What are permanent folds of the mucosa and submucosa; most prominent in the proximal jejunum?
What are permanent folds of the mucosa?
Plicae circularis
Villi
Describe:
Left: Plicae Circularis
Right: Villi on the plicae circularis
In the small intestines, glands and crypts don’t expand deeper than muscularis mucosae except in the ?
duodenum
What 4 major items extend into each villi on the plicae circularis?
arteries, veins, lacteals, muscularis mucosae (for tone)
What are the 2 most common cells on the villi and along crypts in the small intestines?
- Enterocytes — absorptive, columnar cells with microvilli (most common)
- Goblet cells — mucous cells
What cell secrets lysozyme and defensins; contribute to the innate immune system and are found in the fundus of crypts in the small intestines?
Paneth cells
Where are the enteroendocrine cells located in the small intestine and what do they do?
Villi and crypts
paracrine/endocrine functions
What cell type allows for transcellular passage of particles, microorganisms, to facilitate the exposure of antigens to the underlying lymphoid tissues and where would these cells be located?
M (microfold) cells
GALT, Peyer’s patches, lymphoid nodules
Where are stem cells mostly located in the small intestine?
in the crypts
What is pictured here?
Villi in small intestine (mostly lined by enterocytes and goblet cells)
Describe the photos?
Enterocytes and Goblet cells along villi
enterocytes at the bottom
brush border
Enterocytes and Lipid Processing
- Lipids metabolized in the and diffuse across of the microvilli
- Products move into smooth ER and resynthesized into
- Triglycerides processed by Golgi and rough ER into
- Chylomicrons released pass through the basement membrane and enter lacteal ducts
lumen, plasmalemma
triglycerides
chylomicrons
laterally
What cell is located in the fundus of this crypt in this gland?
Which enteroendocrine cell relies on outside info from other cells or blood and which can “taste” or sample lumen contents and respond accordingly?
Closed enteroendocrine cell
open enteroendocrine cell
What type of malignancy would from from enteroendocrine cells?
carcinoid tumors
Review diagram:
Why do the M (Microfold) cells have small openings?
To bring in Antigens for the cell mediated immune system
Take note of the primary and secondary lymphoid nodules in the Peyer’s patches. Which lymphoid nodule demonstrates an active immune response?
What cell is being described?
What cell is being described?
mucous cell
What cell type is being described?
secrets isozymes and defensins; part of innate immune system
What 3 cells are being described and what are their functions:
What submucosal glands occur only in the proximal portion of the duodenum with secretory cells that are lightly-staining?
From these characteristic, what can you infer about its secretory product and function?
The secretory cells secrete an alkaline mucous that function to neutralize the acidic chyme passing into the duodenum from the pylorus (of the stomach)
Which layer of intestine is pictured here?
Muscularis externa
Which of these is the duodenum, jejunum, and lleum and what distinguishes them as such?
from L to R
Duodenum: Brunner Glands in the submucosa
Jejunum: Largest and most plicae circularis
ileum: smaller and fewer plicae circularis and Peyer;s patches
A 35-year-old woman reported to her primary care physician that she has been experiencing intermittent abdominal discomfort and soft stool and diarrhea for the past year. The frequency and severity of these episodes has gotten worse over the past few months. A biopsy of the small intestines is ordered and the pathology report reveals the presence of chronic inflammatory damage in all layers of the intestinal walls. Based on these initial findings, which of disease would this patient most likely have? Explain:
Celiac or Chrohns
Crohn’s dz
Although chronic inflammation and the resulting damage is shared by both diseases, the inflammation related to Crohn disease, which is caused by multiple factors that are not fully understood, can occur in any or all layers of the intestinal wall. Inflammation from celiac disease (a.k.a. celiac sprue), which is caused by an immune response to gluten and other wheat protein, is typically limited only to the mucosal layer, especially the absorptive enterocytes
Review this diagram of the large intestine:
What are the 3 main functions?
storing
compacting
absorbing water
What are the 4 main cell types and their functions in the large intestine?
- Colonocytes — fluid-absorptive, columnar cells with microvilli
- Goblet cells — mucous cells
- Enteroendocrine cells
- Stem cells — pluripotent cells
(no large villi or plicae circularis)\
(lumen with intestinal glands)
Small intestine or large intestine?
large intestine
Review the slides of the large intestine (What is pictured on the top right)?
Lumen ducts (tops slice off)
How does the muscularis externa of the large intestine differ from the small intestine?
The longitudinal external layer is concentrated in 3 spots longitudinally on the side called the tenia coli
They sometimes penetrate the circular inner layer to form pouches of haustra
During a colonoscopy of a 63-year-old male, numerous pouches (out-pocketing) are observed in the colon wall (see images on next slide). What is the name for these physical findings?
Diverticula
Are these pouches (diverticula) symptomatic, in and of themselves? Explain
In and of themselves, diverticula do not necessarily cause any problems and can be asymptomatic. However, if fecal matter get impacted, or immobilized, within the diverticula, it can irritate the mucosa and lead to localized inflammation, infections, or hemorrhaging/ischemia (if the diverticula impacts blood flow).
What is the difference between a true diverticulum and a pseudodiverticulum?
True diverticulum involves all layers of the intestine (which includes the muscularis externa)
Pseudodiverticulum does not involve the muscularis externa
Which part of the large intestine is loaded with lymphoid nodules and possibly housed the healthy microbiome?
the appendix
Sensory endings in the anal canal can distinguish between solids, liquids, and ?
And where are these sensory endings mostly located?
gas
near the pectinate line
What are the differences of the internal and external anal sphincters?
Muscle type
nerves
the internal anal sphincter is a continuation of the smooth muscle of the inner circular muscle layer of the muscularis external and is innervated by the pelvic splanchnic nerves
the external anal sphincter is somatic skeletal muscle and is innervated by the pudendal nerve
What is the rectoanal junction (anal transition zone)?
The transition from columnar epithelia above the pectinate line to keratinized squamous epithelia below the pectinate line
How do external vs. internal hemorrhoids differ in their source, sensory innervation, and presentation in a patient?
External hemorrhoids arise from the external rectal plexus (inferior to the pectinate line) and are innervated by somatic afferent neurons (pudendal nerve). They are typical visible at the periphery of the anus and painful.
Internal hemorrhoids arise from the internal rectal plexus (superior to the pectinate line) and are innervated by visceral afferent neurons (pelvic splanchnic nn). When they are small, they are not visible and do not cause any pain.
