Small intestine structure and function

Question 1

Describe the structure and function of the duodenum

Answer 1

• ~25cm
  
  • Gastric acid neutralisation
  • Digestion
  • Iron absorption

Question 2

Describe the structure and function of the jejunum

Answer 2

• ~2.5m (1/3)

- Nutrient absorption

Question 3

Describe the structure and function of the ilium

Answer 3

• ~2.5m (2/3)

- Water/NaCl absorption

Question 4

Describe the structure and function of the pilca

Answer 4

• Corkscrew like folds

- Increases surface area

Question 5

Describe the structure and function of the villi

Answer 5

• Absorb: fats, amino acids, monosaccharides, water, minerals, vitamins, peptides, NaCl
  
  • Crypt of Lieberkühn: secretes (water + NaCl)
  • Lacteal (absorbs fat)
  • Goblet cells (secretes mucus)
  • Vessels
  • Increases surface area

Question 6

Describe the function of the microvilli

Answer 6

Increases surface area

Question 7

What is segmentation?

Answer 7

• A segment of the muscle contracts and the segments on either side relax and then swap
  
  • Good for mixing
  • Brings chyme in contact with absorbing surface
  • Slow
  • During absorbing nutrients

Question 8

What is peristalsis? (mediated by…)

Answer 8

• Muscles contract just after
  
  • After nutrients are absorbed
  • Clears the small intestine of large undigestible material
  • Mediated by the myenteric plexus

Question 9

What are the generation and inhibition of segmentation and peristalsis?

Answer 9

• Segmentation: pacemaker cells (generation), MMC (stop)
  
  • Peristalsis: MMCs (Migrating motility complexes) generated by lack of food in the stomach
  • MMCs are initiated by Motlin and inhibited by food in the stomach

Question 10

Describe the BER

Answer 10

• Ascent in membrane potential
  
  • > Threshold
  • > Action potential (the more Aps the stronger the contraction
  • > Contraction
  • Decreases in frequency as you go down the GI so that more food moves forwards than back
  • Parasympathetic increases contraction
  • Sympathetic decreases contraction

Question 11

Describe the features which act to increase absorptive surface area along the alimentary canal

Answer 11

• Plica
	- Corkscrew like folds
	• Villi
	- Absorb: fats, amino acids, monosaccharides, water, minerals, vitamins, peptides, NaCl
	- Crypt of Lieberkühn: secretes (water + NaCl) 
	- Lacteal
	- Goblet cells
	- Vessels
	• Microvilli

Question 12

Describe the gastroileal reflux

Answer 12

• Gastroileal reflex

- Gastric emptying causes increased segmentation activity in the ilium which opens the iliocaecal valve 
- Entry of chyme into the large intestine
- Distension of the colon closes the iolocaecal valve 
    - Prevents back flux into small intestine