SI and pancreas anatomy Flashcards
Describe the layers of the SI
Mucosa:
- epithelial layer
- lamino propria
Submucosa
Tunica muscularis
Serosa
Describe the anatomy and function of the mucosa of the SI
Single epithelial layer:
- semi-permeable
- secretion and absorption
- protection
- mucous covered
Lamina propria:
- loose connective tissue
- immune cells
Crypts of Lieberkuhns
Mucosa folds to creates dams to slow flow of chyme
Describe the anatomy and function of the submucosa of the SI
structural support
BVs
lymphatics
nerves
fine smooth muscle layer that projects into lamina propria (muscularis mucosae) that alters folding and ‘pumps’ villi up and down
Describe the anatomy and function of the tunica muscularis of the SI
main smooth muscle
circular and longitudinal layers
provides motility
nerve cell layers control the contractions
Descrive the function of the serosa of then SI
strong
protective, supportive outer layer
Label the SI wall
What adaptations increase the SA of the SI
ridges/folds
villi
microvilli
Describe the function of the crypts of lieberkuhns in the SI
intestinal glands/crypts
contain a stem cell region which produces immature enterocytes and other gut cells
What is the function of mature enterocytes in the SI?
Found on villi
absorb nutrients:
- carbs
- AAs
- lipids
- vits
- minerals
What is the function of lacteals in the SI wall?
blind-end lymphatic capillaries
transport emulsified fats (As chylomicrons) into GIT lymphatic drainage
What is the function of blood capillaries in the lamina propria of the SI?
have large fenestrations so plasma proteins (inculding serum albumin) can move into interstitial space
What is the function of the Brunner’s glands in the duodenum?
tubular sub-mucosal glands
Produce serous or mucous secretion
Secretion protects duodenal epithelium from incoming gastric acid and provides alkaline conditions for intestinal enzymes
What joins the caecum and ileum?
ileocaecal fold
ileocaecal sphincter
How do you identify the ileum?
Double mesentery
Double blood supply from caecum and colon
has mesenteric and antimesenteric blood vessels
What are the 6 cells types in the SI?
What is the function of entero-endocrine cells?
Dark basal granules
secrete peptide hormones and CCK
What is the function of paneth cells in the SI?
apical granules
innate mucosal defences (defensins and lysozymes)
found at bottom of crypts
What is the function of M-cells in the SI?
APC that covers Peyer’s patches
What is the function of tuft cells in the SI?
make links with immune system
Describe the formation and distribution of cells in the SI
stem cell zone at neck of crypts
most cell types migrate up villi:
- enterocyte
- goblet cell
- endocrine cell
Paneth cells migrate down into crypts
How do enterocytes work?
smooth endoplasmic reticulum allows intracellular transport of nutrients
pinocytosis into enterocytes allows foreign materials to enter as vesicles
vesicles fuse with enzyme-packed intracellular lysosomes
tight junctions prevent leakage
Label the villus of the SI
What are the mature enterocyte brush border enzymes?
integral membrane enzymes
peptidases
CHO hydrolases (lactase, maltase, sucrose)
What is the function of entero-endocrine cells?
sample intestinal lumen and react
found along entire GIT epithelium
chemosensors at the luminal surface
Have links with immune system
open type - open into lumen
Closed type - cell sits on basement membrane, no extension to mucosal surface
What is the function of paneth cells in the SI
equids and bovids
produce anti-microbial defensin peptides
keep crypt clear of high bacterial count
What is GALT?
gut associated lymphoid tissues
Describe the anatomy and function of the Peyer’s patches
Raised ovoid areas in the mucosa of the ileum
always in antimesenteric mucosa
lots of macrophages and lymphocytes
Covered by M-cells which transport antigens to lymphocytes and macrophages
Reactive to changes in gut flora - immune responses
Describe the anatomy of lymphoid follicles in the SI
aggregations of lymphocytes and macrophages within lamina propria
No contact with lumen
M-cells over them in epithelial boundary
Where are lymph nodes found in the SI?
within the mesentery
Which section of SI is this?
duodenum
Which section of the SI is this?
jejunum
Which section of the SI is this?
ileum
What is the function of M-cells in the SI?
special epithelial cells that cover Peyer’s patches
direct contact with ingesta (no mucous layer)
folded apical surface increases SA
lymphocytes and macrophages in indentation on basal surface
transport antigens from lumen to immune cells
What is the function of Tuft cells in the SI?
long ‘fingers’ project sideways into neighbouring epithelial cells and into luminal space
modulate responses against protists and metazoa (multicellular endoparasites)
Where is the pancreas found?
duodenal flexure
Why do you need to be careful handling the pancreas in surgery?
heavy handling can lead to pancreatic enzymes being released into the pancreas leading to autolysis (breaking down itself)
Why is there high conc of pancreatic hormones in the liver?
venous drainage of pancreas via hepatic portal vein into liver
What are the secretions of the pancreas?
dual function:
exocrine:
- digestive enzymes
- alkaline fluids
endocrine:
- insulin
- glucagon
- somastostatin
- pancreatic polypeptide
How is the pancreas stimulated?
duodenum entero-endocrine cells sense acidic chyme
secretin release acts on pancreatic ducts
epithelial cells in pancreas ducts produce bicarbonate and water
flush acinar enzymes into SI lumen
What are Islets of Langerhans and what types are there?
enteroendocrine cells in the pancreas
alpha cells - glucagon
beta cells - insulin
delta cells - somatostatin
PP cells - pancreatic polypeptide
- epsilon cells - ghrelin
What GIT structures does the coeliac artery supply?
liver
stomach
rumen
spleen
duodenum
pancreas
What GIT structures does the cranial mesenteric artery supply?
duodenum
pancreas
jejunum
ileum
caecum
large colon
What GIT structures does the caudal mesenteric artery supply?
part of descending colon
rectum
What are the branches of the coeliac artery?
left gastric
hepatic:
- right gastric
Splenic:
- splenic branches
- short gastric
What local nerve networks control the smooth muscles of the GIT?
Meissner’s plexus - submucosa
Auerbach’s plexus - between smooth mm layers
Which nerves supply sensory info to the brain from the GIT?
mechanosense and chemosense - vagus
pain - sympathetics
Describe the sympathetic pathways to the gut
Fibres run through vagus nerve => dorsal vagal trunk => coeliac and mesenteric ganglion => along BVs => gut
Sacral part of parasympathetic NS:
pelvic nerve forms retroperitoneal plexus which supplies descending colon and rectum
What are the autonomic ganglion involved in innervation of the GIT?
sympathetic synapses: paravertebral ganglion
Parasympathetic: prevertebral ganglion (coeliac and cranial mesenteric ganglion = solar plexus)
