Describe about defecation reflex, Biology

Q. Describe about defecation reflex?

An example of a reflex having an autonomic (and somatic) component is the DEFECATION REFLEX:

The rectum is generally empty, but when feces are forced into it by mass movements, stretching of the rectal walls initiates the defecation reflex. This involves mainly the sacral region of the spine, and causes the smooth muscles around the sigmoid colon and rectum to contract, while the anal sphincter is relaxed.

- Walls of sigmoid colon/rectum distend -> sensory nerves send signals to spine -> parasympathetic nerves cause contraction of smooth muscles in rectal region -> propels feces for excretion

Note however that simultaneously cerebral control from cortex is possible, i.e. messages reaching the brain allow us to decide whether the external sphincter (skeletal muscle tissue) will remain open for defecation.

If the decision is to delay, then reflex contractions are ended (and rectum relaxes until next wave of distention).

6_Describe about DEFECATION REFLEX.png

Note: we ordinarily aid defecation by closing the glottis (to keep air in lungs) and contracting the diaphragm (and abdominal muscles) to increase the abdominal pressure. This is called the Valsalva maneuver (which helps forcing feces distally).

Incontinence (normal in infants) occurs as no control has been acquired yet of the ext. anal sphincter, may also occur from spinal cord transections.

Posted Date: 6/1/2013 6:39:18 AM | Location : United States







Related Discussions:- Describe about defecation reflex, Assignment Help, Ask Question on Describe about defecation reflex, Get Answer, Expert's Help, Describe about defecation reflex Discussions

Write discussion on Describe about defecation reflex
Your posts are moderated
Related Questions
Classify biomaterials and list some examples. Biologic classification is based on tissue response and systemic toxicity effects of the implant and is divided into three classes

Which are the main cells of the nervous system? The major cells of the nervous system are the neurons. Besides the neurons the nervous system is also constituted of glial cells

C a n d i d i a s i s (moniliasis or thrush) C and i d a albicans , the causative fungus of the disease, is widespread in the environment and is usually present

Photoorganoheterotrophs and Chemoorganoheterotrophs - Nutritional Types (1) Photoorganoheterotrophs - These microorganisms use light as a source of energy and organic compound

Cnidaria - Protozoa The mature medusoid jellyfishes like Aurelia are the sexual stages. Sperms and eggs produced in the dissimilar (male and female) individuals ale released i

Calf diptheria The disease is a serious one usually affecting calves up to 2 years of age. The lesions are confined to larynx and pharynx, and consist of well-defined areas of nec

What is HMP pathway? Give any two points of its significance The HMP  is an alternate oxidative pathway for the metabolism of glucose. The significance of the pathway  is that

IMPLAN TA TIO N - Attachement of blastocyst on the endometrium of the uterus is called implantation. Generally it occurs 7th day after fertilisation. (6-10 days). Blas

The heart is drained by vessels that travel in the interventricular and atrioventricular grooves. One set runs in the anterior part of the atrio-ventricular groove. The vessels of

Define Factors that effect birth weight and gestational duration? A WHO review has identified 43 factors that influenced birth weight and gestational duration. They are grouped