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Alimentary System > [Physiology] Large Intestine > Flashcards

[Physiology] Large Intestine Flashcards

1
Q

what is the legnth of the colon

A

(1.5 – 1.8 metres)

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2
Q

what are the four parts of the colon

A

ascending, transverse, descending, sigmoid

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3
Q

what muscle layers are complete in the colon

A

Circular muscle layer complete but longitudinal muscle layer incomplete

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4
Q

what are the three bands present in the colon

A

teniae coli (entire length of colon)

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5
Q

what do contractions of the tenia coli result in

A

pouches (haustra) – puckered appearance

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6
Q

what is the mucosa comprised of in the large intestine

A

simple columnar epithelium – flat

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7
Q

what is the rectum

A

Straight, muscular tube (between end of sigmoid colon and anal canal)

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8
Q

what type of mucosa is found in the rectum

A

simple columnar epithelium

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9
Q

how is the muscularis externa characterised in the rectum

A

thick compared to other regions of alimentary canal

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10
Q

how much is the distance between distal rectum and anus

A

2-3cm

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11
Q

is the muscularis externa thicker in the rectum or anus

A

anal canal as there is an internal anal sphincter

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12
Q

what type of muscle is the external anal sphincter comprised of

A

skeletal muscle

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13
Q

what type of epithelium is found in the anal canal

A

simple columnar gradually turning into stratified squamous

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14
Q

what is the role of the colon in nutrient absorption

A

no role in humans

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15
Q

what does the colon actively do

A

Actively transports sodium from lumen into blood

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16
Q

what effect does actively transporting sodium from lumen into blood

A

osmotic absorption of water, dehydrating the chyme producing solid faecal pellets

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17
Q

what takes long residence time in the colon

A

bacterial colonisation

18
Q

colonic microflora

A

10^14 bacteria

19
Q

Bacterial fermentation of undigested carbohydrate

A

Short chain fatty acids (energy source in ruminants)

Vitamin K (blood clotting)

Gas (flatus) - nitrogen, CO2, hydrogen, methane, hydrogen sulphide

20
Q

what is the anus normally closed by

A

internal anal sphincter and external anal sphincter

21
Q

internal anal sphincter

A

smooth muscle under automatic control

22
Q

external anal sphincter

A

skeletal muscle under voluntary control

23
Q

what occurs following a meal

A

Wave of intense contraction (Mass Movement Contraction) from the colon to the rectum

24
Q

what is distension of rectal wall produced by

A

produced by mass movement of faecal material into rectum

25
Q

once there is a mass movement of faecal material into rectum what is stimulated

A

mechanoreceptors → defaecation reflex → urge to defaecate

26
Q

what type of control is the defaecation reflex under

A

arasympathetic control – via pelvic splanchnic nerves (no sympathetic influence)

27
Q

describe the parasympathetic control of defacation

A

Contraction of rectum

Relaxation of internal and contraction of external anal sphincters

Increased peristaltic activity in colon

28
Q

how are faeces expulsed

A

↑ Pressure on external anal sphincter - relaxes under voluntary control ⇒ expulsion of faeces

29
Q

as faeces are expulsed under voluntary control what is there

A

a voluntary delay in defication

30
Q

what causes constipation

A

No absorption of toxins from faecal material following long periods of retention

31
Q

what is the frequency of bowel movements like in a constipated individual

A

vary considerably from individual to individual

32
Q

what are some associated symptoms with constipation

A

Headaches
Nausea
Loss of appetite
Abdominal distension

33
Q

what is diarrhoea

A

Too frequent passage of faeces which are too liquid

34
Q

what are some causes of diarrhoea

A

pathogenic bacteria
protozoans
viruses
toxins
food

35
Q

what is a major killer of children under 5 years of age in developing countries

A

diarrhoea

36
Q

how many cases of child diarhoea are there in a year

A

1500 million
0.5 million deaths

37
Q

what are examples of Enterotoxigenic Bacteria

A

vibrio cholerae, Escherichia coli

38
Q

what does enterotoxigenic bacteria do

A

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells

39
Q

what is increased as a result of maximal turn on of intestinal chloride secretion from crypt cells

A

H2O secretion increased

40
Q

what is elevated by enterotoxigenic bacteria

A

intracellular second messengers:
cAMP
cGMP
calcium

41
Q

H2O secretion swamps absorptive capacity of villus cells → profuse watery diarrhoea (25 litres per day for cholera)

A
42
Q

what is the treatment for secretory diarrhoea

A

Give sodium/glucose solution

or

Secretion still going ⇒ wash away infection
Oral rehydration therapy (ORS)

Alimentary System (44 decks)

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