Histology of the Digestive Tract: Week 1 Flashcards
Purpose of digestive tract…
obtain molecules needed for energy and materials for growth & bodily functions
Function of digestive tract
ingestion
mastication
movement
secretion
release of hormones
digestion
absorption
elimination
List the order of the general plan of the digestive tract
moving from innermost layer to outermost
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
The mucosa layer consists of…
serves as protective barrier btwn tract contents & surrounding tissues
- Epithelium (non-keratinized stratified squamous)
- Lamina propria
- Muscularis Mucosae
- contains blood vessels lymphatics, collagen & some SM, occassional glands
- SM layer controlling movement of mucosa
The submucosa layer consists of…
large lymph vessels & autonomic nerve plexus called the submucosal (Meissner’s) plexus; occasional glands and lymphoid tissue exists
layer of CT containing collagen
Muscularis (externa) consists of…
- inner circular layer & outer longitudinal layer; both SM
- 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
What is the Serosa?
- 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
What are the anatomical regions of the digestive tract, including the accessory glands?
- Oral Cavity
- Esophagus
- Stomach
- Small Intestine
- Colon (Large Intestine)
- Anal Canal
Unique features of the digestive tract: Esophagus
muscular tube ___cm in length (adults)
role=
Has 4 layers which are__
- 25
- transport food from oral cavity/pharynx to stomach
- Mucosa, Submucosa, Muscularis (externa), Serosa
refer to slide 11 for histology image
Unique features of the digestive tract: Esophagus & layers
What makes up esophageal mucosa?
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
Unique features of the digestive tract: Esophagus & layers
What makes up esophageal submucosa?
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
Unique features of the digestive tract: Esophagus & layers
What makes up the muscularis externa?
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
Unique features of the digestive tract: Stomach
most ___ part of the DT
Role =
- 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
What is the Esophagogastric junction?
- 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
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
- cardia: transition zone between the esophagus and the rest of the stomach
- fundus: the part that extends upward above the level of the cardiac notch
- body: the main part of the stomach
- 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
Unique features of the digestive tract: Stomach
What are the 3 histological regions of the stomach?
refer to slide 20 for image
- cardiac stomach: small area where the esophagus empties into the stomach (containscardiac glands)
- fundic stomach: the main part of the stomach (includes both “fundus” and “body”), and is the primary region histologically (contains gastric or fundic glands)
- pyloric stomach: terminal part of the stomach (contains pyloric [mucous] glands)
Unique features of the Esophagogastic junction: mucosa
What makes up the Esophagogastric junction mucosa?
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
Cells of the Esophagogastric junction (in mucosa)
Surface mucous cells are…
- located in the pits
- secrete alkaline substance called “visible mucus” –> protects stomach from damage by abrasion and stomach acid
Cells of the Esophagogastric junction
Mucous Neck cells are…
(located in the neck region of the glands) secrete “normal” mucus under vagal stimulation
Cells of the Esophagogastric junction
Parietal cells are…
(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
Cells of the Esophagogastric junction
Chief cells are…
(located deep in the glands) secrete pepsinogen (which is converted to pepsin when it contacts stomach acid) and gastric lipase
Cells of the Esophagogastric junction
Enteroendocrine cells are…
(located in the glands) secrete paracrine factors or hormones that stimulate gastric function
Cells of the Esophagogastric junction
Stem cells are…
(found in both pits and glands) undergo mitoses to produce all the other epithelial cell types
Unique features of the Esophagogastic junction: mucosa
Lamina propria
- 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
Unique features of the Esophagogastic junction: mucosa
Muscularis mucosae
- a distinct band of smooth muscle that separates the mucosa from the submucosa
Unique features of the Esophagogastic junction: submucosa
What makes up the submucosa?
- typical; contains large blood vessels, lymphatics, lymphoid cells
- includes the submucosal (Meissner’s) plexus
Unique features of the Esophagogastic junction: muscularis externa
What makes up the muscularis externa?
- 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
Unique features of the Esophagogastic junction: serosa
What makes up the serosa?
- peritoneum (abdominal serosa) covers the outer surface of the stomach
Unique features of the Small Intestine:
What is the small intestine and its feautrues?
- 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
Unique features of the Small Intestine: Mucosa
What are the features of the small intestine?
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
Unique features of the Small Intestine: Mucosa
What kind of epithelium is the small intestine mucosa made of and what cells are present?
▪ 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
Unique features of the Small Intestine: Mucosa
Goblet cells are…
interspersed between the enterocytes
Unique features of the Small Intestine: Mucosa
Paneth cells are…
located in the base of the crypts, contain large eosinophilic granules that contain lysozyme, phospholipase A2 and defensins; play a role in innate immunity
Unique features of the Small Intestine: Mucosa
Enteroendocrine cells are…
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)
Unique features of the Small Intestine: Mucosa
M (microfold) cells are…
⬥ 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
Unique features of the Small Intestine: Mucosa
Lamina propria
▪ 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
Unique features of the Small Intestine: Mucosa
Muscularis mucosae
separates the lamina propria in the villi from the submucosa in the plicae
Unique features of the Small Intestine: Submucosa
Characteristics of Small intestine submucosa…
- 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
Unique features of the Small Intestine: Muscularis externa
muscularis externa…
- inner circular and outer longitudinal layers separated by the myenteric plexus
Unique features of the Small Intestine: serosa
Small intestine serosa unique features are…
- the mesothelial covering of the small intestine (visceral peritoneum) is continuous with the mesothelium that makes of the mesentery of the small intestine
Unique features of the Large Intestine (Colon):
What are the 6 regions/subdivisions of the Large intestine?
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)
Unique features of the Large Intestine (Colon):
What is the primary role of the Large intestine?
- the primary roles of the colon are to reabsorb water and electrolytes, and to form fecal matter (feces) from indigestible food materials
Unique features of the Large Intestine (Colon): Mucosa
Features of the epithelium…
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
Unique features of the Large Intestine (Colon): Mucosa
Features of the Lamina Propria…
between the crypts, typical components, but rich in MALT (lymphoid tissue)
Unique features of the Large Intestine (Colon): Mucosa
Features of the Muscularis mucosae…
typical, forms the boundary between mucosa and submucosa
Unique features of the Large Intestine (Colon): Submucosa
Features of the submucosa…
typical
locate in notes the typical submucosal features
Unique features of the Large Intestine (Colon): Muscularis externa
Features of the Muscularis externa…
a) inner circular layer as normal
b) outer longitudinal layer confined to three longitudinal bands of muscle, called teniae coli
Unique features of the Large Intestine (Colon): Anal Canal
Features of the anal canal…
- 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
