L.1 Flashcards
Digestive system is made up of:
1.Gastrointestinal tract (GIT)
2.The accessory organs that help the digestion.
Gastrointestinal tract :
- Mouth , Pharynx.
- Esophagus, Stomach.
- Small intestine.
- Large intestine.
Accessory organs of digestive system:
1) Teeth.
2) Tongue.
3) Salivary glands.
4) Exocrine part of pancreas.
5) Liver.
6) Gall bladder.
The function of the alimentary tract is to provide the body with :
water
electrolytes
vitamins
nutrients.
Functions of the digestive system require:
(1) “Movement” of food through the alimentary tract.
(2) “Secretion” of digestive juices and digestion of the food.
(3) “Absorption “of water, electrolytes, vitamins, and digestive products.
Control of all digestive system functions by :
nervous and hormonal systems.
GIT wall is formed by “four layers” which are from “inside to out” :
1) Mucosa.
2) Submucosa.
3) Muscle layer.
4) Serosa.
Epithelial cells of mucosa is concerned with:
a) Secretion of digestive juices & GIT hormones.
b) Absorption of the digested diet (Food).
The muscle layer formed of :
(circular & longitudinal).
Circular muscle :
Its contraction —> decrease in diameter of GIT lumen
“يضيق”
Longitudinal muscle :
Its contraction —> “shortening” of GIT
(Nervous Control of GIT functions )
Motor & secretory functions of GIT are controlled by :
1) “Intrinsic” innervation (Enteric nervous system).
2) “Extrinsic “innervation (Sympathetic and parasympathetic).
3) “Nervous” regulation of GIT through GIT reflexes.
Intrinsic innervation consists of :
• submucosal plexuses
• myenteric (Auerbach’s) plexuses.
Sub-mucosal plexus:
Site: In the submucosa.
Function: Controls secretion & blood flow
Myenteric plexus :
Site: Between the two muscle layers.
Function: Controls “motility” of GIT.
Enteric nervous system (E.N.S) is considered as the :
second brain or gut brain
All classes of (chemical transmitters) in brain are found in
enteric nervous system
enteric nervous system controls ?
• most functions of the GIT
• function (independently)
even without sympathetic or parasympathetic stimulation
• BUT parasympathetic & sympathetic Stimulation can greatly stimulate or inhibit GIT
Extrinsic innervation The GIT receives nerve supply from:
▪ sympathetic & parasympathetic systems
▪ These fibers “end on “the nerve cells of E.N.S. , controlling their activity.
(Sympathetic)
Carrying nerves:
Carrying nerves:
1.Greater splanchnic nerve
(to abdominal viscera)
- Lesser splanchnic nerve
( to pelvic viscera).
(sympathetic)
Function :
. Inhibitory to most GIT functions
. Inhibits motility & secretion
. Closes sphincters —> (-) evacuation
(Sympathetic)
Chemical transmitter:
Noradrenaline
(Parasympathetic)
Carrying nerves :
1.Vagus nerve
- pelvic nerve
(Parasympathetic)
Function :
• “Excitatory” to most GIT functions
• Stimulates motility & secretion
• Opens sphincters —> (+) evacuation
Functions of chemical transmitters of parasympathetic system :
• Acetylcholine :
دا الاساسي
Increases motility and secretions of GIT.
Functions of chemical transmitters of parasympathetic system :
• Vasoactive intestinal polypeptide (VIP) :
Helps relaxation of GIT sphincters
Functions of chemical transmitters of parasympathetic system :
• Gastrin-releasing peptide(GRP):
Stimulate gastrin release from G cells of stomach
(Nervous regulation of GIT through GIT reflexes)
divided into 3 types according to the center of the reflex :
1- Local enteric reflex
- Ganglionic reflex
3.Central reflex
Local enteric reflexes:
معلومة من الدكتورة
“Center in wall of GIT”
• These reflexes are “integrated” entirely in the “enteric nervous system” .
E.g. : gastrin secretion, peristalsis. مهمة الامثلة
Ganglionic reflexes:
معلومة من الدكتورة
“Center in ganglia “
• These are integrated at collateral sympathetic ganglia
• Ganglia act here as nerve centers.
•e.g. : gastrocolic reflex
Central reflexes:
معلومة من الدكتورة
”Center in CNS “
• These reflexes are “integrated in the CNS” (the brain stem & spinal cord).
• e.g. : spinal defecation reflexes.
