Blood Vessels and Systemic arterial blood pressure Flashcards
Recognize that if the volume of blood in arteries does not decrease but is normal and constant, then there will be sufficient blood pressure to ensure adequate perfusion of tissues. This is particularly important for tissues such as (1) muscle tissue of the heart wall and (2) nerve tissue in the brain that have a continuous high requirement for nutrients and oxygen. On the other hand, recognize that the volume of blood in arteries should not increase as the pressure would then increase. Increased pressure of blood increases the risk of arteries bursting.
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Describe what is meant by peripheral resistance (vascular resistance), mentioning diameter of arterioles, hematocrit and viscosity.
Friction blood encounters as it passes through a vessel
(the more resistance, the more pressure you need to pump blood)
Blood viscosity- increased viscosity = increased resistance
Blood vessel length- The longer the vessel, the greater the resistance
Blood vessel diameter- The larger the diameter,
the less the resistance
- When blood encounters an abrupt change in vessel diameter or a rough tube wall, blood flow becomes turbulent which increases resistance
Given a change in cardiac output state the changes in volume of blood in arteries and so the change in blood pressure.
Blood flow= Volume of blood flowing through a vessel, organ or circulatory system in a specified time period
Measured in ml/min
Overall blood flow is relatively constant but may increase or decrease in certain organs depending on their needs
Blood flow = Cardiac Output (CO)
Given a change in peripheral resistance (increase in diameter of arterioles or decrease in hematocrit, for example) predict the effect on the volume of blood in arteries and so the effect on blood pressure.
increase in diameter of arterioles: decrease resistance
decrease in hematocrit: decrease resistance
decrease in resistance = decrease bp
increase in resistance = increase in bp
Describe what is meant by venous return. And indicate the effect on venous return of a change in any one of the following
depth of breathing
activity of skeletal muscles generally (skeletal muscle pump)
decrease in diameter of veins (caused by increased sympathetic activity).
flow of blood back to heart
depth of breathing: abdominal pressure increases (due to diaphragm moving down) this pushes blood towards the heart
activity of skeletal muscles generally (skeletal muscle pump): contract and relax and push blood past valves so it cannot flow back. if damaged would allow blood to flow back
decrease in diameter of veins (caused by increased sympathetic activity): Sympathetic venoconstriction- under sympathetic control, veins constrict which increases venous return
Given a change in venous return, predict the effect on arterial blood pressure. Mention end-diastolic volume, stroke volume and cardiac output.
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Describe baroreceptor reflexes that help to keep systemic arterial blood pressure constant. Mention baroreceptors (pressure receptors), carotid sinus, aortic arch and cardiovascular center, sympathetic and parasympathetic neurons. Recognize that sympathetic activity plays the major role in maintaining blood pressure because it affects not only the heart but blood vessels, also.
Baroreceptors are stretch receptors located in the carotid sinuses, aortic arch and in the walls of nearly every large artery of the neck and thorax
- detect changes in blood pressure
- Signals medulla in brainstem
3 layers typically form the wall of a blood vessel?
Tunica intima- inner layer (contains endothelium which is simple squamous epithelial that lines lumen)
Tunica media- made of smooth muscle + elastin. * nervous system controls this smooth muscle layer for vasoconstriction & vasodilation
Tunica externa- protects and reinforces the vessel & anchors it to surrounding tissue
Arteries?
Blood leaves heart via arteries
Walls are thick, strong and elastic to accomodate changes in blood pressure (caused by being close to heart & pumping action)
Blood is forced into them and they then recoil passively as blood flows off into the circulation
Branch off into arterioles
Elastic arteries?
thick-walled arteries near the heart (aorta & major branches).
Very elastic (like elastic tubes), large lumens (1-2.5 cm in diameter), conduct blood to medium-sized arteries
Expand and recoil as heart ejects blood .: highest bp
muscular arteries?
distribute blood to specific body organs. Diameter ranges from 1mm to 1cm.
- They have a thick smooth muscle layer in tunica media which makes them important in vasoconstriction.
- Not as elastic as elastic arteries
Arterioles?
Lumen diameter of 10 µm to 1 mm.
Less elastic, tunica media is mostly smooth muscle which allows for vasodilation/vasoconstriction.
Neural, hormonal and chemical controls determine arteriolar diameter which in turn controls blood flow to the capillary bed
- When arterioles constrict->tissues are largely bypassed
- When arterioles dilate -> blood flow into the capillaries increases dramatically
Capillaries?
Blood is brought to capillaries through arterioles and blood is drained from capillaries through venules
Thin walled made of squamous epithelial cells that allow for diffusion of Oxygen, CO2, nutrients and wastes between blood and tissues
blood travels slowly to allow gas exchange
continuous capillaries?
found in most tissues
continuous ring of epithelial cells.
gas/nutrient exchange
fenestrated capillaries?
permeable to water + solutes
has pores
found in tissues that have fluid exchange (kidneys, endocrine glands, intestine)
