GIT (digestive system) l Physiology MCQs (multiple choice question) for dental students
INTRODUCTION in digestive system
v Anatomy
of GIT:
1- Alimentary tract:
- Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus.
2- Digestive gland:
- Salivary gland, gastric gland, intestinal gland, liver and pancreas.
v Histology
of GIT:
1-
Mucosa: (secretory & absorptive layer). It contains:
- Lymph nodes à protection against infections.
- A thin layer of muscularis
mucosa àmucosal fold to é the
surface area.
- Goblet cells à secrete mucus.
2- Submucosa:
- contain Meissner’s plexus à regulate GIT Secretion.
3- Musculosa:
- responsible for segmental and peristaltic Movement of GIT.
- It has inner circular & outer longitudinal muscle.
- Contain Myenteric plexus à control Movements of GIT.
4- Serosa:
- a binding and protective layer.
Regulation of Gastrointestinal Tract
I) Nervous control:
1) External autonomic nerves:
Parasympathetic (dominant)
* Vagus à from esophagus till 1st half
of large intestine. * Sacral (S2, 3, 4)
à rest of GIT till anal
region
-
Contration of wall "excitatory"& Relaxation
Of sphincters. "inhibitory"
-
á Secretion &VD.
-
Evacuation of GIT contents. Ø The preganglionic end on enteric plexus
Sympathetic
- * Greater splanchnic nerve: From
LHCs of lower 8 Thoracic. (T5-T12)
- * Lesser splanchnic nerve: From
LHCs of upper 2 Lumbar.
- Relaxation of wall & Contraction
of sphincters→ inhibit motility
- â Secretion & VC. 3. Some fibers are Excitatory.
- Post ganglionic end
either on:
- Direct on smooth muscle
- 2nd
relay
on enteric plexus.
- on postganglionic cholinergic neuron →
↓Ach
via activation of presynaptic alpa2 receptor
2) Local (or enteric)
nerve plexus:
Myenteric (=Auerbach’s) plexus
- Lies
between smooth Muscle fibers longitudinal and circular muscle fiber.
- Control
Motor activity of GIT (Motility).
- Its
Stimulation à -↑Tonic
contraction. -↑Intensity
and rate of rhythmic contraction. -↑Conduction
of excitatory wave.
- Contain
Excitatory fibers (Cholinergic) & Inhibitory fibers
secrete VIP or Purinergic secrete ATP.
Submucosal (=Meissner’s) plexus :
- Lies
in Submucosal layer supply glandular epithelium ,intestinal and endocrine
cells and sub mucosal blood vessels
- Concerned
with local GIT Secretion
- Its Stimulation à é local Exocrine & Endocrine
secretion.
-
Contain Sensory afferent which arise from
submucosal layer
- Secrete many
transmitters as : GABA,Ach,NA,Serotonin,Encephalin Somatostostatin
&Substance P Polypeptide as CCK , VIP ,Neuropeptides
3) GIT reflexes:
- A. Local Enteric Reflexes (short reflex)
- B. Ganglionic Reflexes
- C.CNS Reflexes
II) Hormonal control:
- GIT hormones are polypeptides secreted by special mucosal cells involved in amine precursor uptake and decarboxylation (APUD) →Secreted under different stimuli→ to blood return to GIT→affect its function.
- They affected by external autonomic nerves and local nerve plexuses.
- Classified according to similarity in function &structure into:
- Gastrin group: Gastrin &
Cholecystokinin.
- Secretin group: Secretin, Gastric
inhibitory peptide (GIP), enteroGlucagon & VIP.
- Motilin & Somatostatin.
Oral cavity
v Mastication
(=chewing):
- mechanical breakdown of
large food particles into smaller ones in the mouth.
Ø
The crushing force of incisors 11-25 & of
molars 20-40 kg.
Ø
Its importance :
- Stimulation of taste & smell receptors → Satiety.
- Help Swallowing by lubrication of food by Saliva.
- Help digestion by break down of indigestive
cellulose membrane of fruits & vegetables and also by á the exposed Surface area to enzymatic effect.
Ø
It is partly voluntary and partly reflex by chewing
reflex:
- Presence of food in mouth → reflex relaxation of chewing muscles → drop of mandible and open the mouth → stretch on the muscles → reflex recontraction and closure of mouth and so on. Mastication ms are supplied by motor branch of trigeminal nerve).
Ø The chewing center
- in Pons.
Parotid
glands Sub maxillary Sub lingual
 l Physiology MCQs for dental students){kind=link}
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