2. The circulatory system
The circulatory system consists of two major sub-circuits, the systemic
circulation and the pulmonary circulation. 2
3. The circulatory system
The Heart:
Four chambered double pump.
Blood vessels:
Carry Blood from the heart to the
vital organs and back.
Arteries carry blood away
from the heart and branch to
form the arterioles. They all
carry oxygenated blood
except the pulmonary arteries.
Veins return blood to the heart
and start as venules. They all
carry deoxygenated blood
except the pulmonary veins.
Blood capillaries are found as a
network Between arteries and
veins. 3
5. Exterior structure of the heart
• Inflow ports consisted of the superior and inferior vena cava and
pulmonary veins.
• Outflow ports mainly the aorta, and pulmonary arteries.
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6. Structure of the heart (interior view)
• Atria (right atrium and left
atrium)
• Ventricles (right ventricle and
left ventricle)
Right and left heart sides are
normally completely separate.
Right atrium and left ventricles
open in the corresponding
ventricles by a valve.
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7. Atrioventricular valves The atria are connected to the ventricles
by atrioventricular valves.
Tricuspid valve on the right side.
Bicuspid valve (mitral valve) on the lefty
side
The valves are passively operated by the
difference in blood pressure between the
heart champers.
The papillary muscles are connected to the
valves by tendons called Chordae tendinae
which help to keep them in place.
There are other valves, called semilunar
valves at the entrance of the aorta and
the pulmonary artery. They are one
way valves!.
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8. Blood vessels
Arteries have muscular walls and smaller lumen.
Veins have thinner walls and bigger lumen.
Blood capillaries are single layer of endothelial cells.
Arteries are high pressure vessels while veins have lower pressure and blood
flow is helped by valves to go back to the heart.
10. Histology of the blood vessels
Both arteries and veins are
Artery Vein composed of three coats
(layers), tunica externa
Tunica (tunica adventitia), tunica
interna media and tunica interna
Valve
(intima).
Elastin
Tunica
media Tunica interna consists of
three parts. Elastic tissue
Tunica
fibers, the basement
externa membrane and the inner
endothelium.
Serosa
The blood capillary is single cell
thick which is endothelium.
Capillary
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11. Cardiac cycle
Cardiac cycle is a repeated pattern of contraction and relaxation. The phase of
contraction is systole and relaxation is diastole.
Average heart rate (beat per minutes) is ~ 75 B/min cardiac cycle lasts
about 0.8 sec.
0.5 sec 0.3 sec
diastole systole
Even before contraction of atria, the
ventricles are filled with blood by up to
80%, the remaining 20% enter the
ventricles after contraction of atria.
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12. States of heart during cardiac cycle
When the ventricles fill up with blood this
is called end diastolic volume (EDV).
The ventricle contract during systole to
eject two third of the amount it contains
(stroke volume (SV)).
Stroke volume (SV): volume of blood ejected
during one cardiac cycle.
The one third left is the end-systolic volume
(ESV).
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13. -Right Atrium = RA
Heart and Circulation -Left Atrium = LA
-Right Ventricle = RV
-Left Ventricle = LV
1- Venous blood containing CO2 returns from body tissues to RA
Tricuspid valve
2- From RA RV
Pulmonary artery
3- From RV Lungs
Pulmonary vein
4- From Lungs LA
5- From LA Bicuspid valve LV
Aorta
6- From LV Body
14. Pressure changes during cardiac Cycle
-Ventricles are filled with blood (e.g. 120 ml) and ventricular muscle contracts without
-change in length this is called isovolumic contraction:
Isovolumetric No change Increase in
contraction in volume intraventricular
pressure
Intraventricular
pressure > Aortic
pressure Ejection
Ejection Volume and pressure decrease
Isovolumic relaxation
The pressure produced by the left ventricle
during systole is about 120 mmHg and during
diastole is about 80 mmHg. The blood pressure
is represented by systole/diastole = 120/80.
15. Heart Sounds
- The valves between atria and ventricles are called atrio-ventricular (AV) valves
-and the valves between right ventricles and pulmonary artery + left ventricle and
-aorta are called semilunar valves.
- Closing of the AV valves and semilunar
valves produces sounds that can be heard
by stethoscope. These sounds are called
heart sounds. They sound like “lub-dub”.
- First sound (“lub”) is produced by closure
of AV valves. Second heat sound (“dub”) is
produced by closure of semilunar valves
lub dub