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Physiology with pharmacology - L1 > Gastrointestinal tract > Flashcards

Gastrointestinal tract Flashcards

1
Q

What organs are involved in the gastrointestinal tract?

A
  • mouth
  • oesophagus
  • stomach
  • small intestine
  • large intestine
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2
Q

What is the GI tract?

A

a tube, differentiated along its length for sequential processing of food

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3
Q

What anchors the suspended intestines within the abdominal cavity?

A

mesenteries (membranes)

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4
Q

What are immunologic omentum?

A

immunological organ that is a source if inflammatory cells & stem cells that play a role in the control of infection through wound-healing & regeneration

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5
Q

What separates the different hollow organs?

A

sphincters & secretory accessory glands/organs

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6
Q

What are sphincters?

A

muscular rings - control the progression of the food from 1 section to the next. They also prevent the backflow of material from one section to the previous one.

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7
Q

What is the function of GI tract?

A
  • motility propels ingested food
  • secretions from associated glands
  • digestion/hydrolysis into absorbable molecules
  • absorption into the bloodstream of nutrients, electrolytes, water
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8
Q

What are the 2 layers of the GI tract?

A
  • mucosal layer
  • submucosal layer
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9
Q

What is in the mucosal layer?

A

in touch with contents of the lumen - contains epithelial cells.
- either absorbable or secretory cells
- lamina propria (connective tissues with blood & lymph vessels)
- thin muscularis mucosae

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10
Q

What is in the submucosal layer?

A

connective tissue (collagen, elastin), glands larger blood vessels (that transport molecules, as well as removing & metabolites

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11
Q

What shape are the 2 smooth muscle layers (enteric neurones between)?

A

circular + longitudinal

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12
Q

What is serosa?

A

squamous epithelia

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13
Q

What is the function of the mouth?

A
  • mechanical disruption of food
  • (mastication) aims to increase the surface area to attack by enzymes & chemicals later in the GI tract.
  • also lubricate the food with the secretions of these 3 glands.
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13
Q

What can be found in the multi-parted exocrine glands?

A

ligual lipase + amylase initiates lipid + starch

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13
Q

What are the 3 sections of the salivary glands?

A
  • parotid gland
  • submandibular gland
  • sublingual gland
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13
Q

What are the roles of saliva?

A
  • lubricate food (bolus)
  • antimicrobial - resists bacterial infection
  • buffering - neutralises acid
  • dissolves food - detection by taste buds
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14
Q

What controls the level of mastication & swallowing?

A

the brainstem (CNS) will control the level of mastication & swallowing

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14
Q

What receptors relay sensory information to the CNS?

A

mechanoreceptors (found in mouth & teeth) & chemoreceptors relay sensory information to brainstem

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14
Q

How do later parts of the GI tract prepare for the arrival of food?

A

they start to secrete, in preparation for the arrival of the bolus

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14
Q

What does stimulation of the central nervous system enable?

A

enables later sections of the GI tract to get ready for the arrival of food?

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15
Q

What does swallowing do?

A

move the bolus into the oesophagus

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16
Q

What is the oesophagus lined with?

A

lumen lined with stratified squamous epithelia

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17
Q

What is the benefit of having stratified squamous epithelia on the lumen of the oesophagus?

A

loose cells at the surface allow cells to be lost without causing damage to the underlying tissue, as they are in contact with the bolus

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18
Q

How does the swallowing reflex work?

A
  • closes upper oesophageal sphincter.
  • initiates primary peristaltic wave, coordinates sequential contractions
  • continued distension (food in the oesophagus) initiates secondary peristaltic wave (by ENS - enteric nervous system - the nervous system within the GI tract)
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19
Q

What initiates the second peristaltic wave?

A

continued distension - food in the oesophagus - with activates the ENS (enteric nervous system)

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20
Q

What is the ENS (enteric nervous system)?

A

nervous system within the GI tract

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21
Q

What does the vasovagal reflex control?

A

lower oesophageal sphincter (LOS) tone

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22
Q

How does the PNS (parasympathetic nervous system) vagus nerve control the LOS (lower oesophageal sphincter) opening?

A

by releasing VIP neurotransmitter

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23
Q

What is the autonomic nervous system made up of?

A
  • sympathetic nervous system
  • parasympathetic nervous system
  • enteric nervous system
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24
Q

What are the extrinsic part of the nervous system that regulate the GI tract?

A

sympathetic & parasympathetic

25
Q

What are the intrinsic part of the nervous system that regulate the GI tract?

A

enteric nervous system

26
Q

What modifies the enteric nervous system?

A

the brain - 2 MAIN plexuses

27
Q

What are the 2 main plexuses in the brain?

A
  • ganglia within submucosal
  • myenteric plexuses (including pancreases + biliary system)
28
Q

How does neural control of the GI tract work?

A
  • parasympathetic ganglia within plexuses coordinates information received from PNS and relay to smooth muscle, endocrine & secretory cells
  • postganglionic neurones are either cholinergic (release ACh) or peptidergic (release peptides)
29
Q

What do sympathetic postganglionic nerve fibres release?

A

they are adrenergic (release norepinephrine)

30
Q

What are nerve fibres a mix of?

A

mixed afferent & efferent i.e sensory & motor information is relayed between GI tract & CNS, coordinated by the plexuses

31
Q

What are the 3 phases to stomach motility?

A
  1. receptive relaxation in thin-walled Orad stomach to receive food.
  2. 3 muscular layers of Caudad region contract to mix food with gastric huice from mucosal glands (ANS control) forming chyme
  3. Gastric emptying through pyloric sphincter into small intestine (SI) - fat content & H+ slows emptying
32
Q

What is chyme a mixture of?

A
  • HCI (hydrochloric acid)
  • Pepsinogen - pepsin (protease)
  • Intrinsic factor
  • Mucus
33
Q

Why is there mucus in chyme?

A

to prevent the acid & proteins damaging the linin

34
Q

What is low level, weak contraction below the threshold called?

A

tone

35
Q

What are contractions called when there are action potentials on top of tone contractions?

A

phasic contractions

36
Q

How many sphincters are there in the Oddi?

A

6+

37
Q

What type of pressure is found in sphincters?

A

positive resting pressure

38
Q

What do sphincters regulate?

A

antegrade (forward) & retrograde (backward) movement of food

39
Q

What is the most contractile tissue?

A

unitary smooth muscle

40
Q

Why is unitary smooth muscle the most contractile tissue?

A

cells electrically coupled via gap junctions –> rapid spread of action potentials leading to coordinated contraction

41
Q

What are 2 types of contractions?

A

tonic - constant level of contraction/tone
phasic - periodic contraction + relaxation (3-12/min)

42
Q

What cells are the gastrointestinal pacemaker cells?

A

interstitial cells of Cajal (ICC) in stomach, SI, LI

43
Q

What is contraction always preceded by?

A

electrical activity

44
Q

What is the function of the small intestine?

A
  • digestion + absorption of nutrients - carbs, amino acids, fats, water & ions
  • chyme is mixed with digestive enzymes + pancreatic secretions
  • many hydrolytic enzymes embedded in membrane of brush border
45
Q

What are the 3 sections of the small intestine?

A
  • duodenum
  • jejunum
  • ileum
46
Q

How does surface area increase?

A

plicae –> villi –> microvilli

47
Q

How much of exocrine secretion occurs into the duodenum per day?

A

1 litre

48
Q

Why is the exocrine solution rich in bicarbonate?

A

to neutralise the H+ delivered from the stomach

49
Q

From which cells is bicarbonate released from?

A

centroacinar & ductal cells

50
Q

How is pancreas secretion controlled by the autonomic nervous system?

A

PNS - stimulates secretion
SNS - inhibits the ‘rest & digest’ response

51
Q

What do liver cells (hepatocytes) secrete?

A

bile

52
Q

When is CCK hormone ejected from the small intestine?

A

when chyme enters - following relaxation of Oddi

53
Q

What is bile made up of?

A
  • water
  • amphipathic bile salts (lipid emulsification)
  • bilirubin - involved in erythrocyte breakdown
  • cholesterol - excretion & recirculation
  • phospholipids - emulsify fats
  • electrolytes - neutralise the acidic chyme
54
Q

How does 95% of bile acids get recirculated to the liver?

A

enterohepatic circulation

55
Q

What type of contractions are seen in the small intestine?

A

peristaltic contractions propel the chyme

56
Q

What do enterochromaffin cells release?

A

serotonin (neurocrine) - peristaltic reflex

57
Q

What happens to the material not absorbed in the small intestine?

A

passes through lleocaecal sphincter into the caecum of the large intestine

58
Q

What are the 3 types of GI peptides classified as?

A
  • hormones
  • paracrines
  • neurocrines
59
Q

Where do GI pepetide hormones come from?

A

GI endocrine cells - e.g. GIP

60
Q

Where do GI pepetide paracrines come from?

A

from endocrine cells, act locally, e.g. somatostatin

61
Q

Where do GI peptide neurocrines come from?

A

released from neurones, following action potential

62
Q

What are the 3 main functions of the large intestine?

A
  1. absorbs water & electrolytes: Na+, Cl-, HCO3, K+.
  2. Make & absorb vitamins K+B.
  3. Forming + propelling faeces (ferments indigestible food - bacteria), to be excreted.
63
Q

What increases Na+ absorption?

A

aldosterone

64
Q

What are the 2 parts of the large intestine?

A
  • surface columnar epithelial cells (absorptive)
  • taenia coli - 3 bands of longitudinal muscle that is shorter than the large intestine caused bunching, forming small sacs - haustra
65
Q

How does food move through the large intestine?

A
  • segmented contraction - caecum + proximal colon, mic contents - haustra.
66
Q

What reflex moves contents through the large intestine?

A

gastrocolic reflex

67
Q
A

Physiology with pharmacology - L1 (17 decks)

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