Large Intestine Structure and Function

Question 1

What is the pathway of the junction between the small intestine and the large intestine

Answer 1

Chyme moves from Illieum through ileocaceal valve into the caesum (blind sac)

The caecum, then drains into the large intestine or can then drain down into the appendix and lymph nodes below,

Question 2

What is the four colon parts of the Large intestine

Answer 2

Ascending
Transverse
Descending
Sigmoid

Question 3

How is the muscularis externa composed in the large intestine

Answer 3

A complete layer of circular muscle

Surrounded by an incomplete layer of Longitudinal muscle
consisting of 3 narrow bands of smooth muscles called Tenia coli

Question 4

What affect does the Tenia Coli have on the large intestine

Answer 4

The teniae coli contract lengthwise to produce the haustra, the bulges in the colon

Pouches from give a puckered appearance

Question 5

What is the mucosa composed of in the large intestine

Answer 5

Simple columnar epithelium

Question 6

What is present in the large straight crypts found in the submucosa layer of the large intestine

Answer 6

Goblet cells

Question 7

What is the purpose of Goblet cells on the large intestine

Answer 7

Produce mucus, which allows lubrication for the movement of faeces

Question 8

Where is the rectum located

Answer 8

Between sigmoid colon and anal canal

Question 9

What is the structure of the rectum

Answer 9

Straight muscular tube composed of simple columnar epithelium

Question 10

Where is the anal canal located

Answer 10

Distal to the rectum and anus (2-3cm)

Question 11

What is the mucularis externia of the rectum and the anal canal compared to the remainder of the alimentary tract

Answer 11

Thicker

But anal canal is even thicker due to the presence of the internal anal spinchter

Question 12

What is the change in the mucosa layer in the anal canal

Answer 12

Changes from simple columnar to stratified squamous epithelium

Question 13

How is the colons of the large intestine involved in nutrient absorption

Answer 13

They aren’t involved

Question 14

What is the function of the colon

Answer 14

Form solid faecal pellets

Question 15

How is solid faecal pellets formed in the colon

Answer 15

Sodium is actively transported from the lumen and into the blood, so water follows osmotic gradient out into the blood, the removal of water dehydrates the chyme creating the solid formation of faeces

Question 16

What is the benefit of the long residence time of chyme in the large intestine

Answer 16

Allows time for bacterial colonisation of colonic microflora

Question 17

What is the function of colonic microflora in the colon

Answer 17

Bacterial fermentation of undigested carbohydrates

Question 18

What is the major benefit of colonic microflora in the colon

Answer 18

Produce additional energy source in short chain fatty acids

Produces Vitamin K which is needed for blood clotting

Produces Flatus

Question 19

What controls the internal and external anal spinchters

in the anus

Answer 19

Internal - smooth muscle under autonomic control

External - skeletal muscle under voluntary control

Question 20

What is the pathway occurring in the large intestine before defaecation occurs

Answer 20

After a meal there is a Mass movement of contraction from colon to rectum - this moves faecel into the rectum and distends the rectal wall upon arrival

This is senses by mechanoreceptors creating the defeaecation reflex, giving you the urge to defaecate

Question 21

What controls the defaecate reflex

Answer 21

Parasympathetic NS innervation the pelvic splanchnic

no sympathetic intervention

Question 22

What is the steps of the defeacation reflex

Answer 22

The stretched wall recoils and the rectum contracts

This causes the relaxation of the internal spinchter and the contraction of the external anal spinchters

Increasing the peristaltic activity in the colon

The increased pressure of the external anal spinchter
Under voluntary control is then relaxed and allows the explosion of faeces

Question 23

How does voluntary delay of defection occur

Answer 23

Voluntary contraction of external spinchter

Question 24

What happens to the toxins during constipation

difficulty emptying bowels

Answer 24

They are not reabsorbed but remain in faecal bulk

Question 25

What can voluntary delay of defecation cause

Answer 25

Constipation

due to delay faeces harden up due to continually water absorption so are then harder to expel

Question 26

What is the symptoms associated with constipation

Answer 26

Headaches
Nausea
Loss of appetite
Abdominal distension

Question 27

What directly causes the symptoms associated with constipation

Answer 27

The distension of the rectum due to the build up of material

Question 28

What is the definition of Diarrhoea

Answer 28

Too frequent passage of faeces which are too liquid

Question 29

What is the causes of Diarrhoea

Answer 29

Pathogenic bacteria 
Protozoans 
Viruses 
Toxins 
Foods 
Stress

Question 30

What is examples of enterotoxigenic bacteria

Answer 30

Vibrio cholerae, Escherichia coli

Question 31

How do enterotoxigenic bacteria cause detrimental diarrhoea

Answer 31

Produce protein enterotoxin bacteria that elevates intracellular secondary messengers that increase intestinal chloride secretion from crypt cells

Due to to increased osmotic gradient this increases H2O secretion that swamps absorptive capacity of villus cells therefore resulting in profuse watery diarrhoea

Question 32

Why is death a possibility in diarrhoea

Answer 32

As your body cannot tolerate that much fluid loss

Question 33

What are the secondary messengers that enterotoxigenic bacteria micmic their physiological mechanism to produce an exaggerated stimulation

Answer 33

cAMP
cGMP
Calcium

Question 34

What affect does enterotoxins have on villus cells

Answer 34

No effect - no damage

Question 35

What is the treatment for diarrhoea

Answer 35

Oral rehydration therapy (ORS)

which is a sodium/ glucose solution

Question 36

What is the purpose of the diarrhoea treatment

Answer 36

Rehydrate - by driving H2O absorption

Wash away infection

Question 37

What is flatulus composed of

Answer 37

Nitrogen 
CO2 
Hydrogen 
Methane 
Hydrogen sulphide