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The Alimentary Canal > Large Intestine Structure and Function > Flashcards

Large Intestine Structure and Function Flashcards

1
Q

What is the sphincter between the ileum and the caecum?

A

Ileocecal valve

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2
Q

What are the 4 parts of the colon?

A

Ascending
Transverse
Descending
Sigmoid

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3
Q

Describe the muscularis externa of the large intestine?

A

Circular muscle layer complete but longitudinal muscle layer incomplete

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4
Q

What are the 3 bands of longitudinal muscle layer called?

A

Teniae coli - extends the whole length of colon

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5
Q

What does contractions of teniae coli cause?

A

Pouches called haustra - puckered appearance

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6
Q

Describe the mucosa of the large intestine

A

Simple columnar epithelium - flat
Large straight crypts lined with goblet cells

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7
Q

What is the function of goblet cells on the crypts?

A

Secrete mucus which lubricates the movement of faeces

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8
Q

Describe the histology of the rectum?

A

Muscular tube
Simple columnar epithelium
Thick muscularis externa

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9
Q

Describe the histology of the anal canal

A

Muscualris thicker than rectum
Simple columnar but moves to stratified squamous outside body

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10
Q

What is the difference between the internal and external anal sphincter?

A

Internal - smooth muscle
External - skeletal muscle so under voluntary control

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11
Q

Describe the function of the colon

A

No important nutrient absorption role
Actively transports Na from lumen into blood so osmotic absorption of water which dehydrates chyme - solid faeces

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12
Q

What does the long residual time in colon cause?

A

Bacterial colonisation (helps break down cellulose)
Bacterial fermentation of undigested carbohydrate

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13
Q

What are the products of bacterial fermentation of undigested carbohydrate?

A

Short chain fatty acids
Vitamin K - blood clotting
Gas - nitrogen, CO2, hydrogen, methane, hydrogen sulphide

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14
Q

Describe defaecation following a meal

A

Wave of intense contraction (MMC) from colon to rectum
Distention of rectal wall activates mechanoreceptors causing defaecation reflex

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15
Q

What nerve system controls the defaecation reflex?

A

Under parasympathetic control by pelvic splanchnic nerve
(no sympathetic control)

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16
Q

Describe the defaecation reflex

A

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

17
Q

What does increased pressure on external anal sphincter cause?

A

Relaxation under voluntary control so them expulsion of faeces

18
Q

What causes a delay in defaecation?

A

Descending pathways

19
Q

What are some symptoms with constipation?

A

Headaches
Nausea
Loss of appetite
Abdominal distention - due to distention of rectum

20
Q

Does constipation effect absorption of faecal material?

A

No absorption of toxins

21
Q

What is diarrhoea?

A

Too frequent passage of faeces which are too liquid

22
Q

What are some causes of diarrhoea?

A

Pathogenic bacteria
Protozoans
Viruses
Toxin
Food

23
Q

What are examples of enterotoxigenic bacteria?

A

Vibrio cholerae
E.coli

24
Q

Describe enterotoxigenic bacteria

A

Produce protein enterotoxins which maximally turn on intestinal Cl secretion from crypt cells which increases water secretion

25
Q

What intracellular messengers does enterotoxins elevate?

A

cAMP - activates CFTR
cGMP
Calcium

26
Q

How does water secretion effect villus cells?

A

Swamps absorptive capacity of villus cells so perfuse watery diarrhoea

27
Q

Do enterotoxins damage villus cells?

A

No

28
Q

What is the treatment of secretory diarrhoea?

A

Give sodium/ glucose solution

29
Q

How does sodium/glucose solution help secretory diarrhoea?

A

Drives H2O absorption so rehydrates
Secretion still going so washes away infection

30
Q

What is the treatment to secretory diarrhoea called?

A

ORS - oral rehydration therapy

The Alimentary Canal (33 decks)

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