Respiratory System Anatomy

• The lecture covers the anatomy of the respiratory system
• The lecturer is assistant lecturer Dr. Firas M Ghazi from the University of Babylon / College of Hammuabi
• Degrees: M.B.Ch.B./ MSc human anatomy

Learning Outcomes

• Describe the structure and respiratory function of the nose, paranasal sinuses, pharynx, and larynx
• Describe the connections between the nose, paranasal sinuses, pharynx, auditory tube, and middle ear
• Discuss the structure of the pleural cavity and lines of pleural reflection
• Explain the lobes of the lung and their surface marking
• Discuss the structure and arrangement of airways and blood vessels in the lungs
• Describe the histology of the lung airways
• Describe a typical thoracic vertebra and rib structure
• Explain the relations and arrangement of muscles in the thoracic wall and diaphragm
• Discuss the function and distribution of the intercostal nerves, arteries, and veins

Objectives

• Describe the bony thorax structure and features of typical ribs and thoracic vertebra
• Discuss the differences between ribs 1, 2, 11, and 12 compared to typical ribs
• Describe the relations and arrangement of muscles in the thoracic wall and diaphragm
• Briefly state their functions and nerve supply
• Describe the distribution of the intercostal nerves, arteries, and veins
• Describe the pleural cavity & pleura, and state the lines of pleural reflection
• Discuss the structure and arrangement of airways and blood vessels in the lungs
• Describe the mediastina and their contents
• Discuss the structure of the pulmonary circulation and its distinguishing characteristics from the systemic circulation
• Describe the mechanical system properties comprising the lungs, chest wall, and diaphragm
• Discuss the roles of the muscles involved in inspiration and expiration from the resting expiratory level
• Describe the diaphragm and accessory respiratory muscles roles in different types of breathing

Thoracic Wall

• Bones include the sternum, 12 pairs of ribs with costal cartilages, and 12 thoracic vertebrae
• Muscles include intercostal muscles, the diaphragm, and pectoral muscles

Thoracic Cage: Sternum

• Flat bone made of three parts: manubrium, body, and xiphoid process

Thoracic Cage: Ribs

• There are 12 pairs of flat bones
• Ribs are divided into true ribs (1-7), false ribs (8-10), and floating ribs (11-12)
• Ribs are also divided into typical ribs (2-9) and atypical ribs (1, 10, 11, 12)

Typical Rib

• Includes a head with two articular surfaces, neck, tubercle with two parts, shaft with an angle and costal groove

Atypical Ribs

• Have a head with one articular surface
• Ribs 11 and 12 do not have a neck
• Ribs 11 and 12 have no tubercle
• Atypical ribs have no costal groove
• The first rib is the shortest and broadest with a flat shaft

Typical Thoracic Vertebra

• Heart-shaped body has two articular demi facets
• Has a long spinous process, circular vertebral foramen, and flat articular processes

Atypical Thoracic Vertebra

• Vertebrae 1, 10, 11, and 12 are considered atypical
• The body has a complete articular facet
• The spinous process becomes shorter downward

Costal Cartilages

• Contribute to the thoracic wall elasticity
• The 8th, 9th, and 10th costal cartilages form the costal margin

Joints: Intervertebral

• Between vertebral bodies (symphyses)
• Between articular processes (synovial)

Joints: Costovertebral

• Synovial joints

Joints: Sterno-costal

• The 1st rib: Primary cartilaginous
• Ribs 2nd- 7th: synovial

Joints: Inter-chondral

• Synovial

Intercostal Muscles

• There are three flat muscles in each intercostal space: external, internal, and innermost intercostal muscles
• Intercostal muscles keep intercostal spaces rigid during respiration

Intercostal Neurovascular Bundle

• Each intercostal space has its own intercostal blood vessels and nerve
• It is protected by the costal groove
• The bundle is arranged from above downward as vein, artery, nerve (V.A.N.)

Diaphragm

• The diaphragm is a musculotendinous structure separating the thoracic cavity from the abdominal cavity

Diaphragm: Attachments

• Attaches to the xiphoid process of the sternum, costal margin of the thoracic wall, ends of ribs XI and XII, and vertebrae of the lumbar region

Structures Passing Through the Diaphragm

• The inferior vena cava passes through at T8
• The esophagus passes through at T10
• Vagus nerves pass through the diaphragm with the esophagus
• The aorta passes through at T12
• The thoracic duct passes behind the diaphragm with the aorta
• Azygos and hemiazygos veins may also pass through the aortic hiatus

Diaphragm: Nerve Supply

• Motor innervation: Phrenic nerves (C3 to C5)
• Sensory innervation: Phrenic and lower intercostal nerves

Thoracic Cavity

• Extends from the thoracic inlet to the diaphragm
• The thoracic inlet is bounded by the T1 vertebra, 1st ribs, and manubrium
• Divided into bilateral pleural cavities and a central mediastinum

Pleura

• The pleural membrane comprises a single layer of flat mesothelial cells and an associated layer of supporting connective tissue
• The pleura has two layers: parietal and visceral
• Parietal lines the chest
• Visceral covers the lungs
• The plural space between the layers contains a thin film of serous fluid

Pleural Reflections

• Extends into the neck, 3-4 cm above the first costal cartilage
• Meet anteriorly at the sternal angle
• The right pleura descends vertically till the 6th costal cartilage
• The left pleura deviates laterally at the 4th costal cartilage and returns medially at the 6th cartilage
• At the midclavicular line, the two pleura cross the 8th rib
• At the mid-axillary line, the two pleura cross the 10th rib
• Runs backward horizontally till reaching the 12th vertebra

Pleural Recesses

• Spaces where the two pleura layers become opposed as the lung does not fill the pleural cavity
• Includes costodiaphragmatic and costomediastinal recesses

Mechanism of Breathing

• The dimensions of the thorax change in the vertical, lateral, and anteroposterior directions during breathing
• The primary respiration muscle is the diaphragm
• During increased respiratory efforts such as an asthma attack, the accessory muscles of respiration assists the diaphragm
• The accessory muscles include the intercostal muscles (I.C.M), pectoral muscles, neck muscles, and abdominal muscles

Breathing Movements: Pump Handle Movement

• Changes the A.P diameter due to ribs and sternum elevation in inspiration along with ribs and sternum depression in expiration
• Occurs at the upper six ribs

Breathing Movements: Bucket Handle Movement

• Increases the lateral dimensions of the thorax
• Occurs at the 7th – 10th ribs

Inspiration

• Increase vertical diameter of the thoracic cavity by the descend (contraction) of the diaphragm
• Increase the anteroposterior diameter of the thoracic cavity by the elevation of anterior parts of ribs with the sternum by pump handle mechanism
• Increase the lateral diameter of the thoracic cavity by the elevation of middle parts of ribs by bucket handle mechanism