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.

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

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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).

 

Kidneys

• 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.

 

Source: 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.

Reabsorption

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

Secretion

• 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.

Sources: Urine formation

Micturition

• 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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