1. Compare the autonomic control of defecation and micturition. 2. How are absor
ID: 3484103 • Letter: 1
Question
1. Compare the autonomic control of defecation and micturition.
2. How are absorption in the digestive tract and reabsorption from the renal tubules similar? (Your answer should concentrate on the molecular level.)
3. The carbonic anhydrase reactions are important for regulating pH because the bicarbonate ion acts as a buffer. What are three cells, one each in the respiratory, digestive, and urinary systems, where the carbonic anhydrase reaction has been described, producing bicarbonate ion that can help to buffer the pH of blood?
Explanation / Answer
Please find the answer of only question 1 (not 2 and 3)
The effect of autonomic nervous system can be summarized in the effects of sympathetic and parasympathetic.
1. Sympathetic nervous system works when there is a crisis or dangerous situation, so in this case you don't feel the urge for urination or defecation , those processes are inhibited by the sympathetic
2. Parasympathetic works when you are relaxing , when you are in your normal life, so urination and defecation work well in this case, you feel the urge for urination or defecation
DEFECATION
Rectum and anal canal nerves
The smooth muscle of the rectum and anal canal is controlled by:
Internal anal sphincter nerves
Your internal anal sphincter is controlled by:
Your internal anal sphincter functions outside your conscious control. This is referred to as involuntary control, meaning that it operates in an automatic (reflex) manner.
External anal sphincter nerves
Your external anal sphincter is controlled by:
MICTURITION
Micturition is fundamentally a spinobulbospinal reflex facilitated and inhibited by higher brain centers such as the pontine micturition center and, like defecation, subject to voluntary facilitation and inhibition.
Mechanisms
In healthy individuals, the lower urinary tract has two discrete phases of activity: the storage (or guarding) phase, when urine is stored in the bladder; and the voiding phase.
When urine is released through the urethra. The state of the reflex system is dependent on both a conscious signal from the brain and the firing rate of sensory fibers from the bladder and urethra. At low bladder volumes, afferent firing is low, resulting in excitation of the outlet (the sphincter and urethra), and relaxation of the bladder.
At high bladder volumes, afferent firing increases, causing a conscious sensation of urinary urge. When the individual is ready to urinate, he or she consciously initiates voiding, causing the bladder to contract and the outlet to relax. Voiding continues until the bladder empties completely, at which point the bladder relaxes and the outlet contracts to re-initiate storage.
The muscles controlling micturition are controlled by the autonomic and somatic nervous systems. During the storage phase the internal urethral sphincter remains tense and the detrusor muscle relaxed by sympathetic stimulation. During micturition, parasympathetic stimulation causes the detrusor muscle to contract and the internal urethral sphincter to relax. The external urethral sphincter (sphincter urethrae) is under somatic control and is consciously relaxed during micturition.
Storage phase of micturition
Action potentials carried by sensory neurons from stretch receptors in the urinary bladder wall travel to the sacral segments of the spinal cord through the pelvic nerves. Since bladder wall stretch is low during the storage phase, these afferent neurons fire at low frequencies. Low-frequency afferent signals cause relaxation of the bladder by inhibiting sacral parasympathetic preganglionic neurons and exciting lumbar sympathetic preganglionic neurons. Conversely, afferent input causes contraction of the sphincter through excitation of Onuf's nucleus, and contraction of the bladder neck and urethra through excitation of the sympathetic preganglionic neurons.
The muscles controlling micturition are controlled by the autonomic and somatic nervous systems. During the storage phase the internal urethral sphincter remains tense and the detrusor muscle relaxed by sympathetic stimulation. During micturition, parasympathetic stimulation causes the detrusor muscle to contract and the internal urethral sphincter to relax. The external urethral sphincter (sphincter urethrae) is under somatic control and is consciously relaxed during micturition.
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