Downing: Histology of Large Intestine, Rectum, Appendix, Pancreas and Gallbladder Flashcards
What are the functions of the LI?
Absorb water
Secrete mucous to lubricate dehydrated feces
What are the major histological features that distinguish the LI?
No villi
No plicae circularis
What are the major layers of the LI?
Mucosa--LP Submucosa Muscularis Serosa Adventitia
What are the 5 types of cells typically seen in mucosal glands?
absorptive columnar Goblet Enteroendocrine (DNES) Paneth (rare) STEM (replace cells every 5-6 days)
Is there a LP present in the mucosa of the LI? What does it contain?
Yes, but it’s not really evident b/c the crypts of lieberkuhn extend down to the muscularis
Lymphatic tissue (diffuse and nodular)
What do the large intestinal glands look like?
crypts of lieberkuhn
What does the submucosa of the LI look like?
similar to the SI
can contain lymph nodules extending from the LP
What does the muscularis of the LI look like?
inner circular layer
outer longitudinal forms taeni coli
Where is the serosa/adventitia present in the LI?
Ascending/descending- adventitia
Transverse- serosa
What are the taeni coli?
3 longitudinal bundles around the LI
How does the rectum appear histologically?
Similar to LI (6-8”)
NUMEROUS GOBLET w/ few columnar
What is the anal canal?
The last 1- 1 1/2” of the LI
How does the epithelium change in the anus?
Simple columnar> stratified sq non-keratinizing at the anus
What part of the anus is susceptible to varicosities?
submucosa that contains large VEINs
What forms the internal anal sphincter?
inner circular layer of smth muscle of hte musclaris externa
What forms the external anal sphincter?
skeletal muscle
Which sphincter provides voluntary control of defecation?
external anal sphincter
What are the histological features of the appendix?
- Mucosa= like LI
columnar, goblet, enteroendocrine, paneth, undifferentiated cells (like LI)
crypts of lieberkuhn are POORLY developed
LP contains MANY lymphocytes and lymphatic nodules - Submucosa
lymphatic nodules
fat - Muscularis
inner circular
outer longitudinal
taeni coli NOT present - serosa
What does the extrinsic nervous system do and what is it composed of?
Modulates the INTRINSIC innervation
Composed of (autonomic NS):
- Sympathetic supply- inhibits gut activity
- parasympathetic supply- stimulate gut activity
What is the diff between the sympathetic and parasympathetic supply of the extrinsic NS?
SYMPATHETIC:
POST adrenergic fibers
Cell bodies= coeliac, S/I mesenteric and hypogastric ganglia
PARASYMPATHETIC:
PRE adreneric fibers from VAGUS terminate in MYENTERIC and SUBMUCOSAL PLEXI
What are the components of the intrinsic innervation to the gut?
- afferent neruons in the wall of gut (chemo/mechano)
- interneurons in the MYENTERIC/SUBMUCOSAL plexi in wall of gut (connect sensory to motor neurons)
- efferent neurons in wall of gut to smooth muscle and secretory cells
What is the fxn of intrinsic innervation?
coordinate GI activity in absence of extrinsic innervation
What is the difference between the myenteric (auerbach’s) plexus and the submucosal (meissener’s) plexus?
Myenteric–between circular and longitudinal fibers of muscularis externa
Submucosal– derived from myenteric and located on submucosa of the intestine
What type of gland is the pancreas?
Exo and endo
similar to parotid
secretes 1200 ml of digestive juice
