Question

How does blood become oxygenated blood in the body?

Answer 1

Respiration can be defined as the breathing in oxygen and giving out of carbon dioxide. Oxygen goes in through the respiratory passage and passes to the alveoli. The alveoli are surrounded by blood capillaries. The capillaries are made up of single-celled thi

Complete answer:
The air containing oxygen goes inside the respiratory passage into the lungs which contain alveoli. The alveoli are made up of single-celled epithelial tissue and are surrounded by blood capillaries. These capillaries are made up of single-celled endothelium. This helps in the exchange of oxygen and carbon dioxide.
Blood capillaries surrounding the alveoli are a part of the pulmonary trunk. As oxygen enters the alveoli, it gets diffused across the layers of the alveoli into the blood capillaries. Here oxygen is taken up by the hemoglobin present in red blood corpuscles and forms oxyhemoglobin.
The capillaries eventually join together to form the pulmonary vein which pours out its contents into the left atrium.
From here the blood gets pushed to the left ventricle where the aorta takes it to the different parts of the body. From the body, the blood reaches the tissues and provides them with oxygen. The complex oxyhemoglobin breaks and releases oxygen. The cells take it up and use it for cellular respiration.
After the completion of cellular respiration, carbon dioxide is released. This carbon dioxide gets diffused out of the tissue in the blood capillaries.
The red blood cells take up carbon dioxide and form carboxyhemoglobin. This carboxyhemoglobin containing blood is known as the deoxygenated blood.
The deoxygenated blood enters into the right atrium via the inferior and superior vena cava.
From there, it moves to the right ventricle and is pushed up by the muscles of the heart to the pulmonary artery.
The pulmonary artery carries into the lungs and their exchange of gases takes place in the alveoli and carbon dioxide exchanged with oxygen.

Note: There is a dilemma here because arteries are supposed to carry oxygenated blood away from the heart and veins are supposed to carry deoxygenated blood towards the heart.
But this is an exception present in the entire body which refers to the pulmonary trunk.
The pulmonary veins carry oxygenated blood away from the heart towards the lungs and the pulmonary artery carries deoxygenated blood towards the heart. So this exception needs to be kept in mind.