[Physiology] Large Intestine

Question 1

what is the legnth of the colon

Answer 1

(1.5 – 1.8 metres)

Question 2

what are the four parts of the colon

Answer 2

ascending, transverse, descending, sigmoid

Question 3

what muscle layers are complete in the colon

Answer 3

Circular muscle layer complete but longitudinal muscle layer incomplete

Question 4

what are the three bands present in the colon

Answer 4

teniae coli (entire length of colon)

Question 5

what do contractions of the tenia coli result in

Answer 5

pouches (haustra) – puckered appearance

Question 6

what is the mucosa comprised of in the large intestine

Answer 6

simple columnar epithelium – flat

Question 7

what is the rectum

Answer 7

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

Question 8

what type of mucosa is found in the rectum

Answer 8

simple columnar epithelium

Question 9

how is the muscularis externa characterised in the rectum

Answer 9

thick compared to other regions of alimentary canal

Question 10

how much is the distance between distal rectum and anus

Answer 10

2-3cm

Question 11

is the muscularis externa thicker in the rectum or anus

Answer 11

anal canal as there is an internal anal sphincter

Question 12

what type of muscle is the external anal sphincter comprised of

Answer 12

skeletal muscle

Question 13

what type of epithelium is found in the anal canal

Answer 13

simple columnar gradually turning into stratified squamous

Question 14

what is the role of the colon in nutrient absorption

Answer 14

no role in humans

Question 15

what does the colon actively do

Answer 15

Actively transports sodium from lumen into blood

Question 16

what effect does actively transporting sodium from lumen into blood

Answer 16

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

Question 17

what takes long residence time in the colon

Answer 17

bacterial colonisation

Question 18

colonic microflora

Answer 18

10^14 bacteria

Question 19

Bacterial fermentation of undigested carbohydrate

Answer 19

Short chain fatty acids (energy source in ruminants)

Vitamin K (blood clotting)

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

Question 20

what is the anus normally closed by

Answer 20

internal anal sphincter and external anal sphincter

Question 21

internal anal sphincter

Answer 21

smooth muscle under automatic control

Question 22

external anal sphincter

Answer 22

skeletal muscle under voluntary control

Question 23

what occurs following a meal

Answer 23

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

Question 24

what is distension of rectal wall produced by

Answer 24

produced by mass movement of faecal material into rectum

Question 25

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

Answer 25

mechanoreceptors → defaecation reflex → urge to defaecate

Question 26

what type of control is the defaecation reflex under

Answer 26

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

Question 27

describe the parasympathetic control of defacation

Answer 27

Contraction of rectum Relaxation of internal and contraction of external anal sphincters Increased peristaltic activity in colon

Question 28

how are faeces expulsed

Answer 28

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

Question 29

as faeces are expulsed under voluntary control what is there

Answer 29

a voluntary delay in defication

Question 30

what causes constipation

Answer 30

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

Question 31

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

Answer 31

vary considerably from individual to individual

Question 32

what are some associated symptoms with constipation

Answer 32

Headaches Nausea Loss of appetite Abdominal distension

Question 33

what is diarrhoea

Answer 33

Too frequent passage of faeces which are too liquid

Question 34

what are some causes of diarrhoea

Answer 34

pathogenic bacteria protozoans viruses toxins food

Question 35

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

Answer 35

diarrhoea

Question 36

how many cases of child diarhoea are there in a year

Answer 36

1500 million 0.5 million deaths

Question 37

what are examples of Enterotoxigenic Bacteria

Answer 37

vibrio cholerae, Escherichia coli

Question 38

what does enterotoxigenic bacteria do

Answer 38

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

Question 39

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

Answer 39

H2O secretion increased

Question 40

what is elevated by enterotoxigenic bacteria

Answer 40

intracellular second messengers: cAMP cGMP calcium

Question 41

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

Question 42

what is the treatment for secretory diarrhoea

Answer 42

Give sodium/glucose solution or Secretion still going ⇒ wash away infection Oral rehydration therapy (ORS)