Unit 4—Maintenance of the Human Body Dr. Achilly

Unit 4—Maintenance of the Human Body

Dr. Achilly

Part 2: The Cardiovascular System

Concepts: Chapter 21-22

The Cardiovascular System

Consists of blood, heart & blood vessels.Heart is the pump that circulates blood

throughout the body.Blood carries nutrients to cells & wastes

away from them. It’s made of:55% plasma—water, proteins, other solutes45% formed elements—platelets, white &

red blood cells

The Cardiovascular System—heart structure

Heart is located in mediastinum (btwn sternum & vert. col).

~2/3 of heart is to the left of midline.

Like a cone lying on its side with apex pointing anteriorly, inferiorly & to left.

Base points posteriorly, superiorly & to the right.


Heart is surrounded by pericardium. Has 2 layers with

pericardial fluid inbtwn.

Prevents overstretching of heart, protects, anchors & reduces friction while heart contracts.


Heart consists of 3 layers:Epicardium—outermost thin, slippery layer

(continuous with inner pericardial layer)Myocardium—muscular layer which is

responsible for the pumping Endocardium—thin inner layer which gives

smooth lining to the heart chambers


Heart has 4 chambers:2 superior atria (sing.—atrium) with small

pouch extensions called auricles that allow each atrium to hold more blood.

2 inferior ventricles



Right atriumReceives deoxygenated blood from 3 veins

Sup. vena cava Inf. vena cavaCoronary sinus

Wall of atrium has muscular ridges called pectinate muscles

Has fossa ovalis (remnant of foramen ovalis in fetal heart)


Blood passes to right ventricle thru an atrioventricular (AV) valve (aka tricuspid valve)


Right ventricle Inside contains muscular

ridges & the chordae tendonae which anchor the flaps of the tricuspid valves.

Blood leaves right ventricle thru pulmonary valve & goes into the pulmonary trunk which splits into the right & left pulmonary arteries.


Left atriumReceives oxygenated blood from lungs via

pulmonary veins.Similar structure to right atriumBlood passes to left ventricle thru the left

atrioventricular valve (aka bicuspid or mitral)


Left ventricleForms apex of heartSimilar structure to right ventricle, but the

myocardium is much thicker here.Blood leaves left vent. thru aortic valve into

the ascending aorta.Some blood goes to supply the heart tissue

via the coronary arteries.Rest of blood goes into arch of aorta &

descending aorta to supply the body.


ValvesWhen the atria contract, blood is forced thru

the AV valves and into the ventricles.When the ventricles contract, the cusps of

the AV valves are forced upward & the tension from the chordea tendonae keeps them from being forced open the wrong way.


The aortic & pulmonary valves are made of 3 crescent moon shaped cusps (so they are aka semilunar valves).

The cusps are forced open when the ventricles contract.

When the vent. relaxes, blood starts to flow backwards, but fills the valve cusps & they close tightly.

The Cardiovascular System—circuits

After birth, the heart pumps blood into 2 circuits:Systemic—serves most of the bodyPulmonary—goes back & forth btwn lungs &

heartThe output of one becomes the input of

the other.


Left side of heart receives oxygen-rich blood from lungs.

Left ventricle ejects blood into aorta.From here it enters progressively smaller

arteries thru out the body, then into smaller arterioles, finally into capillaries.


Nutrient & gas exchange occurs across the thin capillary walls.O2 is unloaded, CO2 is picked up


Usually blood passes thru one capillary bed & then enters a systemic venule.

Venules carry nutrient & oxygen poor blood away from tissues.

They merge into larger systemic veins & then into the superior or inferior vena cava to the right atrium.


Right side of heart is pump for pulmonary circuit.

Blood ejected from right ventricle flows to pulmonary trunk which branches into pulmonary arteries (only arteries that carry deoxygenated blood).

Pulmonary arteries branch to right & left lung.


Oxygen-rich blood returns to left side of heart via pulmonary vein (only vein that carries oxygenated blood).

The trip to the systemic circuit repeats.


Part of the systemic circuit includes coronary circulation.

Blood does not diffuse thru the chambers to the heart tissue, so it needs its own supply.

Coronary arteries branch from the ascending aorta & encircle the heart.

The Cardiovascular System—tissue

Myo fibers that make up myocardium are similar to those that are in skeletal myo.

They are a bit shorter & more branched. Usually mononucleated, but may have more

than one nuclei in a cell. The ends of the cells connect to each other

thru intercalated discs. Helps to hold the cells together.

Channels in the disc allow cells to communicate & for nerve impulses to spread quickly from cell to cell.

The Cardiovascular System—conduction

Cardiac myo fibers are autorhythmic—they generate action potentials that trigger heart contractions.

Heart will beat even when removed from body with all of its nerves cut.

These autorhythmic fibers act as a pacemaker & they form a conduction system that allows contraction to progress thru heart.


1. Excitation begins in sinoartrial (SA) node located in wall of R atrium. The impulse from SA node spreads thru both atria via gaps in the intercalated discs. Both atria contract (aka atrial systole).

2. Nerve impulse reaches atrioventricular (AV) node located in septum btwn 2 atria.


3. Nerve impulse enters AV bundle (bundle of His)

4. Impulse travels thru both right & left bundle branches which are located in the interventricular septum.

5. Impulse travels thru Purkinje fibers to apex of heart & upward. Both ventricles contract (aka ventricular systole).


conduction animation


Nerve impulses from CNS & hormones modify timing & strength of each heartbeat, but they don’t establish the fundamental rhythm.

The Cardiovascular System—electrocardiogram

As nerve impulses travel thru heart, they generate electrical currents (action potentials) that can be detected on body surface.

Electrocardiogram (ECG or EKG) can record these signals.

Electrodes are placed on limbs & chest. Each records slightly different activity.


Helps to determine: if conduction

pathway is normal. If heart is enlarged. If heart regions are

damaged. Cause of chest

pain.


P waveRepresents atrial depolarization as the

impulse spreads from SA node & thru both atria.

QRS complexRapid ventricular depolarization

T waveVentricular repolarization, just as ventricles

are starting to relax (diastole).


Size of waves can indicate abnormalities.Larger P wave = enlarged atriumLarger Q wave may = myocardial infarctionLarger R wave = enlarged ventriclesFlat T wave = heart myo not getting enough

oxygen (from blockage of coronary artery)Larger T wave = high blood K+


Times between waves are called segments or intervals.P-Q interval represents time required for the

impulse to travel thru atria, AV node & rest of conduction fibers. If there is scarring or damage to heart tissue, that “trip” will take longer. P-Q interval lengthens.



S-T segment represents ventricular systole. It can be elevated during acute MI or depressed when heart myo is not getting enough oxygen.

Q-T interval represents beginning of vent. depolarization to the end of repolarization. May be lengthened by myo damage, decreased blood flow or conduction abnormalities.


No P wave (atrial fibrillation)

ST elevation (acute MI)


ST depression (not enough O2 to heart myo)


Some abnormalities may not show unless heart is stressed.Some EKG’s are done during exercise

Some abnormalities are unpredictable.May need 24 hr. monitoring.

The Cardiovascular System—cardiac cycle

All of the events associated with one heartbeat.

Systole & diastole in both atria & ventricles.


Atrial systole (0.1 sec)Depolarization of SA node causes atrial

depolarization.Atrial systole forces blood that has collected

in the atria thru the open AV valves into the ventricles.


Ventricular systole (0.3 sec)Ventricular depolarization begins with the

contraction of vent. walls. Pressure rises so blood is forced against AV valves causing them to shut.

Pressure rises enough to force blood thru both SL valves. Called ventricular ejection.

Total amt of blood ejected = 70 mL


Relaxation period (0.4 sec)Both atria & ventricles are relaxed.As pressure drops, blood from aorta &

pulmonary trunk flows backwards but is stopped by cusps of closed SL valves.

Pressure drops enough so that AV valves open. Blood that collected in atria during atrial diastole rushes into ventricles.

At end of relaxation, P wave appears, atria contract & cycle starts again.


Cardiac cycle animation


During exercise, as the heart beats faster, the relaxation period shortens, but the timing for systole doesn’t change much.

Athletes have stronger systole & can pump more blood with each contraction (increased stroke volume).

The Cardiovascular System—circulatory routes

Blood vessels are organized into routes that carry blood to specific organs.

A part of the cardiac output flows separately to each part of the body.

Deoxygenated blood is returned to the heart in a separate set of veins.

The Cardiovascular System—pulse & blood pressure

Arteries & arterioles are very elastic. Blood comes out of the heart from the left ventricle under great pressure. This pressure expands arteries and can be felt as a pulse in several places thru out the body.

The Cardiovascular System—pulse & blood pressure

The muscular walls of arterioles allow them to play a role in maintaining blood pressure.

By contracting this muscular layer, less blood will flow thru that vessel & this increases the pressure of blood elsewhere in the body.

Pulse points

The Cardiovascular System—blood pressure

Blood pressure is a measure of the pressure in the arteries generated by the left ventricle during systole & the remaining pressure in the vessel during diastole.

Measured using a sphygmomanometer.The top number in the reading

corresponds to systolic pressure & the bottom to diastolic pressure.


Venules & veins do not have walls that are as muscular.

They are distensible so they can adapt to changes in blood pressure & volume.


Many veins have valves that form flaplike cusps.

Because blood pressure is low in the veins, blood returning to the heart can slow & even “back up.”

Valves help to prevent backflow.Myo contraction helps also.


Leaky valves can cause veins to become dilated & twisted. Called varicose veins Caused by:

congenital defects in valves prolonged standing pregnancy aging

Copyright ©2004 American College of Cardiology Foundation. Restrictions may apply.

Cummings, J. E. et al. J Am Coll Cardiol 2004;43:994-1000

Anterior surface of the human heart before coronary artery bypass surgery

Take care of your heart. Don’t end up here

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Unit 4—Maintenance of the Human Body Dr. Achilly