1 of 24© Boardworks Ltd 2009 Urine for a Great Time!!!

1 of 24 © Boardworks Ltd 2009

Urine for a Great Time!!!



Waste removal

The lungs remove carbon dioxide.

The liver converts excess protein into urea.

The kidneys remove unwanted substances such as urea, excess water and salt.

Several organs are important in removing waste from the body.

The skin provides a surface for small amounts of water and salt to move out of the body.


What is urea?

Excess amino acids in the body are broken down by the liver, producing a waste substance called urea.

Once formed, urea is transported by the circulatory system to the kidneys.

The kidneys filter the blood, removing urea and excess water and salt, which forms urine. Urine is stored in the bladder before being excreted from the body.

This process is important because it converts toxic ammonia to urea, which is done using carbon dioxide.


What are the different parts of a kidney?


How does the kidney work?


Stages in the nephron


Controlling water levels

Osmoregulation is the process by which organisms regulate the water content of the body.

Mammals need to ensure the volume of blood plasma and concentration of dissolved substances in the blood and tissue fluid stay relatively constant.

Osmoreceptors in the hypothalamus monitor the water potential of the blood. This varies the amount of antidiuretic hormone (ADH) released into the bloodstream. The kidneys respond to a change in ADH concentration by adjusting the volume and concentration of the urine.


Osmoregulation

normal water potential of blood

increase in water potential

decrease in water potential

change detected by osmoreceptors in the hypothalamus

change detected by osmoreceptors in the hypothalamus

pituitary gland releases less ADH

pituitary gland releases more ADH

ADH increases permeability of collecting ducts

concentrated urine

decrease in permeability of collecting ducts

dilute urine

must expel excess water

must conserve water


Controlling water content


Analysing urine

Changes in the color, clarity, pH and the presence of certain substances in urine can help doctors diagnose medical conditions:

Protein or red blood cells in urine can indicate kidney damage or disease, as these substances would not normally filter through the glomerulus.

Glucose in urine is often an indication of diabetes. A person with diabetes will have a high level of glucose in the blood.



What happens if the kidneys fail?

Kidney failure can occur due to infection, diabetes, long-term high blood pressure or damage in an accident. If left untreated, urea and other toxins can build up in the blood, poisoning the patient.

Humans can survive with just one functioning kidney. If both kidneys become diseased or damaged, it can be fatal.

To counteract this, people with kidney failure can undergo regular kidney dialysis, or receive a kidney transplant.


What is dialysis?

What happens during kidney dialysis?

1. A tube is connected to a vein in the patient’s arm.

Dialysis involves diverting the blood through an 'artificial kidney' machine that cleans it and returns it to the body.

2. The patient’s blood flows along the tube, into the machine.

3. Inside the machine, the blood is pumped through semi-permeable tubes surrounded by dialysis fluid. Dialysis fluid contains sodium, magnesium, calcium chloride and potassium chloride and sodium acetate, in the sameconcentrations as the blood plasma of a healthy person.


Dialysis machine


Disadvantages of dialysis

Dialysis can involve a patient going to hospital up to three times a week and being connected up to the dialyser for about four hours at a time. This could have a large impact on a person’s lifestyle.

It is difficult to control the diffusion of substances in a dialysis machine as well as in a kidney so people on dialysis often have to carefully control their fluid intake and diet.



What is a kidney transplant?

Kidney failure can also be treated by giving a patient a kidney transplant. This involves replacing the damaged kidney with a healthy kidney from a donor.

Healthy organs can come from a living or recently deceased person. Living donors are often close friends or relatives of the patient.

In the US there is an organ donor register. By joining this people agree to the donation of their organs and tissue for transplantation after their death.

Other organs and tissues that can be donated include blood, bone marrow, heart, lungs and cornea.


Kidney transplant data


Preventing organ rejection

If the immune system detects a transplanted organ as a foreign object, it may mount an immune response against it. This is called organ rejection. Several steps are taken to prevent this:

A donor kidney of a similar ‘tissue type’ as the patient, is used. This means that the antigens on the new organ will be as similar as possible to those of the patient.

All cells contain markers on the surface, called antigens. These help the immune system identify a cell as a cell from the body or a foreign cell.

Before and after a transplant operation, a patient takes immunosuppressant drugs. These drugs inhibit the activity of the immune system.


Problems relating to transplants

However, a transplant operation can put the body under a lot of strain and there is potential for problems related to surgery.

A kidney transplant can give a patient a better quality of life, as it provides freedom from dialysis.

Immunosuppressant drugs lower a patients resistance to infection and can make infections hard to treat.

Blood tests are regularly carried out to make sure that the organ is functioning and to monitor the effect of the immunosuppressant drugs.


What do you think?



Labelling the kidney

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