CHAPTER 13:
EXCRETION IN HUMANS
BIOLOGY 0610
BEFORE WE START…
What do you know about excretion?
Examples of excretion in human?
How do plants excrete their waste?
Why do we excrete?
Main organ of excretion in human?
LEARNING OBJECTIVES
13.1 EXCRETION IN HUMANS
1 State that carbon dioxide is excreted through the lungs
2 State that the kidneys excrete urea and excess water and ions
3 Identify in diagrams and images the kidneys, ureters, bladder and urethra
4 Identify in diagrams and images the structure of the kidney, limited to the cortex and medulla
5 Outline the structure and function of a nephron and its associated blood vessels, limited to: (a)
the role of the glomerulus in the filtration from the blood of water, glucose, urea and ions (b)
the role of the nephron in the reabsorption of all of the glucose, some of the ions and most of
the water back into the blood (c) the formation of urine containing urea, excess water and
excess ions
LEARNING OBJECTIVES
13.1 EXCRETION IN HUMANS
6 Describe the role of the liver in the assimilation of amino acids by converting them to proteins
7 State that urea is formed in the liver from excess amino acids
8 Describe deamination as the removal of the nitrogen-containing part of amino acids to form
urea
9 Explain the importance of excretion, limited to toxicity of urea
What are some metabolic waste products?
Carbon dioxide
•
Carbon dioxide is a product of aerobic
respiration of glucose.
•
The liver is involved in the
assimilation of amino acids.
•
Deamination is removal of the
nitrogen-containing part of amino
acids to form urea.
Urea
•
Urea is a waste product from the breakdown
of proteins.
Eating too much meat can increase the
concentration of urea in the blood.
Excess amino acids are deaminated in
the liver to form urea.
Coursebook
pg 263
Can you live without a liver?
What are some metabolic waste products?
Mineral ions
•
Excess ions in the blood can be harmful as they make the blood plasma more concentrated.​
Water
•
Excess water in the body is harmful as it causes the cell to swell and burst. How?
What is excretion?
•
The removal of metabolic waste products, toxic substances and substances that are in excess of
the body’s requirements.
Main excretory products and their excretory organs
Excreted as
Excretory products
Excretory organ
Carbon dioxide
Lungs
Gas in expired air
Excess salts or ions
Kidneys
Skin
Constituent of urine
Constituent of sweat
Excess water
Kidneys
Skin
Constituent of urine
Constituent of sweat
Urea
Kidneys
Skin
Constituent of urine
Constituent (traces) in sweat
Why is excretion important?
•
It prevents the build-up of harmful or toxic substances in our bodies.
What is the difference between
“excretion” and “egestion”?
What makes up the human urinary system?
Human urinary system
Coursebook
pg 262
Structure of a kidney
1. Nephrons are the basic functional units for
kidney. Urine is formed in the nephron.
Nephron is richly supplied with blood
capillaries, which then unite and bring
blood to the renal vein.
2. Renal artery carries blood to the kidney.
Section through a kidney showing the regions and the position of a nephron
Coursebook
pg 264
What is the structure of a nephron?
Section through a kidney showing the position of
a few kidney tubules and the blood supply
Urine is formed in the nephrons.
Nephron with its blood supply
Coursebook
pg 264
How is urine formed?
Filtration
•
Filtration is the process where small molecules (mineral ions, water, glucose, amino acids, urea) are
filtered out of the blood by the glomerulus into the renal capsule.
•
There are numerous glomeruli in the kidney and the blood capillaries are highly coiled. These
provide large surface area for filtration.
Section of a part of the glomerular blood capillary
How is urine formed?
Reabsorption
•
As filtrate passes along the nephron,
useful substances are reabsorbed into
the surrounding blood capillaries.
•
Only substances that the body needs
are reabsorbed.
•
Most of the water is reabsorbed by
osmosis
•
Some mineral ions are reabsorbed by
active transport
•
All glucose and amino acids are
reabsorbed by active transport
•The nephron have many
mitochondria to provide energy for the
active transport of glucose molecules
Overview of urine formation
Coursebook
pg 265
If one kidney fails to function, a person can
still lead a normal life with the other kidney.
However, if both kidneys fail to function, the
person will die unless prompt medical
treatment is given.
Discuss the advantages and disadvantages of these two treatments.
On the second Thursday in March each year, the world
observes World Kidney Day, a day dedicated to raising
awareness about kidney health.
Task
• In group (3 members per group), create a kidney working model.
• You’ll just be provided with plastic bottles, cups, straw & cardboard/box. The rest of the items for
decorations, labelling etc. you have to bring it on your own.