The Aorta.

The aorta is the main and the largest artery in our body. This arterial trunk originates from the left ventricle of the heart and this opening between the left ventricle and the aorta is guarded by the aortic valve which acts as non return valve, allowing blood to flow from the left ventricle into the aorta and preventing back flow of blood from the aorta to the left ventricle.

Function of Aorta.

The aorta carries oxygen rich blood for distribution to all parts of the body through the network of arteries, arterioles and capillaries. This network is called the systemic circulation.

Anatomy and Course of the Aorta.

The aorta begins at the left ventricle of the heart ascends upwards, forms an arch and then descends downwards into the thorax and then to the abdomen.

According to its course, the aorta is divided into 5 parts or segments.

1) Ascending Aorta.

This is the ascending section between the heart and the arch of the aorta.

Branches :

• The coronary arteries which supply blood to the wall of the heart.

2) Arch of the Aorta.

This is the part of the aorta after the ascending section and which forms an arch like an inverted ‘U’.

Branches :

• Brachiocephalic artery which supplies blood to the right side of head, neck and upper right extremity. The right carotid artery arises from the brachiocephalic artery.
• Left common carotid Artery which extends to the neck and similarly supplies blood to the left side.
• Left subclavian artery supplies blood to the left upper extremity.

3) Descending Aorta.

This is that part of the aorta which extends from the aortic arch to the point where it divides into the two common iliac arteries in the abdomen. The descending aorta is again divided into the thoracic part (chest part) and the abdominal part.

Thoracic aorta.

This is that part of the descending aorta which lies within the thorax.

Branches.

• Visceral branches which supply blood to the lungs, the pericardium of the heart, the esophagus and the lymph nodes in the chest.
• Parietal branches which supply blood to the chest muscles, spinal cord and the diaphragm.

Abdominal Aorta.

This is the part of the descending aorta below the diaphragm which lies in the abdomen till its division into the two common iliac arteries at the level of the fourth lumbar vertebra.

Branches.

• Celiac artery which supplies blood the esophagus, stomach, liver, pancreas and spleen through its branches.
• Superior mesenteric artery which supplies blood to the intestines.
• Inferior mesenteric artery which supplies blood to the colon, kidneys and the male or female reproductive organs.
• The common iliac arteries which supply blood o the pelvic structures and the lower limbs.

Image of aorta and its branches.

Click on image to enlarge.

Pressure in Aorta.

The blood pressure in aorta varies during systole and diastole. Normally, the systolic pressure in the aorta is 120 mm of Hg and the diastolic pressure is 80 mm of Hg with slight variations.

Diameter of Aorta.

At its commencement at the left ventricle, the diameter of the aorta is 3 cms. The diameter is reduced as it descends and is 1.75 cms  in the abdominal aorta.

Structure of the Aortic Wall.

The aorta is an elastic artery and quite stretchable. This is because the blood pressure is highest in the aorta. In fact, the blood pressure measured of a person indicates the pulsatile pressure of the flowing blood against the wall of the aorta.

The wall of the aorta is relatively quite thick and consists of a network of tiny capillaries, called the vaso vasorum, which supply blood to the layers of the wall of the aorta. The wall of the aorta consists of smooth muscles, nerves, intimal cells, fibroblasts, endothelial cells and complex extracellular tissue.

The arch of the aorta contains receptors which transmit information regarding blood pressure, ph of blood and carbon dioxide blood levels to the medulla oblongata of the brain. After processing this information, the brain sends the necessary command through efferent fibers of the autonomic nervous system to correct any undesired levels.

The wall of the aorta is made of three layers.

• Tunica Adventitia.

This is the strong outer layer. It is made up of connective tissue and collagen and elastic fibers. These elastic fibers allow the expansion of the aorta due to pressure of blood flowing through it.

• Tunica Media.

      This is the middle layer and consists of smooth muscle and elastic fibers.

• Tunica Intima.

      This is the innermost layer which is made up of one layer of endothelial cells supported by a layer of elastic tissue. This layer is in direct contact with the flowing blood in the aorta.

Related posts:

1. Aortic Valve Anatomy, Function and Diseases.
2. Heart Anatomy and Structure.
3. What Does Heart Do|Function of Heart.
4. Epidermis Structure and Functions.
5. Sleep Importance, Function and Physiology.