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Alimentary > The Large Intestine > Flashcards

The Large Intestine Flashcards

1
Q

What does the large intestine consist of

A 
Colon
Cecum
Appendix
Rectum
Anal canal
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2
Q

What is the caecum

A

Blind pouch distal to the ileocecal valve

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3
Q

What is the appendix

A

Thin, finger-like extension of the caecum (no physiological relevance)

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4
Q

What is the function of the colon

A

Reabsorption of electrolytes and water + elimination of undigested food and waste

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5
Q

What is the size of the colon

A

1.5 m

6cm diameter

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6
Q

Describe the colon structure

A 
Caecum
Ascending colon
Hepatic flexure
Transverse colon
Splenic flexure
Descending colon
Sigmoid colon
Rectum
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7
Q

How is the colon attached to the stomach

A

Wide band of tissue called the greater omentum

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8
Q

Describe the vasculature of the colon

A

Proximal transverse colon - middle colic artery (branch of the superior mesenteric artery)

Distal third of the transverse - inferior mesenteric artery

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9
Q

Describe the peritoneum

A 
Carries fatty tags (appendices epiploicae)
muscle coat (taeniae coli) - 3 longitudinal bands required for motility
Peyer's patches in the small intestine, solitary nodules in the large intestine
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10
Q

What are haustra

A

Pouched ovoid segments that are caused by the shorter Taenia coli (than the circular muscle) in the large intestine
Can contract individually

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11
Q

Describe absorption in the large intestine

A

More in the proximal colon
Na+ and Cl- absorbed via exchange and ion channels
Water follows via osmosis
K+ moves passively into the lumen

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12
Q

How is the rectum distinguished from the colon

A

Histology similar to the colon but has transverse rectal folds in its submucosa
Absence of Taenia coli in the muscular externa

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13
Q

Describe the anal canal

A

Terminal portion of the rectum

Surrounded by internal/ circular muscle and external/striated muscle anal sphincters

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14
Q

Describe the mucosal structure of the large intestine

A

No villi (small SA)
Enterocytes and goblet cells are abundant
Enterocytes have short irregular microvilli for salt resorption (+glyocalyx without enzymes)
Abundant crypts
Stem cells + goblet cells in the crypts

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15
Q

Describe the goblet cells of the large intestine

A

More than in the SI
More prevalent in the crypts than on the surface
no. increases distally
Mucus produced facilitates passage of solid colonic contents + bateria

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16
Q

What stimulates goblet cells secretion

A

Acetylcholine (parasympathetic and enteric nervous system)

17
Q

Describe the muscle layers of the large intestine

A

Muscularis externa consists of an inner circular and outer longitudinal layer
Circular muscles = segmentally thickened
Longitudinal layer = 3 bands as Taenia coli
Bundles of taeniae coli penetrate the circular layer at irregular intervals

18
Q

Describe the motility of the large intestine

A

Colonic contractions are 5-10cm/hr
Promotes absorption + mixing
Anti-propulsive patterns in the proximal colon to retain chyme

Transverse + descending colon = localised segmental contractions to cause back and forth mixing (haustral)
Short propulsive movements every 30mins

19
Q

Describe mass movement in the large intestine

A

1-3 times daily
Resembles a peristaltic wave
propels contents 1/3 - 3/4 of the length of the LI
Fibre, cigarettes and coffee promote rapid transport

20
Q

What controls the large intestine

A

Parasympathetic
ascending colon and transverse colon is innervated by the vagus nerve
Distal colon innervated by the pelvic nerves

Sympathetic
Lower thoracic and upper lumbar spinal cord

21
Q

What controls the external anal sphincters

A

Somatic motor fibres in the pudendal nerves (voluntary movement)

22
Q

What is Hirschsprung’s disease

A

No enteric intramural ganglia

23
Q

Describe the enteric nervous system

A

Myenteric plexus ganglia concentrated below the Taenia coli

Presence of food stimulates mass movement

24
Q

Describe defecation

A

The rectum is filled with faeces by mass movement in the sigmoid colon
Stores stool until convenient
Defecation is controlled by the sacral spinal cord (reflex and voluntary)

25
Q

Describe stimulation of defecation

A

Reflex to sudden distension of walls of rectum
Pressure receptors send signals via myenteric plexus to initiate peristaltic waves in descending, sigmoid colon and rectum
internal anal sphincter inhibited (external is voluntary)
Weak intrinsic signal augmented by autonomic reflex

26
Q

Describe faeces

A

150g a day
2/3 water
solids: cellulose, bacteria, cell debris, bile pigments, salts (K+)

27
Q

What gives the colour of faeces

A

Bile pigments and bacterial fermentation

28
Q

Describe the flora of the large intestine

A

Symbiotic relationship with their gut microbial community (microbiome)
Large intestine has many, diverse, highly metabolically active bacteria
comprises of 1.5kg of live bacteria

29
Q

What are the roles of the intestinal flora

A

Synthesise and excrete vitamins (e.g. K)
prevent colonisation by pathogens by competing for attachment sites for essential nutrients
Antagonise other bacteria through substances that inhibit or kill
Stimulates the production of cross-reactive antibodies
Stimulate the development of the caecum and lymph tissues
Breaking down fibre
Produce short chain fatty acids which can regulate gut hormone release or used as an energy source

30
Q

What are the normal types of flora

A

bacteroides

Gram -ve
Anaerobic
non-spore forming bacteria

31
Q

Give an example of types of normal flora

A

Bifidobacteria
gram +ve
non-spore forming
lactic acid bacteria

32
Q

What is the ileocaecal valve

A

muscular sphincter that separates the distal ileum from the caecum
Tonically active and constricted, only relaxes to allow passage of the fluid chyme into the large intestine. Prevents the microbiota (gut bacteria) from migrating into the ileum.

33
Q

How much water is absorbed in the large intestine

A

capable of 4.5L of water, usually 1.5L

>4.5L will cause diarrhoea

34
Q

What has gut bacteria been linked to

A 
Drug metabolism
Insulin resistance
Bile acid metabolism
Lipid metabolism
Obesity

Alimentary (16 decks)

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