Blood Pressure
Blood
Pressure
Fig 15-4
Hydrostatic Pressure created by ventricular contractility
becomes the driving force for blood flow
Pulsatile blood flow in arteries  Elastic arteries expand
and recoil for continuous blood flow. This is the “pulse”
that we can feel.
Pulse wave disappears past arterioles and the precapillary
sphincters
Arteries vs. Veins

Endothelial lining throughout the cardiovascular
system and heart
– Less sticky than teflon

Arteries have more smooth muscle than veins
– Arteries can vasoconstrict
– Veins are “stretchy” or compliant

Veins have valves to prevent backflow of blood
– Arteries don’t have backflow due to pressure gradient
Cardiovascular System

Blood Flow
– Aorta to major arteries to minor arteries entering
organs to arterioles to capillaries to venules to veins
leaving organs to vena cava

Cardiovascular system transports materials
throughout the body
– Nutrients, water, gases
– Materials that move from cell to cell
– Wastes that the cells eliminate
Why Does Blood Flow?

Liquids and gases flow down pressure
gradients (ΔP)
– A region of higher pressure to a region of
lower pressure
– Blood can flow in the cardiovascular system
only if one region develops higher pressure
than other regions
Pressure Gradients

Pressure is created in the chambers of the heart
when they contract
– Blood flows out of the heart
 The higher region of pressure
– As blood moves through the system pressure is lost
due to friction between the fluid and the vessel walls
 Pressure falls the farther the blood moves from the heart
– Higher pressure in the aorta
– Lowest pressure in the venae cavae just before they
empty into the right atrium
Blood Pressure (BP)
Measurements

Ventricular pressure difficult to measure
 measure arterial BP

BP highest in the arteries – falls
continuously throughout systemic
circulation (Why?)

Read as “Systolic over diastolic”–
normal value  120 / 80 mm Hg
– 2003: New range for blood pressure
readings between 120/80 and 139/89
“Prehypertension”

Diastolic pressure in ventricle: ? mm Hg
Blood Flow Rate  P/ R
Pressure of Fluid in Motion
Decreases over Distance

Pressure in a fluid is the force exerted by
the fluid on its container
– The container is the wall of the artery for
blood pressure

Hydrostatic Pressure
– The pressure exerted if the fluid is not moving
 Force is exerted equally in all directions on the
container
Capillaries
Capillaries contain sphincters
 Sphincters are typically closed to 90% of
the body
 During exercise sphincters all open

– Better perfusion
Veins are Capacitance Vessels

Veins have little smooth muscle
– Veins are “stretchy”
– The stretch is called capacitance
The more the stretch the less pressure is exerted against
the walls
 Veins are located between muscle

– Skeletal, smooth, cardiac

Veins contain valves
– Varicose Veins

Venous Return
– Blood flowing back to the heart through veins
Cardiovascular Physiology

Blood Pressure is controlled by:
– Heart Rate
– Peripheral Resistance
– Blood Viscosity
– Blood Volume
– Stroke Volume
Heart Rate

Tachycardia
– Faster than 60-100 bpm

Bradycardia
– Slower than 60 bpm
Cardiovascular Physiology

CO = HR X SV
Cardiac Output = Heart Rate X Stroke Vol

SV = EDV – ESV
– Stroke Vol = End Diastolic Vol – End Systolic Vol

BP = CO x PR
– Blood Pressure = Cardiac Output X Peripheral
Resistance

FRANK-STARLING’S LAW
Hypovolemia Stimulates
Compensatory Mechanisms

Baroreceptors
– Aoritc arch, carotid arteries, kidneys
– Detect blood pressure changes
– Stimulates the medulla oblongata
 MO stimulates the SNS to release Epi/Norepi

Myogenic Control
– Arterial Spams
Stroke Volume
The amount of blood pumped by one ventricle
during a contraction (ml/beat)
 SV=EDV-ESV
 End Diastolic Volume

– Volume of blood in ventricle before contraction

End Systolic Volume
– Volume of blood in ventricle after contraction
CO = HR x SV
Force of contraction
Length of muscle fibers (Starling
curve/law) due to venous return,
influenced by skeletal muscle pump and
respiratory pump
Sympathetic activity (and
adrenaline)
venous constriction by sympathetic NS and
Increased Ca2+ availability
Stroke Volume

Increase EDV
– Increase Venous Return
– Increase Contraction of Muscles
 Skeletal muscle twitching
– Increase Respiration Rate and Depth
 Negative Intrathoracic Pressure
Afterload

The combined load of EDV and arterial
resistance during ventricular contraction
The force necessary to push the blood out
of the heart into the arteries
Stroke Volume

Decrease ESV
– Increase Force of Contraction in Cardiac
Muscle
 Sympathetic Nervous System Input
 Epi/Norepi bind to receptors to open Calcium gates
on the sarcolemma and sarcoplasmic reticulum
Preload

The degree of myocardial stretch before
contraction begins
– This stretch represents the load placed on
cardiac muscles before they contract
– There is a relationship between stretch and
force according to Drs. Frank and Starling
Frank/Starling Law
Stretching muscle aligns actin and myosin
better to achieve a greater force of
contraction
 Increasing EDV will stretch ventricle

– Ventricle have greater force of contraction
 Decreases ESV and thereby increases SV
– Increases CO and BP
Frank-Starling Law

SV α EDV
– i.e., the heart pumps all the blood sent to it via venous
return




Therefore, Venous Return = SV
Preload = the amount of load, or stretch of the
myocardium before diastole
Afterload = Arterial resistance and EDV combined
Ejection Fraction = % of EDV that is actually
ejected; e.g., 70 ml/135ml x 100 = 52% at rest
Peripheral Resistance
Friction to flow against the walls of the
arteries
 Vasoconstrict the arteries by ½ the
diameter and increase PR 4X
 Laminar Flow

BP Estimated by Sphygmomanometry
Auscultation of brachial artery with
stethoscope in cubital fossa
Based on effects of
laminar flow vs.
turbulent flow
Blood Volume
Baroreceptors in the Kidney are stimulated
due to low blood pressure
 Renin and Angiotensinogen release

– Angiotensin I

Angiotensin I is converted in the lungs to
Angiotensin II by the enzyme Angiotensin
Converting Enzyme (ACE)
– ACE Inhibitors to reduce blood pressure
Blood Volume
Angiotensin II stimulates the Adrenal
Cortex to release Aldosterone
 Aldosterone is a Mineralcorticoid

– Controls Na

+
/K
+
concentrations in the blood
Aldosterone stimulates the kidneys to
retain Na + in the blood and excrete K+
Blood Volume

Increased concentration of Na
osmosis
+
in the blood causes
– Water moves from the intracellular and extracellular fluid into
the blood stream

Increased concentration of Na in the blood stimulates
Osmoreceptors in the Hypothalamus
– Increased osmolarity or osmotic pressure in the blood
– Anti-Diuretic Hormone Release
 Decreased urine output
– Unquenchable Thirst
Blood Viscosity
Typically takes 2 weeks to change
viscosity
 Kidney release Erythropoietin

– Erythropoietin stimulates erythropoiesis in the
red bone marrow
– Increases RBC formation and thickness in the
blood
 Increases PR and BP
Mean Arterial Pressure

Sometimes useful to have single value for driving
pressure: Mean Arterial Pressure

MAP  CO x Rarterioles
– A Calculation: MAP = PD+ 1/3 (PS – PD )

MAP is influenced by
– CO
– Peripheral resistance (mostly at arterioles)
 ANS and endocrine
 Metabolic Needs
– Total blood volume
– Blood distribution
BP too low:

Driving force for blood flow unable to
overcome gravity

O2 supply to brain 

Symptoms?
= generalized circulatory
failure, may have a + feedback
cycle
Shock

Hypovolemic shock  volume loss (dehydration, blood loss,
burns)

Distributive shock  loss of vascular tone (anaphylactic,
septic, toxic)

Cardiogenic shock  pump failure

Dissociative shock (not in book)  inability of RBC to deliver O2 (CO
poisoning)
–
Cell damage due to hypoxia
–
Signs and symptoms?
–
Management ?
BP too high:

Weakening of arterial walls lead to
Aneurysms  Risk of rupture &
hemorrhage
 Cerebral
hemorrhage
 Rupture
of major artery
Pressures at which the Korotkoff . .
. . . sound (= blood flow) first
heard:
. . . sound disappeared:
CD
Animation
Cardiovascular
System:
Measuring
Blood Pressure
Principles of Sphygmomanometry
Slowly release pressure in cuff:
turbulent flow
A patient develops a venous blood clot in one leg which
blocks return of blood. What would you predict would
happen to the net fluid flow in the capillaries?
A. Fluid flow in the direction of the tissues
increases
B. Fluid flow in the direction of the tissues
decreases
C. Fluid flow in the direction of the tissues
remains unchanged
D. The capillary osmotic pressure will increase
Hemorrhage with a large loss of
blood causes
A. A lowering of blood pressure due to change
in cardiac output
B. A rise in blood pressure due to change in
cardiac output
C. No change in blood pressure but a slower
heart rate
D. No change in blood pressure but a change in
respiration
Select the correct statement
about cardiac output
A. A slow heart rate increases end diastolic
volume, stroke volume, and force of
contraction
B. Decreased venous return will result in
increased end diastolic volume
C. If a semilunar valve were partially
obstructed, the end systolic volume in the
affected ventricle would be decreased
D. Stroke volume increases if end diastolic
volume decreases
Which of the following is a chemical control
that can increase blood pressure by acting
directly on blood vessel smooth muscle?
A.
B.
C.
D.
E.
Atrial natriuretic factor
ADH
Alcohol
Adrenal cortex hormones
Brain Naturetic Factor
Peripheral resistance
A. Decreases with increasing length of the
blood vessel
B. Increases as blood vessel diameter increases
C. Increases as blood viscocity increases
D. Is not a major factor in blood pressure in
healthy individuals
Select the correct statement about factors
that influence blood pressure
A. An increase in cardiac output corresponds to
a decrease in blood pressure, due to the
increased delivery
B. Excess red cell production would cause a
blood pressure increase
C. Excess protein production would decrease
blood pressure
D. Systemic vasodilation would increase blood
pressure, due to diversion of blood to
essential areas
Aldosterone will
A.
B.
C.
D.
Promote an increase in blood pressure
Promote a decrease in blood pressure
Result in a large output of urine
Decrease sodium reabsorption
In a mammal, blood pressure is
lowest in the
A.
B.
C.
D.
Aorta
Vena cavae
Capillaries of the arm
Veins of the leg
The term vasoconstriction refers
to
A. Increasing the size of the lumen of the blood
vessel
B. Decreasing the size of the lumen of the
blood vessel
C. Delivering oxygen and nutrients to the body
tissues
D. Delivering waste products to the kidney for
excretion
Which of the following represents the flow of blood
from the heart to the body organs and back to the
heart?
A.
B.
C.
D.
Venules to capillaries to veins to arteries
Arteries to capillaries to veins
Capillaries to arterioles to veins
Veins to arteries to capillaries to arterioles
Blood flowing through a vein
tends to
A.
B.
C.
D.
Spurt
Flow smoothly
Carry oxygen to body cells
Flow at a faster rate than in an artery
If the period of ventricular filling
were increased in duration
A. Less blood would flow into the ventricles for
any given time interval
B. The amount of blood in the ventricles at the
end of diastole would be greater
C. The amount of blood in the ventricles at the
end of systole would be greater
D. The stroke volume would decrease