Anatomy and Histology

Pleural recesses are potential spaces within the thoracic cavity where the two pleurae
are relatively distant

• Costomediastinal: behind the sternum and costal cartilages
• Costodiaphragmatic: between the diaphragm and chest wall
• Vertebromediastinal: between the vertebral bodies and mediastinum
• Phrenicomediastinal: between the diaphragm and mediastinum

The function of these recesses is to allow the increase volume of the lungs during
inspiration.
The liquid between the pleurae  allows the lungs to move smoothly along the walls of
the cavity during breathing.

The mediastinum (from Medieval Latin mediastinus, "midway"^[1]) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax.

Intercostal muscles:

•  Attached between the ribs.
• Manipulate the width of the rib cage
• Three layers:

1. outer layer: external intercostal (raising of the rib cage, assisting
inhalation),
2. Middle layer: internal intercostal
3. Inner layer: innermost intercostal muscles, transversus thoracis and
subcostal muscles

Diaphragm

the diaphragm (Ancient Greek: διάφραγμα diáphragma "partition"), is a sheet of internal skeletal muscle^[2] that extends across the bottom of the thoracic cavity. The diaphragm separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases and air is drawn into the lungs.

• Inspiration, i.e. increased lung volume due to contraction of the external intercostal muscles and the diaphragm
• Expiration, i.e. decreased lung volume due to contraction of internal intercostal muscles and relaxation of the diaphragm

• Three muscle layers:
• External intercostals raise ribs during inspiration (anterioinferior direction)
• Internal intercostals lower ribs during expiration (posteriosuperior direction)
• Innermost intercostals also lower ribs during expiration
• Subcostal and transverse thoracic muscles

1) Sternum: manubrium, body of sternum and xiphoid process
2) Ribs 2 to 10 have three articulations, 2 posterior = cylinder joint, 1 anterior = ball
and socket synovial planar joint (limited movement, flat or slightly
curved surface)
3) Ribs 1 to 7 articulate with sternum
4) Ribs 8 to 10 articulate with inferior margin of the rib above (costal arch)
5) Ribs 11 and 12 are floating ribs, i.e. no anterior articulation

Sternum(Brustbein): manubrium, body of sternum and xiphoid (Schwertvorsatz) process

All of the twelve ribs articulate posteriorly with the vertebrae of the spine. Each rib
forms two joints:

• Costotransverse joint – Between the tubercle of the rib, and the transverse costal facet of the corresponding vertebrae.
• Costovertebral joint – Between the head of the rib, superior costal facet of the corresponding vertebrae, and the inferior costal facet of the vertebrae above.

1) Posterior end articulates with the vertebrae
2) Two (synovial planar) articulations (ball and socket + swivel) form a cylinder joint

1) Is usually an autonomic process, but we can also control the breathing
2) Sensory organs in the brain, aorta and carotid arteries monitor the blood and sense
O2 and CO2 levels.
3) Respiratory centre are three paired nuclei (small groups of neurones), two in the
pons and one in the medulla oblongata
4) Respiratory musculature driven by dorsal (inspiration) and ventral (forced
respiration) respiratory group in the medulla
5) These set the basic pace of ventilation
6) Two nuclei in the pons monitor blood oxygenation and chemistry via
mechanoreceptors and the carotid and aortic chemo‐ and baroreceptors and
7) Pons adjust frequency and depth of ventilation

Functions of the Respiratory System
1) Provide an extensive area (ca. 100 m 2 or one
tennis court) for gas exchange
2) Move air into and out of lungs for exchange
3) Protect respiratory surfaces from dehydration,
temperature change and other environmental
variations
4) Defend the respiratory surface against
pathogens
5) Produce sounds, i.e. communication
6) Assist regulating blood pH, volume, pressure

1) Nasal cavity is responsible for filtration of particles down to 10 μm, humidification
and warming
2) Filtration by nasal hairs and impaction in mucous covered surfaces
3) Nasopharynx, connects the nasal and oral cavities
4) Oropharynx, at the back of the mouth, the entrance to the oesophagus, lined by
non‐keratinized stratified squamous epithelium (due to abrasive action of food)
5) Laryngopharynx, below the oropharynx with similar epithelium

Kehlkopf

1) Tough, flexible tube, ca. 2.5 cm diameter, 11 cm long (fibroelastic tissue and
cartilage)
2) Respiratory epithelial lining sitting atop connective tissue
3) Held open by 15‐20 C‐shaped cartilage rings connected by annular ligaments
4) Expands in diameter and extends in length during inspiration

• The inner layers of the tracheal wall.
• Respiratory epithelium RE of the trachea is similar to the rest of the bronchial tree
and nasal epithelium.

• Tall pseudostratified columnar cells with cilia (more plentiful in the lower trachea )
• Goblet cells (are more common in the upper trachea)
• Serous cells identical to the cells of the submucosal serous glands
• Basal cells which are part of the diffuse neuroendocrine system (are more common in the upper trachea)
• Basal stem cells which are able to divide and differentiate to replace other cell types

• Beneath the basement membrane, the lamina propria LP consists of loose, highly
vascular supporting tissue which becomes more condensed at its deeper aspect to
form a band of fibroelastic tissue.
• Underlying the lamina propria is the loose submucosa SM containing numerous
mixed seromucinous glands which decrease in number in the lower trachea. Edition.

1) Respiratory tree: branching structure of the airways supplying the lungs. At each
division point or generation, one airway branches into two or more smaller airways
2) Trachea bifurcates in the mediastinum forming two bronchi
3) Bronchi enter the lung via the hilum, the right is slightly wider and more vertical,
thus more prone to blockage
4) Enter the lungs at the hilum together with the blood and lymph vessels
5) Primary bronchi divide into secondary lobar bronchi for each lobe

1) Left bronchus has two lobes, superior and inferior
2) Right bronchus has three lobes, superior, middle and inferior
3) These differences reflect the differences in the number of lobes in the lung, two on
the left (sup. inf.), three on the right (sup. mid. inf.)
4) Branch into smaller secondary and tertiary bronchi, which then branch into smaller
tubes, the bronchioles
5) No gas exchange
6) Right main bronchus is wider and shorter and more vertical. Subdivides into three
secondary bronchi (lobar bronchi), delivering O2 to the 3 lobes of the right lung
7) Left main bronchus is smaller in calibre, longer. Divides into two lobar bronchi to
deliver O2 to each lobe of the left lung

Bronchiole: airway of less than 1 mm diameter which has neither cartilage or
submucosal glands in its wall. Ciliated columnar epithelium ells and few goblet cells. In
the terminal and respiratory bronchioles, goblet cells are replaced by Clara cells tall
columnar cells with apical secretory granules.
The wall is also composed of smooth muscle M. A distended thin‐walled pulmonary
artery branch Art lies next to the bronchiole.

Terminal bronchioles T are the smallest diameter passages of the purely conducting
portion of the respiratory tree.
Each terminal bronchiole divides to form short, thinner walled branches called
respiratory bronchioles R which contain a small number of single alveoli A in their
walls. The epithelium of the respiratory bronchioles is devoid of goblet cells and
largely consists of ciliated cuboidal cells and smaller numbers of non‐ciliated cells
called Clara cells.
Clara cells have three functions:

• Production of one of the components of surfactant.
• Act as stem cells, i.e. they are able to divide, differentiate and replace other damaged cell types.
• Contain enzyme systems which can detoxify noxious substances.

Each respiratory bronchiole divides further into several alveolar ducts AD which have
numerous alveoli A opening along their length.
The alveolar ducts end in an alveolar sac AS, which in turn opens into several alveoli.

• Alveolar ducts connect respiratory bronchioles with alveolar sacs
• Ca. 150 million alveolar sacs
• Relaxed diameter is ca. 200 μm
• Extremely well vascularised
• Elastic fibres cause sacs to recoil after inhalation

1) Alveolar wall: surface epithelium, supporting tissue and blood vessels
2) Epithelium: two pneumocytes , type I (cover the majority of the alveolar surface;
large squamous cells ) and II (rounded shape, 60% of the cells in the lining
epithelium, but smaller size, hence smaller area covered) alveolar cells
3) Type I are very thin, 0.1 μm
4) Type II secrete surface‐active material (surfactant), which reduces alveolar surface
tension, preventing alveolar collapse during expiration. Retain capacity for cell
division. Can differentiate into type I pneumocytes
5) Alveolar macrophages patrol the outer surface – free within the alveolar spaces and
in the alveolar septa; derived from circulating blood monocytes. Phagocytosis and
removal of unwanted material which gains access to the air spaces (particulate
matter and bacteria)