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13.4Excretion in Humans

Urea and deamination — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

5 min read 11 parts Lesson 4 of 4 2 quizzes

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision
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Lesson summary

13.4 Urea and deamination — IGCSE BIOLOGY notes: Explain how the liver forms urea by deamination and how kidney failure is treated (Supplement).Delivery — Digested food molecules absorbed in the small intestine are carried to the liver for assimilation.Use — Amino acids are used …

  • Cell death
  • Detoxification
  • Red blood cells
  • Tissue match
  • Transplant
  • Reabsorption

Part 1 of 9Assimilation of amino acids

Delivery
  • Digested food molecules absorbed in the small intestine are carried to the liver for assimilation.
Use
  • Amino acids are used to build proteins such as fibrinogen, a plasma protein needed for clotting.
No store
  • Excess amino acids cannot be stored, so they are broken down.

Part 2 of 9Deamination

1
Enzymes in the liver split up the amino acid molecules.
2
The amino group (NH2), which contains the nitrogen, is removed; this is deamination.
3
The amino group is turned into ammonia, which is highly toxic.
4
The ammonia is immediately converted into urea, which is less toxic.
5
The carbon-containing part is turned into glycogen for storage, or used in respiration.

Part 3 of 9Removal of urea

Transport
  • Urea dissolves in the blood plasma and is taken to the kidneys.
Excretion
  • The kidneys remove it in urine; a small amount is also lost in sweat.
Stored
  • Urine is stored in the bladder and released through the urethra.

Part 4 of 9Effects of high urea levels

Cell death
  • Toxic levels of urea kill cells.
Insulin
  • They reduce the response to insulin, potentially leading to diabetes.
Vessels
  • Deposits form inside blood vessels.

Part 5 of 9Other roles of the liver

Glycogen
  • Stores glycogen and controls blood glucose.
Detoxification
  • Breaks down alcohol and other drugs.
Red blood cells
  • Breaks down old red blood cells.
Bile
  • Makes bile.

Part 6 of 9Kidney dialysis

1
Blood flows from the patient through a machine on one side of a partially permeable membrane.
2
Dialysis fluid flows in the opposite direction on the other side.
3
The fluid contains no urea, so urea diffuses out of the blood.
4
The fluid has normal plasma glucose and ion concentrations, so only excess ions leave and glucose is kept.
5
Sessions last several hours, a few times a week.

Part 7 of 9Kidney transplant

Procedure
  • A healthy kidney from a donor is placed in the patient.
Tissue match
  • The donor tissue must be a close match.
Rejection
  • The immune system may reject the kidney, so immunosuppressant drugs are taken.
Supply
  • A shortage of donors causes long waiting lists.

Part 8 of 9Treatments compared

FeatureDialysisTransplant
How it worksMachine removes urea by diffusion across a membraneDonor kidney filters blood naturally
TimeSeveral hours, several times a weekOne major operation
Main risksInfection, blood clotsRejection and side effects of drugs
AvailabilityAvailable quicklyLimited by donors and tissue match

Part 9 of 9More from the specification

1Human metabolic excretory organs
  • Human metabolic excretory organs kidneys, lungs, and skin act as primary excretory organs removing toxic nitrogenous wastes and carbon dioxide.
2Nephron
  • Kidney tubule that filters blood and forms urine.
3Filtrate
  • The liquid collected in the Bowman's capsule.
4Capillary
  • Vessel one cell thick where exchange takes place.
5Reabsorption
  • Return of useful substances from the filtrate to the blood.
6Organ
  • A structure of different tissues working together for specific functions.
7Product
  • The molecule(s) formed from the substrate in an enzyme-catalysed reaction.
8Active transport
  • Movement of particles against a concentration gradient using energy from respiration.
9Renal artery
  • Vessel bringing blood to the kidney.
10Excretion
  • Excretion carbon dioxide is removed by the lungs, while urea from amino acid breakdown is removed by the kidneys.

Key terms

TermMeaning
DeaminationRemoval of the nitrogen-containing amino group from excess amino acids in the liver.
UreaThe less toxic nitrogen waste made in the liver and excreted by the kidneys.
AmmoniaA highly toxic compound formed when the amino group is removed.
DialysisRemoval of urea from blood by diffusion across a partially permeable membrane.
TransplantReplacement of a failed kidney with a donor kidney.
AssimilationConversion of absorbed food molecules into molecules the body needs.

Avoid these mistakes

1
Saying the kidney makes urea — the liver makes urea by deamination.
2
Saying amino acids are stored — excess amino acids are deaminated.
3
Confusing excretion with egestion — urea removal is excretion.
4
Saying dialysis fluid contains urea — it contains none so urea diffuses out.

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