Gi Physiology

Front 1

What are the main purposes of the GI tract?

Back 1

i. Motility refers to the contractions of the smooth muscle of the GI tract, which result in the orderly movement of ingested material from the mouth to the anus.
ii. Secretion is the release of water, electrolytes, mucus, enzymes, bile acids, and other organic substance into the lumen of the tract by salivary glands, pancreas, liver, and the mucosa.
iii. Digestion is the chemical breakdown of food into molecules able to cross the mucosa to the blood.
iv. Absorption refers to the movement of water, electrolytes, vitamins, and nutrients across the epithelial lining of the gut into the blood.

Front 2

Which part of brain gut interactions is an intrinsic system and directly affects the GI? Which parts are indirect via ganglia and enteric nervous system? Which parts are indirect via ENS? Which is the part indirect via everything else?

Back 2

ENS
Central sympathetic
Central parasympathetic
higher brain centers

Front 3

What are the myenteric nerve plexus and submucosa nerve plexus used for?

Back 3

motor innervation
secretory control

Front 4

What are the 3 types of neurons of the ENS?

Back 4

Sensory, interneurons, motor

Front 5

What GI neurotransmitters are excitatory, which are inhibitory?

Back 5

Excitatory: ACh, Tachykinins (e.g., Substance P), serotonin (5HT) and VIP (stimulates secretion).

Inhibitory: NO, VIP (muscle contraction), ATP, NE and enkephalin (opiates).

Front 6

What effect does the parasympathetic system have on motility and secretion

Back 6

The parasympathetic system generally increases motility & secretion throughout GIT

Front 7

What effect does the sympathetic have on the GI smooth muscle and sphincters?

Back 7

inhibitory
excitatory

Front 8

What are the two types of GI reflexes? Give examples

Back 8

The ENS relays information up and down the GI tract. This activity may result in short or intrinsic reflexes (from the receptors to the ENS to an effector (gland or muscle). These short-loop reflexes are responsible for e.g., peristalsis, intestino-intestinal and secretory reflexes (Figure 11).

The ANS acts mainly via long-loop reflexes. Entero-enteric reflexes regulate one region in relation to others (See an example of this in Figure and contrast a long- and short-loop reflex)

Front 9

Why do unitary or single unit muscles have gap junctions?

Back 9

To contract as a single unit

Front 10

Is smooth muscle contraction dependent on membrane voltage of nerve input?

Back 10

voltage

Front 11

What are slow signals not responsible for? What are they responsible for?

Back 11

contraction
contractile pattern

Front 12

Why are the ICC so close to the ENS neurons.

Back 12

neurotransmitter messages from enteric nerves can be relayed to ICC cells and thus modify the basic
rhythm of slow waves (slow or speed up the cycle, cause excitation or inhibition)

Front 13

What are the effect of parasympathetics and sympathetics on slow waves and digestion.

Back 13

Parasympathetics are excitatory increase digestion. Sympathetics and NE will hyperpolarize system, decreasing digestion.

Front 14

What should we know about pressure when swallowing?

Back 14

Les is lower than diaphragm. Important because abdominal P is higher than thoracic P.

P spike follows food to force it down.

There is a P dip in the around around the LES as the LES opens.

Front 15

What are achalasia, hiatal hernia, and loss of LES tone?

Back 15

Achalasia:
Stenosis of LES, dilation of body of esophagus
“bird-beak” appearance on barium study
Hiatal Hernia
LES protrudes into thoracic cavity
LES tends to be patent due to negative pressure in thoracic cavity
Gerd
Loss of LES Tone:
Increased by Ach, Gastrin
Decreased by Sympathetics.

Front 16

Why do diabetes get heartburn?

Back 16

Relaxation of LES is done by inhibitory vagal “long-loop” neural reflex. Diabetes damages vagus.

Front 17

What are the 3 forms of gastric relaxation?

Back 17

a) Receptive relaxation consists of a brief relaxation during chewing and swallowing. The stimulation of
mechano-receptors in the mouth and pharynx induces vago-vagal reflexes which cause a relaxation of
the gastric reservoir (Figure 15).
Receptive relaxation prepares the stomach to receive a bolus of food.
b) Adaptive Relaxation:
– When the stomach is filled with digesta, mechano- and/or chemoreceptors are stimulated which
elicit gastro-gastric (vago-vagal) reflexes to bring about adaptive relaxation.
4
– Vago-vagal reflexes use enteric neurons to modulate smooth muscle activity.
– The efferent leg of the reflex occurs by NANC inhibition. The major mediators for NANC inhibition are
nitric oxide (NO) and VIP (See lecture 1).
– Adaptive relaxation provides a storage of the digesta until they are sufficiently broken down for
emptying into the duodenum.
– Gastrin, which stimulates the secretion of gastric juice, causes an additional relaxation of the gastric
reservoir. This hormonal control stimulates an increased volume in the stomach for the secreted
gastric juice without increase in intraluminal pressure (Figure 15).
c) Feedback-relaxation
– This also provides for prolonged storage of digesta, and it is a precondition that gastric emptying is
adapted to the process of digestion and absorption of nutrients in the small intestine (More later).

Front 18

What is the gastric consequence of vagus damage from diabetes?

Back 18

The stomach cannot relax, pressure builds up, and GERD

Front 19

What are the 3 stages of flow through the antral pump?

Back 19

1) a phase of propulsion,
2) a phase of emptying and mixing,
3) a phase of retropulsion and grinding (Figure 18).