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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
Digestion What are proteins?
comprised of chains of amino acids linked together by peptide bonds
26
Digestion What are fats?
most often comprised of triglycerides (three long chain carbon molecules called fatty acids linked to 3-carbon glycerol backbone)
27
Digestion What is hydrolysis?
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
28
Digestion What enzymes are involved in carbohydrate digestion?
- amylase - sucrase - lactase - maltase
29
Digestion What enzymes are involved in protein digestion?
- pepsin - trypsin - chymotrypsin - carboxypeptidase - aminopeptidases
30
Digestion What enzymes are involved in fat digestion?
lipase
31
Absorption Where does absorption of digested nutrients, water, and electrolytes predominantly occur?
across membrane of epithelial cells, in small intestine
32
Absorption Where do absorbed digested nutrients, water, and electrolytes travel to? (2)
travel through epithelial cells into: - blood (carbohydrate and protein breakdown products) - lymphatic system (fat breakdown products)
33
Absorption What is absorbed in large intestine? (2)
- water | - some vitamins
34
What are the parts of the GI tract? (6)
- mouth - pharynx - esophagus - stomach - small intestine - large intestine
35
What are the accessory organs (4)?
- salivary glands - liver - gallbladder - pancreas
36
What do accessory organs do?
secrete substances into GI tract
37
What are the 4 primary layers of the wall of the GI tract?
- mucosa - submucosa - muscularis externa - serosa
38
Layer 1: Muscosa What is the mucosa layer?
inner layer that lines luminal surface of GI tract and is subdivided into three components
39
Layer 1: Muscosa What are the 3 components of the mucosa layer?
- mucus membrane - lamina propria - muscularis mucosa
40
Layer 1: Muscosa What is the mucus membrane?
layer of epithelial cells linked together by tight junctions
41
Layer 1: Muscosa What type of cells does the mucus membrane have? (3)
- exocrine cells - endocrine cells - epithelial cells
42
Layer 1: Muscosa What do exocrine cells do?
secrete mucus or digestive enzymes
43
Layer 1: Muscosa What do endocrine cells do?
secrete GI hormones
44
Layer 1: Muscosa What are epithelial cells specialized for?
nutrient absorption
45
Layer 1: Muscosa What is the lamina propria?
- thin layer - connective tissue upon which the epithelium rests - immune cells, capillaries, and lymph ducts
46
Layer 1: Muscosa What is the muscularis mucosa? What does it do?
- thin layer - smooth muscle cells - influence local luminal mixing
47
Layer 2: Submucosa What is the submucosa layer?
thick connective tissue layer that gives GI tract elasticity
48
Layer 2: Submuscosa What does the submucosa contain? (3)
- blood vessels - lymphatic vessels - exocrine glands
49
Layer 2: Submuscosa Where is the submucosal plexus? What does it contain? What does it control?
- within submucosa of small and large intestine - contains network of interconnected neurons - controls GI motility and secretion
50
Layer 3: Muscularis Externa What is the muscularis externa layer?
major smooth muscle layer of GI tract
51
Layer 3: Muscularis Externa What are the two layers of the muscularis externa?
- inner circular layer | - outer longitudinal layer
52
Layer 3: Muscularis Externa What is the layout of muscle fibres in the inner circular layer? What happens when muscles contract?
muscle fibres running circularly around lumen contraction = constriction of lumen
53
Layer 3: Muscularis Externa What is the layout of muscle fibres in the outer longitudinal layer? What happens when muscles contract?
muscle fibres running along length of GI tract contraction = shortening of GI tract
54
Layer 3: Muscularis Externa Where is the myenteric plexus? What does it do?
- lies between these two muscle layers | - coordinates muscularis externa contractions
55
Layer 4: Serosa What is the serosa layer?
connective tissue outer covering
56
Layer 4: Serosa What does the serosa layer do? (2)
- anchors GI tract within abdominal cavity | - secretes lubricating fluid – reduces friction between GI tract and surrounding structures
57
What are the 4 separate factors that coordinate motility and secretion within GI tract?
- intrinsic electrical properties of smooth muscle cells - enteric nervous system (ENS) - autonomic nervous system - GI hormones
58
Intrinsic Smooth Muscle Activity What do specialized smooth muscle cells in GI tract undergo?
spontaneous, transient membrane depolarizations - non-contractile - pacemaker cells “interstitial cells of Cajal”
59
Intrinsic Smooth Muscle Activity What are pacemaker cells?
interstitial cells of Cajal
60
Intrinsic Smooth Muscle Activity What are slow waves?
depolarizing potentials
61
Intrinsic Smooth Muscle Activity What allows flow of electric current between cells?
slow waves propagate from pacemaker cells into adjacent smooth muscle cells through gap junctions
62
Intrinsic Smooth Muscle Activity Where do slow waves generated in pacemaker cells propagate?
along interconnected smooth muscle network
63
Intrinsic Smooth Muscle Activity What happens if slow wave depolarizations reach AP threshold?
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
Intrinsic Smooth Muscle Activity What happens if there is a greater number of APs?
greater number of APs = greater elevation of intracellular Ca2+ = greater strength of contraction (tension) of muscle cell
65
Enteric Nervous System What is the ENS comprised of?
two nerve plexuses within GI tract (submucosal and myenteric) wall
66
Enteric Nervous System Why is ENS considered reflexive?
can operate entirely within GI wall, without external input (ie. brain)
67
Enteric Nervous System What does ENS function via?
electrical communication and release of neurotransmitters between neurons
68
Enteric Nervous System What are the components of the ENS? (3)
- sensory (afferent) neurons - interneurons - secretomotor cells
69
Enteric Nervous System What are the sensory (afferent) neurons? (3)
- mechanoreceptors - chemoreceptors - osmoreceptors
70
Enteric Nervous System What are the interneurons?
- excitatory | - inhibitory
71
Enteric Nervous System What do secretomotor cells do?
influence smooth muscle, epithelial cells that secrete or absorb fluid/electrolytes, and enteric endocrine cells
72
Autonomic Nervous System What innervates the GI tract?
nerve fibres from both branches of ANS
73
Autonomic Nervous System What do nerve fibres from both branches of ANS influence?
motility and secretion by: - influencing ongoing ENS activity - directly affecting smooth muscle and glands - altering GI hormone levels
74
Autonomic Nervous System Where and how do preganglionic sympathetic fibres from CNS synapse?
in prevertebral ganglia postsynaptic fibres enter GI wall and synapse in ENS, or onto GI effector cells using norepinephrine (NE) as neurotransmitter
75
Autonomic Nervous System Where and how do preganglionic parasympathetic fibres from CNS synapse?
enter into GI wall - synapse with postganglionic fibre within ENS - postganglionic fibre releases acetylcholine (Ach) onto their effector cells
76
Autonomic Nervous System What does ANS communicate with?
ENS
77
Autonomic Nervous System What does parasympathetic input do?
increases motility and GI secretions
78
Autonomic Nervous System When does parasympathetic input occur?
during and immediately following ingestion of meal
79
Autonomic Nervous System What does sympathetic input do?
decreases motility and GI secretions
80
Autonomic Nervous System When does parasympathetic input occur?
during stress response
81
GI Hormones What releases GI hormones in response to appropriate stimuli?
endocrine cells dispersed among epithelial cells in mucosa
82
GI Hormones Where are hormones carried?
via bloodstream to other areas of GI system
83
GI Hormones What types of effects do hormones have on smooth muscle or glands?
can be excitatory or inhibitory
84
GI Hormones What are the major GI hormones? Where are they from? (4)
- gastrin: from stomach - secretin: from duodenum - cholecystokinin (CCK): from duodenum - gastric inhibitory peptide (GIP): from duodenum/jejunum
85
What are chemoreceptors?
sensitive to chemical substances within lumen
86
What are mechanoreceptors?
sensitive to stretch or tension within GI tract wall
87
What are osmoreceptors?
sensitive to osmolarity (concentration) of luminal contents

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

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