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Q6:
Explain micturition.
Solution :
Step 1: Physiological Definition of Micturition
Micturition, commonly referred to as urination, is the physiological process by which the urinary bladder empties when it becomes distended. This process involves a coordinated effort between the autonomic nervous system and the somatic nervous system to facilitate the expulsion of urine from the body.
Step 2: The Neural Mechanism and Reflex Arc
The process is governed by the Micturition Reflex. The steps are as follows:
- Stretch Reception: As urine accumulates in the urinary bladder, the walls of the bladder are stretched. This physical distension activates stretch receptors located in the bladder wall [Per the physiological principle of mechanoreceptor activation].
- Signal Transmission: These receptors send sensory impulses (afferent signals) to the central nervous system via the pelvic nerves to the micturition center located in the pons and the sacral region of the spinal cord (segments $S_2$ to $S_4$).
- Integration: The central nervous system processes these signals and generates a motor response (efferent signals).
- Effector Response: The efferent signals travel back to the bladder, stimulating the contraction of the smooth muscles of the bladder (the detrusor muscle) and simultaneously inducing the relaxation of the urethral sphincter.
Step 3: Visual Representation of the Micturition Pathway
Step 4: Coordination and Voluntary Control
While the micturition reflex is largely autonomic, humans possess voluntary control over the process due to the somatic innervation of the external urethral sphincter. The sequence follows:
- The stretch receptors send excitatory impulses to the cerebral cortex.
- This provides the "urge" to urinate.
- If the timing is appropriate, the brain sends inhibitory signals to the external sphincter, causing it to relax.
- Simultaneous contraction of the detrusor muscle expels the urine.
| Structure | Role in Micturition |
|---|---|
| Detrusor Muscle | Contraction to increase intra-vesical pressure. |
| Internal Urethral Sphincter | Involuntary smooth muscle; relaxes under autonomic control. |
| External Urethral Sphincter | Voluntary skeletal muscle; under somatic control. |
Final Solution: Micturition is the neural process of bladder evacuation triggered by the stretching of the bladder wall, mediated by the micturition reflex, and refined by voluntary cortical control over the external urethral sphincter, resulting in the expulsion of urine from the body.
More Questions from Class 11 Biology Excretory Products and Elimination EXERCISES
- Q1: Define Glomerular Filtration Rate (GFR)
- Q2: Explain the autoregulatory mechanism of GFR.
- Q3(a): Indicate whether the following statements are true or false : (a) Micturition is carried out by a reflex.
- Q3(b): Indicate whether the following statements are true or false : (b) ADH helps in water elimination, making the urine hypotonic.
- Q3(c): Indicate whether the following statements are true or false : (c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule.
- Q3(d): Indicate whether the following statements are true or false : (d) Henle’s loop plays an important role in concentrating the urine.
- Q3(e): Indicate whether the following statements are true or false : (e) Glucose is actively reabsorbed in the proximal convoluted tubule.
- Q4: Give a brief account of the counter current mechanism.
- Q5: Describe the role of liver, lungs and skin in excretion.
- Q7: Match the items of column I with those of column II : Column I Column II (a) Ammonotelism (i) Birds (b) Bowman’s capsule (ii) Water reabsorption (c) Micturition (iii) Bony fish (d) Uricotelism (iv) Urinary bladder (e) ADH (v) Renal tubule
- Q8: What is meant by the term osmoregulation?
- Q9: Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why ?
- Q10: What is the significance of juxta glomerular apparatus (JGA) in kidney function?
- Q11(a): Name the following: (a) A chordate animal having flame cells as excretory structures
- Q11(b): Name the following: (b) Cortical portions projecting between the medullary pyramids in the human kidney
- Q11(c): Name the following: (c) A loop of capillary running parallel to the Henle’s loop.
- Q12(a): Fill in the gaps : (a) Ascending limb of Henle’s loop is _______ to water whereas the descending limb is _______ to it.
- Q12(b): Fill in the gaps : (b) Reabsorption of water from distal parts of the tubules is facilitated by hormone _______.
- Q12(c): Fill in the gaps : (c) Dialysis fluid contain all the constituents as in plasma except _______.
- Q12(d): Fill in the gaps : (d) A healthy adult human excretes (on an average) _______ gm of urea/day.
CBSE Solutions for Class 11 Biology Excretory Products and Elimination
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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