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Advanced Physiology > Gastrointestinal Tract Homeostasis > Flashcards

Gastrointestinal Tract Homeostasis Flashcards

1
Q

What are the four layers of the GI tract?

A

Mucosa (inner), submucosa, muscularis, serosa (outer)

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2
Q

What is the mucosa layer?

A

A moist epithelial membrane

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3
Q

What does the submucosa layer contain?

A

A rich supply of blood/lymphatic vessels & nerve fibres

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4
Q

What is the muscularis layer responsible for?

A

Peristalsis and mixing

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5
Q

In areas, thickening of the circular muscularis layer forms __?

A

Sphincters

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6
Q

What is the serosa layer?

A

The outer protective layer

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7
Q

What are the two mechanisms that modulate digestive activity?

A
  • Mechanical and sensory stretch receptors

- Intrinsic/extrinsic neural/endocrine control

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8
Q

What do short reflexes respond to?

A

Internal stimuli in the GI wall

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9
Q

What is the role of long reflexes?

A

Transmit information from chemoreceptors/osmoreceptors/mechanoreceptors to local nerve plexus (gut brain) via CNS and extrinsic autonomic system

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10
Q

Where in the digestive system are mechanical and chemical receptors located?

A

In the wall of the tract organ

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11
Q

What do the digestive receptors induce?

A

Long reflexes through ENS, spinal reflexes and brain stem

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12
Q

What do the digestive receptors respond to?

A

Stretch, osmolarity, pH and food substrates

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13
Q

What do the digestive receptors modulate?

A

Glandular secretion of digestive juices and hormones and smooth muscle contraction (mixing/peristalsis)

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14
Q

What is the intrinsic control centre of the digestive system composed of?

A

Nerve plexus that runs from the oesophagus to the anus (ENS) and the hormone producing cell of the GI tract

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15
Q

What is the extrinsic control centre of the digestive system composed of?

A

Autonomic nervous system (PNS stimulates, SNS inhibits) and endocrine glands/tissues outside of the GI tract

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16
Q

What is the enteric nervous system composed of?

A

Submucosal nerve plexus and myenteric nerve plexus

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17
Q

What type of neurons does the submucosal nerve plexus contain and what does it regulate?

A

Sensory and motor; GI secretions and blood flow

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18
Q

Where is the myenteric nerve plexus located and what does it regulate?

A

Between the circular and longitudinal smooth muscle fibres; regulates motility (mixing & peristalsis)

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19
Q

How is the ENS linked to the CNS?

A

Through afferent visceral fibres and ANS innervation

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20
Q

Which nervous system runs the whole length of the digestive system and which is divided into two sections?

A

SNS (mainly postganglionic); PNS (preganglionic)

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21
Q

What is the result of parasympathetic innervation of the ENS?

A

Enhanced GI activity

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22
Q

What neurotransmitter is released with parasympathetic innervation of the ENS?

A

Acetylcholine - stimulate further ENS excitability

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23
Q

What is the result of sympathetic innervation of the ENS?

A

Inhibited GI activity

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24
Q

What are the two divisions of the ENS innervated by the PNS?

A

Cranial division & sacral division

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25
Q

What neurotransmitter is released with sympathetic innervation of the ENS?

A

Norepinephrine - inhibits ENS activity

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26
Q

What are the three categories of GI reflexes?

A

Local enteric reflexes, reflexes from the pre-vertebral sympathetic ganglia & reflexes from the spinal cord/brain stem

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27
Q

What do local enteric reflexes control?

A

GI secretions, peristalsis, mixing contractions & local inhibitory effects

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28
Q

What is the role of reflexes from the pre-vertebral sympathetic ganglia?

A

Transmit signals to other regions of the GI tract

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29
Q

What are the 3 types of reflexes from pre-vertebral sympathetic ganglia?

A

Gastrocolic reflex: Signal from stomach to empty colon
Enterogastric reflex: Inhibition of motility and secretions in stomach by small intestine/colon
Colonoileal reflex: Inhibits emptying of small intestine into colon

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30
Q

What are the 3 types of reflexes from the spinal cord/brain stem?

A

Reflexes via vagus nerve: Control gastric motor & secretory functions
Pain reflexes: Cause general inhibition of GI functions
Defecation reflex: Provide powerful colonic, rectal & abdominal contractions

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31
Q

What are the two types of electrical waves generated by smooth muscle contraction?

A

Slow waves (change RMP but not APs) and spike potentials (APs, occur at top of slow waves)

32
Q

What are slow waves caused by?

A

Cajal (pacemaker) cells

33
Q

What is the difference between slow waves and spike potentials?

A

Both involve an influx of Na+, but spike potentials have an influx of Ca2+ which causes them to reach threshold and generate an AP

34
Q

What are the main stimulants of GI tract contraction (peristalsis & segmentation)?

A

Distension, chemical/physical irritant & ENS/PNS activation

35
Q

Why is the pyloric valve in the stomach never opened?

A

Because the contents of the stomach would burn the epithelial layer of the small intestine (highly acidic)

36
Q

What hormone acts on the stomach and what does it stimulate?

A

Gastrin; stimulates gastric acid secretion & motility

37
Q

What hormones act on the small intestine?

A

CCK, secretin, gastric inhibitory peptide (GIP) and motilin

38
Q

What does CCK stimulate & inhibit?

A

Stimulates pancreatic enzymes & bile secretions, inhibits gastric emptying

39
Q

What does secretin stimulate & inhibit?

A

Stimulates pancreatic bicarbonate secretion & pepsin secretion, inhibits gastric acid secretion

40
Q

What does GIP stimulate & inhibit?

A

Stimulates gastric & intestinal motility, inhibits gastric acid secretion

41
Q

What does motilin stimulate?

A

Gastric & intestinal motility

42
Q

What class of hormones are the digestive hormones?

A

Peptide hormones

43
Q

Are the digestive hormones water or lipid soluble?

A

Water soluble - diffuse freely in the bloodstream

44
Q

What is chewing controlled by?

A

Nuclei within the brainstem that innervate the jaw muscles

45
Q

What is the chewing reflex?

A

Rhythmic jaw movements are initiated by stretch receptors in the cheeks, gums and tongue in response to a bolus

46
Q

What does salivation allow?

A

Tasting/moistening of food, formation of bolus, chemical breakdown of starches, cleansing of mouth

47
Q

What are the three glands involved in salivation?

A

Sublingual, parotid and submandibular glands

48
Q

What is salivation controlled by?

A
  • PNS in response to chemoreceptors (taste) and mechanoreceptors (tactile)
  • Salivary nuclei in medulla/pons
  • Reflex arcs from stomach
49
Q

What are the three major phases of swallowing?

A

Buccal phase (voluntary), pharyngeal phase (involuntary), oesophageal phase (involuntary)

50
Q

What occurs during the buccal phase?

A

Placement of tip of tongue against hard palate, contraction of tongue to force bolus into oropharynx

51
Q

What occurs during the pharyngeal phase?

A
  • Respiration inhibited
  • Tongue blocks backflow
  • Soft palate blocks nasopharynx
  • Epiglottis blocks respiratory passage
  • Upper oesophageal sphincter relaxes
  • Peristalsis contractions move into the oesophagus
52
Q

What occurs during the oesophageal phase?

A
  • Primary peristalsis waves (continuation of pharyngeal waves)
  • Secondary peristalsis waves (activated by distension of oesophagus, controlled by ENS & higher centres)
53
Q

How is swallowing innervated?

A
  • Pharyngeal wall & upper third of oesophagus: Vagus & glossopharyngeal nerves
  • Lower two thirds of oesophagus: ENS & higher brain centres through modulation of ENS
54
Q

What is the role of the stomach?

A
  • Temporary storage tank
  • Mixing of foods with gastric juices to create chyme
  • Physical/chemical breakdown
  • Slow emptying of chyme into small intestine
55
Q

What glands secrete gastric juice?

A

Oxyntic glands and pyloric gland

56
Q

What do the oxyntic glands secrete?

A

Pepsinogen (protein digestion), intrinsic factor (absorption of vitamin B12) and mucus

57
Q

What does the pyloric gland secrete?

A

Mucus and gastrin

58
Q

What are the major stimulants of gastric juice secretion?

A

Distension, change in pH, detection of amino acids/CHOs/fats, release of gastrin/histamine/HCl-

59
Q

What is mucus composed of?

A

Water, electrolytes & a mixture of glycoproteins

60
Q

What is the function of mucus?

A

Adhere to food, coat GI wall, allow slipping

61
Q

What are the 3 phases of gastric juice secretion?

A

Cephalic, gastric and intestinal phases

62
Q

How does stomach emptying occur?

A

Through intense peristaltic contractions of the antrum and opening of the pyloric sphincter

63
Q

What is the rate of stomach emptying regulated by?

A

Signals from the stomach and duodenum - gastric factors and duodenal factors

64
Q

What are the gastric factors?

A

ENS reflex in stomach stimulated by stretch receptors, release of gastrin promotes stomach emptying

65
Q

What are the duodenal factors?

A

Enterogastric reflex: Slows or prevents further emptying

Hormonal feedback: Release of CCK in response to fatty acids and of secretin and GIP

66
Q

How is the stomach protected from its acidic environment?

A
  • Stomach wall is coated in a thick layer of bicarbonate-rich mucus (binds H+ ions, acts as a buffer)
  • Epithelial cells joined by tight junctions preventing gastric juices from leaking into underlying tissues
  • Damaged epithelial cells quickly shed and replaced
67
Q

Where does the small intestine begin and end?

A

Pyloric sphincter of stomach to ileocecal valve of large intestine

68
Q

Secretions from which organs stimulate digestion in the small intestine?

A

Liver (bile) and pancreas (digestive enzymes)

69
Q

What does the pancreas secrete into the duodenum?

A
  • Digestive enzymes for protein, fat and carbohydrate digestion (stimulated by chyme, Ach and CCK)
  • Bicarbonate ions & water (stimulated by chyme & secretin)
70
Q

What does the liver secrete?

A

Bile directly into the duodenum or gallbladder (storage)

71
Q

What is bile important in?

A
  • Fat digestion/absorption (due to bile salts)

- Excretion of waste products from the blood (bilirubin, excess cholesterol)

72
Q

What is secretion of bile stimulated by?

A

CCK and ACh

73
Q

What is mixing in small intestine stimulated by?

A

Distension of the small intestine by chyme & myenteric ENS

74
Q

What are the primary functions of the colon?

A

Absorption of water and electrolytes from chyme, storage of fecal matter, mixing and propulsion

75
Q

What two reflexes make up the defecation reflex?

A

ENS reflex: Distension of rectum causes peristaltic contractions in colon/rectum
PNS reflex: Stretch receptors - PNS in spinal cord - contraction of colon/rectum/anus through pelvic nerve

76
Q

Where do nutrients from the digestive tract passively/actively move into?

A

Hepatic portal circulation

Advanced Physiology (10 decks)

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