histology of cardiovascular system

1. Microstructure of
CARDIOVASCULAR
SYSTEM
Dr.Saima Masood
Assistant Professor,
Anatomy &Histology.

2. Learning outcomes
1. HISTOLOGY OF HEART
• Understand the structure of heart wall
• understand the significance of cardiac
muscles
• understand the significance & organization
of impulse conducting system of heart
• Identify purkinjie fibers (conducting fibers)
2. HISTOLOGICAL FEATURES OF ARTERIES,
VEINS AND CAPILLARIES

3. heart
• The largest organ of mediastinum
– Located between the lungs
– Apex lies to the left of the midline
– Base is the broad posterior surface

5. Heart chambers
• Four chambers
• Right and left atria - Superior chambers, receive
blood from the pulmonary and systemic circuits
• Right and left ventricles - Inferior chambers, the
pumping chambers of the heart

6. atria
• Right Atrium (RA)-
right upper chamber-
receives blood from
body- deoxygenated
blood
• Left Atrium (LA)-
left upper heart.-
receives oxygenated
blood from lungs and
sends it to the left
ventricle

7. ventricles
• Right ventricle- (RV)-
right lower chamber-
receives blood from right
atrium and sends it to
the lungs through
pulmonary artery
• Left Ventricle (LV)-
lower left chamber-
receives blood from left
atrium and sends it
through the aorta to the
body.

8. Heart wall
• Walls differ in thickness
– Atria – thin walls
– Ventricles – thick walls
• Left ventricle – three times thicker
than right
– Exerts more pumping force
– Flattens right ventricle into a
crescent shape

9. Heart
The thick wall of the heart is primarily composed of cardiac muscle
cells capable of spontaneous rhythmic contractions that pump blood
into the vascular system.
Endocardium: The inner layer of the heart - continuous with the
tunica intrerna of the large blood vessels entering and leaving the
heart
Myocardium: The middle contractile muscular layer
Epicardium: Thickest/outermost layer of the organ
Cardiovascular System

11. Endocardium
• lines the ventricles and atria completely and covers the
cardiac valves and associated structures
• The endocardium usually consists of three layers.
• 1. A continuous endothelium forms the innermost layer.
• 2.The subendothelial layer, located beneath the
endorhelium is composed of dense irregular connective
tissue with collagen and elastic fibers and occasional
smooth muscle cells. Elastic fibers are particularly
abundant in the atrial walls .
Cardiovascular System

12. Endocardiun
• 3.The subendocardial connective tissue is continuous
with that of the myocardium.
• In some locations, modified cardiac muscle cells of the
cardiac impulse conduction system are present in the
subendocardial layer.

17. Myocardium
• The middle and thickest layer of the heart is the
myocardium, which is composed of:
• A .bundles of cardiac muscle cells
• B .branches of cardiac conduction fibers
• C. an extensive capillary network
• D. the cardiac skeleton.
• Bundles of cardiac muscle cells are embedded in
loose connective tissue that contains a dense
capillary network, lymph vessels, and autonomic
nerve fibers.
Cardiovascular System

18. Myocardium (contd.)
• The amount of interstitial connective tissue is
subject to local variations and is greater in the
myocardium of the right ventricle when compared to
that of the left ventricle.
• The atrial cardiac muscle cells are usually smaller
than the ventricular cardiac muscle cells. In atrial
cardiac muscle cells, numerous specific atrial
granules.
• containing atrial natriureric peptide (ANP) are
present. ANP plays an important role in fluid
homeostasis .

19. myocardium
• Cardiac muscle

20. Myocardium(cardiac Skeleton)
• The musculature of the atrial and ventricular walls is
inserted into the cardiac skeleton, which is made up
of three parts:
• (1) the fibrous rings (annuli fibrosi),
(2) the fibrous triangles (trigona fibrosa cordis), and
(3) the fibrous (or membranous) part of the
inrerventricular septum.
• The fibrous rings are composed of intermingling
bundles of collagen and a few elastic fibers that
surround the atrioventricular, aortic, and pulmonary
trunk openings.
Cardiovascular System

21. Components of C.Skeleton
• The fibrous triangles are small areas of connective
tissue that fill the spaces between the atrioven
tricular openings and the base of the aorta.
• The nature of this connective tissue is species- and
age-dependent. The triangles may be predominantly
dense, irregular connective tissue (in pigs, cats, and
rabbits), fibrocartilage (in dogs) hyaline cartilage (in
horses), or bone (in large ruminants).
• The fibrous part of the interventricular septum
consists of collagen fiber bundles.

22. Fibrous triangles
• The fibrous triangles are small areas of connective
tissue that fill the spaces between the
atrioventricular openings and the base of the aorta.
• The nature of this connective tissue is species- and
age-dependent. The triangles may be predominantly
dense, irregular connective tissue (in pigs, cats, and
rabbits), fibrocartilage (in dogs) hyaline cartilage (in
horses), or bone (in large ruminants).
• The fibrous part of the interventricular septum
consists of collagen fiber bundles.

23. Chondrocytes
Cardiac Skeleton, Dog

24. Epicardium and Pericardium
• The myocardium is covered externally by the
epicardium (visceral serous pericardium).
• The outermost layer is mesothelial cells, which line
the pericardial cavity.
• Under this epithelium is a loose connective-tissue
layer rich in elastic fibers that forms protective
sheaths around blood vessels and nerves.
• The connective tissue, which is often rich in
adipocytes, is particularly abundant around the large
coronary blood vessels.

25. Pericardium (contd.)
• The parietal pericardium consists of an
innermost mesothelial cell layer resting on a
thin layer of loose connective tissue, which
fuses with the fibrous peri cardiurm, a thick
layer of collagen fiber bundles and elastic
fibers.

27. Visceral and Parietal Pericardium
Parietal pericardium
Visceral pericardium
Pericardial cavity
Myocardium

28. The Pericardial cavity
• Located between the visceral and parietal
serous pericardium, the pericardial cavity
contains serous fluid that lubricates the
mesothelial surfaces, allowing frictionless
cardiac movement.

29. Conductive System of the Heart

30. Conduction system
• The specialized heart cells of the cardiac
conduction system generate and
coordinate the transmission of electrical
impulses to myocardial cells.

31. Components of the Conduction System
• Sinoatrial Node(pacemaker)
– located in back wall of the right atrium near the
entrance of vena cava.
– The sinoatrial node is composed of a
network of thin, branching nodal muscle
cells that contain scarce myofibrils and lack
intercalated disks.

32. Components of the Conduction
System Continued ….
• Atrioventricular Node
– located in the bottom of the right atrium
near the septum.
– The atrioventricular node is
composed of irregularly arranged,
small, branching nodal muscle
fibers, the morphology of which is
similar to those of the sinoatrial
node.

33. Cardiac Conduction System
Fibers in the atrioventricular bundle are also
known as cardiac conduction fibers (Purkinje fibers).
These fibers are readily identified by their large
diameter, large central spherical nucleus, and scarce
peripheral myofibrils.
• The central area of the cytoplasm is rich in
glycogen and creates a light-staining hallow around
the nucleus.
Cardiovascular System

35. Purkinje Cells
Purkinje Cells, l.s
Purkinje Cells, x.s

36. Conduction System =
Purkinje Fibers
Purkinje Fibers
Muscle

37. HISTOLOGY OF ARTERIES, VEINS &
CAPILLARIES

38. • Vessels have three basic components
(from inside to outside):
1.Tunica intima – a simple squamous
epithelium, called the endothelium,
with underlying loose connective tissue
2.Tunica media – a thicker layer with
smooth muscle and elastic fibers
3.Tunica externa (adventitia) – dense
connective tissue

39. elastic arteries
muscular arteries
arterioles
capillaries
large vein
medium-sized vein
venules
Arteries – ALWAYS carry blood away from heart
Veins – ALWAYS return blood to heart,
contain about 2/3 body's blood at any given time

40. Large arteries (also called elastic arteries or conducting
arteries)
• Include the aorta and its largest main branches.
• a. Tunica intima - thin (relative to other layers in this type of
vessel)
1. Endothelium
2. Subendothelial layer contains some smooth muscle, elastic
fibers, collagen fibers
3. Internal elastic lamina - not as distinct as in other arteries
• c. Tunica media – thick. constitutes the greater part of the
vessel wall. It is made up of multiple elastic lamellae alternating
with thin layers of circularly oriented smooth muscle . The
boundary between the tunica intima and media is not readily
defined.

41. Elastic Artery (contd.)
. Tunica adventita - thin;
essentially lacks elastic lamellae, and is mainly loose
connective tissue and blood vessels (vasa vasorum).

42. Large or elastic arteries
A = tunica intima (interna) B = tunica media C = tunica adventitia (externa)
Aorta–section – H&E – 4x objective

44. Medium to small arteries (also called muscular arteries)
• a.Tunica intima - thin
1. Endothelium
2. Thin subendothelial layer consisting of scattered fine
collagen and elastic fibers and a few fibroblasts
3. Internal elastic lamina - very distinct, usually folded
• c. Tunica media - thick
1. Circular smooth muscle, 5 - 40 layers
2. Small amount of CT with collagen fibers and elastic fibers
(longitudinal orientation) between muscle
3. Thickness decreases as diameter of vessel decreases
• d. Tunica adventita - thick; loose CT

48. ARTERIOLES
• In arterioles, the tunica intima consists of a
continuous endothelium and a very thin
subendothelial layer.
• A thin, fenestrated internal elastic lamina is
present in larger arterioles but absent in
terminal arterioles.
• the tunica media consists of 2 layers of
smooth muscle cells. But in the smallest
arterioles there is a single layer.
• The tunica adventitia is a thin sheath of
connective tissue, which is not easily defined.

49. Large veins –
vena cavae and larger branches
a. Tunica intima - thicker
• Endothelium
• Thin subendothelial layer
• b. Internal elastic lamina - usually distinguishable
• c. Tunica media - thin, poorly developed; mostly CT; little
smooth muscle
• d. Tunica adventita - very thick; moderately dense CT with
spirally arranged collagen fibers, elastic laminae, longitudinal
smooth muscle

51. Pulmonary trunk & aorta
and their major branches
Superior & inferior
vena cava and their
tributaries
Largest, conducting arteries – lead directly
from heart, subject to high pressures

52. Small to medium veins
• a. Tunica intima - thin
1. Endothelium
2. Thin subendothelial layer
3. May be folded to form valves
• b. Tunica media - thin; circular smooth muscle, collagen
fibers, some elastic fibers
• c. Tunica adventita - well developed; loose CT with
longitudinally arranged collagen and elastic fibers, bundles of
longitudinal smooth muscle

53. External and internal
carotids, brachial &
femoral arteries
External and internal
jugular, brachial &
femoral veins
 2 - 9 mm  ~ 4 mm

56. Venules
• Size varies from 10 microns (post-capillary venules) to 1 mm
(muscular venules)
• Larger diameter than capillaries; consist of endothelium
surrounded by pericytes

57.  ~ 10-50 µm
 ~ 30 µm

58. CAPILLARIES
• Capillaries average from 9 to 12 µ m in
diameter, just large enough to permit passage
of cellular components of blood. The wall
consists of extremely attenuated endothelial
cells.

59. Capillaries
Intestinal mucosa Choroid plexus,
endocrine glands, kidneys
Most body regions
Only endothelium
Variably permeable
somewhat
permeable
Characterized by circular fenestrae or pores
that penetrate the endothelium -permit
exchange of larger molecules.
 ~ 8 µm

60. Sinusoids
• Resemble fenestrated capillaries, yet
1. irregular shapes
2. have longer pores
3. thinner (or no) basement membranes
• Blood movement very slow
• Found in the liver, heart, etc. sometimes
called sinusoidal capillary.

61. Capillaries
Arrowheads = capillaries
Striated muscle – cross section – H&E – 40x objective
Capillaries have very small diameters and walls that consist of
only a single layer of endothelium.

62. A few keys to
differentiate various
features of vessels:
1. The major
histological difference
between arteries and
veins lies in the
thickness and
muscularity of the
tunica media;
arteries have a
thicker, more
muscular tunica
media
2. Capillaries are
composed simply of
endothelial cells,
without a tunica
media or adventitia

65. Self-check: Identify the outlined structure

67. Self-check: Identify the outlined structures.

69. Self-check: Identify the structure indicated by the arrows (advance
slide for answer)

71. Self-check: Identify the structure indicated by the arrows