BloodBloodBlood vesselsvesselsvessels

Dr. Carmen E. Rexach Anatomy 35 Mt San Antonio College Types of blood vessels • Arteries – resistance vessels – high pressure – carry blood away from heart •Veins – capacitance vessels – low pressure lines – carry blood to the heart • Capillaries – exchange 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 Systemic veins = low O2 Pulmonary arteries = blood Pulmonary veins = high

low in O2 O2

VenulesvsArterioles

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. •costocervicala. • 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. –rtgastric • 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