1. Activity 6
1) What is the goal of GIT regulation?
vital for proper function
2) Explain the neuronal regulation of GI system.
Neuronal/ nerves system
The specific nerve endings of intrinsic and extrinsic nerves are important in regulating
secretomotor function of GI. The neurotransmitters stored in these nerve endings released upon
electrical signals and diffuse across synaptic cleft to exert its function.
The neurotransmitters include: Acetylcholine
 Norepinephrine
5
-Hydroxytryptamine
 Histamine
 Nitric oxide
 Substance P
 Vasoactive intestinal peptide (VIP)
 Somatostatin
3) Explain the hormonal regulation of GI system.
Endocrine (hormonal) system
Endocrine regulation is critical to integrated function of GI system in response to meal. The GI
hormones are peptides secreted by endocrine glands in GI mucosa.
The hormones of the gut include: Gastrin
 Secretin
 Cholecystokinin (CCK)
 Glucose
-dependent insulinotropic peptide (gastric inhibitory peptide) (GIP)
 Motilin
 Enteroglucagon
The hormones that release from endocrine cells diffuse into lamina propria and thence portal
circulation which they travel to target organs and modify secretion, motility and cell growth.

2. Activity 7 :
1) Identify the location of above mentioned reflexes
2) Explain their function
1. Peristaltic reflex : occur in the esophagus, stomach, and intestines.
onward movement of a bolus of ingesta in the intestine is preceded by a reflex
dilation of the intestine.
smooth muscle contracts in sequence to produce a peristaltic wave, which forces a
ball of food (called a boluswhile in the esophagus and gastrointestinal tract
and chyme in the stomach) along the gastrointestinal tract. Peristaltic movement is
initiated by circular smooth muscles contracting behind the chewed material to
prevent it from moving back into the mouth, followed by a contraction of longitudinal
smooth muscles which pushes the digested food forward. Catastalsis is a related
intestinal muscle process.
2. Vagovagal reflex : afferent and efferent fibers of the vagus nerve
The vagovagal reflex is active during the receptive relaxation of the stomach in
response to swallowing of food (prior to it reaching the stomach). When food enters
the stomach a "vagovagal" reflex goes from the stomach to the brain, and then back
again to the stomach causing active relaxation of the smooth muscle in the stomach
wall. If vagal innervation is interrupted then intra-gastric pressure increases.
3. Enterogastric reflex :
is one of three extrinsic reflexes of the Gastrointestinal Tract. The reflex is stimulated
by the presence of acid levels in the duodenum at a pH of 3-4 or in the stomach at a
pH of 1.5. Upon stimulation of the reflex, the release of gastrin from G-cells in the
antrum of the stomach is shut off. This in turn inhibits gastric motility and secretion
of gastric acid (HCl). In addition to the Enterogastric reflex, the other two extrinsic
reflexes of the Gastrointestinal Tract include the Gastrocolic reflex and
the Colonoileal reflex. Enterogastric reflex activation thus, causes decreased motility.
4. Gastroileal reflex :

Gastroileal reflex is one of the ways in which gastric motility influences intestinal motility

When there is vigorous gastric peristalsis of increased secretion, it stimulates peristalsis in the
ileum

This causes the ileal contents to be pushed into the colon, in turn stimulating colonic peristalsis
and an urge to defecate
5. Sensory fibres (prevertebral sympathetic preganglion reflex) :
When a muscle is stretched, primary sensory fibers (Group Ia afferent neurons) of the
muscle spindle respond to both changes in muscle length and velocity and transmit this
activity to the spinal cord in the form of changes in the rate of action potentials.
Likewise, secondary sensory fibers (Group II afferent neurons) respond to muscle
length changes (but with a smaller velocity-sensitive component) and transmit this
signal to the spinal cord. The Ia afferent signals are transmitted monosynaptically to
many alpha motor neurons of the receptor-bearing muscle. The reflexly evoked activity
in the alpha motoneurons is then transmitted via their efferent axons to the extrafusal

3. fibers of the muscle, which generate force and thereby resist the stretch. The Ia afferent
signal is also transmitted polysynaptically through interneurons (Renshaw cells) which
inhibit alpha motoneurons of antagonist muscles, causing them to relax.
6. Intestino-intestinal reflex :
when a part of the intestine becomes overdistended or its mucosa becomes excessively irritated,
activity in other parts of the intestine is inhibited as long as the distention persists.