anatomy of the small intestine Flashcards
discuss general features of small intestine structure
- lumen contains chyme, food bacteria toxins viruses secretions and FBs
- muscosa = 2 parts: single epithelial layer mucus covered and lamina propria (loose connective tissue and immune cells)
- submucosa for structural support carries vessels, lymphatics and nerves
- tunica muscularis = smooth muscle, circular and longitudinal sections for motility
- serosa = visceral peritoneum
what adaptations to the small intestine increase the surface area
- ridges and folds
- vili
- microvili attached to cells of vili
what are crypts of lieberkuhn
pits below base which contain stem cells which produce immature enterocytes and other gut cells (because get rubbed off easily so need to reproduce)
mature enterocytes on microvilli absorb which nutrients
- carbohydrates
- amino acids
- lipids
- vitamins
- minerals
mature enterocytes are able to absorb nutrients from the chyme filled lumen by:
enzymes bound to surface of cells so product itself is then bound to cell to absorb
what are lacteals
blind end lymphatic capillaires which transport emulsified fats into GIT lymphatic drainage then to cranial vena cava
describe the location and appearance of the duodenum
- always on right side of animal
- distinctive U/J shape
- short mesentery
- wraps cranial mestenteric artery which marks start of jejunum
what are brunners glands
- compund tubular sub-mucosal glands
- stop stomach acid from attacking wall of small intesting (mucus and/or bicarb)
- distinctive of the duodenum
- provides alkaline environment for intestinal enzymes to be active
the ileum is identifiable by:
- has mesentery on BOTH sides
- connected to caecum bu ileocaecal fold
- look for unique antimesenteric blood vessels (antimesenteric = side where no mesentery)
what are the 6 cell types of the small intestin
- enterocyte
- entero-endocrine cell
- goblet cells
- paneth cells
- M cells
- tuft cells
what are enterocytes doing and what do they look like
- columnar epithelial cells covered with microvilli
- smoot ER allows intracellular transport of nutrients
- pinocytsis into enterocyte allows foreign material to enter cell as vesicles
- important for antibody absorption in neonates
- protective: dont let foreign mterial enter circulation
- cell-cell junctions are tight so only what needs to be absorbed is absorbed
discuss teh distribution of cells in the small intestine
- stem cells at neck of crypts
- produce all 6 cell types
- 4 of them migrate upwards on villi
- paneth cells micrate down into crypts
- M cells cover peyers patches
what do enteroendocrine cells do and what do they look like
- small dark basal granules
- scattered along epithelium of entire GIT
- sample intestinal lumen and react (chemosensors)
- different types
- important for endocrine control of digestive secretions and motility
- link to immune system
- secrete gastrin, secretin, cholecystokinin, serotonin, gastric inhibitoy polypeptide, somatostatin etc
what is an open type entero endocrine cell vs a closed type
open = mucosal sensor region
closed = cell sits on basement membrane
what do goblet cells do and what do they look like
- produce mucin
- look like goblets
What do paneth cells do and what do they look like
- apical granules with innate mucosal defences defensins and lysosymes
- only in equids and bovids
- migrate to base of crypts
- keep crypt clear of high bacterial count
what are peyers patches
- slightly raised ovoid areas in the mucosa of the distal SI
- visible grossly
- always in antimesenteric mucosa
- lots of lymphocytes and macrophages
- covered by M cells which transport Ag to the lymphocytes and macros
- reactive to changes in gut flora
what are M cells
- special epithelial cells which cover peyers patches
- single layer of cells
- no mucus layer so are in girect contact with ingesta
- on th basal surface there is a large indentation which contains lymphocytes and macrophages
- means immune cells are very close to gut lumen
- transport antigen from lumen to immune cells
- enable immune response to occur
what are tuft cells
- sparse cells making links to immune system
- to do with parasite immunity
where does the pancreas sit
in the U bend of the duodenum
discuss blood supply to the small intestine and pancreas
3 unpaired branches of the aorta:
- coeliac artery = liver, stomach, spleen, duodenum and pancreas
- cranial mesenteric = duodenum, jejunum, ileum, caecum, large colon
- caudal mesenteric = part of descending colon and rectum
list major branches of ceoliac artery
- left gastric
- hepatic
- hepatic branches
- cyctic branches
- right gastric!!
- cranial pancreatico-duodenal
- right gastro-epicolic - splenic
- pancreatic branches
- splenic branches!!!
- short gastric!!
- left gastro-epiploic
!!! = NTK
list branches of crainial mesenteric artery
- caudal pancreatico-duodenal
- jejunal
- ileo-colic (middle colic, right colic, colic, ileal, caecal)
list branches of caudal menesteric artery
- left colic
- cranial rectal
smooth muscles of the GIT are controlled by which 2 local nerve plexi
- meissners plexus in submucosa
- auerbach’s plexus between smooth muscle layers
sensory information of the SI interns via
mechanosense and chemosense: vagus
pain: sympathetic
intra-pelvic viscera = pelvic plexus
