Small Intestine Structure and Function Flashcards
How long is the small intestine?
~6m
What are the parts of the small intestine and their lengths?
Duodenum - 25cm
Jejunum - 2.5m
Illeum - 3.5m
Functions of duodenum?
Gastric acid neutralization
Digestion
Iron absorption
Functions of the jejunum
Absorbs 95% of nutrients
NaCl absorption for chyme dehydration
Why does the jejunum appear pink?
Highly vascular
What increases the small intestines surface area?
Folds
Villi
Microvilli
What is the plicae circularis?
Folds in small bowel that make chyme flow in a spiral patter to maximise absorption and mixing
What is the myenteric plexus?
Major nerve supply to GI tract that controls motility
What do crypt of lieberkuhn cells secrete?
Cl and H2O
Why do crypt cells secrete water?
Water gives an aq environment for digestion to take place
How does chlorine enter the lumen?
Brought into cell by Na-K-cl transporter (Na and K taken right back out to maintain gradient)
Cl- ion is pumped into lumen by CFTR
CFTR is opened via cAMP to adenosine cyclase conversion
What happens if CFTR doesn’t work?
This is seen in disease - Cystic fibrosis
What do goblet cells do?
Create a diffusion barrier to increase diffusion and secrete mucous
What are lacteals?
Lymphatic capillaries that absorb dietary fats
What does Na+ coupled active transport actually transport in the small bowel?
Glucose
Galactose
Amino Acids
Nucleosides
What 2 types of motility is seen in the small bowel?
Segmentation
Peristalisis
Describe segmentation
The following is the tube:
Relaxed-CONTRACTED-Relaxed-CONTRACTED-Relaxed
In the relaxed areas the chyme moves up and down and mixes further
The relaxed areas then become contracted and vice versa = slower movement towards colon
When does segmentation occur?
During a meal
What makes segmentation?
Pacemaker cells in the longitudinal muscle layer
What does parasympa and sympa activity do for segmentation?
PS via vagal nerve = increased contractions
S - decreased contractions
What determines the freq. of segmentation
frequency of the basic electrical rhythm
What determines strength of contractions?
AP freq.
What is peristalsis?
A strong contraction behind the bolus moving food forward
What generages peristaltic waves?
The migrating motility complex
Describe the MMC.
It starts in the stomach antrum and travels all the way to the ileum
Once at illeum a new one is generated
What initiates the migrating motility complex?
Motilin hormone
What stops the MMC?
Arrival of food in stomach - stops MMC and initiates segmentation
Describe the ENS
PS - vagal nerve - stimulatory
S - splanchnic nerve - inhibitory
Salivation has different effects and PS supplies
What is the law of the intestine?
If intestinal smooth muscle is distended by a bolus of chyme, the mouth side of intestine contracts and anus side relaxes to move the bolus
This is mediated by neurones in the myenteric plexus
What is the gastroileal reflex?
When the ileocaecal sphincter opens to let chyme into colon there is a reflex contraction of the ileocaecal sphincter to prevent backflow
