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