Are you excited to study Histology right now?
I hope so! B/c here it comes….
How long is the SI? What are its 3 regions? What is its main function?
21-25 feet long
duodenum, jéjunum, ileum
digestion & absorption
Which portions of the duodenum are considered retroperitoneal?
2nd, 3rd, 4th portions
What structure separates the duodenum from the jejunum?
ligament of trietz
this part Highi thinks is peritoneal
The majority of the SI is suspended by what?
mesentery
When something has mesentery it is considered____.
peritoneal
Describe the circular plicae in the SI.
They go around the circumference of the SI. Their height drops as we become more distal in the intestine. Once we’re at the distal ileum–>no more circular plicae.
Vasa recta are the arteries that come off of the ____ & go into the ____ & form _______.
Come off of marginal arteries
go into the SI
form vascular planes
When you are proximal in the SI…what do the vascular planes look like? How about when you’re distal?
Proximal: they are large & organized
Distal: they look like a mosaic & are smaller…
What are the histological layers of the SI…starting w/ mucosa?
Mucosa
Submucosa
Muscularis Externa
Adventitia or Serosa
What 2 histological layers is the plicae circularis made up of?
mucosa & submucosa
What are the 2 layers of the muscularis externa in the SI?
Inner Circular
Outer Longitudinal
B/c of surface modifications to the SI…its surface area is increased by what factor?
400-600X
What 3 things increase the surface area of the SI & by what factor?
Plicae circularis: 2-3X
Intestinal Villi: 10X
Simple Columnar epithelium w/ microvilli: 20X
What type of epithelium is on the mucosa of the SI? & What 6 cell types accompany it?
Simple Columnar Epithelium Enterocytes Goblet Cells M cells Enteroendocrine cells Paneth cells Stem cells
What’s the deal with the enterocytes of the mucosal epithelium of the SI?
They are surface absorptive cells.
They transport substances from the lumen to the circulatory system. Intercellular junctions seal off the space in b/w the cells.
Also, microvilli increase the apical surface area.
What is the function of the goblet cells in the mucosal epithelium of the SI?
They secrete mucinogen. This is converted to mucous for protection.
What’s the deal with the M Cells in the mucosa of the SI?
aka Microfold Cells
These are antigen presenting cells.
They are modified enterocytes.
They cover the lymphatic nodules of the LP.
Are the goblet cells in the SI the same as those in the respiratory system?
NO
What’s the deal with the enteroendocrine cells?
They produce peptide hormones…the same ones as in the stomach.
Where are paneth cells mainly found? What do they do? What do they regulate?
Mainly found in the distal ileum…they are found in the crypts…They secrete lysozyme that is antibacterial.
They regulate the intestinal flora.
They protect the SI from the bacteria of the LI.
The stem cells found in the SI mucosa are regenerative cells. How often do they regenerate the epithelial cells? The paneth cells?
Epithelial cells: every 5-6 days
Paneth cells: every 4 weeks
Where are the stem cells located w/i the mucosa?
at the neck of the crypts…they can restore bidirectionally…up the villi & down the crypt.
The fast rate of cell renewal by stem cells means that there is a _______. This allows us to use what type of drugs?
high mitotic index
Anti-mitotic drugs
What does the LP in the SI contain?
CT & lymphatic nodules
villus lacteals
crypts/intestinal glands
Where is the lacteal located w/i the SI? What is its function?
It is located w/i the villus of the SI.
It absorbs compounds that can’t be absorbed by the circulatory system b/c they are too big. This includes chylomicrons.
What is the purpose of chylomicrons?
They make wonderful lipoproteins that help to build our nervous system.
Where do the lymphatic nodules become really large in the SI? What are they called then?
in the distal ileum & appendix
Peyer’s patches…
technically only considered Peyer’s in the ileum, not the appendix.
What is the muscularis mucosae of the SI made up of?
inner circular
outer longitudinal
smooth muscle
What are the layers of the muscularis externa in the SI?
inner circular
outer longitudinal smooth muscle
T/F there are also submucosal & myenteric plexuses in the SI
True
On the outside of the SI layers there is either a serosa or adventitia…which part of the duodenum has a serosa on the outside?
only the first portion b/c it is peritoneal
What is found in the submucosa?
large blood vessels & sometimes glands
Where are glands found in the GI tract? what do they produce?
Submucosal glands are only found in the esophagus & the duodenum (Brunner’s)
They produce urogastrone that inhibits gastric acid secretion & protects the Gi tract. They also produce things that neutralize acid
What extends up the imaginary line in the SI tissue? What extends below the imaginary line?
Up: Villi
Below: Crypts
What does a cross section of a villus look like? Of a crypt?
Villus: solid
Crypt: donut hole
T/F the anal canal & rectum are considered a part of the large intestine.
True.
T/F The cecum w/ appendix is considered a part of the SI.
False. It is considered a part of the large intestine.
What are the main functions of the large intestine?
reabsorption of electrolytes & water & elimination of waste.
Does the LI have mucosal folds or villi?
No. Neither
Does the appendix have mesentery associated w/ it? Is it intra or retro?
Yes. Intraperitoneal.
Hanging off of the transverse colon is the ____.
Greater Omentum
Does the sigmoid colon have mesentery? Is it intra or retro?
Yes. Intraperitoneal
Are the rectum & anus covered in adventitia or serosa? Intra or retro or other?
Covered in adventitia.
Not intraperitoneal. A little retro & sub peritoneal.
The ascending colon & descending colon are in the ______ _______.
paracolic gutters
What are the ascending & descending colon covered in? Serosa or adventitia? Intra or retro?
Adventitia
Retroperitoneal
Their anterior surface has a layer of peritoneum touching it.
The transverse colon has _____ & is therefore intra/retro?
has a transverse mesocolon
intraperitoneal
is the sigmoid colon retro or intra?
Intraperitoneal
What does the large intestine produce large amounts of? Buckets of?
MUCUS! Gross…
The large intestine houses bacteria that produces which 2 vitamins? Which 2 processes are these vitamins important in?
Vitamin B12 (hematopoiesis) Vitamin K (coagulation)
Does the large intestine have crypts?
Yes. Not villi, though. And not submucosal glands.
What type of epithelium is found in the LI?
Simple columnar epithelium
What special cell types are found in the LI?
Many GOBLET cells
Enterocytes
Enteroendocrine cells
What is the purpose of all of the goblet cells in the LI?
It helps lubricate the lumen.
Are there villi in the LI? Crypts? Where is the LP found?
Villi-no
Crypts-yes
LP found b/w the crypts!
Are there paneth cells in the LI?
No.
Are there lacteals found in the LI?
No.
Are there lymphatic nodules found in the LI?
YES…they are in the submucosa & they extend into the LP
Are there lymphatic vessels found in the LI?
No.
What are the layers of the muscularis mucosa in the LI?
Inner Circular
Outer Longitudinal
Smooth muscle
What is found in the submucosa of the LI?
only big vessels
Describe the muscularis externa of the LI.
ICOL smooth muscle
Some distinguishing features: teniae coli & hausfrau
The last layer of the LI is serosa or adventitia depending on where you are in the LI. What is another feature of this layer in the LI?
appendices epiplociae
fat hanging off of the teniae coli
Are the goblet cells in the LI the exact same ones as in the SI?
No.
What is an important anatomical landmark of the rectum?
transverse rectal folds
What things do you have to pass thru to get to the anal canal?
anal valves/anal columns/pectinate line
What is the histology like in the rectum?
Similar to the colon…just that the crypts are fewer & deeper
What are the 3 zones of the anal canal?
Colorectal zone: stops @ pectinate line
Transitional zone: in b/w pectinate line & anoderm
Sqamous zone: @ anus w/ anoderm
What is the tissue like in the colorectal zone?
simple columnar epithelium
What is the tissue like in the transitional zone?
Stratified Sqamous Epithelium, Stratified Cuboidal Epithelium, Stratified Columnar Epithelium
What is the tissue like in the squamous zone?
anoderm–>stratified sqmaous keratinized epithelium
Describe the lymphatic nodules of the appendix.
They are large & numerous & extend into the submucosa. They are like Peyer’s patches, but aren’t technically considered this. They have germinal centers. They’ve seen a lot in their lifetime…
Describe the muscularis externa of the appendix.
It has a thick IC layer & a thin OL layer.
Describe the lumen of the appendix vs. that of the rest of the LI.
It is a smaller lumen w/ the appendix.
What is found in the lamina propria of the anal canal?
sebaceous glands
LAG
hair follicles
large veins
What’s the deal with the muscularis mucosae of the anal canal?
It terminates @ the anal valves. Before that it is ICOL smooth muscle.
What is found in the submucosa of the anal canal?
fibroelastic tissue
this is important b/c it allows for the stretching that is needed in this area…
What’s the deal with the muscularis externa of the anal canal?
ICOL smooth muscle
The IC smooth muscle makes up the internal anal sphincter
What makes up the external anal sphincter?
This is the biggest component of the adventitia. The skeletal muscle of the pelvic floor makes it up.
What is the surgical anal canal?
1-2 cm above the pectinate line…this is in the autonomic nerve region. if sutures are placed here they are less painful.
Pectinate Line is an important dividing line. Embryological tissue?
Above it:
Below it:
Above it: endoderm
Below it: ectoderm
Pectinate Line
Arterial Blood supply
Above it:
Below it:
Above it: IMA
Below it: internal iliac artery
Pectinate Line
Innervation
Above it:
Below it:
Above it: autonomic (more stretching, bloating)
Below it: somatic (localizable pain)
Pectinate Line
Hemorrhoids
Above it:
Below it:
Above it: Internal Hemorrhoids
Below it: External Hemorrhoids
Pectinate Line
Venous Drainage
Above it:
Below it:
Above it: Superior Rectal Vein (From IMV)
Below it: Middle Rectal Vein & Inferior Rectal Vein (from internal iliac vein)
