Cardiovascular 1b – Heart and Circulation, Location of Heart, Role in the Circulatory
System
Anil Chopra
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The human heart beats continuously throughout life, over 2½ billion times.
Movement is dependent of contraction and four valves (tricuspid, mitral,
pulmonary and aortic)
An average adult contains 5l of blood in the body, and heart pumps about 5l per
minute.
1. Location of heart within chest
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It is in the middle of the inferior mediastinum (just left of the midline)
2nd-6th costal cartilage
The left edge (apex) extends to the mid-clavicular line.
The pericardial cavity is between the lungs and above the diaphragm.
The left side of the heart pushes the lung and pleura over and this region is known
as the cardiac notch.
6. Borders of heart
o Anterior right edge
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RIGHT ATRIUM
o Anterior inferior edge
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RIGHT VENTRICLE
o Anterior superior left edge
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LEFT VENTRICLE
o Posterior edge
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LEFT ATRIUM (oesophagus)
The heart is enclosed by pericardium
I. Tough fibrous sac with serosal lining.
II. Parietal layer and inner serosal layer.
III. Fluid in pericardial cavity between the two surfaces allows movement of the heart.
Made from mesothelial cells with rich fibroconnective tissue – rich in blood supply.
IV. Visceral layer – serous pericardium
V. Muscle layer – myocardium
VI. Inner layer – endocardium (continuous with lining of blood vessels)
Cardiac Muscle
 Made from quadrangle cells joined on end (syncitium)
 ANASTOMOSIS of fibres (joining branch diversions)
 No sarcolemma exists.
 Clear oval nuclei.
Surface Grooves
 Atrioventricular groove – separates atria and ventricles and contains the coronary
sinus.
 Inner atrial groove – separates 2 atria (not seen on anterior because arteries cover
it)
 Anterior longitudinal sulcus – sternocostal separation of ventricles.
 Posterior longitudinal sulcus – diaphragmatic separation of ventricles.
2. Major vessels returning blood to heart
Vena Cava - Split into inferior and superior
- Superior is smaller and comes from upper part of the body, it has no
valve.
- Inferior is larger and comes from lower half of the body. Has
rudimentary value.
Coronary
Sinus
- Returns blood from heart muscle
- Goes to right atria
- Has a semicircular valve.
- Foramina venarum minimarum has similar function.
Pulmonary
Veins
- 4 of them return oxygenated blood to the left atrium.
- Have no valves.
3. Major vessel bringing blood to lungs
Pulmonary - Circular opening near ventricular septum.
Artery - Comes from right ventricle
- Guarded by pulmonary semi-lunar valves.
4. Major vessel bringing oxygenated blood to body
Aorta - Comes from left ventricle.
- Guarded by aortic semilunar valves.
- Aortic vestibule below aortic opening.
- Wall is fibrous instead of muscle.
5. Define artery, vein, arteriole, venule, capillary
In adults blood vessels are 100 000 miles long!
 Artery
 passes blood from heart to organs
 high pressure (110-150/60-80)
 main aorta branches out into arteries
 Vein
 Passes blood from organs to heart.
 All (apart from pulmonary vein) carry deoxygenated blood.
 Thin walled.
 Have valves formed by reduplication of lining membrane which prevent the
backflow of blood.
 Low pressure.
 Arteriole
 Smaller arterial branches
 Lead into capillaries
 A resistance vessel
 Venules
 Small tributaries of veins
 Arise from capillaries
 Capacitance vessels
 Capillaries
 Thin walled blood vessels in which gas exchange occurs.
 Concentrated in capillary beds
 Some have small pores in walls to allow movement of fluid,
 Nutrients, wastes and hormones are exchanged.
 Controlled by nervous activation of sphincters.
6. What is artery made of?
Arteries are used to measure blood pressure and pulse rate. They are made up of
different layers:
Artery Layers
Tunica Adventitia
Tunica Media
Tunica Intima
Connective tissue
Nerve fibres
External elastic layer
Smooth muscle
Internal elastic layer
Basement membrane
Endothelium
Lumen
7. What is vein made of
Vein Layers
Connective tissue
Tunica Adventitia
Nerve fibres
Smooth muscle
Tunica Media
Basement membrane
Tunica Intima
Endothelium
Lumen
7. Define the pulmonary circulation
Blood is taken from the right ventricle to
the lungs via the pulmonary artery.
Pulmonary veins then bring blood back
from the lungs to the left atria.
9. Define the systemic circulation
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Ensures nourishment of all tissues in the
body (except heart and lungs)
Left ventricle forces oxygenated blood
through the aorta at high pressure.
Slowly they branch off into smaller
arteries and arterioles. The pressures are
low and elastic tissue is less prominent in
smaller vessels.
Branches also into portal circulation. This
is where the blood from the spleen,
pancreas, stomach, small intestine passes
through the hepatic portal vein to the liver.