Question

1. Know how why EPO would be released, where its released from and what it does at its target site (production of RBCs to aid in O2 levels).

2. Be able to graph a neuronal action potential and show where the 2 phases are on the graph, the names of those phases and where the channels open or close on the graph. Also, are the ions flowing into or out of the cell.

Answer 1

Erythropoietin is a hormone which regulate the process of erythropoiesis. It is a glycoprotein mainly produced by the juxtaglomerular apparatus of kidney. Whenever there is hypoxia or decrease in the number of RBCs (eg after hemorrhage or in hemolytic anaemia) there occurs a release of renal erythropoietic factor from the juxtaglomerular cells of kidney. Renal erythropoietic factor acts on the plasma Alpha globulin called erythropoietinogen to form the erythropoietin. Thus the levels of erythropoietin vary with the degree of hypoxia or number of circulating RBC. This explains how polycythemia is observed in the hypoxic states such as in normal individuals residing at high altitude or in the patients suffering from cardiopulmonary disorder. Actions: erythropoietin increases erythropoiesis by acting at the site of erythropoiesis (it may be yolk sac, liver, spleen and bone marrow depending upon the age). It also promotes every stage of maturation from pronormoblast to mature red cells. (Hemocytoblast, pronormoblast, early normoblast, intermediate normoblast, late normoblast, reticulocyte, mature RBC). Erythropoietin promotes erythropoiesis because of its following actions-

• Erythropoietin exerts its chief effect on the hemocytoblast causing them to differentiate.
• It promotes hemoglobin synthesis by increasing globin synthesis and potentiating delta-amino levulinic acid synthetase.
• It also promotes every stage of maturation from pronormoblast to the mature red cells.
• erythropoietin also promotes release of RBC from bone marrow into the peripheral circulation.

As the RBCs have Hemoglobin which functions to carry oxygen to the peripheral tissues, therefore Erythropoietin promotes the Oxygen Transport so that the levels of pO2 doesn't go down and tissuea don't undergo hypoxia.

The action potential has two major phases called Depolarization (Na channels open and there is rapid influx of Na ions into the cell.) and Repolarization (Na channels close and K channels open and there is movement of K ions out of the cell efflux).