What are the general functions of the small intestine?
digestion
absorb nutrients
produce intestinal hormones using DNES cells
What are the three surface adaptations of the small intestine that increase the surface area?
plicae circulares
villi
microvilli
What is plicae circulares?
permanent folds affecting the mucosa and submucosa
Where are the plicae circulares found?
duodenum, jejunum and proximal ileum
Where are microvilli found?
on the luminal cell surface
What is the surface epithelium of the mucosa of the small intestine?
simple columnar
What other types of cells are found in the mucosa of the intestine?
surface absorptive cells, goblet cells, DNES cells, regenerative cells, paneth cells, M cells
What is the function of surface absorptive cells of the mucosa of the small intestine? what do they contain?
absorb water and nutrients, terminal digestion in glycocalyx
contain microvilli
What is glycocalyx?
cell produce the enzymes and absorb the monosaccharides and peptides created
Where are goblet cells located?
most in ileum, least in duodenum
What types of DNES cells are found in the small intestine?
Type I, Type K and Type S
What do Type I DNES cells do?
produce CCK
What does CCK do?
stimulates gallbladder contraction and pancreatic secretion of enzymes from serous acini
What do type K DNES cells do?
produce Gastric Inhibitory peptide (GIP)
What does GIP do?
inhibits HCl release
What do type S DNES cells do?
produce secretin
What does secretin do?
stimulates pancreas secretion of bicarbonate from pancreatic ducts
also inhibit HCl release and movement of chyme into small intestines
What does bicarbonate do?
buffer’s chyme
Where are regenerative cells found?
crypts (intestinal glands)
Where are paneth cells found?
base of crypts (intestinal glands)
What is the function of paneth cells?
to produce lysozymes
Where are M cells located?
ileum epithelium over Peyer’s patches
What is the cellular structure of M cells?
they contain large intracellular pockets that are fairly open to LP
sample foreign antigens in gut lumen and transfer antigens to lymphocytes and dendritic cells that have entered the M cell pockets
What do M cells do?
promote humoral immunity
maintain appropriate gut flora
What is a result of humoral immunity from M cells?
causes plasma cells to produce IgA which is transferred to epithelial cells (enterocytes) and released into the gut lumen
What makes up the lamina propria of the mucosa of the small intestine?
loose areolar CT
Where is the LP found?
villus core and bordering the intestinal glands
What is contained within the villus core?
lacteals, vascular components and some longitudinal smooth muscle
What are lacteals? What do they do?
lymphatic capillaries
absorp most lipids
Why is smooth muscle important in the lamina propria of the gut?
if it is irritated then the muscle contracts and the villi shorten, which can lead to nutrient deficiencies if this is prolonged
Describe the muscularis mucosae of the mucosa of the small intestine.
thin but present; connects to the smooth muscle in the villi
What makes up the submucosa of the small intestine?
dense fibroelastic CT and large blood vessels (very vascular)
What is the significant structure found in the submucosa of the duodenum?
duodenal (brunner) glands
What are Brunner glands?
seromucous glands that primarily produce alkaline mucus, but also produce urogastrone
Why do Brunner glands produce alkaline mucus?
to neutralize chyme
Why do Brunner glands produce some urogastrone?
to inhibit HCl secretion and increase mitosis of epithelial cells
What are the significant structures of the jejunum?
there are none
What are the significant structures of the ileum?
Peyer’s patches and submucosal (Meissner’s) plexus
What are Peyer’s patches in the ileum?
groups of regularly occuring large lymph nodules
What is the submucosal plexus there for? Where is it?
parasympathetic innervation to influence mucosa
located close to circular muscle in muscularis externa
What is the pattern for the muscularis externa?
normal pattern (inner circular, outer longitudinal)
Where is the Myenteric (Auerbach) plexus found?
in the muscularis externa between the circular and longitudinal muscle layers
What is the function of the myenteric (Auerbach) plexus in the muscularis externa of the small intestine?
stimulate muscularis externa for peristalsis
Where is serosa found?
all of jejunum and ileum as well as the first and last cm of the duodenum
Where is adventita found?
vertical (descending) portion of the duodenum
Where is the ileocecal valve found?
between ileum and cecum of colon
Is the ileocecal valve an anatomical or physiological sphincter?
both