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+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction > Intro to GI Physiology > Flashcards

Intro to GI Physiology Flashcards

1
Q

What does the gastrointestinal system do?

A

processes and transfers nutrients, fluid, and electrolytes from ingested foods into internal environment

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2
Q

What are GI processes controlled by? (2)

A
  • nervous system

- hormones

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3
Q

Which nervous systems control GI processes? What do they each do? (2)

A
  • enteric – the local nervous system

- autonomic (ANS) – mediates central nervous system influences

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4
Q

What do hormones influence in the GI system?

A

movement of contents of GI tract, and secretions that enter its lumen

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5
Q

What are the basic GI processes? (4)

A
  • motility
  • secretion
  • digestion
  • absorption
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6
Q

What is motility?

A

muscular contractions that mix and move forward the contents of GI tract

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7
Q

What is secretion?

A

glands located along GI tract secrete their contents into the tract, assisting in motility, digestion and absorption

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8
Q

What is digestion?

A

biochemical breakdown of large particles and molecules into smaller, absorbable particles

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9
Q

What is absorption?

A

small particles are absorbed from GI tract into blood or lymph

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10
Q

Motility

What confers the ability to move GI tract contents?

A

smooth muscle cells in wall of GI tract

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11
Q

Motility

What do smooth muscle cells maintain?

A

constant level of contraction (tone) at their approximate length midpoint

  • allows either further contraction or relaxation from this point
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12
Q

Motility

What does tone maintain?

A

steady-state pressure on GI tract contents

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13
Q

Motility

What are the two broad categories of movement (motility) superimposed on background muscle tone?

A
  • mixing movements

- propulsive movements

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14
Q

Motility

What do mixing movements do? (3)

A
  • redistribute luminal contents locally
  • enhance exposure to digestive secretions
  • expose luminal contents to GI tract absorbing surfaces
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15
Q

Motility

What do propulsive movements do?

A

move luminal contents forward

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16
Q

Motility

How does the rate of propulsion vary?

A

varies with specific function of region

ie. small intestine = slow
ie. esophagus = rapid

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17
Q

Secretion

What do exocrine glands do?

A

secrete digestive juices into lumen

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18
Q

Secretion

What do digestive juices typically consist of?

A
  • water electrolytes

- organic substances – mucus, enzymes, bile salts

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19
Q

Secretion

What do digestive juice secretions do?

A

perform specific functions within GI tract

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20
Q

Secretion

Why does production of exocrine secretions require energy?

A
  • active uptake of raw materials

- assembly in endoplasmic reticulum

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21
Q

Secretion

What stimulates release of exocrine gland secretory products into GI tract?

A

neuronal or hormonal stimulation

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22
Q

Secretion

What happens to exocrine secretions after they complete their physiological duties?

A

most are reabsorbed

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23
Q

Digestion

What are the 3 primary categories of nutrients?

A
  • carbohydrates
  • proteins
  • fats
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24
Q

Digestion

What are carbohydrates?

A

comprised of either single sugar molecules (6-carbon ring) called monosaccharides, or linked sugar molecules called disaccharides or polysaccharides

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25
Q

Digestion

What are proteins?

A

comprised of chains of amino acids linked together by peptide bonds

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26
Q

Digestion

What are fats?

A

most often comprised of triglycerides (three long chain carbon molecules called fatty acids linked to 3-carbon glycerol backbone)

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27
Q

Digestion

What is hydrolysis?

A

nutrient-specific enzymes mediate addition of H2O molecule to bonds linking component molecules together, causing the molecules to split apart

ie. maltose + H2O → glucose + glucose

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28
Q

Digestion

What enzymes are involved in carbohydrate digestion?

A
  • amylase
  • sucrase
  • lactase
  • maltase
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29
Q

Digestion

What enzymes are involved in protein digestion?

A
  • pepsin
  • trypsin
  • chymotrypsin
  • carboxypeptidase
  • aminopeptidases
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30
Q

Digestion

What enzymes are involved in fat digestion?

A

lipase

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31
Q

Absorption

Where does absorption of digested nutrients, water, and electrolytes predominantly occur?

A

across membrane of epithelial cells, in small intestine

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32
Q

Absorption

Where do absorbed digested nutrients, water, and electrolytes travel to? (2)

A

travel through epithelial cells into:

  • blood (carbohydrate and protein breakdown products)
  • lymphatic system (fat breakdown products)
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33
Q

Absorption

What is absorbed in large intestine? (2)

A
  • water

- some vitamins

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34
Q

What are the parts of the GI tract? (6)

A
  • mouth
  • pharynx
  • esophagus
  • stomach
  • small intestine
  • large intestine
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35
Q

What are the accessory organs (4)?

A
  • salivary glands
  • liver
  • gallbladder
  • pancreas
36
Q

What do accessory organs do?

A

secrete substances into GI tract

37
Q

What are the 4 primary layers of the wall of the GI tract?

A
  • mucosa
  • submucosa
  • muscularis externa
  • serosa
38
Q

Layer 1: Muscosa

What is the mucosa layer?

A

inner layer that lines luminal surface of GI tract and is subdivided into three components

39
Q

Layer 1: Muscosa

What are the 3 components of the mucosa layer?

A
  • mucus membrane
  • lamina propria
  • muscularis mucosa
40
Q

Layer 1: Muscosa

What is the mucus membrane?

A

layer of epithelial cells linked together by tight junctions

41
Q

Layer 1: Muscosa

What type of cells does the mucus membrane have? (3)

A
  • exocrine cells
  • endocrine cells
  • epithelial cells
42
Q

Layer 1: Muscosa

What do exocrine cells do?

A

secrete mucus or digestive enzymes

43
Q

Layer 1: Muscosa

What do endocrine cells do?

A

secrete GI hormones

44
Q

Layer 1: Muscosa

What are epithelial cells specialized for?

A

nutrient absorption

45
Q

Layer 1: Muscosa

What is the lamina propria?

A
  • thin layer
  • connective tissue upon which the epithelium rests
  • immune cells, capillaries, and lymph ducts
46
Q

Layer 1: Muscosa

What is the muscularis mucosa? What does it do?

A
  • thin layer
  • smooth muscle cells
  • influence local luminal mixing
47
Q

Layer 2: Submucosa

What is the submucosa layer?

A

thick connective tissue layer that gives GI tract elasticity

48
Q

Layer 2: Submuscosa

What does the submucosa contain? (3)

A
  • blood vessels
  • lymphatic vessels
  • exocrine glands
49
Q

Layer 2: Submuscosa

Where is the submucosal plexus?
What does it contain?
What does it control?

A
  • within submucosa of small and large intestine
  • contains network of interconnected neurons
  • controls GI motility and secretion
50
Q

Layer 3: Muscularis Externa

What is the muscularis externa layer?

A

major smooth muscle layer of GI tract

51
Q

Layer 3: Muscularis Externa

What are the two layers of the muscularis externa?

A
  • inner circular layer

- outer longitudinal layer

52
Q

Layer 3: Muscularis Externa

What is the layout of muscle fibres in the inner circular layer?

What happens when muscles contract?

A

muscle fibres running circularly around lumen

contraction = constriction of lumen

53
Q

Layer 3: Muscularis Externa

What is the layout of muscle fibres in the outer longitudinal layer?

What happens when muscles contract?

A

muscle fibres running along length of GI tract

contraction = shortening of GI tract

54
Q

Layer 3: Muscularis Externa

Where is the myenteric plexus?
What does it do?

A
  • lies between these two muscle layers

- coordinates muscularis externa contractions

55
Q

Layer 4: Serosa

What is the serosa layer?

A

connective tissue outer covering

56
Q

Layer 4: Serosa

What does the serosa layer do? (2)

A
  • anchors GI tract within abdominal cavity

- secretes lubricating fluid – reduces friction between GI tract and surrounding structures

57
Q

What are the 4 separate factors that coordinate motility and secretion within GI tract?

A
  • intrinsic electrical properties of smooth muscle cells
  • enteric nervous system (ENS)
  • autonomic nervous system
  • GI hormones
58
Q

Intrinsic Smooth Muscle Activity

What do specialized smooth muscle cells in GI tract undergo?

A

spontaneous, transient membrane depolarizations

  • non-contractile
  • pacemaker cells “interstitial cells of Cajal”
59
Q

Intrinsic Smooth Muscle Activity

What are pacemaker cells?

A

interstitial cells of Cajal

60
Q

Intrinsic Smooth Muscle Activity

What are slow waves?

A

depolarizing potentials

61
Q

Intrinsic Smooth Muscle Activity

What allows flow of electric current between cells?

A

slow waves propagate from pacemaker cells into adjacent smooth muscle cells through gap junctions

62
Q

Intrinsic Smooth Muscle Activity

Where do slow waves generated in pacemaker cells propagate?

A

along interconnected smooth muscle network

63
Q

Intrinsic Smooth Muscle Activity

What happens if slow wave depolarizations reach AP threshold?

A

burst of action potentials results

  • number of APs is proportional to duration that slow wave remains above threshold
  • smooth muscle cells contract in response to rise in intracellular Ca2+ levels associated with APs
64
Q

Intrinsic Smooth Muscle Activity

What happens if there is a greater number of APs?

A

greater number of APs
= greater elevation of intracellular Ca2+
= greater strength of contraction (tension) of muscle cell

65
Q

Enteric Nervous System

What is the ENS comprised of?

A

two nerve plexuses within GI tract (submucosal and myenteric) wall

66
Q

Enteric Nervous System

Why is ENS considered reflexive?

A

can operate entirely within GI wall, without external input (ie. brain)

67
Q

Enteric Nervous System

What does ENS function via?

A

electrical communication and release of neurotransmitters between neurons

68
Q

Enteric Nervous System

What are the components of the ENS? (3)

A
  • sensory (afferent) neurons
  • interneurons
  • secretomotor cells
69
Q

Enteric Nervous System

What are the sensory (afferent) neurons? (3)

A
  • mechanoreceptors
  • chemoreceptors
  • osmoreceptors
70
Q

Enteric Nervous System

What are the interneurons?

A
  • excitatory

- inhibitory

71
Q

Enteric Nervous System

What do secretomotor cells do?

A

influence smooth muscle, epithelial cells that secrete or absorb fluid/electrolytes, and enteric endocrine cells

72
Q

Autonomic Nervous System

What innervates the GI tract?

A

nerve fibres from both branches of ANS

73
Q

Autonomic Nervous System

What do nerve fibres from both branches of ANS influence?

A

motility and secretion by:

  • influencing ongoing ENS activity
  • directly affecting smooth muscle and glands
  • altering GI hormone levels
74
Q

Autonomic Nervous System

Where and how do preganglionic sympathetic fibres from CNS synapse?

A

in prevertebral ganglia

postsynaptic fibres enter GI wall and synapse in ENS, or onto GI effector cells using norepinephrine (NE) as neurotransmitter

75
Q

Autonomic Nervous System

Where and how do preganglionic parasympathetic fibres from CNS synapse?

A

enter into GI wall

  • synapse with postganglionic fibre within ENS
  • postganglionic fibre releases acetylcholine (Ach) onto their effector cells
76
Q

Autonomic Nervous System

What does ANS communicate with?

77
Q

Autonomic Nervous System

What does parasympathetic input do?

A

increases motility and GI secretions

78
Q

Autonomic Nervous System

When does parasympathetic input occur?

A

during and immediately following ingestion of meal

79
Q

Autonomic Nervous System

What does sympathetic input do?

A

decreases motility and GI secretions

80
Q

Autonomic Nervous System

When does parasympathetic input occur?

A

during stress response

81
Q

GI Hormones

What releases GI hormones in response to appropriate stimuli?

A

endocrine cells dispersed among epithelial cells in mucosa

82
Q

GI Hormones

Where are hormones carried?

A

via bloodstream to other areas of GI system

83
Q

GI Hormones

What types of effects do hormones have on smooth muscle or glands?

A

can be excitatory or inhibitory

84
Q

GI Hormones

What are the major GI hormones?
Where are they from? (4)

A
  • gastrin: from stomach
  • secretin: from duodenum
  • cholecystokinin (CCK): from duodenum
  • gastric inhibitory peptide (GIP): from duodenum/jejunum
85
Q

What are chemoreceptors?

A

sensitive to chemical substances within lumen

86
Q

What are mechanoreceptors?

A

sensitive to stretch or tension within GI tract wall

87
Q

What are osmoreceptors?

A

sensitive to osmolarity (concentration) of luminal contents

+ CAPS 301: Respiratory, Renal, GI, Endocrinology, Reproduction (32 decks)

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