AnP Chapter 15 (LO6) Flashcards
The human heart beats about —— times in one day, about ——— times in a year and more than—– times during an average lifetime
The human heart beats about 100,000 times in one day, about 35 million times in a year and more than 2.5 billion times during an average lifetime
Mediastinum
a space between the lungs and beneath the sternum
Base
where are the great vessels enter and leave the heart
the produce part of the heart at the upper right
apex
the point of maximum impulse where the strongest be can be felt or heard
The pointed end at the lower left
Key structures of the heart
include the pericardium, the heart wall, the chambers, and the valves
Pericardium
A double walled sac that surrounds the heart
Anchored by ligaments and tissues to surrounding structures
Has two layers the fibrous pericardium in the Serous pericardium
fibrous pericardium
loose fitting sack of strong connective tissue
the outer most layer
serous pericardium
consists of two layers
covers the hearts surface
It folds back on itself at the hearts base to form the parietal layer and visceral layer
Parietal layer
lions inside of the fibrous pericardium
Visceral layer
covers the hearts surface
Pericardial cavity
cavity contains a small amount of serous fluid which helps prevent friction is the heartbeats
Between the parietal layer and visceral layer
The heart wall
Consists of three layers
Endocardium
lines the heart chambers, covers the valves, and continues into the vessels
Very smooth which helps keep blood from clotting as it fills the hearts Chambers
it consists of a thin layer of squamous epithelial cells
Myocardium
composed of cardiac muscles, formed the middle where
it’s the thickest of the three layers and performs the work of the heart
Epicardium
consists of a thin layer of squamous epithelium cells, covers a hard surface ‘
Also known as the visceral layer of the serous pericardium
the epicardium is closely integrated with the myocardium
The heart contains four hollow chambers
the two upper chambers are called atria or atrium for singular
the two lower chambers are called ventricles
great vessels
several large vessels attached to the heart that transport blood to and from the heart
Includes the superior and inferior vena, pulmonary artery (which branches into a right and left pulmonary artery), four pulmonary veins (two for each lung) and the aorta
Atria
Serve primarily as reservoirs receiving blood from the body or lungs
Interatrial septum: a common wall of the myocardium that separates the right and left atria
Don’t have to generate much force because only moves blood a short distance
The walls of the atria not very thick
Ventricles
Service pumps receiving blood from the atria and then pumping it either to the lungs (right ventricle) or the body (left ventricle)
Interventricular septum separates the right and left ventricles
Generates more force than the atria because they pump blood rather than receive
The walls of the ventricles are thicker
heart valves
To ensure that blood moves in a forward direction the heart contains four valves
One between each atrium and it’s ventricle and another at the exit of each ventricle each valve is formed by two or three flats of tissue called cusps or leaflets
atrioventricular (AV) valves
regulate flow between the atria in the ventricles
The right AV valve
prevents backflow from the right ventricle to the right atrium
Also called the Tricuspid valve because it has three leaflets
The left AV valve
prevents backflow from the left ventricle to the left atrium
Commonly known as the mitral valve
Also known as the bicuspid valve because it has two leaflets
The semilunar valves
regulate flow between the ventricles in the great arteries there are two semi lunar valves: pulmonary and aortic
Pulmonary valve
prevents backflow from the pulmonary artery to the right ventricle
Aortic valve
prevents backflow from the aorta to the left ventricle
Skeleton of the heart
semi rigid fibrous connective tissue that in circles each valve
functions of skeleton of heart
Offer support for the heart,
keeps the valves from stretching,
acts as an insulating barrier between the atria in the ventricles preventing electrical impulses from reaching the ventricles other than through a normal conduction pathway
Where the sounds can be heard the loudest in heart
- Aortic area: second intercostal space, right sternal border
- Pulmonary valve: second intercostal space, left sternal border
- Tricuspid area: fourth (or fifth) intercostal space, left sternal border
- Mitral area: fifth intercostal space, left midclavicular line
Valvular insufficiency
a heart valve that fails to prevent the backflow of blood during contraction it’s called incompetent
Valvular insufficiency allows blood to leak backward or regurgitate into the chamber from which it was just pumped
Valvular stenosis
A stenotic valve that’s become narrowed such as from scar tissue
Force the heart to work harder causing it to strain
Heart mummur:
abnormal sound from turbulence as a result of the backflow of blood through an incompetent valve are the force of blood moving through a stenotic valve
Blood Flow through the Heart how it works
- The right atrium receives the auction needed blood returning from the body through the superior and inferior vena cavae
- Once the right atrium is full of contracts
a) this forces the tricuspid valve open and blood flows into the right ventricle
b) when the right ventricle is full the tricuspid valve snaps close to prevent blood from flowing backwards into the atria - After filling the right ventricle contracts forcing the pulmonary valve open
a) Blood is pumped into the right and left pulmonary arteries and onto the lungs
b) After the right ventricle empties the pulmonary valve closes to prevent blood from flowing backwards into the ventricle - After replenishing its supply of oxygen in the lungs the blood enters the pulmonary veins and returns to the heart through the left atrium
- When the left atrium is full it contracts
a) this forces the mitral or bicuspid valve open and blood is pumped into the left ventricle - When the left ventricle is for the mitral valve closes to prevent backflow
a) The ventricles then contracts forcing the aortic valve to open allowing blood to flow into the aorta
b) From there oxygenated blood is distributed to every organ in the body
Coronary Circulation
The heart muscle requires an abundant supply of oxygen and nutrients
Because of its high demand the heart has its own vascular system known as the coronary circulation
Coronary arteries
deliver oxygenated blood to the myocardium while cardiac veins collect the deoxygenated blood
Two main coronary arteries
arise from the descending aorta and serve as the principal routes for supplying blood to the myocardium
The right coronary artery supplies blood to:
the right atrium,
part of the left atrium,
most of the right ventricle,
the inferior part of the left ventricle
the left coronary artery supplies blood to
Left atrium
most of the left ventricle
most of the interventricular septum
After flowing through the capillaries in the myocardium the cardiac veins…
collect deoxygenated blood
Coronary sinus
a large transverse vein on the heart posterior which returns the blood to the right atrium
Post cardiac veins empty into it
Coronary artery disease
results when the coronary arteries become blocked or narrow by a buildup of cholesterol and fatty deposits (atherosclerosis)
Any interruption in blood supply to the myocardium deprived the heart issues of oxygen (ischemia) causing pain and within minutes cell (nercrosis) death occurs
Angina pectoris
sometimes interruption is temporary and a partially blocked vessel spasms or the heart demands more oxygen than the narrowed vessels can supply resulting in chest pain and ischemia
Myocardial infarction
blood flow is completely blocked by a blood clot or fatty deposit resulting in death of myocardial cells in the area fed by the artery once the cells die they produce an area of necrosis
Cardiac Conduction
Does not depend on stimulation by extrinsic nerves to contract
pacemaker cells
specialize cells that generate action potentials to stimulate contraction a trait called automaticity
rhythmicity
the heartbeats regularly
Electrical impulse is generated by the heart follower very specific route to the myocardium shown here:
- Normal cardiac impulses arise in the sinoatrial (SA) node from its spot in the wall of the right atrium just below the opening of the superior vena cava
- An interatrial bundle of conducting fibers rapidly conduct impulses to the left atrium and both atria begin to contract
- The impulse travels along three internodal bundles to the atrioventricular (AV) node
a) They are the impulse slows considerably to allow the atria time to contract completely in the ventricles to fill with blood
b) The hard skeleton insulates the ventricles ensuring that only impulses passing through the AV node can enter - After passing through the AV node the impulse picks up speed
a) If then travels down the bundle of His also called the atrioventricular AV bundle - The AV bundle soon branches into right and left bundle branches
- Purkinje fibers distribute the impulses to the muscle cells of both ventricles causing them to contract almost simultaneously
Ectopic pacemakers
pacemakers other than the SA node
The heart pacemakers and they’re firing rates when the heart is at rest are as follows:
SA node: fires at —- to — bpm
AV node: fires at — to — bpm
Purkinje fibers: fires at — to –bpm
SA node: fires at 60 to 80 bpm
AV node: has a firing rate of 40 to 60 bpm
Purkinje fibers: have a firing rate of 20 to 40 bpm
Electrocardiogram
Cardiac impulses generate electrical currents that travel through the heart that are recorded
Normal sinus rhythm
an ECG that appears normal meaning the impulse originates in the SA node
Arrythmia
irregular heartbeat
P wave
represents atrial depolarization
Atrial depolarization
the transmission of electrical impulses from the SA node through the atria
It occurs right before the atria contract
PR interval
represents the time it takes for cardiac impulse to travel from the atria to the ventricles
QRS complex:
presents ventricular depolarization
Ventricular depolarization
the spread of electrical impulses throughout the ventricles
ST segment
presents the end of ventricular depolarization in the beginning of ventricular repolarization
T wave:
represents ventricular repolarization
Arrythmias
Result when part of the conduction pathway is injured or when part of the myocardium other than the SA node generates a beat
Common cardiac arrhythmias
atrial flutter,
premature ventricular contractions
ventricular fibrillation
atrial flutter
occurs when an ectopic focus in the atria fire is rapidly causing the atria to contract between 200 and 400 bpm
The AV node blocks impulses in excess of 180 bpm protecting the heart from life-threatening ventricular response
Premature ventricular contractions PVCs
may occur as a single beat or inverse of several beats result from the firing of an ectopic focus in the ventricles
may indicate a serious underlying condition but benign causes include a lack of sleep, caffeine, or emotional stress
Ventricular fibrillation
life-threatening emergency resulting from electrical signals arising from different regions of the myocardium, fibrillation causes the heart to quiver rather than contract
Fibrillating heart can’t pump blood and it must be defibrillated immediately
Cardiac Cycle
The series of events that occur from the beginning of one heartbeat to the beginning of the next
here’s what happens during 1 heart beat:
Passive ventricular filling
Returning venous blood has failed the atria causing their pressure to rise above that in the ventricles
The AV valves open and blood flows into the ventricles
The P wave appears on the ECG marking the end of atrial depolarization
here’s what happens during 1 heart beat:
Atrial systole
The AV valves are open in the semilunar valves are closed
The atria contract to eject the remaining volume of blood
The ventricles are relaxed filling with blood
here’s what happens during 1 heart beat:
Isovolumetric contraction
This is a brief period during which the ventricles are beginning to contract but the semi lunar valve’s haven’t opened yet
Iso: equal
volumetric: volume isovolumetric: something having same volume
The volume of blood in the ventricles remains constant but the pressure rises rapidly as the ventricles begin to contract
The R wave tears on the ECG
First heart sound S1 can be heard
here’s what happens during 1 heart beat:
Ventricular ejection
the pressure in the ventricles exceeds the pressure in the pulmonary artery and aorta the semilunar valves open
Blood spots out of ventricle rapidly at first and then more slowly as the pressure drops
residual volume: the remaining blood the end of the ejection period that the ventricles don’t eject in the ventricles
The T wave occurs late in this phase beginning at the moment of peak ventricular pressure
Isovolumetric ventricular relaxation
This is the period at the end of ventricular ejection before the AV valves opened but after the semilunar valves are closed to prevent blood from reentering the ventricles
Volume of blood in the ventricles remains unchanged but the pressure falls dramatically as the ventricles relax
T wave ends on the ECG
The second heart sound S2 can be heard as blood rebounds against the closed semilunar valves
Cardiac output (CO)
refers to the amount of blood the heart pumps in 1 minute
To determine cardiac output multiplying the heart rate by the stroke volume SV (the amount of blood ejected with each heartbeat)
HR X SV = CO
CO increases with exercise but the average CO is 5 or 6 liters per minute
Because cardiac output equals heart rate times stroke volume, the only two ways to affect cardiac output are:
Change the heart rate
Change the stroke volume
Keep in mind when HR increases SV decreases
Bradycardia
Tachycardia
Bradycardia: a persistent pulse rate slower than 60 bpm
Tachycardia: a persistent resting heart rate greater than 100 bpm
medulla effect on heart rate
The medulla in the brain detect changes in the body and sends messages to the sympathetic or parasympathetic nervous system to raise or lower heart rate
how does the medulla affect the heart rate
1.Medulla in the brain contains a cardiac center
The cardiac center contains an acceleratory center and inhibitory center
HEART RATE: Acceleratory center
Factors such as exercise and stress stimulate it
Acceleratory center sends out impulses via the sympathetic nervous system
HEART RATE:inhibitory center
Factors such as a rise in blood pressure stimulate the inhibitory center
The inhibitory center sends signals via the parasympathetic nervous system
HEART RATE: Sympathetic nervous system
sends impulses through cardiac nerves (which secrete norepinephrine) to the SA node, the AV node, and the myocardium
this accelerates the heart rate and increases the force of contractions
HEART RATE: parasympathetic nervous system
Send signals via the vagus nerve (which secretes acetylcholine) to the SA and AV nodes which slows the heart rate
Input to the cardiac center
The cardiac centre in the medulla receives input from multiple sources to initiate changes in the heart rate these include receptors in the muscles, joints, arteries, and brain stem
Proprioceptors
in muscles and joints and signal the cardiac center of changes in physical activity
this allows the heart to increase output even before the muscles demand more blood flow
Chemoreceptors
found in the aortic arch, carotid arteries and medulla
Detect increases in carbon dioxide, decreases in oxygen and decreases in pH
In response to sympathetic nervous system increases heart rate and stroke volume to circulate more oxygen
Carotid body
a cluster of chemo receptors near the fork of the carotid artery
Aortic body
a cluster of chemo receptors in the aorta
Baroreceptors (pressoreceptors):
pressure sensors in the aorta an internal carotid arteries and detect changes in blood pressure
stroke volume
Stroke volume is never 100% of the volume in the ventricles
Typically the ventricles eject 60% to 80% of their blood volume
Ejection fraction
the percent of the volume that the ventricles eject
Factors affecting stroke volume
preload, contractility and afterload
Preload
The amount of tension, or stretch, in the ventricular muscle just before it contracts
The more blood entering the heart, the more the ventricle stretches
Contractility
The force of which ventricular ejection occurs
how much the ventricle is stretched, the more blood return to the heart each minute, the more forcefully it will contract
Afterload
The forces the heart must work against (as the pressure of the blood in the arteries) to eject its volume of blood
An increase in afterload such as high blood pressure opposes the ejection of blood from the ventricles which decreases stroke volume
Inotropic agents
factors that affect contractility
Positive inotropic agents
agents that increase contractility includes access excess calcium and epinephrine
Negative inotropic agents
agents that decrease contractility includes a calcium deficiency as well as a potassium excess
Chronotropic agents
factors that influence heart rate
Positive Chronotropic agents
agents that increase heart rate include epinephrine and low levels of calcium
Negative Chronotropic agents
agents that decrease heart rate include acetylcholine and excess levels of potassium
Left Ventricular Failure
If the left ventricle fails it falls behind and injecting all of the blood it receives from the lungs
Consequently blood backs up in the lungs
This causes:
shortness of breath
a buildup of fluid in the lungs (pulmonary edema )
coughing
Right Ventricular Failure
If the right ventricle fails it falls behind and injecting all of the blood it receives from the systemic circulation
Flat backs up into the vena cava and throughout the peripheral vascular system
This results in:
Generalized swelling throughout the body (systemic edema)
Enlargement of the liver and spleen
Pooling of fluid in the abdomen (ascites)
Distension of the jugular veins
Swelling of the ankles, feet and fingers
