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Ch 15: Blood Vessels & Blood Pressure
Terms in this set (37)
blood vessels that carry blood away from the heart to organ systems for oxygen
Low amount of Endotheliium, some Elastic tissue, the most Smooth Muscle, and some Fibrous Tissue. Large Diameter
Arteries have a thick smooth muscle layer and large amounts of elastic and fibrous connective tissue.
direct distribution of blood flow to individual tissues by selectively constricting and dilating - site of variable resistance. Diameter is regulated by l ocal factors, such as tissue oxygen concentrations and by autonomic nervous system and hormones
Arteriole: Low endothelium, some smooth muscle, no elastic tissue or fibrous tissue.. Small Diameter
arterioles contract or relax under chemical signals.
some arterioles branch into vessels known as metarterioles.
precapillary sphincters are relaxed - blood flowing into metarteriole directed into capillary beds
if they are constricted, blood bypasses capillaries and flows directly to venous circulation
smallest blood vessels where oxygen, nutrients, and wastes are exchanged between the blood and the interstitial fluid
Low endothelium, no elastic tissue, smooth muscle or fibrous tissue. Smallest Diameter
their leaky epithelium allows exchange of materials between the plasma, the interstitial fluid, and the cells of the body. to facilitate exchange they lack smooth muscle, elastic or fibrous tissue reinforcement.
-more pericytes, the less leaky the capillary endothelium
small blood vessel that allows blood to return from capillaries
Low endothelium and fibrous tissue, no elastic tissue or smooth muscle. Small Diameter
blood vessels that return blood to the heart
Low Endotheliium, some Elastic tissue, Smooth Muscle, and Fibrous Tissue. Large Diameter
act as a volume reservoir from which blood can be sent to the arterial side of the circulation if blood pressure falls too low.
To assist blood flow, some veins have internal one-way valves. Ensure that blood flow cannot flow backward. When skeletal muscles compress the veins, they force blood toward the heart (skeletal muscle pump)
More numerous than arteries and have a larger diameter. Large volume, they hold more than half of the blood in the circulatory system. Veins have thinner walls than arteries, with less elastic tissue. They expand easily when they fill with blood.
Arterial compliance is stretchability of arteries
C (compliance) = ΔV (change in arterial blood volume) / ΔP (change in arterial blood pressure)
occurs when the blood vessels that carry oxygen and nutrients from your heart to the rest of body (arteries) become thick/stiff — sometimes restricting blood flow to organs & tissues
compliance - decreases
"hardening of the arteries," in which fatty deposits form inside arterial blood vessels. can restrict blood flow.
compliance - decreases
how elastic and muscular arteries act as "pressure reservoirs"
As ventricle contracts and blood ejects from ventricles flows into the arteries, Aorta and arteries expand and store pressure in elastic walls.
As ventricle relaxes, semi-lunar valves close. Elastic recoil of arteries maintains driving pressure and sends blood forward into rest of circulatory system.
4 factors affect resistance of blood vessels to flow
a) blood viscosity - blood viscosity is determined by the ratio of RBC to plasma, and by how much protein is in the plasma. Resistance increases with viscosity. Blood flow decreases.
b) resistance to flow - the tendency of the cardiovascular system to oppose blood flow. An increase in the resistance of the blood vessels results in a decrease in flow through that vessel, therefore, blood will take the path of least resistance.
c) length of vessels - the resistance to fluid flow increases as the length of the vessel increases.. blood flow decreases
d) radius - diameter increase, resistance decreases, blood flow increases
why arterial blood pressure fluctuates in relation to systole and diastole of the left ventricle
Arterial blood pressure fluctuates due to left ventricular systole and diastole. As the blood is pumped into the arteries, the pressure is at its highest, and falls slightly as the left ventricle relaxes. Distolic pressure in arteries remains high because the arteries are able to capture and store the energy in their elastic walls.
how blood volume may affect the blood pressure
Changes in blood volume will affect blood pressure, i.e. higher blood volume will increase blood pressure and vice versa. Cardiac output would fluctuate depending on an increase or decrease in blood volume.
Identify the determinants of venous pressure and how venous return of blood is enhanced during exercise
Venous pressure is considered low. Pressure has been dropped leading up to the capillaries to ensure a smooth flow for nutrient exchange. Pressure has decreased because of friction and a pressure wave no longer exists. The steady flow of blood from the capillaries helps to push the blood through the veins.
During exercise, venous blood is aided by valves, the skeletal muscle pump and the respiratory pump. Muscle contractions help push the venous blood by compressing the veins and forcing blood through the valves within the veins. Also, as your breathing increases, the diaphragm applies pressure on your liver to help propel blood through the veins. A third determinant is when the ventricles relax, they create suction, thereby pulling blood into themselves.
Be able to calculate pulse pressure (PP) and mean arterial pressure (MAP)
Pulse Pressure (PP) = SP - DP
Mean Arterial Pressure (MAP) = DP + [ (SP-DP) / 3 ]
SP = Systolic Pressure
DP = Diastolic Pressure
Example: SP = 120 DP = 80
PP = 120 - 80 ---> PP = 40 (Yay!)
MAP = 80 + (40 / 3) ---> 80 + 13 ---> MAP = 93 (Yay!)
Fun Fact! MAP will be closer to DP due to the fact that diastole lasts almost twice as long as systole.
List and describe the determinants of MAP
Blood Volume: fluid intake, and fluid loss
Cardiac output: Heart rate x Stroke volume
Resistance of the system to blood flow: Diameter of the arterioles
Relative distribution of blood between arterial and venous blood vessels: Diameter of the veins
why arterioles act as the major site of variable resistance to blood flow
Arterioles are the main site of variable resistance in the systemic circulation; contribute more than 60% of total resistance to flow in the system.
Resistance in arterioles are Variable because of the large amounts of smooth muscle in the arteriolar walls. When smooth muscle contracts or relaxes, the radius of the arterioles changes.
-arterioles constrict, resistance increases
- arterioles dilate, resistance decreases
when arterioles constrict
blood flow decreases, MAP increases
Cardiac output decreases
arterial blood vol. decreases, Map decreases
blood vol in veins decreases, volume in arteries increases, MAP increases
Explain how arterioles regulate the distribution of blood to organs as needed and how vasoconstriction affects resistance and blood flow
Blood flow to organs is set to some degree by the number and size of arterioles feeding a specific organ. Vasoconstriction of an arteriole will decrease blood flow causing an increase in resistance. This allows for the blood to divert to an arteriole with lower resistance. Blood traveling through arterioles will take the path of least resistance.
Describe local controls over variation in arteriolar resistance to blood flow: myogenic autoregulation, paracrine signals
Local (Intrinsic) controls affecting arteriolar resistance
Myogenic autoregulation is the ability for vascular smooth muscle to regulate its own state of contraction. As blood pressure increases within the arteriole, the smooth muscle fibers within the wall are stretched, and causes the wall to constrict, increases resistance thereby reducing the blood flow.
Paracrine signals can also be used to change arteriole resistance.
As an example, when aerobic metabolism increases, tissue O2 levels decrease while CO2 levels increase. Both low O2 and high CO2 dilate arterioles. This vasodilation decreases resistance and increases blood flow, bringing in more O2 and taking CO2 away. When increase in blood flow is accompanied by an increase in metabolic activity, this is known as active hyperemia.
Reactive hyperemia - an increase in blood flow following a period of low blood flow
Blood flow is closed. O2 lvls fall, and paracrine signals CO2 and H+ accumulate in the interstitial fluid. When blood flow resumes, increased concentrations of NO, CO2, and other paracrine molecules trigger vasolidation.
Describe the reflex/extrinsic controls over variation in arteriolar resistance to blood flow
ACh from parasympathetic neurons causes paracrine release of nitric oxide, resulting in vasodilation.
Norepinephrine from sympathetic neurons binding to alpha receptors on vascular smooth muscle cause vasoconstriction. If sympathetic release of norepinephrine decreases, arterioles dilate.
activation of vascular beta receptors by epinephrine causes vasodilation
Tonic control of arteriolar diameter
Ateriole Diameter is controlled by tonic release of norepinephrine.
Moderate signal rate results in a blood vessel of intermediate diameter
Increase Norepinephrine release onto alpha receptors
- As signal rate increases, the blood vessel constricts
Decrease Norepinephrine release onto alpha receptors
- As the signal rate decreases, the blood vessel dilates
Distinguish between the location, chemical mediator, and action of alpha and beta-2 adrenergic receptors in arterioles; also discuss the purpose of vasogenic (myogenic) tone & how it is maintained
Alpha Receptor: Located in blood vessel walls such as SM of arterioles of the Gi tract and skin (and some in SKM arterioles). High sensitivity to Norepinephrine(NE) and low sensitivity to Epinephrine(Epi). Function for vasoconstriction (SM contraction)
Beta 1 Receptor: Located in myocardium such as cardiac conduction and contractile cells. High sensitivity to Epi and NE. Functions to enhance cardiac muscle contraction force and increase BPM by increasing rate of depolarization.
Beta 2 receptor: Located in blood vessel walls such as the SM of the arterioles in the heart, liver, SKM and also found in SM of bronchioles. High sensitivity to Epi and low sensitivity to NE (not innervated by sympathetic neurons, thereby limiting their exposer to NE). Function to vasodilate arterioles (relaxation of SM in blood vessels) and bronchodilation in lungs.
Regulation of Blood Pressure: Identify locations of arterial baroreceptors and their functions Explain how the baroreceptor reflex operates in response to (a) increased blood pressure & (b) decreased blood pressure.
Baroreceptors are located in the walls of the carotid artery and aorta. They continuously monitor the pressure of blood flowing to the brain and to the body. Carotid and aortic baroreceptors fire action potentials continuously at normal blood pressure to the Cardiovascular control center.
(a) Increase in blood pressure will result in AP's firing rate to increase. The CVCC will then increase parasympathetic activity (more ACh released) and lower sympathetic activity (less NE released) to lower heart rate and dilate arterioles. Dilated arterioles will allow for more blood to flow through, and this lowers the blood pressure and MAP.
(b)Decrease in blood pressure will result in AP's firing rate to decrease. The CVCC will then decrease parasympathetic activity (decrease in ACh release) and increase sympathetic activity (more NE released). This will constrict the arterioles causing less blood to flow, and this will increases blood pressure and the MAP.
Define the terms hypotension and hypertension
Hypotension - abnormally low blood pressure
Hypertension - abnormally high blood pressure
Explain how transient (orthostatic) hypotension might occur
When going from a flat position to standing, gravity will pull blood to the lower extremities. This pooling can create a decrease in venous return, so that less blood is in the ventricles at the beginning of the next contraction.
Cardiac output will fall, causing arterial blood pressure to decrease. This is orthostatic hypotension - decrease in blood pressure upon standing. This will normally trigger your baroreceptor reflex, resulting in increased peripheral resistance and increased cardiac output, which together will increase your mean arterial pressure bringing everything back to normal within two heartbeats.
Microcirculation: Describe the function of metarterioles and precapillary sphincters.
Metarterioles can act as a bypass channel, helping to divert blood from the capillary beds and directly into the venous circulation. Precapillary sphincters constrict, closing capillaries in response to local signals. This directs blood to travel from arterioles, to metarterioles, and then directly into the venous circulation. When precapillary sphincters are relaxed, blood will travel through the normal path of arteries, to capillaries, and then to the venous circulation.
Explain why the velocity of blood flow decreases in the capillaries and then increases when funneling from capillary beds into venules
Primary determinant for velocity is not diameter but total cross-sectional arear of all the capillaries.
- pack of spaghetti - small diameter but together total area occupied is large.
-capillaries summed diameter is much larger than total cross sectional area of all the arteries and veins combined. - velocity of flow through them is low
Once the blood flow leaves the capillaries, the cross-sectional area decreases, which will increase velocity of the blood flow. Since nutrient and gas exchange occurs on the capillaries, the slow velocity is ideal for maximum explosive exchange.
Describe the anatomy of a capillary
Capillaries have the thinnest walls of all blood vessels allowing the exchange of nutrients and gases across the vessel wall. The wall is composed of a single layer of flattened endothelial cells supported on a basal lamina. Diameter is barely that of rbc - they squeeze in a file. Cell junctions between the cells allow for leak channels to be present, and vary within different tissues depending on their need for exchange.
There are two types of capillaries, continuous and fenestrated.
Continuous capillaries are those whose endothelial cells are connected by leaky junctions. Found in muscle, connective tissue, and neural tissue.
Fenestrated capillaries have large pores that allow high volumes of fluid to pass rapidly between the ISF and plasma. Found in kidney and intestine.
Compare and contrast the 3 means of capillary exchange: 1) diffusion, 2) transcytosis and 3) bulk flow
Diffusion allows for most small dissolved solutes and gases to easily flow between or through endothelial cells.
Transcytosis allows for large proteins and macromolecules to be transported through the endothelial cells by creating vesicles from caveolae and non-coated pits on the cell surface. In some instances, a chain of vesicles will fuse together to create an open channel that extends across the endothelial cell.
Bulk Flow allows for mass movement of fluids through the endothelium as a result of hydrostatic or osmotic pressure gradients. If the direction of bulk flow in into the capillary, then the fluid movement is called absorption, and if the flow is out of the capillary, it is known as filtration
Bulk Flow - the mass movement of fluid as the result of hydriostatic or osmotic pressure gradients.
Absorption - direction of bulk flow is into the capillaries
Filtration - direction of flow is out of the capillary
net filtration at the arterial end and net absorption at the venous end
except - kidneys (filtration) and intestine (absorption)
Explain how bulk flow is regulated by hydrostatic pressure and osmotic pressure. Be able to calculate the difference in capillary hydrostatic pressure and colloid osmotic pressure
Hydrostatic pressure is the lateral pressure component of blood flow within the capillary that pushes the blood through the capillary pores. This will decrease along the length of the capillary as energy is lost to friction. The hydrostatic pressure in the ISF is very low, so we consider it to be zero. This means water movement due to hydrostatic pressure will be directed out of the capillary.
Osmotic pressure, or more accurately colloid osmotic pressure, is the pressure created by proteins. Since proteins are found in the plasma and not in the ISF, the colloid osmotic pressure will be higher in the plasma, and virtually zero in the ISF. This will favor water movement by osmosis from the ISF into the plasma. The net pressure driving fluid flow across the capillary is determined by the difference between hydrostatic pressure and colloid osmotic pressure.
net pressure = hydrostatic pressure - osmotic pressure
positive net pressure - filtration
negative net pressure - absorption
Summarize the association between the cardiovascular system and the lymphatic system. Then explain how the fluid volume of the ECF is maintained in health by capillary exchange and lymphatic activity.
The lymphatic and cardiovascular systems include a network of capillaries and vessels that assist in circulating the body fluids.
The lymphatic vessels transport excess fluid away from the interstitial spaces of tissues and return it to the bloodstream. Lymphatic activity is responsible for picking up fluid by filtration from the capillaries to the circulatory system. Lymph vessels lie close to capillaries and allow for one-way movement of the ISF from the tissues into the circulation. The pathway consists of lymph vessels joining one another, creating lymphatic vessels that progressively increase in size. Lymph nodes are found along the way which contain immunologically active cells including lymphocytes and phagocytes, to rid the fluid of bacteria. The fluids empty through lymph ducts into the internal jugular veins, and return it to the circulatory system.
Lymphatic system functions:
1. returning fluid and proteins filtered out of the capillaries to the circulatory system
2. picking up fat absorbed at the small intestine and transferring to circ. system
3. serving as a filter to help capture and destroy foreign pathogens
Compare and contrast lymph and blood
Lymph is a clear fluid consisting of interstitial fluid, interstitial proteins, and particulate matter such as bacteria. Lymph removes waste from the system. Lymph movement is in a single direction. Lymph is moved along by smooth muscle contraction, contractile fibers, and external compression of sk. muscles - skeletal muscle pump. One way semi-lunar valves. Lymph is purified by lymph nodes.
Blood is a red fluid consisting of red blood cells, white blood cells, and platelets suspended in plasma. Blood transports oxygen throughout the body. Blood flows in a circulatory system. Blood is pumped through the circulatory system by the heart. Blood is purified by the kidneys. One way by valves.
Discuss factors that may lead to edema
Edema - an accumulation of fluid in the interstitial space.
1. Inadequate drainage of lymph
- parasites, or fibrotic tissue growth caused by radiation can block the movement of lymph
2. disrupt normal balance between capillary filtration and absorption
a. Blood capillary filtrations that greatly exceeds capillary absorption
- an increase in capillary hydrostatic p - heart failure
b. A decrease in plasma protein concentration
- malnutrition or liver failure
- liver mainsite of plasma protein synthesis
- capillary absorption is reduced - swells
c. An increase in interstitial proteins
- excessive leakage of proteins out of the blood decreases colloid osmotic pressure gradient and increases net capillary filtration
Describe "hypovolemic shock"
Hypovolemic shock is a result of the decrease in circulating blood volume. The consequences of hypovolemic shock are low cardiac output and falling peripheral blood pressure. Cells begin to damage from inadequate oxygen and buildup metabolic wastes. To treat, one must administer oxygen, fluids, and norepinephrine to the patient. NE stimulates vasoconstriction and increases cardiac output.
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