Remember that the heart is two pumps in one:
- one for the pulmonary circulation
- one for the systemic circulation
Be able to trace the flow of blood through pulmonary circulation.
deoxygenated blood is carried away from the right ventricle, to the lungs, and oxygenated blood is returned to the left atrium and ventricle of the heart
Be able to trace the flow of blood through systemic circulation.
oxygenated blood carried from the left ventricle, through the arteries, to the capillaries in the tissues of the body… from the tissue capillaries, the deoxygenated blood returns through a system of veins to the right atrium of the heart
What is the definition of an artery?
any vessel that carries blood away from the heart
What is the definition of a vein?
any vessel that carries blood to the heart
Does this mean that arteries always carry well-oxygenated blood? What are the exceptions?
no, arteries from the right ventricle carry deoxygenated blood to the lungs
Where in the body is the heart located? (Be specific!)
(between the lungs) in mediastinum
Describe the three layers of the pericardium.
outer fibrous layer: prevents over-stretching, protection, anchors to surrounding tissue
inner serous layer: makes up the pericardial cavity
visceral pericardium: makes up the epicardium
What type of membranes are the visceral and parietal pericardium?
What is in the pericardial cavity?
serous fluid (acts to reduce surface tension and lubricate)
What is cardiac tamponade?
“heart plug”; a clinical syndrome caused by the accumulation of fluid in the pericardial space, resulting in reduced ventricular filling and subsequent hemodynamic compromise
What are the three layers of the heart wall?
- Epicardium: visceral layer of the serous pericardium
- Myocardium: middle layer; “muscle heart”; composed mainly of cardiac muscle; this is the layer that contracts
- Endocardium: third layer of the heart wall; squamous epithelium resting on a thin connective tissue layer continuous throughout circulatory system
Review cardiac muscle on a cellular level (refer back to muscle lectures).
Cardiac muscle is involuntary, striated, branched, typically mono-nucleate, and contain intercalated discs
What do desmosomes and gap junctions do? Where in the muscle fiber are they located?
- Desmosomes and gap junctions make up intercalated discs
- Gap junctions: connects cytoplasm of one cell to the next and allows movement of charged ions to help flow of electrical activity from one cell to the next; functional syncytium
- Desmosomes: “spot welds”
How does calcium function in heart muscle?
Calcium functions to trigger contraction of the heart
Where does most of the calcium used for heart muscle contraction come from?
Most calcium comes from outside the muscle fiber cells
What is the shape of the graph for heart muscle contraction, and what is going on during each phase?
- upside down U (like a normal curve?)
- pacemaker potential - slow depolarization = opening Na+ channels, closing K+ channels (never a flat line)
- action potential - begins when pacemaker potential reaches threshold, depolarization = Ca2+ influx
- repolarization - due to Ca2+ channels inactivating and K+ channels opening
The heart muscle cells contain many large mitochondria, which make up 25-35% of the cell volume. What does this indicate about how the heart produces energy and its ability to become fatigued?
many large mitochondria for aerobic respiration, indicates that the heart will not fatigue very easily
What is the fibrous skeleton of the heart? What 3 functions does it provide for the heart?
- Annuli fibrosi (dense, fibrous connective tissue) that is the origin of insertion for the heart muscle
- functions: anchors cardiac muscle fibers, supports the valves and keeps them open, prevents passage of electrical activity from atria into ventricles
What are the four chambers of the heart?
What grooves or sulci are found in the heart?
Anterior interventricular sulcus
Posterior interventricular sulcus
Identify the trabeculae carnae, the papillary muscles and the chordae tendineae. What do the last two structures do for the heart?
- papillary muscles anchor chordae tendineae and play a role in valve function
- chordae tendineae: “heart stings”; anchor the cusps to the papillary muscles
Be able to name and locate the four valves of the heart.
Atrioventricular Valves - Tricuspid valve - Bicuspid valve Semilunar Valves - Aortic valve - Pulmonary valve
What are the major arteries and veins that supply blood to the heart itself?
- Left coronary artery: Anterior interventricular artery, Circumflex artery
- Right coronary artery: Right marginal artery, Posterior interventricular artery
# Coronary veins
- Cardiac veins
- Coronary sinus: Great cardiac vein, Middle cardiac vein, Small cardiac vein
- Several anterior cardiac veins
What are anastomoses, and how did they benefit the heart?
junctions that provide additional routes for blood delivery
What is ischemia?
reduced blood flow
What is hypoxia?
reduced oxygen supply
What is myocardial infarction?
- death of an area of tissue due to interrupted blood flow
What is angina pectoris?
- thoracic pain caused by a deficiency in blood delivery to the myocardium
What is the cardiac cycle?
- one complete heartbeat
- systole (contraction) and diastole (relaxation) of both atria and systole/diastole of both ventricles
What are the events of the cardiac cycle?
(1) Ventricular filling: AV valves open; 80% of blood passes into ventricles; atrial systole occurs delivering remaining 20%; end diastolic volume: volume of blood in each ventricle at the end of ventricular diastole
(2) Ventricular systole (atria in diastole): atria relax; ventricles begin to contract; rising ventricular pressure and closing of AV valves; isovolumetric contraction phase—all valves are closed; ventricular pressure exceeds pressure in large arteries forcing SL valves open; end systolic volume: volume of blood remaining in each ventricle after systole
(3) Isovolumetric relaxation (early diastole): ventricles relax; atria relaxed and filling; backflow of blood in aorta and pulmonary trunk closes SL valves; causes dicrotic notch; ventricles totally closed chambers; when atrial pressure exceeds that in ventricles, AV valves open and cycle restarts
How much blood flows into the ventricles passively, and how much enters due to atrial contraction?
80% from ventricles
20% from atrial contraction
What three vessels empty into the right atrium?
Superior vena cava
Inferior vena cava
What are the heart sounds and what causes them?
The two sounds (lub-dup) associated with the closing of heart valves during a heartbeat
AV valves close first, beginning of systole
SL valves close next, beginning of ventricular diastole
Where can you place the stethoscope to hear the sounds for each of the heart valves by itself?
Aortic valve: 2nd intercostal space at right sternal margin
Pulmonary valve: 2nd intercostal space at left sternal margin
Bicuspid: 5th intercostal space in middle of clavicle
Tricupsid: right sternal margin of 5th intercostal space
A heart murmur signals trouble with what part of the heart?
insufficient or incompetent valves fail to close completely
Trace the path of impulse flow through the conduction system of the heart. What is unusual about the resting potential for the cells of the SA node, or pacemaker? How does this occur?
sinoatrial node => both atria => atrioventricular node => 120 ms delay => down bundle of His => signal splits to right and left bundle branches => left activated before right => left bundle splits to left anterior/posterior fascicles => signal spreads through Purkinje fibers => distribute signal between ventricles => causing an organized sequential contraction of heart
sinoatrial node => atrioventricular node => atrioventricular bundle (of His) => right and left bundle branches => Purkinje fibers
unusual by having no true resting potential, but instead generate regular, spontaneous action potentials
How does the fibrous skeleton of the heart affect the flow of electrical activity between the atria and ventricles?
it is made of connective tissue, which slows down the electrical flow between the atria and the ventricles
The SA node, AV node, and Purkinje fibers can all act as pacemakers in the heart. What affects which one sets the rhythm of heart contractions?
SA node = ~75 bpm
AV node = ~50 times per minute
Purkinje = ~30 times per minute
(slower cannot be pacemakers unless faster ones are not functioning)
What is an ectopic pacemaker?
an abnormal pacemaker that may appear and take over the pacing of heart rate (caused by a defective SA node)
Name the waves of an electrocardiogram.
P wave, QRS complex, T wave
What causes each wave?
P wave: atrial depolarization (SA node)
QRS complex: ventricular depolarization atrial repolarization
T wave: ventricular repolarization
Where is the wave for atrial relaxation (diastole)?
Atrial relaxation (diastole—atrial repolarization) occurs in the QRS complex
What is bradycardia?
slow heart rate (<60 bpm)
What is tachycardia?
fast heart rate (>100 bpm)
What part of the brain regulates heart rate?
Trace the path of the sympathetic nerves from the medulla to the heart.
- sympathetic increases heart rate and force of contraction
- secretes epinephrine to accelerator nerves => epinephrine increases heart rate
Trace the path of the parasympathetic nerves from the medulla to the heart.
- parasympathetic decreases heart rate and force of contraction to the vagus nerve
- sends continuous impulses => secretes acetylcholine—decreases heart rate
What effect would acetylcholine have on the heart?
decreases pacemaker rate by increasing potassium and decreasing calcium and sodium movement
What effect would epinephrine or norepinephrine have on the heart?
increases rate and force of contraction of the heart
How does the fetal circulation differ from a postnatal infant?
The interatrial septum of the fetal heart is incomplete. At birth, placental blood flow ceases and lung respiration begins. The sudden drop in right atrial pressure pushes the septum primum against the septum secundum, closing the foramen ovale
What do the ductus venosus, the ductus arteriosus and the foramen ovale bypass? (Be able to name the remnants of these structures in the postnatal individual)
- Ductus arteriosus: a lung bypass in fetuses that exists between the pulmonary trunk and the aorta (remnant: ligamentum arteriosum)
- Ductus venosus: shunts a portion of the left umbilical vein blood flow directly to the inferior vena cava (allows oxygenated blood from the placenta to bypass the liver) (remnant: ligamentum venosum)
- Foramen ovale: “oval door” that connects the two atria and allows blood entering the right heart to bypass the pulmonary circuit and the collapsed, non functional fetal lungs (remnant: fossa ovalis)
What kind of blood does the umbilical vein carry?
What kind of blood does the umbilical arteries carry?
What happens if baroreceptors in the arteries detect an increase in blood pressure?
increased blood pressure in the arteries detected by baroreceptors increases parasympathetic output
What is the Bainbridge or atrial reflex?
Bainbridge (atrial) reflex stimulates both stretch receptors and SA node = increase in sympathetic output
Why does our heart rate increase when we are nervous?
hormones like epinephrine (that increase when we are nervous as a result of the sympathetic nervous system) increases heart rate and contraction by secreting epinephrine to accelerator neurons
How do temperature, blood Ca2+ levels and blood K+ levels, epinephrine and thyroxine affect the heart?
- Increased temperature, increased heart rate by enhancing the metabolic rate of cardiac cells; cold decreases heart rate
- Blood Ca2+ levels
- Low: depress the heart rate
- Normal: increase heart rate
- Very high: disrupt heart function
- Blood K+ levels
- Low and high: dangerous
- Excessive: alters electrical activity in the heart by depolarizing the resting potential and may lead to cardiac arrest
- epinephrine and thyroxine increase heart rate
How do age, gender and physical conditioning affect heart rate?
- Heart rate is fastest in the fetus and declines throughout your lifetime
- Females have a faster heart beat than males
- Physical conditioning
- Exercise raises heart rate by acting through the sympathetic nervous system
- Resting heart rate in those who are physically fit tends to be lower
What is cardiac output? Be able to calculate it.
the amount of blood pumped out of each ventricle in one minute = SV (ml/beat) * HR (beats/min) = CO (ml/min)
What three factors affect how the heart pumps?
- preload, or the stretch on the ventricles prior to contraction
- contractility, or the force or strength of the contraction itself
- afterload, the force the ventricles must generate to pump blood against the resistance in the vessels
Which is the most critical for controlling stroke
What is (Frank-)Starling’s Law? How does this work on the level of the cardiac muscle fiber?
“within limits, the greater the stretching fibers are shorter than optimal length”
- resting cardiac muscle fibers are shorter than optimal length
What affects contractility of the heart?
Ca++ influx, increased sympathetic stimulation, hormones (glucagon, thyroxine, epinephrine, and digitalis), acidosis, increased cellular K+, calcium channel blockers
How does epinephrine work to increase contractility?
an endogenous catecholamine with α- and β-adrenergic effects and at low doses, the β-adrenergic effect predominates in increasing contactility
What is meant by a positive inotropic agent?
strengthens the force of the heartbeat
What are some negative inotropic agents?
acidosis, increased cellular K+, calcium channel blockers
What can cause an increase in afterload?
when aortic pressure and systemic vascular resistance are increased, by aortic valve stenosis, and by ventricular dilation
What is the afterload typically on the aortic vs. the pulmonary valves?
aorta = 80 mm Hg pulmonary = 8 mm Hg