Lecture 27: The small intestine

Question 1

What is the function of the small intestine?

What features does it have that enables it to carry out its function?

Answer 1

Main role = absorption which occurs in the jejunum, most of the chemical digestion occurs in the small intestine aswell

• smooth muscle to enable movements of its contents
• Microvilli and plicae circulares increase the small intestine surface area for absorption
• Enzymes to enable chemical digestion = pancreas secretes enzymes into the duodenum

Question 2

The small intestine is divided into 3 parts:

Answer 2

Duodenum = 25cm
Jejunum= 2.5m
Ileum = 3.5 m

Question 3

What modifications of the gut tube allow the small intestine to carry out digestion and absorption?

Answer 3

• larger surface area: plicae circulare fold into the lumen of the small intestine to increase surface area; found in mucosa and submucosa
• Enzymes: pancreas secretions enter the small intestine via the duodenum and aid in chemical digestion
• Protection: mucous secreting cells in epithelium and mucous secreting glands protect epithelium in duodenum
• Absorption: via absorptive epithelial cells
• Movement; smooth muscle enables movement of contents

Question 4

How is the mucosa layer in the small intestine modified for absorption and digestion?

Answer 4

• Mucosa and submosa is folded into the plicae cirulare which increase surface area for absorption
• The lamina propria and epithelium of the mucosa are filed into villi
• Each villus contains a capillary and lacteal in the lamina propria
  capillary = tranports products of digestion, proteins and carbs
  lacteal(lymph capillary) = transports dietary fats

Question 5

How is the submucosa layer of the small intestine modified for absorption and digestion?

Answer 5

• Arranged into folds called plicae circulares - which fold into the lumen of the small intestine to increase surface area for absorption

Question 6

What are the structural specialisations of the wall of the small intestine which enable it to carry out its function of ABSORPTION?

Answer 6

• The inner surface of the small intestine has leaf-like projection = plicae circulares which increase SA for absorption
• Villus of the small intestine = finger like extension of lamina & covered in epithelium; they increase SA and contain mucous goblet cells for protection and progenitor cells which allow cell renewal
• The core of the villus
  = FCT, capillary network and lacteal

Question 7

What are the structural specialisations of the wall of the small intestine which enable to to carry out its function of DIGESTION?

• describe passage of chyme from stomach into the small intestine
• what does the pancreas secrete

Answer 7

Has mucous secreting epithelial cells and mucous glands in the duodenum to protect if from acid chyme leaving the stomach
Pancreas secretes:
- bicarbonate to neutralise pH
- inactive enzymes which are activated in the small intestine and enable chemical digestion to occur in the jejunum