Chapter #20: The Heart Flashcards
Systems involved in the heart
-Cardiovascular system
-Pulmonary circuit
-Systemic circuit
Parts of the cardiovascular system
-Heart
-Blood
-Blood vessels
Types of blood vessels
-arteries
-veins
-capillaries (exchange vessels)
Arteries
Carry blood away from heart (carries oxygen rich blood away from the heart and to the organs)
Veins
Return blood to heart (carries deoxygenated blood toward the heart)
Capillaries (exchange vessels)
-Interconnect smallest arteries and smallest veins
-Exchange dissolved gases, nutrients, and wastes between blood and surrounding tissues
Anatomy of the heart
-Great vessels connect at base (superior)
-Pointed tip is apex (inferior)
-Sits between two pleural cavities in mediastinum
**look at diagram on slide 5
Pericardium
-Surrounds heart
-Outer fibrous pericardium
-Inner serous pericardium
–Outer parietal layer
–Inner visceral layer (epicardium)
-Pericardial cavity
–Between parietal and visceral layers
–Contains pericardial fluid
**look at diagram on slide 7
Heart wall consists of three distinct layers
- Epicardium (outer layer)
- Myocardium (middle layer)
- Endocardium (inner layer)
**know diagram on slide 10
Epicardium
-Covers surface of heart
-Covered by parietal layer of serous pericardium
Myocardium
Cardiac muscle tissue
Endocardium
Covers inner surfaces of heart
What direction does blood flow?
Blood flows from right atrium to right ventricle
What is the tricupid valve (right atrioventricular valve)
-Has three cusps
-Prevents backflow of blood
Compared to left ventricle, the right ventricle
-Holds and pumps the same amount of blood
-Has thinner walls
-Develops less pressure
-right side of the heart is weaker & thinner because it is only pumping blood to the lungs, while the left side is thicker because it is pumping blood to the body
**know diagram on slide 13
What is the pathway of blood?
Right atrium –> right ventricle –> lungs –> left atrium –> left ventricle –> body
How does contraction and relaxation work?
-atrial contraction –> ventricle relaxation
-ventricle contraction –> atrial relaxation
Function of Heart Valves
Prevent backflow of blood
Atrioventricular (AV) valves
-Between atria and ventricles
-When ventricles contract,
–Blood pressure closes valves
–Papillary muscles contract and tense chordae tendineae
—Prevents regurgitation (backflow) of blood into atria
Semilunar valves
-Pulmonary and aortic valves
-Prevent backflow of blood into ventricles
Heartbeat
-A single cardiac contraction
-All heart chambers contract in series
–First the atria
–Then the ventricles
Two types of cardiac muscle cells
- Autorhythmic cells: Control and coordinate heartbeat
- Contractile cells: Produce contractions that propel blood
Conducting system
-electrical impulses that stimulate contraction
Autorhythmicity
Cardiac muscle tissue contracts without neural or hormonal stimulation
Components of the conducting system
-Pacemaker cells found in
–Sinoatrial (SA) node—in wall of right atrium
–Atrioventricular (AV) node—at junction between atria and ventricles
-Conducting cells found in
–Atrioventricular (AV) bundle, bundle branches, and Purkinje fibers of ventricles
What are the steps to the conducting system?
- SA node depolarizes and atrial activity begins
- Stimulus spreads across the atrial surfaces and reaches the AV node
- There is a 100-msec delay at the AV node and atrial contraction begins
- The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers to the papillary muscles of the right and left ventricles
- The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed and ventricular contraction begins
**look at diagrams on slides 25-29
Step 1 of the conducting system
-SA node depolarizes first
-establishing sinus rhythm (pattern of heart beat)
-parasympathetic stimulation slows heart rate
-beginning line on graph
Step 2 in conducting system
-P wave: atrial depolarization
Step 3 in conducting system
- P-R interval: conduction through AV node & AV bundle
Step 4 in conducting system
-Q wave: beginning of ventricular depolarization
Step 5 in conducting system
- QRS complex: completion of ventricular depolarization
What is an EKG?
-Electrocardiogram (ECG or EKG)
-captures the heart in 3 dimensions
-a recording of electrical events int he heart
-obtained by placing electrodes at specific location on body surface
-abnormal patterns are used to diagnose damage
Features of an EKG
-P wave: depolarization of atria
-QRS complex: depolarization of ventricles and ventricles begin contracting shortly after R wave
-T wave: repolarization of ventricles
Time intervals between EKG waves
- P–R interval:
–From start of atrial depolarization
–To start of QRS complex
-Q–T interval
–Time required for ventricles to undergo a single cycle of depolarization and repolarization
What segment shows a heart attack?
-an elevated S-T segment shows a heart attack
Which segment can be affected by certain medications?
- Q-T interval
-certain medications prolong this interval and slow your heart rate
Cardiac contractile cells
-Form bulk of atrial and ventricular walls
-Receive stimulus from Purkinje fibers
Intercalated discs
-Interconnect cardiac contractile cells
-Membranes of adjacent cells are
–Held together by desmosomes
–Linked by gap junctions
-Transfer force of contraction from cell to cell
-Propagate action potentials
Events in an action potential in a ventricular contractile cell
- Rapid depolarization
- the plateau
- Repolarization
**know diagram on slide 39
Rapid Depolarization of an action potential in a ventricular contractile cell
-Cause: Na+ entry
-Ends with: Closure of voltage-gated fast sodium channels
The plateau of an action potential in a ventricular contractile cell
-Cause: Ca2+ entry
-Ends with: Closure of slow calcium channels
Repolarization of an action potential in a ventricular contractile cell
-Cause: K+ loss
-Ends with: Closure of slow potassium channels
Cardiac Cycle
-From start of one heartbeat to beginning of next
-Includes alternating periods of contraction and relaxation
Phases of the cardiac cycle within each chamber
-Systole (contraction)
-Diastole (relaxation)
Blood pressure in each chamber of the cardiac cycle
-Rises during systole
-Falls during diastole
-Blood flows from higher pressure to lower pressure
–Controlled by timing of contractions
–Directed by one-way valves
What is the average heart rate?
-75 bpm
-smaller people have a higher heart rate
-larger people have a slower heart rate
Phases of the cardiac cycle
- Atrial systole
- Atrial diastole
- Ventricular systole
- Ventricular diastole
** know diagram on slide 43
Steps of the cardiac cycle
- Atrial systole begins: Atrial contraction forces the blood into relaxed ventricles
- Atrial systole ends, atrial diastole begins
- Ventricular systole - first phase: Ventricular contraction, AV valve closes
- Ventricular systole - second phase: as ventricular pressure rises and exceeds pressure in the arteries, the semilunar valves open and blood is ejected
- Ventricular diastole - early: as ventricles relax, pressure in ventricles drops; blood flows back against cusps of semilunar valves
and forces them closed. Blood
flows into the relaxed atria - Ventricular diastole—late: All chambers are relaxed. Ventricles fill passively
Ventricular systole
-Ventricular ejection
–Ventricular pressure exceeds arterial pressure
–Opens semilunar valves, allowing blood to exit
–Amount of blood ejected = stroke volume
-Semilunar valves close
–As ventricular pressure falls
–Ventricles contain end-systolic volume (ESV) (at the end of contraction, what volume of blood is left)
—-About 40 percent of end-diastolic volume
Atrial damage vs. Ventricular damage
-individuals can survive severe atrial damage
-ventricular damage can lead to heart failure
Cardiac output (CO)
-Volume pumped by left ventricle in one minute
-CO = HR × SV
CO = cardiac output (mL/min)
HR = heart rate (beats/min)
SV = stroke volume (mL/beat)
Ejection fraction
- (blood left)/(total blood initially there)
-great measure of how healthy your heart is, especially after a heart attack - Percentage of EDV ejected during contraction
factors affecting heart rate (HR)
- Autonomic innervation (vagus nerve)
- Hormones (epinephrine & norepinephrine)
Factors affecting stroke volume (SV)
- End-diastolic volume (EDV)
- End-systolic volume (ESV)
-Stroke volume (SV) = EDV - ESV
End-diastolic volume (EDV)
Amount of blood in each ventricle at end of ventricular diastole
End-systolic volume (ESV)
Amount of blood remaining in each ventricle at end of ventricular systole
How to measure cardiac reflexes
-cardiac centers
-monitor:
1. blood pressure (baroreceptors)
2. oxygen
3. carbon dioxide (chemoreceptors)
-adjust cardiac activity
Autonomic Tone
-Maintained by dual innervation and release of ACh and NE
-Fine adjustments meet needs of other systems
Hormonal effects on heart rate
-Heart rate is increased by:
1. Epinephrine (E)
2. Norepinephrine (NE)
3. Thyroid hormone (T3)
Effects of autonomic activity on contractility
-Sympathetic stimulation
–NE released by cardiac nerves
–E and NE released by adrenal medullae
–Causes ventricles to contract with more force
–Increases ejection fraction, decreases ESV
-Parasympathetic stimulation
–ACh released by vagus nerves
–reduces force of cardiac contractions
Summary: the control of cardiac output
-Heart rate control factors
-Autonomic nervous system
-Sympathetic and parasympathetic
-Circulating hormones
-Venous return and stretch receptors
