the functions of the lungs, kidneys and skin in the excretion of waste products made in the body

Excretion is the expulsion from the body of the wastes produced by the chemical activity occurring within the living cells of our bodies. Excess salt and water taken in the diet is expelled from the body in sweat and urine. The kidneys also function in keeping the blood at the correct concentration.

OB20 understand the structure and function of the urinary system: the bladder, ureter, urethra, renal artery, renal vein and kidney.

Renal : of the kidney

The Urinary System

a) The Structure and Function of the Urinary System

Two kidneys are in the abdominal cavity below the diaphragm – the kidneys produce urine, the excretory liquid of excess water, excess salts and urea. Renal artery to each kidney from the aorta supplying blood that is oxygenated but carrying urea, excess water and excess salts. A renal vein passes from each kidney carrying blood that is lower in oxygen but is not carrying urea, excess water or excess salts.

Urine is carried from each kidney to the bladder by a muscular tube called a ureter.

The bladder is a muscular bag that temporarily stores the urine

forcing it to the outside by way of the urethra at a time when we choose it is suitable to urinate.

A special circular muscle, or sphincter muscle, at the base of the bladder controls the release of urine by relaxing; when this muscle is contracted the opening from the bladder is closed and urine cannot escape.

Every day our bodies carry out essential chemical reactions, we require some of the products to function but other by-products are not useful for us. All animal organisms have to tidy themselves up and get rid of these waste chemicals. Our body has many things that it needs to get rid of, in the earlier section on digestion we saw egestion, the removal of undigested food passing through the rectum.

The Formation of Urine by the Kidneys

(i) Filtration

The renal arteries deliver a quarter of the blood pumped by the heart to the kidneys. This huge volume is not for the supply of oxygen or nutrients but for cleaning i.e. the removal of wastes. This blood is filtered as it passes through the blood capillaries in the kidneys. The red blood cells, white blood cells, platelets and plasma proteins remain in the blood as they are too big to pass through the tiny holes in the blood capillaries. The filtrate, the liquid that passes through the walls of the blood capillaries, is composed of water, glucose, amino acids and urea.

(ii) Selective Reabsorption

The kidneys then select from the filtrate what is to be taken back into the blood. The urea waste is not selected. Glucose and amino acids are completely taken back. Only the amount of water and salt needed to keep the blood at the correct concentration is returned to the blood. The deselected material (excess water, excess salts and the urea) becomes the urine that passes out of the kidneys for expulsion from the body.

The Urinary system is the set or organs that produce Urine in the body, chiefly made of the organs the bladder, the ureter, urethra and kidneys.

  • The Bladder holds urine until, it is safe to release it.
  • The Urether passes urine from the kidneys to the bladder.
  • The Urethra allows urine to flow from the bladder to the outside.
  • Kidneys filter blood clean of excess salts.
  • renal artery brings blood to the kidneys
  • renal vein takes cleaned blood away from the kidneys

An online map of the human Urinary system is here http://www.infovisual.info/03/058_en.html

Okay you need to sketch down this diagram, either from here or from your book. Take care to notice any difference between the 2 diagrams,

and list functions of

Urine is excess water with excess salt and Urea !

Random factas about pee


The Kidneys

Filter the blood of your body, removing Urea, amino acids (proteins), water and salt. The water & salt that is required is reabsorbed into the body but the remainder is washed down the ureter to the bladder. This remainder is known as Urine.

The Bladder

Stores the Urine

The Ureter

Transports the Urine from the kidneys to the Bladder

The Urethra

Allow the urine to pass out of the body

Renal Artery

Away from the Heart, Renal infers Kidneys, there for this is the unfiltered blood that needs to get cleaned.

Renal Vein

Out of the kidneys comes filtered blood


Urea is made in the liver during the conversion of excess amino acids (proteins) to carbohydrate and fat. This Urea flows about the body with the blood stream, until the blood is passed down the Renal Artery (away from the heart) and through the kidneys, here the excess Urea is removed from the blood.

the Urea Molecule

The kidneys also remove some salts from the blood stream. The Urea and Salts are washed down the Ureter using whatever water the body can spare. This mixture is known as Urine, it collects in the bladder after it is washed down the Ureter. When the bladder is full we can release the Urine through the Urethra (haaaaa) when we relax a muscle controlling the valve at this point.

Interesting other facts about Urea

More than 90% of world production of urea is destined for use as a nitrogen-release fertilizer.

  • A main ingredient in hair removers such as Nair or Veet.

from Wikipedia.org

OB21 name the products of excretion: CO2, water, salt and urea

Urea is made in the Liver, from proteins, it gets absorbed into the blood and gets filtered out in the kidneys.

The urea is diluted with some excess water to make urine.

The urine passes down the ureter into the bladder.


Carbon Dioxide is released from our lungs, as they take in oxygen. So the impression might be that the lungs make Carbon Dioxide, NO this is not the case! This is where the CO2 is simply excreted

So where is the CO2 coming from ?

CO2 is the waste product of from cells.

These cells need energy in the form glucose, this gets burned with oxygen.

The waste products of this reaction carbon dioxide and water.

Every single cell in our body requires energy for survival and life, each of these cells needs fuel to burn in Oxygen for it to carry out its tasks. When Oxygen is burned it makes Carbon Dioxide.

As we would learn in the reactions and atmosphere sections Oxygen is required for burning. The blood vessels carry glucose (fuel) and oxygen to every cell in the body. Here they get burned up and produce H2O (water) & CO2 (carbon dioxide) these by-products get taken back out of the cell by the blood.

The water is used in the body and the Carbon Dioxide is released from the blood in the lungs, which is then released from the body and into the atmosphere.


  • Salts are removed from the blood in the kidneys.
  • Salts are removed by sweat (perspiration).

Salts are created from various minerals in our blood that have become redundant to our purposes, these leave through the urine but also through the skin.

Water excretion is due to Heat release

Water is excreted through the skin as your body regulates its temperature. When we are hot we sweat more this is excreting hot water and therefore lowers your body temperature.

The main reason we pespire (sweat) is to lower the body temperature. Liquid over 37 oC is ejected from the body. This liquid evaporates from the skin, this evaporation removes more heat from the body.

The lungs excrete carbon dioxide and water in the form of gases.

OB22 understand the function of the skin in the excretion of waste products made in the body

The skin excretes water, and a small amount of urea, in a liquid called sweat.

The Excretory Role of the Skin

The skin excretes water, and a small amount of urea, in a liquid called sweat.

At rest about 300g of water is lost per day due to evaporation of water from the skin. If the body becomes overheated the sweat glands in the skin are stimulated to secrete sweat onto the surface of the skin for cooling by evaporation – up to a litre and a half of water per hour can be lost due to sweating. The skin has about 2,500,000 sweat glands. Evaporation of water leaves the solutes behind and that is why the skin has a fine layer of salt on it after sweating.

OB23 recall that waste products are removed from the bloodstream by filtration in the kidneys in the form of urine, which contains urea, water and salts, and that urine is stored in the bladder before being released from the body.

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