Breathing - The thorax Flashcards
Movements of thoracic wall during breathing
The thoracic wall moves in response to respiration through changes in its anterior, lateral, and vertical dimensions:
- Pump-handle movement
- Bucket-handle movement
- Inspiration
- Expiration
- Compliance
Pump-handle movement
The upper ribs elevate, increasing the anteroposterior dimension of the thoracic cavity. This movement is due to the rotation of the ribs at their costotransverse joints
Bucket-handle movement
The lower ribs elevate and move laterally, increasing the transverse dimension of the thoracic cavity. This movement results from changes in the costovertebral and sternocostal joints
Inspiration
The diaphragm contracts, decreasing the height of the domes and increasing the thoracic volume. The external intercostal muscles (aslo contract) elevate the ribs.
Expiration
The diaphragm relaxes, the elastic recoil of the lungs and thoracic wall reduces the volume of the thorax, and the internal intercostal muscles (also contract) assist in depressing the ribs.
Compliance
refers to the expandability of the thoracic cavity and lungs. Greater compliance allows for easier lung expansion, whereas reduced compliance (e.g., in fibrosis) makes breathing more difficult.
Diaphragm in breathing
The primary muscle of respiration; contracts during inspiration, increasing thoracic volume, and relaxes during expiration, decreasing thoracic volume
External intercostal muscles
Elevate the ribs, increasing the anteroposterior and transverse dimensions of the thorax, assisting in inspiration
Internal intercostal muscles
Internal intercostal muscles: Depresses the ribs, reducing thoracic volume, and aids in forced expiration.
Accessory muscles of respiration
ACTIVE ONLY DURING FORCED BREATHING
- Scalene muscles
- Sternocleidomastoid
- Pectoralis minor
- Abdominal muscles
Scalene muscles
Elevate ribs I and II, increasing thoracic volume
Sternocleidomatoid
Elevates the sternum, assisting in deep inspiration
Pectoralis minor
Assists in elevation ribs II to V when the upper limb is fixed
Abdominal muscles
(rectus abdominis, external and internal obliques, transversus abdominis): Increase intraabdominal pressure, pushing the diaphragm superiorly to assist in forced expiration.
Pulmonary circulation major vessels
The pulmonary circulation is responsible for oxygenation of blood:
- Pulmonary arteries
- Pulmonary veins
- Right ventricle
- Left atrium
Pulmonary arteries
Carry deoxygenated blood from the right ventricle of the heart to the lungs. They branch into smaller arteries that accompany the bronchi within the lung.
Pulmonary veins
Carry oxygenated blood from the lungs to the left atrium of the heart.
Left atrium
Receives oxygenated blood from the pulmonary veins, which will be pumped into systemic circulation via the left ventricle.
Right ventricle
Pumps deoxygenated blood into the pulmonary trunk, which bifurcates into the right and left pulmonary arteries.
Bronchial cirrculation
The bronchial circulation supplies oxygenated blood to the tissues of the lungs.
- Bronchial arteries
- Bronchial veins
- Systemic circulation
Bronchial arteries
Arise from the thoracic aorta (or occasionally from posterior intercostal arteries) and supply the bronchi, connective tissue, and visceral pleura.
Bronchial veins
Drains the proximal parts of the bronchi and empty into the azygos vein (on the right) and the accessory hemiazygos vein or superior intercostal vein (on the left).
Systemic circulation
Unlike the pulmonary circulation, the bronchial circulation is part of the systemic circulation, meaning it supplies the tissues of the lungs with oxygen-rich blood.
Key nerves in respiration
Phrenic nerve
Intercostal nerves
Vagus nerve
Autonomic nervous system
Phrenic nerve
Originates in the cervical plexus (C3-C5)
Passes through the neck, superior thoracic aperture, and mediastinum
Provides motor innervation to the diaphragm
Intercostal nerves
Arise from the anterior rami of thoracic spinal nerves (T1-T11)
Provide motor innervation to intercostal muscles and sensory innervation to the thoracic wall and pleura
Vagus nerve
Provides parasympathetic innervation to the lungs.
Controls bronchoconstriction and secretion of mucus.
Autonomic nervous system
Sympathetic innervation: From the sympathetic trunks, causes bronchodilation
Parasympathetic innervation: From the vagus nerve, causes bronchoconstriction and increased mucus secretion.
