Cardiovascular Anatomy.pptx

Cardiovascular
Heart and Blood Vessels
Dr. Adanwali Hassan Ahmed
Rn-Mw, Medical doctor (MD), Health Officer (HO)
Msc-Gyn/Obest.

Introduction
• People always talk about the heart as the seat of
control of emotions.
• One important reference, however about the heart
is that “without a functioning heart, there is no life”.
 The heart is a muscular organ that is essential for
life because it pumps blood through the body.
• Emotions are a product of brain function, not heart
function but without the heart performing its
functions efficiently, brain cells die within a short
time! In this unit your knowledge of the structures
and the organs in relations to the heart will be
explored.

Objectives
• At the end of this unit, you should be able to
– Describe the location, size and shape of the heart
– Highlight the functions of the heart
– List the parts and functions of the pericardium
– Contrast the three layers of the heart wall with respect to
structure and function
– With the aid of a well labeled diagram, describe the position
of the heart.
– With the aid of a well labeled diagram, describe the pathway
for the flow of blood through the heart chambers and large
vessels associated with the heart
– Describe the vasculature of the heart with the aid of a
diagram
– Describe structural variations in some abnormalities of the
heart and the vessels.
– Explain what happens in pericardial effusion and pericarditis

The Pericardium
• The pericardium is a protective sheath that
encloses the heart, it has two parts:
– The fibrous pericardium and
– The serous pericardium.
Pericardium: A serous membrane with two layers
that surrounds the heart

Figure 1.1: The Heart and the Coverings

Cont---
 Fibrous pericardium
• The pericardium has an outer single-layered
fibrous sac that encloses the heart and the
roots of the great vessels, fusing with the
adventitia of these vessels.
• Its broad base overlies the central tendon of
the diaphragm, with which it is inseparably
blended, both being derived from the septum
transversum. Adventitia: An enveloping or covering
membrane or layer of body tissue
Diaphragm: (anatomy) a muscular partition separating the abdominal and
thoracic cavities; functions in respiration

Cont---
• The phrenic nerves lie on the surface of the
fibrous pericardium and the mediastinal
pleura is adherent to it, wherever the two
membranes are in contact with each other.
• The fibrous pericardium is connected to the
back of the sternum by weak sternopericardial
ligaments. Phrenic nerves: One of a pair of nerves that arises from
cervical spinal roots and passes down the thorax to
innervate the diaphragm and control breathing
Mediastinal: The part of the thoracic cavity
between the lungs that contains the heart and
aorta and esophagus and trachea and thymus

Cont---
 Serous pericardium
• A serous layer lines the inside of the fibrous
pericardium, where it is reflected around the roots of
the great vessels to cover the entire surface of the
heart, where it forms the epicardium. (The innermost of
the two layers of the pericardium)
• Between these parietal and visceral layers there are
two sinuses: the transverse sinus and the oblique
sinus of the pericardium.

Cont---
• The transverse sinus is a passage above the heart,
between the ascending aorta and pulmonary trunk in
front and the superior vena cava, left atrium and
pulmonary veins behind.
• The oblique sinus is a space behind the heart, between
the left atrium in front and the fibrous pericardium
behind, posterior to which lies the oesophagus.
• It is through the transverse sinus that a temporary
ligature is passed to occlude pulmonary trunk and aorta
during pulmonary embolectomy and cardiac
operations.
Embolectomy: Surgical removal of an embolus
(usually from an artery)

Cont---
• Nerve supply
 The fibrous pericardium is supplied by the
phrenic nerve.
 The parietal layer of serous pericardium that
lines it is similarly innervated, but the visceral
layer on the heart surface is insensitive.
 Pain from the heart (angina) originates in the
muscle or the vessels and is transmitted by
sympathetic nerves.
 The pain of pericarditis originates in the parietal
layer only and is transmitted by the phrenic
nerve.

Cont---
• Blood supply
 Pericardial blood supply is derived from the
internal thoracic artery, its pericardiophrenic
and musculophrenic branches, bronchial
arteries and the thoracic aorta.
 The veins drain into the azygos system.
The azygos vein is a vein running up the right side of the thoracic
vertebral column draining itself towards the superior vena cava.
It connects the systems of superior vena cava and inferior vena cava and
can provide an alternative path for blood to the right atrium when
either of the venae cavae is blocked

Cont---
 Pericardial drainage
• A needle inserted in the angle between the
xiphoid process and the left seventh costal
cartilage and directed upwards at an angle of 45,
towards the left shoulder, passes through the
central tendon of the diaphragm into the
pericardial cavity.
• The creation of a small pericardial window
surgically through the same route, or through the
anterior end of the fourth intercostal space,
provides more effective drainage.

Gross anatomy of the heart
• The heart, slightly larger than a clenched fist, is a
double, self-adjusting suction and pressure pump,
the parts of which work in unison to propel blood
to all parts of the body.
• The right side of the heart (right heart) receives
poorly oxygenated (venous) blood from the body
through the SVC and IVC and pumps it through the
pulmonary trunk and arteries to the lungs for
oxygenation.
• The left side of the heart (left heart) receives well-
oxygenated (arterial) blood from the lungs through
the pulmonary veins and pumps it into the aorta
for distribution to the body.

Figure 1.2: The Anterior View of the Heart

Chambers of the heart
 The heart has four chambers: right and left atria
and right and left ventricles.
 The atria are receiving chambers that pump blood
into the ventricles (the discharging chambers).
 The synchronous pumping actions of the heart's
two atrioventricular (AV) pumps (right and left
chambers) constitute the cardiac cycle.
 The cycle begins with a period of ventricular
elongation and filling (diastole) and ends with a
period of ventricular shortening and emptying
(systole).

Cont---
 Two heart sounds are heard with a
stethoscope: a lub (1st) sound as the blood is
transferred from the atria into the ventricles
and a dub (2nd) sound as the ventricles expel
blood from the heart.
 The heart sounds are produced by the
snapping shut of the one-way valves that
normally keep blood from flowing backward
during contractions of the heart.

Cont---
• The wall of each heart chamber consists of
three layers, from superficial to deep:
– Endocardium, a thin internal layer (endothelium
and subendothelial connective tissue) or lining
membrane of the heart that also covers its valves.
– Myocardium, a thick, helical middle layer
composed of cardiac muscle.
– Epicardium, a thin external layer (mesothelium)
formed by the visceral layer of serous
pericardium.

The 4 heart valves include
the following:
1. Tricuspid valve. Located
between the right atrium and
the right ventricle.
2. Pulmonary valve. Located
between the right ventricle
and the pulmonary artery.
3. Mitral valve. Located
between the left atrium and
the left ventricle.
4. Aortic valve.
The heart has four
chambers: two atria and
two ventricles.
 The right atrium
receives oxygen-poor
blood from the body and
pumps it to the right
ventricle.
 The right ventricle
pumps the oxygen-poor
blood to the lungs.
The left atrium receives
oxygen-rich blood from
the lungs and pumps it to
the left ventricle.

Contraction of the heart
The walls of the heart consist mostly of myocardium,
especially in the ventricles.
 When the ventricles contract, they produce a wringing
motion because of the double helical orientation of the
cardiac muscle fibers.
 This motion initially ejects the blood from the
ventricles as the outer (basal) spiral contracts, first
narrowing and then shortening the heart, reducing the
volume of the ventricular chambers.
 Continued sequential contraction of the inner (apical)
spiral elongates the heart, followed by widening as the
myocardium briefly relaxes, increasing the volume of
the chambers to draw blood from the atria.

Cont---
• The muscle fibers are anchored to the fibrous
skeleton of the heart.
• This is a complex framework of dense collagen
forming four fibrous rings (L. anulifibrosi) that
surround the orifices of the valves, a right and
left fibrous trigone (formed by connections
between rings), and the membranous parts of
the interatrial and interventricular septa.
The right and left fibrous rings of heart (annuli
fibrosi cordis) surround the atrioventricular
and arterial orifices.

Fig.1.4: The Musculature and Valves of the Heart

The fibrous skeleton of the heart:
A. Keeps the orifices of the AV and semilunar valves
patent and prevents them from being overly
distended by an increased volume of blood pumping
through them.
B. Provides attachments for the leaflets and cusps of the
valves.
C. Provides attachment for the myocardium, which,
when uncoiled, forms a continuous ventricular
myocardial band that originates primarily from the
fibrous ring of the pulmonary valve and inserts
primarily into the fibrous ring of the aortic valve.
Aortic valve: A semilunar valve between the left ventricle and the
aorta; prevents blood from flowing from the aorta back into the heart

Cont---
D. Forms an electrical insulator, by separating the
myenterically conducted impulses of the atria and
ventricles so that they contract independently and by
surrounding and providing passage for the initial part
of the AV bundle of the conducting system of the
heart.
Myenteric: A plexus of unmyelinated fibers and
postganglionic autonomic cell bodies in the
muscular coat of the esophagus and stomach and
intestines

Demarcations
 Externally, the atria are demarcated from the
ventricles by the coronary sulcus (atrioventricular
groove), and the right and left ventricles are
demarcated from each other by anterior and
posterior interventricular (IV) sulci (grooves).
 The heart appears trapezoidal from an anterior
or posterior view, but in three dimensions it is
shaped like a tipped-over pyramid with its apex
(directed anteriorly and to the left), a base
(opposite the apex, facing mostly posteriorly),
and four sides.
Demarcations: The boundary of a specific area

Cont---
• The apex of the heart:
– Is formed by the inferolateral part of the left
ventricle.
– Lies posterior to the left 5th intercostal space in
adults, usually approximately 9 cm (a hand's
breadth) from the median plane.
– Remains motionless throughout the cardiac cycle.
– Is where the sounds of mitral valve closure are
maximal (apex beat); the apex underlies the site
where the heart beat may be auscultated on the
thoracic wall.

Cont---
• The base of the heart:
– Is the heart's posterior aspect (opposite the apex).
– Is formed mainly by the left atrium, with a lesser
contribution by the right atrium.
– Faces posteriorly toward the bodies of vertebrae T6-T9
and is separated from them by the pericardium, oblique
pericardial sinus, esophagus, and aorta.
– Extends superiorly to the bifurcation of the pulmonary
trunk and inferiorly to the coronary sulcus.
– Receives the pulmonary veins on the right and left sides
of its left atrial portion and the superior and inferior
venacava at the superior and inferior ends of its right
atrial portion.

Cont---
• The four surfaces of the heart are the:
– Anterior (sternocostal) surface, formed mainly by the
right ventricle.
– Diaphragmatic (inferior) surface, formed mainly by the
left ventricle and partly by the right ventricle; it is
related mainly to the central tendon of the diaphragm.
– Right pulmonary surface, formed mainly by the right
atrium.
– Left pulmonary surface, formed mainly by the left
ventricle; it forms the cardiac impression in the left
lung.
• The heart appears trapezoidal in both anterior and
posterior views.
Trapezoid: A quadrilateral with two parallel sides

Cont---
• The four borders of the heart are the:
– Right border (slightly convex), formed by the right atrium
and extending between the SVC and the IVC.
– Inferior border (nearly horizontal), formed mainly by the
right ventricle and slightly by the left ventricle.
– Left border (oblique, nearly vertical), formed mainly by
the left ventricle and slightly by the left auricle.
– Superior border formed by the right and left atria and
auricles in an anterior view; the ascending aorta and
pulmonary trunk emerge from this border and the SVC
enters its right side.
• Posterior to the aorta and pulmonary trunk and anterior to the
SVC, this border forms the inferior boundary of the transverse
pericardial sinus.

Cont---
• The pulmonary trunk, approximately 5 cm long
and 3 cm wide, is the arterial continuation of the
right ventricle and divides into right and left
pulmonary arteries.
• The pulmonary trunk and arteries conduct low-
oxygen blood to the lungs for oxygenation.
Pulmonary trunk: The artery that carries
venous blood from the right ventricle of the
heart and divides into the right and left
pulmonary arteries

Figure 1.5: The Posterior View of the Heart

Vasculature of heart
The blood vessels of the heart comprise the coronary
arteries and cardiac veins, which carry blood to and
from most of the myocardium.
 The endocardium and some subendocardial tissue
located immediately external to the endocardium
receive oxygen and nutrients by diffusion or
microvasculature directly from the chambers of the
heart.
 The blood vessels of the heart, normally embedded in
fat, course across the surface of the heart just deep to
the epicardium. Occasionally, parts of the vessels
become embedded within the myocardium.
 The blood vessels of the heart are affected by both
sympathetic and parasympathetic innervation.

Arterial supply of heart
 The coronary arteries, the first branches of the aorta,
supply the myocardium and epicardium.
 The right and left coronary arteries arise from the
corresponding aortic sinuses at the proximal part of
the ascending aorta, just superior to the aortic valve,
and pass around opposite sides of the pulmonary
trunk.
 The coronary arteries supply both the atria and the
ventricles; however, the atrial branches are usually
small and not readily apparent in the cadaveric heart.
 The ventricular distribution of each coronary artery is
not sharply demarcated.

Figure 1.6: The Blood Supply of the Heart

Cont---
• The right coronary artery (RCA) arises from the
right aortic sinus of the ascending aorta and
passes to the right side of the pulmonary trunk,
running in the coronary sulcus.
• Near its origin, the RCA usually gives off an
ascending sinuatrial nodal branch, which supplies
the SA node.
• The RCA then descends in the coronary sulcus
and gives off the right marginal branch, which
supplies the right border of the heart as it runs
toward (but does not reach) the apex of the heart

Cont---
• After giving off this branch, the RCA turns to the
left and continues in the coronary sulcus to the
posterior aspect of the heart.
• At the posterior aspect of the crux (L. cross) of
the heart—the junction of the interatrial and
interventricular (IV) septa between the four heart
chambers—the RCA gives rise to the
atrioventricular nodal branch, which supplies the
AV node.
• The SA and AV nodes are part of the conducting
system of the heart.

Cont---
• Typically, the RCA supplies:
– The right atrium.
– Most of right ventricle.
– Part of the left ventricle (the diaphragmatic
surface).
– Part of the IV septum, usually the posterior third.
– The SA node (in approximately 60% of people).
– The AV node (in approximately 80% of people).

Cont---
• The left coronary artery (LCA) arises from the left
aortic sinus of the ascending aorta, passes between the
left auricle and the left side of the pulmonary trunk,
and runs in the coronary sulcus.
• In approximately 40% of people, the SA nodal branch
arises from the circumflex branch of the LCA and
ascends on the posterior surface of the left atrium to
the SA node.
• As it enters the coronary sulcus, at the superior end of
the anterior IV groove, the LCA divides into two
branches, the anterior IV branch (clinicians continue to
use LAD, the abbreviation for the former term ―left
anterior descending‖ artery) and the circumflex branch

Cont---
• The anterior IV branch passes along the IV groove
to the apex of the heart. Here it turns around the
inferior border of the heart and commonly
anastomoses with the posterior IV branch of the
right coronary artery.
• The anterior IV branch supplies adjacent parts of
both ventricles and, via IV septal branches, the
anterior two thirds of the IVS.
• In many people, the anterior IV branch gives rise
to a lateral branch (diagonal artery), which
descends on the anterior surface of the heart.

Cont---
• The smaller circumflex branch of the LCA follows
the coronary sulcus around the left border of the
heart to the posterior surface of the heart.
• The left marginal branch of the circumflex branch
follows the left margin of the heart and supplies
the left ventricle.
• Most commonly, the circumflex branch of the LCA
terminates in the coronary sulcus on the
posterior aspect of the heart before reaching the
crux of the heart, but in approximately one third
of hearts it continues to supply a branch that runs
in or adjacent to the posterior IV groove.

Cont---
 Typically, the LCA supplies:
– The left atrium.
– Most of the left ventricle.
– Part of the right ventricle.
– Most of the IVS (usually its anterior two thirds),
including the AV bundle of the conducting system
of the heart, through its perforating
Interventricular ( IV) septal branches.
– The SA node (in approximately 40% of people).

Venous drainage of the heart
 The heart is drained mainly by veins that empty
into the coronary sinus and partly by small veins
that empty into the right atrium.
 The coronary sinus, the main vein of the heart, is
a wide venous channel that runs from left to right
in the posterior part of the coronary sulcus.
 The coronary sinus receives the great cardiac
vein at its left end and the middle cardiac vein
and small cardiac veins at its right end.
 The left posterior ventricular vein and left
marginal vein also open into the coronary sinus.
coronary sinus: A short sinus receiving most of the
veins of the heart; empties into the right atrium

Cont---
 The coronary sinus (CS) refers to a collection of
veins that join together to form a large blood
vessel.
• This vein is located between the left atrium and
the left ventricle of the heart.
• The heart is a vital organ and the central
component of the circulatory system.
 The coronary sulcus, also known as the
atrioventricular groove, is a groove that separates
the atria and ventricles of the heart.
 It extends from the upper medial end of the third
left costal cartilage to the middle of the right sixth
chondrosternal joint.

Figure 1.7: Venous Drainage of the Heart

Cont---
• The great cardiac vein is the main tributary of the
coronary sinus.
• Its first part, the anterior interventricular vein,
begins near the apex of the heart and ascends
with the anterior IV branch of the LCA.
• At the coronary sulcus it turns left and its second
part runs around the left side of the heart with
the circumflex branch of the LCA to reach the
coronary sinus.
• (An unusual situation is occurring here: Blood is
flowing in the same direction within a paired
artery and vein!) The great cardiac vein drains the
areas of the heart supplied by the LCA.

Cont---
• The middle cardiac vein (posterior IV vein)
accompanies the posterior interventricular branch
(usually arising from the RCA).
• A small cardiac vein accompanies the right
marginal branch of the RCA.
• Thus these two veins drain most of the areas
commonly supplied by the RCA.
• The oblique vein is the remnant of the embryonic
left SVC, which usually atrophies during the fetal
period, but occasionally persists in adults, replacing
or augmenting the right SVC.

Cont---
• Some cardiac veins do not drain via the coronary sinus.
• Several small anterior cardiac veins begin over the
anterior surface of the right ventricle, cross over the
coronary sulcus, and usually end directly in the right
atrium; sometimes they enter the small cardiac vein.
• The smallest cardiac veins (L. venae cordis minimae)
are minute vessels that begin in the capillary beds of
the myocardium and open directly into the chambers of
the heart, chiefly the atria.
• Although called veins, they are valveless (To control (flow))
communications with the capillary beds of the myocardium
and may carry blood from the heart chambers to the
myocardium.

Lymphatic drainage of the heart
o Lymphatic vessels in the myocardium and
subendocardial connective tissue pass to the
subepicardial lymphatic plexus.
o Vessels from this plexus pass to the coronary
sulcus and follow the coronary arteries.
o A single lymphatic vessel, formed by the union of
various lymphatic vessels from the heart,
ascends between the pulmonary trunk and left
atrium and ends in the inferior tracheobronchial
lymph nodes, usually on the right side.

Innervation of the heart
The heart is supplied by autonomic nerve fibers
from the cardiac plexus, which is often quite
artificially divided into superficial and deep
portions.
 This nerve network is most commonly described as
lying on the anterior surface of the bifurcation of
the trachea (a respiratory structure), since it is most
commonly observed in dissection after removal of
the ascending aorta and the bifurcation of the
pulmonary trunk.
 However, its primary relationship is to the
posterior aspect of the latter two structures,
especially the ascending aorta.
Innervation: The neural or electrical arousal of an organ or muscle or gland

Cont---
 The cardiac plexus is formed of both sympathetic
and parasympathetic fibers end route to the
heart, as well as visceral afferent fibers conveying
reflexive and nociceptive fibers from the heart.
 Fibers extend from the plexus along and to the
coronary vessels and to components of the
conducting system, particularly the SA node.
The sympathetic supply is from presynaptic
fibers, with cell bodies in the intermediolateral
cell columns (IMLs) of the superior five or six
thoracic segments of the spinal cord &
postsynaptic sympathetic fibers, with cell bodies
in the cervical and superior thoracic paravertebral
ganglia of the sympathetic trunks.

Cont---
The post synaptic fibers traverse cardiopulmonary
splanchnic nerves and the cardiac plexus to end in the
SA and AV nodes and in relation to the terminations of
parasympathetic fibers on the coronary arteries.
 Sympathetic stimulation causes increased heart rate,
impulse conduction, force of contraction and at the
same time, increased blood flow through the coronary
vessels to support the increased activity.
 Adrenergic stimulation of the SA node and conducting
tissue increases the rate of depolarization of the
pacemaker cells while increasing atrioventricular
conduction.
Splanchnic nerves: Any of several nerves of the
sympathetic part of the autonomic nervous system
that innervate viscera and blood vessels
Adrenergic: sympathomimetic

Developmental and microanatomy of
the heart
 The cardiovascular system is functionally important
in development.
 Most cells and organs in an embryo do very little
except grow and differentiate—the brain, lungs, liver,
digestive system, gonads, and kidneys all fall into this
category.
 But the cardiovascular system has to do real work
early on.

Cont---
 The reason is that once the embryo has gotten
thicker than 200 to 400 microns, the diffusion of
nutrients, oxygen and carbon dioxide is
inadequate to service an inner mass of very
metabolically active cells.
 A circulatory system is needed to keep these cells
from dying and it needs to do it by the middle of
the fourth week of gestation (circa embryonic day
24).
And this system has to work continuously while
undergoing some serious remodeling.
Microns: A metric unit of length equal to one
millionth of a meter

Remodelling of the Cardiovascular System with
Development
• The cardiovascular system is radically remodeled
several times during development.The system is
revamped at least four times.
– It starts out as an approximately bilateral system of
contractile blood vessels. Parts coalesce at midline to
form a single channel or central pump.
– Parts of the contents regresses in the embryo, including
some early renal structures (the mesonephros). As a
result entire systems of veins (and some embryonic
arteries) also regress.Virtually the entire posterior
cardinal venous system gets re-absorbed

Cont---
– The heart gets split into two pumps.The right
side basically pumps blood straight into the
descending aorta (through the ductus arteriosus
shunt).The left side pumps blood into the rapidly
growing cranium and brain.
– At birth the whole pattern of circulation has to be
modified radically in a matter of minutes.The
main objectives are to shut down the
chorionic/placental circulation and open up the
pulmonary circulation.
Arteriosus: A blood vessel in a fetus that bypasses pulmonary circulation by connecting
the pulmonary artery directly to the ascending aorta; normally closes at birth

The cardiovascular system is not just made up
of splanchnic mesoderm.
• The heart also gets a critical influx of cells from
the neural crest.
• These crest cells contribute to the formation of
the endocardial cushions, which in turn are
critical in converting a simple one-chamber pump
into a complex two-chambered heart with
sophisticated valves.
• They may be called "neural" crest, but these cells
have an almost miraculous ability to make
different types of tissues (cranial skeleton,
adrenals, neurons, glia, even muscles in the
ciliary body).
Splanchnic: Relating to or affecting the viscera
Miracle: Any amazing or wonderful occurrence

Cont----
• The heart and arterial trunk are split into
the adult compartments by six growing
walls of tissue (septae).
• Septum primum: This first septum grows down
the middle of the common atrium and eventually
fuses with tissues that surround the narrow lumen
between the atrium and ventricle (there is only one
atrium and one ventricle at this point in the 5th week
of gestation).

Cont----
• Septum secundum: This slow growing second
atrial septum grows parallel to the 1st septum,
but is delayed by a couple of weeks. It is a more
robust wall. Both the 1st and 2nd septums
(septae) have big holes in them.
• To make it rough on you the hole in the first
septum is called the second hole or for formal
types, the foramen secundum
• The hole in the second septum is called the
foramen ovale

Cont----
• AV septum/endocardial cushion: The
endocardial cushions give rise to most of the cardiac
skeleton that splits the atrial and ventricular sides of
the heart. The cushions also build mitral and
tricuspid valves.
• Interventricular septum, muscular part: A
septum can also form when a central region grows
particularly slowly.
– The surrounding tissue can bulge outward and
fuse. This may be the mode by which the
interventricular septum forms.

Cont----
• Interventricular septum, membranous part:
May be you have felt this part of the septum in the
Gross Lab, tucked out of sight in the aortic vestibule,
maybe not.
– When this membrane forms from a motley crew
of cells from the endocardial cushions and the
bulbar ridges, the heart is finally four-chambered.

Cont----
• Aortico-pulmonary septa, bulbar ridges:
 There is no pulmonary trunk at early stages, just one
big common arterial outflow, called the truncus
arteriosus, that delivers all blood to an aortic sac.
Truncus: A bundle of modified heart muscle
that transmits the cardiac impulse from the
atrioventricular node to the ventricles causing
them to contract

 Heart development, also known
as cardiogenesis, refers to the prenatal
development of the heart.
– This begins with the formation of
two endocardial tubes which merge to form
the tubular heart, also called the primitive
heart tube.
– The heart is the first functional organ
in vertebrate embryos.

Microanatomy of the great vessels
 The cardiovascular system may be divided into
four major components: the Heart, the
Macrocirculation, the Microcirculation and the
Lymph vascular system.
 Essentially, the macrocirculation comprises all
vessels, both arteries and veins that would be
visible to the eye.
 The vessels of the macrocirculation supply and
drain a network of fine vessels interposed
between them, the capillaries.
This network is also called the capillary bed.

Cont----
• Water and other components of the blood
plasma which exude from the blood vessels
form the interstitial fluid, which is returned to
the circulation by the lymph vascular system.

General Structure of Blood Vessels
 The histological appearances of vessels are
different sizes (arterioles vs arteries) and different
types (arteries vs. veins) are different from each
other. ( seen these in the laboratory).
 These differences are the result of quantitative
variations of a common structural pattern that can be
seen in all blood vessels with the exception of
capillaries, i.e. the division of the walls of the blood
vessels into three layers or tunics.
Arterioles: One of the small thin-walled
arteries that end in capillaries

Cont----
1. The Tunica intima: The innermost membrane of an
organ (especially the inner lining of an artery, vein or
lymphatic vessel)
• Tunica intima limits the vessel wall towards the
lumen of the vessel and comprises its endothelial
lining (typically simple, squamous) and associated
connective tissue.
• Beneath the connective tissue, we find the internal
elastic lamina, which delimits the tunica intima from
the Tunica media.
Tunics: An enveloping or covering membrane
or layer of body tissue

Cont----
2. The Tunica media
 The Tunica media is formed by a layer of
circumferential smooth muscle and variable
amounts of connective tissue.
 A second layer of elastic fibers, the external
elastic lamina, is located beneath the smooth
muscle.
 It delimits the tunica media from the tunica
adventitia, which consist of mainly of connective
tissues fibers.
Tunica: An enveloping or covering membrane
or layer of body tissue
The tunica intima is the innermost tunica
(layer) of an artery or vein. It is made up of one
layer of

Cont----
3. Tunica adventitia
• The tunica adventitia blends with the
connective tissue surrounding the vessel.
• The definition of the outer limit of the tunica
adventitia is therefore somewhat arbitrary.
Blends: An occurrence of thorough mixing

Cont----
Vasa Vasorum
 Any small blood vessel ramifying on the outside of a
major artery or vein
• A blood vessel that supplies the vessel that
supplies blood to the wall of the vessel.
• it supplies nutrients to the blood vessel.

Fig. 1.8: Histology of a blood vessel.(showing layers of the blood vessel wall
including the intima, media and adventitia)

Fig. 1.9: VARIATIONS OF VESSEL WALL STRUCTURES Arteries

Cont----
• All arterial vessels originate from either the
pulmonary trunk (from the right ventricle) or the
aorta (from the left ventricle).
 Specializations of the walls of arteries relate mainly
to two factors: the pressure pulses generated
during contractions of the heart (systole) and the
regulation of blood supply to the target tissues of
the arteries.
• The tunica media is the main site of histological
specializations in the walls of arteries.
• Vessels close to the heart (aorta, pulmonary trunk
and the larger arteries that originate from them) are
elastic arteries.

Elastic arteries
o The tunica intima of elastic arteries is thicker than in
other arteries.
o A layer of loose connective tissue beneath the
endothelium (subendothelial connective tissue) allows
the tunica intima to move independently from other
layers as the elastic arteries distend with the increase
in systolic blood pressure.
o Distension of the walls is facilitated by concentric
fenestrated lamellae of elastic fibres in a thick tunica
media.
o In adult humans, about 50 elastic lamellae are found
in the tunica media of the aorta.
Intima: The inner most membrane of an organ (especially the inner lining of an
artery, vein or lymphatic vessel)

Cont---
o The energy stored in the elastic fibres of the
tunica media allows elastic arteries to function
as a "pressure reservoir" which forwards blood
during ventricular relaxation (diastole).
o Smooth muscle cells and collagen fibres are
present between the layers of elastic fibres.
o Both fibre types are produced by the smooth
muscle cells.

Cont---
o Each elastic lamella forms together with
interlamellar fibres and cells to form a lamellar
unit.
o The external elastic lamina is difficult to discern
(understand) from other layers of elastic fibres in
the tunica media.
o The tunica adventitia appears thinner than the
tunica media and contains collagen fibers and the
cell types typically present in connective tissue.
The internal elastic lamina or internal elastic
lamella is a layer of elastic tissue that forms
the outermost part of the tunica intima of
blood vessels

Cont----
o The walls of these large arteries are so thick that
their peripheral parts cannot derive enough
oxygen and nutrients from the blood of the
vessel that they form.
o Larger vessels are therefore accompanied by
smaller blood vessels which supply the tunica
adventitia and, in the largest vessels, the outer
part of the tunica media of the vessel wall.
o The vessels are called vasa vasorum.
o In macroscopic preparations vasa vasorum are
visible as fine dark lines on the surface of the
larger arteries.

Cont----
o The diameter of individual arteries decreases as
we follow them further into the periphery.
o However, their total diameter increases, which
leads to a fall in blood pressure. Also, the
properties of the elastic arteries have to some
extent evened out differences in diastolic and
systolic blood pressure.
o The amount of elastic fibres in the tunica media
decreases with these physiological changes.

Muscular arteries
The tunica intima is thinner than in elastic arteries.
 Subendothelial connective tissue other than the
internal elastic lamina is often difficult to discern. The
internal elastic lamina forms a well- defined layer.
• The tunica media is dominated by numerous concentric
layers of smooth muscle cells. Fine elastic fibers and a
few collagen fibers are also present.
• The external elastic lamina can be clearly distinguished
although it may be incomplete in places. The thickness
and appearance of the tunica adventitia is variable.

Arterioles
• Arterioles are arterial vessels with a diameter
below 0.1 - 0.5 mm (different values in different
textbooks).
• Endothelial cells are smaller than in larger
arteries, and the nucleus and surrounding
cytoplasm may 'bulge' slightly into the lumen of
the arteriole.
• The endothelium still rests on an internal elastic
lamina, which may be incomplete and which is
not always well-defined in histological sections.

Cont----
• The tunica media consists of 1-3 concentric layers
of smooth muscle cells. It is difficult to identify an
external elastic lamina or to distinguish the tunica
adventitia from the connective tissue surrounding
the vessel.
• The smooth muscle of arterioles and, to some
extent, the smooth muscle of small muscular
arteries regulate the blood flow to their target
tissues.
• Arterioles receive both sympathetic and
parasympathetic innervation.
• The final branching of the arterioles finally gives
rise to the capillary network (microcirculation).

Capillaries
• The sum of the diameters of all capillaries is
significantly larger than that of the aorta (by
about three orders of magnitude), which
results in decreases in blood pressure and
flow rate.
• Also, capillaries are very small vessels.
• Their diameter ranges from 4-15 μm.

Cont----
• The wall of a segment of capillary may be formed
by a single endothelial cell. This results in a very
large surface to volume ratio.
 The low rate of blood flow and large surface area
facilitate the functions of capillaries in
 Providing nutrients and oxygen to the
surrounding tissue,
 the absorption of nutrients, waste products and
carbon dioxide, and
 the excretion of waste products from the body.

Cont----
• Three types of capillaries can be distinguished
based on features of the endothelium.
Continuous capillaries - are formed by
"continuous" endothelial cells and basal
lamina.
The endothelial cell and the basal lamina do not
form openings, which would allow substances to
pass the capillary wall without passing through
both the endothelial cell and the basal lamina.
Both endothelial cells and the basal lamina can act
as selective filters in continuous capillaries.

Cont----
Fenestrated capillaries -endothelial cell body
forms small openings called fenestrations,
which allow components of the blood and
interstitial fluid to bypass the endothelial cells
on their way to or from the tissue surrounding
the capillary.

Cont----
• Discontinuous capillaries- are formed by
fenestrated endothelial cells, which may not
even form a complete layer of cells. The basal
lamina is also incomplete. Discontinuous
capillaries form large irregularly shaped
vessels, sinusoids or sinusoid capillaries. They
are found where a very free exchange of
substances or even cells between bloodstream
and organ is advantageous

Venules
 They are larger than capillaries.
 Small venules are surrounded by pericytes (A few
smooth muscle cells may surround larger venules).
 The venules merge to form Small to medium-sized veins
which contain bands of smooth muscle in the tunica
media.
 The tunica adventitia is well developed. In some veins
(e.g. the veins of the pampiniform plexus in the spermatic
cord) the tunica adventitia contains longitudinally oriented
bundles of smooth muscle.
Venules: A minute vein continuous with a capillary

Cont---
• Aside from most veins in the head and neck, small
to medium-sized veins are also characterized by
the presence of valves.
• The valves are formed by loose, pocket-shaped
folds of the tunica intima, which extend into the
lumen of the vein.
• The opening of the pocket will point into the
direction of blood flow towards the heart. One to
three (usually two) pockets form the valve.

Cont---
• Blood flowing towards heart will pass the pockets. If
the flow reverses, blood will fill the pockets which
will occlude the lumen of the vein and prevent the
return of blood into the part of the vein preceding
the valve.
• The ability of the valves to prevent backflow
depends to some extent on the state of
contraction (tone) of the smooth muscle in the wall
of the vein.

Cont----
• The largest veins of the abdomen and thorax do
contain some subendothelial connective tissue in
the tunica intima, but both it and the tunica media
are still comparatively thin.
• Collagen and elastic fibres are present in the tunica
media.
• The tunica adventitia is very wide, and it usually
contains bundles of longitudinal smooth muscle.

Cont----
• The transition from the tunica adventitia to the
surrounding connective tissue is gradual. Valves are
absent.
• Vasa vasorum are more frequent in the walls of
large veins than in that of the corresponding
arteries - probably because of the lower oxygen
tension in the blood contained within them.

Lymphatic system
 Parts of the blood plasma will exude from the blood
vessels into the surrounding tissues because of
transport across the endothelium or because of
blood pressure and the fenestration of some
capillaries (this process is partly counteracted by
the higher osmotic pressure of the blood).
 The fluid entering tissues from capillaries adds to the
interstitial fluid normally found in the tissue.
 The surplus of liquid needs to be returned to the
circulation.
 Lymph vessels are dedicated to this unidirectional
flow of liquid, the lymph.

Cont----
• Three types of lymph vessels can be distinguished
based on their size and morphology
1. Lymph capillaries are somewhat larger than blood
capillaries and very irregularly shaped. They begin as
blind-ending tubes in connective tissue.
 Temporary openings in the endothelial lining of
the lymph capillaries also allow the entry of larger
particles into the lymph capillaries (lipid droplets,
which are absorbed from the lumen of the gut do
not enter blood capillaries, but enter the
circulation via lymph vessels which are found in
the villi of the ileum and jejunum).

Cont----
2. Lymph collecting vessels which are larger and
form valves but otherwise appear similar to lymph
capillaries.
 The lymph is moved by the compression of the
lymph vessels by surrounding tissues. The
direction of lymph flow is determined by the
valves. Lymph vessels empty intermittently into
lymph nodes from which the lymph continues in
efferent lymph vessels.
 Only very little lymph is returned from the limbs if
they are immobilized, which illustrates the
importance of muscular action in lymph transport.

Cont----
3. Lymph ducts which contain one or two layers of
smooth muscle cells in their wall (some textbooks
call this layer the tunica media of lymph vessels).
 The walls of the lymph ducts are less flexible in
the region of the attachment of the valves to the
wall of the duct, which may give a beaded
appearance to the lymph ducts.
 Peristaltic contractions of the smooth muscle
contribute to the movement of lymph towards
the heart in addition to the compression of the
ducts by surrounding tissues.

Cont----
The largest lymph duct of the body, the thoracic
duct, drains lymph from the lower half and upper
left quadrant of the body and empties the lymph
into the circulation by merging with the vascular
system close to the junction of the left internal
jugular and subclavian veins.
That it is the largest lymph duct does not mean
that it is a large vessel when compared to the
large arteries and veins.
 It actually is not much larger (about 5mm in
diameter) than one of the superficial forearm
veins.

Clinical correlates
i) Stroke or Cerebrovascular Accident
Thrombi (clots) form on the walls of the left
atrium in certain types of heart disease.
If these thrombi detach or pieces break off
from them, they pass into the systemic
circulation and occlude peripheral arteries.
Occlusion of an artery supplying the brain
results in a stroke or cerebrovascular
accident (CVA), which may affect vision,
cognition or the motor function of parts of the
body previously controlled by the now-
damaged (ischemic) area of the brain.

Cont----
ii) Valvular Heart Disease
o Disorders involving the valves of the heart disturb
the pumping efficiency of the heart.
o Valvular heart disease produces either stenosis
(narrowing) or insufficiency.
o Stenosis is the failure of a valve to open fully,
slowing blood flow from a chamber.
o Insufficiency or regurgitation, on the other hand,
is failure of the valve to close completely, usually
owing to nodule formation on (or scarring and
contraction of) the cusps so that the edges do not
meet or align.

Cont----
o This allows a variable amount of blood (depending on
the severity) to flow back into the chamber it was just
ejected from.
o Both stenosis and insufficiency result in an increased
workload for the heart.
o Because valvular diseases are mechanical problems,
damaged or defective cardiac valves can be replaced
surgically in a procedure called valvuloplasty.
o Most commonly, artificial valve prostheses made of
synthetic materials are used in these valve-replacement
procedures, but xenografted valves (valves transplanted
from other species, such as pigs) are also used.
 The term xenograft refers to a tissue or organ that is derived from a species that is
different from the recipient of the specimen.
Heart valve disease occurs when one or more of the
heart valves do not open or close properly.

Cont----
iii) Pulmonary valve stenosis
• In pulmonary valve stenosis, the valve cusps
are fused, forming a dome with a narrow
central opening.
• In infundibular pulmonary stenosis, the conus
arteriosus is underdeveloped.
• Both types of pulmonary stenoses produce a
restriction of right ventricular outflow and may
occur together. The degree of hypertrophy of
the right ventricle is variable.
Infundibular: Any of various funnel-shaped parts of the
body (but especially the hypophyseal stalk)

Cont----
iv) Pulmonary valve incompetence
 If the free margins (lunules) of the cusps of a
semilunar valve thicken and become inflexible
or are damaged by disease, the valve will not
close completely.
 An incompetent pulmonary valve results in a
backrush of blood under high pressure into the
right ventricle during diastole.
 Pulmonic regurgitation may be heard through a
stethoscope as a heart murmur, an abnormal
sound from the heart, produced in this case by
damage to the cusps of the pulmonary valve.

Cont----
v) Aortic valve stenosis
 Aortic stenosis occurs when the aortic valve narrows
and blood cannot flow normally. The condition may
range from mild to severe.
 Over time, aortic valve stenosis causes your heart's
left ventricle to pump harder to push blood through the
narrowed aortic valve.
vi) Aortic valve insufficiency
 Aortic regurgitation (AR), also known as aortic
insufficiency, is a form of valvular heart disease in
which the integrity of the aortic valve is compromised
and leads to inadequate closure of the valve leaflets. A
normal aortic valve is comprised of three semilunar
cusps that attach to the aortic wall.

Cont----
vii) Echocardiography
• Echocardiography (ultrasonic cardiography) is a
method of graphically recording the position and
motion of the heart by the echo obtained from
beams of ultrasonic waves directed through the
thoracic wall.
• This technique may detect as little as 20 mL of
fluid in the pericardial cavity, such as that
resulting from pericardial effusion.

Cont----
• Doppler echocardiography is a technique that
demonstrates and records the flow of blood
through the heart and great vessels by Doppler
ultrasonography, making it especially useful in
the diagnosis and analysis of problems with
blood flow through the heart, such as septal
defects, and in delineating valvular stenosis and
regurgitation, especially on the left side of the
heart.

Cont----
 An echocardiogram, or
"echo", is a scan used to
look at the heart and
nearby blood vessels.
 It's a type of ultrasound
scan, which means a small
probe is used to send out
high-frequency sound
waves that create echoes
when they bounce off
different parts of the body.

Cont----
Viii) Coronary atherosclerosis
• The atherosclerotic process, characterized by lipid
deposits in the intima (lining layer) of the
coronary arteries, begins during early adulthood
and slowly results in stenosis of the lumina of the
arteries
• As coronary atherosclerosis progresses, the
collateral channels connecting one coronary
artery with the other expand, which may initially
permit adequate perfusion of the heart during
relative inactivity.

Cont----
• Despite this compensatory mechanism, the
myocardium may not receive enough oxygen when
the heart needs to perform increased amounts of
work.
• Strenuous exercise, for example, increases the
heart's activity and its need for oxygen.
• Insufficiency of blood supply to the heart (myocardial
ischemia) may result in MI.

Cont----
ix) Slowly progressive coronary artery disease
• In slow occlusion of a coronary artery, the collateral
circulation has time to increase so that adequate
perfusion of the myocardium can occur when a
potentially ischemic event occurs.
• Consequently, MI may not result.
• On sudden blockage of a large coronary branch, some
infarction is probably inevitable, but the extent of the
area damaged depends on the degree of development
of collateral anastomotic channels.
• If large branches of both coronary arteries are partially
obstructed, an extracardiac collateral circulation may
be used to supply blood to the heart

Cont----
X) Transplantation
• The patient‘s heart is removed by incisions through the
aorta, pulmonary trunk and both atria.
• The incision line through the right atrium leaves the
two vena cava, the posterior wall of the atrium and the
region of the SA node in situ.
• The posterior part of the left atrium with the four
pulmonary vein orifices is also left intact.
• The donor heart is trimmed through the atria to match
up with the remains of the patient‘s atria, although the
lower end of the donor superior vena cava remains
attached to the right atrium so that the donor heart
retains its own SA node.

Cont----
• For combined heart–lung transplantation, the donor
block is removed through the trachea, right atrium
and aorta, and sutured to the recipient in that order.

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