Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

The Science of Viscera (Splanchnology)
Respiratory System
Mediastinum - Age-related features of the respiratory organs

The Mediastinum is a complex of Organs located in the thoracic cavity between the right and left Lungs. Its anterior boundary is formed by the posterior surface of the Sternum, the posterior boundary by the thoracic spine, and the inferior boundary by the Diaphragm. Superiorly, the mediastinum communicates with the neck region through the superior thoracic aperture. It contains The Heart and Pericardium, the Thoracic Aorta, the SUPERIOR VENA CAVA, the Thymus, the Trachea and main Bronchi, the Esophagus, the Thoracic duct and mediastinal Lymph Nodes, the vagus and phrenic nerves, as well as other Arteries, Veins, and nerves.

The Nasal cavity in a newborn is low (about 17.5 mm in height) and narrow. The nasal conchae are relatively thick, and the nasal meatuses are poorly developed. The Inferior nasal concha contacts the floor of the nasal cavity. The common nasal meatus remains unobstructed, and the choanae are low. By 6 months of age, the height of the nasal cavity increases to 22 mm, and the middle nasal meatus forms; the inferior meatus forms by 2 years, and the superior meatus after 2 years. By 10 years of age, the length of the nasal cavity increases by 1.5 times, and by 20 years, it doubles compared to that of a newborn. Among the Paranasal Sinuses, only the maxillary sinus is present in the newborn, and it is poorly developed. The remaining sinuses begin to form after birth. The frontal sinus appears in the 2nd year of life, the sphenoid sinus by 3 years, and the ethmoid labyrinth Cells by 3–6 years. By 8–9 years of age, the maxillary sinus occupies almost the entire body of the bone. By 5 years, the frontal sinus is the size of a pea. The dimensions of the sphenoid sinus in a 6–8-year-old child reach 2–3 mm. At 7 years of age, the Ethmoid bone sinuses closely abut one another; by 14 years, their Structure resembles the ethmoid cells of an adult.

The Larynx in a newborn is short, wide, funnel-shaped, and located higher than in an adult (at the level of the II–IV vertebrae). The laminae of the thyroid Cartilage form an obtuse angle with each other. The laryngeal prominence (Adam's apple) is absent. Due to the high position of the larynx in newborns and infants, the epiglottis lies somewhat superior to the ROOT of the Tongue; therefore, during swallowing, the food bolus (or liquid) bypasses the epiglottis laterally. As a result, an infant can breathe and swallow (drink) simultaneously, which is of vital importance during suckling.

The laryngeal inlet in a newborn is relatively wider than in an adult. The vestibule is short, positioning the rima glottidis high up. It has a length of 6.5 mm (3 times shorter than in an adult). The rima glottidis increases noticeably During the first three years of the child's life and then again during Puberty. The laryngeal Muscles are poorly developed in newborns and children. The larynx grows rapidly during the first four years of life. During puberty (after 10–12 years), active growth resumes and continues up to 25 years in males and 22–23 years in females. Along with its growth in childhood, the larynx gradually descends, and the distance between its superior margin and the Hyoid bone increases. By 7 years of age, the inferior margin of the larynx is located at the level of the superior margin of the VI cervical vertebra. The larynx assumes its adult position after 17–20 years of age.

Sex differences in the larynx are not observed in early childhood. Subsequently, laryngeal growth in boys proceeds somewhat faster than in girls. After 6–7 years of age, the larynx is larger in boys than in girls of the same age. At 10–12 years of age, the laryngeal prominence becomes noticeable in boys.

The laryngeal cartilages, which are thin in the newborn, become thicker with age, yet retain their flexibility for a long time. In elderly and senile age, calcium salts are deposited in the laryngeal cartilages, except for the epiglottis. The cartilages undergo ossification, becoming brittle and fragile.

The trachea and main bronchi in a newborn are short. The length of the trachea is 3.2–4.5 cm, and the width of the lumen in its middle part is about 0.8 cm. The membranous wall of the trachea is relatively wide, and the tracheal cartilages are poorly developed, thin, and soft. In elderly and senile age (after 60–70 years), the tracheal cartilages become dense and brittle, and easily fracture upon compression.

After birth, the trachea grows rapidly during the first 6 months; its growth then slows down and accelerates again during puberty and adolescence (12–22 years). By 3–4 years of age, the width of the tracheal lumen increases twofold. In a 10–12-year-old child, the trachea is twice as long as in a newborn, and by 20–25 years of age, its length triples.

The mucous membrane of the tracheal wall in a newborn is thin and delicate; the glands are poorly developed. In a 1–2-year-old child, the superior margin of the trachea is located at the level of the IV–V cervical vertebrae, at 5–6 years anterior to the V–VI vertebrae, and in adolescence at the level of the V cervical vertebra. By 7 years of age, the tracheal bifurcation is located anterior to the IV–V thoracic vertebrae, and after 7 years, it gradually stabilizes at the level of the V thoracic vertebra, just as in an adult.

The lungs of a newborn have an irregular conical shape; the superior lobes are relatively small. The middle lobe of the right lung is equal in size to the superior lobe, while the inferior lobe is comparatively large. The mass of both lungs in a newborn is 57 g (ranging from 39 to 70 g), with a volume of 67 cm³. The density of an unventilated lung is 1.068 (the lungs of a stillborn, unventilated child sink in Water). The density of a ventilated child's lung is 0.490. The bronchial tree is largely formed by the time of birth. During the 1st year of life, it undergoes intensive growth (the dimensions of lobar bronchi increase twofold, and main bronchi 1.5-fold). During puberty, the growth of the bronchial tree accelerates again. The dimensions of all its parts (bronchi) increase by 3.5–4 times by age 20 (compared to the newborn's bronchial tree). In individuals aged 40–45, the bronchial tree reaches its maximum size. Age-related involution of the bronchi begins after 50 years. In elderly and senile age, the length and lumen diameters of many segmental bronchi decrease slightly, and bead-like outpouchings of their walls sometimes appear.

The pulmonary acini in a newborn contain a small number of small pulmonary alveoli. Throughout the second year of life and later, the acinus grows due to the appearance of new alveolar ducts and The formation of new pulmonary alveoli in the walls of existing alveolar ducts. The formation of new branches of alveolar ducts is completed by 7–9 years of age, and of pulmonary alveoli by 12–15 years. By this time, the size of the alveoli doubles. The Formation of the pulmonary parenchyma is completed by 15–25 years of age. Between the ages of 25 and 40, The structure of the pulmonary acini remains practically unchanged. After 40 years, a gradual Aging of the lung tissue begins. The pulmonary alveoli become larger, and some interalveolar septa disappear. During postnatal GROWTH AND DEVELOPMENT of the lungs, their volume increases: during the 1st year, 4-fold; by 8 years, 8-fold; by 12 years, 10-fold; and by 20 years, 20-fold (compared to the lung volume of a newborn).

The BOUNDARIES OF THE lungs also change with age. The apex of a newborn's lung is located at the level of the first rib. Later, it projects above the first rib and by 20–25 years of age lies higher than the first rib (2 cm above the clavicle). The inferior border of the right and left lungs in a newborn runs one rib higher than in an adult. As the child grows older, this border gradually descends. In elderly age (after 60 years), the inferior borders of the lungs are located 1–2 cm lower than in individuals aged 30–40.

Review and Self-Assessment Questions:

1. Name the walls of the nasal cavity, indicate where the nasal conchae and nasal meatuses are located, and describe their Functions.

2. List the cartilages and Muscles of the larynx. What is the function of each of these muscles?

3. What is the root of the lung, and what are its constituent structures?

4. Name the surfaces of the right and left lungs and their boundaries (by anatomical lines).

5. What is the bronchial tree? Which structures form it?

6. Describe the STRUCTURE OF THE pulmonary acinus. Which lung structures are referred to as the alveolar tree?

7. What is the Pleura, what parts are distinguished in it, and what functions does it perform?

8. Describe the mediastinum and its boundaries. Which organs are located within the mediastinum?