Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 301 are outside the lungs; they are called extrapulmonary bronchi . The primary bronchi further divide into smaller passageways as they enter the lungs. The branches of the lungs are collectively called the intrapulmonary bronchi. Each primary bronchus divides to form secondary bronchi, also known as lobar bronchi . In each lung, one secondary bronchus goes to each lobe. The right lung has three secondary bronchi, and the left lung has two. The Bronchioles Each tertiary bronchus branches several times within the bronchopulmonary segment, giving rise to multiple bronchioles. Terminal bronchioles are the smallest conducting branches. Roughly 6500 terminal bronchioles arise from each tertiary bronchus. The autonomic nervous system regulates the activity in the smooth muscle layer and, thereby, controls the diameter of the bronchioles. Sympathetic activation causes enlargement of airway diameter or bronchodilation . Bronchoconstriction is stimulated by the parasympathetic division, leading to a reduction in the width of 368 The Bronchi The primary bronchi and their branches form the bronchial tree . The left and right primary bronchi