Transcript The_Heart - Northwest ISD Moodle

Cardiovascular
System
Human heart
Heart Functions
a. Generates the pressure that
propels blood thru blood vessels.
b. Separates oxygenated and
deoxygenated blood.
c. Helps regulate the body’s blood
supply.
Position of the Heart
a. Within the mediastinum, the medial cavity of the
thorax.
b. Apex rests on the superior diaphragmatic
surface and points toward the left hip.
c. Base points towards the right shoulder.
d. Medial to the lungs, anterior to the esophagus
and vertebrae, and posterior to the sternum.
Position of the Heart
Mediastinum
Pericardium
Epicardium
Myocardium
Endocardium
Pericardium
a. Encloses the heart.
b. Outermost layer is the fibrous pericardium – a collagenous
structure that protects and anchors the heart and prevents it from
distending.
c. Deeper is the serous pericardium, a 2 layered serous membrane.
d. Parietal serous pericardium is the outer of the 2 and abuts the
fibrous pericardium.
e. Visceral serous pericardium is the inner of the 2 and is the external
covering of the heart and is a.k.a. the epicardium.
f. Parietal and visceral layers are continuous with one another where
the great vessels leave the heart.
g. Pericardial cavity is the space between the parietal and visceral
layers and contains serous fluid, which reduces friction.
Heart wall
Divided into 3 layers.
A. Epicardium
i. Most superficial and is a.k.a. visceral serous pericardium.
ii. Composed of simple squamous epithelium overlaying thin loose CT.
B. Myocardium
i. Middle layer.
ii. Primarily cardiac muscle, but also contains blood vessels, nerves, and
CT.
iii. Myocardial CT forms a dense network known as the fibrous skeleton,
which supports the heart valves, acts as origin/insertion for the
cardiac muscle cells, and helps direct the spread of electrical
activity within the heart along defined pathways.
C. Endocardium
i. Inner layer
ii. Consists of endothelium (simple squamous epithelium) resting on a
layer of thin CT.
iii. Lines the heart chambers and its folds create the heart valves.
Heart Surface
Heart Posterior
Heart Chambers
a. 2 superior atria and 2 inferior ventricles.
b. Thin interatrial (IA) septum divides the 2 atria
c. Thick interventricular (IV) septum divides the
2 ventricles.
Heart Interior
Human Heart Interior
Heart consists of 2 pumps connected
in series.
a. Each pump sends blood to a different circuit.
b. Pulmonary circuit runs btwn the heart and the lungs.
c. Systemic circuit runs btwn the heart and the rest of the
body tissues.
d. Right side of the heart receives deO2 blood from the
systemic circuit and pumps it thru the pulmonary
circuit.
e. Left side of the heart receives O2 blood from the
pulmonary circuit and pumps it thru the systemic
circuit.
Circulation
Atria
a. Heart’s receiving chambers.
b. Small and thinly muscled. Large muscle
mass is unnecessary, since atrial contraction
propels only a small amount of blood to the
ventricles.
Right atrium
A. Receives deO2 blood from the systemic circuit via 3
vessels:
i. Superior vena cava carries blood from arms, head,
and upper torso
ii. Inferior vena cava carries blood from the legs,
abdomen, and pelvis
iii. Coronary sinus carries blood from the coronary
circulation – which nourishes the heart wall.
B. Sends blood to right ventricle thru tricuspid orifice, via
the tricuspid valve.
Heart Surface
Heart Posterior
Heart Interior
Left atrium
a. Receives O2 blood from the pulmonary
circuit via the 4 pulmonary veins.
b. Sends blood to left ventricle thru mitral
(bicuspid) orifice, via the mitral (bicuspid)
valve.
Heart Surface
Heart Posterior
Heart Interior
Left and right auricles
a. Muscular pouches connected to the left and
right atria.
b. Function as reservoirs for blood.
Heart Surface
Fossa ovalis
a. Remnant of the foramen ovale, a hole in the
fetal atrial septum.
i. Fetal blood flowed through the hole from
RA to LA thus bypassing the pulmonary
circuit (since the fetal lungs are neither
developed nor oxygenated).
Heart Interior
Ventricles
a. Large, muscular chambers.
b. Thick musculature is necessary because they
are the actual pumps.
c. Contain muscular ridges known as trabeculae
carneae as well as muscular bulges known as
papillary muscles.
Right ventricle
a. Discharges blood into the pulmonary trunk,
the first vessel of the pulmonary circuit.
b. Separated from the pulmonary trunk by the
pulmonary semilunar valve
Left ventricle
a. Discharges blood into the aorta, the first
vessel of the systemic circuit.
b. Separated from the aorta by the aortic
semilunar valve.
c. More muscular than the RV.
i. Necessary because the LV pumps blood a
farther distance and against greater
pressure (note – RV and LV pump the
same volume of blood per beat).
Systemic and Pulmonary circuits
Systemic circuit:
LV—Aorta—Systemic arteries—Syst
capillaries—Syst veins—Vena Cava—RA
Pulmonary circuit:
RV—Pulmonary Trunk—Pulm Arteries—Pulm
capillaries—Pulm veins--LA
Systemic and Pulmonary circuits
If we combine the 2 circuits, note that we
have 2 pumps in series:
LA—LV—Syst Blood Vessels—RA—RV—
Pulm Blood Vessels
The circuit then begins again.
Circulation
Ways in which the systemic circuit differs from
the pulmonary circuit
a. Longer
b. Much larger blood volume.
c. Its blood is under far greater pressure.
d. Resistance to blood movement is also far greater.
e. Systemic arteries are O2 rich & CO2 poor. Pulmonary
arteries are O2 poor & CO2 rich.
Systemic veins are O2 poor and CO2 rich. Pulmonary
veins are O2 rich and CO2 poor.
Hepatic Portal Circulation:
a. The hepatic portal circulation collects blood
from the veins of the pancreas, spleen,
stomach, intestines, and gallbladder and
directs it into the hepatic portal vein of the
liver.
b. This circulation enables the liver to utilize
nutrients and detoxify harmful substances in
the blood.
Fetal Circulation:
a. The fetal circulation involves the exchange of
materials between fetus and mother.
b. The fetus derives its oxygen and nutrients
and eliminates its carbon dioxide and
wastes through the maternal blood supply
by means of a structure called the placenta.
c. At birth, when lung, digestive, and liver
functions are established, the special
structures of fetal circulation are no longer
needed.
Coronary circuit
a. Network of blood vessels supplying/draining
the 3 heart layers.
b. Needed b/c the heart requires a prodigious
amount of O2 and nutrients, and little O2 or
nutrients can diffuse thru the thick
myocardium.
Coronary circuit
Basic pathway of blood in the coronary
circuit is:
LV—Aorta—Coronary arteries—Cor.
Capillaries—Cor. Veins—Cor. Sinus--RA
Coronary Arteries
Coronary
Veins
Human Heart
4 Heart valves
a. Ensure 1-way flow within the heart.
b. 2 atrioventricular valves separating the atria
from the ventricles
c. 2 semilunar valves separating the ventricles
from their great vessels.
AV valves
a. Consist of a flap of endothelium with a core of
connective tissue.
b. Tricuspid valve has 3 flaps and prevents backflow of
blood from the RV to the RA.
c. Mitral (bicuspid) valve prevents backflow from the LV to
the LA
d. AV valve flaps are attached to strings of collagen called
chordae tendineae.
e. Chordae tendineae attach to papillary muscles in the
ventricle wall.
f. Blood goes thru an AV valve from atria to the ventricle
when atrial BP > ventricular BP.
i. At this time the chordae tendineae are slack, and
papillary muscles are relaxed.
AV valves
g. When the ventricle contracts:
i. Ventricular BP > atrial BP.
ii. Blood will attempt to flow down its pressure gradient
back into the atria. This pushes the valve flaps
towards the atria (closing them).
iii. Chordae tendineae tighten as papillary muscles
contract thus preventing the valve flaps from
flipping up (prolapsing) into the atrium.
h. Note that the chordae tendinae and papillary muscles
do NOT close the AV valves themselves. Blood’s
attempt to backflow is what pushes the valves shut.
Heart Valve Locations
Surface of Valves
Valves
Mitral Valve Prolapse
Cardiac muscle
a. Comprises the bulk of the heart wall.
b. Involuntary
c. 2 types of cardiac muscle cells – contractile cells and
autorhythmic cells.
d. Contractile cells
i. 99%
ii. Generate the force involved in pumping.
iii. Striated, short, and branched.
e. Autorhythmic cells
i. 1%
ii. Spontaneously depolarize to set the rate of
contraction.
Intercalated discs
a. Link cardiac muscle cells together mechanically and electrically.
b. Contain 2 separate structures: gap junctions and desmosomes.
c. Gap junctions
i. Protein channels that allow ions to flow btwn adjacent cells.
ii. Create an electrical connection btwn cardiac muscle cells.
iii. Allow the depolarization wave initiated by autorhythmic cells to
spread through the cardiac musculature. Electrical excitation
of cardiac muscle cells causes an increase in intracellular
Ca2+ levels. Calcium binds w/ troponin to produce contraction
via the familiar sliding filament mechanism.
iv. Allows the heart to function as a single coordinated unit
(functional syncytium), which helps maximize its efficiency.
d. Desmosomes
i. Protein filaments that physically connect adjacent cardiac
muscle cells and prevent them from separating during
contraction.
Heart Tissue
Fibrous skeleton of the heart
a. Dense irregular CT w/i the heart.
b. Provides origins and insertion points for
cardiac contractile cells.
c. Supports heart valves
d. Separates the atria from the ventricles both
physically and electrically
Intrinsic control of heart rate
a. Performed by the autorhythmic cells
b. 5 main groups of autorhythmic cells:
i. Sinoatrial node (SA node)– group of autorhythmic
cells near opening of the SVC.
ii. Atrioventricular node (AV node)– group of ACs in
inferior IA septum near tricuspid orifice.
iii. Atrioventricular bundle – group of ACs in the
superior IV septum.
iv. Right and left bundle branches – group of ACs in
middle & inferior IV septum.
v. Purkinje fibers – separate autorhythmic cells that
wind through the ventricles.
Conduction System
Intrinsic control of heart rate
c. The above list also gives the path of the
electrical conduction system within the heart.
d. All autorhythmic cells have the ability to
rhythmically and spontaneously depolarize.
e. SA node cells have the fastest rate of
depolarization
i. They set the pace for other autorhythmic
cells as well as the rest of the heart. \
ii. SA node is known as the pacemaker of the
heart.
Intrinsic control of heart rate
f. Spread of depolarization:
SA node cells depolarize
Depolarization wave travels to atrial contractile cells.
Depolarization wave travels to AV node. Depolarization
wave is briefly delayed, allowing atria to complete
contracting before the ventricles begin.
Atrial contractile cells contract. Note that the right
atrium begins to contract before the left.
Depolarization wave travels down AV bundle & bundle
branches. (Fibrous skeleton prevents it from traveling
directly from atria to ventricles)
Depolarization wave travels thru the ventricles via Purkinje
fibers.
Ventricular contractile cells depolarize and then contract.
Intrinsic control of heart rate
g. W/o any input (neural or hormonal), the inherent rate
of SA node depolarization determines heart rate.
i. Normal uninfluenced rate is roughly 100
depolarizations per minute.
h. Fibrous skeleton of the heart electrically isolates the
atria and the ventricles. The AV bundle is the only
electrical connection btwn them.
i.Ventricular depolarization and contraction begin at
the apex of the heart and proceed upward. This
allows blood to be propelled up out of the
ventricles into the great vessels.
P= wave from SA node through
atria
QRS = ventricular depolarization
T wave = ventricular
repolarization
P-Q interval = time from atria
contraction to beginning of
ventricular contraction.
Q-T interval = ventricular
depolarization to repolarization.
Note:
Systole
& Diastole
The Echo Image
Echo Images
Echo - Doppler
Electrocardiogram:
a. The record of electrical changes during each cardiac
cycle is referred to as an electrocardiogram (ECG).
b. A normal ECG consists of a P wave (spread of
impulse from SA node over atria), QRS wave
(spread of impulse through ventricles), and T wave
(ventricular repolarization). The P-R interval
represents the conduction time from the beginning
of atrial excitation to the beginning of ventricular
excitation. The S-T segment represents the time
between the end of the spread of the impulse
through the ventricles and repolarization of the
ventricles.
Electrocardiogram:
c. The ECG is invaluable in diagnosing
abnormal cardiac rhythms and conduction
patterns, detecting the presence of fetal life,
determining the presence of several fetuses,
and following the course of recovery from a
heart attack.
d. An artificial pacemaker may be used to
restore an abnormal cardiac rhythm.
Pacemakers
 Located in the right chest wall, a catheter is
threaded through the subclavian vein, into the
brachiocephalic vein, into the superior vena
cava , then into the right atrium.
 The pacemaker overrides the impulse from
the SA node.
Action Potentials
Action Potential – Ventricle
Extrinsic control of heart rate
a. Refers to factors originating outside of
cardiac tissue that affect heart rate.
b. Most extrinsic control is nervous or endocrine
in nature.
Extrinsic control of heart rate
Medulla oblongata contains 2 cardiac centers that
can alter the heart’s activity.
a. Cardioacceleratory center
i. Projects via the cardiac sympathetic
nerves to the SA node, AV node,
and the ventricular myocardium.
ii. These neurons release NE, which
increases contraction rate and
force.
Extrinsic control of heart rate
b. Cardioinhibitory center
i. Contains parasympathetic neurons that project (via
the vagus nerve, CN X) to the SA node and AV
nodes. T
ii. These neurons release ACh, which causes a
decrease in heart rate but no change in the
heart’s contractile strength.
c. At rest, both parasympathetic and sympathetic
neurons are releasing neurotransmitters onto the
heart, but the parasympathetic branch is dominant.
d. During stress, exercise, and excessive heat the
sympathetic influence is dominant.
Heart sounds
2 associated with each heart beat.
a. 1st heart sound
i. LUB
ii. Caused by the shutting of the atrioventricular
valves
iii. Occurs at the onset of ventricular contraction.
b. 2nd heart sound
i. DUP
ii. Caused by the shutting of the semilunar valves
iii. Occurs at the end of ventricular contraction.
Cardiac cycle
a. Refers to all events associated with blood
flow thru the heart during one heartbeat.
b. Includes the contraction (systole) and
relaxation (diastole) of all 4 chambers.
c. Divided into 4 parts: ventricular filling,
isovolumetric contraction, ventricular
ejection, and isovolumetric relaxation.
d. We’ll discuss the cardiac cycle in terms of the
left side of the heart, but analogous events
are occurring on the right side.
Ventricular filling
a. LA BP is lower than the BP of the pulmonary
vasculature, so blood enters the left atrium.
b. LA BP is greater than LV BP, so blood enters
the LV.
c. B/c LA BP is greater than LV BP, the mitral
valve is pushed open.
d. LV BP is less than aortic BP. As a result,
blood tries to back flow from the aorta into the
LV and this forces the aortic semilunar valve
closed.
e. Neither atrial nor ventricular muscle is
contracting. Both are in diastole.
Ventricular filling
f. About 80% of the ultimate ventricular volume will enter
in this passive manner.
g. At the end of ventricular filling, while the LV is still
relaxing, the LA depolarizes and contracts.
i. This pushes roughly the final 20% of blood into the
LV.
ii. LV now has the maximum volume it will contain
during this particular cycle.
1. This is the end diastolic volume (EDV).
(Typically = 130mL).
h. For the rest of the cycle, the LA will be in diastole.
Isovolumetric contraction
a. LV depolarizes, contracts, and LV BP rises
quickly almost immediately exceeds LA
BP.
b. Blood is pushed upward shutting the mitral
valve– creating the 1st heart sound (LUB).
c. However, the opening of the aortic semilunar
valve requires much more pressure than
was necessary to close the mitral valve.
Isovolumetric contraction
d. So after the mitral valve is shut, the LV
continues to contract and its BP rises, but
until LV BP exceeds aortic BP, the aortic
semilunar valve remains shut.
e. Thus, during this period, the AV and
semilunar valves are shut and the volume
within the LV is not changing. Hence this
phase is known as “iso” “volumetric”
contraction.
Ventricular ejection
a. LV BP now exceeds aortic BP (80mmHg), the
semilunar valve is forced open, and blood is ejected
from the LV into the ascending aorta.
b. Not all of the blood in the LV is ejected. The amount
remaining after ventricular contraction is known as
the end systolic volume (ESV). A typical value is
70mL.
i. This gives a reserve amount of blood that could
also be ejected if necessary (e.g., during
exercise).
c. Amount of blood ejected during this phase is known as
the stroke volume.
i. Stroke volume is the difference btwn end diastolic
and end systolic volumes: SV=EDV-ESV.
ii. A more vigorous contraction will result in a
decreased ESV and an increased SV.
Isovolumetric relaxation
a. Once the LV has completed contracting, its
BP falls and quickly becomes less than
aortic BP and blood tries to back flow, which
shuts the semilunar valve– creating the
2nd heart sound (DUP).
b. However, it takes a bit longer for the LV BP to
drop below the LA BP – and cause the
mitral valve to open.
Isovolumetric relaxation
c. During this time, as LV BP is falling, the AV
and semilunar valves are shut and LV
volume is not changing.
d. Once LV BP falls below LA BP (which is rising
as blood returns to the heart), the
mitral valve will open and the cycle will begin
anew with another round of ventricular
filling.
e. With an average heartbeat of 75/min, a
complete cardiac cycle requires 0.8 sec.
f. A peculiar sound is called a murmur.
LV vs. RV
a. Note that the events on the left side of the
heart during a normal cardiac cycle are
mirrored by the events on the right side of
the heart.
b. Both the right and the left side of the heart
contract at the same rate.
c. They have identical stroke volumes on
average.
LV vs. RV
d. The only difference is the pressure involved.
The LV must contract harder to open its
semilunar valve. This is because the
systemic circuit is under a much higher
pressure than the pulmonary circuit. The left
and right ventricle must have identical stroke
volumes. If LV SV > RV SV, then blood
would back up in the systemic circuit. If LV
SV < RV SV, then blood would back up in
the pulmonary circuit.
Cardiac output
a. Cardiac output (CO) is the amount of blood ejected by
the left ventricle into the aorta per minute. It is
calculated as follows: CO = stroke volume x beats
per minute.
b. Stroke volume (SV) is the amount of blood ejected by
a ventricle during each systole.
c. Stroke volume (SV) depends on how much blood
enters a ventricle during diastole (end-diastolic
volume) and how much blood is left in a ventricle
following its systole (end systolic volume).
d. The maximum percentage that cardiac output can be
increased above normal is cardiac reserve.
Cardiac output
e. Heart rate and strength of contraction may be
increased by sympathetic stimulation from the
cardioacceleratory center in the medulla and
decreased by parasympathetic stimulation from the
cardioinhibitory center in the medulla.
f. Pressoreceptors are nerve cells that respond to
changes in blood pressure. They act on the cardiac
centers in the medulla through three reflex
pathways: carotid sinus reflex, aortic reflex, and
right heart (atrial) reflex.
g. Other influences on heart rate include chemicals
(epinephrine, sodium, potassium), temperature,
emotion, sex (gender and physical activity), and
age.
Cardiac Output
CO = SV x HR
SV = ml/beat
HR = Heart Rate
Nervous system regulation of heart
rate.
a. Increases in heart rate achieved by:
i. Increase in cardioacceleratory center
activity. This increases sympathetic
nerve activity and increases NE
release on the heart.
ii. Decrease in cardioinhibitory center activity.
This decreases parasympathetic nerve
activity and decreases ACh release on
the heart.
Nervous system regulation of heart
rate.
b. Decreases in heart rate are achieved by:
i. Decrease in cardioacceleratory center
activity. This decreases sympathetic
nerve activity and decreases NE
release on the heart.
ii. Increase in cardioinhibitory center activity.
This increases parasympathetic nerve
activity and increases vagus nerve
activity (a.k.a. vagal tone), and
increases ACH release on the heart.
Nervous System Control
Relationship between heart rate and
stroke volume
Note that if heart rate changes without a change
in contractility (the strength of the
contraction), stroke volume will change also.
This is because changing the heart rate alters
the filling time (i.e., the time btwn beats during
which the heart fills up with blood).
Hormonal influences on heart rate
a. Epinephrine, released by the adrenal
medulla (an endocrine organ found atop the
kidneys), increases HR.
b. Thyroxine, released by the thyroid gland
(located in the anterior neck), increases HR.
Other factors that raise heart rate
Increased body temperature
Chemicals: caffeine, nicotine, and ephedrine
Other factors that decrease heart
rate
Decreased body temperature
Drugs such as beta blocker
Regulation of stroke volume
Depends on 3 main variables:
1. Preload
a. Refers to the degree of ventricular stretch during filling.
b. An increase in heart muscle is stretched (up to a
point), causes increased contractile force
c. Increased in stretch causes more optimum crossbridge formation btwn actin and myosin and a
stronger contraction, thus ejecting a larger volume.
d. Frank-Starling law states: “What returns to the heart
will get pumped out of the heart.”
Regulation of stroke volume
Preload cont….
e. As venous return (the volume of blood
returning to the heart per minute)
increases, EDV increases, and stroke
volume increases.
f. A decrease in HR will increase the filling
time and thus increase EDV (and preload).
g. An increase in venous pressure will also
increase EDV (and preload).
h. The stroke volume is greatly influenced by
changes in preload.
Regulation of stroke volume
2. Contractility
a. Strength of the heart’s contraction
independent of its degree of stretch.
b. Increase in contractility will result in an
increase in stroke volume and a decrease in
end systolic volume.
c. Factors that increase contractility include:
increased cardioacceleratory activity; and
hormones such as epinephrine and
thyroxine.
Regulation of stroke volume
3. Afterload
a. Pressure that must be overcome to open the semilunar
valve and eject blood.
b. Equivalent to arterial blood pressure.
c. Increase in arterial BP will increase afterload. This
makes the heart expend more time/energy on
opening the semilunar valve and less on ejecting
blood.
d. Thus, an increase in afterload will cause stroke volume
to decrease and end systolic volume to increase.
e. However, it takes a significant increase in afterload
before the pumping output of the heart is hampered.
Cardiac Output Affected By
 Frank-Starling Law / Marey’s Law
 Cardiac Reserve (Max CO – CO at rest)
 Contractility (hormones, drugs, sympathetic
reactions, etc.
 Afterload (remaining blood in ventricles)
 Congestive heart failure
Risk Factors for CAD
 High blood cholesterol
 High blood pressure
 Smoking
 Obesity
 Diabetes mellitus
 Type “A” personality
 Sedentary lifestyle
Arteries:
a. Arteries carry blood away from the heart. Their wall
consists of a tunica interna, tunica media (which
maintains elasticity and contractility), and tunica
externa.
b. Large arteries are referred to as elastic (conducting)
arteries and medium-sized arteries are called
muscular (distributing) arteries.
c. Many arteries anastomose-the distal ends of two or
more vessels unite. An alternate blood route from
an anastomosis is called collateral circulation.
Arteries that do not anastomose are called end
art.ener
Arteries:
Arterioles:
a. Arterioles are small arteries that deliver blood
to capillaries.
b. Through constriction and dilation they
assume a key role in regulating blood flow
from arteries into capillaries.
Arterioles
Capillaries:
a. Capillaries are microscopic blood vessels through
which materials are exchanged between blood and
tissue cells; some capillaries are continuous, others
are fenestrated.
b. Capillaries branch to form an extensive capillary
network throughout the tissue. This network
increases the surface area, allowing a rapid
exchange of large quantities of materials.
c. Precapillary sphincters regulate blood flow through
capillaries.
d. Microscopic blood vessels in the liver are called
sinusoids.
Capillaries
Venules:
a. Venules are small vessels that continue from
capillaries and merge to form veins.
b. They drain blood from capillaries into veins.
Venules
Veins:
a. Veins consist of the same three tunics as
arteries, but have less elastic tissue and
smooth muscle.
b. They contain valves to prevent back flow of
blood.
c. Weak valves can lead to varicose veins or
hemorrhoids.
d. Vascular (venous) sinuses are veins with
very thin walls.
Veins
Blood Flow and Blood Pressure:
a. Blood flows from regions of higher to lower
pressure. The established pressure gradient
is from aorta (100 mm Hg) to arteries (10040 mm Hg) to arterioles 40-25 mm Hg) to
capillaries (25-12 mm Hg) to venules (12-8
mm Hg) to veins (10-5 mm Hg) to venae
cavae (2 mm Hg) to right atrium (0 mm Hg).
b. Any factor that increases cardiac output
increases blood pressure.
c. As blood volume increases, blood pressure
increases.
Blood Flow and Blood Pressure:
d. Peripheral resistance is determined by blood
viscosity and blood vessel diameter. Increased
viscosity and vasoconstriction increase peripheral
resistance and thus increase blood pressure.
e. Factors that determine heart rate and force of
contraction, and therefore blood pressure, are the
autonomic nervous system through the cardiac
center. chemicals, temperature, emotions, sex, and
age.
f. Factors that regulate blood pressure by acting on
blood vessels include the vasomotor center in the
medulla together with pressoreceptors,
chemoreceptors, and higher brain centers;
chemicals; and autoregulation.
Blood Flow and Blood Pressure:
g. The movement of water and dissolved substances
(except proteins) through capillaries by diffusion is
dependent on hydrostatic and osmotic pressures.
h. The near equilibrium at the arterial and venous ends
of a capillary by which fluids exit and enter is called
Starling's law of the capillaries.
i. Blood return to the heart is maintained by several
factors including increasing velocity of blood in
veins, skeletal muscular contractions, valves in
veins (especially in the extremities), and breathing.
Blood Reservoirs:
a. Systemic veins are collectively called blood
reservoirs.
b. They store blood which through
vasoconstriction can move to other parts of
the body if the need arises.
c. The principal reservoirs are the veins of the
abdominal organs (liver and spleen) and
skin.
Checking Circulation – Pulse:
a. Pulse is the alternate expansion and elastic
recoil of an artery with each heartbeat. It
may be felt in any artery that lies near the
surface or over a hard tissue.
b. A normal rate is between 70 and 80 beats
per minute.
Measurement of Blood Pressure:
a. Blood pressure is the pressure exerted by blood on
the wall of an artery when the left ventricle
undergoes systole and then diastole. It is measured
by the use of a sphygmomanometer.
b. Systolic blood pressure is the force of blood recorded
during ventricular contraction. Diastolic blood
pressure is the force of blood recorded during
ventricular relaxation. The average blood pressure
is 120/80 mm Hg.
c. Pulse pressure is the difference between systolic and
diastolic pressure. It averages 40 mm Hg and
provides information about the condition of arteries.
Disorders - Homeostatic
Imbalances:
a. An aneurysm is a sac formed by an outpocketing of a
portion of an arterial or venous wall.
b. Coronary artery disease (CAD) refers to an
inadequate blood supply to the heart muscle. Two
principal causes are atherosclerosis and coronary
artery spasm.
c. Atherosclerosis is a process in which fatty
substances are deposited in the walls of arteries.
d. Coronary artery spasm is caused by a sudden
contraction of the smooth muscle in an arterial wall
that produces vasoconstriction.
e. Hypertension is high blood pressure and may
damage the heart, brain, and kidneys.