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Biology > Excretory Products > Human Excretory System
Excretory Products

Human Excretory System

You have already learned about excretion. But did you know that in humans, the skin is also an excretory organ? That’s right, sweat is actually the waste of our body. Let us study all about the human excretory system.

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Parts of the Human Excretory System

Every living organism generates waste in its body and has a mechanism to expel it. In humans, the excretory system takes care of waste generation and elimination. It comprises of the following structures:
  • 2 Kidneys
  • 2 Ureters
  • 1 Urinary bladder
  • 1 Urethra

Human Excretory System

Kidneys

Kidneys are the main organ of the human excretory system. Also, every individual has a pair of kidneys. They are located one on each side of the spine at the level of the liver. Kidneys are divided into three regions. Namely, the renal cortex which is the outer layer. Next, the renal medulla which is the inner layer. And lastly, the renal pelvis which carries the urine from the kidney to the ureter. 

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Structure of a Nephron

 

The nephron is the functional unit of a kidney. In fact, each kidney consists of millions of nephrons. They all function together to filter blood and expel waste products. It consists of the following parts:

  • Bowman’s capsule– It is the first part of the nephron. It is a cup-shaped structure and receives the blood vessels. Glomerular filtration occurs here. The blood cells and proteins remain in the blood.
  • Proximal Convoluted Tubule– The Bowman’s capsule extends downwards to form the proximal tubule. Water and reusable materials from the blood are now reabsorbed back into it.
  • The loop of Henle– The proximal tubule leads to the formation of a u-shaped loop called the Loop of Henle. It has three parts: the descending limb, the u-shaped bend, and the ascending limb. It is in this area in which urine becomes concentrated as water is reabsorbed. The descending limb is permeable to water whereas the ascending limb is impermeable to it.
  • Distal Convoluted Tubule– The Loop of Henle leads into the distal convoluted tubule. It is where the kidney hormones cause their effect.
  • Collecting Duct– The Distal Convoluted Tubule of each nephron leads to the collecting ducts. The collecting ducts together form the renal pelvis. Through renal pelvis, the urine passes into the ureter and then into the bladder.

Ureters

There is one ureter that comes out of each kidney as an extension of the renal pelvis. It is a thin muscular tube that carries urine from the kidneys to the bladder.

Urinary Bladder

The bladder is a sac-like structure. And a smooth muscle layer lines it. It stores the urine until micturition. Furthermore, Micturition is the act of expelling urine from the body. The bladder receives urine from the ureters, one from each kidney. In addition, the level of placement of the bladder in the body differs in men and women.

What are the Different Stages of Micturition?

Urethra

The urethra is a tube that arises from the urinary bladder. Its function is to expel the urine outside by micturition. In addition, it is shorter in females and longer in males. Furthermore, in males, it functions as a common path for sperms and urine. Also, sphincter guards the opening of the urethra.

Other Excretory Organs

Apart from the above-mentioned organs, there are other organs that perform excretion. They are:

Skin

The skin is the largest organ in the body. Its primary function is to protect the different organs of the body. In addition, the skin excretes sweat. In particular, the skin eliminates compounds like NaCl, some amount of urea etc.

Lungs

Lungs are the primary respiratory organs. They help take in oxygen and expel carbon dioxide. But, in this process, they also eliminate some amount of water in the form of vapour.

Liver

This organ has an important function in excreting waste from the body. It is the first line of defence when it comes to hormones, fats, alcohol, and drugs. In fact, most drugs undergo first-pass metabolism in this organ. The kidneys also eliminate a few drugs. Furthermore, the liver eliminates excess fats and cholesterol. This is essential to maintain the health of the body.

Functions of the Excretory System

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.

How does Excretion Process look in Plants?

Solved Example for You

Q: Which part of the nephron structure is completely impermeable to water?

(a)    Proximal Convoluted Tubule       (b) Ascending limb of the Loop of Henle

(c)    Distal Convoluted Tubule             (d) Descending limb of the Loop of Henle

Sol. (b). 

FAQ’s for You

Q1. Describe the excretory system of human beings.

Answers: 

The human excretory system comprises of the following structures: two bean-shaped kidneys, two ureters, one urinary bladder, and one urethra.

Kidneys are the main organ of the human excretory system. The kidneys are paired organs and are located one on each side of the spine at the level of the liver. They are divided into three regions- the renal cortex which is the outer layer, the renal medulla which is the inner layer and the renal pelvis which is responsible for carrying the urine from the kidney to the ureter. The functional unit of a kidney is called the nephron.

There is one ureter that comes out of each kidney as an extension of the renal pelvis. The ureter is a thin muscular tube that carries urine from the kidneys to the bladder.

The bladder receives urine from the ureters, one from each kidney. It is a sac-like structure that is lined with smooth muscle layer and is responsible for storage of urine till it is expelled from the body by micturition (urination).

The urethra is a tube that arises from the urinary bladder and expels urine by micturition. The urethra is shorter in females and longer in the males. In males, the urethra functions as a common path for sperms and urine. The opening of the urethra is guarded by a sphincter that is voluntary.

Q2. What is the unit of excretory system?

Answers: Nephron is the basic structural and functional unit of the kidney. The main function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine.

Q3. Explain the Human Excretory System.

Answers: Human excretory system:
(a) In humans, the excretory system consists of a pair of kidneys, a pair of ureters, urinary bladder and urethra.
(b) Kidneys are two bean shaped organs lying at the back of the abdomen, one on either side of the vertebral column. Waste products from the blood and urine are removed by the kidney.
(c) A Nephron is the basic filtration unit of the kidney. It is a cluster of thin walled blood capillaries.
(d) The urine produced by filtering the blood is transported to the urinary bladder. This is done by a pair of ureters. Ureters are long muscular tubes.
(e) Urinary bladder is a muscular bag like structure which can hold urine. The urinary bladder is under the control of nerves. When the bladder is full one get urge to urinate.
(f) This urine is thrown out of the body through urethra.
(g) Apart from the kidney, the skin and lungs are also helpful in the excretion.

Q4. Urine is stored in?

Answers: Urine is made in kidney from the kidney the ureter transports urine into the urinary bladder. The urinary bladder is a muscular sac. When it is empty, it is about the size and shape of a pear. The bladder stores urine, allowing urination to be infrequent and can be controlled. Urge for urination starts as bladder comes to have urine 400-450 ml. In response, the stretch receptors on the walls of the bladder send signals to the CNS. The CNS passes on motor messages to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.
So, the correct answer is ‘Urinary bladder’.

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