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sem 2 Liver and GI > Introduction to the functions and control of the alimentary tract > Flashcards

Introduction to the functions and control of the alimentary tract Flashcards

1
Q

digestive functions of the stomach

A
  • Accommodation & storage
  • Mechanical and enzymatic breakdown
  • Slow delivery of chyme to the duodenum
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2
Q

food in stomach - how does the stomach act as a reservoir

A

food is stored in the fundus and body of the stomach during the first part of digestion

may remain there for quite some time (approx 1 hr) and will be unmixed

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3
Q

food is stored in the fundus and body of the stomach due to relaxation - how does the relaxation happen?

A

through vagal reflex that inhibits inhibits smooth muscle tone

mechanoreceptors, VIP and NO

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4
Q

where does the food mixing occur in the stomach?

A

the antral region

mixing and grinding of food with gastric secretions

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5
Q

how much gastric juice does the stomach store and what is it used for?

A

2-3 litres of gastric juice/24hr

(mucus, pepsinogen, intrinsic factor, HCL, lipase) which help in digestion and absorption of food

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6
Q

mucus

A

secreted by goblet cells and mucus neck cells

acts as a lubricant by acting as a barrier that protects the stomach and colon especially from gastric acid (prevents trauma)

protects stomach from acidic juice

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7
Q

lipase

A

converts triglycerides to fatty acids and glycerol

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8
Q

pepsin

A

secreted by chief cells or peptic cells as pepsinogen

protein digestion

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9
Q

HCl

A

secreted by parietal cells

important in defence

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10
Q

Intrinsic factor

A

secreted by parietal cells

for vitamin B12 absorption

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11
Q

paracrine secretions

A

“local hormones”

secreted from cells in the mucosa

chemical acts locally on adjacent cells via the interstitial fluid

eg. somatostatin inhibits gastrin release in the stomach

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12
Q

endocrine secretions

A
  • Secretions called ‘hormones’ synthesised by ductless glands enter the blood stream, travel from their site of production to their target tissue where they bind to specific receptors to elicit their effects
  • Gastrin: stomach (G-cells in antrum)
  • Secretin: duodenal mucosa - in response to high acidity within the duodenum
  • Pancreozymin-cholecystokinin: duodenal mucosa - in response to fatty foods (secreted under influence of lipids) and allows the contraction of the gall bladder
  • Insulin: pancreas (-cells)
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13
Q

exocrine secretions

A
  • Salivary glands: mucus (lubrication for mastication and speech); lipase
  • Gastric glands: hydrochloric acid, pepsin, mucus

• Pancreas: bicarbonate ions, amylase, lipase, carboxypeptidase
o bicarbonate secretion is under the influence of secretin

• Liver: bile salts, bile acids

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14
Q

where do excretion secretions come from and where do they act?

A

secretions from numerous glands with ducts enter the lumen of the gut and are involved in digestion, lubrication and protection

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15
Q

Exocrine, endocrine and paracrine secretions allow what?

A

active digestion and control of digestion, gastric motility (and energy homeostasis - insulin)

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16
Q

where must nutrients from digestion go?

A

transported across the intestinal epithelium into the blood (glucose, amino acids) or lymph via lacteals (fats/lipids)

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17
Q

small intestine adaptations for absorption

A

– Highly vascularised
– Moist and thin
– Large surface area

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18
Q

absorption mainly occurs where?

A
  • Absorption occurs mainly in small intestine

* Absorption of fluid occurs in the small intestine and colon

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19
Q

colon absorbs how much water

A

90%

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20
Q

movements of the muscular (mostly smooth muscle) wall allows:

A

Movement from one region to another

Mechanical degradation, e.g. gastric antrum

Mixing lumen contents, e.g. small intestine. May be peristalsis or segmentation. Migrating motor complex will sweep anything that isn’t digested out

Transport of nutrients, water and of urea and electrolytes

Digestion and absorption

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21
Q

Migrating motor complex

A

pattern of smooth muscle activity that occurs between meals

sweeps residual undigested material through the digestive tube

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22
Q

ways in which drugs/some products of normal metabolism may leave the body

A

i. Saliva
ii. Bile
iii. Faeces
iv. (Vomit)

• Indigestible food residues (e.g. tomato skin) leave the body in the faeces

23
Q

is the gut sterile - why?

A

unsterile, as it is open to external environment

24
Q

things that help to protect the gut

A
  1. Sight, smell and taste alerts us to harmful food substances
  2. Vomit reflex
  3. Acid in stomach (HCl) kills most harmful bacteria
  4. Mucus secretions
  5. Natural bacterial flora prevents colonisation of harmful bacteria
  6. Aggregation of lymphoid tissue (e.g. Peyer’s patches) able to mount a response to food-borne antigens - analyse and respond to pathogenic microbes.
  7. Peyer’s patches, extend into the submucosa of the ileum
25
Q

when can food poisoning occur?

A

when Peyer’s patches aren’t up to their full capacity

26
Q

parasympathetic and sympathetic effects on digestive system

A

Parasympathetic

  • stimulates salivation, digestive activity and gall bladder
  • relaxes rectum

Sympathetic

  • inhibits salivation and digestive activity
  • relaxes the bladder
  • contracts the rectum
27
Q

enteric nervous system

A

guts “little brain”

has a large neuronal supply, can initiate its own responses to gut stimuli without requiring the higher function of the brain

28
Q

afferent and efferent

A
  • Afferent
    o TO the brain
  • Efferent
    o FROM the brain
29
Q

what substances cause contractions and relaxations

A

o The contractions are initiated by excitatory (motor) reflexes, mediated by ACH and substance P

o Relaxant effects are mediated by VIP and NO

30
Q

splanchnic nerves

A

go from gut muscle to spinal cord, and spinal cord to ENS

31
Q

how can relaxation be differentiated?

A

receptive
-gastric fundus dilates when food passes down the pharynx, mechanical stimulation of pharynx, mechanoreceptors

adaptive
-food entering the stomach, vagal innervation via NO and VIP

feedback
-CCK, relaxation of pyloric sphincter muscle and gastric emptying

32
Q

what are the receptive, adaptive and feedback-relaxation of the stomach mediated by?

A

non-adrenergic, non-cholinergic (NANC) mechanisms (i.e., inhibition involving NO, VIP, etc.) as well as by reflex chains involving release of noradrenaline.

33
Q

what is released very early on when the stomach is ready to receive food?

A

NA is released from the sympathetic nerve fibres which helps the stomach to relax

34
Q

another hormone involved in relaxation other than NO and VIP?

A

PACAP

  • Mediates neuronal regulation of gastric acid secretion, intestinal motility
  • Stimulates relaxation of colonic smooth muscle
  • Stimulates pancreatic, insulin and glucagon secretion in humans
35
Q

how does the structure of the fundus contribute to its function?

A

fundus is thinner, meaning it can expand to allow accommodation to occur

36
Q

Antrum

A

larger than the fundus, provides grinding action

37
Q

what 2 things can cause gastrin release?

A
  • distention of the stomach

- we see food

38
Q

how is gastrin released and what does it cause?

look at diagram in notes

A
  • distention initiates a neural stimulation which promotes GRP release and gastrin release from G cells
  • gastrin travels in the bloodstream and has its effects, GRP is neuronal
  • GRP causes Ach release onto parietal cells which causes HCL release
  • gastrin can bind to ECL and parietal cells - with ECL cells histamine is released which then binds to parietal cells
  • parietal cells release HCL, so gastrin can indirectly and directly stimulate HCL release
39
Q

why can gastrin potential be damaging?

A

because even though the gut has this protective mucus layer, this layer can be removed over time

40
Q

what is released as a protective measure against gastrin?

A

somatostatin

41
Q

when and how are somatostatin released?

A

released by D cells, only when there is hyper secretion of acid
-paracrine control

42
Q

Vago-Vagal Reflex

A
  • VV reflex is active when we are swallowing food and when food is within the stomach
  • stomach is being prepared for being receiving food- receptive relaxation. when the food is actually in the stomach, further relaxation occurs
  • reflex goes from the stomach to the brain and then back to the stomach
  • leads to the active relaxation of the smooth muscles of the stomach. also promotes motility and acid secretion
43
Q

Vago-Vagal Reflex - the pathway

A
  • something occurs within the gut
  • vagal afference gets sent to the NTS
  • integration occurs within the brain stem
  • vagal efference send motor reflexes down from DMVN

gut - afferent - spinal cord - brain - NTS - DMVN - spinal cord- efferent - gut

  • Ach will be released pre ganglionically (long) and post ganglionically (short), and it causes both motility and acid secretion
  • Ach can bind to ECL cells causing acid secretion and motility
44
Q

DMVN and NTS

A

o NTS, Nucleus tractus solitarius
• main site of termination of vagal afferents

o DMVN, Dorsal motor vagal nucleus
• main site of origin of vagal efferents (motor) supplying the gut

45
Q

what 2 nerve fibres are intrinsic to the gut?

A
  1. Myenteric plexus (Auerbach’s plexus): motor function
  2. Submucosal plexus (Meissner’s plexus): secretion

both located in the wall of the colon, connected to CNS by parasympathetic (↑ contraction of proximal colon) and sympathetic fibres (↓ colonic movement), but can also function autonomously

46
Q

the ENS has the same no of neutrons as…

A

the spinal cord

47
Q

what is the cool-colonic reflex?

A

increased motility of the colon in response due to stretch in the stomach and by-products of digestion in the small intestine

48
Q

which is the most prominent plexus?

A

Myenteric plexus (Auerbach’s plexus)

Cholinergic innervation ↑ gastric motility and secretion

Adrenergic stimulation ↓ gastric motility and secretion

49
Q

what is the rate of emptying dependent on?

A

the material’s ability to be absorbed

  • Carbohydrates emptied quickly into duodenum
  • Proteins – slow emptying
  • Fatty foods – even slower
50
Q

FA in the duodenum

A

↓ in gastric emptying by increasing the contractility of pyloric sphincter

lipid content needs to be emulsified- bile is important in this, and it is only released when CCK acts on the gall bladder

51
Q

Peristalsis

A
  • Slower in large intestine compared to small intestine
  • Wave of propulsive contractions moves contents of gut towards the anus
  • Distension initiates contraction
  • Vagal inhibitory and excitatory fibres control movement (regulation of peristalsis requires neural reflexes)
52
Q

when the area just below the fundus is contracting, why is the lower oesophagus sphincter contracted?

A

if it’s relaxed the acidic stuff in the stomach will end up in the oesophagus

unlike the stomach the oesophagus has a thin mucus layer (ie. not well protected against acid) so over time you can end up with a barret oesophagus - potential cause for pharyngeal cancer

53
Q

what size does the material have to be to pass through the pyloric sphincter muscle? if its too large what happens?

A

2mm

if the material is too large
the pylorus will detect this and contract, repulsing the material back. the antrum will then grind this material.

sem 2 Liver and GI (11 decks)

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