this presentation comprises of everything about the process of defecation and the defecation reflex and the nerve supply involved. also discusses about the types of defecation reflexes and deals about them seperately in detail.

1. Defecation Reflex..!

2. Defecation
What is defecation ??
defecation, also called bowel
movement, the act of eliminating
solid or semisolid waste materials
(feces) from the digestive tract.

3. Defecation reflex

5. Internal anal sphincter..
Circular smooth muscle that lies
immediately inside the anus..

6. External anal sphincter..
Composed of straited voluntary muscle
that surrounds internal sphincter and
extend distal to it. The external sphincer is
controlled by nerve fibres in pudental
nerve which is a part of somatic nervous
system.
Under subconscious control the external
sphincter is kept consticted unless
conscious signal inhibits the constriction.

9. The urge of defecation :
This is associated with rectal pressure of
about 18mmHg.
When the pressure rises to about
55mmHg the external and internal anal
sphincter relax and defecation occurs.

10. Two factor play a role in keeping the rectum
free from feces:-
 The weak function sphincter exist about
20cm from the anus at the junction
between the sigmoid colon and rectum.
 A sharp angulation that contributes
resistance to the filling of the rectum.

11. Passage of feces across the anal canal is
prevented by:-
 Internal anal sphincter
 External anal sphincter

12. Types of defecation reflex
 intrinsic myentric defecation reflex
 Parasympathetic defecation reflex

13. Intrinsic defecation reflex
Feces enter the rectum distension of the
rectal wall
This initiate afferent signals spread
though myentric plexus
Initiates peristalsis descending colon,
sigmoid, rectum,forcing feces towards the
anus

14. Peristaltic wave approaches anus internal
anal sphincter relaxes
At the same time the external anal sphincter is
voluntarily relaxed
Defecation occurs

15. Parasympathetic defecation reflex
Nerve endings in the rectum stimulated
Signals transmitted to the spinal cord
Reflex signals via pelvic nerves descending
colon,sigmoid,rectum
These parasympathetic signals travelling in
the pelvic nerves

16. Greatly intensify peristalsis ad relax the
internal anal sphincter
At the same time ,if the external anal
spinchter is voluntarily relaxed
Defecation occurs
parasympathetic defecation reflex enhances this
process and makes the intrinsic reflex much more
powerful.

17. Physiological response associated with defecation
i. Deep inspiration
ii. Closure of glottis
iii. Contraction of abdominal muscle

18. Closure of glottis
Increased intra thoracic pressure
Decrease in the venous return to
the heart
prone to Myocardial infarction

19. Roughage
 Dietary fibre or roughage is a group of food particle
which pass through stomach and small intestine
without being digested and reach the large intestine
unchanged..
 Characteristic feature :-
It is not hydrolyzed by digestive enzyme ,it provides
substrate for micro flora of large intestine and
increases the bacterial mass.
 Roughage in diet plays a role in preventing
constipation..

20. Constipation
 failure of voiding of feces, that produces
discomfort is known as constipation
 Due to the mass movement in colon ,feces
remain in the large intestine for a long time,
resulting in absorption of fluid. So that feces
becomes dry and hard.
 Lack of fiber or lack of liquids in diet is one of
the factors contributing to constipation.
 Other causes include spasm of sigmoid
colon, irregular bowel habit and etc..

21. Clinical physiology
 Automated emptying of rectum :-
this is associated with the
state in which the voluntary conscious
control of external anal spinter is lost..
Noted in : 1. new born babies
2. patient with transection of
spinal cord.

22. Mega colon
 It is an abnormal dilation of colon.
 The dilation is often accompanied by a
paralysis of the peristaltic movements of
the bowel.
 It is due to the deficiency of ganglion cells
in the myentric plexus in a segment of the
sigmoid colon.

23.  Its a form of inflammatory bowel disease..
 Characteristic ulcers or open sore of the
colon.
 Patients usually present diarrhoea with
blood and mucous...
Ulcerative colitis