Lesson · A.4.2

The respiratory system

The HESI A2 tests the respiratory tract from nose to alveolus, plus the mechanics of breathing. Here is the structure, the gas exchange, and the control loop in one pass.

ObjectiveA.4.2Read5 minExam weightCirculation, Respiration and Maintenance ≈ 28% of Anatomy & Physiology

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What you will be able to do

Trace the path of air from the nostrils to the alveoli, naming each structure in order.
Explain the difference between external and internal respiration.
Describe how the diaphragm and intercostal muscles drive inhalation and exhalation.

What the lesson concludes

The respiratory tract splits into an upper part (nose to larynx) and a lower part (trachea to alveoli).
The right lung has three lobes and the left has two, because the heart takes up room on the left.
Gas exchange happens only at the alveoli, across a membrane one cell thick.
Inhalation is active (muscles contract), exhalation at rest is passive (muscles relax and the lungs recoil).
The brainstem, not conscious thought, sets the baseline breathing rate by responding to carbon dioxide levels.