Blood Vessels, Blood Flow and Capillary Exchange

Learning Outcomes: C5 - analyze the functional interrelationships of the vessels of the circulatory system Describe and differentiate among the five types of blood vessels Relate blood pressure and blood velocity to the total cross-sectional area of the five types of blood vessels Describe capillary-tissue fluid exchange

Review: What are the 5 types of blood vessels, in the order that blood flows through them? arteries  arterioles  capillaries  venules  veins

Fig. 13.2

Flow of Blood Arteries bring oxygen- and nutrient- rich blood to all tissues of the body Arterioles branch into capillary networks in tissues At the capillaries, oxygen and nutrients leave the blood CO 2 and wastes enter the blood Capillaries flow into venules and veins

Blood Vessels and Blood Pressure Blood pressure is greatest in the arteries Decreases moving away from the heart and into smaller vessels (arterioles and capillaries) Increases again as it moves into venules and veins

Capillaries have a very large cross- sectional area, so blood pressure and velocity are very low This is where substances move between the blood and tissues Walls are very thin so substances can pass through

Fig

Capillary-Tissue Exchange At the arterial end of the capillary, blood pressure is high Water and small molecules are pushed out of the capillary into the surrounding fluid Nutrients and oxygen diffuse into surrounding cells

At the venous end, blood pressure is lower Osmotic pressure (due to salts and proteins in the blood) brings water back into the capillaries CO 2 and other cellular wastes diffuse into capillaries from tissue fluids

Fig

Excess water enters the lymph capillaries and is returned to the blood at lymphatic ducts