large intestine

Question 1

Recall anatomical facts about the large intestine

Answer 1

Located after the small intestine. Mosly comprised of ascending, transverse, descending, sigmoidal colon. Also has caecum and appendice

Question 2

What is caecum-

Answer 2

Blind pouch just distal to ileocecal valve-mostly matters for herbivores

Question 3

What other structure can you find near the caecum?

Answer 3

Appendix-not physiological relevant, but maybe a way to help repopulation of flora

Question 4

How long is the colon? And what are the main function?

Answer 4

1.5m long, 6cm larger. Main role is absorbing water and bringing undigested food to anus

Question 5

Where does the blood supply of the colon come from? And where does It drain?

Answer 5

Top end of colon (asending and 2/3 or transverse)-superior mesenteric artery. End part (1/3 and transverse and descending)-inferior mesenteric. Drain to Portal vein

Question 6

What are the miain characteristics of colon cell wall?

Answer 6

Peritoneum carry fatty tags. Hs a muscle coat-3thick longitundinal bands (taeniae coli). Lympoid nods are common in the colon

Question 7

What are Haustra?

Answer 7

Like small envagination making pouches in the colon-not always the same due to muscular tone (tenia coli is shorter than in small intestine, meaning it coils more

Question 8

What is the main role of the colon?

Answer 8

Absorb electrolytes and water-mainly in proximal colon. Na/Cl absorbed by ion channels. Water follow osmosis. K+ moves OUT passively (absorbed in small intestine). Can absorb up to 4.5 L (around 1.5 normally)-above that is diarrheae

Question 9

What is the rectum? What is its role

Answer 9

Dilated distal portion alimentary canal. Hitological Similar to colon. Gives into the anal colon-circular muscle (SMC internal muscle sphincter) and striated muscle external anal sphincter under you control

Question 10

What are the major layers of cell in the colon

Answer 10

Serosa in outside. Longitudinal, then circular muscle, then submucosa, then muscularis mucosa, then basement mebrane and epithelium

Question 11

What are the common type of cells in the colon? Why is it smoother than small intestine?

Answer 11

Enterocytes and goblet cells are common, organised in crypts with stem cells at the bottom
Smooth because no villi, and shorter microvilli-don’t aborb macronutrients

Question 12

What are the characteristics of colon Golbet cells?

Answer 12

Higher number than small intestine-more prevalent in crypts, and increase distally-mucus helps transport the solid excrement, and cover bacteria and particulate matter. Can be stimulated by hormones and acetylcholine by PNS)

Question 13

Are there Paneth cells in colon? Why?

Answer 13

No Paneth cells in the colon-maybe because need flora to be alive, also bacteria don’t make it down there easy. Enteroendocrine cells are also rare

Question 14

Goes the large intestine contain glycocylax?

Answer 14

Has it but doesn’t contain digestive enzymes because that should have been done by small intestine

Question 15

How are large intestine muscle organised? What does that cause

Answer 15

Muscularis externa has inner circular and outer longitudinal-3 bands, last one protrudes-teneae coli. The longitudinal sometimes cross the circular. Longitudinal are shorter than circular, which causes the envaginating and crumpling. This is to be able to control/move stuff better

Question 16

What can be said about colon motility?

Answer 16

Colonic contraction-kneading-helps water and electrylyte absorption
In proximal colon, antipropuslive to keep chime
In transverse and descending-localised sehmental contraction cauled hautral contraction to cause mixing (every 30min)

Question 17

What is colon mass movement?

Answer 17

1-3-reseembles peristaltic wave, which expulses the matter-coffe increases that (smoking too)

Question 18

How does the parasympathetic system connectthe large intestine

Answer 18

Acdening and most tranverse are innervated by vagus nerve (which also increase stomach acid, and pancreae release)-but after its pelvic nerve

Question 19

What is the role of the sympathetic nerve connect to large intestine?

Answer 19

Controll vascular tone, and reduce movement

Question 20

What are the different control systems of the large intestine?

Answer 20

Enteric nervous system, myenteric plexus ganglia below taenia coli, presence of food (homonal or neural?). Hormonal/paracrine control (eg: aldrosterone (icrease sodium channels), calcitrol)

Question 21

What happens during defecation?

Answer 21

Rectum filled with faeces by mass movement in sgimoind colon> Store stools until convenient. Controlled ANS and CNS
Dsitention of rectum wall, pressure recepters initate peristatic waves in descending, sigmoid and rectum, inhbit internal sphincter.

Question 22

Why is the end of the rectum called the “social part”?

Answer 22

It can distinguish between liquid, solid, gases very well. BUT it has difficulties distinguish between oil and gas (so orlistat)

Question 23

What are in faeces?

Answer 23

Around 150g per day-2/3 water. Solids are cellulose, bacteria (fermentation gives odour), cell debris, bile pigment (givrs the color), salts

Question 24

Where are most of out intestinal flora located?

Answer 24

Stomach and small intestine have little. Several orders of magnitudes more in colon

Question 25

What are the roles of the intestinal flora?

Answer 25

They are very diverse (nearly 1.5kg)-nearly a big oragan
Synthesis and excrete vitamins for us to absorb (like Vitamin K)
Prevent colonisation by pathogens by being better adapted to environement and taking nutrients
Antagonise other bacteria through actually killing mechanisms
Also possibly has a priming of immune system-stimulates cross reactive AB
And seems to stimulate the development of some tissues like caecu
Can digest by fibers (we as mammals cannot take them in)-produce short FA whiach can then regulate gut hormone release, or be used as energy, or possiblt influence functions like insulin sensitivity

Question 26

What are the main types of normal flora?

Answer 26

Bacteroides-gram negative anaerobic bacteria

Bifidobacteria are gram-positive, lactic acid bacteria-friendly bacteria preventing pathogens