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Q10:
What is the significance of juxta glomerular apparatus (JGA) in kidney function?
Solution :
1. Anatomical Foundation of the Juxtaglomerular Apparatus (JGA)
The Juxtaglomerular Apparatus (JGA) is a highly specialized regulatory structure located at the vascular pole of the renal corpuscle. It is formed by the precise contact point between the distal convoluted tubule (DCT) and the afferent arteriole of the same nephron. [Anatomical Position: Intersection of the Distal Tubule and Renal Corpuscle].
2. Cellular Components and Functional Domains
| Component | Location | Function |
|---|---|---|
| Macula Densa | Wall of the DCT | Chemoreceptors detecting $NaCl$ concentration changes. |
| Juxtaglomerular (JG) Cells | Wall of the Afferent Arteriole | Specialized smooth muscle cells that synthesize, store, and release renin. |
| Extraglomerular Mesangial Cells | Space between arteriole and tubule | Regulatory signaling mediation. |
3. Regulatory Mechanism: The Renin-Angiotensin-Aldosterone System (RAAS)
The significance of the JGA lies in its ability to respond to a drop in glomerular blood pressure or glomerular filtration rate (GFR). The process follows a strict physiological sequence:
- Detection: When GFR falls, the flow of filtrate through the DCT decreases, leading to a reduced concentration of $NaCl$ at the macula densa. [Physiological Trigger: Hypovolemia or Hypotension].
- Activation: The macula densa sends chemical signals to the JG cells of the afferent arteriole.
- Hormonal Release: The JG cells release the enzyme Renin into the bloodstream.
- Conversion Cascade: Renin converts plasma protein Angiotensinogen to Angiotensin I, which is further converted to Angiotensin II by Angiotensin-Converting Enzyme (ACE) in the lungs. [Biochemical Pathway: Renin-Angiotensin cascade].
- Systemic Effect: Angiotensin II acts as a potent vasoconstrictor and stimulates the adrenal cortex to release Aldosterone.
4. Physiological Outcomes
The JGA functions as the primary "thermostat" for systemic blood pressure and fluid homeostasis via two pathways:
- Vasoconstriction: Angiotensin II increases the efferent arteriolar resistance, thereby elevating the glomerular hydrostatic pressure and restoring GFR.
- Reabsorption: Aldosterone promotes the reabsorption of $Na^+$ and water from the distal parts of the tubule. This increases blood volume and, consequently, blood pressure. [Homeostatic Feedback: Negative feedback loop].
Final Solution: The Juxtaglomerular Apparatus (JGA) is a critical regulatory complex that functions as an endocrine sensor to maintain systemic blood pressure and glomerular filtration rate (GFR) through the activation of the Renin-Angiotensin-Aldosterone System (RAAS). It serves as the primary mechanism for correcting hypovolemia and maintaining electrolyte balance in the human 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.
- Q6: Explain micturition.
- 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 ?
- 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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