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PHGY 210- Digestion Exam Study Guide
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PHGY 210- Digestion Exam StudyGuide
Other names for digestive system - Answer - gastrointestinal tract (GI tract)
- alimentary canal
Accessory digestive organs - Answer - teeth
- tongue
- salivary glands
- liver
- gallbladder
- pancreas
What activity mediates secretion? What is its purpose? - Answer Glandular activity - for
chemical breakdown
What activity mediates motility? What is its purpose? - Answer Muscular activity - for
propulsion and physical breakdown
Steps of digestive process - Answer 1. ingestion
2. secretion
3. motility
4. digestion
5. absorption
6. defacation
Absorptive capacity of carbohydrates - Answer 99%
Absorptive capacity of fats - Answer 95%
Absorptive capacity of proteins - Answer 92%
How are propulsive, secretory, and absorptive activities of GIT integrated for
efficiency? - Answer By neural and hormonal mechanisms
Length of GIT - Answer 4.5m (3x taller than standing height)
Why is the GIT longer in cadavers? - Answer In living people, the GIT is under tone
(always partially contracted, relaxed in dead people)
,Role of GI lumen - Answer - central canal that connects to external environment at both
ends (innermost part of tube)
- increases total internal surface area
Internal v. External surface area of GIT - Answer - internal surface area = 200-250 sq.
meters
- 600x larger than external surface area
Layers of the GIT wall (inner to outer) - Answer - mucosa
- submucosa
- muscularis externa
- serosa
Serosa - Answer - thin, tough layer of connective tissue
- in contact with the mesentery which is connected to the peritoneum which holds the
GIT in place
Layers of muscularis externa and their roles - Answer - circular fibers (inner layer):
contraction narrows the GIT
- longitudinal fibers (outer layer): contraction shortens the GIT
Which parts of the GIT are made up of striated/skeletal muscle? - Answer - mouth
- upper 1/3 esophagus
- anus (at the external anal sphincter)
these muscles are controlled voluntarily
Which parts of the GIT are made up of smooth muscle? - Answer - everything below
esophagus and above anus
- these muscles are not under voluntary control
Layers of mucosa (inner to outer) and their roles - Answer - epithelial layer: epithelial
and glandular (secretory) cells play a role in absorption, responsible for increased S.A.
due to invaginations
- lamina propria: loose connective tissue
- muscularis mucosae: smooth muscle
Role of submucosa - Answer loose connective tissue containing neuronal network,
lymphatics, and blood vessels
,What is a plexus? - Answer Collection of nerve cell bodies. Containing all elements
needed for reflex arcs (sensory neurons, motor/effector neurons, interneurons)
What are the 2 plexuses of the GIT/ENS? Where are they located? - Answer - myenteric
plexus: between circular and longitudinal muscle of muscularis externa
- submucosal plexus: between muscularis mucosae and circular muscle
Though the plexuses are anatomically distinct, they behave as one functional unit
Which type of neurons are found in the ENS plexuses? - Answer - sensory neurons: have
receptors in mucosa or muscle (stretch receptors, chemoreceptors, osmoreceptors)
- motor/effector neurons: activate secretory and muscle cells
- interneurons: expand the responses to stimuli in the GIT
Innervation of sensory fibers in GIT wall - Answer - reach from mucosa all the way to
myenteric plexus
- can also reach myenteric plexus from circular muscle
Innervation of motor/effector neurons in GIT wall - Answer - reach from mucosa into
submucosal or myenteric plexus
- can also reach from myenteric plexus into longitudinal muscle
What neurotransmitters do excitatory enteric neurons release? - Answer acetylcholine
(ACh) onto muscarinic receptors
Atropine - Answer - blocks muscarinic ACh receptors (essential in ANS innervation and
secretion by salivary glands)
- ENS activation and inhibition is blocked (no ANS input)
What neurotransmitters do inhibitory enteric neurons release? - Answer
Non-Adrenergic, Non-Cholinergic (NANC) neurotransmitters (i.e. nitric oxide, not ACh,
Epi, or NE)
What cells do excitatory and inhibitory enteric neurons act on? - Answer Smooth
muscular and secretory cells
Pathway of short enteric (intramural) reflexes - Answer 1. stimulus activates
chemoreceptors, osmoreceptors, and/or mechanoreceptors on sensory neurons
2. sensory neurons activate effector ENS neurons in the nerve plexus
3. effector neurons activate smooth muscle or glandular cells to initiate response
ANS innervation of GIT enteric neurons - Answer - Parasympathetic (pre-ganglionic -
come directly from CNS, release ACh onto nicotinic receptors on ENS neurons) neurons
, excite ENS neurons
- Sympathetic (post-ganglionic - come from CNS, releases ACh on other neurons
beforehand, those neurons release noradrenaline onto NA receptors on ENS neurons)
neurons inhibit ENS neurons
Which nerves are responsible for parasympathetic innervation of the GIT? - Answer -
Vagus nerve: innervates lower esophagus, stomach, small intestine, and colon
- Pelvic nerves: innervate lower colon and upper rectum
What are vagal parasympathetic neurons derived from? - Answer dorsal vagal motor
neurons (DMVNs) in brainstem
Which ganglia are responsible for sympathetic innervation of the GIT? - Answer - celiac
ganglion
- superior mesenteric ganglion
- inferior mesenteric ganglion
Where are sympathetic neurons derived from? - Answer the spinal cord
What effect do parasympathetic and sympathetic inputs have on blood vessels? -
Answer - Parasympathetic: dilates blood vessels
- Sympathetic: constricts blood vessels
How does the ANS influence the GIT? - Answer Through activity on the ENS directly
(ANS doesn't synapse directly on muscular or secretory cells, synapse on excitatory or
inhibitory enteric neurons instead)
Which ENS neurons are responsible for longer reflexes? - Answer Sensory ENS neurons
Which nervous system regulates the GIT thru short, intramural reflexes? - Answer ENS
Which nervous system regulates the GIT thru long, extrinsic reflexes? - Answer ANS (by
synapsing with ENS neurons)
What is the role of interneurons in the GIT wall? - Answer They expand the responses to
stimuli in the GIT by connecting different neurons
What causes the activation of the ANS in the context of the GIT? - Answer The response
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