BIO211 Weekly Guide #2
HEART;
CARDIAC PHYSIOLOGY
After completing this laboratory you should be able to:
1) Distinguish clearly between systemic and pulmonary circulations
2) Identify the chambers, great vessels, major external structures, intrinsic vessels, and major internal structure of the heart
3) Recognize and describe the structure of the pericardium, distinguishing between the visceral and parietal pericardium
4) Describe in some detail how the heartbeat originates, spreads, and is physiologically regulated
5) Describe the anatomical and physiological bases of heart sounds and the EKG and the basic technology for assessing these
6) Define heart rate, stroke volume, and cardiac output and be able to state approximate "healthy" values for each in adults, using appropriate units of measurement
7) Define Starling's Law of the Heart and relate it to both cardiac muscle function and passive control of cardiac output
8) Define Fick's Principle and use it to calculate cardiac output from indirect measures
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. The Cardiovascular System {FAP 20-Introduction}
A. Cardiovascular system vs. other circulations
B. Systemic vs. pulmonary circulations
C. "Portal" circulations
D. Role of the heart
II. Heart Anatomy {FAP 20-1}
A. Gross anatomy
location and size
chambers, septa, great vessels, valves, associated structures
blood flow pattern - oxygenated vs. nonoxygenated blood
relative pressure relationships
coronary circulation
fetal cardiac circulation
B. Pericardium
visceral (epicardium) & parietal layers
fibrous and serous layers
pericardial "space" & fluid
C. Histology
endocardium
myocardium
specializations - pectinate muscles, papillary muscles, trabeculae carnae
epicardium = visceral pericardium
valve structure - rings, leaflets, chordae tendineae
III. Heart Physiology {FAP 20-2, 20-3, 20-4}
A. Cardiac cycle
sequence and approximate timing
heart sounds
mechanism
excitation vs. contraction
conduction paths
AV and SA nodes
bundle of His
Purkinje fibers
pressure/volume relationships {FAP Fig 20-17, 20-18}
control
intrinsic rhythms - pacemakers
output regulation by venous return - Starling's Law of the Heart
nervous control - vagus (parasympathetic) vs. sympathetic effects
hormonal control - epinephrine, auriculin
B. Cardiac Assessment {FAP Fig 20-13}
ECG/EKG
heart murmurs
echocardiogram
Fick's Principle
C. Cardiac Syndromes {FAP Spotlight 20-10, 20-14}
myocardial infarction
cardiac arrhythmias
coronary artery disease
congestive heart failure
Gross Anatomy List
Structures Surrounding the Heart:
mediastinum
pericardium
visceral and parietal
Heart External Structures:
apex ascending aorta coronary sinus
base pulmonary trunk aortic arch
diaphragmatic surface superior vena cava brachiocephalic artery
atrioventricular groove inferior vena cava left common carotid artery
interventricular groove pulmonary veins left subclavian artery
auricles coronary arteries ligamentum arteriosum
Heart Internal Structures:
Right Atrium: Left Atrium:
openings: openings:
superior vena cava pulmonary veins
inferior vena cava
coronary sinus
interatrial septum
fossa ovalis
pectinate muscles
Right Ventricle: Left Ventricle:
tricuspid valve mitral (bicuspid) valve
interventricular septum trabeculae carnae
trabeculae carnae papillary muscles
papillary muscles chordae tendineae
chordae tendineae
Pulmonary Trunk: Ascending Aorta:
pulmonary semilunar valve aortic semilunar valve
coronary artery openings
sinuses of Valsalva
Key: Know location and function of all structures
Not required
Guide to Gross Anatomy
Mediastinum {FAP Fig 20--2, 20-3}
The mediastinum is the region in the middle of the thorax, between the lungs, bounded by the mediastinal pleurae, the diaphragm, the thoracic vertebrae, and the sternum and costal cartilages.
- List the structures which share the mediastinum with the heart.
Heart Models {FAP Fig 20-3, 20-6, 20-9; APL Exercise 17-1}
The heart is a muscular organ, about the size of your fist, which lies in the middle region of the inferior mediastinum. It is enclosed in and suspended by the pericardium, a tough double sac of fibrous connective tissue.
a) On the models and heart preparations locate the following regions of the heart:
apex base diaphragmatic surface
- The heart lies obliquely in the thorax, so that roughly 2/3 of it lies to the left of the midsagittal plane. On average, the base is at the level of the sternal articulation of the 3rd costal cartilage, while the apex is at the level of the 5th intercostal space. However, there is a great deal of variation between individuals.
b) On the models and heart preps locate the following external surface structures of the heart:
atrioventricular groove right & left auricles
ant. & post. interventricular grooves
- The atrioventricular groove traces the division between which chambers of the heart?
- The interventricular grooves traces the division between which chambers of the heart?
- Of which heart chambers are the auricles extensions?
c) Locate the following great vessels and related structures:
ascending aorta superior vena cava
aortic arch inferior vena cava
brachiocephalic artery pulmonary trunk
left common carotid artery pulmonary arteries
left subclavian artery pulmonary veins
ligamentum arteriosum
- For each vessel be able to identify the region that it supplies or drains.
- Which vessels carry oxygenated blood? Which carry deoxygenated blood?
- The ligamentum arteriosum is a remnant of the ductus arteriosus, which shunts blood from the left pulmonary artery to the distal aortic arch in the fetus. What is the purpose of this shunt?
d) On the models and heart preps locate the following internal structures of the heart:
left atrium:
pulmonary vein openings
right atrium:
superior vena cava opening coronary sinus opening
inferior vena cava opening pectinate muscles
interatrial septum:
fossa ovalis
left ventricle:
trabeculae carnae cordae tendineae aortic semilunar valve
papillary muscles mitral (bicuspid) valve
right ventricle:
trabeculae carnae cordae tendineae pulmonary semilunar valve
papillary muscles tricuspid valve
interventricular septum
- Trace the flow of blood through one complete circuit of the circulatory system. What is the sequence of heart chambers and great heart vessels that a blood corpuscle would encounter on this circuit?
- Note that the heart is actually two pumps. The left one receives pulmonary (lung) return and supplies the systemic (body) circulation. The right one receives systemic return and supplies the pulmonary circulation. Which side pumps a higher volume of blood? Which side pumps at a higher average pressure?
- The interatrial septum and the interventricular septum form the walls between the two atria and the two ventricles, respectively. A prominent feature of the interatrial septum is the fossa ovalis, a sealed connective tissue flap. At birth, this flap covers the foramen ovale, which shunts blood from the inferior vena cava through the right atrium to the left atrium in the fetus. What is the purpose of this fetal shunt?
- Why is the wall of the left ventricle much thicker than the that of the right ventricle? Similarly, why are the trabeculae carnae and the papillary muscles so much better developed in the left ventricle than the right?
- Study the heart models and heart preps and develop a set of criteria which will allow you to tell the chambers apart, based solely on the appearance of the chamber walls.
- One very common source of confusion for students is the true anatomical (spatial) relationship between the heart chambers. Drawings in texts, charts, and even most models, depict the right and left atria and ventricles as lying side by side, with the septae in roughly horizontal and sagittal planes. In reality the heart spirals from base to apex and is positioned obliquely in the thorax. This places the interatrial and interventricular septae in roughly coronal planes, and the atrioventricular septum in an oblique plane. The left ventricle lies anterior to the right ventricle, while the right atrium lies anterior to the left atrium. Study the model and plasticized hearts until you are comfortable with the spatial relationships.
- The atrioventricular valves prevent backflow of blood from the ventricles to the atria when the ventricles contract (systole). They have broad flat triangular leaves(cusps) which are seated in fibrous rings. Between which two chambers does the mitral (bicuspid) valve lie? Between which two chambers does the tricuspid valve lie? How do the papillary muscles and chordae tendineae contribute to the function of the atrioventricular valves?
- The semilunar valves prevent backflow of blood from the aortic and pulmonary trunks into the ventricles between contractions (intersystole or diastole). They are named for the shape of their cusps. Study diagrams of the cusps until you understand why the backflow of blood causes them to close.
e) The arterial blood supply to the heart is via the coronary arteries. These branch from the ascending aorta immediately after its exit from the heart. Most of the venous drainage of the cardiac circulation is via the network of cardiac veins to the coronary sinus. The coronary sinus empties into the right atrium near the fossa ovalis.
- Identify the right and left coronary arteries and the coronary sinus on the models and heart preps. Which of the surface grooves does each occupy?
- The aortic openings of the coronary arteries are located in small cavities behind two of the cusps of the aortic semilunar valve. These cavities are called the sinuses of Valsalva. A proposed function of these sinuses is to create eddy currents which prevent the valve cusps from blocking the coronary artery apertures when the valves are open.
f) Study the conduction mechanism of the heart.
- On a heart model trace the path of electrical impulse spread, pointing out the location of the major specialized structures - the SA node, the AV node, the bundle of His (AV bundle).
- Locate the vagus nerves which act to slow the heart rate and reduce stroke volume.
g) The heart is surrounded by the pericardium, a doubled sac. The pericardium has an inner visceral (organ) and an outer parietal (wall) layer. The visceral pericardium is fused to the heart muscle, and is identical to the epicardium. The visceral and parietal layers are separated by the pericardial cavity, a "virtual" space which contains a thin layer of serous fluid which provides lubrication and allows the heart to move within the thorax.
- Note that the pericardial cavity lies between the visceral and parietal pericardia and not between the heart and the visceral pericardium. It is very important that you understand this relationship well, because analogous relationships hold for the pleurae of the lungs and the peritoneum of the abdominal cavity. If necessary, have the instructor or a classmate demonstrate the relationship with a plastic bag and his/her fist.
- Note that both the visceral pericardium and the parietal pericardium have two distinct histological layers - a fibrous layer of dense irregular C.T. which provides structural integrity, and a serous pericardium (mesothelium) of simple squamous epithelium which produces the pericardial fluid.
Sheep Heart Dissection {FAP Fig 20-6; APL Exercise 17-1)
Work in small groups to dissect the preserved sheep heart, following the final part of Exercise 1 and the handouts. Be able to identify the surface features, chambers, great vessels, valves, and associated structures in the preserved heart
Guide to Histology
There are no loan collection slides which deal specifically with the heart, except for the cardiac muscle slides which you examined last semester. As a review and clarification of what was presented in the lecture, work through the following:
1) Review the structure and function of the three heart layers, the endocardium, the myocardium, and the epicardium.
2) Review the layers of the pericardium. To which layer of the cardiac wall does the visceral pericardium correspond? What is the product of the serous pericardia?
{FAP Fig 20-4}
3) Review the structure and identifying features of cardiac muscle. In which layer of the cardiac wall is cardiac muscle found? {FAP Fig 20-5; APL Fig 17.12}
4) For what purpose are the specialized cardiac muscle fibers constituting the Purkinje fibers and the moderator band adapted? Where are they located and how do they differ from ordinary cardiac muscle fibers?
Guide to Physiology
Cardiac Conduction {FAP Fig 20-12}
Work through this APL exercise to review the cardiac conduction pathways and the pattern of initiation and spread of excitation in each heart cycle.
EKG {FAP Fig 20-13; APL Exercise 19-5}
1) Start up the computer and log on as PhysioStudent (the instructor will provide the password). Turn on the PowerLab box. Select AP EKG to start the Chart application
with a simple EKG setup.
2) Hookup the subject to the PowerLab, using the following guide:
a) Snap new electrodes onto the three EKG leads (red, white, and black).
b) Stick the WHITE electrode to the subject's RIGHT WRIST.
Stick the BLACK electrode to the subject's LEFT WRIST.
Stick the RED or GREEN electrode to the subject's LEFT ANKLE.
c) Attach the clip on the EKG gray cable somewhere convenient on the subject's clothing.
3) Have the subject relax in a seated position, with her forearms supinated and resting on her thighs. Make sure that her hands are relaxed. Start the Chart display. The instructor will help you adjust the display ranges and any other Chart parameters to produce an effective EEG display with an appropriate plotting range.
4) Note that the upper trace (CH1) is the EKG, while the lower trace and the box insert are monitoring heart rate.
5) Once you have good settings, run the display for at least a minute, to get a good baseline display.
6) Your instructor will show you how to select and "zoom" a section of the EKG and print it out.
7) Transfer the electrode leads to another member of your group.
8) On your printout, identify the following EKG component peaks and measures, and compare them to the "normal" values below.
"Normal" resting baseline values for the duration and voltage of different phases of the EKG complex are:
P wave: 0.1 sec duration P-R interval: 0.13 to 0.16 sec
0.2 mV amplitude Q-T interval: 0.30 to 0.34 sec
QRS complex: 0.08 to 0.12 sec duration P-R segment: 0.03 to 0.06 sec
1.0 mV amplitude S-T segment: 0.08 sec
T wave: 0.16 to 0.27 sec duration
0.2 to 0.3 mV amplitude
Cardiac Heart Sounds {APL Exercise 19-1}
You may be most comfortable listening to your own heart sounds. You can use rom MSC 103 if you want more privacy. BE EXTREMELY CAREFUL WITH THE STETHOSCOPE TAMBOR WHENEVER THE EARPIECES ARE IN YOUR EARS. IT IS POSSIBLE TO DAMAGE YOUR HEARING IF YOU CARELESSLY STRIKE THE TAMBOR AGAINST SOMETHING. IF YOU TAP A STETHOSCOPE TAMBOR OR BELL TO TEST IT, BE VERY, VERY GENTLE.
1) Start by holding the tambour of the stethoscope against the skin immediately below and slightly to the left of the xiphoid process of the sternum (tip of the breastbone). You should be able to distinguish two distinct sounds with each beat, a muffled "lubb" sound, followed by a sharper "dupp".
2) Try other locations for the stethoscope, to see which provide the clearest sounds. You may be able to hear better if you use the stethoscope with both a bell and a tambour. Be sure to rotate this stethoscope head so that you are listening though the bell rather than the tambour.
3) Answer the following questions:
What internal valve events generate the "lubb" and "dupp" events?
How should the "lubb" and "dupp" sounds line up in time with the PQRST sequence of
the EKG?
Calculations of Cardiac Output
There are two central formulae for estimating or calculating cardiac output:
1) CO = HR x SV, so SV = CO/HR
where CO = cardiac output in liters blood/minute
HR = heart rate in beats/minute
SV = average stroke volume in liters blood/beat
remember that CO refers to the output of the venticles and that CO must be
the same for the left and right ventricles (why?)
2) CO = VO2 / ([O2]a - [O2]v)
where CO = cardiac output in liters blood/minute
VO2 = whole body oxygen consumption in mlO2/min
[O2]a = concentration of oxygen in arterial blood in mlO2/liter
[O2]v = concentration of oxygen in venous blood in mlO2/liter
VO is calculated by having the subject breathe through a spirometer and measuring:
the volume of air breathed in
the concentration of O2 in inspired air
the concentration of O2 in expired air
[O2]a is measured from arterial blood obtained from an arterial catheter
[O2]v is measured from venous blood obtained from a venous catheter
Solve the following set of calculations, then check your results within a small group:
Your male patient has an arterial oxygen concentration of 165 milliliters O2/liter blood, a venous oxygen concentration of 105 milliliters O2/liter blood, and a whole body oxygen consumption of 360 milliliters O2/minute.
What is your calculated estimate of his cardiac output?
Is this a reasonable resting value for a healthy adult male?
You measure his pulse rate (heart rate) at 60 beats/min.
What is your calculated estimate of average stroke volume for this subject under
these conditions?
Does this seem reasonable, given what you know about the size of the heart?