autonomic nervous system (Submucosal or Meissner’s plexus)

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8
Q

Muscularis

A
  • With a few exceptions, the muscularis consists of smooth muscle with inner circular and outer longitudinal orientations
  • Between these layers theres is another network of nerves and ganglia known as the Myenteric or Auerbach’s plexus
  • Contractions of the muscularis which mix and propel the luminal contents forward (peristalsis) are generated and coordinated by the myenteric plexus
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9
Q

Adventitia AKA

A

Serosa

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10
Q

Adventitia or serosa

A

Connective tissue surrounding the muscularis externa

When facind the peritoneal cavity, distal esophagus, stomach, jejunum, ileum and parts of the large intestine, this connective tissue is encased with a thin layer of simple squamous epithelium known as the mesothelium

When mesothelium forms the outermost layer of the gut, the combined connective tissue and mesothelium is referred to as the serosa

The moist serosa performs an important function in allowing adjacent portions of the GI to come into contact and be able to slide over each with minimal abrasion

In non-peritonealized or retroperitoneal surfaces, such as the thoracic esophagus, duodenum and ascending and descending colon there are some areas that are devoid of this mucosal lining and only have connective tissue present

Here the outer tunic is referred to as adventitia

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11
Q

Identify

A
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12
Q

What is the esophagus?

A

A muscular organ that extends between the pharynx and the stomach mostly within the thoracic cavity

The empty esophagus is collapsed and thrown into longitudinal folds

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13
Q

Esophagus structure

A

It has the same basic structure as other portions of the GI Tract with a few differences

The mucosa is lined by thick nonkeratinized stratified squamous epithelium to withstand abrasion, also overlies a very thin lamina propria containing lymphocytes which appear as dark purple staining clusters) and a variably thick muscularis mucosa

Submucosa has mucous secreting glands and are known as esophageal glands, in the distal 8 cm of the esophagus the submucosal veins anastamose with branches of the portal vein

Muscularis externa the proximal 1/3 is skeletal muscle, middle 1/3 is a mix of skeletal and smooth muscle, and the distal 1/3 is smooth muscle

Adventitia/serosa the outermost layer of the thoracic portion of the esophagus is a loose connective tissue that blends into the surrounding tissues and is therefore classified as an adventitia

after passing through the diaphragm mesothelium covers this connective tissue and this connective tissue plus the mesothelium layer is referred to as serosa

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14
Q

Stomach main functions

A

digestion of carbohydrates initiated by the salivary enzyme amylase

acidic fluid to the ingested food and mixing its contents into a viscous mass called chyme by the churning activity of the muscularis

The continued digestion of triglycerides initiated by the pancreatic enzyme lipase

the initital digestion of proteins with the enzyme pepsin

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15
Q

Stomach anatomical divisions

A

fundus

cardia

body

pyloric antrum

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16
Q

Mucosa of the stomach

A

simple columnar epithelium consisting entirely of muucous secreting cells

the surface epithlium forms invaginations into the underlying lamina propria giving rise to the gastric glands

the branching gastric glands within the fundus and body open into gastric pits which empty their contents into the lumen of the stomach

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17
Q

Identify stomach

A
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18
Q

Identify stomach section

A
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19
Q

Cell types within the gastric glands

A

regenerative/stem cells

mucous cells

parietal cells

chief cells

enteroendocrine cells

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20
Q

Describe stomach regenerative cells/stem cells

A

Undifferentiated cells that give rise to the other cell types in the glands and the gastric pits

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21
Q

Describe stomach mucous cells

A

Line the lumen of the gastric pits and secrete a thick adherent and highly viscous protective mucous layer that is rich in bicarbonate ions

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22
Q

Describe stomach parietal cells

A

predominate in the upper segment of the gastric gland and produce hydrochloric acid, important for the conversion of pepsinogen to pepsin and intrinsic factor essential for the absorption of vitamin B12

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23
Q

Describe stomach Chief cells

A

Secrete the 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

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24
Q

Describe stomach Enteroendocrine cells

A

Several types that secrete hormones that give effects on gut motility (serotonin) and HCl secretion (gastrin)

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25
Q

The difference in glandular cells throughout divisions of the stomach

A
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26
Q

Identify stomach mucosa

A
27
Q

Identify stomach mucosa

A
28
Q

Submucosa of the stomach

A

there is a characteristic loose connective tissue with coarse collagen bundles

the increased thickness of this layer is responsible for the rugae of the mucosa

nerve supply including Meissner’s plexus is present

29
Q

Muscularis of the stomach

A

Three layers of smooth muscle are present including an inner oblique, middle circular and outer longitudinal

Auerbach’s/myenteric plexus is present between the outer 2 layers

30
Q

Serosa of the stomach

A

The stomach is completely surrounded by the mesothelium and so has an outer serosal layer

31
Q

Small intestine

A

The small intestine consists of a tube approximately 5-7 meters long divided into 3 regions

duodenum, jejunum and ileum

The small intestine continues digestion of chyme from the stomach using pancreatic enzymes and liver bile and absorbs the resulting nutrients

The msmall intestine contains all the usual layers (mucosa, submucosa, muscularis and serosa)

32
Q

Identify sections of small intestine

A
33
Q

Describe the luminal surface of the small intestine

A

the luminal surface of the small intestine is thrown into circular folds called plica that contain small finger like projections called villi (approximately 1.5 mm long)

The plica circulares and villi significantly increase the luminal surface area necessary for absorption of nutrients from the digested food

34
Q

Describe the mucosa of the small intestine

A

the epithelium of the small intestine is a simple columnar epithelium joined by extensive tight junctions several cell types are present including

enterocytes (absorptive cells)

goblet cells (mucus-secreting cells)

Paneth cells (lysozyme-secreting cells)

Enteroendocrine cells (hormone-secreting cells)

Stem cells (replace enterocytes and goblet cells every 3-5 days)

35
Q

Describe absorption in the small intestine

A

to further increase the surface absorptive area, each enterocytes is covered with numerous microvilli (brush border)

enterocytes absorb carbohydrates, proteins, lipids, vitamins, Ca2+ and Fe2+ from the lumen and transport these into the blood or lymph

36
Q

Describe the handling of carbohydrates in the small intestine

A

carbohydrates are digested to monosaccharides and transported to the portal blood

37
Q

Describe the handling of proteins in the small intestine

A

Proteins are digested to amino acids, dipeptides and tripeptides

some further digestion may occur in enterocytes and then amino acids are transported to the portal blood

38
Q

Describe the handling of triglycerides in the small intestine

A

triglycerides 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 are delivered to the portal blood

39
Q

Describe the handling of vitamin B12 in the small intestine

A

Water-soluble Vitamin B12 is absorbed in the ileum and requires intrinsic factor

40
Q

Describe the handling of Ca2+ in the small intestine

A

Ca2+ requires Vitamin D for absorption

41
Q

Identify small intestine section

A
42
Q

Goblet cells in the small intestine

A
  • Goblet cell are interspersed among the enterocytes covering the villi
  • These cells secrete mucus that provides lubrication throughout the small intestine
  • The further down the GI tract the greater the number of goblet cells to meet the need for increased lubrication of the luminal contents
  • Goblet cells appear clear in H&E stained sections
43
Q

Crypts of Lieberkuhn

A

The epithelium at the base of the vili invaginates into the lamina propria to form the short intestinal glands or Crypts of Lieberkuhn

44
Q

Identify

A
45
Q

What are paneth cells?

A

Paneth cells are found at the base of the crypt and stain a characterisitc orange-red color with H&E stain

Their color is due to the presence of numerous cytoplasmic granules filled with lysosome (an antibacterial substance) tumor necrosis factor-α TNF-α (a proinflammatory factor) and defensins (anti-bacterial and anti-parasitic)

These cells 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 rejuvenate the small intestinal epithelium

Dysfunction of Paneth cell biology contributes to the pathogenesis of chronic inflammatory bowel disease

46
Q

What are these?

A
47
Q

Enteroendocrine cells secretions

A

Cholecystokinin

Secretin

Gastric inhibitory peptide

glucagon-like peptide

48
Q

What is Cholecystokinin

A

Secreted by enteroendocrine cells in response to small peptides, amino acids and fatty acids in the gut lumen

stimulates secretion from pancreatic acinar cells and release of bile from gall bladder

49
Q

What is secretin?

A

Secreted by enteroendocrine cells in response to H+ and fatty acids in gut lumen

stimulates release of HCO3 from pancreas and biliary tract of the liver

50
Q

What is gastric inhibitory peptide?

A

Secreted by enteroendocrine cells in response to glucose, amino acids and fatty acids in the gut lumen

Stimulates insulin secretion from pancreatic islets

51
Q

What is glucagon-like peptide?

A

Released in response to glucose, amino acids and fatty acids in the gut lumen

Stimulates insulin secretion and inhibits glucagon secretion

52
Q

Brunner’s Glands

A

A specialized set of glands found only in the submucosa of the duodenum adjacent to the stomach.

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

53
Q

Peyer’s Patches

A

large numbers of lymphocytes critical for the immunological defense of the small intestine are found throughout the lamina propria

The highest concentration of lymphocytes will be present in the ileum as individual cells or as groups of lymphoid nodules referred to as Peyer’s PAtches

This is referred to as Gut Associated Lymphoid tissue (GALT)

54
Q

What is this?

A
55
Q

Myenteric plexus AKA

A

Auerbach’s plexus

56
Q

Myenteric plexus

A

As in other regions of the GI tract, components of the enteric nervous system can be found in the muscularis region

the myenteric plexus originates from neural crest cells and forms between the inner and outer layers of smooth muscle

57
Q

What is this?

A
58
Q

Large intestine

A

The colon or large intestine is a large diameter tube that absorbs about 4/5 of the water, Na+ Cl- from the fluid presemmted to it from the ileum concentrating and solidifying it to form feces

59
Q

Mucosa of the large intestine

A

The mucosa lacks villi and except in the rectum has no major folds

The mucosa consist of simple columnar epithelial cells which regularly invaginate to form tubular intestinal glands

A majority of the surface cells and cells of the glands are goblet cells

Undifferentiated stem cells are present within the bases of the glands and migrate upward to form the other cell types

Dispersed enteroendocrine cells may also be found within the mucosal epithelium

60
Q

IDentify large intestine section

A
61
Q

Muscularis of the large intestine

A

The muscularis of the colon has inner longitudinal and outer circular layers but differs from that of the small intestine, with fibers of the outer layer gathered into three separate longitudinal bands called teniae coli.

Intraperitoneal portions of the colon are covered by serosa which is characterized by small pendulous protuberances of adipose tissue called appendix epiploica

62
Q

Appendix

A

The appedix is a small blind-ended diverticulum of the cecum with layers similar to those of the large intestine

the characteristic features of the appendix are the accumulations of lymphoid tissue resent within the lamina propria

63
Q

Identify

A
64
Q
A

GINME (63 decks)

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