CH 20 - Cardiovascular System Flashcards
What are the 4 functions of the heart?
Generate blood pressure
Separate pulmonary/systemic circulations
Ensure one-way blood flow with valves
Regulate blood supply
Where does pulmonary circulation occur?
The right side of the heart pumps blood to the lungs, then blood returns to the left side of the heart
Where does systemic circulation occur?
The left side of the heart pumps blood to the body, then blood returns to the right side of the heart
How big is the heart?
Slightly larger than a closed fist
Where is the heart located?
Within the mediastinum of the thoracic cavity, directly behind the sternum
Which intercostal space does the base of the heart sit behind?
Second intercostal space
Which intercostal space does the apex of the heart sit behind?
Fifth intercostal space
Pericardium
Sac-like membrane around the heart, divided into 2 layers
What are the 2 layers of the pericardium?
Fibrous pericardium
Serous pericardium
Describe the fibrous pericardium.
Outer layer made of dense fibrous tissue that anchors the heart to the sternum and diaphragm, and prevents overdistention
Describe the serous pericardium.
Inner layer made of thin, transparent simple squamous epithelium, divided into 2 layers
What are the 2 layers of the serous pericardium?
Parietal pericardium Visceral pericardium (epicardium)
Describe the parietal pericardium.
Outer layer that lines the fibrous pericardium
Describe the visceral pericardium.
Inner layer that covers the surface of the heart
Pericardial cavity
The space between the parietal and visceral serous layers
Contains 15-50 mL of pericardial fluid secreted by the serous membranes to lubricate heart movements
What are the 3 layers of the heart wall?
Briefly describe them.
Pericardium - outer membrane
Myocardium - cardiac muscle
Endocardium - inner membrane
Pectinate muscles
Muscular ridges in the auricles and right atrial wall
What separates pectinate muscles and the smooth part of the atrium?
Crista terminalis
Trabeculae carneae
Muscular ridges and columns on the inside of ventricle walls
Which 3 large veins bring blood to the heart?
Superior vena cava
Inferior vena cava
Pulmonary veins
Which 2 large arteries take blood away from the heart?
Aorta
Pulmonary trunk
How does blood get to the anterior part of the heart?
Anterior interventricular artery
How does blood get to the lateral wall of the left ventricle?
Left marginal artery
How does blood get to the posterior wall of the heart?
Circumflex artery
How does blood get to the lateral wall of the right ventricle?
Right marginal artery
How does blood get to the posterior and inferior aspects of the heart?
Posterior interventricular artery
Which vein drains blood from the left side of the heart?
Great cardiac vein
Which vein drains blood from the right margin of the heart?
Small cardiac vein
Where do veins empty before going to the right atrium?
Coronary sinus
What are 2 other names for the bicuspid valve?
Left atrioventricular valve
Mitral valve
What is another name for the tricuspid valve?
Right atrioventricular valve
How many cusps are within atrioventricular valves?
Tricuspid valve - 3 cusps
Bicuspid valve - 2 cusps
What is the function of atrioventricular valves?
They prevent blood from flowing back into the atria when moving to the ventricles.
Papillary muscles contract when the ventricles contract and prevent the valve from opening by pulling on the chordae tendineae attached to cusps.
How many cusps are within semilunar valves?
Both have 3 cusps
What is the function of semilunar valves?
They prevent blood from flowing back into the ventricles when moving to the great vessels.
When blood flows backwards, it fills the cups, causing them to meet in the middle of the vessel and close it.
List the route blood flows through the heart.
Superior & inferior vena cava Right atrium Tricuspid valve Right ventricle Pulmonary semilunar valve Pulmonary trunk Pulmonary arteries Lungs Pulmonary veins Left atrium Bicuspid valve Left ventricle Aortic semilunar valve Aorta *Body, back to start *Coronary arteries, heart, coronary sinus, cardiac veins, right atrium
How does the right atrium receive blood from the body?
Superior vena cava
Inferior vena cava
Coronary sinus
How does the left atrium receive blood from the lungs?
Pulmonary veins (4)
What does the right ventricle open to?
Pulmonary trunk
What does the left ventricle open to?
Aorta
How many nuclei are in a cardiac muscle cell?
1-2 centrally located nuclei
Where are T tubules of cardiac muscle found?
Why are they here?
Near the Z disk of sarcomeres
Calcium must diffuse a greater distance from SR in order to experience longer contractions to build pressure within the heart
What is the function of intercalated disks?
Speed communication between cells
What is the function of gap junctions in cardiac muscle?
They allow cytoplasm to flow, resulting in low electrical resistance between cells.
This allows AP’s to pass quickly among cells so that the heart depolarizes as a single unit (in sync)
Why are mitochondria and myoglobin abundant in heart muscle?
The heart is almost fully dependent on aerobic metabolism
What is the plateau phase?
Voltage-gated calcium channels remain open for a longer period of time, slowing repolarization.
This causes longer contractions, allowing pressure to build within the heart.
Conducting system
A network of specialized cardiac muscle cells (pacemaker and conducting cells) that initiate and distribute a stimulus to contract
What are the 5 components of a conducting system?
Sinoatrial (SA) node Internodal pathways Atrioventricular (AV) node AV bundle and bundle branches Purkinje fibers
Describe the sinoatrial (SA) node.
Pacemaker cells located in the posterior wall of the right atria, near the superior vena cava
A spontaneous AP is generated here to create a heartbeat, and spreads to conducting cells
Describe internodal pathways.
Conducting cells that distribute signals through both atria
Describe the atrioventricular (AV) node.
Backup pacemaker cells located between atria and ventricles that activate when SA node fails
Slower pacing than SA node
Describe the AV bundle.
Conducting cells that transmit signals from the AV node through a hole in the cardiac skeleton to get to the interventricular septum.
The only electrical connection between the atria and ventricles.
Describe bundle branches.
Conducting cells that transmit signals to the apex, then spread out into ventricular walls
They extend beneath endocardium to apex
Left bundle branch is larger
Describe purkinje fibers.
Thick conducting cells with few myofibrils that radiate up through ventricular walls
Propagate AP’s as fast as myelinated neurons (many gap junctions)
Stimulate ventricular myocardium and trigger a contraction
List the steps of the conducting system.
SA node creates AP that travels across atria walls to AV node
AP passes through AV node along AV bundle into the interventricular septum
AV bundle divides into bundle branches, allowing AP to travel to apex of each ventricle
Purkinje fibers carry AP to ventricular walls and papillary muscles
Autorhythmicity
Cardiac muscle’s ability to contract at its own pace, independent of neural/hormonal stimulation
Pacemaker potential
Spontaneously developing local potential due to movement of sodium, potassium, and calcium
What type of activity do electrocardiograms record?
Electrical heart activity
Summation of all APs in a given time period
What does the P wave represent?
Atrial depolarization
Signals onset of atrial contraction
What does the QRS complex represent?
Ventricular depolarization
Signals onset of ventricular contraction, and simultaneous repolarization of atria
*Larger wave due to larger ventricular muscle mass
What does the T wave represent?
Ventricle repolarization
Precedes ventricular relaxation
What does the PQ (or PR) interval represent?
Period from start of atrial depolarization to start of ventricular depolarization
Atria contracts and begins to relax
Ventricles begin to contract
What does the QT interval represent?
Time for ventricles to undergo a single cycle
Ventricles contract and begin to relax
What event is not seen on an electrocardiogram?
Atrial repolarization - hidden in QRS complex
Cardiac cycle
Repetitive pumping process that begins with onset of contraction and ends with beginning of next contraction
Systole
Contraction of a chamber (blood leaves)
Time between first and second heart sounds
Diastole
Relaxation of a chamber (chamber refills)
Time between second heart sound and next first heart sound
List the 5 steps of the cardiac cycle.
Atrial systole, active ventricular filling
Ventricular systole, period of isovolumetric contraction
Ventricular systole, period of ejection
Ventricular diastole, period of isovolumetric relaxation
Ventricular diastole, passive ventricular filling
What is the state of the heart at the beginning of the cardiac cycle?
Atria and ventricles relaxed
AV valves open
Semilunar valves closed
What happens during atrial systole, active ventricular filling?
Depolarization of SA node creates APs that spread over atria (P wave)
Atria contracts and fills ventricles, beginning cardiac cycle
Atrial diastole until next cycle
What happens during ventricular systole, period of isovolumetric contraction?
Pressure builds in the ventricles, causing AV valves to close (all valves now closed)
End diastolic volume - 120mL of blood left in ventricles from last diastole
Begins at completion of QRS complex
What happens during ventricular systole, period of ejection?
Pressure in ventricles > pressure in pulmonary trunk/aorta, so semilunar valves open and blood is ejected
Left ventricle pressure is much higher than right
End systolic volume - 60mL of blood left in ventricles
What happens during ventricular diastole, period of isovolumetric relaxation?
Completion of T wave results in ventricular repolarization and relaxation
Pulmonary trunk/aorta pressure > ventricular pressure
Semilunar valves close (AV valves also closed) which begins ventricular diastole
What happens during ventricular diastole, passive ventricular filling?
While ventricles were in systole, atria were filling with blood
Atrial pressure > ventricular pressure, AV valves open
Blood flows into relaxed ventricles
Cardiac output
The amount of blood pumped by the heart per minute
Stroke volume x heart rate = cardiac output
Stroke volume
The amount of blood pumped during each heart beat
Heart rate
The number of times the heart beats per minute
Peripheral resistance
The total resistance against which blood must be pumped
Venous return
The amount of blood returning to the heart from systemic circulation
What does the first heart sound “lubb” represent?
Closure of atrioventricular valves and surrounding fluid vibrations at beginning of ventricular systole
What does the second heart sound “dupp” represent?
Closure of semilunar valves at beginning of ventricular diastole (lasts longer)
What is intrinsic regulation controlled by?
Normal heart function
Preload
The amount of stretch of the ventricular walls
The greater the stretch, the greater the force of the contraction
*AKA Starling’s law of the heart
Afterload
The pressure that the contracting walls must produce to overcome the pressure in the aorta to get blood to aorta
*Heart is more sensitive to preload
What is extrinsic regulation controlled by?
Neural and hormonal control
Describe parasympathetic stimulation within extrinsic regulation of the heart.
Supplied by the vagus nerve
Brainstem - heart wall - SA node - AV node - coronary blood vessels - atrial myocardium
Little effect on stroke volume, but can increase since more blood is filling
ACh hyperpolarizes heart, causing longer contractions and a decreased HR
Describe sympathetic stimulation within extrinsic regulation of the heart.
Thoracic spinal cord - cervical sympathetic chain ganglia - SA and AV nodes - coronary blood vessels - atrial/ventricular myocardia
Increases HR, cardiac output, force of contraction, stroke volume
Norepinephrine increases rate of depolarization, AP frequency
What are the effects of blood pressure?
Baroreceptors in the walls of the internal carotids and aorta monitor blood pressure
Sensory info goes to cardioregulatory center in medulla oblongata to increase or decrease heart rate
What are the effects of pH, CO2, and O2?
Chemoreceptors for pH/CO2 are found in the hypothalamus
Chemoreceptors for O2 are found in the internal carotids and aorta
Low O2 increases HR, which increases blood pressure to deliver more O2
Chemoreceptor reflexes regulate heart activity to maintain pH and blood gas values
What are the effects of extracellular ion concentration?
Increase or decrease in EC K+ decreases HR
Heart block can result, which is the loss of AP conduction through the heart
What are the effects of body temperature?
Body temperature increases cause HR increases and vice versa
