overview of the GIT

Question 1

what does the gastrointestinal tract consist of?

Answer 1

• mouth
• oesophagus
• stomach
• small intestine
• large intestine
• appendix
• rectum
• anus
• accessory organs

Question 2

what separates the gut into sections?

Answer 2

sphincters

Question 3

overview of motility:

how does food get ingested?

Answer 3

• mastication (chewing food into smaller pieces)
• swallowing

Question 4

what are the motor functions of the stomach?

Answer 4

• storage
• mixing/propulsion of food
• stomach emptying and its regulation

Question 5

what are the movements of the small intestine?

Answer 5

• mixing contractions
• propulsive movements
• prevention of back flow

Question 6

what are the movements of the large intestine?

Answer 6

• mixing/propulsive movements (the is called frustrations)
• defecation

Question 7

describe the overview of splanchnic circulation:

(what happens to the blood flow once we have absorbed nutrients)

Answer 7

• blood from the gut, spleen and pancreas flow to the liver via the portal vein
• blood is filtered by liver sinuses before leaving via the hepatic vein into the vena cava

Question 8

what does the filtration of blood before leaving hepatic system into the vena cava allow?

Answer 8

• it allows the removal of bacteria/particulate matter that might enter the blood from the GI tract
• it will prevent the direct transport of potentially harmful agents into the body

Question 9

what type of cells will remove bacteria from the gut?

Answer 9

reticuloendothelial cells

Question 10

describe the action of nervous control of the GIT blood flow?

Answer 10

parasympathetic stimulation:
- to the stomach and lower colon
- it will increase blood flow and glandular secretions

sympathetic stimulation:
- vasoconstriction of arterioles (switches off blood flow to the gut)
- happens during exercise
- circulatory shock

Question 11

what are the 7 layers of the GIT?
(from outside to inside)

Answer 11

• serosa
• longitudinal muscle
• myenteric plexus
• circular muscle
• submucous muscle
• submucous plexus
• mucosa (gut epithelium with sub epithelial connective tissue)

Question 12

what is the purpose of mucosa?

Answer 12

increases the surface area to allow for more time for absorption

Question 13

what 2 things will the oesophagus and the rectum lack in terms of its general organisation?

Answer 13

serosa and mesentery

Question 14

where is the submucosal plexus be found?

Answer 14

small and large intestine

Question 15

when stimulates, what are the main effects of the myenteric plexus?

Answer 15

• increased tonic contraction (tone of the wall)
• increased intensity of rhythmical contractions
• increased rate of rhythm of contraction
• increased velocity of conduction od excitatory waves along the gut wall

Question 16

how does the structure of the GIT smooth muscle allow the contraction of a syncytium?

Answer 16

• the muscle fibres are connected by gap junctions and focal adhesions (adherens junctions)
• actin and myosin filaments aligned diagonally along the axis of cells
• filaments anchored at dense bodies that are scattered throughout the sarcoplasm
• contractile arrays anchored to sarcolemma by dense plaques.

Question 17

what are the 2 different neural controls of the GIT function and describe them?

Answer 17

EXTRINSIC- neuronal and hormonal
- Ach excites
- Noradrenaline and adrenaline inhibits

INTRINSIC (enteric) - myogenic, neural and chemical
- does not need sympathetic or parasympathetic (they will only modify the action.

• all GIT motilities do not require external nerve supply
• they are generated by enteric nervous system and extrinsic factors will only modify them.

Question 18

Enteric nervous system:

1- what does it consist of?

2- where does it receive input from?

3- where does it lie between?

4- what is its main function?

Answer 18

1- consists of sensory, inter and motor neurons

2- receives inout from the ANS, but it can function independently from it

3- lies between the circular and longitudinal smooth muscle layers (it will innervate both layers)

4- main function is motor control of the GIT.

Question 19

submucosal plexus:

1- where does it lie between?

2- what does it innervate?

Answer 19

1- it lies between the circular smooth muscle layer and the mucosa

2- it innervates the epithelium, endocrine glands and blood vessels (controls GIT secretion and local blood flow)

Question 20

what are the 2 components of the extrinsic nervous system?

Answer 20

sympathetic and parasympathetic ns (branches of the autonomic nervous system)

Question 21

parasympathetic neurons:

1- what are they branches of?

2- what do they innervate?

3- what is its main function?

Answer 21

1- they are branches of the vagus, pelvic and splanchnic nerves

2- they innervate neurons in the myenteric plexus

3- main function is to stimulate GIT motility and secretion.

Question 22

sympathetic neurons:

1- where do they originate from?

2- where do they terminate?

3- what is their main function?

Answer 22

1- they originate from the celiac, superior and inferior mesenteric and hypogastric plexus

2- they terminate on the enteric nerves, smooth muscle and mucosa

3- main function is to inhibit GIT motility and secretion

Question 23

what is the function of:
- intermediate filaments
- gap junctions
- focal adhesions

Answer 23

intermediate filaments = maintain cytoskeleton organisation

gap junctions = couples adjacent cells electrically and chemically in some smooth muscle types

focal adhesions = couples adjacent cells mechanically

Question 24

what are the 2 types of waves of electrical activity in the GI tract? And what is the difference between them?

Answer 24

Slow waves - these are fluctuations that will not initiate smooth muscle contraction. (Basel electrical rhythm, pacesetter potentials)

Spikes = these are action potentials that will allow for enough calcium release to cause smooth muscle contraction.

Question 25

1- what is GI smooth muscle stimulated by? 2- where and by what is it initiated by?

Answer 25

1- stimulated by continual slow, intrinsic electrical activity 2- initiated in the stomach by interstitial cells of Cajal (ICC)

Question 26

describe what slow waves are? describe what they do?

Answer 26

- they are not action potentials but slow undulating changes in resting membrane potential - they do not themselves cause muscle contraction (they may only in the stomach) - they will excite appearances of spike potentials

Question 27

what is the intensity and frequency range of slow waves?

Answer 27

intensity = 5-15mV frequency = 3-12 per min

Question 28

what are spike potentials? when do they occur? how can they be effected by slow wave potential?

Answer 28

- true action potentials - they occur when resting membrane exceeds 40mV - the higher the slow wave potential, the greater the frequency of spike potentials

Question 29

how long do spike potentials last?

Answer 29

10-50x as long in gastrointestinal muscle in large nerve fibres - each GI spike lasts 10-20 ms - baseline membrane potential can also vary.

Question 30

what is the difference in excitability of GIT between depolarisation and hyperpolarisation?

Answer 30

- depolarisation leads to increased excitability - hyperpolarisation leads to decreased excitability

Question 31

what are 3 examples that can stimulate depolarisation? what are 2 things that can stimulate hyperpolarisation?

Answer 31

1- stretch 2- ach 3- PSNS 1- Norepinephrine 2- SNS

Question 32

the electrical activity of smooth muscle will spontaneously fluctuate between what 2 values? what is this initiated by?

Answer 32

-65 and -45 mV - this is initiated by the pacemaker cells known as interstitial cells of Cajal

Question 33

describe how the electrical activity of smooth muscle works? how does the activity start and stop?

Answer 33

- it is initiated b the pace maker cells (interstitial cells of Cajal) - the activity is mainly due to the opening of the calcium ion channels leading to the influx of Ca into the cells. - this is then terminated by Ca - dependant K efflux.

Question 34

what are the 2 main types of GIT motility? what does each consist of?

Answer 34

1- FED state: - consists of peristalsis and mixing movement 2- INTERDIGESTIVE state - also known as migrating motor complexes (gets rid of all the remaining remnants before we have another meal)

Question 35

1- what is peristalsis? 2- when does it occur? 3- what direction does it move food (endless pathology) ?

Answer 35

1- peristalsis is an autonomic reflex in response to stretch of the GIT wall 2- it will occur during a fed state in all parts of the GIT from the oesophagus to the rectum. 3- it will always move food from oral to rectal direction at 2-25cm If there is pathology this can be reversed leading to vomitting.

Question 36

what controls peristalsis? what happens to the different layers during peristalsis?

Answer 36

- peristalsis requires an active myenteric plexus - the stretch initiates the circular muscles infront of the plexus to contract and the longitudinal muscles behind it to relax.

Question 37

what is the function of segmentation? What is it?

Answer 37

1- the function of segmentation is to mix digested food It is contractions of circular muscle layer at short intervals along the GIT, these contractions start as 1 opposite and then they move forward and contract in a new original area. (2 opposite)

Question 38

when does migrating motor complexes occur? what is their function?

Answer 38

they occur during periods of fasting/between meals their function is to clear the stomach and small intestine of debris and bacteria.

Question 39

what are the 4 phases of MMC?

Answer 39

Phase 1= (45-60mins) - quiescent period with slow waves Phase 2= (30-35mins) - action potential activity on slow waves but sporadic contractions of circular muscle Phase 3= (2-12mins) action potential activity on slow waves but regular contractions of circular muscle Phase 4= period in which action potential activity and contraction reduce and merge into phase 1

Question 40

describe the spike potential between phases 1-3 of MMC?

Answer 40

phase 1= no spike potentials and no contractions phase 2 = irregular spike potentials and contractions phase 3= regular spike potential na contractions.