Final answer:
Blood viscosity and osmolarity increase in response to a higher concentration of erythrocytes and plasma proteins. Erythrocytes are the major blood cells affecting viscosity, while plasma proteins affect both viscosity and osmolarity.
Step-by-step explanation:
Viscosity and osmolarity will both increase if the amount of erythrocytes and protein in the blood increases. Blood viscosity is directly affected by the number of formed elements, primarily erythrocytes, and the amount of plasma proteins. Blood becomes more viscous, for instance, when there is an overproduction of erythrocytes, a condition known as polycythemia, or when there is an excessive intake of synthetic erythropoietin (EPO), commonly done to enhance athletic performance. Similarly, plasma proteins, largely produced by the liver, contribute to both viscosity and osmolarity. Conditions like liver disease, which lead to decreased production of plasma proteins, can decrease blood viscosity.
Osmolarity is influenced by plasma proteins because they are suspended in their fluid medium, forming a colloid rather than a solution, and create a colloidal osmotic pressure. Hence, an increase in plasma protein concentration can also lead to an increase in osmolarity. Conversely, when plasma protein levels fall, for example due to kidney disease which causes protein loss in urine, the blood's osmolarity can decrease, potentially leading to widespread edema or other serious conditions.