CBSE Class 11 Biology Chapter 19 Revision Notes

Chapter 19: Excretory Products and their Elimination Revision Notes

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Multiple Choice Questions

  1. Which excretory product requires maximum water for its elimination? ________
  2. The extension of cortex in medulla is known as ___________.
  3. Glomerulus along with Bowman’s capsule is called ____________.
  4. Brush border epithelium is a characteristic of which of the following? ________
  5. Where does filtration of blood occur? __________
  6. Which of the following regulates the functioning of the kidney? ___________
  7. Neural mechanism of micturition is called ____________.
  8. Kidneys play a significant role in its removal of ammonia directly. __________
  9. Which of the following can stimulate the glomerular blood flow and thereby help in bringing the GFR back to normal? _____________
  10. Which of the following substances are secreted by tubular cells during urine formation? ______________
  11. Which of the following parts has minimum reabsorption? ______________
  12. Which of these will be completely reabsorbed from glomerular filtrate under normal conditions in the nephrons? ________________
  13. Which of the following is to be observed if Henle’s loop were to be absent from mammalian nephrons? ______________
  14. Assertion: Ammonia is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions.Reason: Ammonia is readily soluble.

  1. Assertion: During micturition, urine is prevented from flowing back into the ureters.Reason: Urethral sphincters contract during micturition.

Human Excretory System

  • Excretion is the act of elimination of wastes and other metabolites from the body of an animal, which is generally related to the process of maintaining osmotic levels or osmoregulation
  • Both excretion and osmoregulation are crucial for homeostasis or maintaining a steady internal environment in the body, which is required for regular living functions. 
  • The main nitrogenous wastes emitted by mammals are ammonia, urea, and uric acid.
  • These compounds accumulate in the animal’s body through metabolic activity or other mechanisms such as excessive consumption
  • The most hazardous substance is ammonia, whereas the least toxic substance is uric acid.
  • Ammonotelism is the process of eliminating ammonia, and species that excrete ammonia are termed ammonotelic
  • Ureotelic organisms produce urea as a nitrogenous waste product (mammals, terrestrial amphibians).
  • Uric acid is excreted by uricotelic organisms (reptiles, birds).




  • The kidneys are a pair of reddish-brown bean-shaped structure between the last thoracic and lumbar vertebrae.
  • The ureter, blood arteries, and nerves all enter through a notch on the inner side of each kidney called the hilum
  • The renal pelvis, a large funnel-shaped area inside the hilum, bears projections termed calyces
  • The kidney is divided into two zones: the outer cortex and the inner medulla.
  • The medullary pyramids extending into the calyx divide the medulla. 
  • Between the medullary pyramids, the cortex forms the renal column known as the Columns of Bertini
  • The nephron is the functional unit of the kidney. A million nephrons are found in each kidney. 
  • The glomerulus and renal tubules are two elements of each nephron.
  • The tuft of capillaries created by the afferent arteriole is the glomerulus.
  • The efferent arteriole transports blood out from the glomerulus. 
  • Bowman’s capsule is the beginning of the renal tubules, split into Proximal Convoluted tubules, Henle’s loop, and Distal Convoluted tubules
  • The nephron’s malpighian tubules, PCT, and DCT, are located in the cortical area, whereas Henle’s loops are located in the medulla.


KidneySource: Kidney Anatomy

Nephrons are classified into two categories based on their location in the kidney. 

Cortical nephron

  • The loop of Henle is too short in most nephrons, extending just a few millimeters into the medulla and lying in the renal cortex.


Juxtamedullary Nephrons

  • Juxtamedullary Nephrons are a kind of nephron that is found between the medulla
  • The Henle loop is particularly lengthy in certain nephrons and extends far into the medulla.


The cortical nephron accounts for around 80% of the overall nephron count, with the juxtamedullary nephron accounting for the remaining 20%

Urine formation

The three primary phases in the production of urine are glomerular filtration, reabsorption, and secretion.

Glomerular filtration

  • Glomerular filtration takes place in the glomerulus, which filters blood.
  • The epithelium of Bowman’s capsule, the endothelium of glomerular blood vessels, and a membrane in between these two layers are all involved in this process.
  • The blood is filtered such that all of the plasma’s elements, excluding proteins, enter the Bowman’s capsule.
  • As a result, this procedure is called ultra filtration.


  • The renal tubules reabsorb around 99% of the filtrate collected.
  • This is referred to as reabsorption. This is accomplished by active and passive transportation.


  • Tubular secretion is the next phase in the urine production process.
  • Tubular cells release hydrogen ions, potassium ions, and other ions into the filtrate.
  • The ionic, acid-base and other bodily fluid balances are maintained by this mechanism.
  • Urine is formed when the released ions interact with the filtrate.
  • The urine exits the nephron tubule and flows into a collecting duct.

Function of the tubules

PCT (Proximal Convoluted Tubule)

  • This section reabsorbs nearly all important nutrients and 70-80% of electrolytes and water.
  • PCT also aids in the maintenance of bodily fluid pH and ionic equilibrium by selective secretion.

Loop of Henle

  • In the ascending limb of Henle’s Loop, resorption is at a minimum.
  • On the other hand, this area is important for maintaining the high osmolarity of medullary interstitial fluid.
  • The loop of Henle’s descending limb is permeable to water but nearly impervious to electrolytes.

Distal Convoluted Tubule (DCT)

  • Conditional reabsorption of Na+ and water occurs in the DCT.

Urine formation

Sources: Urine formation


  • Urine is stored in the urinary bladder till a voluntary signal from CNS carries out its release through the urethra, i.e., micturition.
  • The signal for this process begins by the stretching of the urinary bladder as it gets filled with urine.
  • The neural mechanism causing micturition is known as Micturition reflex

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