Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Introduction to medicine (Year 1) > Alimentary Transport 1: Along the GI tract > Flashcards

Alimentary Transport 1: Along the GI tract Flashcards

1
Q

How is food moved along the oesophagus into the stomach?

A
  • Waves of muscle contractions (peristalsis) - forces food down through oesophagus to stomach
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the 3 anatomical regions of the stomach?

A
  • Fundus (top)
  • Body (middle)
  • Antrum (bottom)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 2 functional regions of the stomach and what are their roles?

A
  • Gastric reservoir - allow tonic contractions where the muscle is thin (at top) to allow for relaxation
  • Gastric pump - allows the phasic contractions at the bottom where the muscle is thicker (peristalsis contractions)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does motility of the stomach contribute to its digestive functions?

A
  • Accommodation and storage
  • Mechanical and enzymatic breakdown
  • Slow delivery of chyme to aboral regions of gut allowing digestion and absorption
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

List the mechanisms which allows the fundic area of the stomach to relax and accommodate more stomach volume

A
  • Vago-vagal reflex
  • Chewing/swallowing
  • Mechanoreceptors
  • Vagal nerve innervation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Which nervous mechanisms influence the relaxation of the fundic area?

A
  • Reduced cholinergic activity
  • Activation of NANC inhibitory systems - mediated by NO/VIP
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is reciprocal control of gastric motility?

A
  • During accommodation Ach released as well as VIP/NO- during eating accommodation occurs so VIP/NO overrides Ach
  • Once accommodated, the effects of Ach become more prominent = Increased cholinergic acitivity, decrease NANC activity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is gastric motility myogenically controlled?

A
  • Intrinsic basic electric rhythm (BER)-Produced by ICC cells (these are the pacemaker cells of the gut)
  • Smooth muscle cells produce electric depolarisations from resting potential
  • Ripples move towards the antrum
  • Fundus is under vagal excitatory control
    Slow wave from ICC (Interstitial cells of Cajal) -regular recurring migrating ripples (3 waves/min) known as BER (rhythm of depolarisation-repolarisation)
  • BER allows the smooth muscle cell to depolarise and contract rhythmically when exposed to hormonal signals
  • Depolarisation of the GI smooth muscle is caused by calcium-sodium entry
  • Repolarisation of the GI smooth muscle is caused by K+ efflux
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are ICC cells?

A

Mesenchymal cells located within the muscle layers of the alimentary tract that mediate communication between the autonomic nervous system and smooth muscle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why must gastric emptying be regulated?

A

To ensure adequate:

  • Neutralisation of acidic chyme
  • Emulsification of fats
  • Appropriate functioning of pancreatic enzymes
  • Mechanical breakdown
  • Too much volume is not handled by the duodenum to avoid swamping it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What factors determine the rate of gastric motility?

A
  • Type of food eaten: carbohydrates > proteins > fatty foods
  • Osmotic pressure of duodenal contents: hyperosmolar chyme causes decreased gastric emptying
  • Vagal innervation upon over-distension of duodenum/duodenal acid decreases gastric motility
  • Hormones (somatostatin, secretin, CCK) - inhibit emptying
  • Motilin increases fundic contractions
  • Injury to intestinal wall decreases motility, as does injury to the GI tract
  • Bacterial infections can increase gastric motility
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is regulation of gastric motility and emptying elicited from the stomach?

A
  • Gastro-gastric reflexes provide balance between gastric reservoir and antral pump.
  • Distension of the reservoir stimulate antral contractions (excitatory reflex) - the astral pump is switched on and intensified as food enters the stomach and distension of the gastric reservoir increases
  • Distension of the antrum enhances and prolongs relaxation of the reservoir- But distension of the reservoir induces inhibitory reflexes via prolonged relaxation of the gastric reservoir
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the 3 parts of the small intestine?

A
  • Duodenum
  • Jejunum
  • Ileum
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What part of the small intestine contains the pyloric sphincter?

A

Duodenum - Pyloric sphincter modulates passage of food from bottom of antrum into the duodenum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How is pyloric activity modulated?

A
  • By antral inhibitory and duodenal excitatory reflexes
  • Contraction of the middle antrum induces a descending inhibitory reflex causing pyloric relaxation (mediated by NO/VIP)
  • Duodenal stimuli (e.g. presence of acidic chyme (HCL) or lipids/fatty acids) induces an ascending excitatory reflex causing pyloric contractions and increasing smooth muscle tone- this prevents duodeno-gastric reflux
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How is gastric emptying mediated by a negative feedback system?

A
  • Antral over-distension- Vago-vagal reflex
  • Duodenal over-distension and chemical stimulation - Vago-vagal reflex and hormones
  • The pyloric sphincter contracts in response to antral or duodenal rhythm; fatty acids in duodenum cause contraction of pylorus
17
Q

What hormones and nervous factors initiate and maintain peristalsis and mixing in the small intestine?

A

Hormones:
- Gastrin - Stimulates contractions
- Motilin - Causes the cyclical bursts of gastro-duodenal contractions during fasting
- CCK - Stimulates contractions, and with motilin, speed small bowel transit
- Secretin - inhibits contractions

Nervous factors

  • Ach
  • SP
  • NO
  • VIP - slow transit/decrease motility
18
Q

What is the emptying of the gastric reservoir caused by?

A
  • Transport of digester from the gastric reservoir is caused by 2 mechanisms: tonic contraction and peristaltic waves in the region of the gastric corpus
  • Tonic contractions - contractions that are maintained from minutes up to hours at a time
  • Can occur in stomach and sphincter of GIT
19
Q

Describe storage and gastric emptying

A

Storage- proximal stomach relaxes to store food at low pressure, whilst it’s acted on by acid, enzyme and mechanically

Emptying- carefully regulated to ensure adequate acidification/neutralisation, action of enzymes, mechanical breakdown and to avoid swamping of the duodenum

20
Q

What is gastric emptying dependent on?

A
  • Propulsive force generated by the tonic contractions of the proximal stomach
  • Stomach’s ability to differentiate types of meals ingested and their components
  • Fatty, hypertonic, acidic chyme in the duodenum decreases the force and rate of gastric emptying
21
Q

Summarise the emptying of different food
components (liquids, solids, fatty foods and
indigestible solids).

A
  • Liquids - rapidly disperse, empty without lag time, rate of emptying influenced by nutrient content, greater nutrients, longer retention
  • Solids - 2 phases (lag + linear phase), duration of lag time related to size of particle
    Liquid part emptied, solid component is retained in proximal stomach
    Trituration of larger particles to smaller ones (trituration is a form of reducing particle size, or creating a homogenous solution through thorough mixing)
    Pylorus regulates passage of material
  • Fatty foods: Liquefy at body temperature, flat on top of liquid layer and empty slowly, fasts are potent inhibitors of gastric motor events and gastric emptying
  • Indigestible solids: Don’t empty in immediate post-prandial period, need to be emptied by migrating motor complex (MMC)
22
Q

Describe MMC

A
  • Highly organised motor activity
  • Cyclically recurring sequence of events
  • Occurs between meals when the stomach/intestine are ‘empty’
  • Bursts of high frequency, large amplitude contractions that migrate along the length of intestine and die out
  • Begins at antrum -> duodenum -> jejunum -> ileum
23
Q

What are the 3 phases of MMC?

A
  • Phase I = quiescence
  • Phase II = Irregular propulsive contractions
  • Phase III = uninterrupted peristaltic rush
24
Q

What are the functions of MMC?

A
  • Indigestible residues moved out of stomach by large contractions and wide opening of the pyloric sphincter during phase III
  • Removes dead epithelial cells by abrasion
  • Prevents bacterial overgrowth
  • Prevents colonic bacteria from entering small intestine
  • Occurs following digestion and absorption of a meal (empty stomach)
  • Causes mass movement of intestinal contents, leading to evacuation of faeces
25
Q

How is MMC controlled?

A
  • Not fully known
  • Smooth muscle cells of stomach can produce ‘slow waves’
  • Contractions coordinated by the ENS by interstitial cells of Cajal (pacemaker cells)
  • Initiated by the vagus nerve in the upper tract
  • Some evidence for cyclical secretion of the hormone motilin from stomach and duodenum
  • Feeding inhibits release of motilin
26
Q

Describe segmentation (mixing contractions)

A
  • Stationary contractions and relaxation
  • Originates in the pacemaker cells (ICC)
  • Segmentation -> divisions and subdivisions of chyme, bringing chyme in contact with intestinal walls
  • Segmentation causes the slow migration of chyme towards ileum
  • Dudoenum/jejunum- 10-12 contractions/min
  • Ileum- 8-9 contractions/min
27
Q

Describe peristalsis (propulsive)

A
  • In stomach (3 waves/min) - migrating motor complex, mass movements (evacuation)
  • Is a propagating contraction of successive sections of circular smooth muscle preceded by a dilatation
28
Q

Describe the difference between segmentation and peristalsis

A
  • Peristaltic (propulsive) contractions spread the food out allowing digestive enzymes to mix with it, but primarily push the food towards the anus
  • Segmenting (mixing) contractions primarily churn the food, but also propel it towards the anus
29
Q

Outline the pathway for the small intestinal peristaltic reflex

A
  • Sensory neurones detect luminal contents
  • They relay action potentials to the vagal centre of the medulla
  • The medulla relays vasovagal reflexes to integrating and programme circuits within the ENS
  • These circuits stimulate motor neurones, which stimulate contraction or relaxation in the small intestine
30
Q

Describe Haustral/segmental contraction in the colon (large intestine)

A
  • Haustra = sacs of colon caused by band-like arrangement of the taenia coli smooth muscle
  • Contraction of taenia coli causes haustra to bunch up, mixing contents of colon
31
Q

Describe the peristalsis contractions in the colon (large intestine)

A
  • Propulsive contractile waves moving the contents of the colon towards the anus
  • They are initiated by distension of the intestinal wall activating mechanoreceptors
  • Peristalsis in the colon is much slower than the small intestine
32
Q

Describe Maas movement in the colon

A

Powerful contractions in the mid-transverse colon that sweep contents to the rectum

33
Q

What is the sympathetic innervation of the GI system?

A
  • Thoracic splanchnic nerves - celiac plexus
34
Q

What is the parasympathetic innervation of the GI system?

A
  • Vagus nerve
35
Q

What organs does the celiac trunk supply?

A
  • Stomach
  • Liver
  • Spleen
36
Q

What organ does the superior mesenteric artery supply?

A
  • Small intestine (duodenum, jujenum, ileum)
37
Q

What organ does the inferior mesenteric artery supply?

A
  • Large intestine (colon, cecum, rectum, alimentary canal)
38
Q
A

Introduction to medicine (Year 1) (55 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions