1. General Principles of GASTROINTESTINAL SYSTEM
Dr . Moizuddin Khan
Dr. Beenish Mukhtar

2. Learning objectives:-
Physiologic anatomy of gastrointestinal wall
The general characteristics of smooth muscle
The specific characteristics of smooth muscle
Control of gastrointestinal function (ENS)
Functional types of movements in the gastrointestinal tract
Gastrointestinal blood flow (Splanchnic circulation)
Effects of gut activity and metabolic factors on GI blood flow

3. اسم ورقم المقرر – Course Name and No.
4/19/2019

10. Special characteristics of GI smooth muscles:-
Contracts as a syncytium:-
Muscle fibres of GIT are micrometres in length and 2-10 micrometres in breadth.
Muscle bundles are connected by gap junctions
Each muscle layer represents a branching latticework of smooth muscle bundles, functioning as syncytium.
Action potential travels in all directions

11. Electrical activity of GIT muscle
Slow waves:-
undulating changes in RMP
5-15 Mv
Frequency is 3 waves per min in stomach,12 in duodenum and 8 in ileum
By interstitial cells of cajal….electrical pace makers
Slow waves excite appearance of spike potentials

13. Spike potentials:-
True action potentials
Occur at RMP of -40mV
Higher the slow wave pot. Greater is the frequency of spike pot.
Frequency is 1-10 spikes per second
Ca-Na channles are responsible
At peak of slow waves increased quantities of Ca enters the fibers to cause contraction

15. Types of Smooth Muscle contraction in GIT
Phasic contractions
- Periodic contractions followed by relaxation; such as in gastric antrum, small intestine and esophagus
Tonic contractions
- Maintained contraction without relaxation; such as in orad region of the stomach, lower esophageal, ileocecal and internal anal sphincter
- not associated with slow waves

16. Neural supply of GIT Intrinsic (Enteric)
Myenteric or Auerbachs plexus and
Submucosal or Meissners plexus
Extrinsic
Sympathetic and parasympathetic

17. Myenteric or Auerbach s plexus
Linear chains of interconnecting neurons extending up to the entire length of GIT
On stimulation it causes increased tone of gut wall
Increased intensity, velocity and rate of contraction
Both excitatory and inhibitory depending on type of neurotransmitter secreted
Sub-mucosal or Meissner's plexus
Controls secretion, absorption and local contraction of sub- mucosal muscle and blood flow

19. Important neurotransmitters of enteric neurons are
Ach
Norepinephrine
Serotonin
Dopamine
Cholecystokinin
VIP (Vasoactive intestinal peptide),
Substance P
Leu-enkephalin met-enkephalin

20. Parasympathetic innervation
Parasympathetic supply to gut is divided into cranial and sacral divisions
Cranial part - Almost entirely in vagus nerve providing innervation to esophagus, stomach and pancreas
Sacral part- originate in 2nd ,3rd, 4th sacral segments of spinal cord and pass thru pelvic nerves to large intestines, rectum and anus.
Post ganglionic neurons of parasympathetic are located in Submucosal and Myenteric plexuses

21. Sympathetic Innervation
From T-5 to L-2
Fibers go to symp. ganglionic chain from where they relay in separate ganglions e.g. celiac and mesenteric
Post gang fibers supply whole GIT more extensively in oral cavity and anus
Neuro transmitter is mainly norepinephrine.
Functions by inhibiting intestinal smooth muscle
On strong stimulation motor activity is blocked hence causing stasis of food in gut

23. LAW OF GUT
The contractile ring appears on the orad side of the distended segment pushing the intestinal contents in anal direction for cms before dying out and simultaneously the gut relaxes towards anus….Receptive relaxation.
This is termed as myenteric reflex or peristaltic reflex along with anal direction of movement is called law of gut

27. Splanchnic circulation
It is the blood supply of:-
Intestine
Pancreas
Spleen
Liver

29. Blood flow to gut increases eight fold during active absorption but decreases back to the resting level over another 2 to 4 hours.
Increased blood flow is due to hormones VIP, Gastrin, Secretin, Cholecystokinin
Increased metabolism leads to decreased oxygenation causing increase in Adenosine that leads to increased blood flow

30. COUNTER CURRENT FLOW IN VILLI
Arterial and venous flow around the villi are in opposite directions
80% arteriolar oxygen diffuses out to the venules without being carried to villous tips
Normally this shunting is not harmful
But in conditions like circ. Shock villi suffer ischemic death.
اسم ورقم المقرر – Course Name and No.
4/19/2019

31. Parasympathetic stimulation causes vasodilation
Sympathetic stimulation causes vasoconstriction.
After few mins of vasoconstriction , blood flow returns to normal by means of auto regulatory escape.
This occurs due to metabolic vasodilators which are released due to fall in oxygen conc.
Vasoconstriction is imp during heavy exercise ,conditions like shock so that blood is deviated to more vital areas.

32. THANK YOU
اسم ورقم المقرر – Course Name and No.
4/19/2019