Cambridge IGCSE Biology

1. EXCRETION
IN HUMANS

2. Egestion vs. Excretion

3. LO:
• State where and from what is urea formed
• State that carbon dioxide is excreted through the lungs
• State the place of excretion urea and excess water and salts
• Explain factors that affect that the volume and concentration of urine
produced
• Identify on drawings, diagrams and images, the ureters, bladder and
urethra
Supplement
• Describe the role of the liver in the assimilation of amino acids
• Define deamination
• Explain the need for excretion

4. • Outline the structure of the kidney, limited to the cortex, medulla and
ureter
• Outline the structure and functioning of a kidney tubule
• Explain dialysis in terms of salt balance, the maintenance of glucose
concentration and the removal of urea
• Describe the use of dialysis in kidney machines
• Discuss the advantages and disadvantages of kidney transplants,
compared with dialysis

5. LO: Define the term excretion; Explain the need for excretion
EXCRETION
• is the removal from the body of the waste products of
metabolism, toxic materials and substances in excess or
requirements
• Importance:
• To prevent the build up of waste products in tissues; these
substances would reach toxic level and destroy the tissues if
not excreted

6. LO: Name the excretory products and organs that are involved in their excretion
EXCRETORY PRODUCTS
• CO2 – carbon dioxide – product of respiration
• Made in body tissues
• Transported to lungs in the blood plasma
• Diffuses out of the blood into the air in alveoli and is breathed out
• Urea
• Made in liver from excess amino acids (digestion of proteins in small intestine)
• Carried to the kidneys in blood plasma
• It is filtered out by kidneys and leaves the body in the form of urine

7. LO: Understand the process of assimilation; Describe the role of the liver in the
assimilation of amino acids
ASSIMILATION
• Food molecules that have been absorbed now become part of the
cells or are used by the cells
• Important organ involved in assimilation = LIVER
• Regulates the level of glucose in blood – converts the glucose to glycogen and
stores it
• Uses amino acids to make proteins
• Breaks down excess amino acids, alcohol and drugs
• Converts fatty acids and glycerol into fat which is stored around the body
• Produces cholesterol

8. LO: Describe the role of the liver in the assimilation of amino acids
LIVER

10. LO: Describe the role of the liver in the assimilation of amino acids

11. LO: Describe the deamination of amino acids
DEAMINATION OF AMINO ACIDS
• Amino acids produced in digestion
of proteins cannot be stored
therefore are broken down in liver
into two parts = deamination (part
containing N – amino group is
removed)
• One molecule is converted into fat or
carobhydrate and used as a source of
energy
• The other molecule = ammonia – NH3
combines with carbon dioxide to form
UREA
• Urea is transported in the blood to the
kidneys where it is filtered out and
excreted with the urine

12. 1. Explain how each of these excretory
products are produced and removed from
the body
•Carbon dioxide
•Urea

13. 2. Distinguish between EGESTION and
EXCRETION

14. 3.Describe what happens during
deamination

17. LO: Outline the structure of the kidney, limited to the cortex, medulla and ureter
THE KIDNEYS (one pair)
• Part of urinary system
• Responsible for excretion of urea and excess water and salts from the
body = remove the toxic waste product urea from the circulating
blood – it carries out excretion
• Control the water and ion content of blood = regulate the water
content of the blood – it carries out the osmoregulation
• Blood enters kidneys through the renal arteries
• Made of millions of renal tubules

18. LO: Identify on drawings, diagrams and images, the ureters, bladder and urethra

19. LO: Identify on drawings, diagrams and images, the ureters, bladder and urethra
• Renal artery – good supply of blood at high pressure; high urea
concentration
• Renal vein – blood with lower urea concentration
• Kidneys are made of nephrons
• The ureter – exit tube, carry away the urine
• The bladder – stores the urine
• Sphincter – ring of muscles that controls the flow of urine
• Urethra – carries urine from bladder to outside

20. LO: Outline the structure of the kidney, limited to the cortex, medulla and ureter
• Renal cortex
• Brown outer area; contains
glomerulus and upper proximal
tubule; filtering of blood
• Renal medulla
• Reddish inner area; contains the
loop of Henle and collecting duct
• Renal pelvis
• A white area
• Ureter

22. LO: Describe the structure of kidney tubule
STRUCTURE OF A KIDNEY TUBULE = NEPHRON
• Glomerulus = is a network (tuft) of
capillaries that performs the first
step of filtering blood
• Bowman capsule = The glomerulus
is surrounded by Bowman’s
capsule.
• The blood plasma is filtered
through the capillaries of the
glomerulus into the Bowman's
capsule under high pressure =
ultrafiltration

23. LO: Describe the structure of kidney tubule; Outline the structure and functioning of
a kidney tubule
• First coiled tubule = useful
molecules plus most of water
are selectively reabsorbed into
the blood
• Loop of Henlé = alters salt
concentrations in the medulla to
aid reabsorbtion of water from
the collecting duct

24. LO: Describe the structure of kidney tubule; Outline the structure and functioning of
a kidney tubule
• Collecting duct = kidney can
reabsorb water from here and
return it to the blood according
to the body’s demands, under
the influence of anti-diuretic
hormone (ADH)
• Branch of renal vein = blood
containing useful molecules and
water but cleared of wastes is
now returned to the circulation

26. LO: Define the term reabsorbtion
REABSORBTION
• All of the glucose, salts and much of the water are needed by the body –
they are reabsorbed from the kidney tubule; active transport involved
• Cells in the lining of tubules contain:
• Microvilli – to increase the surface area
• Numerous mitochondria to provide energy for active transport
• After reabsorbion – urea and excess salts dissolve in water, as it passes
through the tubule some water is reabsorbed if the body is low in water
• The fluid that enters the collecting dusts = URINE - Flows down the
collecting duct to the ureter and bladder where it’s stored
• Blood leaving kidney in the renal vein has a much lower concentration of
waste chemicals

27. LO: Explain dialysis in terms of salt balance, the maintenance of glucose
concentration and the removal of urea
OSMOREGULATION
• The control of the amount of water that is returned to the blood and
balancing it with the amount of water taken in in the diet and the
amount of water lost from the body by other means
= control of water balance
• Controlled by antidiuretic hormone

28. LO: Describe the use of dialysis in kidney machines
DIALYSIS
• Nephrons stop working efficiently
• Body cannot control the composition and amount of urine
• Can lead to death if not corrected
• Dialysis = using kidney machine
• Kidney transplant

30. LO: Discuss the advantages and disadvantages of kidney transplants, compared with
dialysis
Kidney transplant
• Surgically transferring a healthy
kidney from one person – the
donor, to a person with kidney
failure – the recipient
• Tissue rejection – the recipient’s
immune system will attack the
donor kidney and slowly destroy it
unless the recipient takes drugs to
stop this happening
• Advantages: in the long term, a
transplant is much cheaper; the
patients life is less disrupted

31. 1.Describe what happens in
kidney tubules to form urine

32. 2. Label the diagram

33. 3. Explain why the presence
of protein in the urine may
indicate the kidney
damage