rem erythropoetin is not stimulated by loss of blood but instead by loss of circulating oxygen carrying capacity

• a) List the causes of release of erythropoietin by the kidneys.

Typical triggers of erythropoietin include:

being at altitude, loss of red blood cells due to haemorrhage or excessive red blood cell destruction and increased tissue oxygen demands.

• b) List the functions of erythropoietin.

the function is to inc oxygen carrying capacity of blood Circulating Circulating erythropoietin stimulates bone marrow cells that are committed to becoming red blood cells. As a consequence, the reticulocyte (young red blood cell) levels in the blood rise rapidly one or two days after a haemorrhage.

• c) Describe how chronic renal failure affects the release of erythropoietin and what the consequence of this is.

As chronic renal failure progresses, the scarring that occurs leads to a decrease in functioning cells and a drop in the release of erythropoietin. As a consequence, there is a reduced capacity of the blood to carry oxygen and the patient may present with lethargy as a result of anaemia. Synthetic erythropoietin is now used in therapy to counter these effects.

• d) Describe how low levels of erythropoietin are treated in chronic renal failure.

Synthetic erythropoietin is now used in therapy to counter these effects.

• e) List the main actions of calcitriol (1,25-dihydroxycholecalciferol).

Calcitriol is produced by hydrolyzation of vitamin D firstly into 25-hydroxycholecalciferol which the kidneys then add a further hydroxyl group to - to produce 1,25-Hydroxycholecalciferol also known as calcitriol

stimulation of calcium absorption It does so by increasing the expression of calcium channels used to transport calcium across the cell membrane of the intestinal mucosa. Phosphate absorption is also increased. In addition, there is stimulation of calcification of bone matrix, partly as a result of increased calcium and phosphate levels in the plasma, but also by direct stimulation of osteoblasts and osteoclasts, facilitating the remodelling of bone.