Download ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
DISSECTION 3
TOPIC 3-A: MEDIASTINUM
 Mediastinum: The region in the thorax located between the 2 pleural sacs
 Boundaries of the Mediastinum:
o Superior: Thoracic inlet (T2)
o Anterior: Sternum
o Inferior: Diaphragm
o Posterior: Vertebral column
o Lateral: Medistinal pleura
 A horizontal plane that transects the T4-5 vertebra posteriorly and the manubriosternal
angle anteriorly divides the mediastinum into superior and inferior regions; this plane is also
at the level of the carina (tracheal bifurcation)
 The inferior mediastinum is divided into 3 regions: middle, anterior, and posterior
Contents of the Superior Mediastinum
 Digestive Layer: The esophagus
 Respiratory Layer: The trachea (doesn’t descend below the superior level because it
bifurcates at the dividing line)
 Arterial Layer: Aortic arch and its branches:
o Brachiocephalic artery
o Left common carotid artery
o Left subclavian artery
 Venous layer: the superior vena cava and its tributaries, the right and left brachiocephalic
veins (which are formed by the union of the internal jugular and subclavian veins)
 Glandular layer: The thymus (positioned over the trachea)
 Nerves:
o Left vagus nerve: descends into the superior mediastinum, passing anterior to the aortic
arch; one branch becomes the left laryngeal nerve; the rest continues inferior to the
anterior surface of the esophagus
o Left recurrent laryngeal nerve: passes under aortic arch, inferior to ligamentum
arteriosum and continually inferiorly until it reaches the anterior surface of the
esophagus
o Right vagus nerve: descends into the superior mediastinum after giving off a branch to
the right recurrent laryngeal nerve (which never enters the superior mediastinum); it
continues inferiorly to reach the posterior surface of the esophagus
Contents of the Inferior Mediastinum
Anterior Mediastinum
 Region between pericardium and sternum
 Contains fat, retrosternal lymph nodes, and branches of the interna thoracic/mammary
artery
Middle Mediastinum
 Contains the heart (in pericardial sac)
Posterior Mediastinum
 Descending aorta
 Thoracic duct
1
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs





Azygous vein: Vein on Right vertebral column; drains the right posterior intercostal veins;
also provides a “backup” route to the superior vena cava in case of a block
Hemiazygous vein: Vein on Left vertebral column; drains the left posterior intercostal veins
Esophagus
Vagus nerves (continuing down from the superior mediastinum)
Sympathetic trunks: sympathetic division of nervous system; runs from skull to coccyx, and
allows nerves to enter spinal cord at a particular level (despite their origin)
TOPIC 3-B: DEVELOPMENT OF THE CELOMIC SACS & MESENTERIES (Lecture)
Definitions
 Serous Membranes: Epithelium with CT base; produce some serous fluids to facilitate the
frictionless movement (“slippage”) of the organs against the body walls
 Parietal Membranes: “Coat”/line the inner surface of the body wall (i.e. chest wall);
“parietal” means body wall. For example: parietal pleura = sac for lungs (there are 2)
 Visceral Membrane: Cover the surface of organs directly. For example: visceral pleura
around the lungs.
 Cavities: The space between visceral & parietal membranes. For example: pleural cavity is a
miniscule space between the visceral & parietal pleura that provides “slippage”
 Four coelomic sacs in the adult: 2 pleural sacs, a pericardial sac, and the peritoneal sac that
surrounds the abdominal organs
 Serous membranes of the heart (the pericardial membranes):
o Parietal pericardium
o Visceral Pericardium
o Pericardial cavity with serous fluid
 Peritoneal membranes are associated with the abdominal cavity (more on these later)
Development of the Intraembryonic Coelom
 During neurulation, the folding of the embryo into a
cylinder/tube causes the lateral plate mesoderm,
which was growing alongside the neural tube to fold
and become hollow
o Extraembryonic mesoderm still surrounds the
embryo
o As the folding continues, this leads to formation of
the intraembryonic coelom, surrounded by
lateral mesoderm
o Two layers of lateral plate mesoderm result from
the folding:
 Splanchnic mesoderm: associated with the
roof of the yolk sac (eventually becomes the
circulatory system & gut wall)
 Somatic mesoderm: layer associated with the ectoderm & presumptive body wall
(~the filling of the embryo) (eventually becomes the body wall)
 Body cavities are derived from the intraembryonic coelom, which forms from a
combination of the lateral plate mesoderm and part of the cardiogenic mass
2
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Bending of embryo during neurulation plays a role in forming the gut tube and the heart,
along with the intraembryonic coelom
o Neural tube grows so much at cranial end that it pushes the cardiogenic mass beneath the
neural plate  cardiogenic mass takes a place ventral to
the foregut
o Embryo grows into the amniotic cavity ; the roof of the
yolk sac (endoderm) is incorporated into the embryo as
the gut tube
 Double layers of mesoderm are called mesenteries; vessels
& nerves passing to & from the gut in the posterior body wall
travel between the mesentery layers
o Dorsal mesentery: between posterior body wall & gut
o Ventral mesentery: between gut and the anterior body
wall (disappears over time, so the right & left coelomic
cavities in the abdominal region merge to form one
continuous space)
Development of the Heart & Other Organs
 The cardiogenic mass begins anterior to the oral plate; “differential development” leads to its
re-positioning anterior to the gut tube
 Cardiogenic mass = heart + additional tissue anterior to the esophagus
 A portion of the cardiogenic mass (located between the intraembryonic coelom on either side
of the gut tube) cavitates and forms a connection between the IE coelomic tubes
 The formation of an inverted-U-shaped coelomic tube is the beginning of the formation of the
pericardial, pleural & peritoneal cavities
 The mass of the future heart itself is located between the “pericardial” portion of the coelom
& the gut tube
Development of the Pericardium
 The portion of the cardiogenic mass that cavitated (and united the 2 coelomic tubes) will be
“pinched off” by the pleuropericardial folds
 Heart grows into the pericardial portion of the coelom like a fist pushing into a balloon
o Inner portion of the sac, directly touching the heart = visceral pericardium or
epicardium
o Outer portion of the sac, the outer layer of the pericardial sac = parietal pericardium
o Pericardial cavity: space between the pericardia, which contains a small amount of fluid
Development of the Pleura
 Lungs develop as outgrowths of the foregut
o Single bud grows out; then bifurcates into right & left lung buds
 Lung buds grow laterally & invaginate the coelomic tubes in the region where the pericardial
sac was pinched off
o Portion of coelom in direct contact with lung bud = visceral pleura
o Portion of coelom in contact with the body wall = parietal pleura
 Pleuropericardial folds separate the pleural sacs from the pericardial sacs
 Pleuroperitoneal folds separate the pleural sacs from the more caudal ends of the coelomic
tubes (which eventually become the peritoneal cavity)
o Located where the diaphragm will develop; contribute to its formation
3
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Elements contributing to the formation of the diaphragm:
o Pleuroperitoneal folds
o Body wall tissue
o Some tissues associated with the esophagus
o Septum transversum, part of the cardiogenic mass (this explains why the phrenic nerve
comes from C3, 4 & 5 spinal nerves; the diaphragm is partially derived from tissues that
were “pulled down” from the cranial end of the embryo)
Formation of Peritoneal Sac (more on this later)
 Peritoneal cavity begins as the paired, caudal portions of coelomic tubes (formed by the
lateral plate mesoderm)
o Initially suspended along the whole length by dorsal & ventral mesenteries
o Mesenteries carry vessles & nerves to & from the organs in the abdomen; functional
mesenteries persist, non-functional mesenteries degenerate
o Ventral mesentery of foregut persists (liver develops there)
o Ventral mesentery of midgut & hindgut degenerate (tubes become continuous across the
midline & form the single peritoneal cavity)
TOPIC 3-C: HEART DEVELOPMENT (Lecture)
Development of the Heart
 The heart begins as the cardiogenic mass – mesoderm that starts out cranial to the oral
plate, but during neurulation & differential development, moves anterior to the gut tube
 Cardiogenic mass cavitates to form two single tubes that fuse to form a single heart tube,
surrounded by the developing pericardial cavity
Fetal Blood Circulation
 Oxygenated blood flows from placenta into the embryo via the umbilical vein
 Oxygenated blood flows from umbilical vein, through heart (sinus venosus, atrium, ventricle,
bulbus cordis, and aortic arches) and out into the body
 Deoxygenated blood from the body return and flows back out in the placenta where it
belongs
Growth & Bending of the Heart Tube
 Names for the developing tube reflect
their fate in the adult structure:
o Conus/truncus becomes the aorta
&
pulmonary artery
o Primitive ventricle becomes the
ventricles; primitive atrium
becomes the atria (but note that we
start out with only one!)
o Sinus venosus will form part of the
future atria (begins at the caudal
end
of the tube)
 Blood flow within the tube:
o Sinus venosus, primitive atrium
(passes through atrioventricular valve), primitive ventricle, truncus, out
4
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Two tubes of cardiogenic mass develop next to another, and are brought together as the
embryo folds in on itself on the sides (to form a tube)
 Looking at it from the front, the tube has two central “bulges,” plus two “vessels” extending
off each end (cranial & caudal)  see below for pictures
Growth & bending of the Heart Tube

The structures of the heart tube (atrium, bulbus cordis, and ventricle) grow rapidly in both
diameter and length
 The pericardial cavity doesn’t grow as rapidly, so the tube is forced to bend; it always bends
to the right
 Between the bulbus cordis & ventricle, and between ventricle & atrium, the tube doesn’t
grow as fast, so these regions get “pinched”
 Sinus venosus an atrium move both posteriorly & cranially
 Bulbus cordis grows to become large enough to be subdivided into several structures:
o The future right ventricle
o An outflow tract of the conus cordis and truncus arteriosus
 Bulboventricular sulcus1 separates bulbus cordis (right) and left ventricles; aligns with the
interventricular sulcus
 The once most caudal portion (the sinus venosus/atrium) is now posterior to the most
cranial end
 Despite bending, heart is still a simple tube, with blood flowing in through the sinus venosus,
common atrium (now posterior), through an atrioventricular canal to the left ventricle,
through an interventricular canal to the right ventricle, then out through the conus & truncus
Septation of the Atrioventricular Canal by the Endocardial Cushions
 Technically, the ventricle is still a single structure
 The common atrium is connected to the left ventricle by the H-shaped atrioventricular
canal (a.k.a the common canal)
o It’s centered above the incomplete but developing interventricular septum
o H shape is due to the presence of two growing superior and inferior endocardial
cushions (which will eventually grow together to subdivide the canals into the left and
right AV valves)
o This forms the tricuspid and mitral valves
Septation of the Common Atrium
 Since the oxygenated blood from the placenta enters the right atrium and must be delivered
immediately to the systemic circuit, septation has to occur in a way that will allow this
connection to be preserved
1
5
A sulcus is a fissure or depression in an organ
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Growth of the septum primum is the first event in atrial septation
o A crescent-shaped disc develops from the roof of the atrium and grows downward,
towards the endocardial cushions
o A hole in the septum primum called the ostium primum, is found on the inferior margin
of the atria as the septum primum closes
o Before blood flow is completely obstructed between the two atria, fenestrations develop
in the septum primum and enlarge to form the ostium secundum on the superior margin
 Growth of the septum secundum occurs as the ostium secundum is opening (and the ostium
primum is closing)
o Septum secundum also grows from the roof of the atrium, but in a perpendicular angle to
the angle of the growth of the septum primum
o The septum secundum is to the right of the septum primum, and is a much thicker/rigid
structure
o At the lower posterior edge (“opposite” the ostium secundum in the septum primum),
there is a persistent hole in the septum secundum, called the foramen ovale
 Separation of the atria after formation of septum secundum is physical but NOT FUNCTIONAL
in the embryo
o Atrial pressure in the right atrium is sufficient to push oxygenated blood (from Inferior
Vena Cava/umbilicus) through the ostium secundum and the foramen ovale to reach the
left atrium and continue on to the systemic circuits
o Blood is not allowed to flow from left to right, because any pressure from the left atrium
would push the delicate septum primum up against the septum secundum; because the
forman ovale and the ostium secundum don’t directly communicate, this shuts off the
passage of blood
o After birth, when normal circulation begins and the fetus takes its first breaths, this is
what happens (the pressure differential shifts to have higher pressures in the left atrium),
and the foramen ovale closes, closing the shunt and leading to the vestigial fossa ovalis
 ASD (Atrial Septal Defect) is a congenital heart defect resulting from several mechanisms that
lead to some oxygenated blood “sneaking through” into the left atrium
Partitioning of the Primitive Ventricles
 Occurs mostly due to the growth of the interventricular septum; a muscular portion of
mesenchyme grows up towards the inferior endocardial cushion
 Four tissue elements make up the interventricular septum:
o Right truncoconal ridges
o Left truncoconal ridges
o Muscular interventricular septum
o Portion of inferior endocardial cushion
 Complete partitioning occurs when the muscular septum meets the endocardial cushions (the
portion that formed the AV valves) and the partitioning of the truncus arteriosus occurs (next
step)
Dividing the Outflow Tract
 Blood flows out the ventricles through the conus cordis and the truncus arteriosus (TA)
 Partitioning of the TA will complete the septation of the ventricles as well (as soon as the
membranous portion of the muscular septum forms)
6
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Formation of right and left truncoconal ridges divides the common outflow tract (truncus
arteriosus) into the pulmonary trunk and aorta
o The ridges are septa (derived from neural crest cells) that grow on opposite sides of the
TA and fuse in the middle
o The septa form a spiral, which ensures that the pulmonary trunk leaves from the right
ventricle, and the aorta from the left
o Inferior portion of spiral septum meets the muscular interventricular septum
 Complete partitioning of the outflow tracts & ventricles involves the growth of 3 structures:
o Conotruncal ridges
o Endocardial cushions
o Muscular intraventricular septum (IVS)
 The converge of the three structures listed occurs at the top of the IVS and forms the
membranous portion; due to the multiple structures involved, this is a common site for
congenital defects
Fetal Circulation
 Blood flow in the fetus is not the same as in the adult; there are 5 structures that are
functional only in fetal circulation:
o Umbilical vein: carries blood from placenta to liver
o Ductus venosus: allows most of the blood returning to fetus in umbilical vein to bypass
the liver and enter the inferior vena cava
o Foramen ovale: Shunts blood from right atrium to left atrium
o Ductus arteriosus: connects the left pulmonary artery and aorta, shunting most of the
blood from the artery to the aorta (right to left)
o Umbilical arteries: carry blood from internal iliac arteries to the placenta
 Fetal circulation allows oxygenated blood (from placenta) to mix with deoxygenated blood
(from fetal tissues), but since fetal hemoglobin can carry more oxygen and exists at higher
levels than hemoglobin in adult tissues, the amount of O2 present in the mixed blood is
generally sufficient
 Fetal circulation ensures that regions with the highest need for oxygen & nutrients (head,
neck, heart, upper limbs), get the “best” blood
 Major circulation: Circuit of blood coming from the placenta & going to the body
o Oxygenated blood from umbilical vein is shunted through the liver before reaching the
heart via the inferior vena cava (IVC); here it mixes with deoxygenated blood from the
fetal body
o 70% of the blood entering the right atrium is directed towards the foramen ovale
(directly oxygen-rich blood to systemic circuit, where the 1st branches of the aorta supply
the head & neck)
o Deoxygenated blood from the head & neck returns via the Superior Vena Cava and is
directed to the minor circuit
 Minor Circuit: The pulmonary circuit
o 30% of oxygenated blood entering right atrium from IVC mixes with the deoxygenated
blood from SVC (a valve-like structure “shunts” the two inflows)
o SVC blood tends to be driven to the right ventricle (due to fluid dynamics) and flows
through pulmonary arteries to feed the lungs
7
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
o Lungs are non-functioning and capillary beds are collapsed during fetal life; this creates
high resistance for blood flow, so most of the blood to the lungs is actually shunted to the
aorta via the ductus arteriosus (connects left pulmonary artery to the aorta, but enters
distal to the aorta arch, so that this deoxygenated blood doesn’t go back to the head)
Changes in Circulation at Birth
 Foramen ovale closes when the pressure gradient in the atria reverses at birth
o Events inducing closure: loss of placental blood & opening of pulmonary capillary bed
o Clamping of umbilical cord stimulates baby to take its first breath; this opens the lungs,
decreases the resistance in the lungs, and allows more blood to pass through the lung
capillary beds and return via the pulmonary veins to the left atrium
o Increase in pressure in the left atrium reverses the pressure gradient between the atria;
this pushes the septum primum against the foramen ovale; growth of fibrous tissue will
close it permanently and it will be called the fossa ovalis
 The ductus arteriosus closes
o Ductus arteriosus remains open during fetal life due to circulating prostaglandins and low
oxygen partial pressure
o Lung function increases the oxygen content of the blood; prostaglandins fall; both events
stimulate the smooth muscle of the ductus arteriosus to contract and close it
 Closure of the ductus venosus and umbilical vein
o Umbilical vein & ductus venosus are both kept patent by blood flow & circulating
prostaglandins
o Clamping the cord eliminates the blood flow through the umbilical vein & ductus venosus;
lowered prostaglandins leads to contraction of the smooth muscle in the vein walls (and
closure of the veins
o These structures will be converted into the ligamentum venosum and ligamentum teres,
respectively
TOPIC 3-D: HEART (Lecture)
Surface Projections of the Heart
 Superior Margin: Left 2nd intercostal space to Right 3rd costal cartilage
 Right Margin: Right 3rd intercostal space to right 6th intercostal space 0.5” to the right of the
sternum
 Inferior Margin: Right 6th intercostal space to Left 5th intercostal space 3.5” to the left of the
sternum
 Left Margin: Left 5th intercostal space to 2nd left intercostal space, 3.5” to the left of the
sternum
 Right ventricle forms the anterior surface of the heart that contacts the sternum
 Left atrium forms the posterior surface
 Left ventricle forms the diaphragmatic surface of the heart
Surface Anatomy of the Heart: Heart Sounds
 Aortic valve (“dub”) is best heard over 2nd intercostal space, to the Right of the sternum
 Pulmonic valve (“dub”) is best heard over 2nd intercostal space to the Left of the sternum
 Tricuspid valve (“lub”) is best heard at the level of the 5th costal cartilage on the Left
 Mitral valve (“lub”) is best heard over the apex of the heart (approx. the 5th costal space, on
the midline between the sternum & the axilla)
8
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Pericardium
 The coelomic sacs around the lungs (pleural sacs) and the heart (pericardial sacs) come
from the lateral plate mesoderm and cardiogenic mass mesoderm, respectively
 Parietal Pericardium: A dense CT sac; a.k.a fibrous pericardium; it attaches the heart to
the sternum & diaphragm, and is tough
 Visceral Pericardium: A thin layer of CT that directly covers the heart & its vessels
 A thin layer of fluid is expected to be found in the region between the visceral & parietal
pericardium; this provides lubrication between the layers when the heart pumps
 Excess fluid in the pericardium leads to cardiac tamponade (strangulation of the heart) and
can be due to:
o Inflammation (pericarditis)
o Bleeding from rupture of heart wall or coronary vessel
 Pericardiocentesis is the removal of excess fluid from the pericardial sac via a needle
o Insert needle between xiphoid process & left costal margin, angled superiorly &
posteriorly toward the Left shoulder
o Push the needle through the chest wall, penetrate the central tendon of the pericardial sac
o ECG leads are used to make sure the needle doesn’t enter the myocardium
 Pericardial Sinuses
o Form where parietal & visceral pericardium reflect (“dead-end”) around major inflow &
outflow vessels
o Oblique Sinus forms posterior to the heart, where pericardium reflects off the inflow
vessels (veins)
o Transverse Sinus forms to separate the inflow & outflow vessels & can be used in
surgery to clamp aorta & pulmonary trunk without cutting into the pericardium
Phrenic Nerve
 Phrenic Nerves arise from cervical spinal cord levels C3-C52; enter the superior
mediastinum between the subclavian artery and brachiocephalic veins and lie between the
mediastinal pleura and the fibrous pericardium
o Right phrenic nerve: found to the right of the right brachiocephalic vein, superior vena
cava, and right atrium (between SVC & mediastinal pleura)
o Left phrenic nerve: crosses arch of aorta, passes inferiorly along left ventricle & left
atrium
o Both phrenic nerves pass anterior to the root of their respective lung
 Phrenic nerve innervates the diaphragm (somatomotor fibers)
 Phrenic nerve also contains sensory and visceromotor axons
o Forms from spinal nerves (has to have all three)
o Sensory fibers transmit info from the mediastinal pleura, pericardium, and diaphragm
o Since info from these fibers is carried in nerves that also carry info from sensory input
from skin/muscles at base of neck & upper limbs, irritation of the diaphragm can be
referred pain that is experienced as pain at the base of neck or shoulders
Cardiac Skeleton
 Cardiac Skeleton is a CT network (mostly dense CT; some adipose & elastic fibers) that
provides the central support of the heart, especially the major vessels
2
9
“C3, 4 and 5 keep the diaphragm alive”
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Cardiac skeleton is composed of four annulus fibrosi, rings of dense CT that are located at
the openings between the atria and the ventricles (where AV valves attach) and at the base of
the pulmonary trunk & aorta (where the semilunar valves attach)
 There are no cardiac myocytes in the cardiac skeleton
 Two functions of cardiac skeleton
o Attachment site for cardiac myocytes & valves
o Electrical insulation between atria & ventricles to allow them to contract separately
 If AP went straight from atria to ventricles, the ventricles would contract from the top
first, pushing the blood towards the bottom of the chamber
 Conduction system (Bundle of His) must carry the impulse through the fibrous
skeleton, traversing the atrioventricular boundary; it continues on to the apex of the
heart before stimulation contraction (allowing ejection of the blood)
o [Can also be used to secure sutures during surgery]
Valves of the Heart
 Attach to the dense CT skeleton of the heart
 Control the direction of blood flow
 Cusp of the valves are all composed of dense CT that’s continuous with the cardiac skeleton
 All the components of the valve (including muscles, tendons, & valve cusp CT) are covered in
endothelium to prevent clotting, because they are in direct contact with blood
 Atrioventricular Valves are found between an atrium & a ventricle
o Bicuspid: right side (a.k.a mitral valve)
o Tricuspid: left side
o Attached to Chordae Tendineae and Papillary Muscles, both projections of the
myocardium in the ventricle that contract during ventricular systole to pull the valves
shut and prevent back flow
 Semilunar valves are found between a ventricle & an outflow vessel
o Pulmonic Valve: right side, between right ventricle & pulmonary trunk
o Aortic Valve: left side, between left ventricle & aorta
o Don’t have chordae tendinea or papillary muscles
 Pathology: Stenosis (narrowing of the valve)
o E.g. mitral stenosis, which occurs after rheumatic fever
o Inflammation, leading to scarring/fibrosis distorts valve leaflets & shortens the chordae
tendineae
o Altering the range of motion of the valve leaflets causes insufficiency of the valve
Conducting System of the Heart
 Sinoatrial (SA) Node can initiate contraction at a rate of 100 bpm independent of
sympathetic innervation
o SA Node = bundle of automatic cells located at junction of superior vena cava & Right
atrium
o The “Pacemaker” of the heart; it sets the inherent heart rate, but can be modified by
sympathetic or parasympathetic (autonomic) innervation
o Sends fibers to:
 Right Atrium
 Left Atrium
 Atrioventricular (AV) Node
10
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

AV Node delays (momentarily) the conduction of the electrical impulse from the atria to the
ventricles
o Cells located in the interatrial septum (anterior & superior to the opening of the coronary
sinus into the Right atrium)
o Cells are automatic (like SA node) but don’t set the pace of contraction under normal
circumstances
 Atrioventricular Bundle: descends through the membranous interventricular septum (IVS),
then divides into two bundle branches or crura
o Crura descend along the IVS, along either side
o Left bundle branch (left crus) branches multiple times along the wall, entering the Left
ventricle along trabeculae carnae
o Right bundle branch (right crus) reaches the Right ventricle via the Septomarginal
Band, a trabeculum that reaches through the IVS to the trabeculae carnae at the apex of
the Right ventricle
o Each crura ends in Purkinje Fibers, fast conducting cells that stimulate contraction of the
myocytes in the ventricle
Innervation of the Heart
Motor Innervation
 SA & AV nodes are both innervated by both divisions of the Autonomic Nervous System
(ANS), which modify the rate of generation of AP in the nodal cells
o Vagal efferent fibers are parasympathetic preganglionic fibers from the vagus nerve
 They synapse in ganglia in the cardiac plexus or in the walls of the atrai
 Decrease heart rate; constrict coronary arteries
o Sympathetic efferent fibers are postganglionic fibers from the sympathetic trunk
 They come from cervical & upper thoracic ganglia
 Increase heart rate and the contractile strength of each beat (thereby regulating
cardiac output as well)
 Cardiac myocytes do NOT depend on innervation to initiate contraction
o Not an elaborate innervation like in skeletal muscle; no NMJs or direct synapses
o Axons lie in the endomysium, amongst myocytes, and release neurotransmitters when
stimulated
o Heart will continue to beat (at intrinsic rate set by SA node) when innervation is removed
Sensory Innervation
 Sensory afferent information from the heart is NOT part of the ANS, but still travels on
sympathetic & parasympathetic fibers in nerves to reach the CNS
 Vagal afferents carry information related to reflex reactions, BP, Carbon Dioxide & Oxygen
content of the blood; do not carry pain
 Afferents traveling with sympathetic nerves play a role in reflex reactions, but also can relay
pain
o Pain from the heart is perceived as pain in the skin of shoulder & arm, due to referred
pain phenomenon
o Cardiac sensory afferents converge with skin sensory afferents to synapse on the same
dorsal horn cells in the spinal cord (lower cervical/upper thoracic levels)
o Any pain in the heart will be perceived as located in the skin, since that’s what the brain
normally associates with stimulation of those cells
11
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Coronary Circulation
Two major coronary arteries branch from the aorta just above the aortic valve; they supply the
heart tissue with oxygen & nutrients
 Left Coronary Artery arises from the Left side of the aorta; it passes between the pulmonary
trunk & left auricle to reach the coronary sulcus3 (depression that separates the atria from
the heart) where it bifurcates:
o Anterior Interventricular Artery, a.k.a. Left Anterior Descending (LAD): descends
down the interventricular sulcus on the anterior surface of the heart; it supplies the
ventricles & anterior region of muscular IVS. It runs with the Great Cardiac Vein
o Circumflex Artery wraps around the coronary sulcus to pass to the posterior surface of
the heart; it supplies the Left ventricle & Left atrium. It also runs with the Great Cardiac
Vein (a continuation of the same vein that runs with the LAD)
 Right Coronary Artery arises from the Right side of the aorta & lies in the coronary sulcus; it
branches in several places:
o Sinoatrial Nodal Artery: branches superiorly & runs underneath the Right atrium
o Right Marginal Artery: branches and runs down the “lateral” surface (margin) of the
Right ventricle; it runs with the Small Cardiac Vein
o Posterior Interventricular Artery runs down the posterior interventricular sulcus; it
supplies both ventricles and the posterior region of the IVS. It runs with the middle
cardiac vein.
 All the major cardiac veins (there are more beyond those mentioned here) drain into the
coronary sinus, a large vein located in the posterior coronary sulcus that delivers the
deoxygenated blood to the Right atrium
 Other veins (anterior cardiac veins and smallest cardiac veins) empty directly into the
Right atrium via microscopic openings
 Collateral Circulation exists in the heart; connections between the anterior & posterior IV
arteries can widen when there is a gradual obstruction of the vessels to ensure adequate
supply to the myocardium. This can’t occur in a heart attack, though (see below)
Atherosclerosis
 This is a hardening of the arteries due to fatty buildup and/or calcifications in the tunica
intima
 Commonly affects the coronary arteries, whose circulation in the heart is critical due to its
high metabolic needs
 Fat accumulates in the wall of the vessel, and grows to obstruct the lumen of the heart
 Risk factors:
o Age
o Tobacco Use
o High cholesterol diet
o Sedentary lifestyle
o Gender
Sulcus = depression or fissure. In the heart, sulci are landmarks and often places where vessels
run.
3
12
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Myocardial Infarction or “Heart Attack”
 When blockage of a coronary artery (due to atherosclerosis, a clot, etc) occurs too quickly for
collateral circulation to take over, a heart attack, or MI, can occur, and myocytes begin to die
from ischemia (lack of oxygen) leading to Left, Right or bilateral heart failure
 Symptoms include chest pain, referred pain in shoulder, chin, or arm, sweating (due to
activation of the sympathetic NS) or dizziness (brain isn’t getting enough blood)
 When symptoms of an MI are felt, take aspirin immediately to increase blood flow
 Left heart failure:
o Dilation of the ventricle occurs
o Ventricle fails to empty completely (normal ejection fraction) during systole
o Myocardium in Left ventricle hypertrophies
o Left atrial & pulmonary pressures rise, resulting in pulmonary congestion
 Right heart failure
o Dilation & hypertrophy of the ventricle also occurs
o Increased venous pressure results in systemic congestion & edema (especially in ankles,
or in presacral region in bed-ridden patients
 Treatment: Angioplasty
o Balloon-tipped tube is inserted in the blocked coronary artery, & the balloon is inflated
o A stent (~ wire cage) is inserted to hold the expanded vessel open, and left in
permanently (the balloon is removed)
 Treatment: Atherectomy
o The clot itself is removed
o Dangerous because if not all the plaque is removed/if some returns to the circulation, this
can cause a stroke
 Treatment: CABG (Coronary Artery Bypass Grafts)
o Vein from calf (saphenous vein), internal thoracic vein, or radial artery from arm is
removed; these vessels are all found in areas of collateral circulation
o The vessel is grafted onto the heart to bypass the blocked artery
o
TOPIC 3-E: CARDIOVASCULAR I: BLOOD VESSELS
Generic Histology of the Blood Vessels
Tunica Intima
 Layer of endothelium that lines the blood vessel lumen, plus a thin layer of loose CT
 In some vessels (arteries) there is an internal elastic membrane separating the tunica
intima from the tunica media
Tunica Media
 The middle layer consists of circularly arranged smooth muscle fibers
 In some vessels there are elastic laminae interspersed among the layers of smooth muscle
 Elastic laminae are elastic sheets (overlapping like shingles on a roof) that are secreted by
the smooth muscle cells; they are usually found in the elastic arteries
Tunica Adventitia/Tunica Externa
 Outer layer of loose CT surrounding the blood vessel
 Merges with the surrounding CT, so it doesn’t have a distinct boundary
13
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Contains vasa vasorum (blood vessels that supply the outer layers of the tunica media) and
autonomic nerves
Arteries
 To distinguish from veins: arteries have an internal elastic membrane between the tunica
intima & media
 In arteries, the tunica media is always the thickest tunic; depending on the size/functional of
the vessel, it may also contain some collagen III & elastic laminae
 Two types of arteries exist: elastic & muscular
Elastic Arteries
 The largest arteries, closest to the heart:
o Aorta
o Pulmonary trunk (off of Right ventricle) & pulmonary arteries (L & R)
o Brachiocephalic trunk
o Common Carotid
o Subclavian
o Common Iliac
 Distinguishing characteristic of elastic arteries is the presence of elastic membranes in
the tunica media
 During systole, the elastic membranes stretch to accommodate the large volume of blood
leave the ventricles (this protects the smaller vessels downstream)
 During diastole, the elastic membranes recoil to keep pressure & flow in the downstream
vessels relatively constant (this recoil pressure creates what we call diastolic pressure)
Muscular Arteries
 Most of the named arteries are muscular
 Compared with elastic arteries (who respond to pressure), muscular arteries are much better
able to control their lumen diameter & blood flow rates
 The contraction of the smooth muscle in tunica media is regulated by innervation
 Muscular arteries can be distinguished based on the presence of an external elastic
membrane between the tunica media & tunica adventitia
Arterioles
 Arterioles are the smallest arteries; they are distinguished from arteries based on the # of
smooth muscle layers in the tunica media:
o Arterioles have 1-4 layers of smooth muscle
o Arteries have 5+ layers of smooth muscle
 ± Internal elastic lamina; usually don’t have an external elastic lamina
 Arterioles are the entry portals to capillary beds
o Constriction of precapillary sphincters located just before the initial segment of the
capillaries controls whether or not blood enters, and how much
o Normally, precapillary sphincters are relaxed; when blood needs to be diverted to
another more active tissue, sphincters in certain beds will constrict to increase the blood
flow to the necessary area
Arterial Disease
Hypertension
 Total peripheral resistance is one of the main determinants of systemic BP
14
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Peripheral resistance is partially dependent on the tone (degree of constriction) of the
arterioles, so arteriolar constriction is a significant contributor to hypertension
 Vasoconstriction is regulated by:
o Sympathetic Vasoconstrictor nerve fibers
o Norepinephrine (NE)
o Vasopressin (a.k.a. ADH)
o Angiotensin II
 Vasodilation is regulated by:
o Sympathetic Vasodilator nerve fibers
o Atrial Natriuretic Factor (ANF)
o Epinephrine (vasodilates in the heart, lungs, & liver)
o Vasodilator drugs (i.e. Nitroglycerin)
Atherosclerosis
 When endothelium is damaged, monocytes (macrophage precursors) and LDL Cholesterol
can enter the tunica intima
 Proliferative signals & cytokines lead to growth of the plaque (including any smooth muscle
cells that may have migrated in)
 The plaque can calcify, or the central part can die when cut off from blood supply
 Potential problems that can develop as the result:
o Clot develops on the plaque & obstructs the vessel
o Part of the plaque breaks off (embolizes) and causes obstruction of a vessel at a distant
site
o The plaque weakens the arterial wall, which can form an aneurysm & rupture
Capillaries
General Characteristics:
 Capillaries have a small diameter (7-9µm, roughly the size of an RBC)
 Capillaries have only one layer: endothelium (plus a basement membrane) to maximize
exchange of material between blood & surrounding tissue
 All capillary networks are not the same; they’re adapted to the tissue where they’re found
(i.e. very branched in lungs, kidneys & liver but not so much elsewhere)
Continuous Capillaries
 Found where tight control is necessary (i.e. blood brain barrier)
 All cells are bound by tight junctions (spot desmosomes, etc)
 All material passes via transcytosis (highly regulated)
Fenestrated Capillaries
 Found where freer exchange in desirable (i.e. kidneys, liver, intestinal villi)
 Endothelial cells are still attached by tight junctions, but the cells themselves have
perforations or windows (fenestrae) where the basal & luminal membranes meet, allowing
more rapid exchange between blood & surrounding tissue
 Fenestrae can have diaphragms that can remain closed, or they can open to allow a substance
to pass through (still too small for RBCs to pass through)
Discontinuous Capillaries
 Present where minimal control is necessary, and where it’s necessary for RBCs to pass
through the capillary wall (spleen, liver, bone marrow)
15
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Wall is still one layer of squamous endothelium thick, but there junctional complexes might
be lacking, as might the basement membrane, leading to discontinuities
 In the organs listed prior, the discontinuous capillaries are called sinusoids, and they are
twisted, anastomotic capillaries that slow the blood flow down, allow RBCs to be removed if
necessary, and provide lots of time for macrophages to eat antigens or for nutrients/wastes
to diffuse in/out of tissues
Lymphatic Capillaries
 “Their own class” because they contain lymph, not blood
 Begin blindly in the connective tissue; the capillaries run alongside blood capillaries and pick
up any extracellular fluid that’s leaked out of the blood
 Structurally similar to discontinuous capillaries (allows recovery of ECF)
 Lymphatic capillaries merge into larger lymphatic vessels that run through lymph nodes (site
of removal of antigens) and up to the thoracic and right lymphatic ducts (site of returning
plasma proteins to the blood  main function of lymph)
 Lymphatic vessels contain valves to prevent backflow (structurally similar to venous valves)
Mechanism of Transport Across Endothelial Cells
 Diffusion: only lipid soluble substances, including gases
 Vesicular Transport: includes pinocytosis and transcytosis
 Paracellular Pathway: in continuous & fenestrated capillaries, the tight junctions between
cells can open (especially in the presence of chemicals like histamines) to allow substances to
pass between the cells to the other side
 Fenestrae: semi-regulated passage of substances from one side to the other through the
fenestrae
 Endothelial discontinuities: allow large particles (up to & including cells) to pass through
Venules & Veins
Venules
 Venules are the smallest veins that drain the capillaries; they become venules once their
inner diameter is greater than 10µm (and they run with arterioles)
 The smallest venules are structurally similar to capillaries (endothelium with basement
membrane only) & can participate in exchange
 Like capillaries, venules are susceptible to histamines (become more permeable)
 Venules join together, increasing their diameter as they make their way back to the heart
o 50µm+ diameter: smooth muscle cells & fibroblasts appear
o 200µm+ diameter: all three tunica are present (once there’s lots of CT, exchange stops)
 If it runs with an arteriole, call it a venule. If it runs with an artery, call it a vein.
Veins
 Have a typical structure:
o Tunica intima = endothelium + basement membrane (no internal elastic membrane)
o Tunica media = smooth muscle
o Tunica adventitia (the largest layer) = lots of loose CT
 Veins larger than 2mm have valves
o Valves are in-pockets of the tunica intima that form a semilunar shape
o Valves prevent the backflow of blood; when blood tries to flow away from the heart, the
leaflets of the valve close
o Found mostly in extremities; not found in head, neck or trunk
16
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Since there is low pressure, venous return requires several mechanisms to return blood to
the heart (since there is no “heart” that can pump venous blood back up)
o Valves aid venous return
o Compression of veins when nearby skeletal muscles contract also helps push blood
“upward”
Comparing Veins & Arteries
 When one of each of the vessels run together, the vein has the larger lumen4
 Internal elastic lamina = artery (they are rarely found in veins)
 Tunica media is much thicker in arteries; tunica adventitia is much thicker in veins
 Valve = vein
Arteriovenous Anastomosis (AV Shunts)
 AV Shunts take blood directly from the arterial system to the venous system, bypassing the
capillaries
 The function of an AV shunt is temperature regulation; it’s found on soles of feet, palm of
hand, skin of fingertips/nose/lips, and erectile tissue
 Normally, the AV shunt is contracted (closed) and blood flows through the capillary, allowing
heat to be lost as the blood flows through it
 When the tissue with the shunt gets cold, the AV shunt opens & decreases flow to the
capillaries (since the shunt is the path of least resistance). This minimizes heat lost.
Angiogenesis
 Angiogenesis: the development of a new blood vessel from an existing vessel (occurs in
anoxic or damaged tissue, or in tumors)
 New vessels always start as capillaries developed from venules or capillaries
 There are five steps of angiogenesis:
o Endothelial cells enzymatically dissolve the basal lamina in a small area. Cells begin
to migrate, secreting new basal lamina as they go, and maintaining contact with other
endothelial cells
o Endothelial cells migrate (leaders of the sprout) & align to form a solid sprout.
o Endothelial cells proliferate (trailing cells)
o The sprout hollows
o Sprout fuses with another vessel (venule, capillary, or other sprout) to form an
anastomotic loop
 Anastomoses are common throughout the body; they are the basis of collateral circulation,
which provides several alternate routes for blood flow. The subclavian artery gives rise to the
internal thoracic artery which becomes the superior epigastric vessel; it anastomoses with
the inferior epigastric vessel, which came from the external iliac artery in the groin. This
allows a bypass around the aorta if necessary, to get blood flow past the blockage into the
iliac region.
o
TOPIC 3-F: CARDIOVASCULAR II: HEART(Lecture)
Histology of the Heart Wall
The reverse is true in cadavers, where the fixation process collapsed the veins but the elastic in
the arteries helped them retain more of their shape & luminal diameter
4
17
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Layers of the heart (endocardium, myocardium, epicardium) correspond to the layers of blood
vessels (endothelium/tunica intima, tunica media, tunica externa)
Endocardium
 Layer of endothelium (simple squamous epithelium), plus layer of loose CT
o All surfaces that contact blood, including valves, are covered in endothelium
o Endothelium is continuous with the endothelium of veins & arteries that enter/exit the
heart
o Endothelium provides a tight barrier (tight junctions between the cells)
 Conducting cells (i.e. Purkinje fibers) are found running through the CT
 CT layer connects the endocardium with the myocardium
Myocardium
 Middle layer of the heart; also the thickest
 Made of bundles of cardiac myocytes (muscle cells) that are oriented spirally around the
heart (this allows blood to be squeezed out of the ventricles during contraction)
 Fasicle: myocytes run in groups, but aren’t organized/bundled as in skeletal muscle
 Myocytes are connected by intercalated discs
Epicardium
 Also called the visceral pericardium
 Composed of squamous mesothelium5 with a layer of fat & loose CT
o Underlying layer of CT contains many capillaries & blood vessels; this is necessary
because the heart never stops pumping & has high energy requirements
o Unilocular adipose tissue predominates (especially found coronary sulcus)
 Branches of coronary arteries & cardiac veins that run through the pericardial CT layer are
like the vasa vasorum of the heart
 Visceral pericardium reflects off of the surface of the great vessels to connect with the
parietal pericardium (which also contains mesothelium)
Cardiac Muscle
 Myocardium is composed of cardiac muscle whose primary function is to circulate the blood
 Cardiac Myocytes are individual, mostly mononucleated cells
o Nucleus is centrally located at the poles of the cell, euchromatic, and ~rectangular with
rounded edges
o Some myocytes contain 2 nuclei (when they have replicated DNA but not yet undergone
cytokinesis/cell division)
o Contain large numbers of mitochondria, mostly at the poles of the cells
o Other organelles are also located at the ends, near the nuclei (RER, Golgi, lysosomes) since
the myofilaments take up most of the cytoplasm
o T-Tubules carry the AP to the center of the cell, unlike in skeletal muscle fibers, the Ttubules are found at the Z line of the sarcomere; they are closely in contact with the SR
 The myocyte is shaped like an oil drum, but has branched ends that can contact 3-5 myocytes
on either end; this extensive contact leads to the formation of fascicles
 Due to arrangement of myocytes & their blood supply, they appear to branch
Layer of cells, derived from the embryonic mesoderm, that is found on certain membranes and
secretes a lubricant to allow ~frictionless movement of various membranes (i.e. peri- and
epicardium)
5
18
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Intercalated Discs are dark-staining structures between myocytes at the end of the cell
o The function of the ID is to join adjacent cells, and has 3 components:
o Gap junctions: Establish electrical continuity between the fasicles
 AP can be transmitted between myocytes via the gap junctions
 Found perpendicular to the spot desmosomes (so they experience the least stress)
 Connexons are the pores themselves, made up of 6 connexin protein subunits
 Can connect multiple myocytes in a fascicle
 Adjacent membranes of cells are close enough to allow connexons to communicate
o Spot Desmosomes
 A.k.a macula adherens
 Insertions of intermediate filaments and desmins
 Desmins are muscle-specific intermediate filaments that attach to the edges of
adjacent Z bands to keep myocytes in the same orientation/phase during contraction
 Function: Connect cardiomyocytes & transmit the force of contraction
o Fascia Adherens
 Insertions of actin filaments of the I band into the membrane
 Function: to transmit the force of contraction (why the heart doesn’t need lots of CT)
 Found on same part of membrane, and are intermixed with, spot desmosomes
 Elements of the sarcomere: the same as in skeletal muscle
T-Tubules & SR
 T-tubules = tubular invaginations of the plasmalemma that provide extra surface area to
allow the entry of extracellular Ca2+ during an AP & carry the AP into the deepest layer of the
myocyte to allow synchronous contraction
 T-tubules ound like a series of bracelets around each myofibril at every Z line
 T-tubules are always in contact with the SR as they move through the cell
 SR in cardiomyocytes are extensive; don’t have the same arrangment as in skeletal myocytes
 SR & T-tubule form a diad (single SR cistern is associated with each T tubule)
 Cardiac muscle uses extracellular Ca2+ for contraction; this stimulates Calcium-Induced
Ca2+ Release (CICR) from the SR
Myocytes (3 Types)
 Ventricular myocytes
 Atrial myocytes: smaller than ventricular myocytes because they work against less resistance
 Conduction myocytes are specialized, automatic myocytes
o Nodal cells in the SA & AV nodes
o Bundle of His and Purkinje fibers
Connective Tissue Investment of the Heart
 Cardiac muscle depends on loose CT for its nutrients, because the extensive vasculature runs
through the CT to get to the myocytes
 Though CT is sparse in the heart, the abundant capillaries are sufficient to supply all nearby
cells
 Cardiac Skeleton is dense CT that is the structural pattern for the heart
o Provides attachment points for myocytes
o Provides insertion sites (annuli fibrosi) for valve leaflets
o Insulates atrial cells from ventricular cells to allow separation of contraction of the two
 Interesting fact: there are more cardiac fibroblasts than cardiac myocytes
19
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Secretion of the Heart
 Myocytes make & store vesicles of Atrial Natriuretic Factor (ANF)
 When BP is too high, ANF vesicles are released, and stimulate kidneys to excrete Na+ (water
will follow, lowering BP)
 ANF also causes the vascular smooth muscle (esp. in the blood vessels) to relax & allow
decrease of BP
Heart Disease & Regeneration
 Cardiac stem cells are in place to replace myocytes lost to normal wear & tear; they can’t
replace cells lost en masse to disease processes
 Following an MI, scar tissue forms in place of necrotic myocytes; fibrotic tissue can’t contract,
so other cardiac myocytes must hypertrophy to compensate
 Over time, hypertrophy leads to compromised function, cardiac dilation, and heart failure
 Other ischemic heart disease includes atherosclerosis (in coronary arteries can lead to an MI)
 MI is a huge public health problem (1.2 million every year, 700,000 new ones 500,000
recurrent episodes) – 40% of MI’s are fatal
 Risk factors:
o Age
o Diet
o Obesity
o Excessive alcohol
o Gender
o Smoking
o Sedentary lifestyle
 Treatment of an MI includes
o Thrombolytic therapy (removing the blockage of the artery surgically)
o Angioplasty/bypass surgery or Stent placement
o Heart transplant (in cases of heart therapy)
 Cardiac stem cells show promise
o There are endogenous cardiac stem cells in the myocardium, and mesenchymal stem cells
in the bone marrow, that can contribute to heart regeneration after disease
o Even though these cells are normally present, their usual level of activity is inadequate to
induce regeneration of cells after an MI, so current research is looking into finding ways
to activate & amplify the response of these cells
Familial Hypertrophic Cardiomyopathy
 Disease of the sarcomere; symptoms include:
o Asymmetric thickening of the myocardium
o Heart failure
o Arrythmia
 Histological markers include:
o Defect in myocyte growth (hypertrophy)
o Disorganized myofibrils
o Myocardial scarring & abnormalities of the small coronary arteries
 Often due to a missense mutation in a cardiac myosin Isoform; other less common mutations
are found in thin filament proteins or troponin/tropomysin
TOPIC 3-I: LUNGS (Lecture)
Lung Development
 Lateral plate mesoderm forms that pleural sacs
20
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
o Grow into the medial side of the coelom on each side
o Forms both visceral & parietal pleura
 Endoderm (foregut) forms the lungs; lung buds form from the ventral surface of the gut tube
 Cardiogenic mass (cranial & anterior) in addition to form portions of the heart & pericardial
sac, it forms the part of the diaphragm
 Pleuroperitoneal folds are also involved in forming the diaphragm
Pleural Sacs & Recesses
 Pleural Sacs: Reduce friction during inhalation & exhalation; there is a thin fluid-filled cavity
between the visceral pleura(on the surface of the lung) and parietal pleura lining the
thoracic wall
 Visceral Pleura = mesothelium (simple squamous epithelium lining a body cavity)
o Mesothelioma: Looks like cauliflower stuck to the visceral & parietal pleura due to
tumors of the mesothelial cells. Lung shrinks within the thoracic cavity
 Parietal Pleura lines the rib cage
o Costal Pleura: Lines the inner surface of the rib cage
o Mediastinal Pleura: Lines the midlines organs of the mediastinum
o Diaphragmatic Pleura: Lines the diaphragm
 Pleural Recess: where the lungs don’t completely fill the parietal pleura
o Costodiaphragmatic recess/Costophrenic Angle: clinically more important; costal &
diaphragmatic pleurae reflect back on each other & form the space below the lungs that
can be filled with fluid
o Costomedistinal recess/Cardiophrenic Angle: formed by costal & mediastinal pleurae;
bilateral but larger on the left due to the cardiac notch on the left lung
 Phrenic Nerves
o Descend between the pericardial & pleural sacs
o Originate from Cervical 3, 4 & 5
o This is the only motor innervation of the diaphragm
o Contain: somatomotor, visceromotor, & sensory nerves
o “Weird nerve”: it’s not a splanchnic nerve, despite the fact that it’s so deep (it was
“dragged down” from the head when the cardiogenic mass moved during development
from the cranial end to just anterior to the developing foregut)
o Sympathetic visceromotor fibers in the phrenic nerve go to innervate blood vessels
o Diaphragm is controlled by somatomotor neurons; even though contraction is usually a
reflex action, you can also use an upper motor neuron to control contraction
Lobes & Fissues of the Lung
Lobes
 Upper lobe:
 (Middle lobe): Present only in the right lung
 Lower lobe
Fissures
 Oblique fissure in the Left lung divides it into upper & lower lobes
 Heart forms an indentation in the lungs called the cardiac notch on the left lung; the tonguelike projection below is the lingula
 Oblique/major and Horizontal/minor fissures in the Right lung divide it into Upper,
Middle, and Lower lobes (horizontal fissure is superior to the oblique fissure)
21
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Surface Anatomy of the Lung
 Inferior margins of the pleura: At rib level 8 (midclavicular line), 10 (midaxillary line), and 12
(para vertebral line)
 Inferior margines of the lungs are 2 rib levels up from the pleura: At rib levels 6, 8, & 10
 This means that the costodiaphragmatic recess is found in 8th & 9th intercostal spaces, and
can be accessed with a needle to remove excess fluid. See thoracocentesis, below.
 Pneumothorax: a penetrating wound to the chest wall allows air to come in; the air pressure
causes the lung to collapse
 Pain in the parietal pleura is mediated by intercostal (costal pleura) & phrenic nerves
(mediastinal & diaphragmatic plurae)
 There is no sensory innervation to the visceral pleura
Procedures Relating to the Lung
Thoracocentesis
 When fluid or air accumulates in the chest cavity, you can insert a needle into the chest wall &
draw out the fluid/air
 Fluid accumulation leads to respiratory insufficiency (can be auscultated or visualized on an
X-ray)
 Stick needle in just superior to the inferior rib of the intercostal space; this way you avoid
puncturing the neurovascular bundle, which is found just inferior to the inferior edge of
every rib
 For air removal, the needle is inserted in the 2nd or 3rd intercostal space
 For fluid removal, the needle is inserted in the intercostal space 1-2 spaces below the fluid
level, 5-10cm lateral to the spine
Chest Tubes
 Inserted in nearly every patient undergoing surgery involving the thorax; allows drainage of
accumulating fluid, blood, or air during surgery over a period of time
 Commonly inserted in 5th or 6th intercostal space, at the midaxillary line
 Incision over the 6th rib first; then add a tunnel, puncture the parietal pleura (without hitting
the lung tissue) & insert chest tube
 Tie chest tube in place; also add purse-string suture around the tube to allow the wound to be
closed as the tube is pulled out
Trachea & Bronchi
 Trachea: Begins at neck at inferior margin of the larynx, running anterior to the esophagus
o Arch of the aorta passes anterior to the trachea
o Ends by bifurcating into Right & Left primary bronchi anterior to the T5 vertebral body
o At the carina (bifurcation), the trachea is covered in the cardiopulmonary nerve plexus
(which contains sympathetic, parasympathetic, & sensory fibers)
 The Right primary bronchus is oriented more vertically than the Left, and is more likely to be
the site where an aspirated object gets lodged
Hilus of the Lung
 Bronchus: Thickest structure in the hilus; contains hyaline cartilage in its walls to ensure it
doesn’t collapse. Branches into secondary bronchi very quickly in the right lung
 Pulmonary Artery: The middle thickest vessel
 Pulmonary Veins :The thinnest vessel present in the hilus in a cadaver; usually the most
inferior & anterior vessels
22
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

RALS: Right lung: Pulmonary artery is ANTERIOR to the bronchus. Left lung: Pulmonary
artery is SUPERIOR to the bronchus
 Hilar Lymph Nodes: trap the
 Bronchial Artery/Bronchial Vein: Tiny little vessels (diameter ~1-2mm) that nourish &
support the bronchial tree.
o These are the vessels that supply oxygenated blood to the lung (via bronchial arteries,
which branch off of the aorta) and remove wastes (via bronchial veins).
o Bronchial veins drain to the azygous vein
o You can’t distinguish these in a cadaver; you can say “Bronchial vessel” in an exam
situation.
 Pulmonary Plexus
Bronchopulmonary Segments
 Elaborate branching occurs in the lung
o Trachea splits into primary bronchi; which split into secondary bronchi within a few cm
of entering the hilus of the lung
o Secondary bronchi split into tertiary bronchi (we stop naming them anymore)
o Tertiary bronchus is the basis for dividing the lung into 10 segments
 Each bronchopulmonary segment is supplied by a tertiary bronchus; each is an
independent anatomical & functional unit
 A single bronchopulmonary segment can be surgically removed without damaging any other
segments
Blood Supply
 Bronchial arteries deliver oxygenated blood to the lung; this is to support the function of
the bronchioles
 Pulmonary arteries deliver deoxygenated blood to the alveoli so it can be re-oxygenated.
They always branch in parallel with the bronchi (intersegmental because they pass through
various segments)
 Pulmonary veins carry oxygenated blood back to the Left side of the heart to be pumped
into systemic circulation. They are always are found at the interfaces of each pulmonary
segment (intrasegmental, because they are only found between segments)
Lymphatic Drainage of the Lung
 Lungs have a rich lymphatic network, with deep lymphatic channels that follow the bronchi &
pulmonary vessels to the hilus
 Lymph flows through several nodes before reaching the hilar lymph nodes (found at the
hilus)
 Lymph from the lungs travels superiorly to the trachea; makes it to the supraclavicular
nodes
 Sentinel nodes: Supraclavicular nodes are often the site of lung cancer metastases; when
these nodes are palpable, it signals possible lung disease
TOPIC 3-J: RESPIRATORY SYSTEM (Lecture)
Respiratory System
 Function: exchange carbon dioxide for oxygen
 Conducting portion: cleans, conditions & conducts the air
23
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

24
o Vestibule of the nose, nasal cavities/sinuses, nasal choncha/turbinate, nasopharynx,
oropharynx, laryngopharynx, larynx, trachea, carina (tracheal bifurcation), right & left
primary bronchi, intrapulmonary bronchi (secondary & tertiary), bronchioles, terminal
bronchioles
Respiratory portion: exchange of gases
o Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
Respiratory Epithelium
 Respiratory Epithelium = pseudo-stratified columnar epithelium with cilia & goblet cells,
plus basal, brush, and granule cells
 Has a mucous layer and a serous layer
o Mucous layer prevents dehydration of the epithelium & traps particulates from the air
o Mucous floats on the serous layer; this prevents the viscous mucous from ‘clogging up’
cilia
o Serous layer comes from cells in the lamina propria (seromucous glands)
 Cilia all beat in a coordinated, unilateral way towards the oropharynx; the mucous is pushed
towards the oropharynx, where it can either evaporate or be swallowed
 Basal cells are the stem cells (found on basement membrane) that make all of the cells in the
respiratory epithelium
 Brush cells are columnar cells with microvilli. These are sensory; when stimulated, they
send and AP that starts the coughing response
 Granule cells are endocrine
The Conducting Portion
 The cartilage maintains a patent (open) airway so that air can be exchanged
 Conditions the air by:
o Cleaning it: Mucous traps inhaled particulates, then cilia move the mucous toward the
oropharynx where it’s swallowed
o Warming it: there is heat exchange from the blood in the capillaries & venules in the
lamina propria running near the respiratory epithelium
o Humidifying it: with serous & mucous fluids from glands
Vestibule of the Nose
 Vestibule is continuous with the skin on the fact, so it’s lined with keratinized stratified
squamous epithelium
 Contains vibrissae (large hairs associated with sebaceous glands); the oily secretions & hairs
together trap particles that enter the nose, and encapsulate them so they can be removed
Nasal cavities
 Most of the nasal cavity is lined with respiratory epithelium (except for olfactory portion)
 Conchae/turbinates cause airflow turbulence, which allows air to move around, trap more
antigens/particulates, and contact more mucous to allow these particulates to be eliminated
 Air is warmed when it passes near capillary plexuses in the lamina propria, and moistened by
the serous fluids
Olfactory Epithelium & Plasma Cells
 Bipolar neurons; dendrites contain specialized cilia that contain olfactory receptors
 Odor molecules are sensed by the receptors when they’re bound up in a complex; the
receptor sends an AP that heads back to the brain
 Plasma cells secrete IgA molecules into the fluid on the surface of the olfactory epithelium
Pharynx
 The pharynx is a muscular organ used by both the digestive & respiratory tracts. It’s divided
into 3 regions: nasopharynx, oropharynx, and laryngopharynx
 Nasopharynx: Located directly behind nasal cavity & above the soft palate; it’s the only part
of the pharynx that’s lined with respiratory epithelium
25
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Oropharynx, laryngopharynx, Epiglottis, and vocal folds: All are lined with mucosal
stratified squamous epithelium (withstands the abrasion of food & chewing & swallowing)
 Oropharynx is located behind the oral cavity; it’s shared with the digestive tract (allows
mucous beaten up from lower layers of the conducting system to be swallowed/enter the
digestive system
 The rest of the larynx is lined with respiratory epithelium
Larynx & Trachea
Larynx
 Lined by respiratory epithelium, so air continues to be conditioned
 Hyaline cartilage of the larynx has two functions:
o Maintains an open airway
o Serves as an attachment point for muscles of the vocal folds
 Air passes either through nasal cavity or through mouth to reach the larynx & trachea
 The epiglottis guards the vestibule of the larynx
o Made of elastic cartilage
o Tongue pushes epiglottis over the vestibule when it swallows food; this prevents foreign
objects/food/liquid from entering the airway
o Lined with mucosal stratified squamous epithelium (to withstand abrasion of movement)
 Within the larynx are the vocal folds, which allow us to vocalize & communicate
o Covered with a very thin stratified squamous epithelium covers free edges of vocal folds
o During speech, rapid air flow past vocal folds allows them to vibrate & make sounds
Trachea
 Top layer: respiratory epithelium
 Middle layer: lamina propria, plus seromucous glands and elastic fibers
 Bottom layer: Cartilage & smooth muscle layer
 18 C-shaped cartilaginous rings support the anterior & lateral walls
 Tracheal rings are incomplete near the esophagus, where the tracheal wall also contains
smooth muscle & connective tissue to ‘fill in the holes’
o Smooth muscle found in trachea decrease the diameter of the respiratory passage
Bronchi & Bronchioles
 Trachea bifurcates at the carina (located above the 4th or 5th thoracic vertebra) into Right &
Left primary bronchi; these have similar cartilage arrangements
Bronchi
 Except at very low magnification, primary bronchi can’t be distinguished from the trachea in
histological sections (both have C-shaped cartilage rings)
 Intrapulmonary bronchi: includes both secondary & tertiary bronchioles; both have
irregular plates of cartilage, and a more prominent layer of smooth muscle
 Bronchus diameter can be modified by smooth muscle contraction
 Cartilage is lost gradually as the conducting portion narrows
 Elastin increases as the conducting portion narrows, to keep the airway patent (and replace
the diminishing cartilage)
Bronchioles
 Defined by the fact that they do not have any cartilage associated with them; also don’t
have glands
26
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs

Transition from tall respiratory epithelium to a simple epithelium (a thick epithelium would
restrict airflow in the smaller passageways, and wouldn’t be ideal for gas exchange in the
alveoli)
 There is no cartilage at all in the lamina propria
 Increased smooth muscle layer, plus more elastic fibers
 Have a diameter of ≥1mm; branch to form 5-7 smaller terminal bronchioles
Terminal Bronchiole
 Simple ciliated cuboidal cells
 No goblet cells, seromucous glands, or cartilage
 Contain Clara cells: columnar in appearance with dome-shaped apical surfaces
o Secrete a surfactant-like agent that reduces surface tension to prevent bronchiolar
collapse during expiration
o Also make a secretory protein with an anti-inflammatory & immunomodulatory function
in the lung
o Stem cells for part of the conducting portion
 Contains smooth muscle
o Limited to one or two layers
o Innervated by the autonomic nervous system (i.e. sympathetic causes increase in
diameter of bronchioles by causing muscle to relax)
Respiratory Portion
 Every structure in the respiratory is capable of gas exchange
 Begins with respiratory bronchioles (branches of the terminal bronchioles; respiratory
bronchioles represent the transition because they’re capable of gas exchange)
o Resp. bronchiole branches into 2-4 alveolar ducts
o Several alveoli are found in each Alveolar Sac that opens off the end of an alveolar duct;
also have Clara cells & cilia that continue the function of the terminal bronchiole
o Atria are entrance points to multiple alveoli
 Alveoli
o The wall of the alveolus (alveolar septa) is lined by a simple squamous epithelium that
contains 95% Type I and 5% Type II Alveolar Cells
o Roughly spherical structures
o Where bulk of gas exchange occurs
o Wrapped with a meshwork of capillaries that are visual in scanning EM
o Elastic fibers also form meshworks around alveoli; they enable the alveoli to expand with
inspiration & contract passively during expiration. Crucial to the function of the lung
o Contain pores, which are connections to other alveoli
o Alveolar Septum has portions that are thicker/where no gas exchange occurs; contains:
 Elastic fibers (essential for
 Fibroblasts
recoil)
 Macrophages
 Collagen fibers
 Lymphatic vessel
 Type II cells
 Endothelial & Type I cell nuclei
Gas Exchange
 First occurs in respiratory bronchioles that lead into alveolar ducts
 Alveolar ducts are lined with alveolar sacs & alveoli
Type I Alveolar Cells (95%)
27
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs





Provide a barrier of minimal thickness
Readily permeable to gases
Contain reticular fibers
Form the blood-air barrier
Type I Alveolar Nuclei have flattened nuclei; not always visible because they’re pushed out of
the way to maximize gas exchange
 Elongated nucleus & minimal cytoplasm; the apical & basal membranes nearly touch because
the cell is so flattened
Alveolar Macrophages
 A.k.a. dust cells that crawl along the wall of the alveoli
 Remove smoke, dust, pollen, surfactant
 Resident Macrophages: Many are replaced quickly (removed or swallowed)
 Interstitial Macrophages: Found in the septa between alveoli; can remain in the lung for
years
 Recruited Macrophages: Enter from the blood to fight infection
Type II Alveolar Cells (5%)
 Cuboidal; “bulge” into the lumen of the alveolus
 Secrete surfactant to lower alveolar surface tension during expiration
 Usually found in the corners of the alveoli, so they can secrete onto several walls
simultaneously
 Contains surfactant granules in the cytoplasm
 Microvilli on the cell’s surface maximize surface area
 Stem cells for the respiratory portion; the other stem cell is the bronchioalveolar stem cell
Air-Blood Barrier (passage of oxygen from air to blood; listed in order of structures it crosses)
 First: Surfactant (the surface lining)
 Alveolar epithelium (Type I cell)
 Fused basal lamina (between Type I cell & endothelial cell)
 Last: Endothelium (very thin & flattened)
 [Plasma, then RBC membrane]
Elastic Fibers in the Alveoli
 They are ubiquitous from the trachea to the alveoli & are important for elastic recoil
 Emphysema from long-term smoking breaks down elastic fibers so it takes as much energy to
exhale as inhale (they’ve lost the elastic recoil)
o Airspace distal to the bronchioles are enlarged
o Destruction of elastic fibers & other components in the alveolar wall
o Loss of respiratory portions leads to gaping holes in the lung tissue
Asthma
 Inflammation & prolonged contraction of bronchiolar smooth muscle; this blocks the passage
of air to the respiratory of the lung
 Due to high level of particulates in the air
 Inhalers (corticosteroids & bronchodilators) are treatment to block the immune response
causing the constriction
 Accounts for ¼ of all ER visits in the US each year
Respiratory Distress Syndromes
28
ANATOMY Dissection 3: Serous Sacs, Heart, and Lungs
 In infants with incomplete lung development, 6 weeks or more before term
 Affects about 1% of newborn infants & is the leading cause of death in preterm infants
 Treated with oxygen & surfactant
Lung Cancer
 Squamous cell carcinoma is the principle lung tumor
 Is the leading cause of cancer death in the US among every ethnic group
29