Question

Left aortic arch is found in
A) Some animals
B) All mammals
C) Not present
D) Only man

Answer 1

Hint: It is a connection between ascending and descending aorta and is found in all the animals that have features like a stiff rod running through the length of the animal with a hollow tube of nervous tissue above it and the gastrointestinal tract below.

Complete answer:
All the vertebrate animals have left aortic arches as a connection between the ascending and the descending aorta. These arches are the segment of the aorta that helps in the distribution of blood to the upper parts of the body like head via the left subclavian artery, the left common carotid, and the brachiocephalic trunk. Since all mammals are vertebrates, the left aortic arch is found in all mammals.

Additional information:
Aortic arch has three branches out of which the largest one is its right branch which is the brachiocephalic trunk and lies to the right of the other two branches. Its left branch gives rise to the common carotid artery which ascends through the superior mediastinum along the left side of the trachea. The leftmost part of the aortic arch gives rise to the left subclavian artery which ascends with left common carotid through the superior mediastinum.

Fig.- Branches of the aortic arch

The aortic arches are made of three layers – tunica intima, tunica media, and tunica adventitia. Simple squamous epithelial cells are present in tunica media and it surrounds the lumen while tunica media is composed of smooth muscle cells and some elastic fibers. Loose collagen fibers form the third layer tunica adventitia.

So, the correct answer is ‘All mammals’.

Note: Considering the development, the fourth aortic arch, the leftmost part in the early life of the fetus forms the central part of the fully developed aortic arch. In fetal life, the lower parts of the arch are connected together by the ductus arteries that allow the blood to bypass the pulmonary vessels from when blood is pumped from the right ventricle.
Some variations are found in the branching of aortic arches in different individuals and the branching in normal in about 75% individuals but in rest, the left common carotid artery either originates from the brachiocephalic artery or the brachiocephalic artery splits into three arteries.