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Histology: Winter Quarter > Histology of the Digestive Tract: Week 1 > Flashcards

Histology of the Digestive Tract: Week 1 Flashcards

1
Q

Purpose of digestive tract…

A

obtain molecules needed for energy and materials for growth & bodily functions

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2
Q

Function of digestive tract

A

ingestion
mastication
movement
secretion
release of hormones
digestion
absorption
elimination

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3
Q

List the order of the general plan of the digestive tract

moving from innermost layer to outermost

A

Mucosa, Submucosa, Muscularis (externa), & Serosa

All areas of DT have the above, but serosa could be adventitia elsewhere

Despite the variations of dif locations of Digestive Tract (DT), certain structures throughout the regions are the same

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4
Q

The mucosa layer consists of…

serves as protective barrier btwn tract contents & surrounding tissues

A
  1. Epithelium (non-keratinized stratified squamous)
  2. Lamina propria
  3. Muscularis Mucosae

  1. contains blood vessels lymphatics, collagen & some SM, occassional glands
  2. SM layer controlling movement of mucosa
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5
Q

The submucosa layer consists of…

A

large lymph vessels & autonomic nerve plexus called the submucosal (Meissner’s) plexus; occasional glands and lymphoid tissue exists

layer of CT containing collagen

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6
Q

Muscularis (externa) consists of…

A
  1. inner circular layer & outer longitudinal layer; both SM
  2. Myenteric (Auerbach’s) autonomic nerve plexus (located in CT btwn inner & outer muscularis externa; made up of ganglion & nerve fibers)

Autonomic nerve plexus indicates presence of symp. & parasymp. ganglions

3 sections of esophagus:
1. upper 1/3 = skeletal muscle (INNERVATED BY SOMATIC NERVE FIBERS FROM VAGUS PLEXUS)
2. middle 1/3 = skeletal & smooth muscle
3. lower 1/3 = smooth muscle ONLY

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7
Q

What is the Serosa?

A
  • mesothelium covering (simple squamous serous epithelium) found in majority of digestive tract (DT)

in certain regions such as esophagus, the serosa is absent and the digestive tract is
covered by adventita

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8
Q

What are the anatomical regions of the digestive tract, including the accessory glands?

A
  • Oral Cavity
  • Esophagus
  • Stomach
  • Small Intestine
  • Colon (Large Intestine)
  • Anal Canal
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9
Q

Unique features of the digestive tract: Esophagus

muscular tube ___cm in length (adults)
role=
Has 4 layers which are__

A
  • 25
  • transport food from oral cavity/pharynx to stomach
  • Mucosa, Submucosa, Muscularis (externa), Serosa

refer to slide 11 for histology image

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10
Q

Unique features of the digestive tract: Esophagus & layers

What makes up esophageal mucosa?

A

epithelium = non-keratinized stratified squamous

lamina propria= typical

muscularis mucosae = longitudinal smooth muscle

NOTE: “cardiac” (mucous) glands are located in the lamina propria of the distal esophagus

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11
Q

Unique features of the digestive tract: Esophagus & layers

What makes up esophageal submucosa?

A

the submucosal (Meissner’s) plexus = made of ganglion cells and nerve fibers

glands (mostly mucous)

lymphocyte infiltrations are common

submucosa is dense irregular CT containing large vessels and lymphatics

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12
Q

Unique features of the digestive tract: Esophagus & layers

What makes up the muscularis externa?

A

circular layer and an outer longitudinal layer of muscle fibers

in the upper 1/3, middle 1/3, and lower 1/3 of the esophagus

the myenteric (Auerbach’s) plexus is located between the inner and outer layers of the
muscularis externa = consists of ganglion cells and nerve fibers (NOTE: the skeletal
muscle in the upper 1/3 of the esophagus is innervated by somatic nerve fibers coming from
the vagus)

refer to slide 14 for myenteric plexus histology

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13
Q

Unique features of the digestive tract: Stomach

most ___ part of the DT
Role =

A
  • Dialated
  • continue the digestive process:
  • carbohydrate –> mouth via salivary amylase
  • Proteins –> HCl & pepsin
  • Lipids –> gastric lipase
  • secretes intrinsic factor that binds vitamin B12; makes it available for absorption
  • mixes and partially digests ingested food, producing chyme, which then is ejected into the duodenum
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14
Q

What is the Esophagogastric junction?

A
  • abrupt transition from stratified squamous epithelium to simple columnar epithelium
  • cardiac glands are found in the lamina propria on both sides of the junction
  • while the mucosa of the esophagus has a fairly even surface, the mucosa of the
    stomach is characterized by pits

refer to slide 16 for histology image

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15
Q

Unique features of the digestive tract: Stomach

What are the 4 anatomic regions of the stomach?

refer to slide 18 for images of stomach & regions

A
  1. cardia: transition zone between the esophagus and the rest of the stomach
  2. fundus: the part that extends upward above the level of the cardiac notch
  3. body: the main part of the stomach
  4. pylorus: the terminal funnel-shaped part of the stomach that empties into the duodenum

inner walls have rugae = longitudinal folds allowing stomach to stretch out when filled

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16
Q

Unique features of the digestive tract: Stomach

What are the 3 histological regions of the stomach?

refer to slide 20 for image

A
  1. cardiac stomach: small area where the esophagus empties into the stomach (containscardiac glands)
  2. fundic stomach: the main part of the stomach (includes both “fundus” and “body”), and is the primary region histologically (contains gastric or fundic glands)
  3. pyloric stomach: terminal part of the stomach (contains pyloric [mucous] glands)
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17
Q

Unique features of the Esophagogastic junction: mucosa

What makes up the Esophagogastric junction mucosa?

A

epithelium: simple columnar, invaginates to form gastric pits (@ base of pits –> gastric glands, also made of simple columnar epithelium)

Cells: surface mucous cells, mucous neck cells, parietal cells, chief cells, enteroendrocrine cells, and stem cells

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18
Q

Cells of the Esophagogastric junction (in mucosa)

Surface mucous cells are…

A
  • located in the pits
  • secrete alkaline substance called “visible mucus” –> protects stomach from damage by abrasion and stomach acid
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19
Q

Cells of the Esophagogastric junction

Mucous Neck cells are…

A

(located in the neck region of the glands) secrete “normal” mucus under vagal stimulation

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20
Q

Cells of the Esophagogastric junction

Parietal cells are…

A

(located in the glands) are stimulated by parasympathetic innervation and by paracrine release of histamine and gastrin from enteroendrocrine cells

typically large and pyramidal or rounded in shape with a spherical nucleus, very eosinophilic cytoplasmic
➢ intracellular canaliculi opens to the lumen of the gland
➢ a tubulovesicular system is made up of membranes rich in proton pumps that can be inserted into the intracellular canaliculus to increase the surface area during acid secretion

21
Q

Cells of the Esophagogastric junction

Chief cells are…

A

(located deep in the glands) secrete pepsinogen (which is converted to pepsin when it contacts stomach acid) and gastric lipase

22
Q

Cells of the Esophagogastric junction

Enteroendocrine cells are…

A

(located in the glands) secrete paracrine factors or hormones that stimulate gastric function

23
Q

Cells of the Esophagogastric junction

Stem cells are…

A

(found in both pits and glands) undergo mitoses to produce all the other epithelial cell types

24
Q

Unique features of the Esophagogastic junction: mucosa

Lamina propria

A
  • connective tissue found between the pits and glands
  • in addition to the typical contents of lamina propria (fibroblasts, reticular fibers. some smooth muscle fibers), it often contains lymphoid cells
25
Q

Unique features of the Esophagogastic junction: mucosa

Muscularis mucosae

A
  • a distinct band of smooth muscle that separates the mucosa from the submucosa
26
Q

Unique features of the Esophagogastic junction: submucosa

What makes up the submucosa?

A
  • typical; contains large blood vessels, lymphatics, lymphoid cells
  • includes the submucosal (Meissner’s) plexus
27
Q

Unique features of the Esophagogastic junction: muscularis externa

What makes up the muscularis externa?

A
  • made up of three indistinct and partial layers:
    a) outer longitudinal layer
    b) middle circular layer
    c) inner oblique layer
  • these muscles serve to thoroughly mix the stomach contents with HCl and enzymes, producing chyme
  • the middle layer thickens at the pylorus to form the pyloric sphincter
28
Q

Unique features of the Esophagogastic junction: serosa

What makes up the serosa?

A
  • peritoneum (abdominal serosa) covers the outer surface of the stomach
29
Q

Unique features of the Small Intestine:

What is the small intestine and its feautrues?

A
  • the site where digestion is completed and nutrients are absorbed
  • about 5-6 meters in length
  • consists of three distinct regions:
    a) duodenum
    b) jejunum
    c) ileum
30
Q

Unique features of the Small Intestine: Mucosa

What are the features of the small intestine?

A

plicae circulares – circular folds in the walls of the intestine, covered by mucosa, with submucosa core
o the mucosa is arranged in finger-like projections called villi (sing. villus) that project into the lumen, between intestinal crypts (of Lieberkühn) which are pits extending below the surface
o both the villi and crypts are covered/lined with simple columnar epithelium

31
Q

Unique features of the Small Intestine: Mucosa

What kind of epithelium is the small intestine mucosa made of and what cells are present?

A

▪ simple columnar absorptive cells called enterocytes
⬥ oval basally located nucleus
⬥ apical end covered by brush/striated border made up of microvilli: ~3000/cell

  • cells = goblet cells, Paneth cells, Enteroendocrine cells, & M (microfold) cells
32
Q

Unique features of the Small Intestine: Mucosa

Goblet cells are…

A

interspersed between the enterocytes

33
Q

Unique features of the Small Intestine: Mucosa

Paneth cells are…

A

located in the base of the crypts, contain large eosinophilic granules that contain lysozyme, phospholipase A2 and defensins; play a role in innate immunity

34
Q

Unique features of the Small Intestine: Mucosa

Enteroendocrine cells are…

A

hormone-secreting cells that regulate digestive function

(see table 15-1 in the textbook for a list of cells, locations and hormones with their functions)

35
Q

Unique features of the Small Intestine: Mucosa

M (microfold) cells are…

A

⬥ located in the mucosa of the ileum overlying the Peyer’s patches
⬥ have a pocket formed of invaginated basolateral membrane that contains lymphocytes, macrophages and dendritic cells
⬥ capture intestinal microorganisms and antigens and transfer them to the immune cells that they shelter

36
Q

Unique features of the Small Intestine: Mucosa

Lamina propria

A

▪ forms the core of the villi, carrying blood, lymphatics, smooth muscle and nerves
▪ lacteals are special lymph capillaries in the middle of a villus that absorb fats and carry them to the venous system via the thoracic duct

37
Q

Unique features of the Small Intestine: Mucosa

Muscularis mucosae

A

separates the lamina propria in the villi from the submucosa in the plicae

38
Q

Unique features of the Small Intestine: Submucosa

Characteristics of Small intestine submucosa…

A
  • connective tissue forming the core of the plicae circulares, and separating the mucosa from the muscularis externa
  • large blood and lymph vessels, submucosal plexus
  • in the duodenum only, large mucous glands (Brunner’s glands are present –> secrete alkaline mucus that neutralizes acidic chyme coming from stomach)
  • Peyer’s patches (mucosa-associated lymphoid tissue or MALT), aggregations of lymph nodules, are present in the terminal part of the ileum
39
Q

Unique features of the Small Intestine: Muscularis externa

muscularis externa…

A
  • inner circular and outer longitudinal layers separated by the myenteric plexus
40
Q

Unique features of the Small Intestine: serosa

Small intestine serosa unique features are…

A
  • the mesothelial covering of the small intestine (visceral peritoneum) is continuous with the mesothelium that makes of the mesentery of the small intestine
41
Q

Unique features of the Large Intestine (Colon):

What are the 6 regions/subdivisions of the Large intestine?

A

is formed of 6 regions or subdivisions:
a) cecum – located in the lower right quadrant of the abdomen; the ileocecal valve is the point where the ileum empties into the cecum; the (vermiform) appendix is suspended from, and opens into, the cecum
b) ascending colon – located on the right side of the abdomen
c) transverse colon – crosses from the upper right quadrant to the upper left quadrant of the abdomen
d) descending colon – descends along the left side of the abdomen
e) sigmoid colon – named for its “S” shape, connects the descending colon to the rectum
f) rectum – terminal straight part of the colon, where feces are stored before evacuation (defecation)

42
Q

Unique features of the Large Intestine (Colon):

What is the primary role of the Large intestine?

A
  • the primary roles of the colon are to reabsorb water and electrolytes, and to form fecal matter (feces) from indigestible food materials
43
Q

Unique features of the Large Intestine (Colon): Mucosa

Features of the epithelium…

A

simple columnar epithelium made of absorptive cells (“colonocytes”) and a predominance of goblet cells lining intestinal crypts (NO VILLI, JUST CRYPTS!); these cells are interspersed with enteroendocrine cells, along with stem cells found in the bottom third of the crypts

NOTE: the appendix, and extension of the cecum, has abundant lymph nodules, and virtually no absorptive function

44
Q

Unique features of the Large Intestine (Colon): Mucosa

Features of the Lamina Propria…

A

between the crypts, typical components, but rich in MALT (lymphoid tissue)

45
Q

Unique features of the Large Intestine (Colon): Mucosa

Features of the Muscularis mucosae…

A

typical, forms the boundary between mucosa and submucosa

46
Q

Unique features of the Large Intestine (Colon): Submucosa

Features of the submucosa…

A

typical

locate in notes the typical submucosal features

47
Q

Unique features of the Large Intestine (Colon): Muscularis externa

Features of the Muscularis externa…

A

a) inner circular layer as normal
b) outer longitudinal layer confined to three longitudinal bands of muscle, called teniae coli

48
Q

Unique features of the Large Intestine (Colon): Anal Canal

Features of the anal canal…

A
  • distal end of the GI tract
  • the simple columnar epithelium of the rectum transitions to stratified squamous as rectum transitions to skin

we will not learn the other layers

Histology: Winter Quarter (3 decks)

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