Structure of the GI Tract and Motility

Question 1

What is the digestive tract?

Answer 1

a series of hollow organs connected by sphincters

Question 2

What is the function of the mouth?

Answer 2

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

Question 3

What is the function of the oesophagus?

Answer 3

delivers food to the stomach

Question 4

What is the function of the stomach?

Answer 4

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

Question 5

What is the function of the small intestine?

Answer 5

principle site of digestion and absorption of nutrients

Question 6

What is the function of the large intestine?

Answer 6

reabsorbs fluid and electrolytes, stores faecal matter before regulated expulsion

Question 7

What are the accessory structures of the digestive tract?

Answer 7

salivary glands, the pancreas, the liver and the gallbladder

Question 8

What is the name given to the liver and gallbladder?

Answer 8

the hepatobiliary system

Question 9

What are the different salivary glands?

Answer 9

parotid
sublingual
submandibular

Question 10

What do the salivary glands secrete?

Answer 10

a-amylase and lingual lipase for digestion

Question 11

What are the basic digestive processes?

Answer 11

motility
secretion
digestion
absorption

Question 12

Describe the process of motility

Answer 12

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

Question 13

Where is skeletal muscle involved in motility?

Answer 13

the mouth, upper oesophagus, external anal sphincter

Question 14

Describe the process of secretion

Answer 14

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

Question 15

What do digestive secretions contain?

Answer 15

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

Question 16

Describe the process of digestion

Answer 16

the biochemical breakdown of complex foodstuffs to smaller, absorbable units

Question 17

How are carbohydrates broken down?

Answer 17

converted to monosaccharides which is mediated by amylases and disaccharides

Question 18

How are proteins broken down?

Answer 18

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

Question 19

How are fats broken down?

Answer 19

converted to monoglycerides and FFAs - mediated by lipases

Question 20

Describe the process of absorption

Answer 20

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

Question 21

What is contained within the mucosa?

Answer 21

epithelial cells
exocrine cells
endocrine gland cells
lamina propria
muscularis mucosa

Question 22

WHat is contained within the submucosa?

Answer 22

connective tissue
blood and lymph vessels
nerve network

Question 23

What is contained within the muscularis externa?

Answer 23

circular muscle
myenteric plexus
longitudinal muscle layer

Question 24

What is contained within the serosa?

Answer 24

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

Question 25

What does circular muscle contraction result in?

Answer 25

a narrower and longer lumen

Question 26

What does longitudinal muscle contraction result in?

Answer 26

shorter and fatter intestine

Question 27

What does muscularis mucosae contraction result in?

Answer 27

change in absorptive and secretory area of mucosa

Question 28

How is spontaneous activity modulated in the smooth muscle?

Answer 28

intrinsic (enteric) and extrinsic (autonomic) nerves | numerous hormones

Question 29

How is the smooth muscle connected in the gut?

Answer 29

gap junctions

Question 30

What does slow wave activity determine?

Answer 30

the maximum frequency, direction and velocity of rhythmic conctractions

Question 31

What cells drive slow wave activity?

Answer 31

Intersticial cells of cajal

Question 32

How are the APs of slow waves modulated?

Answer 32

VGCCs ad Voltage K channels

Question 33

What is the slow wave amplitude dependent on?

Answer 33

neuronal stimuli hormonal stimuli mechanical stimuli

Question 34

What is the BER frequency in the stomach/?

Answer 34

3 slow waves/min

Question 35

What is the BER frequency in the sm. intestine?

Answer 35

1-12 waves/min in duodenum | 8 waves/min in terminal ileum

Question 36

What is the BER frequency in the large intestine?

Answer 36

8 waves/min in proximal colon | 16 waves/min in distal colon

Question 37

Where are the ganglia of the ENS located?

Answer 37

the myenteric plexus

Question 38

What is the ENS comprised of?

Answer 38

sensory neurons interneurons effector neurons

Question 39

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

Answer 39

ACh

Question 40

What are the excitatory influences from the parasympathetic system?

Answer 40

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

Question 41

What are the inhibitory influences of the parasympathetic system?

Answer 41

relaxation of some sphincters, receptive relaxation of stomach

Question 42

Where does the parasympathetic stimulation of the gut occur from?

Answer 42

Sacroileal spine S2-S4

Question 43

Where does the sympathetic stimulation of the gut occur from?

Answer 43

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

Question 44

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

Answer 44

decreased motility, secretion and blood flow

Question 45

What is the local reflex in the gut?

Answer 45

peristalisis - gut-gut signalling

Question 46

What is the short reflex in the gut?

Answer 46

gut -> prevertebral ganglion -> gut extrinsic nerves

Question 47

What is the long reflex in the gut

Answer 47

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

Question 48

What are the major motility patterns in the GI tract?

Answer 48

Peristalisis Segmentation Tonic Contractions

Question 49

What is peristalisis?

Answer 49

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

Question 50

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

Answer 50

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

Question 51

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

Answer 51

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

Question 52

What is segmentation?

Answer 52

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

Question 53

What is segmentation called in the large intestine?

Answer 53

haustration

Question 54

What are tonic contractions?

Answer 54

sustained contractions found in the sphincters of the GI tract

Question 55

What are the different parts of the mouth?

Answer 55

``` palate uvula tongue pharynx teeth ```

Question 56

Where is saliva secreted from?

Answer 56

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

Question 57

What are the functions of saliva?

Answer 57

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

Question 58

What are the two stages of saliva formation?

Answer 58

primary secretion by acinus | secondary modification by duct cells

Question 59

What is the composition in the acinus?

Answer 59

Na, K, Cl, HCO3, H2O

Question 60

What are the modifications made in the duct?

Answer 60

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

Question 61

What are the various rates of saliva production?

Answer 61

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

Question 62

How does saliva composition vary with flow rate?

Answer 62

HCO3 increases with high flow rate

Question 63

How is saliva regulated?

Answer 63

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

Question 64

What does the parasympathetic stimulate?

Answer 64

glossopharyngeal and facial nerves | large watery volume, enzyme rich and mediated by mAChRs

Question 65

What does the sympathetic stimulate?

Answer 65

postganglionic fibres from superior cervical ganglia | small thick volume, mucus rich, mediated by b-adrenoceptors

Question 66

What are the two stages of swallowing?

Answer 66

oropharyngeal | oesophageal

Question 67

What happens in the voluntary phase of the oropharyngeal phase?

Answer 67

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

Question 68

What happens in the involuntary phase of the oropharyngeal phase?

Answer 68

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

Question 69

What happens during the oesophageal phase of swallowing?

Answer 69

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

Question 70

When does the lower oesophageal sphincter open?

Answer 70

2-3s after swallowing, prevents reflux

Question 71

What is secreted by the oesophagus?

Answer 71

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