3. Size and Location
• About the size of the fist and weighs less
than a pound
• Enclosed within the mediastinum, medial
cavity of the thorax
• Rests on superior surface of diaphragm
• Anterior to vertebral column and
posterior to sternum
• Lungs flank laterally and partially
obscure it
• ~ 2/3 of it lies to left
• Broad, flat base or posterior surface
4.
5. Coverings
• Heart enclosed in double-wall sac
called the pericardium
• Loosely fitting superficial part of sac
is the fibrous pericardium
• The pericardium:
– Protects heart
– Anchors it to surrounding surfaces
– Prevents overfilling of the heart with
blood
6. Coverings (con’t)
• Deep to fibrous pericardium is the
serous pericardium, which is thin
and slippery and composed of 2
layers.
– The two layers have a film of serous
fluid between them
– Allows the hear to work in a relatively
friction-free environment
7. Coverings (con’t)
• Inflammation of the pericardium,
pericarditis, hinders production of
serous fluid and roughens the
surfaces.
• Creates a creaking sound that can be
hear with a stethoscope and pain
deep to the chest.
• If persists, can cause adhesions and
impede heart activity
8. Layers of Heart
1. Epicardium
- visceral layer of the serous pericardium
- often infiltrated with fat
2. Myocardium
- composed mainly of cardiac muscle
- forms bulk of heart
- layer that contracts
3. Endocardium
- glistening white sheet of endothelium
- lines heart chambers and covers valves
11. The internal partition that
divides the heart is the
interatrial septum when it
separates the atria and the
interventricular septum
when it separates the
ventricles.
12.
13. Atria: The Receiving
Chambers
• The atrium has two basic parts:
– A smooth-walled posterior part
– An anterior part with ridged walls
• The interatrial septum has a shallow
depression called the fossa ovalis.
This marks the spot where the
foramen ovale existed in the fetal
heart.
14. Atria (con’t)
• Receiving chambers for blood
returning to the heart from the
circulation.
• Contract minimally to push blood
into the ventricles; therefore, they
are relatively small and thin.
15. Atria (con’t)
• Blood enters the right atrium
through 3 veins:
– Superior vena cava – returns blood
from body regions superior to the
diaphragm
– Inferior vena cava – returns blood from
body areas below the diaphragm, and
– Coronary sinus – collects blood from the
myocardium
16. Atria (con’t)
• Four pulmonary veins enter the left
atrium, which make up most of the
heart’s base.
• The pulmonary veins transport
blood from the lungs back to the
heart.
• These vessels are best seen in a
posterior view of the heart.
17. Ventricles: The Discharging
Chambers
• Make up most of the heart
• Right ventricle forms heart anterior
surface
• Left ventricle forms inferior surface
• When contracted, blood is propelled out of
the heart into circulation.
– Right ventricle pumps blood into pulmonary
trunk to the lungs for gas exchange
– Left ventricle pumps blood into the aorta to
the body’s systems
19. • Heart is two side-by-side pumps
• Each side serves two different
circuits:
– Pulmonary Circuit
– Systemic Circuit
20.
21. Pulmonary Circuit Pump
• Right side
• Blood returns from body, which is oxygen-
poor and carbon dioxide-rich and enters
the right atrium.
• Then, it passes into the right ventricle,
which pumps it to the lungs via the
pulmonary trunk.
• In the lungs, blood unloads the carbon
dioxide and pucks up oxygen.
• Freshly oxygenated blood is carried to the
left side of heart.
22. Systemic Circuit Pump
• Left side of heart
• Freshly oxygenated blood leaves lungs to
return to left atrium and passes into left
ventricle, which pumps into the aorta.
• Blood is transported via smaller arteries
to body tissues, where gases and nutrients
are exchanged.
• Blood loaded with carbon dioxide and
oxygen depleted, returns through the
systemic veins to right side of heart,
where enters venae cavae.
23. Pathway (con’t)
• Although equal volumes are
pumped, 2 ventricles have unequal
workloads.
– Pulmonary circuit is short and low-
pressure.
– Systemic circuit is very long and high-
pressure.
•Encounters 5x’s as much friction
•Walls are 3x’s as thick
•Cavity is nearly circular
24.
25. Coronary Circulation
• Feeds the heart and is the shortest
circulation of body
• Actively delivers blood when heart
is relaxed, but are ineffective when
ventricles are contracting because:
– They’re compressed by contracting
myocardium, and
– The entrances are partly blocked by
flaps of valves.
26.
27. Coronary Circulation
(con’t)
• Myocardial cells are weakened by
temporary lack of oxygen, but don’t
die.
• Complete blockage of a coronary
artery leads to tissue death and a
myocardial infarction, or heart
attack or coronary.
• Cardiac muscle is amitotic, which is
replaced by noncontractile scar
tissue.
28.
29. Heart Valves
Blood flows through the heart in one
direction: from atria to ventricles.
One way traffic is enforced by heart
valves.
Valves open and close in response to
changes in blood pressure.
30.
31. Atrioventricular (AV)
Valves
• Located at each atrial-ventricular
junction, preventing backflow into
the atria when the ventricles are
contracting.
• Right AV valve, the tricuspid valve,
has 3 flaps. Left AV valve, the
bicuspid valve, has 2 flaps.
• Attached to the valve flaps are tiny
white collagen cords called chordae
tendineae, or “heart strings,” anchor
flaps to heart walls.
32.
33. AV Valves
• When heart is relaxed, AV flaps hang limply
into ventricular chambers below; blood
flows into atria and through open AV valves
into ventricles.
• When ventricles contract, blood is
compressed into chambers, intraventricular
pressure rises, forcing blood upwards
against valve flaps.
• Valve flap edges meet, closing valves.
• Chordae tendineae serve as guidewires to
anchor flaps in place.
34.
35. Semilunar (SL) Valves
• Aortic and pulmonary SL valves guard
bases of large arteries that exit the
ventricles.
• When ventricles are contracting and
intraventricular pressure rises, the SL
valves are forced open and flaps flatten
against the arterial walls and blood rushes
by.
• When ventricles relax, blood flows back
toward the heart and closes the valves.
36.
37. Cardiac Cycle
• Heart writhes in the chest when it
contracts
• Forces blood out of chambers when
it contracts and fills with blood
when it relaxes.
• Two terms are used to refer to heart
contraction/relaxation:
– Systole contraction
– Diastole relaxation
38. Cardiac Cycle (con’t)
• Includes all events associated with
the flow of blood through the heart
during one heartbeat.
• Marked by a succession of pressure
and blood volume change in heart.
• Lasts about 0.8 seconds
– Atrial systole 0.1 s
– Ventricular systole 0.3 s
– Total heart relaxation 0.4 s
(quiescent period)
39. Cardiac Cycle (con’t)
• Two important points:
1. Blood flow through the hear tis
controlled by pressure changes, and
2. Blood flow along a pressure gradient is
always from higher pressure to lower
pressure through any available
opening.
40. Heart Sounds
• Two distinguishable sound during
cardiac cycle can be heard.
• Often described as “lub-dup”, which
is associated with the closing of the
heart valves.
• Pause between lub-dup is the
quiescent period.
41. Murmurs
• An abnormal or unusual heart sound
• Caused by obstruction along blood
pathway
• Fairly common in young children
• Indicate valve problems (or possible
hole in heart)
• If a valve is incomplete, a swishing
sound can be heard.
42. Cardiac Output (CO)
• Amount of blood pumped out be
each ventricle in 1 min.
• Highly variable and increases in
response to demands
• Difference in resting and maximal
CO is called the cardiac reserve.
– Nonathletes’ reserve is 4-5x’s normal CO
– Athletes’ reserve can be 7x’s the normal
CO
43. Regulation of Heart Rate
• With a healthy cardiovascular system the
amount of blood pumped (stroke volume) is
relatively constant.
• When blood volume drops sharply or the
heart is weakened, stroke volume declines
and the heart maintains the CO by beating
faster.
• Also, the nervous system can affect heart
rate. Fear, anxiety, stress, etc. causes an
increase in norepinephrine, which causes the
pacemaker to fire more rapidly and the
heart beats faster.