Human Excretory System- Class 11 | Chapter – 19 | Biology Short Notes Series PDF

Human Excretory System: A dedicated system of organs that removes waste products from the human body is called the human excretory system. The major waste product generated in the human body is urea. Along with which some other toxins are also generated. Urea is eliminated by kidneys in the form of liquid by the process of urination and solid wastes are removed from the body by the intestines.

Organs of Human Excretory System

Organs of the human excretory system include:

  • A set of kidneys

  • A ureter and a uretero-uretero-uretero

  • A bladder that stores urine

  • The urethra

Human Excretory System


The kidneys are bean-shaped organs that are positioned on either side of the backbone and are protected by the ribs and back muscles. They are primarily responsible for the production of urine. Kidneys collect waste from our bloodstream and turn that waste into a simpler form (urine) which is then eliminated from the body. Kidneys are present in the abdomen, just below the diaphragm. Each adult human kidney measures 10-12 cm in length, 5-7 cm in breadth, and weighs 120-170g.

The kidneys have a concave inner structure. The blood vessels, ureter and nerves enter the kidneys through the hilum, which is a notch at the inner concave surface of the kidney. The renal pelvis, a large funnel-shaped space that is present inner to the hilum, has many projections known as calyces.

Kidneys are made up of a number of subunits called nephrons. The kidney is divided into two major structures-


The capsule refers to the outer layer. The kidney is divided into two zones: the cortex on the outside and the medulla on the inside. As renal columns are known as columns of Bertin, the cortex spreads between the medullary pyramids.

  1. Outer renal cortex

The outer part of the kidneys consists of the glomerulus and convoluted tubules from the outer cortex. The outer cortex is surrounded by the renal capsule. The renal cortex provides the space for the renal artery and veins and glomerular capillaries. Apart from providing a protective layer it also manufactures the hormone Erythropoietin, which is necessary for the synthesis of new blood cells. 

  1. Inner renal medulla

The inner smooth part of the kidney which consists of the Loop of Henle and renal pyramids forms the Renal Medulla.


The functioning units of the kidney are known as nephrons. Each of our kidneys has as many as 1 million nephrons in each human kidney. The basic functions of nephrons are to carry out secretion as well as the process of excretion. Each nephron is made up of two parts: the glomerulus and the renal tubule. 

  • Glomerulus – Glomerulus is a mass of capillaries Glomerulus is a collection of capillaries created by afferent arterioles which absorb protein from the blood that travels through the Malpighian Body. Different arterioles transport blood out from the glomerulus.

  • Renal Tubule – Bowman’s capsule, which encloses the glomerulus, forms the beginning of the renal tubule. The malpighian body is made up of the glomerulus and the Bowman’s capsule. The proximal convoluted tubule is the heavily coiled structure in the tubule adjacent to Bowman’s capsule. Renal Tubule is composed of a Proximal convoluted tubule that lies in the cortex and absorbs water, sodium, and glucose back into the blood, a distal convoluted tubule that reabsorbs sodium into the blood and absorbs potassium and acid from blood and Loop of Henle. 

Henle’s loop

Henle’s loop is the long ‘U tubule’ which has an ascending and descending limb and is the next section of the tubule. As a distal convoluted tubule, the ascending loop continues. Many nephrons have distal convoluted tubules that open into the collecting duct. It is primarily involved in the recovery of water and sodium chloride from urine is Loop of Henle. The Loop of Henle produces very concentrated urine. Therefore, desert animals have a highly efficient Loop of Henle to carry out excretion with a very less amount water. The Loop of Henle lies in the medulla region.       

Nephrons are of two types, namely

  1. Cortical Nephrons – The nephrons which are at a higher position in the cortex with a Short Loop of Henle which does not penetrate into the medulla are called Cortical Nephrons.

  2. Juxtamedullary Nephrons – Juxtamedullary nephrons have a longer Loop of Henle which runs deeper into the Renal Medulla.


Each kidney is connected to the renal pelvis by a thin and muscular tube. This tube is called the Ureter. The function of the ureter is to propel urine from the kidneys to the urinary bladder from time to time.

Urinary Bladder

Urinary bladder is the organ that controls the passage of urine. It is a muscular sac-like structure present above the pubic bone that stores urine. The average capacity of a human bladder is 400-600 ml. It holds urine until its capacity and expels it by the process of micturition when it is full. The bladder is lined by muscular tissue, which squeezes during micturition allowing the urine to flow out.


The urethra is a tube made up of fibro-muscular tissue and emerges from the lower opening of the urinary bladder and extends through urogenital and pelvic diaphragms and opens out of the body through an external urethral orifice. It aids in the removal of urine from the body. In males, it carries the sperms as well. The Urethra is guarded by the sphincter which relaxes during urination.

These organs work together to remove nitrogenous waste- urea from our bodies.

The excretory system performs many functions such as:

  • Eliminating waste products such as urea, uric acid ammonia, and other chemical products via urine.
  • Maintaining the osmotic level of blood and plasma
  • Maintaining the electrolyte balance in the body
  • And it also helps in the metabolism of those drugs that do not get metabolized in the liver.

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By Team Learning Mantras