Excretion: Answers

Which organs of the human body are involved in excretion?

Excretion is the removal of carbon dioxide and water produced by our body from respiration. The lungs, skin and bladder are all organs involved in the removal of these products through exhalation, sweating and urination respectively.

List the substances which move out of the glomerulus and into the nephron tubule during ultrafiltration.

During ultrafiltration, high pressure forces small molecules out of the bloodstream and into the Bowman’s capsule of the nephron. Glucose, water, salts and urea are all small enough to pass through the pores of the capillaries and can enter the nephron tubule. Larger molecules, such as proteins and blood cells, are too big to squeeze through the gaps in the blood vessels so these stay in the bloodstream.

What type of blood vessels are found in the glomerulus?

The type of blood vessel found in the glomerulus are capillaries. These vessels are very small (sometimes only a single cell thick) which allows substances to pass out of them easily.

Why is there no glucose in urine?

Even though glucose enters the kidney during ultrafiltration, it is then all reabsorbed back into the bloodstream. This process is called selective reabsorption and happens in the proximal convoluted tubule. It involves active transport to ensure every glucose molecule is returned back to the bloodstream.

On a hot day there is less water in urine. Explain how the kidney is able to reduce the water content of urine produced on a hot day.

On a hot day we lose more water in our sweat, reducing the water levels in our blood. Our brain detects the low water levels and responds by secreting a hormone from the pituitary gland. This hormone is called anti-diuretic hormone (ADH) which travels to the kidneys. It makes the walls of the collecting duct (the last part of the nephron) more permeable so that more water is able to leak out of the kidney and return to the bloodstream. This increases the amount of water in our blood and makes the urine more concentrated.

Compare the disadvantages of the different types of treatment for someone with kidney failure.

Someone with kidney failure can be treated by dialysis or with a kidney transplant. Dialysis treatment requires the patient to be connected to a dialysis machine for long periods of time, several times a week and the individual has to adhere to a strict diet. If a patient undergoes a kidney transplant, there is a risk that their body may reject the kidney. They may be given immunosuppressant drugs to prevent rejection but then this leaves them vulnerable to catching other diseases, as their immune system is suppressed.

Kidney failure can be treated by transplanting a healthy donor kidney into the patient. The procedure involves connecting two blood vessels and a tube to the transplanted kidney. Name the two blood vessels and the tube.

The blood vessels that take blood towards and away from the kidney are the renal artery and renal vein. The tube is called the ureter, which connects the kidney to the bladder.