Digestive System: Small intestines Flashcards
What are the general functions of the small intestines (SI)?
Digestion
Absorb nutrients
Produce intestinal hormones using DNES cells (produce CCK)
What 3 surface adaptations increase surface area by a factor of 400+?
- Plicae circulares (valves of Kerckring)
- Villi
- Microvilli
What are the plicae circulares?
Permanent folds affecting the mucosa and submucosa; found throughout duodenum, jejunum, and proximal ileum
Where are the microvilli?
On the luminal cell surface
What is the surface epithelium of the intestinal mucosa?
Simple columnar
What cell types are present in the surface epithelium of the mucosa?
Surface absorptive cells (enterocytes) Goblet cells DNES cells (Type I, Type K, Type S) Regenerative cells Paneth cells M (microfold) cells
What are the main functions of the surface absorptive cells/enterocytes?
Absorb water and nutrients
Terminal digestion in glycocalyx; cells produce the enzymes and absorb the monosaccharides and peptides created
What do the surface absorptive cells/enterocytes contain?
Microvilli
How are the goblet cells distributed in the SI?
Few in duodenum, most in ileum
How many DNES cell types are present in the SI?
11 types (we only need to know 3)
What do Type I DNES cells produce and do?
Produces cholecystokinin (CCK) to stimulate GB contraction and pancreatic secretion of enzymes from serous acini
What do Type K DNES cells produce and do?
Produces GIP (gastric inhibitory peptide) which inhibits HCL release
What do Type S DNES cells produce and do?
Produces Secretin which stimulates pancreatic secretion of bicarbonate from the pancreatic ducts; secretin also inhibits HCL release and the movement of chyme into SI
How long do the regenerative cells of the SI live? Where are they found?
5-7 days
Found in crypts (intestinal gands)
How long do the Paneth cells of the SI live? Where are they found?
20 days, they are long lived
Found in base of crypts (intestinal glands)
What is the function of the Paneth cells of the SI?
Produce lysozyme
Where are the M (microfold) cells found in the SI?
Ileum epithelium over Peyer’s patches
What is the cell structure of the M (microfold) cells?
Contain large intracellular pockets that are fairly open to the LP; M cells sample foreign antigens in gut lumen and transfer antigens to lymphocytes and dendritic cells that have entered the M cell pockets
What is the function of the M (microfold) cells?
Promote humoral immunity; results in plasma cells producing IgA which is then transferred to epithelial cells and released into gut lumen. M cells are also important in maintaining appropriate gut flora
What is the lamina propria of the SI made up of?
Loose areolar CT
Where is the villus core located?
In the lamina propria
What is found in the villus core?
Lacteals
Vascular components
Some longitudinal smooth muscle
What are lacteals and what’s their function?
They are lymphocyte capillaries
Function in most lipid absorption
Are the vascular components of the villus core larger or smaller blood vessels?
Smaller
What is the importance of the longitudinal smooth muscle in the villus core?
If irritated then muscle contracts and the villi will shorten; this can lead to nutrient deficiencies if irritation is prolonged
What does the lamina propria of the SI border?
Intestinal glands (crypts of Lieberkuhn)
Is muscularis mucosae present in the SI mucosa?
Yes, but it’s thin. It connects to smooth muscle in villi
What makes up the submucosa of the SI?
Dense fibroelastic CT
How vascular is the SI submucosa?
Very vascular due to larger blood vessels
What are the parts of the SI submucosa?
Duodenum
Jejunum
Ileum
What glands are present in the duodenum?
Duodenal (Brunner) glands (seromucous glands)
What do the duodenal glands produce?
Alkaline mucus
Urogastrone
What is the function of alkaline mucus?
Neutralizes chyme
What is the function of urogastrone?
Inhibits HCL secretion and increases mitosis of epithelial cells
Where are Peyer’s patches located?
Ileum
What are Peyer’s patches?
Groups of regularly occurring large lymph nodules
What plexus is found in the ileum and what type of innervation does it conduct?
Submucosal (Meissner’s) plexus- parasympathetic innervation
Where is the submucosal found and what is its function?
Found close to circular muscles in muscularis externa
Functions to influence mucosa
How is the pattern of the muscularis externa of the SI?
Normal; inner circular, outer longitudinal
What plexus is found in the muscularis externa and what is its function?
Myenteric (Auerbach) plexus
Functions to stimulate muscularis externa for peristalsis
Where is the myenteric plexus found within the muscularus externa?
Between the circular and longitundinal layers of muscle in muscularis externa
Where is the serosa found in the SI?
In all of the jejunum and ileum, first and last 1-2 cms of duodenum
Where is the adventitia found in the SI?
In the vertical/descending portion of duodenum
Where is the ileocecal valve found?
Between ileum and cecum of colon
What type of sphincter is the ileocecal valve?
Physiological AND anatomical
