All organisms' lives depend on certain basic processes, one of which is excretion. Different animals follow different modes of excretion. Humans have a specialized system for excretion called the human excretory system.

Human beings get their nutrients from different sources, which are digested and metabolized in their bodies. After those reactions, the body extracts both useful and toxic substances. Useful substances are good for your health, but toxins may be harmful. That's why the body removes all the metabolic wastes by the process called excretion.

Excretory system organs

The human excretory system organs include:

• Kidney
• Ureter
• Urinary bladder
• Urethra

Kidneys filter blood and remove unwanted substances. The process releases urine. The process is divided into three steps:

• Glomerular filtration,
• Reabsorption,
• Secretion

1. The Glomerular Filtration

In this step, wastes and fluids are filtered out by the kidneys from the blood.

2. Reabsorption

Reabsorption is the second step in urine formation. Water and small solutes are filtered by the glomeruli out of the bloodstream. The Tube wall is very helpful to reabsorb the needed substance into the adjacent capillaries.

3. Secretion

At the time of reabsorption, waste hydrogen ions from capillaries pass into renal tubules. This process is called secretion.

Nephron Definition

A nephron is the functional unit of kidneys that has glomeruli and tubules through which glomerular filtrate passes after which it emerges as urine.

A nephron is the functional and structural unit of the kidney. They are very small in size. The nephron comes from the Greek word 'nephrons,' which means kidney. In each human kidney, there are millions of nephrons.

Functions of Nephron

There are many functions of nephrons.

The primary function of the nephron is converting blood into the urine, removing all the waste from the body, reabsorption, and secretion.

The small molecules travel into the glomerular capsules as the blood passes with the help of the glomeruli with high pressure.

Through the renal blood vessels, the blood near the nephron travels reverses into the body. These renal blood vessels are free from other excess substances and toxins.

As the filtrate passes through the nephron, its osmolarity changes as water and ions are reabsorbed. In a countercurrent mechanism, the exchange of two fluids can take place from one direction to another with their concentrations. The definition of the countercurrent mechanism for all mammals and fishes is the same, but the mechanism may be different.

There are three different types of Counter Exchange Systems.

• Countercurrent exchange
• Current exchange 
• Contra-current exchange

Kidneys are the primary excretory organs. Kidneys are concerned with the excretion of urea in the form of urine. The function of our kidneys is regulated and monitored by feedback mechanisms. Feedback mechanisms involve the juxtaglomerular apparatus (JGA), hypothalamus, and heart.

When there is a change in the volume of blood, there is an excessive loss of fluid. This activates osmoreceptors, and they trigger the release of an Antidiuretic hormone (ADH) from the neurohypophysis. ADH stimulates the reabsorption of water from the distal parts of the tubules and thereby prevents water loss.

Regulation involving Juxtaglomerular Apparatus (JGA)

The regulation by Juxtaglomerular Apparatus (JGA) is known as the "Renin-Angiotensin mechanism." When blood flow in the glomerulus decreases, renin is released from juxtaglomerular cells. Renin converts angiotensin in the blood in two forms: angiotensin I and angiotensin II.

Angiotensin II also stimulates the release of aldosterone from the adrenal cortex gland. It facilitates reabsorption of the sodium ion and water from distal parts of the tubule and also causes an increase in the glomerular blood pressure and glomerular filtration rate.

The ANF, which stands for Atrial Natriuretic factor, is released when there is an increase in the blood flow to the atria of the heart. ANF causes vasodilation and helps to decrease blood pressure in the blood vessels. The Atrial Natriuretic Factor mechanism provides the necessary check to the Renin-Angiotensin mechanism.

The micturition shows a synchronized easing of the outer and inner urethral sphincters, with strong shrinkage of the detrusor muscle.

In adults, the bladder normally accommodates up to 300-400 ml. It is perceived as the full bladder sensation; when the bladder is distended, it sends the signals to the brain.

The nervous signals are regulated by the process of emptying the urine into the urethra. It is regulated by both the somatic and the autonomic nervous systems. The autonomic nervous system consists of the parasympathetic and sympathetic nervous systems.

The urinary bladder has two states of function:

• Storage phase 
• Emptying phase

The skin, lungs, and liver also help in the elimination of excretory wastes; that’s; the other than kidneys.

Skin

The skin is the largest organ in the human body. It consists of many layers. There are two types of glands in these layers of the skin - sweat glands and sebaceous glands. The sweat glands' function is to produce sweat, which contains amino acids, NaCl, glucose, and water.

Lungs

Our lungs are the primary organs of respiration in humans. Lungs help to remove large amounts of carbon dioxide (CO₂) (approximately 200mL/minute).

Liver

The liver, the largest gland in our body, plays a vital role in forming and eliminating urea. This is transported to the kidneys for elimination. The liver is known as the 'graveyard of RBCs' because it is here that they are destroyed.

There are some prominent diseases of the excretory system –

Kidney Failure or Renal Failure

Kidney failure occurs when the kidneys struggle to filter the urine by glomerular filtration. Kidney failure is classified into two types- acute kidney failure and chronic kidney failure.

Acute kidney failure happens when a kidney stops working suddenly.

On the other hand, chronic renal failure occurs when the kidneys lose their capacity gradually.

Kidney Stone

Kidney stones are the deposits of acid salts and minerals within the kidney. They vary from one person to another, that's why the exact reason for this disease is hard to find.

Uraemia

Uraemia is the result of an increase in the level of urea in the blood. It happens when the kidney is unable to filter the waste from the body.

Nephritis

Nephritis is another significant excretory system disease in which the nephrons become inflamed.

Other disorders of the excretory system are:

• Renin secretion
• Urethritis
• Edema
• Anuria
• Polyuria

1. What is Meant by Glomerular Filtration Rate and its Self-regulatory System?

Our kidneys filter our blood by removing the waste and extra water from the body to make urine. The glomerular filtration rate (GFR) is also known as the kidney's filtration rate. GFR is the measurement used to determine how well a kidney is filtering. The GFR of a healthy person is approximately 125 ml per minute.

2. What is the Amount of Urine Excreted by Humans Per Day?

800 to 2,000 milliliters per day is the normal range of excretion of urine. It happens when someone takes a normal fluid of about 2 liters per day.

3. Explain the autoregulatory mechanism of GFR.

The glomerular filtration rate is regulated by the kidney. When glomerular filtration decreases, renin is released by the juxtaglomerular cells. It brings GFR normal, the mechanism is called the autoregulatory mechanism of GFR.

4. Why should I learn Chapter 19 of NCERT Solutions for Class 11 Biology thoroughly?

Chapter 19 of NCERT Solutions for Class 11 Biology is helpful to enhance the knowledge of the student about the Excretory Products and their Elimination. Excretory Products and their Elimination is a very important chapter of biology. These solutions will help the students to understand the concepts in easy and simple language.

These NCERT solutions, if practiced regularly, will clear all doubts about complex topics.