i want 30 mcq with their model answer below each question about Objectives
Recognize the histological structure of the heart wall. Identify the impulse conducting system of the heart. Describe general microscopic structure of blood vessels wall.Circulatory system
Blood vascular system
(Cardiovascular system)
Heart
Blood
vessels
Lymphatic vascular system
Lymphatic
capillaries
Lymphatic
vesselsHEART
• It is a muscular organ.
• It has 4 chambers (2 atria and 2
ventricles).
• It pumps and distributes blood through
a series of closed vessels in the body.The wall of heart consists of three layers
Inner layer: Endocardium
Middle layer: Myocardium
Outer layer: EpicardiumLayers of the heart wallThe Endocardium
consists of 3 layers:
An inner layer
of
endothelium
(simple
squamous
epithelium).
& supporting
C.T.
Myoelastic
layer
A middle layer
(myoelastic layer)
of connective
tissue, having
elastic fibers and
scattered smooth
muscle cells
A deep layer
of connective
tissue called
subendocardial
layer.
Subendocardial
layer
Purkinje fibers
Endothelium
Branches of impulse-conducting system of the heart
are located in the subendocardial layer.
EndocardiumThe Myocardium
❑The thickest layer.
❑It consists of cardiac muscle fibers
embedded in richly vascularized, loose
connective tissue (endomysium).
❑The myocardium is much thicker in the
walls of the ventricles, particularly the
left, than in the atrial walls (because
ventricles require strong force to pump
blood through the systemic and
pulmonary circulations).Intercalated
disk
Myocardium
LS
Branching and
anastomosing
cardiac muscle
fibers
Central
nuclei
Blood
capillaries
Cardiac
muscle
fibers
TSThe Epicardium
❖It is the visceral layer of serous pericardium.
❖It consists of mesothelium (simple squamous
epithelium) supported by a layer of loose
connective tissue and adipose tissue that
cushions the heart.
❖Containing coronary blood vessels and
autonomic nerves.
Mesothelium
C.T.
Fat cells
Coronary
vessels
MyocardiumEpicardium
Cardiac muscle
fibers
nerve fibers
Adipose tissue
Coronary blood
vesselsThe pericardium
Fibrous Pericardium
Dense Fibrous C.T.
Serous pericardium
Visceral Layer
= Epicardium
Fibrous
pericardium
Parietal layer
Formed by
reflection of the
epicardium back at
the great vessels
entering and
leaving the heart.Pericardial cavity
❖The space between the visceral and
parietal layers.
❖It contains a lubricant fluid
produced by serous mesothelial
cells of both layers.
❖This fluid prevents friction within
serous pericardium.Fibrous skeleton of the heart
Definition: Regions of dense irregular connective tissue
covered by endothelium.
Sites:
❑Valve rings (surrounds valves orifices).
❑Valve cusps.
❑Chordae tendineae.
❑Membranous part of the interventricular and interatrial septa.
Functions:
✓ Anchoring and supporting the heart valves.
✓ Providing firm points of insertion for cardiac muscle.
✓ Helping coordinate the heartbeat by acting as an electrical
insulator preventing the free flow of electrical impulses
between atria and ventricles.
Chordae
tendineaeHeart valves
Folds of endocardium that
prevent backflow of the blood
➢ Consists of fibroelastic C.T.
core
➢ Covered by a thin layer of
endothelium continuous
with that lining the heart
chambers and great
vessels.
Valve cusps are normally
avascular (have no blood
vessels)
Endothelium
Lt Ventricle
Lt Atrium
A valve cusp
EndotheliumImpulse conducting system of the heart
• Consists of modified cardiac muscle cells.
• Site: within the subendocardial layer.
• Function: generation and propagation
of waves of depolarization that spread
through the myocardium to stimulate
rhythmic contractions.Impulse conducting system of the heart
❖Includes:
✓Sinoatrial (SA) node (pacemaker)
✓Atrioventricular (AV) node.
✓AV bundle (Bundle of His).
✓Rt & Lt bundle branches.
✓Purkinje fibers
(Subendocardial conducting network)
Arise at the apex of the heart as final
divisions of Rt and Lt bundle branches.
Cells of SAN and AVN are smaller than the
contractile atrial cardiac muscle cells.
Cells of AV bundle, bundle branches and Purkinje
fibers are larger than contractile ventricular cardiac
muscle cells.Purkinje fibers
➢ Modified cardiac muscle fibers specialized for impulse
conduction.
➢ Structure:
✓ Size: larger than the adjacent contractile muscle fibers.
✓ Nuclei: one or two large, rounded & centrally located.
✓ Sarcoplasm:
▪ Its center is pale-stained, as it is filled with glycogen
that dissolve during H&E staining.
▪ Sparse (few) myofibrils are displaced peripherally by
abundant glycogen.
✓ Joined by intercalated discs specialized for impulse
conduction not contraction (desmosomes and gap
junctions).Types of blood
vessels
Arteries
Veins
Arteriovenous
connection
Small vein
Venule
Arteriole
Small arteryGeneral structure of blood vessels wall Except capillaries
The walls of arteries and veins are composed of
three layers called tunics
• Tunica intima: the innermost layer in contact
with blood.
• Tunica media: the middle layer.
• Tunica adventitia: the outermost layer.Tunica Intima
❖ Consists of:
✓ Endothelium (simple squamous epithelium)
resting on basal lamina & joined by tight junction.
✓ Subendothelial CT: a thin layer of loose connective
tissue sometimes containing smooth muscle fibers
✓ Internal elastic lamina: Found in arteries.
- It is a fenestrated sheet of elastin separating
tunica intima from media.
- Appears as wavy pink line in H&E.
- N.B. Fenestrations or holes allowing better
diffusion of substances from blood deeper into
the wall.
The innermost layer of the vesselEndothelial cells with their
long axis parallel to the
direction of blood flow
Internal elastic lamina:
▪ Well developed in muscular arteries
and absent in arterioles.
▪ Prevent occlusion of arteries.
Endothelium
Tunica
Intima
Internal elastic laminaTunica Media ❖The middle layer of the vessel wall consists of:
Concentric layers of smooth muscle cells
Elastic fibers
(Fenestrated elastic lamellae)
Reticular fibers
Proteoglycans
Produced
by vascular
smooth
muscle
cells
External elastic lamina: found in arteries
It is a layer of elastin that separates
tunica media from adventitia.Concentric
layers of
smooth
muscle cellsFenestrated elastic lamellae
Smooth
muscle cells
Tunica mediaTunica Adventitia (tunica externa) ❖ the outermost connective tissue layer
❖ Consists of
longitudinally arranged
collagen fibers (type I)
Elastic fibers
Fibroblasts
Vasa vasorum
(vessels of the vessel)
Nervi vasorum
(vasomotor nerves)
In adventitia of
large vesselsLongitudinally
arranged
collagen fibers
(type 1)
FibroblastsVasa vasorum
(vessels of the vessel)
❑They are arterioles, capillaries, and venules in the
tunica adventitia and outer part of tunica media of
large vessels.
❑Provide these tunics with nutrients and oxygen and
remove waste products.
❑Vasa vasorum are more numerous in large veins
than arteries (why??)Nervi vasorum
(vasomotor nerves)
➢ Network of autonomic nerve fibers.
➢ control contraction of the smooth
muscle in the vessel walls.
➢ Their density is greater in arteries
than veins.Tunics of blood vessel wall
Tunica intima
Tunica media
Tunica adventitiaTissues found in vascular wall & their Functions
Walls of arteries and veins contain: smooth muscle, connective tissue & endothelial lining
(epithelial tissue).
Smooth muscle fibers
Permit vasoconstriction
and vasodilation
regulating the blood
pressure.
Extracellular matrix
production (mainly of
tunica media).
Elastic fibers
Expansion of the
vascular wall under
pressure.
Collagen fibers
Subendothelial C.T.
T. media
T. adventitia
Mainly those of tunica
adventitia, prevent over
expansion of the arterial
wall beyond physiologic
limits during systole of
the cardiac cycle.Semipermeable
barrier
Regulation of
cell growth
Regulation of
local immune
responses
Endothelial
cells
Functions
Regulation of
local vascular
tone and blood
flow
Nonthrombogenic
surfaceSemipermeable
barrier
By mediating bidirectional
exchange of molecules by:
▪ Simple diffusion.
▪ Active transport.
▪ Receptor-mediated
endocytosis.
▪ Pinocytosis & transcytosis
Nonthrombogenic
surface
By secreting
antithrombogenic agents
(such as heparin)
Regulation of
local vascular
tone and
blood flow
by secreting vasoconstrictors
(stimulate smooth muscle
contraction) as
angiotensin converting enzyme
or vasodilators (stimulate smooth
muscle relaxation) as nitric oxideRegulation of local immune responses
Endothelial cells of postcapillary venules express on their luminal surface adhesion molecules (as selectin), that regulate leukocyte migration to sites of injury or infection.
Regulation of cell growth
Secretion of growth-stimulating factors e.g. Vascular endothelial growth factor (VEGF) that: -stimulates formation of vascular system from embryonic mesenchyme (vasculogenesis) -maintains vasculature in adults (repair of vascular damage during wound healing).