The large intestine Flashcards

1
Q

what does the large intestine consist of?

A

consists of the colon, caecum, appendix, rectum and the anal canal

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2
Q

what is the caecum?

A

the caecum is a blind path

it is not often used in humans

it is usually fermenting

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3
Q

what is the appendix?

A

the appendix is a thin fingerlike projection extension of the caecum

  • not very useful in humans
  • potentially a lifeboat for mirobiome
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4
Q

what are the dimensions of the colon?

A

1.5 m long , 6cm diameter

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5
Q

what is the function of the colon?

A

to reabsorb electrolytes and water and also to flush the waste

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6
Q

where are the ascending colon, transverse colon, descending colon and sigmoid colon positioned?

A

the ascending colon = caecum to the hepatic flexure

transverse colon = hepatic flexure to splenic flexure

descending colon = splenic flexure to sigmoid colon

sigmoid colon = descending colon to rectum

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7
Q

what is the blood supply of the colon?

what is the proximal transverse colon supplied by?

what is the distal third colon supplied by?

A

Proximal transverse colon supplied by middle colic artery

(branch of the superior mesentric artery)

Distal third of transverse colon supplied by inferior mesenteric artery.

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8
Q

what are some of the structural features of the colon?

and what are the functions of these features?

A
  • fatty tags (appendices epiploicae)

protective function against infection

  • longitudinal muscle bands ( taeniae coli)

Creates haustra, necessary for large intestine motility.

  • nodules of lymphoid tissue (Solitary nodules)
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9
Q

what are the histological differences of the rectum?

A

Histologically similar but absent taeniae coli ( longitudinal muscle bands) and transverse rectal folds in submucosa.

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10
Q

what control is the internal anal sphincter and external sphincter under?

A

internal anal sphincter - unconcious control

external spinchter - voluntary control

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11
Q

Diagram of the Rectum ?

A
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12
Q

what are the similarities between the large intestine and the small intestine?

A
  • abundant enterocytes
  • abundant goblet cells
  • abundant crypts with stem cells present
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13
Q

how is the large intestine distinguishable from the small intestine?

A
  • there are no villi in the large intestine
  • Enterocytes have short and irregular microvilli
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14
Q

what is the mucosal structure?

A
  • goblet cells present
  • More goblet cells than the small intestine with number higher in the crypts and more distally in the colon
  • no paneth cells
  • Enteroendocrine cells are rarer than small intestine
  • Glycocalyx present on microvilli BUT does not hold digestive enzyme in ‘unstirred layer’
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15
Q

what are the muscle layers of the large intestine ?

A
  • like small intestine
  • inner circular and outer longitudinal is present
  • 3 clear bands – taeniae coli
  • there are oval segments called haustra that can contract induvidually
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16
Q

what are the movements of the rectum and anal canal?

A

these movements are substantial and continuous – used for kneading contents.

17
Q

how fast are the colonic contractions?

A

5- 10 cm / AN HOUR

18
Q

What are the movements of the colon and proximal colon like?

A

the colon is slow propulsion promotes absorption of electrolytes and water.

the proximal colon is ‘anti-propulsive’ patterns

19
Q

what are the movements like in the transverse and descending colon?

A

haustral contractions cause back and fourth mixing

There are then short propulsions ever 30 minutes

these increase in frequency following a meal

20
Q

when do mass movements happen and what can they propel?

A
  • occur 1- 3 times a day
    • propel contents 1/3-3/4 length of large intestine in a few seconds

these movements depend upon fibre

21
Q

what is the nervous control of the large intestine?

parasympathetic ?

sympathetic ?

enteric?

A

parasympathetic ? ascending colon, most of transverse colon by VAGAL nerve. More distal by PELVIC nerves

sympathetic ? – lower thoracic and upper lumbar spinal cord.

enteric

Myenteric plexus ganglia concentrate below the taeniae coli.

22
Q

where do the faeces travel and where are they stored?

A

the rectum becomes filled with faeces by mass movements in sigmoid column which then stores the stool

23
Q

what is the defecation reflex controlled by?

A

controlled by the sacral spinal-cord

24
Q

how does defecation work?

A
  • reflex inhibition of internal sphincter to balloon the walls of the rectum
  • pressure receptors send signals to Myenteric plexus to initiate peristaltic waves
  • external sphincter under voluntary control which means one can choose whether to defecate or resist the urge
25
Q

what can the last few centimetres of the rectum determine?

A

determines solid, liquid or gas

26
Q

where are most of the the bacteria present?

A

the stomach and small intestine has a few bacteria

the large intestine has many bacteria - essential to function

27
Q

what are the functions of the intestinal flora to humans?

A
  • they synthesis and excrete vitamins like vitamin K
  • they prevent colonisation by pathogens by outcompeting them
  • they kill pathogens by producing antibacterials
28
Q

what are the beneficial roles of the intestinal flora to humans ?

A
  • immunity - production of cross-reactive antibodies
  • growth - stimulates the development of certain tissues like the caecum
  • fibre breakdown - flora can breakdown the fibre
  • fatty acids - produces short-chain fatty acids which might be used as hormone release, energy, or influence food intake
29
Q

what are the most prevalent bacteria?

A
  • gram negative bacteria

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