Blood vessels
Dr. Carmen E. Rexach Anatomy 35
Mt San Antonio College
• Arteries – resistance vessels – high pressure – carry blood away from heart
• Veins – capacitance vessels – low pressure lines – carry blood to the heart
• Capillaries – exchange vessels
Types of blood vessels
Tunics
• tunica intima (interna) – endothelium
– loose CT + simple squamous epithelium
• tunica media – smooth muscle (not
cardiac)
– may have elastin
• tunica externa – adventitia
– fibrous CT with elastin
Arteries • characteristics
– Smaller diameter than veins – thick tunica media – Lots of elastin
• function – carry blood away from the heart – not always oxygenated
Artery
Types of arteries • Elastic
– largest (major) arteries – largest diameter – abundant elastin
• Distributing – branches from the aorta – most distribute to organs directly (except trunks)
• Muscular – within organs – distribute to “lobes” of an organ
• Arterioles – the smallest of all arteries – have “plates” of smooth muscle – small diameters, branch into capillaries – greatest resistance to blood flow.
Arterioles
Veins
• Characteristics – relatively large diameters
– thin tunica media
– thick tunica externa
– large veins have valves (especially in legs)
• Function of veins – carry blood back to the heart (not always
deoxygenated)
Types of veins • Vena cavae
– largest of all veins – superior VC and inferior VC – drain blood from most organs
• Veins – tributaries to the vena cavae – drain organs and lobes of organs
• Venules – smallest of all veins – drain capillaries
Arteries vs veins Characteristics Artery Vein Diameter Narrower Wider, often collapsed
Wall thickness Thicker Thinner
X-section Keeps circular shape collapses
Thickest tunic Tunica media Tunica externa
Fibers More elastic/collagen Less
Blood pressure >90 mm Hg in larger Approx 2 mm Hg
Blood flow Away from heart Toward heart
Oxygen levels Systemic arteries = high O2
Pulmonary arteries = blood low in O2
Systemic veins = low O2
Pulmonary veins = high O2
Venules vs Arterioles
Capillaries
• Structure – Tunica intima only (endothelium)
• Function – Diffusion and exchange of substances
with tissues
Regions of the aorta
• Ascending Aorta
• Aortic Arch – bends to the left and posteriorly
• Descending Aorta – thoracic aorta
• descending aorta superior to the diaphragm
– abdominal aorta • descending aorta inferior to the diaphragm
Major branches from the aorta
from the ascending region: – R & L Coronary arteries
• supply the myocardium
• First to receive oxygenated blood
– Rt. Coronary branches • to the marginal artery and posterior
interventricular artery
– Lt. Coronary branches • to the anterior interventricular a. and
circumflex a.
From the arch • brachiocephalic
– to rt. subclavian a. and rt. common carotid a.
• L. common carotid a.
• Branches to internal and external carotid a.
• L subclavian a. passes under clavicle toward the left arm. – Branches to:
• vertebral a.
• thyrocervical a.
• costocervical a.
• internal thoracic a.
• axillary a.
From the thoracic aorta: • posterior intercostals arise from the
thoracic aorta – anterior intercostals arise from the
internal thoracic a. or costocervical a
• pericardial, bronchial, esophageal, and superior phrenic arteries – supply the pericardium, bronchi,
esophagus, and diaphragm
From the abdominal aorta (abdominal region)
• inferior phrenic arteries
• celiac trunk – branches to:
• hepatic, lt. gastric, splenic
• other gastric arteries – lt. gastroepiploic a.
– rt gastric
• suprarenal arteries supply the adrenal (suprarenal) glands
• superior mesenteric artery – supplies small intestines, pancreas,
appendix, many portions of the colon
• renal arteries – supply the kidneys
• gonadal arteries – either spermatic or ovarian a.
• inferior mesenteric artery – other areas of the colon not supplied by
the superior mesenteric a.
• lumbar arteries – muscles and spinal cord of lumbar region
Branches from the abdominal aorta (pelvic region)
• median sacral artery (middle sacral artery) – supplies the sacrum and coccyx
• common iliac arteries – branch into external and internal iliac a.
– Blood to lower extremities
Circle of Willis
Circle of Willis
Veins
• Superior vena cava – formed by 2 brachiocephalic veins and
azygous system of veins
– brachiocephalic veins • Formed by internal jugular and subclavian
veins
• external jugular veins empties into the subclavian veins
– azygous system drains the thorax
Veins • Inferior vena cava receives blood
from: – R and L hepatic veins
– R suprarenal (L drains into the renal vein)
– R gonadal (L drains into the renal vein)
– lumbar veins
– common iliac veins
Vascular anastomoses
• Connection between two blood vessels, bypassing the capillaries – 2 parallel arteries
(collaterals)
– arteriovenous
venous sinuses
• A channel that carries venous blood
• Found in: – dural space surrounding the brain
• sagittal, straight (rectus), cavernous
– liver • sinusoids
– spleen
Portal systems: • Throughout most of the cardiovascular
system, the circuitry is laid out in parallel with arteries ultimately branching to capillaries which remerge into veins which return blood back to the heart.
• The heart receives blood from many different locations at approximately the same time. In portal systems, two capillary beds are in series.
Parallel circuit
A portal circuit
Examples of major portal systems of the body
• 1. hypothalamopituitary portal vessel
• 2. renal portal system
• 3. hepatic portal system
Hepatic Portal System
Fetal Circulation
Fetal Circulation • All major blood vessels are in place by the 3rd month
of development & flowing in the same direction • 2 major differences:
– fetus supplies blood to placenta – fetal respiratory organ is in the placenta and fetus does not
breathe
• umbilical vessels – Paired U. arteries (arise from internal iliac a. in pelvis) carry
deoxygenated blood from the fetus --> placenta – Unpaired U. vein carry oxygenated blood into the ductus
venosus
• Shunts – Shunts away from liver
• ductus venosus – Shunts away from the pulmonary circuit:
• foramen ovale – an opening between the atria to shunt blood from R-L; a valve
• ductus arteriosus – a shunt between the pulmonary trunk and aorta – prevent overload on the immature lungs
all returning blood to the fetus proceeds to hepatic veins, inferior vena cava and right atrium