Circulatory System

Medical Laboratory Science

College of Allied Medical Professions
Lyceum of the Philippines University-
Batangas
 COPYRIGHT NOTICE
This material has been reproduced and communicated to you or on behalf of
Lyceum of the Philippines University- Batangas pursuant to
PART IV: The Law of Copyright of Republic Act
RA 8293 or the "Intellectual Property Code of the Philippines".
The University does not authorize you to reproduce or communicate this material.
The material may contain works that are subject to copyright protection under RA 8293.
Any reproduction, and/or communication of the material
by you may be subject to take legal action against such infringement.

Do not remove this notice.

This material is prepared by the Faculty of the Department of Medical Laboratory
Science,
LPU-Batangas College of Allied Medical Professions,
solely for the use of students enrolled in Human Histology (MLS 202) for the A.Y. 2022-
2023.

Please do not distribute without permission.

Cardiovascular System
Component Structures :
• Heart
• Blood vessel
➢Arteries
➢Capillaries
➢Veins
Functions of Circulatory
system
• Brings nutrients, oxygen, hormones and
other vital substances to the cells of the
body from varying points of origin.
• Helps maintains the body's homeostasis
and aids in fighting off pathogenic
organisms by providing and transporting
the cells and substances needed for these
purposes
• Includes cardiovascular (blood) and
lymphatic system (lymph),
Heart
• A hollow muscular organ about the size of
a clenched fist located in the mediastinum
of the thoracic cavity.

3 Major layers :
1. Endocardium
2. Myocardium
3. Epicardium
Heart
• Has four chambers: right and left ventricles;
right and left atria
• left ventricle: pump of the systemic circulation
• right ventricle: pump of the pulmonary
circulation
• left atrium: drains and receives oxygenated
blood from the pulmonary veins
• right atrium: drains and receives
deoxygenated blood from the systemic
circulation
 HEART
• Interatrial septum: separates right from left atrium
• Interventricular septum: separates right from left ventricle
• Mitral valve: prevents backflow of blood from the left
ventricle to the left atrium
• Tricuspid valve: prevents backflow of blood from right
ventricle to the right atrium
• Semilunar valves: guards the semilunar orifices
(pulmonary and aortic)
• Superior vena cava: drains the upper portion of the body
• Inferior vena cava: drains the lower portion of the body
• Coronary sinus: drains the cardiac veins
Histologic layers of the Heart
• Myocardium
- Middle layer composed of cardiac muscle cell
and responsible for heart contractions
- The muscle fibers originate and inserts in the
cardiac skeleton

• Epicardium
- outermost histologic layer of the heart
- simple squamous mesothelium
Histologic layers of the heart
• Endocardium
- Surrounds the numbers of modified cardiac muscle fibers
that comprise the heart’s impulse conducting system
- Thinnest layer, lines the internal surface of the heart
• Consists of four sublayers
• Endothelium
• lines the luminal surface and consists of simple squamous
epithelium
• Subendothelial layer
• consist of loose connective tissue
• Dense connective tissue layer
• Subendocardium
• contains many blood vessels and Purkinje fibers
Heart Wall

20-12
Cardiac Skeleton
• Refers to the dense fibrous connective tissue that forms the
central support of the heart into which the cardiac muscles
and valves are attached
• Three main components:
• septum membranaceum
• part of the cardiac skeleton that is in the
interventricular septum
• annuli fibrosi
• surrounds the AV orifices and the origins of the aorta
and pulmonary artery
• trigona fibrosa
• located between the semilunar and AV orifices
Cardiac Skeleton
Conducting system of the
Heart
• specialized to generate and conduct waves of
depolarization
• Triggered by a population of modified cardiac muscle
fibers called PURKINJE FIBERS that are noncontractile but
are specialized to initiate and conduct electrical impulses
• Components:
• Sinoatrial node (SA): cardiac pacemaker
• Three internodal tracts
• Atrioventricular node (AV)
• AV bundle of His
• Two bundle branches
• Purkinje fibers
Conducting system of the
Heart
• Impulses are passed on to individual cardiac fibers via
the GAP JUNCTIONS that exists in the intercalated disks
• The cardiac musculature does not need neural
stimulation to contract but is controlled by the efferent
fibers of the autonomic nervous system
• Vagal fibers: inhibit heart action
• Sympathetic fibers: stimulate heart action
Conducting System of
Heart

20-17
Tissues of Vascular wall
Two factors
1. Mechanical factors
2. Metabolic

• The luminal surface of all the blood vessels,

as in the heart, is lined by simple squamous
epithelium (endothelium)
• The walls of capillaries consists only of
endothelium
Tissues of Vascular wall
• Endothelium
• specialized epithelium that acts as a
semipermeable barrier between two major
internal compartments
• squamous, polygonal, and elongated with the
long axis
Functions :
• Presents a Nonthrombogenic layer ( Heparin,TPA)
• Regulate blood flow (ACE)
• Local immune response ( P selectin)
• Secretes growth factors ( VEGF )
Tissues of Vascular wall
Cardiac muscle
• Elongated, branching cells containing 1-2
centrally located nuclei
• Contains actin and myosin myofilaments
• INTERCALATED DISK: Specialized cell-cell
contacts
• Electrically, cardiac muscle behaves as
single unit
Tissues of Vascular wall
• Smooth muscle
➢Occurs at wall of all vessels larger than
capillaries
➢Helically arranged
Connective tissue
➢Collagen fibers are found in the subendothelial layer,
➢Elastic fibers provide the resiliency required for the
vascular wall to expand under pressure
Have three concentric layers :
➢Intima, media and adventitia
Vasculature
Types of Capillaries
• Continuous
• Found in muscles, lungs, CNS and skin
• Fenestrated
• Found in the mucous membranes of the
gastrointestinal tract, many endocrine glands,
pancreas and renal glomerulus
• Sinusoidal
• Found in the parenchyma of some organs like
liver, spleen, bone marrow, and certain
endocrine organs
Histologic layers (arteries &
veins)
• Both arteries and veins are consist of three
layers namely
• Tunica intima
• innermost histologic layer of arteries
and veins
• consist of endothelium and
subendothelial layer made up of
loose connective tissue
Histologic layers(arteries &
veins)
• Tunica media
• Middle histologic coat of arteries and
veins
• In arteries with relatively large caliber, an
additional layer, external elastic
membrane, is present.
• Tunica adventitia
• Outermost histologic coat of arteries and
veins
 SMALL MEDIUM LARGE
ARTERIOLES MUSCULAR ARTERIES ELASTIC ARTERIES; CONDUCTING
Types of Diameter ranges from They distribute blood from different ARTERIES
ARTERIES 40-400 um parts of the body
Consists most of the named
arteries

Consists only of With three distinct layers Consist of an endothelium,

endothelium and/or (endothelium, subendothelium, subendothelium made up of
internal elastic internal elastic membrane) loose connective tissue that has
membrane. There is a sprinkling of smooth muscle
Tunica practically no cells and internal elastic
intima subendothelial tissue membrane

Single to multiple layers Consist of circularly arranged thickest layer, consist mainly of
of smooth muscle cells. smooth muscle cells. The number sheets of elastin called elastic
of layers can be as much as 40. lamellae arranged
Tunica The external elastic membrane is concentrically
media very prominent

Composed of loose Consists of loose connective tissue relatively thin and merges with
connective tissue sometimes as thick or even thicker the surrounding connective
than the tunica media. It contains tissue. It contains vasa vasorum
Tunica lymphatic vessels and vasa
adventitia vasorum
Sensory organs associated with
arteries
• Carotid bodies
• sensitive to changes in oxygen and carbon dioxide
tension in the blood
• afferent nerve endings in the carotid bodies come
from glossopharyngeal nerve
• Aortic bodies
• sensitive to changes in oxygen and carbon dioxide
tension in the blood
• afferent nerve endings in the aortic bodies come
from vagus nerve
• Carotid sinus
• contains baroreceptors
• afferent nerve endings in the carotid bodies come
from glossopharyngeal nerve
Veins
• Compared to the arteries that they
accompany, veins have bigger calibers,
more irregular lumens, and thinner and less
elastic walls.
• Classified into small (venules), medium and
large veins
• Many medium-sized veins are provided
with valves that ensure unidirectional flow
of blood
 SMALL MEDIUM LARGE
Types of VENULES Includes almost all the Includes almost all the
Diameter ranges named veins and their named veins and their
VEINS principal tributaries principal tributaries
from 1mm or less Diameter ranges from 1-9 Diameter ranges from >10
mm mm

Consist of endothelium and Similar to medium veins

Tunica thin subendothelial layer except larger
intima with minimal amounts of
connective tissue
Have a luminal Composed of small Similar to medium veins
Tunica diameter of at bundles of circularly except larger
arranged smooth muscles
media least 50 um and is thinner than arteries
of the same caliber
Thicker than Forms the bulk of the wall Very thick and consists of
arteries but has three layers:
significantly ▪ internal zone of
dense fibroelastic
smaller tunica
connective tissue
media
▪ middle zone of
Tunica
smooth muscle fibers
adventitia ▪ outer zone consisting
of a coarse network
of collagen and
elastic fibers
Well supplied by vasa
vasorum
 Modifications in the
Organization of Blood Vessels
Arteriovenous
anastomoses ( AV
Shunt)
• Found in skin of the
palm, sole, lip and the
nose
• Venules connect
directly to arterioles by-
passing the capillaries
Lymphatic System
Lymphatic System
• Fluid from the interstitial space enters the lymph
vascular system through the lymphatic
capillaries and become known as lymph
• Lymph is a milky substance which aside form
water and proteins, contains lymphocytes and
fat droplets.
• Unlike blood capillaries that are connected at
either ends to arteries and veins, lymphatic
capillaries
• start blindly
• branch and anastomose more freely
• more variable in shape and caliber
Functions
• The pressure induced by the heart within
the capillaries lead to the escape of some
water and plasma proteins into the
interstitial space
• It is the function of the lymphatic system to
collect these escapees from plasma and
return them to the venous side of the
circulation
Lymphatic vessel
• Only slightly thicker than the wall of
lymphatic capillaries
• Interrupted along their course by lymph
nodes
• In lymph nodes, lymph is filtered by the
phagocytes. Some lymphocytes stay in the
lymph nodes while some rejoin the
circulating pool
Lymphatic ducts
• All lymphatic vessels drain into two
lymphatic ducts
• Right lymphatic duct
• drains into right subclavian vein
• drains the right side of the body above the
diaphragm
• Thoracic duct
• collect lymphs from parts of the body not served by
tributaries from the right lymphatic duct
• drains into left subclavian vein