CARDIOVASCULAR SYSTEM

CARDIOVASCULAR SYSTEM – HEART

ANATOMY AND PHYSIOLOGY SUMMER, 2002

I HEART

A. GENERAL FEATURES - hollow muscular organ; approx. 11 oz.; beats > 100M/day; pumps >1000 gal (3784 L)/day through 60M miles of blood vessels

1. LOCATION - obliquely situated between lungs: within mediastinum; 2/3 lies left of midline; APEX - pointed end, at tip of left ventricle

B. ANATOMY -

1. PERICARDIUM - encloses and maintains heart location

a. FIBROUS (OUTER)- thick heavy fibrous connective tissue; prevents
over-distention of heart; anchoring function

b. SEROUS (INNER) - thinner delicate membrane forms double layer around
heart

1) PARIETAL - directly beneath fibrous layer

2) VISCERAL (EPICARDIUM) - attaches to myocardium (heart muscle)

3) PERICARDIAL (SEROUS) FLUID - fluid between parietal and visceral
layers; decreases friction between membranes as heart expands and
contracts

4) PERICARDIAL CAVITY - potential space between parietal and visceral
layers; where pericardial fluid is

2. HEART WALL

a. EPICARDIUM (EXTERNAL) - visceral layers of serous pericardium; thin
transparent layer composed of serous tissue and mesothelium

b. MYOCARDIUM (MIDDLE ) - constitutes bulk of heart; primarily cardiac
muscle (involuntary, striated & branched); responsible for heart contractions

c. ENDOCARDIUM - thin layer of endothelium overlying thin layer of connective tissue; lines

myocardium; covers heart valves and tendons which hold them open

3. HEART CHAMBERS (4)

a. ATRIA (UPPER) – right and left; thin walled

1) AURICLE – appendage for each atrium; increase atrium surface area

2) MUSCLI PECTINATI - projecting parallel muscle bundles lining
auricles and anterior walls of atrium

3) INTERATRIAL SEPTUM - separates atrium to right and left; has

prominent oval depression (FOSSA OVALIS)- vestigial remnant of foramen ovale.

b. VENTRICLES (LOWER) - right and left; thick walled (thickest in left side)

1) INTERVENTRICULAR SEPTUM - separates ventricles to right and left

2) CORONARY SULCUS - deep superficial groove separating atria and ventricles

4. HEART VALVES - insure one way flow; made of collagen

a. ATRIOVENTRICULAR (AV) VALVES - between atria and ventricles

1) TRICUSPID VALVE - on right side; has 3 flaps (cusps) - outgrowths
of heart wall covered with endocardium

a) CHORDAE TENDINEAE - cords which connect cusps tip areas to papillary muscles

2) BICUSPID (MITRAL) VALVE - on left side; has 2 flaps

MECH: Valve opens down as atrium contracts allowing blood into ventricle. Papillary muscles relax as well as chordae tendineae. Ventricular contraction causes some blood to be driven back toward atrium. This forces cusp edges up until they meet and close opening; tightening of chordae tendineae and papillary muscles help keep it closed.

b. SEMILUNAR VALVES - on arteries leaving heart; consist of 3 semilunar
cusps

1) PULMONARY- at junction between right ventricle and pulmonary

trunk

2) AORTIC - at junction between left ventricle and aorta

5. MAJOR VESSELS TO/FROM HEART

a. SUPERIOR VENA CAVA - brings blood to heart from superior areas of body

b. INFERIOR VENA CAVA - brings blood to heart from inferior areas of body

c. CORONARY SINUS – collects blood from vessels supplying wall of heart

d. PULMONARY TRUNK – exit vessel of right ventricle; divides into right
and left pulmonary arteries which carry blood to lungs

e. PULMONARY VEINS (4)- vessels returning blood from lungs into left atrium

f. ASCENDING AORTA – exit vessel for left ventricle. This feeds the descending aorta
and aortic arch.

g. LIGAMENTUM ARTERIOSUM – remnant of ductus arteriosus - shunt vessel during fetal
life connecting pulmonary trunk to aorta so no blood to non-functioning fetal lungs

6. BLOOD SUPPLY OF THE HEART

a. CORONARY (CARDIAC) CIRCULATION - flow of blood through numerous vessels piercing the myocardium

1) ASCENDING AORTA divides into left and right Coronary artery.

• Left (part of ascending aorta) divides into Anterior Interventricular branch feeding
both ventricles and Circumflex branch which feeds left atrium and left ventricle.

• Right divides into Marginal branch which feeds right ventricle and Posterior
Interventricular branch feeding both ventricles

a) ANASTOMOSIS - where 2 or more arteries supply same area and are connected with each other; most parts receive blood from more than 1 artery

b) MYOCARDIAL INFARCTION (HEART ATTACK) - death to tissue due to interruption of blood supply (i.e. thrombus in coronary artery)

C. PHYSIOLOGY

1. CONDUCTION SYSTEM: innervated by ANS - controls rate not an initiator

a. COMPONENTS:

1) SINOATRIAL (SA) NODE – pacemaker; located in right atrium wall inferior to

opening of superior Vena Cava; spontaneously depolarizes initiating action potential (AP) for heart; causes impulse to spread over both atrium causing them to contract; generates AP faster than all other components; rate can be influenced by ANS and hormones

2) ATRIOVENTRICULAR (AV) NODE - located near inferior part of interatrial septum;
last part of atria to be depolarized

3) BUNDLE OF HIS (ATRIOVENTRICULAR BUNDLES) - tracts of conducting fibers
from AV node to medial surfaces of ventricles

4) PURKINJE FIBERS - continuation of conducting fibers passing into myocardial cells;
causes ventricular contraction

b. SELF EXCITABILITY - ability to spontaneously and rhythmically generate AP (nerve impulse)

1) MECHANSIM:

• Membrane very permeable to Na; even in resting state Na diffuse into cell causing
membrane potential to become more positive. This continues till reaches
threshold level - AP.

• Membrane becomes less permeable to Na and permeable to K and this diffuses
out of cell causing the inner area to become more negative. This reversal of
charges stops the AP.

• Use Na/K pump to ACTIVELY re-establish resting state. This sequence occurs approx. 75 times/minute

3. ELECTROCARDIOGRAM (ECG) - each part of cardiac cycle produces different electrical impulses -these are translated into deflection waves

a. P WAVE - small upward wave; indicates atrial depolarization

b. QRS COMPLEX - initial downward deflection followed by large upright wave followed by small
downward wave; represents ventricular depolarization; masks atrial repolarization; enlarged R
portion - enlarged ventricles; enlarged Q portion - probable heart attack

c. T WAVE - dome shaped wave; indicates ventricular repolarization; flat when insufficient oxygen;
elevated with increased K levels

d. P - R INTERVAL - interval from beginning of P wave to R wave; represents conduction time
from initial atrial excitation to initial ventricular excitation; good diagnostic tool; normally < 0.2
sec.

e. S-T SEGMENT - time from end of S to beginning to T wave; represents time between end of
spreading impulse through ventricles and ventricular repolarization; elevated with heart attack;
depressed when insufficient oxygen.

f. Q-T INTERVAL - time for singular depolarization and repolarization of the ventricles.
Conduction problems, myocardial damage or congenital heart defects can prolong this.

4. BLOOD FLOW THROUGH HEART - based on pressure gradients

a. VALVE FUNCTIONING- controlled by pressure changes in each heart chamber

b. MYOCARDIUM CONTRACTIONS/RELAXATIONS - changes pressure within

chambers

1) ATRIAL PRESSURE - pressure in atria

2) VENTRICULAR PRESSURE - pressure in ventricles

3) ARTERIAL PRESSURE - pressure in aorta or pulmonary trunk

5. cardiac cycle - approx. 0.8 sec

a. TERMINOLOGY:

• SYSTOLE - phase of contraction (atria - 0. 1 sec; ventricle - 0.3 sec )

• DIASTOLE - phase of relaxation (atria - 0.7 sec; ventricle - 0.5 sec )

• CARDIAC CYCLE - consists of systole and diastole of both atria and ventricles

b. STEPS:

1) ATRIAL SYSTOLE – Blood from superior and inferior vena cava + coronary

sinus flows into right atrium (through tricuspid); blood from pulmonary veins flows into left atrium (through bicuspid).

70% moves passively into ventricles; final 30% is pushed in via atrial contraction

2) VENTRICULAR FILLING – When ventricles are contracted, AV valves are closed and atrial pressure increases. As ventricular pressure drops (once ventricular contraction is over) atrial pressure pushed AV valves open to fill ventricles

3) VENTRICULAR SYSTOLE - AP from AV node through ventricles cause's contraction
(see QRS Complex); coincides with 1st heart sounds.

• ISOVOLUMETRIC CONTRACTION - 1st 0.05 sec when AV and Semilunar values
are closed, contraction causes increase pressure

• EJECTION PERIOD - once ventricular pressure > arterial pressure forcing semilunar
valves open and dispels contents

• STROKE VOLUME - blood pumped by each ventricle during ejections period; usually
1/2 contents

4) VENTRICULAR DIASTOLE - Decrease in ventricular pressure without change in
volume

• ISOVOLUMETRIC RELAXATION - ventricular pressure drops rapidly due to the
elasticity of muscle to re-expand toward resting dimensions.

PRELOAD - degree of stretching experienced during ventricular diastole. This is directly proportional to (EDV) end diastolic volume.

6. HEART SOUNDS

a. LUBB - closure of AV valves after ventricular systole begins

b. DUBB - closure of semilunar valves at end of ventricular systole

7. CARDIAC OUTPUT: = STROKE VOLUME (SV) X HEART RATE; typically

5.25L/min (70ml for SV and 75 for Heart rate)

a. STROKE VOLUME - depends on how much blood enter ventricles during diastole (EDV - end
diastolic volume: usually 120-130ml) & how much is left following systole (ESV - end systolic
volume: usually 50-60 ml)

b. STARLING'S LAW OF HEART - the greater the length (stretch) of cardiac muscle fibers (within
limits), the greater the force of ventricular contraction

c. MAREY'S LAW OF HEART - blood pressure is inversely proportional to heart rate

d. CARDIAC RESERVE - maximum % cardiac output can increase above normal: 4-6X

e. HEART RATE - primarily influenced by ANS

1) CARDIOACCELATORY CENTER (CAC) - group of neurons within medulla; contain
sympathetic fibers and innervate SA node, AV node and myocardium

• Bradycardia - slower rate

• Tachycardia - faster rate

2) CARDIOINHIBITORY CENTER (CIS) - group of neurons within medulla; contain
parasympathetic fibers that reach heart via Vagus N. & innervate SA node and AV node

3) BARORECEPTOR (PRESSURE) RECEPTORS - nerve cells capable of responding to blood pressure changes and ultimately effect heart rate