The Circulatory System: Heart Flashcards
cardiovascular system
consists of heart and blood vessels
circulatory system
refers to heart, vessels, and blood
pulmonary circuit
carries blood to and from gas exchange surfaces of lungs
right ventricle-> lungs -> left atrium
systemic circuit
carries blood to and from the body
left ventricle -> body-> right atrium
arteries
carry blood away from heart
veins
carry blood to heart
capillaries (exchange vessels)
networks between arteries and veins
exchange material between blood and tissues
dissolved gases, nutrients, wastes
the heart
left of midline, between 2nd rib and 5th intercostal space
posterior to sternum, in pericardial cavity in mediastinum
fist sized, <1 lb
beats 100,000 times/day moving 8,000 liters blood/day
surrounded by pericardium: serous and fibrous layers
serous membranes
visceral and parietal
secrete pericardial fluid, reduce friction
parietal pericardium
outer layer
visceral pericardium
inner layer of pericardium
heart is located
directly behind sternum
pericarditis
inflammation of pericardium, usually due to infection
causes friction
cardiac tamponade
buildup of fluid in pericardial space
superficial anatomy of the heart
coronary sulcus and anterior and posterior interventricular sulci
external divisions of the heart
great veins and arteries at the base
pointed tip is apex
coronary sulcus
divides atria and ventricles
anterior and posterior interventricular sulci
separate left and right ventricles
contain blood vessels of cardiac muscle
4 chambers of the heart
right atrium, right ventricle, left atrium, left ventricle
right atrium
collects blood from systemic circuit
right ventricle
pumps blood to pulmonary circuit
left atrium
collects blood from pulmonary circuit
left ventricle
pumps blood to systemic circuit
2 for each circuit
left and right: 2 ventricles and 2 atria
2 atria
superior, thin walls
smooth posterior walls internally
pectinate muscles (ridges) anteriorly
has expandable flap called an auricle lateral and superior
left and right separated by interatrial septum
2 ventricles
inferior, thick walls, lined with trabeculae carneae (muscular ridges)
left and right separated by interventricular septum
left ventricle 3x thicker, 5x more friction while pumping, same volume as right one
left is round, right is crescent
left and right ventricles
have significant structural differences
3 layers of the heart wall
epicardium
myocardium
endocardium
epicardium
thin outer layer
visceral pericardium: serous membrane
loose CT attached to myocardium
myocardium
thick middle layer
cardiac muscle tissue with CT, vessels and nerves
endocardium
thin inner layer
simple squamous epithelium lining with basal lamina
continuous with endothelium blood vessels
cardiac muscle tissue
muscle cells=cardiocytes
uses actin and myosin sliding filaments to contract
rich in mitochondria, resists fatigue but dependent on aerobic respiration
cells connected by intercalated discs
contraction is all or none
longer contractile phase than skeletal muscle
fibrous skeleton of the heart (tough CT) acts as the tendon
intercalated discs
interconnect cardiac muscle cells
secured by desmosomes
linked by gap junctions
convey force of contraction
propagate action potentials
the heart valves
one-way valves prevent backflow during contraction
atrioventricular (AV) valves
connect atria to ventricles
permit blood flow in 1 direction: atria to ventricles
flaps=cusps
pressure closes valve cusps during ventricular contraction
1. tricuspid valve: right side, 3 cusps
2. bicuspid/mitral valve: left side, 2 cusps
Cusps
Cusps attached to chordae
tendineae from papillary muscles on ventricle wall
Contraction of papillary muscles prevent cusps opening backward during ventricle contraction
Prevent back flow
Cusps hang loose when ventricles not contraction, allow ventricles to fill with blood
semilunar valves
Between ventricles and arteries
3 cusps
No chordae tendineae or muscles
Forced open by blood from ventricular contraction
Snap closed to prevent backflow
Valvular heart disease
Valve function deteriorates to extent that heart cannot maintain adequate circulation
Rheumatic fever: childhood reaction to streptococcal infection, chronic carditis, VHD in adult
Heart murmur
Leaky valve
Mitral valve prolapse - murmur of left AV valve, cusps don’t close properly, blood regurgitates back into left atrium
Congestive heart failure
Decreased pumping efficiency- Diseased valves, damaged muscle
Blood backs up → fluid leaks from vessels and collects in lungs and tissues
the pulmonary circuit
- Blood flows from right ventricle to pulmonary trunk
– through pulmonary semilunar
valve
* Pulmonary trunk divides
into left and right pulmonary arteries
* Blood from the lungs gathers into left and right pulmonary veins - Pulmonary veins deliver blood to left atrium
* Blood from left atrium passes to left ventricle
– through left atrioventricular (AV) valve (bicuspid valve or mitral
valve)
the systemic circuit
- Blood leaves left ventricle and goes into ascending aorta
– through aortic semilunar valve
* Ascending aorta → aortic arch
supplies blood to the tissues
* Blood from the tissues gathers into Superior and Inferior vena cava - Superior and Inferior vena cava delivers systemic circulation to right atrium
– through right atrioventricular
(AV) valve (tricuspid valve) blood is delivered to the right ventricle
The Vena Cava
delivers systemic circulation to right atrium
superior and inferior
Superior vena cava
receives blood from head, neck, upper limbs, and
chest
Inferior vena cava
receives blood from trunk, and viscera, lower
limbs
Foramen ovale
Before birth, is an opening through interatrial septum in the right atrium
Connects the 2 atria
~25% of blood bypasses directly
the left atrium
Closes at birth leaving scar called fossa ovalis
Ductus arteriosus
Connects pulmonary trunk to aorta
~90% of blood bypasses lungs
Closes at birth leaving the
ligamentum arteriosum
Failure of either to close
poor
oxygenation of blood, cyanosis,
“blue baby syndrome”
The heart has 4 chambers:
– 2 for pulmonary circuit:
* right atrium and right ventricle
– 2 for systemic circuit:
* left atrium and left ventricle
Left ventricle has a greater workload
more massive than right ventricle, but the two chambers
pump equal amounts of blood
AV valves
prevent backflow from ventricles into atria
Semilunar valves
prevent backflow from aortic and pulmonary trunks into ventricles
Coronary Circulation
- Coronary arteries and cardiac veins
- Supplies blood to muscle tissue of heart
- Heart = <1% body mass, requires 5% of blood
- Coronary arteries
– originate at base of ascending aorta
– branch to capillary beds for diffusion - Blood returns via cardiac veins
– Cardiac veins empty into right atrium
Coronary artery disease
- Partial or complete block of coronary
circulation, results in coronary ischemia - Can lead to myocardial infraction (heart attack)
– Heart tissue denied oxygen dies - Common symptom
– Angina pectoris: - plan in the chest, especially during activity, as a result of
ischemia
Coronary bypass surgery
- Use healthy veins (from
legs) to create anastomoses
around blockages - Most people have 4 major
coronary arteries →
“quadruple bypass”
The Heartbeat
A single contraction of the heart
* Conducting system
* Contraction of Myocardium
– Systole and diastole
* Heart sounds
* Cardiodynamics/volumes
types of cardiac muscle cells
conducting system and contractile cells
Conducting system
Controls and coordinates heartbeat (1% myocardial
cells autorhythmic)
–Depolarize without neural or endocrine stimulation
Contractile cells
Produce contractions that propel blood
Structures of the Conducting System
Depolarization transmitted to other myocardial cells through cardiac conduction system
1. Sinoatrial (SA) node
2. Atrioventricular (AV) node
3. Conducting cells
SA node
Right atrium wall near superior vena cava
AV node
Inferior portion of interatrial septum above tricuspid valve
Conducting cells
throughout myocardium
– controls and coordinates heartbeat
– connect nodes and myocardium
– distribute stimulus through myocardium
In the atrium contracting cells
Interconnect SA and AV nodes
In the ventricles contracting cells
AV bundle, bundle branches and Purkinje fibers
Conducting System and the Cardiac Cycle
- Begins with action potential at SA node
– gradually depolarizes toward threshold
– transmitted through conducting system
– produces action potentials in cardiac muscle cells
(contractile cells) - SA node is called also pacemaker potential
- SA node depolarizes first, establishing heart
rate
The Cardiac Cycle
- Cells of nodes cannot maintain resting
membrane potential, drift to depolarization:
– SA node: 80-100 action potentials/min - “natural pacemaker”
– AV node: 40-60 action potentials/min - Resting rate (sinus rhythm)
– ~75 bpm set by SA node + parasympathetic
stimulation
Abnormal Pacemaker Function
- Normal average heart rate = ~70-80 bpm
– Max = ~230 bpm, but inefficient above 180
1. Bradycardia: <60 bpm
– abnormally slow heart rate
2. Tachycardia: >100 bpm
– abnormally fast heart rate
Electrocardiogram (ECG or EKG)
- A recording of electrical events in the heart
- Obtained by electrodes at specific body locations
- Abnormal patterns diagnose damage
Features of an ECG
- P wave: atria depolarize
– Depolarization wave from SA node through atria
~80ms - PQ segment: time (approximately ~160ms) between P
and Q deflections - QRS complex: ventricles depolarize
– Atrial repolarization and ventricle depolarization
~80ms - ST segment: time between S and T deflections
- T wave:
– Ventricle repolarization ~160ms
EKG used to diagnose heart problems
- Cardiac Arrhythmias
– Abnormal patterns of cardiac electrical activity - Fibrillation
– Rapid, irregular, out of phase contractions due to
activity in areas other than SA node
– Defibrillation to stop all activity so SA node can
resume control
Heart rate is normally established by cells of
SA node
Rate can be modified by
autonomic activity, hormones,
and other factors
From the SA node, stimulus is conducted to
AV node, AV bundle, bundle branches, and Purkinje fibers before
reaching ventricular muscle cells
Electrical events associated with the heartbeat can be
monitored in an
electrocardiogram (ECG)
The Cardiac Cycle
- The period between
the start of 1
heartbeat and the
beginning of the next - Alternation
contraction and
relaxation
Two Phases of the Cardiac Cycle
Within any 1 chamber:
– systole (contraction)
* Contraction
* High pressure
* Blood gets pushed to next chamber
– diastole (relaxation)
* Relaxation
* Low pressure
* Chamber fills with blood
Blood Flow
Blood flows from high to low pressure:
* Controlled by timing of contractions
* Directed by one-way valves
Blood Pressure
– In any chamber
* Rises during systole
* Falls during diastole
4 Phases of the Cardiac Cycle
- Atrial systole
- Atrial diastole
- Ventricular systole
- Ventricular diastole
Cardiac Cycle and Heart Rate
- At 75 beats per minute:
– cardiac cycle lasts about 800 msecs - When heart rate increases:
– all phases of cardiac cycle shorten, particularly
diastole
Heart Sounds
- S1: “lubb”
– produced by AV valves closing at start of ventricular systole - S2: “dubb”
– produced by semilunar valves closing at start of ventricular
diastole - S3, S4:
– soft sounds
– blood flow into ventricles and atrial contraction
Heart Murmur
Sounds produced by regurgitation through valves
Cardiodynamics
The movement and force generated by cardiac
contractions
cardiac output
Amount of blood pumped by left ventricle in one
minute, depends on heart rate (HR) and stroke
volume (SV)
CO= HR x SV
End-diastolic volume (EDV)
~120 ml
Volume of blood in ventricle before contraction
End-systolic volume (ESV)
~50 ml
Volume of blood in ventricle following a beat
Stroke volume (SV)
~70 ml
Amount of blood pumped by ventricle
SV = EDV — ESV
Usually SV is constant, you need to change HR to increase CO as needed.
Stroke Volume
Volume (ml) of blood ejected per beat
Cardiac Output
Cardiac output (CO) ml/min =
Heart rate (HR) beats/min x Stroke volume (SV) ml/beat
Organization of cardiovascular system
pulmonary and systemic circuits
3 types of blood vessels
arteries, veins, and capillaries
