Download Ch. 11 Notes ch._11_notes

Cardiovascular System: Blood vessels
As the heart beats, blood is propelled into the large arteries leaving the heart.
It moves to successively smaller and smaller arteries.
Then to arterioles which feed the capillary beds in the tissues.
Capillary beds are drained by venules which in turn empty in to veins that finally enter
into the great veins entering the heart.
Only the tiny hair-like capillaries, which extend and branch through the tissues and
connect the smallest arteries (arterioles) to the smallest veins (venules), directly serve the
needs of the body cells. It is only through their walls that exchanges between the tissue
cells and the blood can occur.
The walls of blood vessels have 3 coats, or tunics.
Tunica intima: lines the lumen or interior of the vessels. (Endothelium)
Tunica media: Bulky middle coat. Mostly smooth muscle and elastic tissue. The smooth
muscle is controlled by the sympathetic nervous system, is active in changing the
diameter of the vessels.
Vasoconstriction: BP Increases
Vasodilation: BP decreases
Tunica externa: outermost tunic.
Composed mostly of fibrous connective tissue
Supports and protects vessels
Artery walls are much thicker than those of veins.
Pressure is low in veins and flow back to heart is usually against gravity- so veins have larger
lumens and the larger veins have valves that prevent backflow of blood.
Capillaries are only one cell layer thick, just the tunica intima. Because of this thinness
exchanges are made easily.
Pulse: Alternating expansion and recoil of an artery that occurs with each beat of the left
ventricle, creates a pressure wave that travels through the entire arterial system.
 Pulse averages 70-76 beats/min. in normal resting person.
Blood Pressure: The pressure the blood exerts against the inner walls of the blood vessels, and it
is the force that keeps blood circulating continuously even between heart beats.
 If a vein is cut blood flows evenly from the wound
 A lacerated artery produces rapid spurts of blood
Systolic Pressure: Pressure in arteries at the peak of ventricular contraction.
Diastolic Pressure: Pressure when the ventricles are relaxing.
Auscultatory Method: Measures BP in brachial artery
Figure: 11.17
Peripheral Resistance: amount of friction encountered by the blood as it flows through the
blood vessels.
Effects on peripheral resistance:
Sympathetic nervous system activity
Atherosclerosis
^ blood volume or viscocity
Effects on BP
Age
Weight
Time of day
Exercise
Body position
Emotional
Various drugs etc.