The excretory system
When your cells use nutrients and oxygen, they also produce waste substances that cannot be left in the blood. The excretory system is responsible for cleaning the blood, filtering it over and over again throughout the day.
The urinary system: organs and the path of urine
You drink around two litres of water a day and your cells constantly release waste into the blood, yet the volume of fluid in your body stays stable and you do not poison yourself. Which organs make up the circuit that cleans your blood without ever stopping, and which route do those waste products take to leave your body?
Name in order the structures of the excretory system through which urine passes from the moment it is formed in the kidney until it leaves the body, and state which of…
Name in order the structures of the excretory system through which urine passes from the moment it is formed in the kidney until it leaves the body, and state which of them temporarily stores it.
Name the four organs of the urinary system and state which of them filters the blood and which one expels urine to the outside.
Name the four organs of the urinary system and state which of them filters the blood and which one expels urine to the outside.
Relate the excretory and circulatory systems: explain why excretion requires a continuous blood supply to the kidneys and what would happen if a renal artery were…
Relate the excretory and circulatory systems: explain why excretion requires a continuous blood supply to the kidneys and what would happen if a renal artery were blocked.
The nephron: filtration and reabsorption
In the diagram of a nephron, several structures have been labelled. Write the name of the structures labelled with letters A, B, and C, and briefly explain what happens…
In the diagram of a nephron, several structures have been labelled. Write the name of the structures labelled with letters A, B, and C, and briefly explain what happens in each during urine formation.
Explain what a nephron is and why it is said to be the functional unit of the kidney.
Explain what a nephron is and why it is said to be the functional unit of the kidney.
Describe the two major processes that take place in the nephron to produce urine (filtration and reabsorption), and explain what happens to the blood and to useful…
Describe the two major processes that take place in the nephron to produce urine (filtration and reabsorption), and explain what happens to the blood and to useful substances in each of them.
What is eliminated and what is recovered
In a medical test of a healthy person, the blood contains about $1\ \text{g}$ of glucose per litre and plenty of proteins, whereas in their urine the amount of both is $0\ \text{g}$ and the urea is highly concentrated. How do the kidneys manage to select so precisely which molecules stay in and which are thrown away?
Explain which substances are mainly eliminated in urine and where these substances come from within our body.
Explain which substances are mainly eliminated in urine and where these substances come from within our body.
Urea is one of the waste substances eliminated in urine. Explain where this substance comes from inside our body and why it is necessary to eliminate it.
Urea is one of the waste substances eliminated in urine. Explain where this substance comes from inside our body and why it is necessary to eliminate it.
The fluid filtered at the start of the nephron contains water, salts, glucose, amino acids and urea; the final urine contains mainly water, salts and urea. Compare both…
The fluid filtered at the start of the nephron contains water, salts, glucose, amino acids and urea; the final urine contains mainly water, salts and urea. Compare both compositions and explain which process in the nephron causes the differences and why it is beneficial that it occurs.
Excretion and the body's balance
Besides the kidneys, other organs eliminate substances from the body. State what the lungs eliminate and what the skin eliminates, and explain why they are also said to…
Besides the kidneys, other organs eliminate substances from the body. State what the lungs eliminate and what the skin eliminates, and explain why they are also said to take part in excretion.
A person drinks little water on a hot day and notices that their urine is sparse and dark in colour. Explain, taking into account the function of the kidneys, why the…
A person drinks little water on a hot day and notices that their urine is sparse and dark in colour. Explain, taking into account the function of the kidneys, why the volume and colour of the urine change and what the body is trying to keep constant.
In a clinic, hemodialysis is performed on a patient with kidney failure by connecting their blood through a semipermeable membrane to a circuit containing dialysis…
In a clinic, hemodialysis is performed on a patient with kidney failure by connecting their blood through a semipermeable membrane to a circuit containing dialysis fluid.
- a) Justify what urea concentration the dialysis fluid should initially have (zero, or similar to the patient's blood?) so that urea moves out of the body. Predict what would happen if, by mistake, a fluid with a higher urea concentration than that of the patient were introduced.
- b) A classmate says: "The dialysis machine and a transplanted kidney do exactly the same thing, so in terms of health it makes no difference whether you are connected to the machine for life or receive a transplant". Refute this statement by explaining two fundamental limitations of dialysis compared to the complete, continuous activity of a healthy transplanted kidney.