AlexMccourt The Student Room Biology Notes Essay

1881 Words Dec 20th, 2013 8 Pages
F214 Communication, Homeostasis and Energy
Module 2 Excretion
4.2.1 Excretion
a. Define the term excretion
Excretion-The removal of metabolic waste from the body which are by products or unwanted substances from cell processes.
b. Explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste from the body
Carbon dioxide
Excess carbon dioxide is toxic and has three main effects:
The majority of carbon dioxide is carried in the blood as hydrogencarbonate ions but in the process hydrogen ions are made inside red blood cells with carbonic anhydrase. These hydrogen ions compete with oxygen for space on the haemoglobin. Therefore too much carbon dioxide can cause a reduction in oxygen
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f. Describe the histology and gross structure of the kidney

g. Describe the detailed structure of a nephron and its associated blood vessels

h. Describe and explain the production of urine, with reference to the processes of ultrafiltration and selective reabsorption
Ultrafiltration
1. Blood flows into the glomerulus from the afferent arteriole which is wider than the efferent arteriole which carries the blood away from the glomerulus.
2. This means that the blood in the capillaries is under increased pressure.
3. The blood pressure in the glomerulus is higher than in the Bowman’s capsule.
4. So fluid from the blood is pushed in the Bowman’s capsule.
5. Molecules with a higher molecular mass than 69,000 cannot get through the basement membrane so are held in the capillaries of the glomerulus. Molecules with a higher mass include most proteins and all blood cells.
6. The substances which are filtered out of the blood include: water, amino acids, glucose, urea and inorganic ions including sodium, chloride and potassium.
Selective reabsorption
1. The sodium-potassium pumps remove sodium ions from the cells in the proximal convoluted tubule. This is done via active transportation.
2. The concentration of sodium ions in the cell cytoplasm is reduced
3. Sodium ions are transported into the cell with glucose or amino acids via facilitated diffusion.
4. Glucose and amino acid concentrations increase in the cell.
5.

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