A&P II Lecture Chapter 15: Blood Flow and the Control of Blood Pressure
compensation for increased blood volume slow response:
-increased BP triggers compensation by kidneys -which leads to excretion of fluid in urine and decreased blood volume -bring BP to normal
Compensation for increased blood volume fast response:
-increased blood pressure triggers compensation by cardiovascular system. -leads to vasodilation and decreased cardiac output -this brings blood pressure to normal
The kidneys can't restore lost fluid, but only conserve blood volume and thereby prevent further decreases in blood pressure.
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Veins have thinner walls than arteries, with less elastic tissue. as a reult they expand easily when they fill with blood.
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angiogenesis includes the development of new blood vessels. -This is necessary for normal development -contributes to would healing and uterine lining growth -enhances heart and skeletal muscle blood flow -needed for malignant tumor growth
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blood brain barrier/ diabetic retinopathy
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blood vessel growth is necessary for normal development in children and in adults it takes place as would heal and as the uterine lining grows after menstruation.
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during inflammation capillaries will become more permeable (swollen areas)
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elasticity of arteries -pressure reservoir -elastic recoil maintains pressure during diastole
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endothelial cells secrete many paracrines and play important roles in the regulation of BP, blood vessel growth and absorption of materials
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even distribution of blood (when you lay down for a while) raises arterial pressure, triggering the kidneys to excrete what is perceived as excess fluid. Over 3 days, excretion of water leads to a 12% decrease in blood volume.
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metarterioles can acts as bypass channels
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not all vasoactive paracrines reflect changes in metabolism (kinins and histamate, serotonin)
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pericytes are basically going to block off the capillary beds
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pericytes are in all capillaries, make up blood brain barriers?
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poiseuille's law slide length=total length, fairly constant
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precapillary sphincters can close off capillaries in response to local signals
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some arterioles branch into vessels known as metarterioles. True arterioles have a continuous smooth muscle layer, but the wall of a metarteriole is only partially surrounded by smooth muscle
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systemic veins serve as an expandable volume reservoir
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what four factors that influence mean arterial pressure?
1. blood volume 2. effectiveness of the heart as pump (cardiac output) 3. resistance of the system to blood flow 4. relative distribution of blood between arterial and venous blood vessels
Besides cardiac output and arteriole resistance two other factors can influence MAP:
1. distribution of blood in the systemic circulation 2. total blood volume
What is blood volume determined by? (2)
1. fluid intake 2. fluid loss (may be passive, regulated by kidneys)
what is the effectivemenss of the heart as a pump (cardiac output) (2)?
1. heart rate 2.. stroke volume
What 3 things influence arteriolar resistance (local and systemic control mechanisms)
1. local control of arteriolar resistance matches blood flow to the metabolic needs of the tissue 2. sympathetic reflexes mediated by the CNS maintain MAP and govern blood distribution for certain homeostatic needs (temp regulation) 3. hormones- particularly those that regulate salt and water excretion by the kidneys- influencing BP by acting directly on the arterioles and by altering autonomic reflex control.
what two factors influence peripheral blood flow?
1. pressure gradient 2. resistance to flow (poiseuille's law)
Flow of arteriole is proportional to
1/R (arteriole)
resistance is proportional to
1/radius^4
arteries hold ____% of total blood volume while veins hold about ___
11, 60
After sitting/laying for a while and when the cardiovascular system is unable to restor normal pressure because of the loss of blood volume. As a result...
the person is dizzy/faints from reduced delivery of oxygen to the brain when they stand up
pulse (pressure wave)
the rapid pressure increase that occurs when the left ventricle pushes blood into the aorta
pericytes are highly branched contractile cells that surround the capillaries, forming a mesh like outer layer between the capillary endothelium and the interstitial fluid. they contribute to the ____ of capillary permeability: the more pericytes the ___ leaky the capillary endothelium
tightness less
arteriole diameter is controlled by
tonic release of norepinephrine.
diastole lasts ____ as long as systolic
twice
venous return (blood return to the heart) is aided by
valves, the skeletal muscle pump and the respiratory pump.
NE bind to alpha receptors on vascular smooth muscle causes _____. If sympathetic release of norepinephrine decreases, the arterioles _____.
vasoconstriction dilate
Epinephrine from the adrenal medulla travels through the blood and also binds with alpha receptors, reinforcing ______. But alpha receptors have a lower affinity for epinephrine and dont respond as strongly to it as they do to NE.
vasocontriciton
during fight or flight, increases sympathetic activity at arteriolar alpha receptors causes ______. The increase in resistance diverts blood from nonessential organs, such as the GI tract, to skeletal muscles, liver and heart
vasocontriction
increased parasympathetic activity and decreased sympathetic activity slow heart rate and cause widespread _______. Cardiac output and peripheral resistance both decrease, triggering a precipitous drop in ___
vasodilation, BP
Reactive hyperemia follows a period of decreased blood flow. -Decrease in tissue blood flow to occlusion leads to -metabolic ____ accumulating in the ECF -arterioles dilate, but occlusion prevents ___ ____ -remove occlusion -decreased resistance creates increased blood flow. -as vasodilators wash away, arterioles ___ and blood flow returns to normal
vasodilators, blood flow, constrict
the leastic systemic arteries are a pressure reservoir that maintains blood flow during _____ ______
ventricular relaxation
hypertension
when bp is chronically elevated, high pressure on the walls of lood vessels may cause weakened areas to rupture and bleed into the tissues. EX: if a rupture occurs in the brain, it is called a cerebral hemorrhage. Rupture of major artery is fatal. 140/90 may be a sign you have it.
If tissues need more oxygen, its supplied by the cardiovascular system.
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How does myogenic autoregulation work at the cellular level?
--when vascular smooth muscle cells in arterioles are stretched, mechanically gated channels in the muscle membrane open, -cation depolarizes the cell, the depolarization opens voltage gated Ca channels, and the Ca flows into the cell down its electrochemical gradient. -ca entering the cell combines with calmodulin and activates myosin light chain kinase -MLCK in turn increases myosin ATPase activity and crossbridge activity, resulting in contraction
Length tension curve- as sarcomere stretches out you get a stronger contraction --> push more blood out.
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1. an arteriole contricts this leads to increased ___ and increased total peripheral resistance (TPR) 2. with a greater TPR * cardiac output (CO) leads to increased ______. 3. with a high MAP, ____ fire which triggers the ____ relfex -(assuming that tissue blood flow is matched to tissue need and doesn't need to change) 4. with an activated baroreceptor reflex, this leads to _____ cardiac output. a higher TPR*lowered Cardiac output= _____ restored to normal
-resistance -mean arterial pressure (MAP) -barorecptors, baroreceptor -decreased, MAP
1. isovolumic ventricular relaxation. 2. semilunar valve shuts, preventing flow back into the ventricle 3. elastic recoil of arteries sends blood forward into rest of circulatory system
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1. ventricle contracts 2. semilunar valve opens. blood ejected from ventricles flows into arteries. 3. aorta and arteries expand and store pressure in elastic walls
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Active hyperemia: 1. increased tissue metabolism 2. increased release of metabolic vasodilators into ECF 3. arterioles dilate 4. decreased resistance creates increased blood flow 5. O2 and nutrient supply to tissue increases as long as metabolism is increased
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Baroreceptor reflex flow map (memorize)
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Changing stroke volume-contractility. Increase contractility with sympathetic innervation.
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Cardiovascular function can be modulated by input from peripheral receptors other than baroreceptors. Ex:
Arterial chemoreceptors activated by low blood oxygen levels increase cardiac output
hypotension
BP falls too low, the driving force for blood flow in unable to overcome opposition by gravity. Blood flow and oxygen supply to the rain are impaired, and the person may become dizzy or faint.
blood flow is highest in the arteries and decreases continuously as blood flows through the circulatory system. Why does this decrease occur?
Because energy is lost as a result of the resistance to flow offered by vessels.
The relative distribution of blood between arterial and venous blood vessels is determined by
the diameter of the veins
the of systemic blood varies according to the metabolic needs of individual organs and is governed by a combination of local contral mechanisms and homeostatic reflexes.
Ex: skeletal muscles at rest receive about 20% of cardiac output. During exercise when the muscles use more oxygen and nutrients, the receive as much as 85%
BP is also subject to modulation by higher brain centers such as the hypothalamus and cerebral cortex.
Hypothalamus: mediates vascular responses involved in body temperature regulations and for the fight or flight response Cerebral cortex: learned and emotional responses may originate here- blushing, fainting
what does contraction of smooth muscle depend on?
the entry of Ca from the extracellular fluid through Ca channels
the primary function of the CVCC is to ensure adequate blood flow to the brain and heart by maintaining sufficient ____.
MAP
pressure gradient=
MAP-right arterial pressure (=0)
Local regulation also takes place by changing arteriolar resistance in a tissue. This is accomplished by paracrines (including the gases ___, __, and ___) secreted by the vascular endothelium or by cells to which the arterioles are supplying blood.
O2, CO2, and NO
myogenic autoregulation
a process in which vascular smooth muscle has the ability to regulate its own state of contraction
Korotkoff sound
a thumping noise=blood squeezes through the still compressed artery
what creates the condition of muscle tone?
in most blood vessels, smooth muscle cells maintain a state of partial contraction at all times
if BP changes, the frequency of ___ ____ traveling from the baroreceptors to the medullary cardiovascular control center changes.
action potentials
reactive hyperemia
an increase in tissue blood flow following a period of low perfusion (blood flow)
Contraction of the ventricles pushes blood into the elastic ____, causing them to stretch
arteries
veins are more numerous than ___ and have a larger diameter. As a result of their large volume, the veins hold more than half of the blood in the ______ system.
arteries, circulatory
Low O2 and high CO2 both ___
arterioles
the _____ are the main sit of variable resistance in the systemic circulation and contribute more than ___ of the total resistance to flow in the system
arterioles, 60%
why does the resistance in arterioles vary?
because of the large amounts of smooth muscle in the arteriolar walls. (radius changes)
precapillary schincters are muscle rings, and if relaxed,
blood flowing into a metarteriole is directed into adjoining capillary beds.
blood is diverted from high resistance arterioles to lower resistance arterioles.
blood takes the path of least resistance
How do you stretch the sarcomere?
by increasing preload (diastolic volume).
exchange between the blood and cells takes place only at the _______
capillaries
when precapillary sphincters are relaxed, blood flows through all _____ in the bed
capillaries
B2 mediated vasodilation enhances blood flow to the heart, skeletal muscles, and liver, tissues that are active during the ____ or ___ response
fight or flight
Epinephrine bind to Beta2 receptors found on vascular smooth muscles of ____, ____ and skeletal muscle arterioles. These receptors are not innervated and therfore respond primarily to circulating epinephrine. activation of B2 by epinephrine causes _____.
heart, liver, vasodilation
reflex control of blood flow to selected tissue change MAP so the CVCC is constantly monitoring and adjusting its output as required to maintain _____.
homeostasis
if precapillary sphincters are constricted, metarteriole blood bypasses the
capillaries and goes directly to the venous circulation.
output from the CVCC can alter either ____, ____ or both
cardiac output , arteriolar resistance
medullary network=
cardiovascular control center (CVCC)
the ______ coordinates the reflex control of blood pressure and distribution of ____ to the tissues. the main integrating center is in the ____ _____.
central nervous system, blood, medulla oblongata
cardiovasculcar control: stimulus to sensor to integrating center to output signal to target.
changing in blood pressure to carotid and aortic baroreceptors to medullary cardiovascular control center to para and sympathetic neurons to SA node, ventricles, veins, and arterioles
coronary heart disease
condition in which blood flow to the myocardium is decreased by fatty deposits that narrow the lumen of the coronary arteries.
increased norepinephrine release (as the signal increases) onto alpha receptors, the blood vessel
constricts
angiogenesis is controlled by ____
cytokines
resistance of the system to blood flow is determined by
diameter of the arterioles
Elastic recoil in the arteries maintains driving pressure during ventricular _____
diastole
MAP=
diastolic + 1/3(systolic-diastolic) =93.3mmHg
as the NE signal rate decreases the blood vessel
dilates
The high diastolic pressure in arteries reflects the ability of those vessels to capture and store energy in the ____ walls
elastic
pericytes secrete factors that influence capillary growth, and they can differentiate to become new _____ or smooth muscle cells
endothelium
the inner lining of all blood vessels is a thin layer of ____
endothelium
active hyperemia matches blood flow to ___ _____
increased metabolism
in the absence of autoregulation, an increase in BP ____ blood flow through an arteriole
increases
the carotid and aortic baroreceptors are tonically active stretch receptors that fire action potentials continuously at normal blood pressures. When increased BP in the arteries stretches the baroreceptor membrane, the firing rate of the receptor ____.
increases
sphygmomanometer
inflatable cuff and a pressure gage we use to estimate arterial blood pressure
together, the heart and ____ play a major role in maintaining homeostasis of blody fluids, an excellent example of the integration of organ system function
kidneys.
blood flow into the aorta is equal to the cardiac output of the __ _____
left ventricle
concentrations of many paracrines change as cell become more or less _____ _____
metabolically active
If precapillary sphincters constrict, blood flow bypasses capillaries completely and flows through
metarterioles
Growth factors that promote angiogenesis are
mitogens- they promote mitosis (cell division). They are normally produced by smooth muscle cells and pericytes.
The nucleotide Adenosine is another vasodilator paracrine. In response to low tissue oxygen, the _____ cells release adenosine. It dilates coronary arterioles in an attempt to bring additional blood flow into the muscle.
myocardial
tonic discharge of norepinephrine from sympathetic neurons helps maintain _____ tone of arterioles
myogenic
angiogenesis is the process by which
new blood vessels develop.
pericytes are closely associated with many capillaries. They decrease capillary _______. They can differentiate into endothelial cells and ____ muscle cells
permeability, muscle
baroreceptor reflex is the
primary reflex pathway for homeostatic control of MAP
the arterioles shown with adjustable screws that alter their diameter, are the site of variable ______
resistance
peripheral resistance
resistance to flow offered by the arterioles
The ____ _____ pump is in use when the skeletal muscles compress the veins, blood is forced toward the heart
skeletal muscle
baroreceptors
stretch sensitive mechanocreptors that are located in the walls of the carotid arteries and aorta where they can monitor the pressure of blood flowing to the brain (carotid) and to the body (aortic).
the ____ branch controls most vascular smooth muscle
sympathetic
pulse pressure=
systolic-diastolic 120-80=40mmHg
orthostatic hypotension is
the decrease in BP upon . it normally triggers the baroreceptors reflex.
