Chapter 17, Section 2 A Closer Look at Blood Vessels Tuesday, March 16, 2010 Pages

Objectives Describe the functions of the arteries, capillaries, and veins. Identify the cause of blood pressure.

Vocabulary Words Coronary artery Diffusion Pressure Blood pressure sphygmomanometer

Arteries Blood leaving the heart travels through arteries. Every organ receives blood from arteries that branch off the aorta. The first branches are called coronary arteries.

Coronary Arteries -- cont’d Other branches carry blood to the brain, intestines, and other organs. Each artery branches into smaller and smaller arteries.

Artery Structure Arterial walls are generally very thick. Arterial walls are made up of three layers. –EPITHELIAL: innermost layer; smooth. –MUSCULAR: middle layer. –CONNECTIVE: outer layer; flexible. Structure is both strong and flexible.

Pulse Your pulse is caused by the alternating expansion and relaxation of the artery wall. The number of artery pulses = the number of heartbeats.

Regulating Blood Flow Arterial muscles are involuntary -- they contract without your thinking about it. At contraction, the arterial opening becomes smaller. When relaxed, the arterial opening becomes larger. These muscles act like control gates and adjusts the amount of blood to different organs.

Capillaries Capillaries are where materials are exchanged between blood and the body’s cells. Capillary walls are one cell thick (thin). Allows passage of oxygen and glucose to pass easily from blood to cells. Cellular wastes travels in the opposite direction from cells to the blood (diffusion).

Capillaries -- cont’d Materials that are exchanged between the blood and the body’s cells happens through diffusion.

Veins Larger blood vessels called are called veins. Veins carry blood back to the heart. Walls of the vein have three layers (like arteries with the muscle layer in the middle), but are thinner.

Veins -- cont’d Factors that move blood through the veins include: –Contraction of muscles Example: your skeletal muscles contract and squeeze the veins in your legs. –Larger veins have valves that prevent blood from flowing backward. –Breathing movements exert a squeezing pressure against veins in the chest that forces blood toward the heart.

Blood Pressure It is the pressure that is exerted by the flow of blood against the walls of the blood vessels. It is caused by the force with which the ventricles contract. As blood moves away from the heart, the pressure decreases. Blood flowing through arteries exerts the highest pressure. Blood pressure in capillaries and veins is much lower than in arteries.

Blood Pressure -- cont’d Blood pressure is measured by an instrument called a sphygmomanometer. The first number recorded (the higher of the 2), is a measure of blood pressure while the ventricles contract and pump blood into the arteries. The 2nd number measures the blood pressure while the ventricles relax between heartbeats. Typical for a young adult is 120/80.

Homework Workbook 17.2 (3/18) Vocabulary qui 17.2 (3/18)