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HEART AND VASCULAR SYSTEM
CAPILLARIES
Function = exchange of gas, nutrients, metabolites, water
Structure = Endothelium +pericyte + basement
membrane
Pericyte =undifferentiated cells that becomes smooth
muscle or fibroblast
CAPILLARY SYSTEMS
Vary regarding:Diameter
3-4 μm to 30-40 μmAbundance
Heart, liver > TendonArterio-venous shunts
Direct connections between arterial + venous system
Types of endothelium
1. Continuous: 1. Most common 2. Basement membrane is present3. Uninterrupted lining with tight junctions
2. Fenestrated: 1. Found in gut, kidney, endocrine glands2. Basement membrane is present
3. Large pores
From: Wheater’s Functional Histology, B Young and JW Heath
3. Discontinuous: No basement membrane Large diameter Continuous interface between lumen and
surrounding tissue Sinusiods of liver, spleen and bone marrow
ARTERIES AND VEINS
Inner
Tunica intima: endotheliumTunica media: elastic and/or smooth muscleTunica adventitia: collagen, elastic fibres
Outer
ARTERIESARTERIOLI
Control blood flow by dilation or constriction
Tunica intima Endothelium
Lamina elastica interna (2 or more layers of a fenestrated elastic membrane)
Tunica media Few layers smooth muscle cells
Tunica adventitiaLoose connective tissue
MUSCLE/MEDIUM SIZED ARTERIES
Blood flow to organs
Tunica intima:1. Endothelium2. Either Lamina elastica interna
or Subendothelial layer of thin loose connective tissue
MUSCLE/MEDIUM SIZED ARTERIES
Tunica media: 1. Most prominent2. Spirally arranged smooth muscle3. Little connective tissue4. Lamina elastic externa
MUSCLE/MEDIUM SIZED ARTERIES
Tunica adventitia: Usually thinner, loose connective tissue
lamina elastica interna
smooth muscle of tunica medialamina elastica externa
ELASTIC ARTERIES
Pulmonary trunk/aorta + major branches
Stretch/systole/heart contracts/blood ejected
from ventricles – diastole/recoil
Tunica intima:1. Endothelium 2. Subendothelium layer
3. Lamina elastica interna
ELASTIC ARTERIES
Tunica media:1. 40-70 fenestrated concentric layers of
elastic fibre2. Amorphic ground substance with collagen
& smooth muscle cells
Tunica adventitia: 1. Irregular connective tissue, few elastic fibers
endotheliumsubendothelium layerlamina elastica interna
tunica media
tunica adventitia
tunica intima
THE VENOUS SYSTEM
Thinner walls than arteries, larger lumen
VENULESTunica intima:
Endothelial layer
Tunica media: Pericytes ____ smooth muscle
fibres Tunica adventitia:
Longitudinal collagen fibres
SMALL /MEDIUM VEINS
Small= 0.2-1 mm + Medium =1-10 mm
Tunica intima:1. Endothelium 2. Subendothelial layer 3. Lamina elastica interna (poorly developed)
Tunica media: 1. Layers of circular smooth muscle fibres
2. Loose connective tissue
SMALL /MEDIUM VEINS
Tunica adventitia: 1. Thick, longitudinal collagen fibres
2. Loose connective tissue3. Elastic fibres4. Fibroblasts and macrophages
Valves Folds intima strengthened with connective tissue & elastic fibres
NB! Note difference to heart valve structure
LARGE MUSCULAR VEINS
Tunica intima: Similar to medium veins
Tunica media: Similar to medium veins
Tunica adventitia: Thick, bundles longitudinal collagen Elastic fibresSmooth muscle Numerous vasa vasorum
endothelium
subendothelial layer
lamina elastica interna
smooth muscle bundles
collagen fibers
tunica media tunica adventitia
tunica intima
From Basic Histology, 4th Ed, LC Junquera, J Carneiro
LYMPHATIC SYSTEM
Begin blind in connective tissue as lymph capillariesLarge pores- cells, bacteria and macromolecules
LYMPH CAPILLARIES
Similar structure to blood capillaries
Large lumen
No pericytes
Basal membrane is often absent
SMALL/LARGER LYMPH VESSELS
Layers difficult to distinguish
Tunica intima: Similar to large veins
Tunica media: Concentric/diagonal muscle bundles
Tunica adventitia: 1. Longitudinal/diagonal bundles of smooth muscle 2. Bundles of collagen fibres3. Outer layer of collagen fibres
From Basic Histology, 4th Ed, LC Junquera, J Carneiro
NERVE SUPPLY
Most blood vessels have a well developed nerve supply
Efferent, Afferent, Motor, Baro and chemoreceptors
HEART
Tunica intima= Endocardium (inner)
Tunica media = Myocardium (middle)
Tunica adventitia= Epicardium (outer)
pericardium
Epicardium (t.a.)
Myocardium (t. m.)
Subendocardium (s.e.)
Endocardium (t.i.)
A: ENDOCARDIUM(inner/contact with blood)
1. Endothelium 2. Delicate layer of collagenous tissue 3. Robust fibro-elastic layer -contains
smooth muscle cells
B: SUBENDOCARDIUM1. Loose connective tissue
2. Fat cells 3. Purkinje fibers4. Small blood vessels+ nerves +
branches of conducting system
C: MYOCARDIUMBundles of cardiac muscle (thickest)
Pericardium
Epicardium (t.a)
Myocardium (t. m.)
Subendocardium (s.e.)
Endocardium (t.i.)
D: EPICARDIUM (Outer)External 1. Mesothelium - flattened epithelial cells 2. Fibroelastic tissue (thin) 3. Broad layer adipose tissue4. Coronary vessels + autonomic nerves pass
through the epicardium to supply the myocardium
pericardium
Epicardium (t.a.)
Myocardium (t. m.)
Subendocardium (s.e.)
Endocardium (t.i.)
SKELETON OF THE HEART
Thick fibrous rings at the origin of aorta + pulmonary arteries Connected by trigonum fibrosum with rings at arterio-ventricle openings
VALVES
Plate/flap of fibroelastic connective tissue Extending from the fibrous skeleton Covered by endocardium
CONDUCTING SYSTEM
The coordinated contraction of the myocardium
is mediated by a specialized conducting
system of modified cardiac muscle fibers
1. SINOARTRIAL (SA) NODE - PACEMAKER REGION (Right atrium (top))
2. ATRIOVENTRICULAR (AV) NODE (Right atrium (bottom))
3. ATRIOVENTRICULAR BUNDLE (BUNDLE OF HISS) (interventricular septum)
SA Node
AV Node
HOW DOES IT WORK?
Impulse starts at SA node Spreads throughout atrium Causes contraction Blood into ventricles
Then! Impulse spreads to AV node
Passed via bundle of Hiss Divides into smaller branches bundles
of Purkinje fibers
Then!Passes to subendocardial connective tissue Penetrates the ventricular myocardiumDepolarization and contraction
LA
RA
LVRV
SA Node
AV Node
Bundle of Hiss
Right branch
Left branch
A: SINOARTRIAL (SA) NODE
Group of collagen & elastic fibresWell developed capillary system In middle:
Nodal myocyotes or P cells Borders on narrow transitional cells Border of the Purkinje Cardiac muscle cells
Region contains many axons of sympathetic and parasympathetic nervous system
Impulse moves from the → P-cells (Pale cells/pacemakers)
→ Transitional cells:fewer myofibrils→ Purkinje cells: large, abundant glycogen,
few myofilaments, extensive gap junctions
→ Cardiac muscle cells
B: ATRIOVENTRICULAR(AV) NODE
Right atrium, microscopically similar to the SA node
C: ATRIOVENTRICULAR BUNDLE (BUNDLE OF HISS)
Longitudinal transitional cells of AV node Down the interventricular septum Divide into left and right bundle Moves through subendocardium
C: ATRIOVENTRICULAR BUNDLE (BUNDLE OF HISS)
Half way down septum, transitional cells are replaced with Purkinje cells Two branches divide further, form the Purkinje cell network
Contact between Purkinje cells and cardiac muscles cells of myocardium
Practical
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