W.3.1 Thorax

THORAX VIDEO LECTURE WORKSHEET

BOUNDARIES OF THE THORAX

• Roof: Suprapleural membranes

• Posterior: Vertebral bodies

• Lateral: Ribs

• Anterior: Sternum and costal cartilages

• Floor: Diaphragm (not explicitly stated, but implied by structure)

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RIB CATEGORIZATION

Ribs 1 – 7

• Description: True ribs

• Articulation: Each attached to the sternum via its own costal cartilage

Ribs 8 – 10

• Description: False ribs

• Articulation: Attach to the sternum by "hitchhiking" with the costal cartilage of rib 7

Ribs 11 & 12

• Description: Floating ribs

• Articulation: No anterior articulation

TYPICAL RIBS (3-10)

• Head: Articulates with vertebrae

• Tubercle: Articulates with transverse process of vertebrae

• Body: Main section of the rib

• Costal Groove: Along inferior surface for vessels/nerves

• Neck: Section just before the head

• Angle: Location where rib bends

• Cup for Costal Cartilage: Area of attachment to cartilage

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ATYPICAL RIBS

• Rib 1:

  • Grooves for subclavian artery and vein

  • Tuberosity for serratus anterior

  • Scalene tubercle

  • Single facet on head (articulates directly with one vertebral body)

• Ribs 11 & 12:

  • No neck or tubercle

  • No costal cartilage cup

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RIBS: ANTERIOR ARTICULATIONS

• Manubrium: Articulates with first rib

• Sternomanubrial Joint: Also known as the "sternal angle"

• Body of Sternum: Articulates with ribs 2-7

• Xiphoid Process: Terminus of the sternum

• Costal Cartilage: Various joints formed (costochondral and sternochondral) for ribs 1-7

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RIBS: POSTERIOR ARTICULATIONS

• Superior Articular Facets: Articulate with head of ribs

• Costocorporeal Joint: For head of the rib articulations

• Costotransverse Joint: For tubercle of rib articulation

• Transverse Processes: Important for rib movement

  • Elevation and depression axes for rib movement during respiration

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RIB ARTICULATIONS

• Costal Cartilage: Connects ribs to sternum and vertebrae

• Demifacets & Intervertebral Discs (IVD): Important for rib articulation with vertebrae

• Intra-Articular Ligament: Aids in stabilizing the rib heads for movement

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ist the 4 different joints of rib articulation

1. Costocorporeal Joint: Articulation between the head of the rib and the vertebrae.

2. Costotransverse Joint: Articulation between the tubercle of the rib and the transverse process of the vertebrae.

3. Costochondral Joint: Joint that connects the rib to its costal cartilage.

4. Sternocostal Joint: Articulation between the costal cartilage of ribs 1-7 and the sternum.

Histological Classification:

1. Costocorporeal Joint:

   • Synovial joint formed between the head of the rib and the demifacets of adjacent vertebrae.

2. Costotransverse Joint:

   • Synovial joint formed between the tubercle of the rib and the transverse process of the corresponding vertebra.

3. Costochondral Joint:

   • Primary cartilaginous joint (synchondrosis) connecting the rib to its costal cartilage.

4. Sternocostal Joint:

   • Synovial joints (for ribs 2-7) formed between the costal cartilage of the ribs and the sternum. Rib 1 has a non-synovial joint (costal cartilage to manubrium).

Functional Classification:

1. Costocorporeal Joint:

   • Function: Facilitates rib movement during respiration, allowing elevation and depression of ribs that modify thoracic volume.

2. Costotransverse Joint:

   • Function: Aids rib rotation and movement, contributing to the mechanics of respiration.

3. Costochondral Joint:

   • Function: Provides stability and flexibility at the junction where ribs meet costal cartilage, aiding in respiratory movements.

4. Sternocostal Joint:

   • Function: Allows the ribs to attach securely to the sternum while permitting limited movement, essential for accommodating thoracic expansion during breathing.

Movements at Rib Articulations

1. Costocorporeal Joint

• Movements: Facilitates rib movement during respiration, allowing for elevation and depression of ribs that modify thoracic volume.

2. Costotransverse Joint

• Movements: Aids rib rotation and lateral movement, contributing to the mechanics of respiration.

3. Costochondral Joint

• Movements: Provides stability and flexibility at the junction where ribs meet costal cartilage, aiding in respiratory movements.

4. Sternocostal Joint

• Movements: Allows the ribs (1-7) to attach securely to the sternum while permitting limited movement, essential for accommodating thoracic expansion during breathing.

EMBRYOLOGY

Trilaminar Embryo

• Three Layers:

  • Ectoderm: Surface

  • Mesoderm: Body wall

  • Endoderm: Forms gut tube

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Body Wall vs. Coelomic Cavities

• Somatic Lateral Plate Mesoderm: Forms body wall, innervated by:

• Splanchnic Lateral Plate Mesoderm: Forms gut tube, innervated by:

• Coelom: Potential space in ventral body cavity

• pericardial, pleural, peritoneal spaces

  • Development of thorax and abdomen share common embryonic tissues that have homologous components

OPEN COELOMIC CAVITIES

• Pulmonary Cavities: Surround the lungs

• Mediastinum: Contains heart and related structures

• Abdominal Cavity: Contains digestive and other organs

• Pelvic Cavity: Contains reproductive organs

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SEROUS MEMBRANES

• Contain liquid and provide lubrication to organs in coelomic cavities (specific details not present)

• A serous membrane is a thin layer of tissue that lines certain cavities in the body and covers the organs within those cavities. It secretes a lubricating fluid called serous fluid that reduces friction between the organs and the walls of the cavities. For example, serous membranes line the pleural cavities around the lungs, the pericardial cavity around the heart, and the peritoneal cavity in the abdomen.

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OPEN vs. POTENTIAL CAVITIES

• Lungs: Real space (open respiratory pathway)

  • Contains: Lung tissue

  • Boundaries: Muscle and bone of body wall, mediastinal and suprapleural fascia

  • Internal Surfaces: Lined with pleura

• Pleural Cavity:

  • Potential space, contains serous fluid (small volume)

  • Boundaries formed by:

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PLEURA

• Visceral Pleura: Attaches to lungs

• Parietal Pleura: Attaches to thoracic cavity wall

• Surface Tension: Provided by pleural fluid, negative pressure (2-8 mm Hg)

  • Puncture Effect: If punctured, air enters the pleural cavity causing lung deflation

POTENTIAL SPACES

• Pleural Cavity: Between visceral and parietal pleura

• Mediastinum: Space for heart and vessels

• Pericardial Cavity: Between parietal pleura and pericardium (surrounding heart)

RESPIRATION

Overview of Respiration

• Phase 1: Inspiration (Breathing In)

  • Drawing air into the lungs

  • In response to increased thoracic volume

  • Dependent on muscle activity (diaphragm and accessory muscles of respiration)

• Phase 2: Expiration (Breathing Out)

  • Air passing out of the lungs

  • In response to decreased thoracic volume

  • Quiet respiration: Passive process (elastic recoil of diaphragm and lungs)

  • Forced respiration: Active process (contraction of accessory muscles of respiration)

THORACIC DIAPHRAGM

• Superior View: Central tendon, pericardium, costodiaphragmatic recess where lungs expand

• Inferior View:

  • Parts include Left Crus, Right Crus, costal origin, Central Tendon, median arcuate ligament, Aortic Hiatus, Oesophageal Hiatus, Caval Opening

• Left and Right Crus: Support base of diaphragm

• Openings: Aortic hiatus, esophageal hiatus, caval opening (T8, T10, and T12)

INNERVATION OF DIAPHRAGM

• Cervical Roots: "C3, 4, 5: Keep the diaphragm alive."

• Outer Edges: Innervated by lower intercostal nerves

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RIB MOVEMENTS

General Rib Movement Mechanics

• Movement occurs in a specific plane

• Elevation of ribs increases anterior-posterior dimensions of thorax

• Inferior ribs move more than superior ribs

Upper Ribs Movement

• Movement in sagittal plane

• Elevates ribs anterioly

• Increases vertical A-P dimensions of thorax- Elevates ribs, increasing dimensions of thorax

• Inferior ribs move more than superior ribs

Lower Ribs Movement

• Movement in corronal plane

• Elevates ribs laterally

• Increases transverse dimensions of thorax

• Inferior ribs move ___more___ than superior ribs

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INSPIRATION AND EXPIRATION Modality- RIB MOVEMENTS

Passive vs. Forced Breathing

• Passive Inspiration/Expiration: Basic respiratory process

• Forced Inspiration:

  • Diaphragm lowers as it contracts

  • Thorax expands

• Forced Expiration:

  • Diaphragm rises as it relaxes

  • Thorax contracts

INTERCOSTAL MUSCLES

• Origin (O): Inferior border of ribs

• Insertion (I): Superior border of rib below

• Innervation (N): Intercostal nerve

Types of Intercostal Muscles

• External Intercostals: Function like "hands in pockets"

• Internal Intercostals: Perpendicular to externals, primarily during forced expiration

• Innermost Intercostals:

  Located deep to the internal intercostals, these muscles assist in the mechanics of breathing by stabilizing the ribcage during contraction.

INTERCOSTAL NEUROVASCULAR BUNDLE

The Intercostal Neurovascular Bundle consists of the intercostal vein, artery, and nerve, located in the subcostal groove of the ribs. It plays a critical role in supplying blood and innervating the intercostal muscles. The clinical relevance of this bundle is its location, which is important for procedures such as needle insertion.

To drain the pleural cavity, a needle is typically inserted in the 5th intercostal space at the anterior axillary line (mid-axillary line) to avoid injury to the intercostal neurovascular bundle. This site is chosen to effectively access the pleural space while minimizing risk of complications.

INTERCOSTAL MUSCLES

Anatomy and Function

• External Intercostals

  • O: Inferior border of ribs

  • I: Superior border of the rib below

  • N: Intercostal nerve

  • Function: Hands-in-pockets movement

• Internal Intercostals

  • Perpendicular to external intercostals

  • Mainly involved in forced expiration

• Innermost Intercostals

• Related anatomy of the intercostal neurovascular bundle includes:

  • Subcostal groove

  • Intercostal vein

  • Intercostal artery

  • Intercostal nerve

Worksheet:

• Pleural Linkage: Refers to the connection between the lungs and the thoracic wall.

• Surface Tension: Pleural fluid creates surface tension that helps maintain the close apposition of the visceral (lung) and parietal (thoracic wall) pleura.

• Negative Pressure: The pleural cavity maintains a negative pressure (2-8 mm Hg) which keeps the lungs inflated by adhering the pleura to the thoracic wall and preventing lung collapse.

• serous fluid inbetween parietal and visceral pleura

The two mechanisms that contribute to pleural linkage are: 1. Surface Tension: The pleural fluid creates surface tension between the visceral and parietal pleura, which helps in maintaining the close apposition of the two layers. 2. Negative Pressure: The negative pressure within the pleural cavity (ranging between 2-8 mm Hg) plays a crucial role in keeping the lungs inflated by adhering the pleura to the thoracic wall and preventing lung collapse.