6 important points to keep in mind while studying: Excretory Products & their elimination

By Prashant Kumar|Updated : October 4th, 2018

This topic is quite important from view point of NEET exam. Questions have been prompted from this topic in the past few years. Let’s get started. 

1. Human Excretory System

So I won’t start on with the basics I believe that we all are good on that ground. Sometimes in NEET we have seen simple questions coming up from this topic related to the labeling, order of placement of tubules in nephron, pathway of excretion. So yes questions do come from the basics so don’t leave this unattended.

Here are a few details from the parts of Excretory System:


  • The right kidney is slightly lower than the left and the left kidney is a little nearer to the middle plane than the right.
  • The kidney is
  • The medulla is divided into a number of conical areas, the medullary pyramids (15 or 16) having their broad base towards the cortex.
  • Each renal med­ullary pyramid terminates into a structure, the renal papilla.



  • The ureter of each kidney leaves from the renal pelvis in the hilus re­gion.
  • Each ureter is about 25 to 30 cm in length.
  • They carry urine from the kidneys to the urinary bladder.

Urinary Bladder:

  • It lies in the pelvic cavity and is somewhat pear shaped, muscular, sac-like structure.
  • Internally, the urinary bladder has a triangular area, the trigone, between the three openings— two openings through which the ureters enter the bladder and one opening through which the urethra leaves the bladder.
  • The urinary bladder stores urine temporarily


  • It is a canal like structure which extends from the neck of the bladder and leads to exterior.
  • In male, urethra is much longer (about 20 cm in length) which opens out at the tip of the penis by urinogenital aperture. Thus the urethra of male carries both urine and semen. 

2. Urine formation

The three vital processes are important to know and study about: Glomerular Filtration, Re-absorption and Secretion. 

The glomerular capillaries are narrower than the afferent renal arterioles. Therefore, the blood pressure in the glomerular capillaries becomes very high so that there is continuous process of ultrafiltration (filtration under pressure) through the semi-permeable glomerular capillaries. 

From the Bowman’s capsule, the glomerular filtrate enters the proximal convoluted tubule. Absorption of selected materials takes place from the filtrate into the blood of the capillaries or vasa recta. It is termed the tubular reabsorption. 

The cells of the renal tubule no. only remove substances from the filtrate by the process of reabsorption and send them to the blood capillaries but also excrete additional wastes from the blood stream into the filtrate by the process of secretion.

3. Nephron- Function 

 (i) Proximal Convoluted Tubule (PCT):

The cells of PCT have numerous mitochondria near the surface, which allows the reabsorption of salts by active transport. The filtrate is isotonic to blood plasma.











 (ii) Loop of Henle:

It starts at the end of proximal convoluted tube and its major part lies in the medulla. It consists of a descending limb and an ascending limb.

(a) Descending limb of loop of Henle:

  • As the filtrate flows in it, its water is reabsorbed due to increasing osmolality of interstitial fluid.
  • Sodium and other solutes are not reabsorbed

(b) Ascending limb of loop of Henle:

  • It is impermeable to water but permeable to K+, Cland Na+ and partially permeable to urea.
  • Thus in the thick ascending limb of the loop of Henle sodium, potassium, calcium, magnesium, and chloride are reabsorbed. 

(iii) Distal Convoluted Tubule (DCT):

  • There is active reabsorption of sodium ions from the filtrate under the influence of aldosterone (hormone secreted by the cortex of adrenal glands).
  • Chloride ions are also reabsorbed in the distal convoluted tubules.
  • Water is reabsorbed here under the influence of antidiuretic hormone (ADH) secreted by posterior lobe of pituitary gland. 

(iv) Collecting duct:

  • From distal convoluted tubule filtrate enters the collecting duct where further reabsorption of water takes place.
  • The entire duct is permeable to water.
  • Sodium is reabsorbed in the collecting duct under the influence of aldosterone.
  • The filtrate is now called urine

4. Counter current mechanisms

This mechanism depends on the loop of Henle, the vasa recta, collecting ducts and interstitial fluids.

The flow of filtrate in the two limbs of loop of Henle is in opposite directions and thus forms a counter current.

The flow of blood in the ascending capillary and descending capillary of vas rectum is also in opposite direction and therefore, form a counter current. 

5. Neural regulation of excretion

  • Control by Anti diuretic hormone (ADH)

The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the osmolarity of the blood. In this situation the osmoreceptor cells also promote thirst. It increases the reabsorption of water in the DCT and collecting duct. 

  • Control by Juxtaglomerular apparatus (JGA)

Juxtaglomerular cells secrete an enzyme, renin, into the blood stream. Renin changes a plasma protein called angiotensinogen to a peptide called angiotensin II, which works as a hormone, which increases blood pressure by causing arterioles to constrict.

  • Control by Atrial Natriuretic Factor (ANF)

The walls of atria of heart release ANF in response to an increase in blood volume and pressure. ANF inhibits release of renin from JGA and thereby inhibits NaCl reabsorption. 

6. Disorders

  • Uremia- Urea accumulation in blood is comparatively high in uremia. Hemodialysis is done in patients to remove the urea.
  • Kidney Failure- decrease or cessation of glomerular filtration. 
  • Renal calculi (Kidney Stones)- stone or insoluble mass of crytalized salts is formed within the kidney.
  • Nephritis- Inflammation in the Kidney.
  • Oedema- accumulation of excess fluid in tissues is called oedema.

Diabetes Insipidus- Deficienc


All the best!!

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Pragati Dwivedi
Ma'am please provide a video lectures on cell structure and functions and on biomolecules also  ....thnq
Ajay Shinde
Thanks for share
Krishna Tanwar
Genetic ke notes
Amit Mishra
Thanks A lot...its quite helpful
Gandharb Majhi
Thank you sir
immanuel john isaac
Thank you so much mam @Neha Johar 👌✌🙋

AbeenaMar 21, 2019

Sir can u plz provide the video for the chapter : Neural control......The Ear portion... am 😕 confused with the explanation on its structure.....!!!!@Prashant Kumar 🙏🙏🙏

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