Respiratory System: Nose and Nasal Cavity

• The respiratory system is responsible for respiration, which involves carrying oxygen in and carbon dioxide out.
• The components are the nose, nasal cavity, pharynx, larynx, trachea, bronchial tree, and lungs.

Nose

• The nose is formed by the external nose and nasal cavity.
• The external nose is formed of an upper bony part and a lower cartilaginous part.
• The nostril is part of the external nose, along with the ala.

Nasal Cavity

• Two nasal cavities are separated by a nasal septum.
• Each cavity opens on the face through the anterior nasal opening.
• The cavities open posteriorly in the nasopharynx through the posterior nasal opening.
• The purpose of the nose is for smelling, filtration/warming of the air, and optimizing olfaction.
• Nasal conchae increase the surface area of the nasal cavity, which magnifies air turbulence, improving olfaction
• The nasal mucosa has three parts, vestibule prevents dust from entering, respiratory warms incoming air, and the olfactory enables smell

Lateral Wall of Nasal Cavity

• The lateral wall has three elevations called the superior, middle, and inferior conchae (turbinates)
• 3 meatuses receive openings of the para-nasal sinuses - superior, middle and inferior

Paranasal Sinuses

• Paranasal sinuses are air-filled spaces in the skull bones surrounding the nose, opening into the nasal meatuses.
• The four paranasal sinuses are frontal, maxillary, sphenoidal, and ethmoidal.
• The frontal sinus is located in the frontal bone.
• The maxillary sinus is the largest air sinus in the maxilla.
• The sphenoidal sinus is in the body of the sphenoid bone below the pituitary gland.
• Primary functions are to decrease skull weight, increase voice resonance, and act as air cushions for the brain, eye, and pituitary gland.

Larynx

• The larynx begins at the root of the tongue and ends at the C6 vertebra, continuing as the trachea.
• Functions include the passage of air to the trachea and lungs, voice production by vocal cords, and reflex expulsion of foreign bodies.
• It consists of nine cartilages including 3 single and 3 paired, connected by membranes and ligaments, and moved by special muscles.
• The larynx contains the vocal cords responsible for voice production.
• The single cartilages of the larynx are the thyroid, cricoid, and epiglottis.
• The three paired cartilages are the arytenoid, cuneiform, and corniculate cartilages.
• Adam's apple is a midline prominence of the thyroid cartilage.

Trachea

• The trachea is a 10 cm tube.
• It lies in the midline, with its upper half in the neck and its lower half in the thorax.
• The trachea begins at the C6 level as a continuation of the larynx.
• It ends in the thorax at the sternal angle (lower border of T4), dividing into two main bronchi.
• The structure consists of 16-20 C-shaped cartilages.
• The trachea transmits air from the larynx to the lungs.

Bronchi

• The right bronchus is shorter, wider, and more in line with the trachea.
• The left bronchus is longer, narrower, and angled with the trachea.
• Inhaled foreign bodies usually pass to the right bronchus rather than the left one.
• The bronchi divide into secondary bronchi, then tertiary bronchi, terminal and respiratory bronchioles, alveolar ducts, and finally alveoli.

Lungs

• Each lung is nearly half cone-shaped, with an apex above and a base below, and has lateral and medial surfaces; they are divided into lobes by fissures.
• The medial surface contains the hilum, through which structures enter and leave the lung such as the pulmonary artery, 2 pulmonary veins and main bronchus.
• The right lung is short and wide, with two fissures (oblique and horizontal) and three lobes (upper, middle, and lower).
• The right lung has ten segments.
• The left lung is long and narrow, with one fissure (oblique) and two lobes (upper and lower).
• The left lung has eight segments.

Pleura

• The pleura is a serous membrane surrounding the lung.
• It consists of two layers, visceral and parietal, with a cavity in between.
• The visceral layer lies directly and adheres to the surface of the lung.
• The parietal layer lines the inner surface of the thoracic wall.
• The pleural cavity is a potential space between the two layers, containing a thin film of fluid to prevent friction.

Applied Anatomy

• Pleural effusion means accumulation of large amount of fluid in pleural cavity
• Pneumothorax means air in the pleural cavity

Inspiration

• Inspiration is the inhalation of air that requires increased thoracic dimensions.
• Diaphragm contraction causes its descent, increasing the vertical thoracic diameter.
• Intercostal muscle contraction elevates the ribs upwards and outwards, increasing both transverse and antero-posterior thoracic diameters.

Expiration

• Expiration is a passive process involving the recoil of respiratory muscles, leading to decreased thoracic diameters and expelling air from the lungs.