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Human Epithelial Biology > Structure of the GI Tract and Motility > Flashcards

Structure of the GI Tract and Motility Flashcards

1
Q

What is the digestive tract?

A

a series of hollow organs connected by sphincters

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2
Q

What is the function of the mouth?

A

chop food, lubricate it, start carbohydrate and fat digestion, propel food to oesophagus

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3
Q

What is the function of the oesophagus?

A

delivers food to the stomach

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4
Q

What is the function of the stomach?

A

stores food temporarily, continues digestion and initiates protein digestion regulates delivery of chyme to small intestine

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5
Q

What is the function of the small intestine?

A

principle site of digestion and absorption of nutrients

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6
Q

What is the function of the large intestine?

A

reabsorbs fluid and electrolytes, stores faecal matter before regulated expulsion

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7
Q

What are the accessory structures of the digestive tract?

A

salivary glands, the pancreas, the liver and the gallbladder

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8
Q

What is the name given to the liver and gallbladder?

A

the hepatobiliary system

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9
Q

What are the different salivary glands?

A

parotid
sublingual
submandibular

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10
Q

What do the salivary glands secrete?

A

a-amylase and lingual lipase for digestion

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11
Q

What are the basic digestive processes?

A

motility
secretion
digestion
absorption

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12
Q

Describe the process of motility

A

mechanical activity mostly involving smooth muscle and skeletal muscle which given propulsive movements, mixing movements and tonic contractions

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13
Q

Where is skeletal muscle involved in motility?

A

the mouth, upper oesophagus, external anal sphincter

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14
Q

Describe the process of secretion

A

secretion in to the lumen from the digestive tract and accessory structures in response to hormonal and neural signals

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15
Q

What do digestive secretions contain?

A

water
electrolytes
organic compounds e.g. enzymes, bile salts, mucus

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16
Q

Describe the process of digestion

A

the biochemical breakdown of complex foodstuffs to smaller, absorbable units

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17
Q

How are carbohydrates broken down?

A

converted to monosaccharides which is mediated by amylases and disaccharides

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18
Q

How are proteins broken down?

A

converted to constituent amino acids, dipeptides and tripeptides mediated by proteases and dipeptidases

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19
Q

How are fats broken down?

A

converted to monoglycerides and FFAs - mediated by lipases

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20
Q

Describe the process of absorption

A

transfer of all the absorbable products of digestion with water, electrolytes and vitamins from the tract to the blood or lymph

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21
Q

What is contained within the mucosa?

A 
epithelial cells
exocrine cells
endocrine gland cells
lamina propria
muscularis mucosa
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22
Q

WHat is contained within the submucosa?

A

connective tissue
blood and lymph vessels
nerve network

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23
Q

What is contained within the muscularis externa?

A

circular muscle
myenteric plexus
longitudinal muscle layer

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24
Q

What is contained within the serosa?

A

connective tissue
has mesentery connecting to the abdominal wall
secretes liquid to help intestine move smoothly against abdomen

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25
Q

What does circular muscle contraction result in?

A

a narrower and longer lumen

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26
Q

What does longitudinal muscle contraction result in?

A

shorter and fatter intestine

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27
Q

What does muscularis mucosae contraction result in?

A

change in absorptive and secretory area of mucosa

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28
Q

How is spontaneous activity modulated in the smooth muscle?

A

intrinsic (enteric) and extrinsic (autonomic) nerves

numerous hormones

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29
Q

How is the smooth muscle connected in the gut?

A

gap junctions

30
Q

What does slow wave activity determine?

A

the maximum frequency, direction and velocity of rhythmic conctractions

31
Q

What cells drive slow wave activity?

A

Intersticial cells of cajal

32
Q

How are the APs of slow waves modulated?

A

VGCCs ad Voltage K channels

33
Q

What is the slow wave amplitude dependent on?

A

neuronal stimuli
hormonal stimuli
mechanical stimuli

34
Q

What is the BER frequency in the stomach/?

A

3 slow waves/min

35
Q

What is the BER frequency in the sm. intestine?

A

1-12 waves/min in duodenum

8 waves/min in terminal ileum

36
Q

What is the BER frequency in the large intestine?

A

8 waves/min in proximal colon

16 waves/min in distal colon

37
Q

Where are the ganglia of the ENS located?

A

the myenteric plexus

38
Q

What is the ENS comprised of?

A

sensory neurons
interneurons
effector neurons

39
Q

What are the is the stimulation from the preganglionic neurons in the parasympathetic nervous system?

A

ACh

40
Q

What are the excitatory influences from the parasympathetic system?

A

increased gastric, pancreatic and sm. intestinal secretion, blood flow and smooth muscl contraction

41
Q

What are the inhibitory influences of the parasympathetic system?

A

relaxation of some sphincters, receptive relaxation of stomach

42
Q

Where does the parasympathetic stimulation of the gut occur from?

A

Sacroileal spine S2-S4

43
Q

Where does the sympathetic stimulation of the gut occur from?

A

Thoracic to lumbar spine - through celiac, superior and inferior mesenteric nerves

44
Q

What are the inhibitory influences of sympathetic stimulation of the gut?

A

decreased motility, secretion and blood flow

45
Q

What is the local reflex in the gut?

A

peristalisis - gut-gut signalling

46
Q

What is the short reflex in the gut?

A

gut -> prevertebral ganglion -> gut extrinsic nerves

47
Q

What is the long reflex in the gut

A

gastro-ileal reflex -> gut -> medulla oblongata -> gut extrinsic

48
Q

What are the major motility patterns in the GI tract?

A

Peristalisis
Segmentation
Tonic Contractions

49
Q

What is peristalisis?

A

a wave of contraction that normally proceeds along the gut wall in the aboral direction - triggered by distension of the gut wall

50
Q

How does distension affect the motor neurons at the oral end of the wave?

A

longitudinal muscle relaxes via release of VIP and NO from inhibitory interneuron
circular muscle contracts via release of ACh and substance P from excitatory interneuron

51
Q

How does distension affect the motor neurons at the aboral end of the wave?

A

longitudinal muscle contracts via release of ACh and substance P from excitatory interneuron
circular muscle relaxes via release of VIP and NO from inhibitory interneuron

52
Q

What is segmentation?

A

the mixing and churning movements that occur in rhythmic contractions of the circular muscle layer that mix and divide luminal contents

53
Q

What is segmentation called in the large intestine?

A

haustration

54
Q

What are tonic contractions?

A

sustained contractions found in the sphincters of the GI tract

55
Q

What are the different parts of the mouth?

A 
palate
uvula
tongue
pharynx
teeth
56
Q

Where is saliva secreted from?

A

parotid - 25%
submandibular - 75%
sublingual - 5%

57
Q

What are the functions of saliva?

A

lubrication, solvent, anti-bac, digestion of carbohydrates, neutralisation of acid

58
Q

What are the two stages of saliva formation?

A

primary secretion by acinus

secondary modification by duct cells

59
Q

What is the composition in the acinus?

A

Na, K, Cl, HCO3, H2O

60
Q

What are the modifications made in the duct?

A

Na excreted, Cl excreted, HCO3 added, K added, H2O dilutes

61
Q

What are the various rates of saliva production?

A

0.05ml/min sleep, 0.5ml/min wake and 5ml/min during salivation

62
Q

How does saliva composition vary with flow rate?

A

HCO3 increases with high flow rate

63
Q

How is saliva regulated?

A

unconditioned i.e. chemoreceptors

conditioned i.e. extrinsic ANS from saliva centre in the medulla

64
Q

What does the parasympathetic stimulate?

A

glossopharyngeal and facial nerves

large watery volume, enzyme rich and mediated by mAChRs

65
Q

What does the sympathetic stimulate?

A

postganglionic fibres from superior cervical ganglia

small thick volume, mucus rich, mediated by b-adrenoceptors

66
Q

What are the two stages of swallowing?

A

oropharyngeal

oesophageal

67
Q

What happens in the voluntary phase of the oropharyngeal phase?

A

bolus formed in the mouth
tongue forces bolus into the pharynx
pressure stimulates pharyngeal pressure receptors
afferent impulse to swallowing centre in medulla

68
Q

What happens in the involuntary phase of the oropharyngeal phase?

A

efferents initiate all or nothing reflex sequence of muscle movements
upper oesophageal sphincter opens
food passes through pharynx into oesophagus

69
Q

What happens during the oesophageal phase of swallowing?

A

swallowing centre (medulla oblongata) triggers primary peristalic wave and closure of upper oesophageal sphincter mediated by skeletal muscle and smooth muscle in distal regions

70
Q

When does the lower oesophageal sphincter open?

A

2-3s after swallowing, prevents reflux

71
Q

What is secreted by the oesophagus?

A

entirely mucus for lubrication and protection of the epithelium
rapid turnover of epithelium

Human Epithelial Biology (20 decks)

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