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Year 1: Alimentary System > 4. Large Intestine > Flashcards

4. Large Intestine Flashcards

1
Q

What does the large intestine consist of?

A

Colon, cecum, appendix, rectum and anal canal

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2
Q

What is the cecum?

A

A blind pouch just distal to the ileocecal valve – larger in herbivores

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3
Q

What is the appendix?

A

A thin finger like extension of the cecum - no relevance in humans

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4
Q

What is the function of the colon?

A

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

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5
Q

What is the length of the colon?

A

1.5m, 6cm in diameter

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6
Q

Which side of the body is the ascending colon?

A

Right

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7
Q

Describe the landmarks signifying the transverse colon?

A

Runs from the hepatic flexure to the splenic flexure. It hangs of the stomach from the greater omentum.

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8
Q

How the descending colon orientated?

A

From the splenic flexure down to the sigmoid colon

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9
Q

What is the sigmoid colon?

A

The s shaped colon connecting the descending colon to the rectum

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10
Q

What blood supplies the proximal transverse colon?

A

Middle colic artery which is branch of the superior mesenteric artery

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11
Q

What does the inferior mesenteric artery supply?

A

The distal third of the transverse colon?

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12
Q

What does the different blood supply of the transverse colon reflect?

A

Embryological division between the midgut and hindgut

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13
Q

What does the peritoneum carry?

A

Fatty tags (appendices epiploicae)

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14
Q

Describe the muscle coat of the large intestine?

A

it has 3 thick longitudinal bands of muscle called the taeniae coli

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15
Q

What is the name of the gut walls pouches?

A

Haustra

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16
Q

What is the function of taeniae coli?

A

Large intestine motility

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17
Q

What are the appendices epiploica?

A

Pouches of peritoneum filled with fat

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18
Q

What is responsible for creating haustra?

A

The Taeniae coli which contract to form the pouches

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19
Q

Where does most of absorption occur in the large intestine?

A

Proximal colon

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20
Q

What does the colon absorb?

A

Electrolytes and water

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21
Q

Where is most of the water absorbed?

A

small intestine

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22
Q

How is Na+ and Cl- absorbed?

A

Exchange mechanisms and ion channels. Water follows by osmosis

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23
Q

Where is the rectum?

A

Dilated distal portion of the alimentary canal

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24
Q

What is the histology of the rectum?

A

Similar to the colon - has transverse rectal folds in its submucosa and absence of taenia coli in its muscularis externa

25
Q

What is the terminal portion of the alimentary system?

A

Anal canal

26
Q

What is the anal canal surrounded by?

A

Internal (circular muscle) and external anal sphincters (striated muscle)

27
Q

Describe the layers of the gut tube of the large intestine

A

Same as small intestine

28
Q

What cells exist in both the small and large intestine?

A

Enterocytes, goblet cells and stem cells found in crypts

29
Q

Why doe the mucosa of the large intestine appear smooth at the gross level

A

It has no villi

30
Q

Which intestine has the higher number of goblet cells?

A

Large intestine

31
Q

Describe how the number of goblet cells change as you move along the large intestine

A

The number of goblet cells increase as tou move distally towards the rectum

32
Q

What is the function of mucus in the large intestine?

A

It facilitates the passage of the increasingly solid colonic contents and converts bacteria and particulate matter

33
Q

What stimulates goblet cell secretion

A

Acetylcholine (parasympathetic and enteric nervous system)

34
Q

What cell dominates the crypts?

A

goblet cells

35
Q

What cells are rarer in the large intestine compared to the small intestine?

A

Paneth and enteroendrine cells

36
Q

Do the glycocalyx on the microvilli in the large intestine contain digestive enzymes?

A

No - everything should have been digested in the small intestine

37
Q

What are the muscle layers of large intestine?

A

Same as small intestine - muscularis externa consists of a inner circle and outer longitudinal layer

38
Q

What is the longitudinal layer of muscle called in the muscularis externa?

A

taenia coli

39
Q

Describe colonic contractions

A

It is a kneading process that is minimally propulsive about 5-10cm/hr at most

40
Q

What does colonic contractions promote?

A

absorption of electrolytes and water

41
Q

Describe the motility of the proximal colon?

A

Antipropulsive patterns - retain chyme

42
Q

Describe the motility of the transverse and descending colon?

A

Localised segmental contractions of circular muscle called haustral contractions - causes back and forth mixing

43
Q

Define mass movement

A

1-3 times daily resembles peristaltic wave propelling contents 1/3-3/4 of length of large intestine in a few seconds

44
Q

What food promotes rapid transport through colon?

A

high in fibre foods

45
Q

What is the large intestine innervated by?

A

Parasympathetic: ascending and transverse colon is innervated by the vagus nerve. More distal innervated by pelvic nerves.
Sympathetic: Lower thoracic and upper lumbar spinal cord
Enteric nervous system - the myenteric plexus ganglia concentrated below taenia coli

46
Q

What is the external anal sphincter controlled by?

A

Somatic motor fibres in the pudenal nerves

47
Q

What can stimulate mass movement?

A

Presence of food, hormonal/paracrine control

48
Q

How does faeces reach the rectum

A

The rectum is filled with faeces due to mass movement in the sigmoid colon.

49
Q

What controls the defecation reflex?

A

Controlled primarily by the sacral spinal cord (reflex and voluntary)

50
Q

Describe the process of defecation

A

Pressure receptors send signals via the mysenteric plexus to initiate peristaltic waves when there is a sudden distension of walls of the rectum. The external anal sphincter is under voluntary control

51
Q

How many grams of faeces are produced a day?

A

150g

52
Q

How much water is in faeces?

A

2/3

53
Q

What is in solid faeces?

A

cellulose bacteria, cell debris, bile pigment, salts (K+)

54
Q

What gives faeces its colour?

A

Bile pigment - stercobillin

55
Q

What gives faeces its colour?

A

Bile pigment - stercobillin

56
Q

What fives faeces its odour?

A

Bacterial fermentation

57
Q

Describe the relationship between mammals and their gut microbial community?

A

Symbiotic relationship

58
Q

What are the roles of intestinal flora

A

Synthesize and secrete vitamins
Prevent colonisation by pathogens
Antagonize other bacteria by inhibition or killing no-indigeneous species
Stimulate the development of certain tissues

Year 1: Alimentary System (15 decks)

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