Download Circulatory System Part 2

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THE HEART
Heart – an organ the size of your fist and weighing less than a pound that rests on the
diaphragm; 2/3 of the heart lies on the left of the midsternal line: Lungs flank the heart: The
pointed apex of the heart points toward the left hip and the base (from which the great vessels
emerge) points toward the right shoulder
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1. Pericardium - double walled sac that encloses the heart
a) Fibrous Pericardium – outer layer around heart that is tough Connective Tissue
i.
Protects the heart
ii.
Anchors it to the surrounding structures (i.e. diaphragm and great vessels)
iii.
Prevents overfilling of heart - because it does not stretch
b) Serous Pericardium – thin slippery 2 layer serous membrane separated by serous
fluid
i.
Parietal pericardium– internal surface of fibrous pericardium
ii.
Visceral pericardium (epicardium) – external surface of the heart
Pericarditis – inflammation of the pericardium resulting in decreased serous
fluid and increase in friction and sticking of the pericardial layers, inhibiting
heart function
2. Layers of the Heart Wall (all three layers
are richly supplied with blood vessels)
a) Epicardium – visceral serous
pericardium often infiltrated with fat
b) Myocardium – middle; cardiac
muscle (contracts)
c) Endocardium – most internal layer
of glistening endothelium that lines
chambers (this layer lines the heat
cavities and is continuous with
blood vessels, capillaries, etc)
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3. Four Chambers (2 atria and 2 ventricles) and associated Great Vessels
a) Atria (2) – small, thin walled receiving chambers on the top of the heart, they
contribute little to the contraction of the heart
i.
Blood enters the right atrium through three veins
 Superior Vena Cava – returns blood from body regions superior to
the diaphragm
 Inferior Vena Cava – returns blood from body regions inferior to the
diaphragm
 Coronary Sinus – collects blood from coronary veins that drain from
the myocardium itself
ii.
Blood enters the left atrium through four pulmonary veins . Pulmonary
veins return O2 rich, CO2 poor blood back to the heart.
b) Interatrial septum – tissue that separates the atria
c) Ventricles (2) –the larger chambers in the bottom of the heart that are responsible
for pumping or discharging blood from the heart
i.
Blood is pumped from the right ventricle into the pulmonary trunk which
splits into the pulmonary arteries and routes the blood to the lungs for gas
exchange.
ii. Blood is pumped from the left ventricle into the aorta, the largest artery in
the body which delivers oxygenated blood to the body’s tissues
d) Interventricular Septum – tissue that separates the ventricles
4. Blood Flow
a) Pulmonary Circuit – the blood vessels that carry blood to and from the lungs
(Veins in this system carry O2 rich, CO2 poor blood back to the heart)
b) Systemic Circuit – the blood vessels that carry blood to and from all other parts
of the body (Veins in this circuit carry CO2 rich, O2 poor blood back to the heart)
c) Blood returning from the body (systemic system) that is CO2 rich and O2 poor
enters the right atrium and passes into the right ventricle, which pumps the blood
to the lungs
d) Freshly oxygenated blood from the lungs then is carried though the pulmonary
veins back to the left atrium. It then passes to the left ventricle, which pumps it
into the aorta. Blood is then transported into smaller systemic arteries to the
body tissues
e) The walls of the left ventricle (feeds systemic circuit) are three times thicker than
the walls of the right ventricle (feeds pulmonary circuit)
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Bronchial Arteries – blood pumped into lungs to “feed” lungs; these arteries come off the aorta
(oxygen rich blood comes from the aorta) Coronary arteries – arteries that come off aorta and “feed”
heart (oxygen rich blood) – blood can only “feed” the cells
of the myocardium when the heart is not contracted. When
the heart beats at a very rapid rate the myocardium may
become deprived of oxygen resulting in crushing chest pain
called “angina pectoris” which if ignored results in death of
myocardial cells and may result in a myocardial infarction
or “heart attack”
Pulmonary arteries – Do Not “feed” lungs; Do Not carry oxygen rich blood; push blood
through lungs to pick up oxygen
Heart pumping by the numbers!
There are six quarts of blood in an average human
In one day the heart pumps the six quarts of blood over 1000 times
Meaning that is actually pumps 6000 quarts of blood in a single day!
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5. Microscopic anatomy of the heart – multinucleate, striated, branched and interconnected
thru intercalated discs
a) Intercellular space: loose Connective Tissue matrix and many capillaries
b) Plasma membrane of adjacent cardiac cells interlock at intercalated discs
i. Prevent adjacent cells from separating during contraction (prevent tearing
of muscles)
ii. Ions pass from one cell to the next = depolarize entire heart (allows the
heart to contract as a cohesive unit)
c) Large amount of mitochondria = 25% of the total volume of a cardiac cell =
resists fatigue
6. Heart Valves (4 total)
a) Atrioventricular (AV)Valves (2)
i. Located between the atrium and ventricle, prevent back flow from
contracting ventricles
ii. Right AV Valve is the tricuspid valve (has three flexible flaps “cusps” of
connective tissue)
iii. Left AV Valve is the bicuspid valve or mitral valve (has two flexible
flaps of connective tissue)
iv.
Chordae Tendineae – “heart strings” that anchor the cusps to the walls
of the ventricles. These keep valves from opening in the opposite
direction.
b) Semilunar Valves (2)
i. Aortic Semilunar Valve = guards the base of the aorta and prevents
backflow into the left ventricle
ii. Pulmonary Semilunar Valve = guards the base of the pulmonary trunk
and prevents backflow into the right ventricle
Leaky Valves – forces the heart to pump and re-pump the same blood doing
more work than necessary and decreasing heart function
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7. Conduction System – noncontractile cardiac cells that will initiate and distribute
impulses throughout the heart to contract orderly and sequentially (In other words, the
heart does not depend on the nervous system in order to contract. The contractile
property is a function of the heart muscle itself)
8. Innervation – although the heart sets its own pace, the autonomic nervous system can
control the force and pace at which the heart beats
a) Sympathetic = increase rate and force of heart beat
b) Parasympathetic = slow rate
c) Cardiac centers are located in the medulla oblongata
9. The intrinsic conduction system or nodal system – composite of muscle and nervous
system found only in the heart that creates and action potential that passes throughout the
heart
The Action Potential (Electrical Charge) of the heart passes (from a-e) as follows
a) Sinoatrial (SA) node – also called the “pacemaker” located in the right atrial wall
and sets the pace for the heart as a whole, initiates signal and determines the heart
rate.
b) Atrioventricular (AV) node –
from the SA node, the
depolarization passes through the
internodal pathway to the AV
node located in the interatrial
septum. The AV node delays the
signal for a fraction of second
before triggering the ventricles to
contract.
c) Bundle of His = (AV bundle) –
also located in the interatrial
septum
d) Right and left bundle branches
– branch into the interventricular
septum
e) Purkinje fibers – completes the
depolarization process
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CARDIAC CYCLE AND HEART SOUNDS
Blood Pressure (BP) – force per unit area exerted on the wall of a blood vessel by its contained
blood, expressed in millimeters of Mercury (mm Hg)
As blood is pumped from the heart, the Systemic Circuit is under greater pressure than the
Pulmonary Circuit. Also, arteries closer to the heart are under greater pressure than those farther
from the heart.
1. Systolic Pressure – blood pressure
during ventricular contraction,
averages 120mm Hg
2. Diastolic Pressure – blood pressure
during ventricular relaxation,
averages 70-80mm Hg
Diastole = period when either the atria or
ventricles are relaxing
Systole = period when either the atria or
ventricles are contracting
Cardiac Cycle – refers to events of one
complete heartbeat (average 75 beats per minute)
Heart Sounds: “lub” and “dup”
Lub – the closing of the AV valves
Dup – the closing the semilunar valves
Cardiac output (CO) – the amount of blood
pumped by each ventricle in one minute (HR x
SV)
Stroke Volume (SV) – the amount of blood
pumped by each ventricle during one heartbeat
Regulation of Stroke Volume – Amount of
venous return: if venous return increases the
walls of the heart will stretch farther and
therefore contract more intensely and they will
also increase in speed of contraction
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Electrocardiography
1. EKG – ECG (Electrocardiography) Electrocardiograph –Electrocardiogram
b) See Page 334
c) Electrocardiograph – illustrates the action potential of the heart
d) P wave = atrial depolarization (contraction)
e) Q, R, S Complex = (act as a Unit) = ventricular depolarization (contraction)
f) T wave = ventricular repolarization (movement back to resting state)
g) We do not see a wave of atrial repolarization because it is obscured by ventricular
depolarization
h) Enlarged R wave = enlarged ventricles
i) Flat T wave = ischemia = dead tissue
j) Prolonged Q-T interval = risk of ventricular arrhythmia