Transcript BLOOD VASCULAR SYSTEM - University of Pretoria

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 μm
Abundance
Heart, liver > Tendon
Arterio-venous shunts
Direct connections between
arterial + venous system
Types of endothelium
1.
Continuous:
1. Most common
2. Basement membrane is present
3. Uninterrupted lining with tight junctions
2. Fenestrated:
1. Found in gut, kidney, endocrine glands
2. 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: endothelium
Tunica media: elastic and/or smooth muscle
Tunica adventitia: collagen, elastic fibres
Outer
ARTERIES
ARTERIOLI
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 adventitia
Loose connective tissue
MUSCLE/MEDIUM SIZED ARTERIES
Blood flow to organs
Tunica intima:
1.
2.
Endothelium
Either Lamina elastica interna
or Subendothelial layer of thin loose connective tissue
MUSCLE/MEDIUM SIZED ARTERIES
Tunica media:
1.
2.
3.
4.
Most prominent
Spirally arranged smooth muscle
Little connective tissue
Lamina elastic externa
MUSCLE/MEDIUM SIZED ARTERIES
Tunica adventitia:
Usually thinner, loose connective tissue
lamina elastica interna
smooth muscle of
tunica media
lamina elastica externa
ELASTIC ARTERIES
Pulmonary trunk/aorta + major branches
Stretch/systole/heart contracts/blood ejected from
ventricles – diastole/recoil
Tunica intima:
1.
2.
Endothelium
Subendothelium layer
3.
Lamina elastica interna
ELASTIC ARTERIES
Tunica media:
1. 40-70 fenestrated concentric layers of elastic
fibre
2. Amorphic ground substance with collagen &
smooth muscle cells
Tunica adventitia:
1.
Irregular connective tissue, few elastic fibers
endothelium
tunica intima
subendothelium layer
lamina elastica interna
tunica media
tunica adventitia
THE VENOUS SYSTEM
Thinner walls than arteries, larger lumen
VENULES
Tunica 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.
3.
4.
Loose connective tissue
Elastic fibres
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 fibres
Smooth muscle
Numerous vasa vasorum
tunica intima
endothelium
subendothelial layer
lamina elastica interna
collagen fibers
smooth muscle bundles
tunica media
tunica adventitia
From Basic Histology, 4th Ed, LC Junquera, J Carneiro
LYMPHATIC SYSTEM
Begin blind in connective tissue as lymph capillaries
Large 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 fibres
3. 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.
2.
3.
Endothelium
Delicate layer of collagenous tissue
Robust fibro-elastic layer -contains smooth
muscle cells
B: SUBENDOCARDIUM
1. Loose connective tissue
2.
3.
4.
Fat cells
Purkinje fibers
Small blood vessels+ nerves + branches of
conducting system
C: MYOCARDIUM
Bundles of cardiac muscle (thickest)
Pericardium
Epicardium (t.a)
Myocardium (t. m.)
Subendocardium (s.e.)
Endocardium (t.i.)
D: EPICARDIUM (Outer)
External
1.
2.
3.
4.
Mesothelium - flattened epithelial cells
Fibroelastic tissue (thin)
Broad layer adipose tissue
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 myocardium
Depolarization and contraction
SA Node
LA
RA
Bundle of Hiss
AV Node
RV
Right branch
LV
Left branch
A: SINOARTRIAL (SA) NODE
Group of collagen & elastic fibres
Well 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
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