HISTOLOGY OF THE
CARDIOVASCULAR SYSTEM
Dr Anastasiya Spaska
Objectives
• By the end of this lecture, students are supposed:
• Provide the general histological layout of blood vessels
• Identify and describe the histological structure of the three layers foundin
the large (elastic) arteries
• Compare and contrast the histological structure of the medium sized
(muscular) artery with medium sized vein
• Compare and contrast the histological structure of the arterioles with
venules
• Provide the general histological structure and ultrastructure of the three
types of capillaries
• Explain histology of the heart
• Identify structural features of the lymphatic capillaries
Cardiovascular system overview
 Major constituencies/components
• Heart
• Blood vessels
• Lymphatic vessels
The walls of the heart
• Cardiac muscle
• Fibrous skeleton
• Impulse-conducting system
 The fibrous
skeleton gives
origin and
insertion of the
heart
muscle making a
structural
framework of the
valves.
•
4 fibrous rings
•
2 fibrous trigones
•
Membranous part of the Inter arterial and
Interventricular septae (no cardiac muscle)
 Composition
•
Dense irregular connective tissue
 Function
• Attachment site for 4 valves and
myocardium of atria and ventricles
•
Electrical insulation
Impulse conduction system
• Initiation and propagation of electrical impulses for cardiac
muscle contraction
• Intrinsic regulation of the heart
• Electrical activity initiated in the heart
• SA node 60-100/min
• Internodal tracts
• AV node
• AV bundle (of His)
• Purkinje fibers
 Structure and function
• Modified cardiac muscle cells
• Larger than normal cardiac muscle cells
• 4x faster
• Convey impulses across fibrous skeleton
• Coordinates contractions of atria and ventricles
Walls of the heart
 EPICARDIUM
• Mesothelium + CT (adipose tissue)
 MYOCARDIUM
• Cardiac muscle
Contractile (typical) myocardiocytes
Conducting (atypical) myocardiocytes
Atrial endocrinocytes (natriuretic peptide)
 ENDOCARDIUM
• INNER LAYER - Endothelium and
subendothelial loose CT
• MIDDLE LAYER - CT and smooth muscle cells
• DEEPER LAYER-SUBENDOCARDIUM - CT
and Purkinje fibers
Wall of the heart
Think pair share
 Which epithelium forms the endothelium of heart and bloodvessels?
 What functions endothelial cells execute?
Cardiac muscle
• Cardiomyocytes are striated, like skeletal muscle, as the actin and myosin
arranged in sarcomeres,
• usually have a single (central) nucleus.
• often branched, and are tightly connected by intercalated discs- form syncythium
ENDOCARDIUM
EPICAR
DIUM
 TAKE NOTE OF THE COMPONENTS
OF THE EPICARDIUM VS
ENDOCARDIUM.
MYOCARDIUM
 WHAT ARE THE DIFFERENCES?
DL
ML
IL
INNER LAYER - Endothelium and subendothelial loose CT
MIDDLE LAYER - CT and smooth muscle cells
DEEPER LAYER-SUBENDOCARDIUM - CT and Purkinje fibers
 Purkinje fibres
• The Purkinje fibers are specialised
conducting fibers
• composed of electrically excitable
cells.
• larger than cardiomyocytes with
fewer myofibrils and many
mitochondria.
• conduct cardiac action potentials
more quickly and efficiently than any
other cells in the heart.
General structure/organisation of blood vessels
 Tunica intima
• Endothelium and basal lamina (BL)
• Subendothelium (loose CT and occasional SM)
• Internal elastic membrane (IEM)
(in arteries and arterioles)
 Tunica media
• Circumferentially arranged smooth muscle cells
• Elastic and reticular fibers
• External elastic membrane (EEM)
 Tunica adventitia
• Collagen and elastic fibers
• Vasa vasorum
• Nervi vascularis
 Present in Large vessels
 Variation in these components characterises various types of
blood vessels
Layers/tunics of blood vessels
Classification of arteries:
1. Arterioles – relatively thin tunica media
2. Small and medium-sized (musculartype) arteries – prominent internal and
external elastic laminae
3. Large (elastic-type) arteries - tunica
media enriched with concentric elastic
laminae
Classification of veins:
1. Venules
2. Small and medium-sized veins
3.Large veins
Veins compared to arteries:
• Has irregular shaped lumen
• Consist valves
• Lack internal and external elastic laminae
• Tunica adventitia is predominating
• Wall is thicker and lumen larger then
these of corresponding artery
Elastic arteries (Aorta and pulmonary arteries)
 Tunica intima
• Endothelium and BL
• Subendothelium with collagen, elastic fibers and
smooth muscle
• Indistinct IEM
 Tunica media
• Broad fenestrated elastic lamellae (40-70 in adults) -
diffusion
• Smooth muscle adopts fibroblasts function
• EEM combines with TM
 Tunica adventitia
• Collagen and elastic fibers
• Fibroblasts and macrophages
• Vasa vasorum and Nervi vascularis
Muscular arteries= medium sized arteries
 Tunica intima
• Thinner with prominent internal elastic
membrane/lamina (IEM)
 Tunica media
• Predominant smooth muscle
• Very little elastic material
• No fibroblasts
• Recognizable external elastic membrane (EEM)
 Tunica adventitia
• Same thickness or thinner than TM
IEM
•
•
•
•
•
•
Smooth muscle, also called involuntary
Muscle shows no cross stripes under
microscopic magnification.
it consists of narrow spindle-shaped cells with
a single, centrally located nucleus.
unlike striated muscle, contracts slowly and
automatically.
smooth muscle fibers group in branching
bundles.
bundles do not run strictly parallel and
ordered, but consist in a complex system
Small arteries and arterioles
 Small artery
• Up to 8-10 SM layers
• IEM
 Arterioles
• 1-2 layers of SM
• Present or absent IEM
• Regulate blood amount
leading to capillaries
Capillaries
• Smallest blood vessels
• Form blood vascular networks
• Single layer of endothelial cells and BL
• FUNCTION: Two-directional exchange of fluid
containing metabolites, gases and waste
Classification of capillaries
 Continuous capillaries
 Features: presence of:
• Occluding junctions
• Pinocytotic vesicles - Transport
• Pericytes – Unspecialised cell
• Complete basement membrane
• Continuous endothelium
 LOCATION:
• Muscle, lung and CNS
 Fenestrated capillaries
 Features
• Fenestrations; some with diaphragm
• Pinocytotic vesicles
• Complete basal membrane
• Fenestrated endothelial cells
 LOCATION:
• Endocrine glands, gall - bladder and GIT
• Passage on macro molecules
Discontinuous capillaries
 Features
• Large in diameter and irregular in shape
• Basal Lamina partially or completely absent
 LOCATION:
• Liver, spleen and bone marrow
Think pair share
 Compare the 3 types of capillaries and indicate their locations
Venules
• Closely associated with arterioles
• Continuous endothelium
• Collapsed and irregular
• Thin wall adapted for fluid exchange and diapedesis
• With arterioles and capillaries form microvascular bed
Medium sized veins
• Valves to aloow unidirectional flow of blood
 Tunica intima
• Subendothelium with occasional SM
• Thin IEM
 Tunica media
• SM+collagen and elastic fibers
 Tunica adventitia
• Thick
• Collagen fibers and network of elastic fibers
Large veins
 Tunica intima
•
Endothelium + BM
 Subendothelium
•
Loose CT and smooth muscle
 Tunica media
•
SM + collagen fibers + fibroblasts
 Tunica adventitia
•
Bundles of longitudinal smooth muscle fibers
Collagen, elastic fibers and fibroblasts
Vasa vasorum
Large vein
Neurovascular bundle
Lymphatic vessels
• convey fluids from the
tissues to the bloodstream
• Unidirectional (from tissues)
• begin as “blind-ended”
lymphatic capillaries
• Endothelium and
discontinuous BL
• More permeable than blood
capillaries
• Valves
• Lymph nodes interspaced
along the vessels
• Lymphatic capillaries