Heart lec 1

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Questions and Answers

What is the primary function of the intercostal muscles?

Facilitating rib cage movement during breathing (correct)

Connecting ribs to the sternum

Stabilizing the vertebrae

Protecting the thoracic organs

Which structure is NOT part of the thoracic wall?

Diaphragm (correct)

Ribs

Costal cartilages

Sternum

How does the diaphragm contribute to respiration?

By relaxing to pull air into the lungs

By creating negative pressure in the thoracic cavity (correct)

By supporting the ribs during exhalation

By contracting to increase thoracic pressure

Which of the following structures is responsible for the blood supply to the thoracic wall?

Thoracic aorta Signup and view all the answers

What is the role of the pleura in the pulmonary cavities?

Reducing friction during lung expansion and contraction Signup and view all the answers

What is the significance of the sternal angle (of Louis)?

It serves as a landmark for the bifurcation of major vessels Signup and view all the answers

Which of the following best describes the thoracic skeleton?

Includes the costal cartilages and vertebrae Signup and view all the answers

Which ribs are classified as true ribs?

Ribs 1-7 Signup and view all the answers

What is the primary function of the intercostal muscles during respiration?

They assist in lung inflation and expiration. Signup and view all the answers

Which structures are primarily involved in the formation of the thoracic wall?

Ribs and intercostal muscles. Signup and view all the answers

How does the diaphragm contribute to the process of respiration?

It contracts and increases the thoracic cavity volume. Signup and view all the answers

What is the primary role of the thoracic neurovasculature?

To innervate the thoracic wall and provide blood supply to thoracic organs. Signup and view all the answers

What is the main difference between the pleura and the pulmonary cavity?

Pleura are serous membranes; pulmonary cavity is the space surrounding the lungs. Signup and view all the answers

Which of the following best describes the mediastinum?

The central compartment within the thoracic cavity, housing the heart and great vessels. Signup and view all the answers

What is the role of the av valves and semilunar valves in the heart?

They regulate the flow of blood between heart chambers and into the arteries. Signup and view all the answers

Which structures are uniquely associated with the hilum of the lung?

Pulmonary arteries and bronchi. Signup and view all the answers

What is the primary function of the diaphragm during inspiration?

To expand the thoracic cavity by contracting Signup and view all the answers

Which layer of pleura covers the surface of the lungs?

Visceral pleura Signup and view all the answers

What structures form the root of the lung?

Pulmonary veins and arteries Signup and view all the answers

Which of the following best describes the function of the pleural cavity?

To allow smooth sliding between pleura layers Signup and view all the answers

How does the sympathetic nervous system affect the bronchial tree?

Leads to bronchodilation of the bronchial tree Signup and view all the answers

What does the mediastinum contain?

All thoracic viscera except the lungs Signup and view all the answers

What is the main role of pleura in respiration?

To facilitate lubrication and movement during breathing Signup and view all the answers

Which of the following statements about the right main bronchus is true?

It is wider and more vertical, making it prone to foreign-body aspiration Signup and view all the answers

What distinguishes the left lung from the right lung?

It contains a cardiac notch and lingula Signup and view all the answers

Which layer is part of the pericardium covering the heart?

Fibrous pericardium Signup and view all the answers

Which component provides sensory innervation to the fibrous pericardium?

Phrenic nerve Signup and view all the answers

What happens in the pericardial cavity during cardiac tamponade?

Fluid accumulates, compressing the heart Signup and view all the answers

Which of the following best describes the thoracic wall anatomy?

Composed of ribs, intercostal muscles, and connective tissue Signup and view all the answers

What does the term 'proximal' refer to in anatomical terminology?

Closer to the point of attachment or origin Signup and view all the answers

Which movement is described by the term 'abduction'?

Moving away from the median plane Signup and view all the answers

In the anatomical position, which of the following is NOT a characteristic feature?

Hands on the hips Signup and view all the answers

Which term describes the action of straightening or increasing the angle between bones?

Extension Signup and view all the answers

What is the primary role of identifying origin and insertion in muscles?

To study the muscle's function during contraction Signup and view all the answers

What is the location of the collateral nerve and vessels in relation to the ribs?

At the superior margin of the rib below Signup and view all the answers

Which structures pass through the diaphragmatic apertures?

Esophagus, aorta, and inferior vena cava Signup and view all the answers

Which structure forms the esophageal hiatus in the diaphragm?

Right crus Signup and view all the answers

What vertebral level corresponds to the caval opening of the diaphragm?

T8 Signup and view all the answers

What is the primary nerve responsible for the motor and sensory innervation of the diaphragm?

Phrenic nerve Signup and view all the answers

What is the primary function of the thoracic wall?

To protect thoracic structures and provide support Signup and view all the answers

Which structure forms the superior boundary of the thoracic cavity?

Superior thoracic aperture Signup and view all the answers

Which ribs are classified as false ribs?

Ribs 8-10 Signup and view all the answers

What landmark is formed at the junction of the manubrium and body of the sternum?

Sternal angle (of Louis) Signup and view all the answers

Which components are included in the skeleton of the thoracic wall?

12 pairs of ribs, costal cartilages, thoracic vertebrae Signup and view all the answers

What is the role of costal cartilages in the thoracic wall?

Facilitate the expansion of the thoracic cavity Signup and view all the answers

Which of the following best describes the inferior thoracic aperture?

Closed by the diaphragm, separating thorax from abdomen Signup and view all the answers

What is the function of the thoracic wall muscles during respiration?

They serve as accessory muscles of respiration Signup and view all the answers

Which structure is the most variable in the human body?

Veins Signup and view all the answers

What is the primary structural difference between the hilum and the root of the lung?

The root includes major bronchi and pulmonary vessels. Signup and view all the answers

What best describes the function of papillary muscles in the heart?

They prevent inversion of valves during contraction. Signup and view all the answers

Which statement correctly describes the pericardium?

It has a fibrous and a serous component. Signup and view all the answers

What is the primary function of the pleural cavity?

To reduce friction during lung expansion. Signup and view all the answers

Which of the following structures is least variable in the human body?

Nerves Signup and view all the answers

Which chamber of the heart receives oxygenated blood from the lungs?

Left atrium Signup and view all the answers

What distinguishes intrinsic innervation from extrinsic innervation of the heart?

Extrinsic innervation impacts heart rate and contraction force. Signup and view all the answers

Which of the following best describes the primary function of the lungs?

To oxygenate the blood Signup and view all the answers

What is the location of the hilum in relation to the lung?

On the mediastinal surface Signup and view all the answers

What characterizes the right main bronchus compared to the left?

Wider and more vertical Signup and view all the answers

In which part of the mediastinum is the heart located?

Middle mediastinum Signup and view all the answers

What is the role of the autonomic nervous system in relation to bronchial smooth muscle?

Both inhibits and stimulates bronchial smooth muscles Signup and view all the answers

Which structure passes through the transverse pericardial sinus?

Ascending aorta Signup and view all the answers

What does the pleural cavity primarily contain?

Serous fluid Signup and view all the answers

What anatomical feature identifies the boundaries of the inferior mediastinum?

Transverse thoracic plane Signup and view all the answers

Which layer of the pericardium is tough and fibrous?

Fibrous pericardium Signup and view all the answers

Which chamber of the heart primarily receives oxygenated blood?

Left atrium Signup and view all the answers

What type of neurons are involved in the presynaptic pathway of the autonomic nervous system?

Presynaptic neurons within the CNS Signup and view all the answers

Where does the cardiac tamponade occur?

In the pericardial cavity Signup and view all the answers

Which vessels are part of the root of the lung?

Pulmonary arteries and veins Signup and view all the answers

What feature distinguishes the left lung from the right lung?

Cardiac notch Signup and view all the answers

What term is used to describe the movement of a body part toward the median plane?

Adduction Signup and view all the answers

In anatomical position, which directional term describes a structure that is situated farther from the midline of the body?

Lateral Signup and view all the answers

Which of the following statements accurately describes the anatomical context of 'origin' in muscle anatomy?

The fixed point of attachment that usually remains stationary. Signup and view all the answers

What is the primary distinction between 'superficial' and 'deep' in anatomical terminology?

'Superficial' indicates closer proximity to the outer body surface than 'deep'. Signup and view all the answers

In the context of anatomical planes, which description best matches the term 'transverse'?

Separates the body into upper and lower portions. Signup and view all the answers

Which of the following apertures in the diaphragm allows for the passage of the esophagus?

Esophageal hiatus Signup and view all the answers

What is the primary nerve that provides both motor and sensory innervation to the diaphragm?

Phrenic nerve Signup and view all the answers

At which vertebral level does the caval opening of the diaphragm lie?

T8 Signup and view all the answers

Which statement accurately describes the right crus of the diaphragm?

Contains the esophageal hiatus Signup and view all the answers

What is the primary function of the diaphragm during the process of inspiration?

To expand the thoracic cavity and lower pressure Signup and view all the answers

What is the primary role of the external intercostal muscles during respiration?

Elevating the ribs to assist with inspiration Signup and view all the answers

Which statement correctly describes the direction of fiber orientation in the internal intercostal muscles?

They run directly from the sternum to the angles of the ribs Signup and view all the answers

What is the main artery supplying the upper six anterior intercostal spaces?

Internal thoracic artery Signup and view all the answers

Which muscles lie deep to the internal intercostals and have the same fiber orientation?

Innermost intercostals Signup and view all the answers

Where do the majority of the posterior intercostal arteries originate?

Thoracic aorta Signup and view all the answers

Which of the following veins primarily drain the posterior intercostal spaces?

Azygos and hemiazygos venous system Signup and view all the answers

What anatomical structure provides sensory innervation to the muscles along the thoracic wall?

Intercostal nerves Signup and view all the answers

Which muscle is primarily involved in the expiration process by depressing the ribs?

Internal intercostals Signup and view all the answers

What is the significance of the fossa ovalis in the adult heart?

It serves as a remnant of a fetal structure that facilitated blood bypass. Signup and view all the answers

Which structure in the heart has thicker walls due to higher pressure requirements?

Left ventricle Signup and view all the answers

What is the role of the papillary muscles during ventricular contraction?

They prevent backflow of blood into the atria. Signup and view all the answers

How many semilunar cusps does the pulmonary valve have?

3 Signup and view all the answers

What is the primary function of the sinoatrial (SA) node?

To initiate and regulate impulses for heart contractions. Signup and view all the answers

Where is the atrioventricular (AV) node located?

Near the opening of the coronary sinus. Signup and view all the answers

Which innervation system decreases heart rate and force of contraction?

Parasympathetic nervous system Signup and view all the answers

Which of the following is true about the chordae tendineae?

They connect the papillary muscles to the valve cusps. Signup and view all the answers

What type of fibers are primarily responsible for regulating heart contractions and heart rate?

Autonomic nerve fibers Signup and view all the answers

What are the characteristics of the right main bronchus that differentiate it from the left main bronchus?

It is wider and more vertical in orientation. Signup and view all the answers

Which structure is primarily responsible for the vasodilation of pulmonary vessels during the autonomic regulation of the lungs?

Parasympathetic nervous system stimulation Signup and view all the answers

Which feature distinguishes the left lung from the right lung in terms of anatomical structure?

Presence of the cardiac notch Signup and view all the answers

What is the primary function of the serous fluid found in the pleural cavity?

To facilitate movement between the pleurae during respiration Signup and view all the answers

Which of the following layers forms the outermost cover surrounding the heart?

Fibrous pericardium Signup and view all the answers

In the autonomic nervous system, which nerves are associated with the sympathetic supply to thoracic viscera?

Cardiopulmonary splanchnic nerves Signup and view all the answers

Which structure passes through the mediastinum, connecting the heart with the body?

Inferior vena cava Signup and view all the answers

What condition is indicated by an excessive fluid collection in the pericardial cavity?

Cardiac tamponade Signup and view all the answers

Which component of the respiratory system primarily facilitates the exchange of gases in the lungs?

Alveoli Signup and view all the answers

Which of the following layers of pericardium lines the inner surface of the fibrous pericardium?

Parietal layer Signup and view all the answers

What anatomical term describes the section of the thoracic cavity that is central and contains the heart, great vessels, and esophagus?

Mediastinum Signup and view all the answers

What term describes the thin, serous membrane lining each pulmonary cavity?

Pleura Signup and view all the answers

Which structures are responsible for creating the two pericardial sinuses?

Reflections of serous pericardium Signup and view all the answers

Which structure serves as the primary point of entry or exit for bronchial and pulmonary vascular structures in the lung?

Hilum of the lung Signup and view all the answers

Study Notes

Thoracic Wall

The superior part of the trunk between the neck and abdomen.
Contains: Heart, lungs, thymus, distal part of trachea, and most of esophagus
Thoracic wall consists of skin, fascia, neurovasculature, muscles, cartilages, and bones
Functions: Protects thoracic structures, Resists negative internal pressures, Provides attachment and support for upper limbs, muscles of neck, abdomen, back, and muscles of respiration

Skeleton of the Thoracic Wall

12 pairs of ribs and costal cartilages, thoracic vertebrae, and intervertebral discs
Sternum

Ribs

12 pairs of ribs
- True Ribs (1-7)
- False Ribs (8-10)
- Floating Ribs (11-12)

Costal Cartilages

Flexible attachment for anterior ends of ribs to sternum
1st-7th costal cartilages attach directly to sternum
8th, 9th, and 10th indirectly attach to sternum via costal cartilage above
7th-10th costal cartilages form the costal margin

Sternum

Manubrium, body, and xiphoid process

Landmarks

Jugular (suprasternal) notch: On superior aspect of manubrium, Trachea lies deep to the notch
Sternal angle (of Louis): Manubrium and body lie in slightly different planes, Superior/inferior to junction (manubriosternal joint) forming a projecting angle. Landmark for: Bifurcation of pulmonary trunk, Aortic arch, Bifurcation of trachea, Point of articulation of 2nd ribs, At level of T4-T5 IV disc
Xiphoid process: Midline marker for superior extent of liver, central tendon of diaphragm, and inferior border of heart

Thoracic Apertures

Superior Thoracic Aperture (Thoracic Inlet): Structures passing through: Trachea, Esophagus, Vessels, Nerves. Bounded by: T1 vertebra, First pair of ribs and costal cartilages, Superior border of manubrium
Inferior Thoracic Aperture (Thoracic Outlet): Closed by diaphragm, Separating thorax from abdomen. Structures passing between thorax and abdomen pass through openings in diaphragm. Bounded by: T12 vertebra, 11th and 12th ribs, Costal margin, Xiphisternal joint

Thoracic Wall Muscles

Some muscles attached to and/or covering the thoracic cage are primarily involved in serving other regions.
They also serve as accessory muscles of respiration.

Diaphragm

Dome-shaped, muscular partition that separates the thoracic cavity from the abdominal cavity.
Important in respiration.
It has a central tendon and peripheral muscular part that is attached to the costal margin, xiphoid process, and lumbar vertebrae.
Innervation: Phrenic nerves (C3-C5)

Pleura

Each pulmonary cavity is lined by pleura (thin, serous membrane) that also reflects onto and covers the surface of lungs.
Visceral pleura covers the lung and adheres to all of its surfaces.
Parietal pleura lines the pulmonary cavities.

Pleural Cavity

The potential space between the two layers of pleura.
Contains a very thin layer of serous fluid that lubricates pleural surfaces.
Serous fluid allows the two layers of pleura to slide smoothly during respiration

Lungs

Organs of respiration; Main function is to oxygenate the blood.
Apex – blunt superior end ascending above 1st rib into neck.
Base - concave inferior surface, resting on the diaphragm.
3 surfaces:
- Costal surface
- Mediastinal surface
  - Hilum: Where structures of the root of the lung enter/exit
- Diaphragmatic surface

Right Lung

Lobes: Superior, Middle, Inferior
Fissures: Horizontal & Oblique

Left Lung

Lobes: Superior and Inferior
- Cardiac notch: Indentation formed from apex of heart
- Lingula: Thin, tongue-like process of superior lobe
Fissure: Oblique

Root of the Lung

Structures passing from mediastinum into/out of the lung.
- Pulmonary veins
- Pulmonary arteries
- Bronchi
- Pulmonary plexus of nerves
- Lymphatics

Hilum of the Lung

Region on the mediastinal surface where structures forming the root pass to enter/exit the lung.

Bronchi

Trachea divides into right and left main (primary) bronchi, which then split into:
- Lobar (secondary) bronchi
  - 3 in the right lung and 2 in the left lung.
  - Right main bronchus is shorter, wider, and more vertical than the left → right main bronchus more prone to the entrance of aspirated foreign bodies
- Segmental (tertiary) bronchi
  - 8-10 segmental bronchi

Lungs: Innervation

Innervation to the lungs is derived from the pulmonary plexuses located anterior and posterior to the roots of the lungs.
Pulmonary plexuses - nerve networks that contain parasympathetic and sympathetic fibers.

Autonomic Nervous System

Part of the PNS that innervates smooth muscle, cardiac muscle, and glands.
Subdivided into Sympathetic and Parasympathetic systems (often act in antagonistic fashion to regulate blood flow, secretions, and organ function)
Two-neuron pathway:
- Presynaptic neuron: Within CNS (brainstem or spinal cord)
- Postsynaptic neuron: Within PNS (ganglia)

Parasympathetic Nervous System

Primarily concerned with maintenance, conservation, and protection of body resources ("Rest, Digest, Read").
Vagus nerve (CN X) joins cardiac, pulmonary, and esophageal plexuses to supply thoracic viscera.

Sympathetic Nervous System

Principally involved with expenditure of body resources or energy ("Fight or Flight").
Cardiopulmonary splanchnic nerves (from sympathetic chain) enter cardiac, pulmonary, and esophageal plexuses to supply thoracic viscera.

Lungs: Innervation

Parasympathetic:
- Smooth muscle of the bronchial tree → Bronchoconstriction
- Pulmonary vessels → Vasodilation
- Glands of bronchial tree → Secretomotor
Sympathetic:
- Smooth muscle of bronchial tree → Bronchodilation
- Pulmonary vessels → Vasoconstriction
- Glands of bronchial tree → Inhibitory

Mediastinum

Central compartment of the thoracic cavity located between the two pulmonary cavities.
Contains all of the thoracic viscera and structures (except lungs).
Divided into superior and inferior portions at the transverse thoracic plane (T4/T5).

Superior Mediastinum

Superior to the transverse thoracic plane.

Superior Mediastinum: Contents:

Aortic arch and its branches
Left and right brachiocephalic veins (becoming the superior vena cava)
Bifurcation of the trachea
Esophagus
Phrenic nerves
Vagus (CN X) nerves
- Left recurrent laryngeal nerve

Inferior Mediastinum

Extends between the transverse thoracic plane and the diaphragm.
Can be further subdivided by the pericardium into Anterior, Middle, and Posterior mediastinum.

Anterior Mediastinum

Between the body of the sternum and the pericardium; extends inferiorly to the diaphragm.
Consists mainly of thymus (in children), loose connective tissue, fat, lymphatic vessels, lymph nodes, and internal thoracic vessel branches.

Middle Mediastinum

Situated between the pulmonary cavities; extends to the diaphragm.

Middle Mediastinum: Contents

Pericardium, heart, roots of great vessels (ascending aorta, pulmonary trunk, superior vena cava), phrenic nerves.

Posterior Mediastinum

Between pericardium and vertebral column, extending to the diaphragm.

Posterior Mediastinum: Contents

Esophagus, azygous system of veins, thoracic aorta, thoracic duct, sympathetic trunk/chain, splanchnic nerves.

Pericardium

Fibroserous membrane that covers the heart and beginning of the great vessels.

Pericardium Layers

Composed of two layers:
- Fibrous pericardium: Tough outer connective tissue layer; attached to the central tendon of the diaphragm.
- Serous pericardium: Inner layer composed mainly of mesothelium (single layer of flattened epithelial cells)
  - Parietal layer: Lines the inner surface of the fibrous pericardium.
  - Visceral layer (epicardium): Covers the surface of the heart.

Pericardial Cavity

Potential space between the parietal and visceral layers of the serous pericardium.
Normally contains a thin film of serous fluid that limits friction for the beating heart.
Cardiac Tamponade: Collection of excess fluid within the pericardial cavity. Life-threatening, fluid compresses the heart, preventing heart chambers to fill properly with blood.

Pericardial Sinuses

Parietal layer of serous pericardium is continuous with the visceral layer around the roots of great vessels.
These reflections of the serous pericardium occur in two locations:
- Transverse pericardial sinus
- Oblique pericardial sinus

Transverse Pericardial Sinus

Transversely running passage within the pericardial cavity.
Posterior to ascending aorta and pulmonary trunk; anterior to SVC and superior pulmonary veins.
Important for cardiac surgery: finger can be passed through the transverse sinus posterior to ascending aorta and pulmonary trunk, allowing placement of surgical clamp/ligature.

Oblique Pericardial Sinus

Inverted U-shaped cul-de-sac between the pulmonary veins and IVC.
Placing hand under the apex of the heart and moving superiorly will enter the oblique sinus.

Heart

Four-chambered muscular pump responsible for circulating blood to both lungs (pulmonary circulation) and the rest of the body (systemic circulation).
Right side (pulmonary circuit) receives poorly oxygenated (venous) blood from the body via SVC and IVC; Pumps it through pulmonary trunk and arteries to lungs for oxygenation.
Left side (systemic circuit) receives well-oxygenated (arterial) blood from lungs via pulmonary veins and pumps it into the aorta for distribution to the body.

Heart Chambers

4 chambers: Right/Left Atria and Right/Left Ventricles.
Atria are receiving chambers that pump blood into the ventricles (the discharging chambers).
Synchronous pumping actions of the right and left chambers (atrioventricular pumps) constitute the cardiac cycle.

Right Atrium

Receives venous blood from SVC, IVC, and coronary sinus.
Auricle: Ear-like muscular pouch projecting from the right atrium; increases atrial capacity.

Right Atrium Interior:

Smooth, thin-walled posterior part (sinus venarum) where SVC, IVC, and coronary sinus open.
Rough, muscular anterior wall composed of pectinate muscles.
Crista terminalis: Internal vertical ridge that separates the rough vs. smooth parts of the right atrium.

Learning Objectives

Understand the structural and functional roles of the thoracic structures (i.e. skeleton, muscles, pleura).
Describe the location of various organs within the thoracic cavity (lungs, heart, great vessels) and their relationship to one another.
Describe the innervation of the diaphragm.
Understand the structure of the lung and associated structures (e.g. bronchi, pulmonary vessels).
Understand the difference between the hilum and root of the lung. Describe what structures are found at each.
Describe the mediastinum and its subdivisions.
Understand the structure and function of the pericardium.
Describe each of the chambers of the heart. Describe the unique characteristics of each.
Understand the function of the papillary muscles and chordae tendineae in the ventricles of the heart.
Describe how blood flows through the heart and the role of the atrioventricular and semilunar valves.
Understand the difference between the extrinsic and intrinsic innervation of the heart.

Anatomical Position and Directional Terms

Anatomical descriptions are based on the anatomical position.
Four imaginary planes intersect the body in anatomical position: sagittal, coronal, transverse, and oblique.
Medial refers to structures closer to the midline.
Lateral refers to structures further from the midline.
Superior/cranial refers to structures above.
Inferior/caudal refers to structures below.
Anterior/ventral refers to structures in the front.
Posterior/dorsal refers to structures at the back.
Superficial refers to structures close to the surface.
Deep refers to structures further from the surface.
Proximal refers to structures closer to the origin.
Distal refers to structures further from the origin.
Supine is lying face up.
Prone is lying face down.

Joint Movements

Flexion decreases the angle between bones or body parts.
Extension increases the angle between bones or body parts.
Abduction moves a limb away from the median plane.
Adduction moves a limb towards the median plane.

Muscles

Muscles typically extend between bones.
Each muscle has an origin (proximal end) and an insertion (distal end).
The origin remains fixed during contraction, while the insertion moves.

Thoracic Wall Muscles

True muscles of the thoracic wall: intercostal muscles, serratus posterior muscles, levatores costarum muscles, transversus thoracis muscles, and subcostal muscles.

Intercostal Muscles

External intercostals run from the inferior border of a rib to the superior border of the rib below.
They extend from the vertebral column to the external intercostal membranes.
Their fibers run obliquely downward from lateral to medial (hands in a pocket).
They assist with inspiration by elevating the ribs.
Internal intercostals run deep to the external intercostals.
Their fibers run at right angles to those of the external intercostals.
They assist with expiration by depressing the ribs.
Innermost intercostals run deep to the internal intercostals.
Their fibers run in the same direction as the internal intercostals.
They also assist with expiration.

Other Thoracic Wall Muscles

Serratus posterior superior and inferior: help elevate and depress ribs, respectively.
Levatores costarum elevate ribs.
Subcostal and transversus thoracis depress ribs.

Thoracic Wall: Arteries

Anterior intercostal arteries: originate from the internal thoracic artery.
Posterior intercostal arteries: mostly originate from the thoracic aorta.
Anterior and posterior intercostal arteries anastomose (connect).

Thoracic Wall: Veins

Anterior intercostal veins drain into the internal thoracic veins.
Posterior intercostal veins drain into the azygos/hemiazygous venous system.
Anterior and posterior intercostal veins anastomose.

Neurovasculature of Thoracic Wall

Intercostal vein, artery, and nerve lie in the costal groove.
They pass between the internal and innermost intercostal muscles.
Collateral nerve, artery, and vein arise from the intercostal nerves and vessels.
They are located at the superior margin of the rib below.

Diaphragm

The diaphragm is the primary muscle of respiration.
It separates the thoracic cavity from the abdominal cavity.
It descends during inspiration, increasing thoracic volume and decreasing intrathoracic pressure, causing air to enter the lungs.
It attaches to the sternum, ribs, and lumbar vertebrae.
It has a central tendon called the aponeurosis.
The crura are musculotendinous bands arising from L1-L3 vertebrae.
The right crus has an opening for the esophageal hiatus.
The left crus is more slender.
Diaphragmatic apertures allow structures to pass between the thorax and abdomen:
- Caval opening: for the inferior vena cava.
- Esophageal hiatus: for the esophagus.
- Aortic hiatus: for the aorta.
The diaphragm is innervated by the phrenic nerves (C3-C5), providing both motor and sensory innervation.
The phrenic nerves cause the diaphragm to contract during inspiration, flattening it and increasing thoracic volume.

Pleura

The pleura is a thin serous membrane that lines the pulmonary cavity.
Visceral pleura covers the lung.
Parietal pleura lines the pulmonary cavity.
The pleural cavity is a potential space between the two layers of pleura.
It contains a thin layer of serous fluid.

Lungs

The lungs are the organs of respiration.
Their main function is to oxygenate the blood.
Apex: superior end ascending above the 1st rib into the neck.
Base: concave inferior surface resting on the diaphragm.
Surfaces: costal, mediastinal, and diaphragmatic.
Hilum: where structures of the root of the lung enter/exit.
Right lung: superior, middle, and inferior lobes.
Left lung: superior and inferior lobes.

Root and Hilum of the Lung

The root of the lung contains structures passing to and from the lung: pulmonary veins, pulmonary arteries, bronchi, pulmonary plexus of nerves, and lymphatics.
The hilum is the region on the mediastinal surface where these structures enter/exit the lung.

Bronchi

The trachea divides into right and left main (primary) bronchi.
Each main bronchus further divides into:
- Lobar (secondary) bronchi: 3 in the right lung, 2 in the left lung.
- Segmental (tertiary) bronchi: 8-10 in each lung.
The right main bronchus is shorter, wider, and more vertical than the left main bronchus. This makes it more prone to aspiration of foreign bodies.

Lungs: Innervation

The autonomic nervous system innervates the lungs.
The pulmonary plexuses located anterior and posterior to the roots of the lungs contain both parasympathetic and sympathetic fibers.

Autonomic Nervous System

The autonomic nervous system controls smooth muscle, cardiac muscle, and glands.
It is divided into sympathetic and parasympathetic systems which often act antagonistically.
The autonomic nervous system has a two-neuron pathway: presynaptic neuron in the CNS and postsynaptic neuron in the PNS (ganglia).

Parasympathetic Nervous System

The parasympathetic system is concerned with maintenance, conservation, and protection of body resources (rest, digest, read).
The vagus nerve (CN X) supplies thoracic viscera through the cardiac, pulmonary, and esophageal plexuses.

Sympathetic Nervous System

The sympathetic system is involved in expending body resources or energy (fight or flight).
Cardiopulmonary splanchnic nerves from the sympathetic chain enter the cardiac, pulmonary, and esophageal plexuses to supply thoracic viscera.

Innervation of the Lungs

Parasympathetic: bronchoconstriction, pulmonary vessel vasodilation, secretomotor innervation of bronchial glands.
Sympathetic: bronchodilation, pulmonary vessel vasoconstriction, inhibitory innervation of bronchial glands.

Mediastinum

The mediastinum is the central compartment of the thoracic cavity.
It contains all thoracic viscera and structures except the lungs.
It is divided into superior and inferior portions at the transverse thoracic plane (T4/T5).

Superior Mediastinum

The superior mediastinum is above the transverse thoracic plane.
It contains the aortic arch and its branches, left and right brachiocephalic veins, bifurcation of the trachea, esophagus, phrenic nerves, and vagus (CN X) nerves, including the left recurrent laryngeal nerve.

Inferior Mediastinum

The inferior mediastinum extends from the transverse thoracic plane to the diaphragm.
It can be subdivided by the pericardium into anterior, middle, and posterior compartments.

Anterior Mediastinum

The anterior mediastinum is between the body of the sternum and the pericardium.
It contains the thymus (in children), loose connective tissue, fat, lymphatic vessels, lymph nodes, and branches of the internal thoracic vessels.

Middle Mediastinum

The middle mediastinum is between the pulmonary cavities.
It contains the pericardium, heart, roots of great vessels, and phrenic nerves.

Posterior Mediastinum

The posterior mediastinum is between the pericardium and the vertebral column.
It contains the esophagus, azygos system of veins, thoracic aorta, thoracic duct, sympathetic trunk/chain, and splanchnic nerves.

Pericardium

The pericardium is a fibroserous membrane that covers the heart and the beginning of the great vessels.
It has two layers:
- Fibrous pericardium: tough outer connective tissue layer, attached to the central tendon of the diaphragm.
- Serous pericardium: inner layer composed of mesothelium.
  - Parietal layer: lines the inner surface of the fibrous pericardium.
  - Visceral layer (epicardium): covers the surface of the heart.

Pericardial Cavity

The pericardial cavity is a potential space between the parietal and visceral layers of the serous pericardium.
It contains a thin film of serous fluid.
Cardiac tamponade is a life-threatening condition where excess fluid in the pericardial cavity compresses the heart.

Pericardial Sinuses

Transverse pericardial sinus: transverse passage within the pericardial cavity.
Oblique pericardial sinus: inverted U-shaped space between the pulmonary veins and IVC.

Heart

The heart is a four-chambered muscular pump that circulates blood to the lungs (pulmonary circulation) and the rest of the body (systemic circulation).
The right side receives deoxygenated blood from the body through the SVC and IVC and pumps it to the lungs.
The left side receives oxygenated blood from the lungs through the pulmonary veins and pumps it to the body.

Heart Chambers

The heart has four chambers: right atrium, left atrium, right ventricle, and left ventricle.
The atria receive blood and pump it into the ventricles.
The ventricles are the discharging chambers.
The synchronous pumping actions of the right and left chambers form the cardiac cycle.

Right Atrium

The right atrium receives venous blood from the SVC, IVC, and coronary sinus.
It has an auricle, an ear-like pouch increasing its capacity.
The sinus venarum is the smooth posterior wall where the SVC, IVC, and coronary sinus open.
The anterior wall contains pectinate muscles, which are rough and muscular.
The crista terminalis is a vertical ridge separating the smooth and rough parts of the right atrium.
The fossa ovalis (oval fossa) is a remnant of the foramen ovale, a fetal shunt allowing blood to bypass the lungs.

Left Atrium

The left atrium has a larger smooth-walled portion and a smaller auricle with pectinate muscles.
The pulmonary veins enter the smooth posterior wall.

Ventricles

The right ventricle has trabeculae carneae (muscular ridges on the inner surface of its wall) and papillary muscles (conical projections that attach to AV valve cusps via chordae tendineae).
The left ventricle forms the apex of the heart.
It has thicker walls than the right ventricle because of the higher pressure in the systemic circulation.
It has thinner and more numerous trabeculae carneae.

Heart Valves

Atrioventricular (AV valves):
- Tricuspid (right AV valve): 3 cusps (anterior, septal, posterior).
- Mitral (bicuspid, left AV valve): 2 cusps (anterior, posterior).
Semilunar valves:
- Pulmonary (semilunar) valve: 3 cusps (anterior, right, left).
- Aortic (semilunar) valve: 3 cusps (posterior, right, left).

Innervation of the Heart: Intrinsic

Sinu-atrial (SA) node: pacemaker of the heart. It initiates and regulates impulses for contractions.
Atrioventricular (AV) node: Located near the opening of the coronary sinus. It distributes impulses to the ventricles through the AV bundle (bundle of His).
Septomarginal trabecula (moderator band) carries the right bundle branch to the anterior papillary muscle.
Purkinje fibers: arise from the right/left bundle branches and stimulate the papillary muscles and ventricle walls.

Innervation of the Heart: Extrinsic

Autonomic nerve fibers regulate heart rate, force of contraction, and cardiac output.
Cardiac plexus: contains parasympathetic and sympathetic fibers.
- Parasympathetic (from vagus nerve): slows heart rate and reduces force of contraction.
- Sympathetic (from sympathetic trunk): increases heart rate and force of contraction.

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