Tunica Interna – innermost endothelium of simple squamous epithelium + basement membrane Arteries – have an “internal elastic lamina” of elastic CT to allow for expansion under pressure Veins – may have “valves” (folds of endothelium + CT) to prevent backflow of blood due to low pressure Microscopic, very thin-walled vessels comprised of endothelium with basement membrane; allows for filtration and reabsorption Found in all tissues of the body except for those that are “avascular” Usually form branching networks (“capillary beds”) within tissues for increased surface area blood flow into capillaries may be regulated by “pre- capillary sphincters” may have a central or “thoroughfare” channel that provides direct connection between “metarteriole” (terminal end of arteriole) & venule

1. Anatomy of Blood Vessels & their
distribution
Date- 14-11-2017
BY - GAURAV PANDEY

2. Basic Anatomy of Circulatory routes
Arteries
Arterioles
Capillaries
Venules
Veins Carry
blood
away from
the heart
Control
blood flow
into
capillaries
& help
regulate BPAllow for “exchange”
(filtration/reabsorption) of
Connect
capillaries to
veins
Carry blood
towards the
heart

3. Structure of Blood Vessels

4. Arteries & Veins
Both are comprised of 3 layers of tissue surrounding “lumen”
through which blood will flow: tunica interna, tunica media &
tunica externa
Structural difference between arteries & veins primarily due
to differences in pressure of blood flowing within

5. Arteries & Veins
Tunica Interna – innermost endothelium of simple squamous
epithelium + basement membrane
 Arteries – have an “internal elastic lamina” of elastic CT to allow
for expansion under pressure
 Veins – may have “valves” (folds of endothelium + CT) to prevent
backflow of blood due to low pressure

6. Arteries & Veins
Tunica Media – middle layer containing smooth muscle (for
contractility/vasoconstriction) & elastic CT (for elasticity)
 Arteries – have relatively thick tunica media allowing for
significant vasoconstriction & elasticity
 Elastic/conducting arteries – relatively more elastic tissue than smooth
muscle; ie. aorta, pulmonary trunk, etc.
 Muscular/distributing arteries - relatively more muscle tissue than elastic
tissue; ie. brachial, femoral, etc.
 Veins – relatively thin tunica media therefore no significant
constriction/elasticity

7. Arteries & Veins
Tunica Externa – made of collagenous CT
 Arteries – thin layer
 Veins – thickest layer of vein, trying to support against gravity &
low pressure

8. Arteries & Veins

9. Arterioles & Venules
Very small, almost microscopic vessels with only 2 layers of tissue
surrounding lumen
 Arterioles – endothelium (tunica interna) + very thin layer of smooth
muscle cells (tunica media); regulate blood flow to tissues & affect arterial
blood pressure
 Venules – endothelium (tunica interna) + thin layer of CT (tunica externa)

10. Capillaries  Microscopic, very thin-walled vessels
comprised of endothelium with
basement membrane; allows for
filtration and reabsorption
 Found in all tissues of the body except
for those that are “avascular”
 Usually form branching networks
(“capillary beds”) within tissues for
increased surface area
 blood flow into capillaries may be
regulated by “pre- capillary sphincters”
 may have a central or “thoroughfare”
channel that provides direct connection
between “metarteriole” (terminal end of
arteriole) & venule
Capillaries can be classified as continuous,
fenestrated, or sinusoids

11. Circulatory
Routes -
overview

12. Circulatory Routes – Pulmonary Circuit

13. Circulatory Routes – Systemic circuit
Ascending aorta
(gives off coronary
arteries)
Aortic arch
Brachiocephalic trunk
Left common carotid artery
Left subclavian artery
Thoracic (descending) aorta
Abdominal aorta
Common iliac arteries
 Arterial blood from left ventricle
into ascending aorta
 Venous return to right atrium
through SVC, IVC & coronary
sinus

14. Systemic
circuit -
Arteries

15. Systemic
circuit -
Veins

16. Cerebral circulation
Cerebral arterial
circle (“circle of
Willis):
Basilar artery
(from union of
vertebral arteries)
+ Internal carotid
arteries

17. LIVER
Hepatic Portal Vein
Cystic vein
Lt. gastric vein
Splenic vein
Inferior
mesenteric veinSuperior
mesenteric vein
A
O
R
T
A
(blood mixes in
sinusioids)
Hepatic Veins
I
V
C
Hepatic artery
Hepatic portal circulation
Venous blood flow from GIT &
spleen to liver – ensures
delivery of nutrients to liver
first

18. Hepatic portal circulation
 Cystic vein, left gastric
vein, splenic vein,
inferior & superior
mesenteric veins
Hepatic portal vein
 Hepatic portal vein
(deoxygenated/nutrient
rich blood) + Hepatic
artery (oxygenated
blood) sinusoids of
liver
 Sinusoids of liver 
Hepatic veins  IVC

19. Fetal Circulation
Placenta – O2/CO2 &
nutrient/waste between mom &
baby
Umbilical cord – (2) umbilical
arteries (baby  mom) & (1)
umbilical vein (mom  baby)
Umbilical vein
(O2/nutrient rich blood)
 hepatic portal vein &
ductus venosus  IVC 
Rt. atrium
Rt. Atrium  some blood to rt. Ventricle,
most shunts across foramen ovale in
interatrial septum  lt. atrium  lt.
ventricle

20. Blood from Rt. Ventricle 
pulmonary trunk  across
ductus arteriosus to aorta
Aorta  systemic arteries
internal iliac arteries 
umbilical arteries  placenta
Fetal Circulation

21. Fetal Circulation- Changes at Birth
 Umbilical vein  ligamentum teres
(round ligament)
 Umbilical arteries  lateral
umbilical ligaments
 Ductus venosus  ligamentum
venosum
 Foramen ovale  fossa ovalis
 Ductus arteriosus  ligamentum
arteriosum
 Placenta delivered (“afterbirth”)

22. Upper extremity arteries & veins

25. Coronary circulation

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