Large intestine structure and function

Question 1

Describe the structure of the large intestine

Answer 1

• Caecum
	• Ileocecal sphincter
	• Ascending colon
	• Transverse colon
	• Descending colon
	• Simple columnar epithelium 
	• Muscles
	- Complete circular
	- Incomplete longitudinal 
	- Teniae coli (3 strips that continue for the whole colon)
	- Haustra (circular muscle puffs out)
	• Rectum→ anal canal

Question 2

What are the functions of the large intestine?

Answer 2

• Absorb sodium chloride and water: dehydrate chyme, turning it into faecal matter
• No important nutrient absorption
- Bacteria break bonds that we have no enzymes to break (cellulose) and turn them into short chain fatty acids and gas (N2, CO2, methane, H2 and hydrogen sulphide)

Question 3

Describe the importance of intestinal bacteria in the digestive system

Answer 3

• Intestinal bacteria can breakdown indigestible carbohydrates
They produce: SCFAs, vitamin K (clotting) and gas (N2, CO2, methane, H2 and hydrogen sulphide)

Question 4

Describe the rectum

Answer 4

• Smooth muscle
  
  • Large muscularis
  • Simple columnar
    
    • Straight

Question 5

Describe the anal canal

Answer 5

• Bigger muscularis than rectum
  
  • Simple columnar which turns to satisfied squamous
  • Internal and external anal sphincters
  • Internal= smooth muscle
  • External= skeletal muscle

Question 6

Describe the mechanisms controlling defecation

Answer 6

• MMC (migrating motility complex) wave all through colon to rectum
→ Pushes faecal matter to rectum
→ Rectum distension
→ Mechano receptors
→ Defecation reflex
→ Urge to defecate
• Parasympathetic (sympathetic has no effect)
• Contraction of rectum causes the relaxation of the internal and external sphincters which increase perisristalic activity in the colon
→ This increases the pressure on the internal and external sphincters
→ Releases voluntary
→ Expulsion of faeces
• Voluntary delay

Question 7

Describe the causes mechanisms which cause secretory diarrhoea

Answer 7

• Causes
	- Pathogenic bacteria
	- Food
	- Protozoans
	- Viruses
	- Toxins
	- Stress
	• Mechanisms (bacteria)
	- Bacteria turn on crypt cells which result in the increased secretion of H2O
	- They do this via: cAMP, cGMP and calcium
	- The large intestine is not able to absorb enough water 
	- Liquid faeces

Question 8

Explain how secretory diarrhoea can be treated with simple salt/ sugar

Answer 8

• Cells are not damaged
  
  • Take in more salt then more water is absorbed
  • Secretions wash infections away