Introduction:
The human body relies on oxygen to carry out various physiological processes. Oxygen is primarily obtained through respiration, where it enters the bloodstream and is distributed throughout the body. However, there are certain parts of the body that directly extract oxygen from the air, bypassing the circulatory system. Let's explore these areas in detail.

1. Lungs:
The primary function of the lungs is to facilitate the exchange of gases between the air and the bloodstream. When we inhale, air enters the lungs and travels through the bronchial tubes. The bronchial tubes branch out into smaller air sacs called alveoli. These alveoli have thin walls, richly supplied with tiny blood vessels called capillaries. Oxygen from the inhaled air diffuses across the alveolar walls and into the bloodstream. This allows direct oxygenation of the blood without relying on the circulatory system.

2. Alveoli:
The alveoli play a crucial role in the oxygenation of blood. With their thin, moist walls, they provide a large surface area for efficient gas exchange. The oxygen in the alveoli diffuses across the alveolar membrane into the surrounding capillaries, binding to hemoglobin and forming oxygenated blood. Conversely, carbon dioxide, a waste product of cellular respiration, diffuses from the capillaries into the alveoli to be exhaled.

3. Pulmonary Capillaries:
The pulmonary capillaries are an intricate network of tiny blood vessels surrounding the alveoli. Their close proximity to the alveolar walls allows for efficient gas exchange. Deoxygenated blood from the heart is pumped to the lungs through the pulmonary arteries. These arteries branch out into smaller vessels, eventually forming the pulmonary capillaries. As the blood flows through these capillaries, oxygen diffuses across the alveolar walls, binding to hemoglobin and oxygenating the blood.

4. Respiratory Membrane:
The respiratory membrane is the interface between the alveoli and the capillaries. It consists of the alveolar epithelium, the capillary endothelium, and their shared basement membrane. This membrane is extremely thin, facilitating the diffusion of gases. Oxygen passes from the alveoli to the capillaries, while carbon dioxide moves in the opposite direction.

Conclusion:
In summary, while most parts of the human body receive oxygen through the bloodstream, the lungs, alveoli, pulmonary capillaries, and the respiratory membrane allow for direct oxygenation of the blood from the inhaled air. This intricate system ensures that oxygen is efficiently transported to the body's tissues, supporting various physiological processes and sustaining life.