Chapter 15Cardiovascular System

Cardiovascular System

• Provides O2 & nutrients to all tissues

• Removes CO2 & wastes

• Consists of heart & b.v.

• The heart is a 4 chambered,

hollow, muscular organ

• Avg. size: 9 cm wide,

14 cm long

Location

• Located in the mediastinum, resting on the diaphragm

• Base – top of heartbeneath 2nd rib

• Apex – point at bottom(points toward left) at5th intercostal space

• Bordered by lungs laterally& sternum anteriorly

Coverings

1. Fibrous pericardium – tough, outer layer

2. Parietal pericardium – inner lining of pericardial cavity

Pericardial cavity – space filled w/serous fluid; reduces friction

3. Visceral pericardium – membrane that covers the heart (same as epicardium)

Coverings

Fibrouspericardium→

Fibrous Visceralpericardium pericardium

Layers of Heart Wall

1. Epicardium –

same as vis.

pericardium; thin

connective tissue;

protection &

secretes fluid

2. Myocardium – thick;

consists of cardiac muscle; contracts to pump blood

3. Endocardium – epithelial & connective tissue; lines all

chambers & valves; helps keep surfaces smooth

Heart – External Features

• Auricle – ext. flaps• Sulci – grooves for

b.v.• During an avg. lifetime,

the heart beats approx. 2.5 billion times

• It pumps an avg. of approx. 300 million L of blood

Internal Anatomy

• The heart has been

described as 2 pumps

that lie side by side• The 2 sides of the

heart are separated by a

wall called the septum• The 2 thinner-walled upper

chambers that receive

blood are called atria• The 2 thicker-walled

bottom chambers that

pump blood are called ventricles

Internal Anatomy• The atria are separated

from the ventricles byvalves

• Valves prevent thebackflow of blood

• Tricuspid – on rt.• Bicuspid (mitral) on

left• Rt. side of heart receives

deoxy. blood from body &pumps it to the lungs toget oxygenated (colored blue)

• Left side receives oxygenated blood from lungs & pumps it to body (colored red)

Heart Valves

• 2 types:1. Atrioventricular valves

(A-V valves) – located between the 2 atria & ventricles:tricuspid & bicuspid (mitral)

2. Semilunar valves (S-L valves) – located in the b.v. leading away from the heart:

pulmonary & aortic

Chordae Tendinae

• In the right and left ventricle chordae tendinae are strong fibers attached to the A-V valves.

• They prevent the valve from extending into the atrium chamber.

• Attached to papillary muscles.

Heart Sounds

• Produced by the closing of the heart valves

• A typical heartbeat is heard as “lub-dup”

• A-V sounds:• Mitral – heard at 5thintercostal

space• Tricuspid – at tip of sternum• S-L sounds:• Aortic – at 2nd intercostal space

on rt.• Pulmonary – 2nd intercostal space

on left

Blood Supply to the Heart (anterior view)

• The left & rt. coronary arteriesbranch off the aortato supply bloodto the heart itself

• The l.c. art. branchesinto circumflex & left ant. descending artery (or left interventricular artery)

Blood Supply to the Heart(anterior view)

• The rt. coronaryartery branches intothe marginal artery& the posterior inter-ventricular artery(on posterior view – next slide)

Coronary Circulation

Blood Supply to the Heart

• Blood leaves arteries & passes through capillaries of the myocardium

• Blood then passes into cardiac veins

• Cardiac veins empty into coronary sinus (lg. vein on post. side of heart)

• Coronary sinus empties into rt. atrium

Cardiac Conduction System

• The heart has its

own pacemaker that

can initiate a heart-

beat; called the

sinoatrial node (S-A

node)• Located in the upper

rt.atrium; causes both

atria to contract almost

simultaneously

Cardiac Conduction System

• Impulse travels tothe atrioventricularnode (A-V) locatedin the interatrial septum

• Impulse then movesto A-V bundle (orbundle of His) & thento bundle branches

• Purkinje fibers carryimpulse to distant partsof ventricles

The Cardiac Cycle

• A series of

contractions &

relaxations that

constitute one

heartbeat• Atria contract while

ventricles relax &

vice versa• Diastole –

relaxation of a

heart chamber• Systole – contraction of a heart chamber

Electrocardiograms (EKGs)

• Measures electrical activity of the heart

• Results from depolarization & repolarization of the myocardium

• 12 electrodes are placed on various places on the body

• Changes can indicate arrhythmias & other heart-related conditions

Parts of an EKG

• P wave – contraction ofthe atria

• QRS complex – contrac-tion of ventricles

• T wave – relaxation of ventricles • Relaxation of atria (repolarization) – not

seen (hidden by QRS complex)

EKG Measurements

• P wave to P wave -

1 complete ♥ beat

• P-Q interval – time

it takes impulse to

travel from S-A

node to A-V node

EKG Measurements • Q-T interval - the period from the

beginning of ventricular depolarization until the end of ventricular repolarization

• The QT interval is

prolonged if it clearly

measures more than

half the R-R interval 

• Called long QT syndrome

Abnormal EKGs

• Long QT syndrome

Bundle Branch Block

• The QRS complex is

the time required to

depolarize the ventricles.

• A normal QRS is 0.08-0.12 s

• > than 0.12 seconds is considered a BBB (block in a bundle branche, or the electrical impulse was conducted abnormally)

Arrhythmias

• Normally the ♥ contracts about 60-100 times/min

• Each contraction represents one ♥ beat

• Abnormal ♥ rates & EKGs – called arrhythmias

Arrhythmias

Sinus rhythm → 60-80 beats/min

• •

Tachycardia > 100 beats/minBradycardia < 60 beats/min

Arrhythmias

• Atrial Flutter – many

more P waves

compared to QRS

complexes • Atrial Fibrillation – P

waves absent

Arrhythmias

• Junctional Rhythm –

S-A node nonfunctional;

P waves absent; heart being

paced by A-V node (40-60

beats/min)• Ventricular Fibrillation –

Chaotic depolarization of

ventricles; extremely irreg. as

seen in heart attack, elec. shock

Blood Pressure

• Pulse – alternate expansion & relaxation

of arteries

• Pulse pressure – difference b/t systolic

& diastolic pressure

• Central venous pressure – pressure in

rt. atrium

Factors That Affect B.P.BP

An incr. in any of these causes an incr. in BP:1. Heart Action

– Cardiac Output (CO) = Vol. of blood discharged from the ventricles/min.

– Stroke Volume (SV) = Vol. of blood discharged w/each contraction (approx. 70 ml at rest)

– Heart Rate (HR) = number of beats/min– CO = SV X HR– CO = 70 ml X 70 beats/min– CO = 4900 ml/min

Factors That Affect B.P.P

2. Blood Volume = sum of formed elements

+ plasma (usually 5L); (ex. - hemorrhage

results in drop in B.P.)

3. Peripheral Resistance – force produced

from the friction on blood from b.v. walls

(expansion or dilation of b.v. changes

resistance)

4. Viscosity = ease w/which blood flows (an

incr. of RBCs incr. viscosity; anemia or

hemorrhage decr. it)

Blood Pressure

• Force blood exerts against inner walls of b.v. (usually arteries)

• Avg. = 120/80

• Measured w/a sphygmomanometer

• 120 = systolic – maximum pressure during ventr. contraction

• 80 = diastolic – lowest pressure during ventr. relaxation

Measurement of BP

Blood Vessels

• Include arteries, veins & capillaries• Arteries & veins have 3 layers:

1. tunica intima – single layer squamous cells;

secretes substances to stem blood flow

2. tunica media – makes up most of the b.v.;

mostly smooth muscle & some

connective tissue; allows for expansion

3. tunica externa – connective tissue;

provides attachment to surrounding tissue

Blood Vessels

• 2 differences b/t

arteries & veins:

1. thickness of

tunica media

2. veins have

valves

Capillaries

• Smallest b.v.; connect

arterioles to venules• Resp. gases & other

substances are

exchanged in

capillaries thru

diffusion

Capillary Bed

Movement In Capillaries

• Water & other substances leave capillaries at the arteriolar end b/c of a net outward pressure

• Water & other substances leave at venular end b/c of a net inward pressure

Movement in Capillaries

Capillaries

• Arrangement of capillaries control

permeability of substances • In spleen, liver & red marrow,

capillaries have large openings

b/t cells; allow large subst. to

diffuse• Blood-brain barrier –

tight arrangement of

capillaries around brain;

few substances pass thru;

protects brain