The bones, muscle, fasciae, nerves, blood vessels and lymphatic dranaige of the thoracic wall. The histology of the mammary gland. The formation and differentiation of the extraembryonic mesoderm.

The bones, muscle, fasciae, nerves, blood vessels and lymphatic dranaige of the thoracic wall. The histology of the mammary gland. The formation and differentiation of the extraembryonic mesoderm.

Flash Cards:

Thoracic Wall - Joints and Fascia

Thoracic Wall - Ribs, musc, movements

Thoracic Wall - Intercostal spaces and arteries, nerves, etc

Thoracic Wall Blood supply lymph nerves

Anatomy: The bones, muscle, fasciae, nerves, blood vessels and lymphatic dranaige of the thoracic wall.

Anatomy of Thoracic Wall

Function: protects contents of thoracic cavity, mechanical function of breathing

Thoracic Inlet: T1, 1st pair of ribs +their costal cartilages, sup border of manubrium

Thoracic Outlet: T12, 11th,12th ribs, costal cart of ribs 7-10, xiphisternal joint

Structure:
Bones
12 ribs, sternum, vertebral column

Sternum
Has 3 parts:
Head = Manubrium

• has 2 clavicular notches to that articulates laterally w/ clavicle
• Sup margin has jugular notch
• lat side articulates w/ 1st rib
• @ level of T3-T4
  

Body

• Joins w/ manubrium @ Manubriosternal joint = sternal angle
  • located @ border b/w T4-5
  • Important marking point for:
    • Jxn b/w manurbium and sternal body
    • @ 2nd rib articulates w/ sternum
    • aortic arch begins and ends
    • trachea –> R & L bronchi
    • inf border of superior mediastinum
• Body starts as 4 sternabrae that fuse in life
  • fusion lines = transverse ridges

Xyphoid process

• joins body @ Xyphisternal joint – @ level of T9/T10
• is flat and cartilaginous @ birth
  • slowly ossifies
  • becomes fully bone @ middle age
• CLINICAL NOTE – People notice it in their 40’s and think there is a new growth in the area
• Marks:
  • border b/w thorax & abdominal cavity
  • ant attachment of diaphragm
  • sup surface of liver
  • R margin of heart
  • stomach

Ribs
Parts:
Head, Neck, Tubercle, Body, angle

Classicification of Ribs:
1-7 true ribs – attach directly to sternum via cartilagenous extension (vertebrocostal)
8-12 false ribs – do not attach directly to sternum

• 8-10 attach to ant costal margin (Vertebrochondral)
  
• 11-12 do not have an anterior attachment, but “float” , only articulate w/ vert bodies post (vertebral, free)
  

Movements of ribs:
3 important joints:

• Costovertebral – head articulates w/ vertebral bodies, each head attaches to 2 vertebrae, @ their junction pt
  
• Costotransverse – tubercle of rib attaches to transverse processes to vertebrae
• Sternocostal – ribs 1-7
• Costochondral – ant connection w/ ribs and cartiliage that attaches them to sternum, ant costal margin

2 types of movements:

1. “pump handle” —
   
   • change the ant-post diameter,
     
   • when upper ribs are elvated, inc the ant-post diametere
     
2. “bucket handle” —
   
   • change lateral diameter
   • when middle parts of lower ribs move lat, when elevated

Anim: Movements of Ribs during breathing

See Diaphragm, Lung topic for more on breathing process.

Joints & Fascia of Thoracic Wall
Joints:
1. Sternoclavicular Joint

• b/w manubrium of sternum, head clavicle
• moves like ball and socket, saddle type joint
• fibro cart articular surface
• 2 synovial cavities, sep b/ w IV disk, like TMJ
• Ligs = ant/post sterno-clavicular, costo-clavicular joint

2. Costovertebral Joint

• 2 joints in one:
  • Costovertebral – b/w head of rib and articular facet of vertebral body
  • Costotransverse – b/w tubercle of rib & transverse process of vertebra
• plane type joint
• Ligs =
  • (ant) radiate lig, intra articular lig
  • (post)lat/sup costotransverse lig
    • b/w sup c.t. lig and vertebrae allowes spinal n and dorsal br of IC a to come out
      

3. Sternocostal =

• b/w ribs and sternum, either directly, indirectly
• rib 1 = primary cartiligenous connection
• 2-7 = synovial plane joint
  • Lig = ant/post radiate sternocostal
• 8-10 = cxt w/ costal margin, not sternum,
• 11-12= do not connect w/ sternum

Other joints:

• Intervertebral joints (see vertebral column)
• Costochondral- b/w ribs and costal cartilage
  
• Interchondral- b/w costal cartilages & ant costal margin
  
• Manubriosternal – listed above
  
• Xyphisternal – listed above
  

Fascia of Thoracic Wall
1. Sub cutaneous tissue = superficial fascia aka Camper’s fascia

• loose CT just below skin w/ ligament = retinacula cutis
• contains: a/v/n,  sweat glands, lymph vessels, mammary glands
• Remember it this way – Campers go out in the woods and hunt and eat, so they have more fat – therefore the fatty fascia is Camper’&s
  

2. Deep (investing) fascia

• thin fibrous membrane b/w subcut tissue and skin
• NO fat
  
• covers and invests muscle & their tendons = epimysium
• holds thorax together
• is barrier to infection
• Named for part covered:
  • Pectoral – breast bed, pectoralis major m
  • Clavi-pectoral – clavicle, pect minor m
  • Endothoracic – inf side of thoracic cage
• Located where fleshy portions of IC m missing
• cont as IC membrane
• CLINICAL NOTE – Endothoracic fascia is thin fibro-alveolar layer b/w int aspect of thoracic cage and lining of pulmonary cavity–> opened surgically to gain access to intra thoracic structures

Muscles of Thoracic Wall
* all innervated by IC n, except levator costarum (dorsal primary rami of C8-T11)

3 layers of musc in IC spaces:
1. Ext layer – Ext IC m
2. Middle layer – Internal IC
3. Internal layer – Innermost IC, Subcostal, Transverse Thoracis, Levator Costarum

Elevators of ribs:

• External IC
  • tubercles of ribs –> costochondral junctions, run inf/lat direction
  • cont inf w/ ext oblique m
    
• Internal IC – ant portion (chondral)
  • run deep and perpendicular to Ext IC m
  • floors of costal groove –> inf/post –> sup borders of ribs inf
    
• Innermost IC –
• Subcostalis
• Levator costarum – transv pr of C7,T1-12 –> run inf/lat –> rib tubercles
  

Depressers of ribs:

• Internal IC – post portion (costal)
• Transverse Thoracis
  • 4/5 strips of m that attach to post side of body of xyphoid process/sternum –> run sup/lat–> 2-6 costal cart
    

Muscles of Thoracic wall not related to IC spaces:
Serratus post m – Inspiration

• Superior part:
  • (nuchal lig (inf), spinous processes of C7, T1-T3 –> runs inf/lat –> sup border of 2-4th, 5th rib)
  • => elevate 1st 4 ribs
• Inf part:
  • (sp processes of T11-12, L1-2 –> runs sup/lat –> T8-T12 inf border)
  • depresses last 4 ribs
  • prevents them from pulled up by diaphragm

Superficial Musc of Thorax:

• Pectoralis major – flexes and adducts the arm, medially rotates the arm
• Pectoralis minor – draws the scapula forward, medialward, and downward
• Serratus ant – rotate & hold scapula, it draws the scapula forward; the inferior fibers rotate the scapula superiorly
• Scalene m – lift ribs 1+2 in forced breathing
• Subclavius m

Intercostal Spaces – structure, content, related structures

Layers of IC space:

1. skin
2. subcutaneous CT
3. Ext IC m and membrane
4. Int IC m and membrane
5. IC a/v/n – located in costal groove, @ inf border of rib
6. Innermost IC m
7. Endothoracic fascia
8. Parietal wall of pleura

IC blood supply:

• Subclavian a
  • Int thoracic a – 1st branch, Thoracic part
    • gives off pericardiophrenic a
    • ant IC 1-6 a
      
    • ant perforating br –> med mammary br
    • thoracoepigastric a
      • runs behind/lat to sternocostal joint and gives 1st 6 IC a
    • sup epigastric a –> runs in rectus sheath, and anatomoses w/ inf epigastric a
    • musculophrenic a
      • gives off IC a 7-9 a
      • anatomosis w/ deep circumflex iliac a
  • NOTE – IC spaces b/w 10/11th rib, and 11/12 ribs do NOT HAVE a ant IC a
  • supreme IC a
    • and from costocervical trunk
    • gives of 1st 2 post IC a
• Axillary a –> gives off lat thoracic a
• Thoracic aorta –> gives post IC a
  • as mentioned above, 1st 2 post ICa come from costocervical trunk of subclavian a
  • post IC 3-11a direct from of thoracic aorta
• Br of IC a
  • dorsal br
  • lat cut br
  • ant perforating br
  • collateral br

NOTE – Each IC space has 1 post IC a, the collateral branch of post IC a and 2 ant IC a

In order, there is, from deep ->sup, the IC v, then a, then nerve = VAN OUT

Blood Supply of Thoracic Wall

Venous Drainage: Azygos system
Ant IC v:
IC 1-6 –> int thoracic v
IC 7-11 –> musculophrenic v

Post IC v:
(R) –> azygos v
(L) –> hemiazygos v inf, accessory hemiazygos v superiorly
both hemiazygos can flow into azygos, crosses midline @ T8
or acc. hemiazygos v can flow into hemiazygos, or angulus venosus

Nerves of IC spaces:
11 pairs of nerves, + subcostal n

IC 1-3n = Intercostobronchial n
IC 4-6n = Thoracic n
IC 7-12n = Thoracoabdominal n

originate from ventral rami of Thoracic spinal n

supply sk m, skin,
carry autonomic innervation to sweat glands, cutaneous vessels, hair follicles

Br of IC n

1. Lat cut br – pierce int/ext IC m on lat side, has ant/post br => skin of lat thoracic and ab wall
2. Ant cut br – pierce m @ parasternal line, had med/lat br => skin of ant thoracic and ab wall
3. Collateral br – aid  w/ IC m supply
4. white/gray br for SNS trunk (rami communicantes) => SNS trunk on same ggl –> desc br => a/v, sweat glands, smooth m
5. Musc br for m => IC m, subcostalis m, transv thoracis m, levator costarum, serratus post m

Each spinal n supplies
1 dermatome
1 myotome
1 sclerotome

CLINICAL NOTE: Thoracic puncture
Necessary when pleural cavity fills w/ fluid or air
done @ phrenico-costal sinus b/w post axillary & scapular line in 10th and 11th IC spaces
b/w lower margin of upper rub & upper margin of lower rib

Nerve Supply of Thoracic Wall

Lymph Drainage of Thoracic Wall:

All of the lymphatic drainage of the thorax is directed toward the bronchomediastinal trunks, thoracic duct, and descending intercostal lymphatic trunks, but the actual lymphatic trunks themselves are highly variable.

The thoracic duct extends from the abdomen to the neck, where it ends in one of the large veins

• It begins as either a plexus or a dilatation called the cisterna chyli,
• passes through or near the aortic opening of the diaphragm
• ascends in the posterior mediastinum between the aorta and the azygos vein.
• Next it crosses obliquely to the left, posterior to and then along the left side of the esophagus.
• Finally it passes posteiror to the left subclavian artery, enters the neck (where it forms an arch above the level of the clavicle),
• ends in the left internal jugular vein
• The thoracic duct receives the left subclavian and jugular trunks and often the left bronchomediastinal trunk.

CLINICAL NOTE: Most of the lymph in the body reaches the venous system by way of the thoracic duct, but anastomoses are so extensive that no serious effects result if the thoracic duct is ligated.

On the R  side, the bronchomediastinal trunk forms various combinations with the subclavian and jugular trunks.

all three unite to form a right lymphatic duct, which then empties directly into the junction of the internal jugular and subclavian veins.= R angulus venosus

Flow of Thoracic Lymph Drainage, starting from abdomen

Breast

General Info:
Location = 2-6th ribs, parasternal line –> midaxillary line

• Breast bed = rests in deep pectoral fascia (2/3), other (1/3) in fascia over serratus ant m
• b/w the 2, loose CT = retromammary space
• held to skin w/ retinacula cutis via suspensory lig (of Cooper) –> support tubules of glands
• has nipple surrounded by pigmented circular area = areola
  • nipple has no fat, hair, sweat glands, only smooth m, in circular layers
• has a tail portion (of Spence), that runs towards the axillary region

Mammary glands:

• in subcut. tissue over the pectoral m.
• are modified sweat glands , no capusle or sheath
• lacitferous ducts have 15-20 lobules – run towards the nipple to open there
• below areola, ducts dilated to form lactiferous sinus, where milk collects
  
• enlarge in pregnancy
• Areola –> have sebaceous glands that inc in # pregnancy, secrete oil to protect nipple from irritation

Blood supply:

• int thoracic a
  • med mammary br (perforating br)
  • ant IC br
• axillary a
  • lat thoracic a
  • thoraco-acromial a
• Post IC a = 2,3,4 IC spaces

Venous Drainage: axillary v, int thoracic v

Nerves of Breast

• ant & lat cut br of 4-6 IC n
• sensory to skin of breast (SS)
• SNS to a/v of breast & smooth m of skin & nipple

Lymph Drainage

1. Subareolor l.n. nipple, areola, gland lobules
2. Axillary l.n = lat quadrants
   • pectoral l.n.
   • interpectoral l.n
   • deltopectoral l.n
   • supraclavicular l.n.
   • inf deep cervical l.n.
3. Parasternal l.n. = med quadrants –> can go opposite breasts
4. Interpectoral l.n. = upper quadrants –-> supraclavicular l.n.
5. Subdiaphragmatic l.n. = inf phrenic
   • Clavicular –> subclavian lymph trunk –> angulus venosus + jugular lymph trunk
   • bronchiomediastinal trunk –> jugular l.n
   • Jugular lymph trunk –> (L) thoracic duct, R lymph duct

Histology: The histology of the mammary gland.

Embryology: The formation and differentiation of the extraembryonic mesoderm.

• Develops from epiblast (yolk sac cells) and consists of loosely arranged cells – new cell population forms b/w inner and outer surface of cavity
• layer fills space b/w exocoelemic membrane & cytotrophoblast
• Large spaces develop in extraembryonic mesoderm, and group to form extraembryonic coelem
• Extraembryonic coelem splits mesoderm into somatic & visceral mesoderm
  • Somatic mesoderm lines trophoblast, forms connecting stalk, and covers amnion
  • Visceral mesoderm covers yolk sac
• Syncytiotrophoblast & cytotrophoblast & somatic mesoderm together forms chorion
• Embryonic coelem = chorionic cavity – surrounds the primitive yolk sac and amniotic cavity, except where the germ disc is connected to the trophoblast/embryoblast by connecting stalk

14. The pleura and pericardium. Bone formation. Formation of the blastocyst and the bilaminar germ disc.

14. The pleura and pericardium. Bone formation. Formation of the blastocyst and the bilaminar germ disc.

Flash cards:

Pleura 1

Pleura 2 - reflections

Pericardium 1

Pericardial reflections

Anatomy:  The pleura and pericardium.

Pleura:

• serous membrane covering the Lung
• Double layer:
  • Inner visceral – covers lung itself
  • Outer parietal -covers inner surface of thoracic wall
• B/w 2 layers = Pleural cavity – 4 ml of serous fluid
• Function:
  • lubricates the 2 pleural surfaces
  • allows layers of pleura to slide smoothly over each over during respiration
  • surface tension allows lung surface to stay touching thoracic wall
  • Creates a seal b/w 2 pleural surfaces
• The two layers combine around the root of of the lung – so the root of lung has no pleural coverage, the layers combine to form the pulmonary ligament, which runs inf and attaches the root of the lung to the diaphragm
  
• CLINICAL NOTE: When parietal pleura is punctured, lungs collapse due to air rushing (air pressure higher outside than in) = pneumothorax

Pleural surfaces and recesses

Parietal Pleura – senses PAIN, lines inner surface of thoracic wall
4 parts:

1. Cupula pleura (aka cervical pleura) – part of pleura which project above clavicle
   • located w/in scalenus tent
   • strengthened by a layer of endothoracic fascia call the suprapleural membrane = Sibson’s fascia
2. Diaphragmatic pleura – faces domes of diaphragm inf
   • , also separated from diaphragm via endothoracic fascia,
   • only attached to lateral sides of diaphragm
   • as central tendon of diaphragm attaches to pericardium
3. Sternocostal pleura – attaches to rib and sternum
   • separated from ribs via a part of endothoracic facsia called phrenicopleural fascia
4. Mediastinal pleura – faces vert column and midline space b/w two areas of pleura = mediastinum

3 Pleural reflections: Lines where the surfaces of parietal pleura meet each other

• Sternal line = costal –> mediastinal (ant)
• Costal line = costal –> diaphragmatic (inf)
• Vertebral line = costal –> mediastinal (post)

* first 2 have a sharp,defined border, the last is a gradual rounded border

Nerve supply:

• IC n (sternocostal pleura, and peripheral part of diaphragmatic pleura)
• Phrenic n (central diaphragmatic pleura, and mediastinal pleura)

Blood supply = Int thoracic a, post IC, sup phrenic a, sup IC a

Visceral Pleura – sensitive to STRETCH, lines lung ext and dips into all fissures
Nerve supply = contains vasomotor fibers and sensory ending of CN X for respiratory reflexes

Blood Supply = bronchiol a, pulmonary v

Surface Projection:

1. Lat –  lat wall thorax = lat wall of pleura
2. Sup = Cupula Pleura= dome of pleura,
   • projects into neck
   • above neck of 1st rib
   • 2 cm above clavicle @ med end
   • middle 1/3 clavicle b/w midclavicular line and midline
3. Med border:
   • R – R sternoclavicular joint –> desc to lower border of R 6th rib
   • L – goes toward midline from apex, but never reaches it, follows the lung and desc down to 4th rib, runs a bit laterally and then comes back towards midline @ 6th rib, to form the pleural cardiac notch
4. Inf border
   • @ parasternal line – inf border crosses border of 6th/7th rib
   • @ midclavicular line – inf border crosses 8th rib
   • @ mid axillary line – 10th rib
   • @ paravertebral line – T12, 11th rib

Surface Projection of Pleura

Pleural recesses:
If you notice, the surface projection of pleura is larger than the surface projection of the lung itself.

In between parietal pleura, are a series of recesses:

1. Costo-mediastinal recesses – vertical in direction, costal & mediastinal pleura meet
2. Phrenico-mediastinal recess – ant-post direction, b/w mediastinal & diaphragmatic pleura
3. Costo-diaphragmatic recess – b/w costal & diaphragmatic pleura
   • largest of the 3, horseshoe shaped,
   • accumulates fluid when standing
   • potential space that allow lung to expand into them when inhaling
   • can collect sample of pleural fluid from here
   • deepest point of sinus is @ mid-ax line where space b/w lung and pleura = 12 cm, or 4 fingers

Pleural Recesses

Pericardium.
strong fibrous layer, double walled sac w/ heart w/in
originates from intraembryonic somato and splanchno pleura

Layers of Heart itself: (sup –> deep)

1. Fibrous pericardium –
   • bound to central tendon of diaphragm for deep inspiration,heart follows diaphragm, so heart is more vertical,
   • in deep expiration, heart rises due to upward movement of diaphram – heart is more horizontal
2. Serous pericardium
   • Has a parietal layer – stong dense reg CT, prevent heart from over dilating
   • Visceral layer – simple squamous epithelium (mesothelium), that lines the heart itself aka Epicardium
   • B/w 2 layers = Pericardial cavity
3. Subepicardial CT
4. Myocardium – muscular wall – striated cardiac m
5. Subendocardial CT
6. Endocardium – simple squamous epithelium (endothelium), same epith as blood vessels

Layers of Pericardium

Pericardium moves along w. movements of structures around it b/c:

• fused w/ tunica adventia of great vessesl entering/leaving heart
• attached to post surface of sternum by sternopericardial ligaments
• fused w. central tendon of diaphragm

Blood supply = mostly from pericardiophrenic a (int thoracic a) musculophrenic a (int thoracic a), bronchiol, esophageal, sup phrenic a (thoracic aorta), coronary arteries

Innervation = phrenic n (C3-C5), vagus n (CN X), SNS trunk

Reflections of pericardium: where 2 layers of pericardium meet each other

1. @ arterial end – Transverse sinus
   • where pul a and aorta leave heart,
     
   • when doing surgery on aorta or pulmonary a, can stop circulation to this area by making a stitch through this sinus,
   • reach by reaching under pulmonary trunk and ant to SVC
2. @ venous end – Oblique sinus =
   
   • where SVC,IVC pulmonary v enter heart,
     
   • reach via inserting finger under apex of heart and pushing up and right towards root of R lung

Development of Sinuses:

• Form during embryonic life due to folding of embryonic heart tube
• As heart tube folds, venous end moves posterior and up, so venous end then is up by arterial end, separated by transverse sinus
• As veins of heart grow and expand, oblique sinus is formed, a recess, a blind sac behind post side of the heart,

Development of pericardium

Histology: Bone formation.

Embryology: Formation of the blastocyst and the bilaminar germ disc.

Blastocyst

Image via Wikipedia

• fluid is secreted within the morula (16 cell) = blastocyst cavity
• now called blastocyst, and has 2 distinct cell layers
  
• inner cell mass = embryoblast –> is the future embryo
• outer cell mass = trophoblast –> will form the placenta

Bilaminar Germ Disk

Bilaminar Disc Formation:

• In the 8th day, the blastocyst has the inner cell mass & outer cell mass
• Each cell mass  differentiated into 2 different cell layers
• Trophoblast = outer cell mass – splits into:
  • Cytotrophoblast – inner layer of mononucleated cells – distinct cell barriers
  • Syncytiotrophoblast – outer layer of mutlinucleated cells – no  obvious cell boundaries
  • cells are probably created in cytotrophoblast, and then migrate into syncytiotrophoblast
• Embryoblast = inner cell mass – splits into:
  • Epiblast – layer of high columnar cells, next to amniotic cavity
  • Hypoblast – layer of small cuboidal cells, next to blastocyst cavity
  • small cavity forms in epiblast – is amniotic cavity , epiblast cells next to the cytotrophoblast = amnioblasts
  • Cells at periphery of hypoblast migrate over inner surface of cytotrophoblast – forming thin layer extraembryonic endoderm = Heuser’s membrane
  • Blastocyst cavity = is then called primitive yolk sac
• Uterus endometrium has interstitial edema (increased interstitial fluid b/w cells), and increased # of a/v