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Cardiovascular System
Lecture II
Circulatory system
The circulatory system or cardiovascular system is the organ system, which circulates
blood around the body of most animals.
It consists of Heart - Aorta - Arteries - Arterioles - Capillaries - Venules - Veins - Venae
cavae - Pulmonary arteries - Lungs - Pulmonary veins - Blood
AORTA
The largest artery in the human body, the aorta originates from the left ventricle of the
heart and brings oxygenated blood to all parts of the body in the systemic circulation.
The course of the aorta
The aorta is usually divided into several segments. The portion above the diaphragm (in
the thorax) is called the thoracic aorta and is sometimes further subdivided into the
ascending aorta, aortic arch and descending (thoracic) aorta. The portion below the
diaphragm (in the abdomen) is known as the abdominal aorta.
Thoracic aorta
The initial part of the aorta, the ascending aorta, rises out of the left ventricle, from which
it is separated by the aortic valve. The two coronary arteries of the heart arise from the
aortic root, just above the cusps of the aortic valve.
The aorta then arches back over the right pulmonary artery. Three vessels come out of the
aortic arch,
Brachiocephalic artery,
Left common carotid artery, and
Left subclavian artery.
These vessels supply blood to the head, neck, thorax and upper limbs.
The aorta gives off several paired branches as it descends in the thorax. These includes
the
Bronchial arteries,
Esophageal arteries and
Intercostal arteries.
ABDOMINAL AORTA
The abdominal aorta travels down the posterior wall of the abdomen, the abdominal aorta
runs on the left of the inferior vena cava, giving off major blood vessels to the gut organs
and kidneys. There are many recognized variants in the vasculature of the gastrointestinal
system. The most common arrangement for the abdominal aorta is to give off (in order) a
Celiac artery,
Superior mesenteric artery and
Inferior mesenteric artery.
The renal arteries usually branch from the abdominal aorta in between the celiac artery
and the superior mesenteric artery.
The aorta terminates by dividing into two branches, the left and right common iliac
arteries that branch to supply blood to the lower limbs and the pelvis.
Features
The aorta is an elastic artery, and as such is quite distensible. When the left ventricle
contracts to force blood into the aorta, the aorta expands. This stretching gives the
potential energy that will help maintain blood pressure during diastole, as during this time
the aorta contracts passively.
Diseases
Aneurysm of sinus of Valsalva
Aortic aneurysm
Dissecting aortic aneurysm
Aortic coarctation
Marfan’s syndrome
Inborn cardiovascular defects
ARTERY
Arteries are muscular vessels that carry blood away from the heart to the tissues and
organs of the body (The vessels which return blood to the heart are veins).
The circulatory system is extremely important in sustaining life. Its proper functioning is
responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of
carbon dioxide, waste products, maintenance of optimum pH, and the mobility of the
elements, proteins and cells, of the immune system. In First World countries the two
leading causes of death, myocardial infarction and stroke, are each direct results of an
arterial system that has been slowly and progressively compromised by years of
deterioration.
Description
The arterial system is the higher-pressure portion of the circulatory system. Arterial
pressure varies between the peak pressure during heart contraction, called the systolic
pressure, and the minimum, or diastolic pressure between contractions, when the heart
rests between cycles. This pressure variation within the artery produces the pulse which is
observable in any artery, and reflects heart activity.
Anatomy
Arteries are composed of distinct layers of tissue; The innermost layer, which is in direct
contact with the flow of blood is the tunica intima, commonly called the intima. This
layer is made up of mainly endothelial cells. Outside this layer is the tunica media, or
media, which is made up of smooth muscle cells and elastic tissue. The outermost layer is
known as the tunica adventitia or the adventitia, and is composed of connective tissue.
Types of arteries:
There are several types of arteries in the body:
Pulmonary arteries
The pulmonary arteries carry oxygen deficient blood that has just returned from the body
to the lungs, where carbon dioxide is exchanged for oxygen.
Systemic arteries
Systemic arteries deliver blood to the arterioles, and then to the capillaries, where
nutrients and gasses are exchanged.
The Aorta
The aorta is the root systemic artery. It receives blood directly from the left ventricle of
the heart via the aortic valve. As the aorta branches and these arteries branch in turn, they
become successively smaller in diameter, successively down to the arteriole. The
arterioles supply capillaries, which in turn empty into venules.
ARTERIOLES
Arterioles, the smallest of the true arteries, help regulate blood pressure and deliver blood
to capillaries.
Arterioles and Blood Pressure
Arterioles have the greatest collective influence on both local blood flow and on overall
blood pressure. They are the primary "adjustable nozzles" in the blood system, across
which the greatest pressure drop occurs. The combination of heart output (cardiac output)
and total peripheral resistance, which refers to the collective resistance of all of the body's
arterioles, are the principal determinants of arterial blood pressure at any given moment.
Capillaries
Though not considered true arteries, the capillaries are where all of the important action
happens in the circulatory system:
Functions of capillaries
These vessels have no smooth muscle surrounding them and have a diameter less than
that of a red blood cell; a red blood cell is typically 7 micrometers outside diameter,
capillaries typically 5 micrometers inside diameter. The red blood cells must distort in
order to pass through the capillaries.
This small diameter of the capillary provides a relatively large surface area for the
exchange of gases and nutrients.
What are the functions of capillaries:
In the lungs, carbon dioxide is exchanged for oxygen
In the tissues, oxygen and carbon dioxide and nutrients and wastes are exchanged
In the kidneys, wastes are released to be eliminated from the body
In the intestine nutrients are picked up, and wastes released
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