CIRCULATORY
SYSTEM
BY:
DR. ANTOINETTE T.
LEUTERIO
SPECIFIC OBJECTIVES
• 1. Describe the histologic structures of the heart and blood vessels.
• 2. Identify the layers of the heart and blood vessels.
• 3. Explain the different types of blood vessels.
• 4. Enumerate the types, subtypes, and major functions of each circulatory system component.
• 5.Explain the three tunics that make up the walls of all circulatory system
• components, and know the tissue type in each tunic.
• 6. Compare circulatory system components in terms of size and wallstructure.
• 7. Relate the wall structure of each circulatory component to its major functions.
• 8. Describe the heart’s impulse-generating and conducting system in
• terms of structure, function, location, and how the impulse is conveyed
• to the cardiac muscle fibers.
• 9. Recognize the types of vessels present and
• identify all of their structural components microscopically
• 10.Distinguish between cardiac muscle and Purkinje fibers, and identify
• the endocardium, myocardium, epicardium, and valves of the heart microscopically
• 11.Predict the functional consequences of a structural defect
• in any circulatory system component.
Circulatory system
•Heart, blood vessels, & lymphatic
•Pulmonary & systemic circulation
•Endothelium
•Complete Circuit of Closed Tubes
- heart, arteries,capillaries,veins
- lymphatics
functions-
Neovascular bundle
Blood Vascular system
function: conducts nutrients,
oxygen, & hormones to all parts of the
body
CAPILLARIES
terminal arterioles and venules
fundamental vascular unit
devoid of layers of its walls
allow red blood cells to pass in single file
its lumen is lined by single layers of
endothelial cells
- polygonal endothelial cells
-vimentin ( fx)
- fasciae occludentes
Capillaries- selective permeability
-some diffuse and some actively
transported
(small & large pores)
-diapedesis
spongy meshwork
pinocytic vesicles
transverse sections
thin ring (nucleus)
CAPILLARIES
Functionally most important of all blood
vessels (nutrients & oxygen)
metabolic fxs of cap include the following
( endothelial cells)
a. angiotensin I - angiotensin II
b. deactivation of active substances
c. breakdown of lipoproteins
( triglycerides & cholesterol)
d. release of prostacyclin
Types of Capillaries
1.continuous(somatic) capillaries or type I
-lack fenestrae (1)
-numerous pinocytic vesicles (2)
-continuous BL (3)
-loc:nervous tissue, muscle, C.T.,
exocrine glands and lungs (4)
Types of Capillaries
2. Fenestrated(visceral) cap or type II
-with fenestrae (1)
-few PV (2)
-continuous BL (3)
-loc:endocrine glands, int., pancreas,
glomeruli of kidneys (4)
Types of Capillaries
3. Sinusoidal capillaries
-many large fenestrae (1)
-lack PV (2)
-discontinuous BL (3)
-loc:liver, spleen, BM, lymph
nodes (4)
Blood flow into cap beds
- from metarterioles or terminal
arterioles ( cap) to small venules
bypassing a cap bed
- arteriovenous anastomoses
- thermoregulation
False capillaries
definition
Sinusoids and rete mirabile
SINUSOIDS
-passages bet larger vessels
-BM laking
-Reticulo-endothelial system
RETE MIRABLE
-inserted in course of an arteriole or
venule
-uncommon
Precapillaries & Postcapillaries
definition
Larger than capillaries
Precapillaries (arterial cap)
-arterial side
-smallest( endo & smooth M)
postcapillaries(venous cap)
-venous side
-smallest (endo & C.T.)
Precapillaries & Postcapillaries
Fx.
-precapillary sphincters
( control flow through
capillary beds)
Structural Plan of Blood Vessels
All blood vessels except capillaries
Three concentric coats(tunics,layers)of wall
1.tunica intima(internal)
2.tunica media
3.tunica adventitia(external)
tunica intima
-innermost
-lined by endothelium
-subendothelial coat (fibroelastic)
-internal elastic membrane
Tunica media
-middle
-smooth muscle (circular)
-elastic fibers
Tunica adventitia
-outermost
-external elastic layer
-external elastic membrane
-remainder fibro-elastic tissue
-areolar tissue nearby
VASA VASORUM
Small vessels supply nutrients to large
artery or vein
“vessels of vessels”
more than 1mm dia
NERVES
vasomotor fibers
sensory fibers
ARTERIES
Fx- conduct blood away from the
heart to organs & tissues
Three groups(types)
1.arterioles(smallest)
2.small to medium-sized
arteries(muscular)
3.large arteries(elastic)
Arterioles
Invisible
between 0.04mm & 0.3mm dia
regulate BP
tunica intima
internal elastic membrane(always
present)
tunica media (almost always thickest &
most prominent )
Small and medium sized
arteries
Muscular A ( distributing A)
vasa vasorum (t. adventitia)
Smallest (visible)
Tunica adventitia
elastic layer (collagenous)
Large arteries
Elastic A
Conducting A
vasa vasorum (T. media / T.adventitia)
tunica intima
- lined by polygonal endothelial cells
tunica media
-thickest
tunica adventitia
-collagenous fib
Metarterioles
Narrow vessels that arise from
arterioles
Vasoconstriction
-arterioles
-sympathetic stimulation
Vasodilatation
-parasympathetic stim. by release:
1.acetylcholine release EDRF
2.EDRF(endothelial-derived relaxing
factor)
Sensory N. endings
1.Baroreceptors
BP changes
Carotid sinus
2.Chemoreceptors
bld levels of O2 & CO2 changes
Carotid and aortic bodies
VEINS
Conduct blood away from organs to the
heart
Three classes
1.venules
2.small to medium- sized veins
3.large veins
also possess three layers
(tunica intima, media & adventitia)
Venules
0.2 to 1mm dia
tunica intima
no IEL
thin (gen)
tunica adventitia
thickest layer
exchange of metabolites & diapedesis
Small and medium sized veins
inc.cutaneous br.; deeper veins of
forearm & leg;veins of the head,trunk &
viscera(exc main vessels & their
tributaries)
tunica intima
lined by short polygonal endothelial
cells
tunica adventitia
longitudinal smooth m. ,
no ext. elastic layer
Large veins
Inc. superior & inferior vena cava, portal veins
pulomnary vein
tunica intima
thicker subendothelial layer
tunica media
smooth muscle reduced
tunica adventitia
Thickest (vasa vasorum)
longitudinal smooth muscle (almost all)
no ext. elastic layer
three zones:inner,middle & outer
VALVES
Pocket-like in veins
Absent (cranium)
Occurs in pairs
Distal to entry of a tributary vein
Fx-
Folding of intimal tunic
Covered by endothelium
ARTERIO-VENOUS ANASTOMOSES
Ex. palm,sole,terminal
phalanges,lips,nose,eyelids
For circulation and BP regulation
Comparison of artery & vein of
same size
Transverse sec
smaller lumen of A (1)
A wall thicker (2)
V wall thin with large lumen
Media thickest-A (3)
A-IEL (4)
V valves (5)
Why do coronary arteries generally
have a thicker tunica media than the
pulmonary arteries?
• The thickness of the tunica media
correlates with the blood pressure to
which the vessel is exposed.
Since coronary arteries are exposed to a
higher blood pressure than the
pulmonary vessels , the coronaries will
have a thicker tunica media.
HEART
•Four-chambered (atria,ventricle)
•sym & parasym fibers
•three cardiac layers (tunicae)
1.endocardium
2.myocardium
3.epicardium
Endocardium
T.intima
endothelium
Myocardium – forms mainmass of the
heart
middle coat (t. media)
Composed of cardiac muscle
Epicardium
Ext. coat (t.advent)
outermost
Mesothelium
Cardiac Skeleton
Central support
Cardiac myocytes attach to the fibrous skeleton of the heart
main components of the skeleton:
1.septum membranaceum of the
interventricular septum
2.annuli fibrous or fibrous ring -
supports atrioventricular and pulmonic valves
3.trigona fibrosa - supports aortic valve
The connective tissue skeleton also acts as an insulator between the atria and
ventricle,ensuring that electrical conduction will occur a long the designated
route.
Heart Valves
Reduplication of endocardium
Bicuspid valves
tricuspid valves
semilunar valves
Impulse-conducting system
Initiate heartbeat
comprises
SA node
seat of impulse
pacemaker
AV node
AV bundle of his
purkinje fibers (subendocardium)
VESSELS & NERVES
Coronary A and cardiac V
Nerve supply from Vagus
LYMPHATIC VASCULAR SYSTEM
lymphatic cap, lymphatic
vessels,lymphatic ducts
LYMPHATIC VESSELS
One-way flow
lack lymphatic cap
ex:brain,spinal cord,eyeball,internal
ear,bone marrow
lymphatic capillaries
-broader
-dense network
LYMPHATIC VESSELS
Valves
-more closely spaced
main lymphatic trunks
-thoracic and R.lymphatic ducts
FUNCTION OF LYMPHATICS
Chief route for uptaking large
molecule
CLINICAL CONSIDERATION
Aneurysm
Atherosclerosis - atheroma deposits
Rheumatic heart-valve dse (mitral val)
Ischemic(coronary) hrt dse - due coronary
atherosclerosis
Tetralogy of Fallot
Varicose Veins (hemorrhoids)
Metastasis of malignant tumors
occur via lymph vessels or blood
