CardiovascularSystem

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. Endocardiumi. 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

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.

Systemic and Pulmonary circuits

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.

Basic pathway of blood in the coronary circuit is:

LV—Aorta—Coronary arteries—Cor. Capillaries—Cor. Veins—Cor. Sinus--RA

Coronary circuit

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:

Depolarization wave travels to atrial contractile cells.

SA node cells depolarize

Atrial contractile cells contract. Note that the right atrium begins to contract before the left.

Depolarization wave travels to AV node. Depolarization wave is briefly delayed, allowing atria to complete contracting before the ventricles begin.

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/beatHR = 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 cross-bridge 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 (100-40 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.