SITEMAP *  HOME PAGE * SEARCH * UK KS3 level Science Quizzes for students aged ~13-14

UK GCSE level BiologyChemistryPhysics ~14-16 * Advanced pre-university Chemistry ~16-18

UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes

Homeostasis: 2. Three important functions of the kidney

Doc Brown's Biology exam study revision notes

There are various sections to work through, after 1 they can be read and studied in any order.

Sub-index of biology notes on homeostasis: Kidney structure and function - osmoregulation


(2) The three functions of the kidneys (and mention of associated liver function)

The kidneys are bean-shaped organs found in the abdomen, one on either side of the aorta.

The kidneys are really important in control of ...

(i) Water control

The kidneys help to regulate the water content of the body by controlling how much water is reabsorbed and how much is lost in urine.

Water is lost through the skin in sweating and the lungs when breathing out, but these losses cannot be controlled by any organ in the body, including the kidneys.

We also lose water when the kidneys remove urea in urine.

So, this water loss must be balanced by water we consume in food and drinks.

But, the kidney will excrete excess water too.

Water balance is strongly related to ion concentrations in the body fluids.

(ii) Ions and small molecules concentration control

Ions such as sodium, iron and calcium are taken into our body in food and drinks and then reabsorbed into the bloodstream.

If the ion content of the body is wrong. it can upset the balance between ion concentration and water and too much water can be absorbed into cells by osmosis - so the wrong balance can lead to cell damage e.g. extreme dehydration from lack of water OR excess hydration (caused by some illegal drugs) and both situations can be fatal.

Important ions like sodium and chloride, are lost in sweat, which tastes salty as a consequence, but this situation is not regulated by the body.

Hence the importance of the kidneys in maintaining water AND ion balance in the body.

The correct amount of ions are reabsorbed and excess ions are removed in urine.

So, the kidneys are also an important high pressure 'filtration' system for removing unwanted materials and waste products out of the blood passing through the kidneys, which would otherwise cause harmful effects on the body if not removed.

The kidneys filter out these substances as the blood through - hence the process name of filtration.

Glucose, ions and other useful substances and appropriate amount of water are re-absorbed back into the blood stream - this process is called selective reabsorption.

This process is essential to adjust the levels of ions to their appropriate concentration.

(iii) Urea removal

What else does the kidney remove to maintain the right balance of various substances?

After the filtration, the principal waste substance removed by the body in the urine is urea from the blood.

Urea is made from excess nitrogen, often from amino acids from metabolised food and urea is less toxic than ammonia.

removal of excess nitrogen deamination amino acid to ammonia and urea in kidney gcse biology igcseNeither proteins or amino acids can be stored in the body, so excess amino acids are converted into fats and carbohydrates, but these molecules do not contain nitrogen, so the nitrogen part of amino acids must removed in some way.

This process, called deamination, happens in the liver and produces the waste product ammonia.

However, ammonia is toxic and is converted to urea and transported to the kidneys where it is filtered out and excreted in urine.

See (3) Details on how the kidney works in conjunction with the urinary and blood systems


Keywords, phrases and learning objectives for this part on varied functions of the kidney

Be able to describe three functions of the kidneys including water control, ion and small molecule concentrations and the removal of urea.

Be able to explain why ammonia must be converted to urea (deamination) for excretion.


WHAT NEXT?

TOP OF PAGE

INDEX of biology notes on homeostasis: Kidney structure and function - osmoregulation

INDEX of all my BIOLOGY NOTES

BIG website, try using the [SEARCH BOX], maybe quicker than the many indexes!

Basic Science Quizzes for UK KS3 science students aged ~12-14, ~US grades 6-8

BiologyChemistryPhysics for UK GCSE level students aged ~14-16, ~US grades 9-10

Advanced Level Chemistry for pre-university age ~16-18 ~US grades 11-12, K12 Honors

Find your GCSE/IGCSE science course for more help links to all science revision notes

email doc brown - comments - query?

Use your mobile phone or ipad etc. in 'landscape' mode?

SITEMAP Website content Dr Phil Brown 2000+. All copyrights reserved on Doc Brown's biology revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries and references to science course specifications are unofficial.

Using SEARCH some initial results may be ad links you can ignore - look for docbrown

TOP OF PAGE