Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 161

Each terminal bronchiole branches into several respiratory bronchioles and alveolar ducts which finally terminate in the alveolar air sacs. Collectively, these areas have a berry-like appearance (Figure 4.5) and are referred to as acini (Latin for berries). Acini are the functional units of the lungs where gas exchange takes place. In a healthy young adult, more than 30,000 of these acini are present in each lung, with each acinus having approximately 10,000 alveoli. Around 3 litres (3000 ml) of air is held within the lung acini of a typical adult male. This contrasts with the relatively small volume of air in the conducting airways, which totals only around 150 ml; this volume is known as the anatomical dead space since the air here does not reach the alveoli to participate in gas exchange.

Figure 4.5 A small portion of a respiratory acinus, showing alveoli and associated blood capillaries