Heart
Chapter 12

Heart
System of a pump and pathway for blood
to travel
Arteries- vessels that carry blood away
from the heart
Veins- vessels that carry blood to the
heart
Capillaries are very small vessels that
connect the two at the microscopic level
-
Exchange nutrients for waste
Exchange O2 for CO2
Heart lies in the pericardial cavity in the
lower portion of the mediastinum resting
on the diaphragm.
The inferior portion has a point or tip called
the apex.
Broad upper surface called the base
The pericardium consists of two principle
portions.
1- fibrous pericardium
2- serous pericardium
Fibrous pericardium: tough and inelastic
- rests on and attaches to diaphragm.
- provides protection
Serous pericardium:
- thinner, delicate, double layered.
-
-
-
1- Visceral pericardium: (epicardium)
contacts the surface of the heart
2- Parietal pericardium: fused to the fibrous
pericardium
Pericardial cavity: separates two layers with
pericardial fluid (lubricates membranes)
- cardiac tamponade
Heart consists of three layers:
1- Endocardium: lines inside of heart
and heart valves
2- Myocardium: thick heart muscle.
Blood supplied by coronary
arteries.
involuntary, striated, intercalated disks
3- Epicardium: smooth outer layer
Heart is a double pump
Right side of the heart is the receiving side.
- pulmonary circulation
Left side of the heart is the giving side.
- systemic circulation (the body)
Heart has four chambers
Two upper chambers are called atria (sing.
atrium)
Right and left
Two lower chambers called ventricles
Right and left
Right and left ventricles are separated by a
thick walled structure called the
Interventricular septum
Blood flow between chambers and larger
arteries pass through valves.
Valves that connect the upper atria to the
lower ventricles are termed
atrioventricular valves (AV). There are
two
1- Tricuspid valve. This “3 flapped” valve
connects the right atria to the right
ventricle
2- Bicuspid valve (mitral): This “2 flapped”
valve connect the left atria to the left
ventricle
AV Valves
Valves that connect the lower ventricles to
the larger arteries carrying blood away
from the heart are called semilunar
valves.
1- Pulmonary semilunar valve: Valve
located between the right ventricle and
the pulmonary artery
2- Aortic semilunar valve: Valve located
between left ventricle and aorta.
Contraction of the heart is systole
Relaxation of the heart is called diastole
When the heart beats the atria contract first
and together then the ventricles contract
second and together.
Deoxygenated blood drains into right
atrium from
- superior vena cava
- inferior vena cava
- coronary sinus (from heart)




Blood is supplied to the heart by the first two
branches of the aorta, right and left coronary
arteries. These arteries arise from the base of
the aorta and encircle the heart in the
atrioventricular groove.
Left coronary artery:
anterior interventricular artery - supplies
blood to the interventricular septum and anterior
walls of both ventricles
circumflex artery - supplies blood to the left
atrium and the posterior walls of the left
ventricle




Right coronary artery:
Posterior interventricular artery - runs
to the apex and supplies blood to the
posterior ventricular walls
Marginal artery - supplies blood to the
myocardium of the right side of the heart
The myocardium needs a constant supply
of oxygen in order for the heart to
continually pump. Myocardium capillaries
are branches of cardiac veins which join to
form the coronary sinus, an enlarged vein
which empties into the right atrium.

Coronary veins:
-Great cardiac vein,
-Middle cardiac vein,
-Small cardiac vein…
… drains into cardiac sinus which drains
into right atrium.
Conduction and Pacemaker
Conductility- ability to conduct an electrical
impulse
These impulses must be coordinated.
Intercalated disks are electrical connectors
that join the muscle fibers.
Remember: Atria contract together then
ventricles.
Intrinsic
1- Sinoatrial node (SA node) pacemaker of
the heart.
2- Atrioventricular (AV node)
3- Bundle of His- interventricular septum
- right and left bundle branches
4- Purkinje fibers- ventricle walls
Beating heart
Cardiovascular (CV) center is located in the
medulla of the brainstem.


Sympathetic nervous system: cardiac
accelerator nerves coming off of thoracic
spinal cord segments. Increases heart rate
Parasympathetic nervous system: Vagus
nerve (CNX) coming off of medulla
(brainstem). Decreases heart rate.
Extrinsic
ELECTROCARDIOGRAM
(ECG or EKG)
(Action Potential) Conduction
system can be measured

P QRS T
P wave: SA node firing and atria contract
(depolarization)
QRS wave: atria relax (repolarization) and
ventricles contract (depolarization)
T wave: ventricle walls relax (repolarization)
Myocardial infarction
Elevated ST segment
1- Enlarged P-wave: Atrial hypertrophy
2- Missing or inverted P-wave: SA node
damage.
3- Enlarged Q-wave: Myocardial infarct.
4- Enlarged R wave: Ventricular hypertrophy
5- Abnormal T-wave: Hypoxia or
hyperkalemia (K+)
6- Inverted QRS: Premature Ventricular
Contractions (PVC’s)
7- Elevated S-T segment: MI
Sinus bradycardia
Apart from fit, but otherwise normal
individuals, there's a long list of situations
where sinus bradycardia occurs, including:
 hypothermia;
 increased vagal tone (due to vagal
stimulation or e.g. drugs);
 hypothyroidism;
 marked intracranial hypertension;
 obstructive jaundice, and even in uremia;
 structural SA node disease, or ischemia.










Sinus tachycardia
Always consider pain as a possible cause of
tachycardia.
Any cause of adrenergic stimulation (including
pain);
thyrotoxicosis;
hypovolemia;
vagolytic drugs (e.g. atropine)
anemia, pregnancy;
fever
myocarditis
Cardiac cycle
Auscultation of the heart

“Lubb – Dupp”
“Lubb”: AV valves closing. (S1) Systole
“Dupp”: Semilunar valves closing. (S2)
-Diastole
1- Pulmonary valve: ribs 2 & 3 on left
2- Aortic valve: ribs 2 & 3 on right
3- Biscuspid valve: ribs 5 & 6 on left
mid line of clavicle
4- Tricuspid valve: ribs 5 & 6 on right
sternal margin
Factors Affecting SV

Preload
Contractility
Afterload

Frank-Starling Law



Inotropic: Contractility
-Positive Inotropic Agents
- Sympathetic NS
- Digitalis
- Glucagon (pancreas)
- Epinephrine
- Hypercalcemia
- Negative Inotropic Agents
- Hyperkalemia
- Hypocalcemia
- Cardiac hypoxia
- Cardiac hypercapnia

Chronotropic: Heart Rate
- Postive Chronotropic Agents
- Sympathetic stimulation
- Epinephrine
- Thyroid hormone
- Hypocalcemia
- Hypercapnia (acidosis)
- Digitalis
- Negative Chronotropic Agents
- Parasympathetic NS
- Acetylcholine
- Hypokalemia
- Hypercalcemia
- Hypoxia
Homeostasis