Defecation..( the guyton and hall physiology)

Definition:
“Voiding of feces is known as defecation”.

Feces is formed in the large intestine and stored in sigmoid colon.
internal sphincter
Composed of circular smooth muscle
Lies immediately inside the anus
external sphincter
Composed of striated voluntary muscle
Controlled by pudendal nerve. therefore, it is under voluntary, conscious.
reflex pathway
When feces enter rectum
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Distension of rectal wall
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Impulses from the nerve endings are transmitted via afferent fibers of pelvic nerve to the defecation center, situated in sacral segments (center) of spinal cord.
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The center in turn, sends motor impulses to the descending colon, sigmoid colon and rectum via efferent nerve fibers of pelvic nerve.
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Motor impulses cause strong contraction of descending colon, sigmoid colon and rectum and relaxation of internal sphincter.
Simultaneously, voluntary relaxation of external sphincter occurs. It is due to the inhibition of pudendal nerve.
VOMITING
Definition:
“Vomiting or emesis is the abnormal emptying of stomach and upper part of intestine through esophagus and mouth “.

1. Defecation Source: The Guyton and Hall physiology Maryam Fida(o-1827)

2. Defecation Definition: “Voiding of feces is known as defecation”. Feces is formed in the large intestine and stored in sigmoid colon.

3. Internal anal sphincter External anal sphincter Composed of circular smooth muscle Lies immediately inside the anus Composed of striated voluntary muscle Controlled by pudendal nerve. therefore, it is under voluntary, conscious. SPHINCTERS Tanveer Raza MD MS MBBS [email protected]

4. DEFECATION Defecation involves 2 reflexes: involuntary reflexes intrinsic reflex, mediated by enteric nervous system and parasympathetic nerves from the spinal cord (S2-3-4) and travel through pelvic nerve. voluntary reflexes external anal sphincter is relaxed by nervous impulses from brain.

5. Pathway for Defecation Reflexes When feces enter rectum | Distension of rectal wall | Impulses from the nerve endings are transmitted via afferent fibers of pelvic nerve to the defecation center, situated in sacral segments (center) of spinal cord. | The center in turn, sends motor impulses to the descending colon, sigmoid colon and rectum via efferent nerve fibers of pelvic nerve. | Motor impulses cause strong contraction of descending colon, sigmoid colon and rectum and relaxation of internal sphincter. Simultaneously, voluntary relaxation of external sphincter occurs. It is due to the inhibition of pudendal nerve.

6. Tanveer Raza MD MS MBBS [email protected]

7. VOMITING Definition: “ Vomiting or emesis is the abnormal emptying of stomach and upper part of intestine through esophagus and mouth “. CAUSES OF VOMITING 1. The presence of irritating contents in GI tract 2. Mechanical stimulation of pharynx 3. Pregnancy 4. Excess intake of alcohol 5. Nauseating sight, odor or taste 6. Drugs like antibiotic, opiates, etc 7.Acute infection like urinary tract infection, influenza, etc

8. VOMITING REFLEX: Vomiting is a reflex act. The sensory impulses for vomiting arise from the irritated or distended part of GI tract and are transmitted to the vomiting center through vagus and sympathetic afferent fibers. The vomiting center is situated bilaterally in medulla oblongata near the nucleus tractus solitarius . Motor impulses from the vomiting center are transmittes through V, VII, IX, X and XII cranial nerves to the upper part of GI tract; and through spinal nerves to diaphragm and abdominal muscles. Center for Vomiting during Motion Sickness and Vomiting Induced by Drugs such as morphine is on the floor of fourth ventricle. This area is called chemoreceptor trigger zone. Center for Psychic-stimuli-induced Vomiting such as nauseating odor, sight or noise is in cerebral cortex.

9. Mechanism of Vomiting 1. NAUSEA “ It is unpleasant sensation which induces the desire for vomiting”. It is characterized by secretion of large amount of saliva containing more amount of mucus. 2. RETCHING “ Strong involuntary movements in the GI tract start even before actual vomiting and intensify the feeling of vomiting.” Tanveer Raza MD MS MBBS [email protected]

10. Act of vomiting Antiperistalsis from ileum towards the mouth through the intestine pushing the intestinal contents in to the stomach within few minutes. The velocity of the antiperistalsis is about 2-3 cm/second. Deep inspiration followed by temporary cessation of breathing. Closure of glottis. Upward and forward movement of larynx and hyoid bone Elevation of soft palate Contraction of diaphragm and abdominal muscle Compression of stomach between diaphragm and abdominal wall leading rise in intragastric pressure Stimultaneous relaxation of lower esophageal sphincter, esophagus and upper esophagus sphincter. Forceful expulsion of gastric content (Vomitus) through esophagus, pharynx and mouth. Tanveer Raza MD MS MBBS [email protected]