Excretion (OCR A Level Biology)

One of the main functions of the mammalian liver is the formation of urea via the ornithine cycle.

An outline of the ornithine cycle is shown below.

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If there is a problem with the ornithine cycle, the level of ammonia in the blood will rise, causing hyperammonemia.

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Keto acid is another product formed during the deamination of an amino acid. Keto acid may enter the Krebs cycle to be respired or converted into glucose.

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The table below shows the concentration of some components of blood, glomerular filtrate and urine.

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An individual's kidney function can be assessed by measuring their Glomerular Filtration Rate (GFR).

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                                 eGFR = GFR x               . 

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Kidney failure can be treated with haemodialysis.

Explain why it is important to maintain a counter-current flow of blood and dialysate throughout the dialysis process.

The image below shows a cross section of the cortex of a mammalian kidney.

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Gestational diabetes insipidus is a rare complication of pregnancy caused by excessive vasopressinase activity.

Vasopressinase is an enzyme produced by the kidney which destroys the mother’s ADH (also called vasopressin).

Suggest and explain a symptom that a mother may have as a result of gestational diabetes insipidus.

A synthetic hormone similar to vasopressin, called desmopressin can be used to treat gestational diabetes insipidus.

Suggest how desmopressin can be used to treat this disease.

Urine can be used for a variety of medical diagnoses.

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Urine can also be tested for the use of anabolic steroids in sport.

The graph below shows tests carried out by the International Olympic Committee (IOC) on athletes between 1986 and 1994.

• The bars represent the number of urine samples tested.
• The line shows the percentage of samples testing positive for elevated levels of the steroid testosterone.

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 Use data from the graph above to evaluate the following statement:

“Steroid abuse in sport has decreased since 1988”.

Fig. 22.1 is a cross-section of part of the cortex of a mammalian kidney.

Studies of the cell surface membranes of the distal convoluted tubule have provided the following evidence:

• Sodium-potassium pumps:
  • move potassium ions from the blood to the tubule fluid
  • move sodium ions from the tubule fluid to the blood
  • use ATP in these processes.
• Sodium-calcium co-transport proteins:
  • move calcium ions from the tubule fluid to the blood
  • move sodium ions into the tubule fluid
  • use the electrochemical gradient of sodium ions to drive this process.

Fig. 22.2 shows a podocyte from the kidney. The many gaps between the microscopic processes form fenestrations in the Bowman’s capsule.

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The process of ultrafiltration in the kidney shares similarities with the formation of tissue fluid.

Describe the similarities and differences between ultrafiltration and the formation of tissue fluid.

A person’s glomerular filtration rate (GFR) provides an indication of the health of their kidneys. The GFR is a measure of the volume of blood that can be filtered by the kidneys every minute.

GFR can be estimated by monitoring the blood concentration of creatinine, which is a breakdown product of creatine phosphate in muscles.

Cirrhosis of the liver can result from long-term liver damage. Alcohol or other toxins can cause this damage.

Scientists have suggested that cirrhosis can be detected by taking samples of body fluids and testing them for two different molecules: C-reactive protein and copeptin.

The liver produces these two molecules, and increased levels can indicate liver damage due to cirrhosis.

Different bodily fluids from a patient suspected of having cirrhosis were tested for C-reactive protein and copeptin.

Fig. 17.1 is a graph of the results.

Fig. 17.1

Different bodily fluids have different concentrations of the different molecules.

Answer = ................................ molecules cm^-3  [2]

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Fig. 17.2 is an image of a Kupffer cell from the liver.

Fig. 17.2

The diameter of the Kupffer cell in the image is 9.1 cm. Assuming it is spherical, calculate the actual volume of this cell. Note that a cm ruler has been added to Fig. 17.2.

Give your answer to four significant figures. Show your working.

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Fig. 17.1 is a diagram of the external view of a mammalian liver.

Fig. 17.1

Identify, with reasons, each of the blood vessels labelled A – C in Fig. 17.1.

A .........................................

B .........................................

C .........................................

One of the main functions of the liver cells is the formation of urea by the ornithine cycle, an outline of which is shown in Fig. 17.2.

Fig. 17.2

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