Chapter 18- The Blood Vessels Flashcards
What are the two circuits that that carry blood through the body?
Systemic and pulmonary circuits
Describe arteries
Distribution functions
Carry blood away from the heart to the lungs and other extremities to distribute oxygenated and deoxygenated blood
Describe capillaries
Smallest vessels act as an exchange system in tissues for oxygen and CO2
Branching networks called capillary beds
Describe veins
Collect blood from the lungs and other tissues to return it to the heart
Drain blood from capillary beds
Become larger as they approach the heart
What is the lumen?
Central space within blood vessels
What are the three tunics of blood vessel walls?
Tunica intima
Tunica media
Tunica externa
What is the tunica intima composed of?
Endothelium
What are the two layers of the tunica media?
Smooth muscle
External elastic lamina
What does the smooth muscle of the blood vessels control?
Vessel diameter and therefore the amount of blood flowing to the organs
What innervate the smooth muscle of the vessel walls?
Sympathetic nervous system
Vasomotor nerves
What is vasoconstriction?
When the smooth muscle contracts to narrow the opening of the lumen and restrict blood flow
Raises BP
What is vasodilation?
When the smooth muscles relax and the lumen diameter widens allowing blood to flow freely
Lowers BP
What is the tunica externa composed of?
Dense irregular collagenous connective tissue
Supports vessel and prevents overstretching
What are the two big differences between a typical artery wall and the wall of a typical vein?
Arteries have a thicker tunica media
Internal and external lamina are more extensive in arteries
What are the different size arteries in order from largest to smallest in diameter?
Elastic arteries
Muscular arteries
Arterioles
Metarterioles
Which vessels directly feed the capillary beds?
Metarterioles
What do baroreceptors do?
Detect blood oxygen, CO2 and hydrogen ion concentration in the aorta and common carotid artery
Characteristics of veins
Outnumber arteries
Larger lumens
Function as blood reservoirs
Can be diverted to other parts of the body because they have thinner walls, fewer elastic fibers, less smooth muscle
What are the smallest veins called?
Venules
Thin tunica media
What prevents blood from flowing backward in the venous circuit?
Venous valves
What are vascular anastomoses?
Locations where vessels connect via pathways called collateral vessels
What is hemodynamics?
Physiology of blood flow in the cardiovascular system
What is blood pressure and in which vessels is it highest and lowest?
The outward force exerted by blood on the walls of blood vessels
Highest in the large systemic arteries and lowest in the large systemic veins
What is the main factor that determines blood flow?
The magnitude of the blood pressure gradient
What is blood flow?
The volume of blood that flows per minute
Matches cardiac output
Directly proportionate to the pressure gradient: blood flow increases when the pressure gradient increases and vice versa
What is resistance?
Any impedance to blood flow
Blood flow is inversely proportionate to resistance: when resistance increases, blood flow decreases
What effect does cross sectional area have on blood flow? Where is it highest?
Cross sectional area is highest in the small vessel branches as they split off from the larger vessels
As this area increases, the velocity of blood flow decreases. Blood flow is fastest in the aorta and slowest in the capillaries
Factors that determine blood pressure
Resistance
Cardiac output
Blood volume
What is peripheral resistance?
Any factors that slow blood flow through the vessels
As resistance increases, BP increases
Variables that contribute to resistance
Vessel radius
Viscosity
Vessel length
What is cardiac output?
The amount of blood the heart pumps through the circulatory system in one minute
What is cardiac output the result of?
Stroke volume X heart rate
2 factors that determine the pressure gradient that drives circulation
Cardiac output
Peripheral resistance
DeltaP= CO x PR
Final major factor that determines overall blood pressure
Volume of blood in circulation
What is total blood volume directly linked to?
The amount of water in the blood
More water= higher blood volume
What is compliance? Which vessels are most compliant?
Ability of vessels to stretch due to small increases of blood volume
Veins
What are the average blood pressures in the pulmonary and systemic circuits?
Pulmonary= 15mmHg Systemic= 95mmHg
What is ventricular systole?
What is average systolic pressure?
Period of contraction in the heart
120 mmHg
What is ventricular diastole? What is average diastolic pressure?
Period of relaxation in the heart
80mmHg
What is pulse pressure?
The different between the systolic and diastolic pressure, about 40mmHg
What is the name of the tool used to take blood pressure?
Sphygmomanometer
What is mean arterial pressure (MAP)? How is it measured?
Average pressure on a patients arteries during one cardiac cycle
MAP= diastolic pressure+1/3(pulse pressure)
Typically maintained at 95mmHg
What is systemic capillary pressure? Why does it happen?
The drop in pressure between the arteriolar and ventilate ends of the capillary beds. About 35mmHg to 15mmHg
Reduction in blood volume from fluid loss
What accounts for the extremely low pressure in the inferior vena cava and right atrium?
The high compliance of veins and reduction in pressure as the veins grow larger as they get nearer the heart
Ways in which the rate of venous return is increased
Skeletal muscle pump
Respiratory pump
Valves
What immediate effects does the sympathetic nervous system have on blood pressure? How?
Releases epinephrine and norepinephrine onto cardiac cells to increase heart rate and cardiac output as well as vasoconstriction which increases resistance
What immediate effects does the parasympathetic nervous system have on blood pressure? How?
Acetylcholine released onto pacemaker cells decreases heart rate which decreases cardiac output
What is the baroreceptor reflex?
Negative feedback loop that senses increase and decreases in blood pressure
Stretch receptors that respond to the pressure induced stretching of the vessels in which they are found
What do we call abnormally high blood pressure?
Hypertension
