Mediastinum

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Mediastinum Apex Base
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Fibrous pericardium
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Double membrane surrounds the heart itself.
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FIBROUS PERICARDIUM
PARIETAL LAYER OF SEROUS PERICARDIUM
Pericardial cavity filled with pericardial fluid
VISCERAL LAYER OF SEROUS PERICARDIUM
HEART WALL
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Heart Wall

• Epicardium
• Visceral layer of the serous pericardium
• Myocardium
• Endocardium

Outside of the heart
Inside of the heart
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What type of tissue? Why?
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Mostly cardiac muscle but also contains the
fibrous skeleton of the heart
Needed for electrical isolation!
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What type of tissue? Why?
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Interatrial septum
LA
Interventricular septum
RA
LV
RV
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Right Ventricle
Right Atrium
Pulmonary Circuit
Systemic Circuit
Left Ventricle
Left atrium
2 pumps in series
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Not a lot of muscle in the atria. Why?
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Upper Body Circulation (above the diaphragm)
Coronary Circulation
Superior Vena Cava
Coronary Sinus
Right Atrium
Inferior Vena Cava
Lower Body Circulation (below the diaphragm)
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Interior (cut-away) view of the right atrium.
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Lungs
Pulmonary Veins
Left Atrium
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Interior (cut-away) view of the right atrium.
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Look at all the muscle? Which is thicker? Why?
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Left Ventricle
Aorta
Systemic Arteries
Systemic Circuit
Systemic Capillaries
Systemic Veins
Venae Cavae
Right Atrium
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Right Ventricle
Pulmonary Trunk
Pulmonary Arteries
Pulmonary Circuit
Pulmonary Capillaries
Pulmonary Veins
Left Atrium
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Left Ventricle
Systemic and pulmonary circuits are in series
Left Atrium
Aorta
Systemic Arteries
Pulmonary Veins
Pulmonary Capillaries
Systemic Capillaries
Systemic Veins
Pulmonary Arteries
Venae Cavae
Pulmonary Trunk
Right Atrium
Right Ventricle
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Left Ventricle
Aorta
Coronary Arteries
Coronary Circuit - A special branch of the
systemic circuit
Why is the coronary circuit necessary?
Coronary Capillaries
Coronary Veins
Coronary Sinus
Right Atrium
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Anastomoses Collateral routes End arteries
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Which coronary artery is normal?
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• Ischemia
• Angina
• Infarction

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4 Heart Valves - 2 atrioventricular - 2
semilunar
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Flap of connective tissue covered by endothelium
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Cardiac Muscle Cells
Contractile Cells
Autorhythmic Cells
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Cardiac Contractile Cells

• Striated
• Uninucleate
• Branching
• Linked by intercalated disks
• Desmosomes mechanical connection
• Prevents cells from separating.
• Allows force to be transmitted from cell to cell
• Gap junctions electrical connection
• Allow the heart to act as a functional syncytium

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Autorhythmic Cells

• Intrinsically control heart rate
• (extrinsic effects on heart rate are via nerves,
  and hormones)
• Spontaneously and rhythmically depolarize
• Connected to other cardiac muscle cells via gap
  junctions

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6 Main Groups of Autorhythmic Cells

• Sinoatrial node
• Internodal pathway
• Atrioventricular node
• Atrioventricular bundle
• Right and left bundle branches
• Purkinje fibers

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What ensures that the electrical signal follows
this path?
Pacemaker
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Normal
Arrhythmic
Fibrillation
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• Ectopic Focus
• Another tissue takes over the pacemaker role
• Caffiene, nicotine, fatigue
• Can result in premature ventricular contractions.
• Whats the danger?

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HEART BLOCK
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Extrinsic Control
Cardioinhibitory Center
Cardioacceleratory Center
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Increased cardioinhibitory center activity
APs sent down the vagus nerve to the heart
ACh released onto the SA and AV nodes
Heart rate declines
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Increased cardioacceleratory center activity
APs sent sympathetic cardiac nerves to the heart
NE released onto the SA and AV nodes
Heart rate increases
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ANS Influence on the Resting Heart
Parasympathetic influence
Sympathetic influence
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An Incredibly Important Concept

• Blood moves from one place to another because of
  a PRESSURE GRADIENT

High Pressure
Valves can only help direct blood flow.
Blood Flow ?
Low Pressure
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Cardiac Cycle
Ventricular Filling
Isovolumetric Relaxation
Isovolumetric Contraction
Ventricular Ejection
Cardiac cycle everything that occurs from the
start of 1 heartbeat to the start of the
next. -includes contraction (systole) and
relaxation (diastole) of all 4 chambers
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Ventricular Filling

• Ventricles are in diastole LOW PRESSURE.
• At first the atria are in diastole.
• Pressure is higher in the atria than in the
  ventricles, BUT lower in the atria than in the
  venae cavae and in the pulmonary veins.
• Passive.
• Then the atria are in systole.
• Pressure is definitely higher in the atria than
  in the ventricles.
• Active.

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Ventricular Filling

• During this stage
• The AV valves are open. WHY?
• The semilunar valves are closed. WHY?
• Think about pressures!!!!

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Ventricular Filling

• At its conclusion, no more blood will enter the
  ventricle until the next cycle begins.
• The amt of blood in the ventricle right now is
  known as the END DIASTOLIC VOLUME.
• If pressure in the venae cavae increased, what
  would happen to EDV???

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Isovolumetric Contraction

• As the ventricle contracts, pressure rises within
  it.
• The AV valve slams shut quickly creating the
  1st heart sound (LUB).
• It takes a little more contracting and thus more
  pressure before the semilunar valve opens.
• Thus for a little while, both valves are closed
  while the ventricle is contracting.
• With both valves closed, no blood is entering or
  exiting, hence isovolumetric contraction.

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Left atrium
Left ventricle
Aorta
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Ventricular Ejection

• The semilunar valve opened when ventricle
  pressure was greater than arterial pressure.
• Blood will flow out of the ventricle and into the
  aorta until the gradient no longer exists.
• When the ventricle stops contracting and begins
  to relax, the gradient will soon disappear.

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Ventricular Ejection

• The ventricle will not eject all of its blood
  some will remain.
• The remaining blood is called the END SYSTOLIC
  VOLUME. Why?
• Why would it be bad if the ventricle ejected 100
  of its blood with each contraction?
• Think about exercise!

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Ventricular Ejection

• The amt of blood ejected by each ventricle during
  a single cardiac cycle is known as stroke volume.
• Stroke Volume End diastolic volume End
  systolic volume.
• SV EDV ESV
• The stroke volumes of the 2 ventricles must be
  EQUAL!

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Isovolumetric Relaxation

• Kind of the reverse of isovolumetric contraction.
• When ventricle pressure dips below arterial
  pressure, the semilunars shut (causing the 2nd
  heart sound (DUP)). But, pressure is still
  higher in the ventricles than in the atria and
  the AV valves remain closed.
• Eventually ventricle pressure will drop (as the
  ventricle continues relaxing) until it is below
  atrial pressure and then the AV valves will
  open.
• The period in between the shutting of the
  semilunar valves and the opening of the AV valves
  is isovolumetric relaxation.

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Ventricle Volume
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• Given that
• Aortic Pressure 82mmHg
• Left Atrium Pressure 11mmHg
• Left Ventricle Pressure 61 mmHg and falling
• Answer the following
• The tricuspid valve is
• The mitral valve is
• The pulmonary semilunar valve is
• The aortic semilunar valve
• LV volume is
• LA volume is
• The phase of the cardiac cycle is
• The most recent heart sound was caused by

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Cardiac Output

• The volume of blood pumped by one ventricle in
  one minute.
• Cardiac Output Heart Rate x Stroke Vol.
• CO HR x SV

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Heart Rate Will Increase If

• Cardioacceleratory activity increases.
• Sympathetic activity increases.
• There is increased NE release on the heart.
• Cardioinhibitory activity decreases.
• Parasympathetic activity decreases.
• Vagus nerve activity (vagal tone) decreases.
• There is decreased ACh released on the heart.
• Plasma epinephrine levels increase.
• Plasma thyroxine levels increase.
• Caffeine is used.
• Nicotine is used.
• Sympathetic mimics (ephedrine) are used.

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Heart Rate and Filling Time

• If heart rate increases
• The time between beats will _____________
• Filling time will ________________________
• The end diastolic volume will_____________

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Regulating Stroke Volume

• Preload
• Contractility
• Afterload

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• PRELOAD -- The more the ventricle is stretched
  the more force it generates.

More blood returns to the heart.
The ventricle is stretched.
There is a more optimum overlap between actin
myosin.
More force is generated by the ventricle.
More blood is pumped out.
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Systolic Force
Diastolic Volume
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• As venous return increases, stroke volume will
• As end diastolic volume decreases, stroke volume
  will
• As heart rate increases, stroke volume will

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Contractility

• The harder the ventricle muscle contracts, the
  more blood will be ejected.
• Contractility can be increased by
• Increased sympathetic activity (i.e., increased
  NE release on the heart).
• Increased levels of plasma hormones such as
  epinephrine and thyroxine.
• Drugs such as digitalis.

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Afterload

• Consider the following

Aorta
LV
In this situation, the man with the yellow head
has 5 seconds to open the blue door and then move
as many red bricks as he can from the LV to the
aorta.
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Afterload
Aorta
LV
In this situation, the man with the yellow head
still has 5 seconds to open the blue door and
move as many red bricks as he can. But now,
theres someone pushing on the door. Hell have
to spend more time opening the door and hell
have less time to move the red bricks from the LV
to the aorta.
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• The higher the pressure in the aorta
• The longer it takes to open the aortic semilunar
  valve
• The smaller the amount of time for ejecting blood

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• As afterload increases, stroke volume will
• As afterload increases, end systolic volume will

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Homeostatic Imbalances

• Tachycardia
• Bradycardia
• Congestive heart failure