Biology 201 Dr. Edwin DeMont St. Francis Xavier University Circulation

St. Francis Xavier University Circulation The evolution of multicellularity required the development of fluid transport systems. Why?

St. Francis Xavier University Circulation An internal transport system is useful because it reduces the distances over which substances must diffuse—substances can be brought close to a target point via the blood and then diffuse outward from that point

St. Francis Xavier University Circulatory Systems Internal transport systems of invertebrates range from simple fluid filled cavities to open systems and some even have closed systems, analogous to vertebrate systems. Open circulatory system: the heart pumps fluid out into the body cavity or at least to parts of the body cavity, and bathes the cells, tissues and organs. Closed circulatory system: fluid circulates in the confines of tubular vessels.

St. Francis Xavier University Transport Systems

St. Francis Xavier University Transport Systems

St. Francis Xavier University Circulatory Systems Fluid: HemolymphHigh volume and slow circulation Cells: Hemocytes

St. Francis Xavier University Circulatory Systems Blood is always in arteries, arterioles, capillaries, venules, veins, or within the chambers of the heart.

St. Francis Xavier University Fluid flow Heart generates high pressure. Blood moves at high velocity. Total cross-sectional area of capillaries is large and velocity of flow is very small. Diffusion occurs here so need low velocity. Best to move blood over large distances in large vessels.

St. Francis Xavier University Vertebrates The disadvantage of this system is the low pressure flow through the gills supports only a low metabolic rate. Energy is lost as the blood flows through the capillaries – why?

St. Francis Xavier University Vertebrates A double circuit occurs when blood from the lungs is sent directly to the heart, and blood from the tissues also goes to the heart— these systems are the pulmonary and systemic circulations, respectively

St. Francis Xavier University Blood vessels Arteries are characterized as elastic vessels that carry blood away from the heart (high pressure). Veins are larger, less elastic vessels that carry blood to the heart (low pressure). Capillaries are one cell layer thick – to allow diffusion.

St. Francis Xavier University Blood Blood contains a fluid matrix called plasma and cellular elements called formed elements. Plasma is primarily composed of water, and also contains proteins, ions, hormones, nutrients, and wastes.

St. Francis Xavier University Blood: Formed elements Erythrocytes (red blood cells) contain hemoglobin, which binds to oxygen for transport from lungs to other tissues. Leukocytes (white blood cells). These cells function in immunity. Thrombocytes (platelets). They function in clotting of the blood in response to injury.

St. Francis Xavier University Red Blood Cells Each cell has about 280 million molecules of hemoglobin. The biconcave shape of RBCs is adaptive, as it gives 30% more surface area than a sphere. RBCs are slightly larger than capillaries and have to squeeze through the tiny capillaries. This is adaptive. Why?