Excretory System in Humans

The labelled diagram of the urinary system in humans is shown below:

The human urinary system consists of following parts:

1. Kidneys — These are a pair of reddish-brown, bean-shaped structures that are located just above the waist on either side of the backbone. They filter the impure blood and produce urine.
2. Ureters — These are narrow tubes that lead out from each kidney. These tubes carry urine from the kidneys to the urinary bladder.
3. Urinary bladder — It is a pouch-like muscular structure in which urine is stored temporarily. In an adult male, the average capacity of the urinary bladder varies from 150 to 300 mL.
4. Urethra — It is a tube-like opening at the bottom of the urinary bladder through which urine is passed out.

A nephron is the functional unit of a kidney. Each nephron consists of a cup-shaped structure at one end called the Bowman's capsule. It extends into a long urinary tubule that is surrounded by a network of renal capillaries. The urinary tubules of nephrons in each kidney join to form a common tube called the ureter. Inside the Bowman’s capsule, is a network of blood capillaries called glomerulus. The Bowman’s capsule and glomerulus together form the Malpighian body.

Below diagram shows the structure of a nephron:

The process of blood filtration by kidneys and urine formation can be explained in the following steps:

1. Filtration — The renal artery brings the blood containing waste material to the kidneys. It then enters the glomerulus under high pressure. Water and small solutes are filtered in the Bowman’s capsule.
2. Reabsorption — The filtrate passes through the thin walls of the Bowman’s capsule into the urinary or renal tubule. As it passes through the tubule, water and many useful substances are reabsorbed by the renal blood capillaries.
3. Secretion — The remaining liquid, along with waste such as urea, uric acid and so on, is called urine and is collected in the urinary bladder.
4. Excretion — Urine leaves the kidneys and passes into the urinary bladder through the ureters. When the urinary bladder is full, urine is passed out through the urethra.

Below diagram shows the process of urine formation:

Kidneys play an important role not only by filtering the blood and getting rid of waste products, but also by balancing the salt levels in the body, controlling blood pressure and stimulating the production of red blood cells. A person can lead a normal life with one kidney but when both of them stop functioning, it can prove fatal if no treatment is provided. An artificial kidney or a dialyser is a machine used to filter the blood of a patient whose kidneys are damaged. This process is called dialysis. In this process the blood is directed from veins into the dialyser through a tube connected to veins. The dialyser filters the blood and filtered blood is again directed inside the body.

1. Urinary tract infection
   Causes — Urinary tract infection (UTI) usually occurs when bacteria such as E. coli enters the urinary tract.
   Symptoms — Following are the symptoms of UTI:
   • a burning sensation while passing urine.
   • a frequent urge to urinate.
   • pain in the back or lower abdomen.
   • cloudy and strange-smelling urine.
   • fever-like feeling if the infection has reached the kidneys.
2. Kidney Stones
   Causes — When urine becomes concentrated with calcium oxalate and uric acid, an accumulation of these dissolved minerals sticks together forming kidney stones. The main cause of kidney stones is lack of water in the body.
   Symptoms — Following are the symptoms of kidney stones:
   • severe pain in the sides of the abdomen
   • blood in the urine
   • nausea and vomiting
   • reduced amount of urine excreted
   • burning sensation during urination
   • persistent urge to urinate

We need to remove waste products from our body from time to time because they may become toxic or poisonous if allowed to accumulate inside the body.

The types of excretory products in humans are:

1. Nitrogenous waste products
2. Extra salts
3. Bile pigments
4. Excess Vitamins
5. Carbon dioxide and water

The two distinct regions shown in the longitudinal section of a kidney are:

1. Outer dark region called Cortex.
2. Inner lighter region called Medulla.

Urinary tract infection (UTI) is an infection that occurs in the urinary system due to bacteria such as E. coli. The infection starts at the opening of urethra but can spread to urinary bladder and kidney.

When the urine becomes concentrated and contains more Calcium Oxalate and Uric acid, the dissolved material stick together forming a mass known as kidney stones. These are formed due to less consumption of water.

False

Corrected Statement — The organs that help our body to get rid of waste are called excretory organs.

True

False

Corrected Statement — Each kidney contains millions of microscopic filtering units called nephrons.

True

True

1. (6) Blood containing waste material enters the kidneys through the renal artery.
2. (1) Blood enters the glomerulus under high pressure.
3. (4) Water and small solutes are filtered in the Bowman’s capsule.
4. (2) The filtrate passes through the thin walls of the Bowman’s capsule into the renal tubule.
5. (3) As the filtrate passes through the tubule, water and many useful substances are reabsorbed by the walls of the blood capillaries.
6. (5) The remaining liquid, along with waste is called urine and is collected in the urinary bladder.

Liver produces bile pigments from the haemoglobin of broken RBCs.

Kidneys are a pair of reddish-brown, bean-shaped structures that lie on the either side of the backbone.

Urine contains ammonia, uric acid and Urea as nitrogenous waste.

Ureter carries urine from the kidney to the urinary bladder.

The network of blood capillaries inside the Bowman's capsule is called Glomerulus.

Lung

Reason — Lung is a part of respiratory system while others are parts of excretory system.

Heart

Reason — Heart is part of circulatory system while others organs are part of the excretory system.

Blood

Reason — Except blood, all are waste materials.

respiration

Reason — Except respiration, all are steps of urine formation.

1. The organ in the picture is Kidney. The labelled diagram is shown below:

2. A person with failed kidneys has to undergo dialysis frequently to filter their blood.

1. Kidneys
2. Nephrologist
3. Dialysis

kidneys

Reason — Nitrogenous waste products like urea, ammonia and uric acid are removed through kidneys.

urethra

Reason — A tube-like opening at the bottom of the urinary bladder through which urine is passed out is called urethra.

nephron

Reason — Each kidney contains millions of filtration units called nephrons.

Malpighian body

Reason — The Bowman’s capsule is a cup shaped structure at one end of nephron inside which there is a network of blood capillaries called glomerulus. These form Malpighian body.

renal artery

Reason — Blood containing waste material enters the kidneys through the renal artery.

E. coli

Reasons — E. coli causes Urinary tract infections when it enter the urinary tract through urethra.