Lecture 7: small intestine Flashcards
what is the function of the small intestine?
- completion of digestion
- majority of absorption and secretion
what are the 3 distinct regions of the small intestine?
- duodenum (nearest to stomach)
- jejenum (middle)
- ileum (nearest to large intestine)
what are the** 3 main surface area adaptions** of the small intestine?
- Plicae circularis (the largest folds towards the lumen of SI)
-
Villi - smaller folds on the plicae circularis
3.** microvilli** - additional folds, ‘ brush border’, only seen on electron microscope
What are the crypts of lieberkuhn?
- tubular glands found between the villi
- mostly present in the duodenum and jejenum
- contain undifferentiated cells that proliferate to replace lost enterocytes
what are brunners glands?
- glands present in the duodenum that secrete an alkaline mucous
what are the** 4 main types of cells** present in the small intestine & what is their function?
- enterocytes - absorption
-
goblet cells - secretory
3. paneth cells - defence - enteroendocrine cells -hormonal
what is the sphincter of oddi?
- a ring of smooth muscle
- controls the entry of bile & pancreatic juice into the small intestine
what are** histological characteristics **of the duodenum?
- secretory brunners glands in the submucosa
- lots of goblet cells
what are the** key histological features** of the jejenum?
- lots of plicae - circular folds toward the lumen
- lots of enterocytes & goblet cells
what are the** key histological features** of the** ileum**?
- fewer plicae
- presence of peyers patches - lymphoid tissue (immunity function)
Where does secretion mostly occur?
in the duodenum
what contents are present in the SI secretions?
- hormones (entero endocrine cells)
- mucous - goblet cells
- lysozyme (kills bacteria) - paneth cells
- isotonic fluid - secreted by the crypts
- alkaline mucous - brunners glands
What are examples of hormones that are secreted by entero endocrine cells of the SI?
- Cholecystokinin (CKK)
- Motilin
- secretin
- serotonin
what are the** 2 types of contraction **involved in SI motility?
* mixing contractions - called segmentation
* moving contractions- peristalisis & **migrating myoelectrical complex **
what are segmentation contractions?
- mixing contraction
- segments of the SI undergo static contractions (not wave like/peristalisi contractions)
- important for **mixing the chyme in both directions with the digetsive enzymes **in the SI
what are peristalisis contractions in the SI?
- sequence of adjacent contractions that result in foward movement of chyme
- occurs in response to the SI lumen stretching
What is the migrating motor (myoelectrical) complex? what is it’s function?
‘house keeping contractions’
- occurs during fasting or once a meal has been processed
- slow waves of peristalisis
- occurs every 70-90 mins
- function: to sweep out the last remains of deigested foods along with bacteria into the large intestine
what** hormone** stimulaes the migrating motor complex?
- motilin
- secreted by the entero endocrine M cells of the duodenum and jejenum
What 3 things control SI motility?
remember the triangle
- autonomic - parasympathetic stimulates motility
- enteric - basal electrical rhythms always present
- hormones - motilin (migrating motor complex) & gastrin - stimulates the ileum
how does the vagus nerve impact motility along the GI tract?
- the contribution of the vagus nerve to GIT motility decreaes along the length of the GIT
Describe 2 examples of intestinal reflexes?
* ileo-gastric reflex - refers to the reduction in gastric motility that occurs in response to the stretching of the ileum
* gastro- ileo reflex - describes the increase in motility of the terminal ileum that occurs whenever there is an increase in secretory/motor activity of the stomach
