Download 2-Arterial Blood pressure

Cardiovascular Physiology
Function of cardiovascular system:
1-Transport and distribute essential substance to the tissues.
2-Remove by-product of metabolism.
3-Regulate body temperature.
4-Humoral communication throughout the body.
5-Adjustment of O2 and nutrient supply in different physiology
states.
The CVS consists of:
1-Pump(heart)
pulmonary circulation , systemic circulation
2-Distributing and collecting tubes (arteries and veins).
3-Extensive system of thin vessels which permit rapid exchange
between tissues and vascular channels (capillaries).
Hemodynamics
The arterial blood flow is pulsatile in character (due to cardiac
ejection) and become steady in the capillaries because of large
surface area so the exchange of diffusible substance occur
between blood and tissue.
*The heart is an extremely complication pump.
*The blood vessels are multi branched elastic tubes of varying
diameters.
*The blood is not a simple fluid, it is a suspension of cells (RBCs,
WBCs, platelets), lipid globules, proteins.
Velocity of Blood Stream
Velocity The rate of displacement with respect to time (cm/sec.)
or (distance per unit time ) .
Flow: volume per unit time (cm3/sec.)
V=velocity
Q= flow
A=cross-sectional area
Steady flow: is the absence of variation of flow in time (non
pulsation flow).
Laminar flow: is a gradient of flow rate between the stationary
peripheral layer of fluid and the rapidly flowing central layers of
fluid.
Viscosity: is the friction exerted by the movement of laminae of
blood relative to each other.
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Resistance: hydraulic resistance is the ratio of pressure drop to
flow.
The Vascular System
1-Blood flow: the amount of blood that passes through a blood
vessel in a given time. Factors which control blood flow are:
a- differences in pressure between the two ends of the tube.
b- resistance of flow which means friction between tube wall and
fluid and between the molecules of the fluid. So resistance depend
on the nature (property) of the fluid (viscosity) and the geometry
of the tube (length and radius).
*The flow is directly proportional to the pressure difference and
inversely proportional to the resistance.
Fraction
viscosity
resistance
flow
Length
flow (but it is constant in blood vessels).
*radius is markedly determine the resistance while the length of
blood vessels and viscosity of blood is constant.
2-Arterial Blood pressure:
The contraction of the ventricles ejects blood into the systemic
and pulmonary arteries during systole.
This will distends the arteries by raising arterial blood pressure.
The systolic pressure: is the maximum pressure reachen during
peak ventricular ejection.
The diastolic pressure: is the minimal pressure occur just before
ventricular contraction.
The blood pressure :is generally recorded as: Systolic /
Diastolic=120/80 mm Hg.
Plus pressure: can be felt in an artery is due to the difference
between systolic and diastolic pressure.
Plus pressure= systolic pressure-diastolic pressure
= 120-80=40mmHg.
Factors which change pulse pressure are:
1- an increased stroke volume will systolic pressure.
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2-decreased arterial distensibility (as in arteriosclerosis) will
systolic pressure.
The bood pressure is regulated by:
1-Cardic output (SV and HR) C.O
BP.
2-Peripheral resistance R
BP.
3-Blood viscosity B.vis.
BP.
*Polycythemia and plasma proteins
viscosity.
Mean arterial pressure:
Is the most important pressure because it is the average pressure
driving blood into the tissues throughout the cardiac cycle.
Mean arterial pressure is not the value half way between
systolic and diastolic pressure because diastolic usually lasts
longer than systole.
Mean arterial pressure= 1/3 syst.pr.+2/3 diast.pr.
= 1/3x120+2/3x80
= 93 mmHg
Hypertension : increased arterial blood pressure than normal.
Hypotension: decreased arterial blood pressure than normal.
Baroreceptors: are pressure or stretch receptors located in the
carotid sinus and aortic arch. They respond to the changes in the
arteries induced by changes in arterial blood pressure through
either inhibition or stimulation of the vasomotor center in the
medulla oblongata.
Mareys Law: is the relationship between increased blood pressure
and decreased heart rate during regulation of blood pressure.
Chemoreceptors: are receptors found in the vasomotor center that
sensitive to CO2 and in the aortic are carotid bodies that sensitive
to O2.
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Cerebral Circulation
R. external carotid artery supplies right side of thyroid gland ,
tongue, throat, face , ear , scalp and Dura matter.
R. internal carotid artery supplies brain , right eye, and right sides
of forehead and nose.
L. external and internal carotid arteries are similar to that of right
.
* Inside the cranium , anastomoses of left and right internal
carotids along with basilar artery from a hexagonal arrangement
of blood vessels at base of brain near sella turcica called cerebral
arterial circle (circle of Willis). From this circle arise arteries
supplying most of the brain .
The function of the cerebral arterial circle are:
1-to equalize blood pressure to brain
2-provide alternate routes for blood to brain in case of arterial
damage.
Exchange of gases and material occur in the sinuses of the brain.
Right and left internal jugular veins receive blood from face and
neck. They arise as continuation of sigmoid sinuses at base of
skull.
Intracranial vascular sinuses are located between layers of Dura
matter and receive blood from brain, Other sinuses that drain into
internal jugular include superior sagittal sinus, inferior sagittal
sinus, straight sinus and transverse (lateral) sinuses.
Internal jugulars descend on either side of neck and join with sub
clavian veins in the same side to form right and left
brachiocephalic veins. From here blood flows into superior vena
cava.
Right and left external jugulars. They drain blood from parotid
(salivary) glands, facial muscle, scalp and other superficial
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structures into subclavian veins, then into brachiocephalic veins
and then into superior vena cava.
Fetal circulation :
It is not necessary for the fetal heart to pump much blood
through either the lungs or the liver because :
1-the lungs are nonfunctioning during fetal life.
2-the liver is only partially functional.
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