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GI Anatomy > Physiology - small + large intestine > Flashcards

Physiology - small + large intestine Flashcards

1
Q

Length of small intestine - average & range

A

6m

Range 4.5 - 9m

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2
Q

Length of duodenum + 3 functions of duodenum

A

25cm
Neutralise gastric acid
Digestion
Fe absorption

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3
Q

Length of jejunum + function

A

2.5m

Nutrient absorption

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4
Q

Length of ileum + function

A

3.5m

NaCl/ H2O absorption –> chyme dehydration

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5
Q

3 structural features of small intestine

A

Folded to add surface area for absorption
Villi present on mucosal surface
Microvilli line the villi

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6
Q

What are found at the base of villi

A

Crypts

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7
Q

What secreting cells are found in the villi

A

Goblet cells

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8
Q

Function of villi (absorption of 8 things)

A 
ABSORPTION OF
 NaCl
 Monosaccharides
Amino acids
Peptides
Fats
Vitamins
Minerals - Fe, Zn
Water
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9
Q

Function of crypt cells

A

SECRETION OF

Cl and water

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10
Q

What happens to the K+ that’s pumped into epithelial cells via Na/K ATPase

A

K is recycled via K recycler protein back out of cell because cell would become too positive inside which would remove the ELECTRICAL PART of the ELECTROCHEMICAL GRADIENT

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11
Q

What fluid does small intestine secrete

A

Intestinal

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12
Q

How much water do crypt cells secrete a day

A

1500ml

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13
Q

Why is secretion of water from crypt cells passive (osmotic)

A

Because crypt cells actively secrete Cl- into lumen so water follows that osmotic gradient

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14
Q

Why is H2O secretion important in SI (4)

A
  1. Maintains lumen contents in liquid state - easier for digestion
  2. Promotes mixing of nutrients with digestive enzymes
  3. Helps nutrients to get closer to absorbing surface
  4. Dilutes and washes away potentially harmful substances
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15
Q

What transporter transports Cl across the epithelial cells of crypts + how does it work

A

Na/K/Cl co-transporter
Moves 2 Cl- , 1 Na+ , 1 K+ into epithelial cell
The Na+ that enters gets pumped back out via Na/K pump
The K+ that enters also leaves the cell via K+ recycler protein (late K+ channels) to stop cell getting too positive

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16
Q

Once Cl- is pumped into epithelial cell via Na/K/Cl co-transporter, how does it get out of cell into intestinal lumen

A

Leaves through apical membrane via chloride channels - CFTR protein

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17
Q

How is the CFTR channel regulated (3)

A

An enzyme in the basolateral membrane called ADENYLATE CYCLASE (AC) converts ATP –> cAMP
cAMP then phosphorylates protein kinase A (PKA)
PKA then activates CFTR, opening it

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18
Q

3 features of SI that increases surface area

A

Circular folds (plicae)
Villi
Microvilli

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19
Q

2 types of intestinal motility

A

Segmentation

Peristalsis

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20
Q

Describe segmentation

A

Contraction + relaxation of short intestinal segments
Contraction moves chyme into adjacent areas of relaxation then relaxed areas contract and push chyme back to where it was so the content isn’t actually moving down the intestine

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21
Q

Purpose of segmentation

A

Allows mixing of contents in SI with digestive enzymes

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22
Q

What are segmentation contractions generated by + description of the contractions

A

Basic electrical rhythm

Segmentation contractions are constant due to pacemaker cells in the longitudinal muscle layer

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23
Q

What does the intestinal basic electrical rhythm do

A

Produces back and forth changes in membrane potential

When the membrane potential hits depolarisation threshold, AP fires –> causing segmentation contraction

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24
Q

What determines strength of segmentation contraction

A

AP frequency

Therefore frequency of segmentation contractions are determined by BER

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25
Q

Parasympathetic activity in vagus nerve and sympathetic activity in spinal nerves has what effect on segmentation

A

Parasympathetic - increases segmentation contractions

Sympathetic - decreases segmentation contraction

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26
Q

Describe peristalsis

A

Occurs after segmentation

Muscle on oral side of bolus contracts and muscle on anal side of bolus relaxed, pushing bolus down the SI

27
Q

What complex does peristalsis involve + describe what it is

A

Migrating motility complex (MMC) is a wave of electrical activity triggering peristaltic waves
MMC starts in the gastric antrum and ends in terminal ileum

28
Q

Function of MMC

A

Moves undigested material into LI

Limits bacterial colonisation of SI (inhibits migration of bacteria in colon into terminal ileum)

29
Q

What hormone initiates a MMC

A

Motilin

30
Q

What stops MMC and initiates segmentation

A

Arrival of food in stomach (gastric emptying)

31
Q

Describe the gastroileal reflex (3)

A

Increased segmentation activity opens ileocaecal valve allowing entry of chyme into LI –> distends colon –> causing reflex contraction of ileocaecal valve to stop more chyme entering colon

32
Q

Length of large intestine

A

1.5 - 1.8m

33
Q

5 parts of large intestine

A

Caecum –> ascending colon –> transverse colon –> descending colon –> sigmoid colon

34
Q

Which muscle layer of muscularis externa is incomplete in LI

A

Longitudinal

35
Q

What is the longitudinal muscle layer called in the LI

A

Teniae coli

36
Q

Contractions of the teniae coli create what structures

A

Haustra - pouches

37
Q

Crypts in the large intestine are lined with lots of what cells + purpose of these cells

A

Goblet cells which secrete mucus onto mucosal surface, providing lubrication for faeces to move

38
Q

What does the rectum do + type of epithelium in rectum

A

Connection between sigmoid colon and anal canal

Simple columnar

39
Q

Where is the anal canal

A

Between distal rectum and anus

40
Q

What’s special about the musularis externa of the rectum and anal canal

A

Muscularis of rectum is very thick compared to other regions of GI tract but muscularis of anal canal is EVEN THICKER THAN RECTUM

41
Q

The muscularis externa of the anal canal forms what

A

Internal anal sphincter (smooth muscle)

42
Q

What kind of muscle forms the external anal sphincter allowing us to control it voluntarily

A

Skeletal muscle

43
Q

What does the epithelium change to in anal canal

A

Stratified squamous

44
Q

Function of colon (3)

A

Reabsorbs sodium and therefore osmotic absorption of water into blood –> dehydrates chyme –> forming solid faeces

45
Q

How much bacteria in colon

A

10^14

46
Q

Importance of colonic bacteria

A

Allows fermentation of carbohydrates that can’t be digested by digestive enzymes, i.e. CELLULOSE

47
Q

Products of bacterial fermentation of carbohydrates

A

Short chain fatty acids (energy source)

Vitamin K (needed for blood clotting)

Gas - due to nitrogen, CO2, hydrogen, methane products

48
Q

What initiates defaecation reflex (3)

A

Distension of rectal wall due to mass movement of faecal material into rectum –> mechanoreceptors sense the pressure from the distension –> initiating defaecation reflex

49
Q

What controls the defaecation reflex (neural)

A

Parasympathetic nervous system via pelvic splanchnic nerves S2-4

50
Q

What actually happens in the defaecation reflex (4)

A
  1. Rectum contracts
  2. Internal anal sphincter relaxes
  3. External anal sphincter contracts
  4. Increased peristalsis in colon –> puts pressure on external sphincter –> relaxing it voluntarily –> expelling faeces
51
Q

When does constipation occur

A

When there’s no absorption of toxins from faecal material following long periods of retention

52
Q

What is diarrhoea

A

Too frequent passing of faeces which are too liquid

53
Q

Causes of diarrhoea

A 
Pathogenic bacteria - e.g. c.diff
Protozoans
Viruses
Toxins
Food
54
Q

What specific type of bacteria cause diarrhoea

A

Enterotoxigenic bacteria

55
Q

What do enterotoxigenic bacteria do

A

Produce enterotoxins which cause EXCESSIVE INTESTINAL CHLORIDE SECRETION from crypt cells –> EXCESSIVE H2O SECRETION INTO LUMEN

56
Q

The enterotoxins produced by enterotoxigenic bacteria elevate levels of what

A

Intracellular second messengers - cAMP, cGMP, calcium

57
Q

Treatment of secretory diarrhoea + how it works

A

Sodium/glucose solution - ORAL REHYDRATION THERAPY

Drives villi to reabsorb H2O –> rehydration

58
Q

Colorectal area supplied by what artery

A

IMA

59
Q

Superior rectal artery is a branch of what

Middle and inferior rectal arteries are branches of what

A

IMA

Internal iliac

60
Q

Small and large intestine peristalsis is mediated by intrinsic and extrinsic neural control from what (2)

A

Intrinsic control - enteric nervous system

Extrinsic control - autonomic innervation

61
Q

What is the enteric nervous system

A

Intrinsic nervous system, one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the GI tract

62
Q

enteric nervous system consists of what 2 plexuses

A

Myenteric plexus (Auerbach’s plexus)

Submucosal plexus (meissner’s plexus)

63
Q

Location of myenteric plexus

A

between inner circular and outer longitudinal muscle layer

GI Anatomy (21 decks)

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