The small intestine Flashcards
how long is the small intestine?
what is the diameter?
6m long
3.5 cm in diameter
what are the parts of the small intestine?
how long is each one?
(duodenum=25cm, jejunum=2.5m, Ileum=3.75m
what is the mesentry?
- The small intestine is lined on the inside by fan-shaped mesentery
- increases the surface area of the intestine with folds and supports the blood supply.
- The mesentery then has villi (~1mm tall) covering it
what are the layers of the small intestine?
- external wall has longitudinal and circular muscles
- the internal mucosa are arranged in circular folds
- the mucosa are covered in villi
there are invaginations known as the crypts of lieberkuhn
what are the villi made up of?
what is the function of villi?
The Villus is comprised of simple columnar epithelium:
o Primarily enterocytes (absorptive cells).
o Scattered goblet cells.
o Enteroendocrine cells.
needed to increase the surface area
what are the crypts of lieberkuhn made of?
- Stem cells – to replace the high turnover of enterocytes.
- Paneth cells – base of crypt, secrete acidophilic granules, lysozyme etc
features of enterocytes?
life span?
- most abundant cell types
- Feature a basal nucleus and is specialised for absorption
- Has a brush border of microvilli, each of which is covered in glycocalyx.
SHORT life span
what is the glycocalyx?
– carbohydrate layer that traps a layer of water and mucus to regulate rate of absorption and to protect
surface of microvilli from pH of lumen.
how much is the SA increased by the mesentry folds, microvilli and the villi?
x500 increase
features of the goblet cells?
- 2nd most abundant
- Produces mucus (large glycoproteins
- abundance increases as you get further through the bowel as more lubrication is needed
features of Enteroendocrine Cells?
- columnar epithelial cells
- secrete hormones to influence gut motility
- Found in lower parts of the crypts.
where are paneth cells found?
what do they contain?
the base of the crypts
- they contain large acidophilic granules which have
- lysozymes (antibacterial to protect stem cells)
- glycoproteins ( to protect the enzymes from themselves.)
- zinc (co factor to the enzymes)
Can have phagocytic roles to bacteria and protozoa.
life span of Enterocytes & goblet cells ?
short life span (36 hours)
what type of stem cells are in the villi?
how do the stem cells move?
stem cells are PLURIPOTENT
- The stem cells are continually shunted up the villus to replace old cells lost at the tips.
Dividing stem cells in crypt shunted up → at tip, cells become senescent →
apoptosed cells sloughed into lumen → apoptosed cells digested and reabsorbed by intestine.
whys is a rapid turnover of enterocytes needed?
- enterocytes are the first line of defence so may be directly affected by toxic
substances in the diet →
interference in cell function →
short life-span means any lesions are short lived.
what are the characteristics of the Duodenum?
- Brunner’s Glands present
- Submucosal gland found in crypt base, secreting alkaline fluid into chyme.
what are the functions of the alkaline fluid in the duodenum?
- Neutralise acid to protect small intestine epithelium.
- Optimise pH for pancreatic
enzymes.