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Histo second semester 23-24 > Histo block II: digestive tract > Flashcards

Histo block II: digestive tract Flashcards

digestive tract

1
Q

The digestive tract and associated glands is composed of?

A

*mouth and oral cavity
*esophagus
*stomach
*small intestines (duodenum, jejunum, ileum)
*large intestine (with cecum, appendix, rectum and anus)

*salivary glands
*liver (gall bladder)
*Pancreas

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2
Q

What is the primary function of the digestive system?

A

The primary function of the digestive system is to obtain from ingested foods the metabolites necessary for the growth and energy needs of the body, and to eliminate the undigested residue.

Both secretion (enzymes, bile, HCl) and absorption (metabolites, water, minerals) are important for this function.

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3
Q

What are the layers of the wall of tubes in de digestive tract?

A

*Mucosa = Epithelium + lamina propria + muscularis mucosa

*Submucosa = loose or dense irregular CT

*Muscularis externa = 2 - 3 layers smooth muscle

*Serosa or Adventitia = CT (adventia) or CT + mesothelium (serosa)

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4
Q

What are the plexuses in the enteric nervous system?

A

*Meissner’s plexus - submucosa
*Myenteric (Auerbach’s) plexus- between layers of muscularis externa

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5
Q

identify

A

Scanning EM showing the complex of neuronal ganglion cells in the myenteric plexus

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6
Q

identify

A

Low magnification and high magnification light micrographs of sections through the small intestinal wall showing the myenteric plexus of the enteric nervous system

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7
Q

What is GALT?

A

Gut associated lymphatic tissue

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8
Q

WHat are the components of GALT?

A

*IgA dimers(secretory immunoglobulin)- secreted into lumen

*diffuse lymphatic tissue - lymphocytes, granulocytes, plasma cells, mast cells, macrophages in lamina propria

*isolated lymphatic nodules

*M-cells over lymphatic nodules

*Peyers Patchs in ileum

*Langerhans cells in esophageal epithelium

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9
Q

What is the major histologival difference of the digestive tube segments?

A

epithelium and its arrangement and in the muscle arrangement in the muscularis externa

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10
Q

digestive tube is lined by a

A

simple columnar epithelium, Except for oral cavity, oral pharynx, esophagus, and opening of anus

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11
Q

explain the specialization of the epithelium of digestive tract

A

The epithelium of the digestive tract can be specialized for resistance to abrasion (oral cavity and esophagus- stratified squamous epithelium), secretory or glandular activity (simple columnar), or for absorption (simple columnar).

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12
Q

explain the muscle arrangement in muscularis externa

A

may be specialized for churning/agitation (segmental contractions) or propulsion of the contents along the tube) (peristaltic contractions), or most commonly both. Typically 2 layers: an inner circular and outer longitudinal layer are present except in stomach with an additional inner obliques and colon with taenia coli.

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13
Q

Primary function of esophagus and embryological origin?

A

conduit from oral cavity & oral pharynx to stomach.

Foregut.

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14
Q

describe epithelium of esophagus

A

*Epithelium: a non-keratinized stratified squamous epithelium

*Muscularis externa = both skeletal muscle and smooth muscle. Skeletal muscle in upper 1/3, mixed skeletal and smooth muscle in middle 1/3, smooth muscle only in bottom 1/3

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15
Q

what are the glands in the esophagus

A

1.Esophageal glands proper in submucosa secrete a slightly acidic mucus which acts as a lubricant.
2.esophageal cardiac glands in lamina propria near stomach secrete a neutral mucus which may help protect esophagus from stomach acid

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16
Q

identify

A

Micrograph of cross-section of esophagus and its layers

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17
Q

identify

A

Micrograph of esophagus and its layers

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18
Q

describe th elayers of esophagus (muscularis externa)

A

Upper one-third of esophagus has skeletal muscle only in muscularis externa
Middle one-third of esophagus has mixed smooth and skeletal muscle
Bottom one-third of esophagus has smooth muscle only

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19
Q

identify

A

Low magnification and high magnification light micrographs of sections through the muscularis externa of the middle 1/3rd of esophagus showing both smooth muscle (SM) and skeletal muscle (SK).

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20
Q

what is the epithelium of the junction of the esophagus and stomach?

A

Change from stratified squamous non-keratinized epithelium of esophagus to simple columnar epithelium of stomach glands

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21
Q

identify

A

Junction of the esophagus on right with stomach on left

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22
Q

identify

A

Junction of the esophagus on right with stomach on left

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23
Q

What are the anatomical parts of the stomach, histological and its embryologic origin?

A

Anatomically = cardiac, fundic, corpus, and pyloric regions
Histologically = cardiac, fundic/corpus, pyloric
Embryological Origin = foregut

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24
Q

what are the orimary functions of the stomach?

A

*mechanically fragment & mix food with acid and digestive enzymes
*digestion by HCl and pepsin
*storage of food

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25
Q

what are th ehistological features of the stomach

A

*Simple columnar epithelium
*rugae = folds when nondistended
*mucosa containing glands
*muscularis externa - additional inner oblique layer

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26
Q

describe the rugae of stomach and function

A

The rugae of the stomach are folds in the wall of the stomach that are present when it is non-distended in the absence of food.

They are non-permanent folds that disappear when the stomach is filled with food

They function to allow expansion of the surface area and volume of the lumen of the stomach to accommodate the intake and accumulation of food following the eating (ingestion) of a meal

Note that they differ from the permanent folds called plicae circulares found in the wall of the small intestine

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27
Q

what glands are present in the mucosa of stomach?

A

1.The cardiac glands located in the cardiac region of the stomach
2.The fundic glands located in the fundic/corpus region of the stomach
3.The pyloric glands located in the pyloric region of the stomach

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28
Q

What characteristics does the cardiac, fundic and pyloric glands share?

A

*Gastric pit = funnel shaped opening to gland lined by mucus-secreting cells.

*Isthmus = short segment at base of gastric pit which is the site of stem cells.

*The main gland (secretory portion) frequently divides into 2 or 3 branches & consists of :
neck segment containing secretory cells & mucus neck cells. This is typically relatively long region

fundic segment containing secretory cells

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29
Q

What is the gastric pit and its function

A

Gastric pit = funnel shaped opening to gland. Lined by surface mucous cells which secrete a viscous mucus plus bicarbonate.

This alkaline mucus functions to protect the epithelial cells and wall of stomach from damage by acid and proteolytic enzymes in lumen

Prostagladins (PGE2) stimulate secretion of both mucus and bicarbonate.

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30
Q

identify

A

Micrographs of gastric glands in pyloric (left) and fundic (right) regions of stomach showing gastric pits and lumen of stomach lined by surface mucus cells

31
Q

what are mucous neck cells and function

A

Mucous neck cells make a soluble less viscous and less alkaline mucus than do the surface mucus cells

They are located in the long neck segment of all the gastric glands (cardiac, fundic, and pyloric glands) but are often most easily seen in fundic glands

The mucus most probably helps protect the epithelial cells in the gland

32
Q

idenitfy

A

mucous neck cells

33
Q

describe GLANDS IN CARDIAC & PYLORIC REGIONS:

A

Secretory portion in both regions contains mucous secreting cells as the primary secretory components of the gland & occasional enteroendocrine cells.

The pits in the pyloric region are longer than in cardiac region & make up ~50% of height of gland.

The secretory cells in pyloric region resemble the surface mucous cells; those in the cardiac region resemble esophageal cardiac gland cells

Mucus neck cells in pyloric region also secrete lysozyme.

34
Q

identify

A

Micrograph of cardiac glands

35
Q

identify

A

Micrograph of pyloric glands

36
Q

describe GLANDS IN CORPUS/FUNDIC REGION (Oxyntic Glands):

A

These glands are typically referred to as the fundic glands of the stomach

The Major Secretory portion - contains two additional cells:
-parietal cell (oxyntic cell) which stains very eosinophilically
-chief cell located near the base of the gland stains very basophilically.

Thus differs from cardiac and pyloric segments which have only mucous secreting cells

37
Q

identify

A

Micrograph of section through fundic stomach showing the parietal (large round eosin-staining cells and basophilic chief cells at base of glands

38
Q

idenitfy

A

Fundic glands in the fundic/corpus region of the stomach

39
Q

characteristics of parietal cells

A

large rounded acidophilic cells

Contain an intracellular canaliculus & tubulovesicular system

Large numbers of mitochondria

40
Q

identify

A

Medium and high magnification images of fundic stomach showing the large round eosinophilic parietal cells

41
Q

what are the function of the parietal cells

A

Secrete:
*HCl - for digestion & for setting pH optimum for pepsin.
Secretion of acid involves H+, K+ ATPase pump & the exchange of K+ (external) for H+ (internal), and the secretion of Cl- ion. Stimulation of receptors for gastrin, histamine-H2, or acetylcholine M3 activates secretion. Gastrin is the main regulator.

*(gastric) intrinsic factor - cofactor for absorption of vitamin B12 in ileum. Lack of vitamin B12 gives pernicious anemia

42
Q

INTRACELLULAR CANALICULIS & TUBULOVESICULAR SYSTEM OF PARIETAL CELLS

A

Inactive to Active Cell Transition:
Tubulovesicular system is prominent in cytoplasm of inactive cell, but disappears in active cell. It is thought that the tubulovesicular system provides extra membrane for increasing surface area of intracellular canaliculus & thus for secretion.

43
Q

identify

A

Electron micrograph of active parietal cell

44
Q

identify

A

Electron micrograph of parietal cell tubulovesicular system

45
Q

Clinical Considerations: Intrinsic Factor & Vitamin B12 Deficiency

A

A number of different conditions can result in the destruction of the gastric mucosa and the loss of the parietal cells and a deficiency of their secretion of gastric intrinsic factor. This leads to a deficiency of vitamin B12 absorption in the ileum and pernicious anemia. In addition, deficiency of vitamin B12 is associated with improper myelination in the nervous system and has been linked to changes in gait, equilibrium, and mental confusion that can mimic dementia and Alzheimer’s disease.

Factors leading to loss of parietal cell function and a lack of intrinsic factor resulting in vitamin B12 deficiency include:
-Achlorhydria: a chronic autoimmune disease characterized by destruction of the gastric mucosa
-Peptic ulcer disease: often associated with chronic infection by Helicobacter pylori bacterium
-Tape worm or other parasitic infections
-Administration of histamine H2 receptor-antagonist drugs: to block acid secretion also block intrinsic factor secretion
-Partial or total gastrectomy

46
Q

What are the characteristics of chief cells?

A

Basophilic staining cells at the base of the fundic glands. Characterized by apical secretory granules near the lumen of gland and basophilic-staining cytoplasm in the basal portion of cell

47
Q

identify

A

High and medium magnification images of fundic stomach showing basophilic staining chief cells at base of glands

48
Q

identify

A

High and medium magnification images of fundic stomach showing basophilic staining chief cells at base of glands

49
Q

identify

A

Low magnification TEM image of typical protein secreting cell with basal RER and apical secretory granules

50
Q

identify

A

High magnification image of fundic stomach showing basophilic staining chief cells at base of glands with apical secretory (zymogen) granules

51
Q

function of chief cells

A

Secrete the enzymes:
pepsin - protease for digestion proteins. Released in inactive form called pepsinogen. Pepsinogen converted to pepsin by the acid in the lumen of the stomach.
gastric lipase – Unlike most of the pancreatic lipases, this lipase can enter into and breakdown the fat droplets in breast milk, and therefore is essential for the newborn.

52
Q

What are enteroendocrine cells in GI?

A

Enteroendocrine cells are isolated endocrine or neuro-endocrine cells found within the epithelium of the GI tract

Based upon staining properties and/or functional properties they have also been called: Argentaffin or Chromaffin Cells, amino-precursor-uptake and decarboxylation cells (APUD cells), and diffuse neuroendocrine system cells (DNES Cells)

As a group they synthesize and release more than 20 different endocrine or neuroendocrine molecules

Although they constitute only approximately 1% of the epithelial cells in the digestive tract, as a whole they represent the largest endocrine organ in the body

53
Q

Where are enteroendocrine cells located and what do they seecrete?

A

the enteroendocrine cells are typically located at the base of the glands.

They secrete a number of endocrine products or neuroendocrine including:
*serotonin (EC cells in fundic) - stimulates gut motility
*gastrin (G-cells in pyloric) - stimulates parietal cells to secrete acid
*somatostatin (D-cells in pyloric) - inhibits release other hormones including gastrin
*ghrelin (Gr-cells) – appetite stimulation

54
Q

identify

A

Medium magnification image of fundic stomach showing basophilic staining chief
cells at base of glands and the clear enteroendocrine cells among them. Note that
the enteroendocrine cells sit basally in epithelium

55
Q

what are the functions of enteroendocrine cells and the types

A

Some of these cells have a paracrine mode of secretion where the primary target are local cells e.g. somatostatin

Cells basally located in epithelium (away from lumen) with basal neuro-secretory granules

Are of 2 types:
*“closed” cells which do not reach lumen and “open” cells which do.

56
Q

identify

A

Electron micrograph of enteroendocrine cell in stomach epithelium

57
Q

explain Zollinger ellison syndrome

A

Zollinger-Ellison syndrome or gastrinomas is characterized by excessive secretion of hydrochloric acid (HCl) by continuously stimulated parietal cells. The acid cannot be completely neutralized in the duodenum leading to both gastric and duodenal ulcers.
The syndrome results from excessive secretion of gastrin from the neuroendocrine secreting G-cells located in the duodenum or in the pancreatic islets of Langerhans; typically because of a tumor of these cells.
Gastric ulcers are present in 95% of patients with this syndrome and are 6 times more prevalent than duodenal ulcers. Patients typically, experience intermittent abdominal pain, diarrhea, and excretion of stool containing large amounts of fat.
Normally treated with proton pump inhibitors and removal of the tumor if possible.

58
Q

explain TURNOVER-TIME OF CELLS IN STOMACH

A

Although most of the cells of the stomach glands derive from division of stem cells in the isthmus region of the glands, the turnover-time of the cells varies:

Surface mucous cells: Have the shortest turnover-time at 3-5 days. Probably because of their constant exposure to the acidic and protease environment in the lumen of stomach

Mucous neck cells: About 6 days, also because of their increased exposure to the acid and protease activity

Chief cells and parietal cells: Deeper in the fundic glands they have a longer turnover-time. Chief cells have a turnover-time of 60-90 days; while parietal cells have a turnover-time of ~150-200 days

59
Q

Small instetine is divided into:

A

duodenum = foregut (initial section)
jejunum = midgut
ileaum =midgut

60
Q

histological feature of small intestine

A

Permanent folds called plicae circulares. These folds have a large central core of submucosal CT. Thus both mucosa & submucosa form these folds.

mucosal projections called villi

mucosal glands (crypts of Lieberkuhn)

Simple columnar epithelium with absorptive cells called enterocytes

61
Q

identify

A

Micrographs of jejunum showing plicae circulares at low magnification (top panel), villi and intestinal glands (bottom left) and intestinal epithelium (bottom right

62
Q

functions of small intestine

A

*
Site for final stages of digestion - by enzymes and bile from pancreas & liver & by enzymes on glycocalyx and microvillar membrane.
*
Major site of absorption of metabolites.
Note that the plicae circulares, villi, and the microvilli on surface of enterocytes all act to provide an enormous increase of surface area in small intestine for digestion and absorption

63
Q

function and localization of villi

A

*
The villi project out from the surface of the small intestine thus increasing surface area for absorption.
*
The crypts of Lieberkuhn are glands invaginating into the CT from the surface

64
Q

identify

A

Micrograph of small intestine showing villi and the crypts of Lieberkuhn intestinal glands

65
Q

what are the cells present in the villi

A

Enterocytes (columnar absorptive cells) - the main absorptive cell

Goblet cells - unicellular mucous gland. Mucous both for protection & lubrication

M-cells – modified enterocytes associated with regions in which have underlying lymphatic nodules

Enteroendocrine cells - occasionally

66
Q

identify

A

Low magnification image of intestinal villus

67
Q

identify

A

low magnification micrographs of small intestine showing the intestinal epithelium lining the villi

68
Q

identify

A

high magnification micrographs of small intestine showing the intestinal epithelium lining the villi

69
Q

SPECIALIZATIONS OF ENTEROCYTE PLASMA MEMBRANE

A

Apical Specializations
Microvilli (on LM striated or brush border) with a core of actin filaments

Glycocalyx = carbohydrate coating on surface of microvilli that functions for protection & site of final digestive enzymes for disacharides & dipeptides

Lateral Specializations

Junctional complexes that seal intercellular space, such that active transport can occur in the lateral membranes below junction to pump water, ions, and absorbed metabolites into this space, & their subsequent movement into capillaries & lymphatics in lamina propria

70
Q

enterocytes explain

A

Major function is the absorption of nutrients

Specific transporter molecules associated with the microvillus plasma membrane and glycocalyx play a key role in the breakdown and/or absorption of dipeptides, tri-peptides, disaccharides, and lipids. Following absorption, amino acids, sugars, nucleotides, other small molecules move into blood capillaries; while lipid chylomicron particles into central lacteals.

Dipeptides, tripeptides, amino acids, sugars, nucleotides, other small molecules >Absorbed by cells > Blood Capillaries

Lipids > Broken down into fatty acids & glycerol > Absorbed by cells > Reassembled into lipids combined with protein to form chylomicron particles >
Central Lacteal (Lymphatic Capillary

71
Q

explain celiac disease

A

Gluten-Sensitive Enteropathy (Ciliac Disease)

Celiac disease is characterized by a chronic inflammation and damage of the small intestine epithelium which results in a reduction in the number of finger-like projections (villi) of the inner intestinal surface.

This is thought to result from an autoimmune reaction against gluten (also prolamin and glutelin) which is present in many grains. Gluten has cross-reactivity with a plasma membrane protein in the enterocytes. If gluten gets past the zonula occludins junction and down into the CT, it can cause T-lymphocytes to mount an autoimmune attack on the enterocytes resulting in their destruction. This can result in malabsorption of nutrients

72
Q

idenitfy

A
73
Q

function of goblet cells

A

Mucus from goblet cells serves to protect the cells lining the intestine from digestive
enzymes and to lubricate the passage of the partially digested food. Characterized by
apical mass of mucus granules, and narrow basal region with extensive RER &
mitochondria. Well developed Golgi just apical to nucleus

74
Q

describe cells of crypt

A

goblet cells - fewer than on villi

paneth cells - at base of crypts. Secrete lysozyme

Intermediate cells – most of the cells in lower half of gland. Can still divide & are in process of committing to become enterocytes or goblet cells

undifferentiated crypt stem cell - replenish other cells

enteroendocrine cells

Histo second semester 23-24 (19 decks)

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