Arterial System.pdf

8/11/2019 Arterial System.pdf

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Section ISYSTEMS


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A veyne called Arteria . . . to bere and brynge kindely heete from the

herte to al the membres.

TREVISABarth. De P.R. V.lvi, 1398

DEVELOPMENT OF THE ARTERIALSYSTEM

Dorsal Aorta

In the third week of gestation, the right and left aortic archesturn caudally to form the corresponding dorsal (descend-ing) aortas. These connect with thevitelline arteryover theyolk sac. The first of the longitudinal veins, thepostcardinalveins,develop ventrally. The intersegmental arteriesbranch

from each aorta (Fig. 1-1).A week later, the two dorsal aortasfuse to form the single dorsal (descending) aorta so that by8 weeks, a single aortic arch and dorsal aorta are in place.

SEGMENTAL ARTERIES

The dorsal aortaat each dermatome gives off a pair of inter-segmental arteries, the dorsal somatic arteries. Each of thesearteries has a dorsal branch supplying the vertebral regionand neural tubeand aventral branchhaving lateral and ter-minal branches to supply the body wall (Fig. 1-2).The poste-rior intercostal, subcostal, and lumbar arteries are derivedfrom the dorsal somatic arteries. The enlarged 5th lumbarintersegmental artery, as the common iliac artery, will providethe blood supply to the pelvis and lower extremities.

Chapter 1Arterial System

FIGURE 1-1. (Adapted from Moore KL: The Developing Human, 4thed. Philadelphia, WB Saunders Company, 1988.)


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SECTION I SYSTEMS4

Two other sets of segmental arteries are formed: (1) theventral splanchnic arteries that extend to the yolk sacand gut and (2) the lateral splanchnic arteries that supplythe urogenital system. After the dorsal aortas have fused,the pairedventral splanchnic arteries combine to form theceliac trunk and the superior and inferior mesentericarteries. The lateral splanchnic arteriessupply the meso-nephros(and also the adult kidney) and the genital ridge,including the testis or ovary, and part of the adrenalgland.

Development of the Vasculatureof the Body Wall

The segmental vasculature develops deep to the muscles ofthe body wall, following the pattern of the segmentalnerves. At 5 weeks, the descending aorta gives off 30 pairsof dorsal segmental arteries, 1 pair at each dermatome.These have a dorsal branchsupplying the vertebral regionand neural tube and a ventral branchthat, in turn, has lat-eral and terminal branches. These branches supply themajor muscles of the trunk and overlying skin by way of theintercostal, subcostal, and lumbar arteries. The more ante-rior portion of the body wall is supplied by a ventral aortathrough anastomotic arteries,which will form the internalmammary and superior and inferior epigastric arteries(Fig. 1-3).

From the segmentally arranged vessels such as the inter-costal or lumbar arteries, branches run perpendicularlythrough the muscle as perforatorsto the skin, where theybecome cutaneous vessels.

Umbilical Artery

The umbilical arteriesoriginate as ventral branches of thepaired dorsal aortas and enter the umbilical cordlateral tothe allantois (Fig. 1-4A,B).

After aortic fusion, the umbilical arteries arise from thedorsally placed 5th lumbar segmental artery, the vessel thatis destined to become the common iliac artery. The umbili-cal artery eventually becomes a section of the superior vesi-cal artery, and its distal portion becomes the obliteratedhypogastric artery (Fig. 1-4C).

Fetal Circulation

The persistent left umbilical veincarries oxygenated bloodfrom the placenta and delivers half of it to the hepatic sinu-

soids of the left lobe of the liver. After entrance of the portalvein into the umbilical vein, the combined placental andportal flow is discharged into the inferior vena cavathroughthe ductus venosus, where sphincteric action regulates therelative flow. From the inferior vena cava, hepatic bloodmixed with venous blood from the lower body passes into theright atrium and through the foramen ovale into the leftatrium (Fig. 1-5).There, it is joined by blood from the pulmo-nary veins. After traversing the atrium, the blood goesthrough the left ventricle into the ascending aorta. Someblood remains in the right atrium to be directed by the valveof the foramen ovale into the right ventricle and on into thepulmonary trunk. Because pulmonary resistance is high, onlya small portion of the blood goes to the lungs; most of itpasses through the ductus arteriosus into the aorta. Most ofthe blood, with some addition from the left ventricle, has al-ready circulated through the head and upper limbs. It passesdown the aorta to supply the abdomen and lower extremitiesand into the right and left umbilical arteriesto the placenta.

Circulatory Alterations at Birth

Five vascular structures become obsolete at birth: the fora-men ovale, ductus venosus, ductus arteriosus, and thepaired umbilical vessels. As the pressure in the left atriumrises from the relative increase in pulmonary flow over that

FIGURE 1-2.


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CHAPTER 1 ARTERIAL SYSTEM 5

A

B

C

FIGURE 1-4.

FIGURE 1-3.


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SECTION I SYSTEMS6

of the right atrium, the valve of the foramen ovale closes.The ductus venosus in the liver closes to become the liga-mentum venosum. The ductus arteriosus is constricted bybradykinin from the lungs. The portions of the umbilicalarteries nearest the umbilicus thrombose to become themedian umbilical ligaments(obliterated hypogastric arteries),leaving the superior vesical arteries functioning proximally.The thrombosed left umbilical vein becomes the ligamen-tum teres (Fig. 1-6).

ARTERIAL SYSTEM: STRUCTUREAND FUNCTION

The structure of blood vessels varies with their function. Ingeneral, as the distance from the heart and the degree ofbranching increase, the cross-sectional area of an arterydecreases and conversely, its stiffness increases. At the arte-riolar and capillary levels, the cross-sectional area becomesgreater in keeping with the reduced flow and systolic andpulse pressures.

The response of a blood vessel to clamping, ligating, orsuturing depends on its wall structure.

Structure of the Arterial Wall

All vessels have three analogous layers: intima(tunica intima),media (tunica media), and adventitia (tunica adventitia),as shown in the histologic cross-section of a medium-sizedartery (Figs. 1-7and 1-8).In arteries, the intima is composedof the single endothelial cell lining, supported by longitudi-nally oriented connective tissue. The media is a fibromus-cular layer lying between the internal and external elasticlaminae(Fig. 1-9).The adventitia is composed of longitudi-nally oriented connective tissue fibers and is covered by athin sheath.

The vasa vasorumof the adventitia usually arises fromthe vessel itself but may come from an adjacent one. Theynourish the outer portion of the media through a capillarynetwork, whereas the inner portions are supplied by diffu-sion from within the artery. Stripping the adventitial sheathremoves the vasa vasorum, but an adequate supply remainsfrom within. Efferent sympathetic nerves supply constantstimulation to maintain the vasomotor tone of the vessels.

Arteries may be classified by function. The major arter-ies are conducting arteries, which are rich in elastic qualitiesand so can absorb the force of the heart and change it to a

FIGURE 1-5.


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FIGURE 1-6.

FIGURE 1-7.

Tunica intima

Tunica mediaTunica adventitia

FIGURE 1-8.


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SECTION I SYSTEMS8

less pulsatile flow. Medium and small arteries are distribut-ing arteries, with muscular walls that aid in regulating flow.Arterioles are resistance vessels, which by restricting the flowaffect the blood pressure. The capillaries, sinusoids, and post-capillary venules are exchange vessels, their function being toallow the ingress and egress of tissue fluid.

Abdominal Aorta

The abdominal aortaextends from the aortic hiatusof thediaphragm at the level of the 12th thoracic vertebra tothe level of the 4th lumbar vertebra. It gives off four setsof branches: The dorsal, lateral, and ventral branches cor-respond to the embryological development of the dorsalsomatic, lateral splanchnic, and ventral splanchnic vessels(see Fig. 1-3).The dorsal branches enter the body wall asthe lumbarand middle sacral arteries. The lateral branchessupply viscera via the inferior phrenic, adrenal, renal,andgonadal arteries. The ventral branches, which supply theviscera of the digestive tract, are the celiac trunkand thesuperiorand inferior mesenteric arteries (Figs. 1-10,1-11,and 1-12). These vessels are described under the organsthey supply.

The anterior aspect of the aorta lies under the celiacplexus and the omental bursa. The pancreas with the un-derlying splenic vein crosses the aorta, with the superiormesenteric artery and left renal vein between. Caudal to thepancreas, the third part of the duodenum crosses the aorta.Further down, the aorta is covered by the posterior pari-etal peritoneum and the mesentery of the bowel. The pos-terior aspect lies against the upper four lumbar vertebrae,

FIGURE 1-10.

Tunica

intima

Tunica

media

Tunica

adventitia

Nerve

External elastic

membrane

Vasa

vasorum

Internal elastic

membrane

FIGURE 1-9.


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the corresponding intervertebral discs, and the anteriorlongitudinal ligament, with the 3rd and 4th lumbar veinsintervening. The cisterna chyli, the thoracic duct, the azygosvein, the right diaphragmatic crus, and the right celiac

ganglion lie to the right of the aorta. To the left are the left

diaphragmatic crus and the left celiac ganglion, as well asthe ascending portion of the duodenum and its junctionwith the jejunum and the sympathetic trunk.

The major arteries supplying specific parts of the genito-

urinary tract are described in the appropriate chapters.

Celiac trunkSuperior mesentericartery

Aorta

FIGURE 1-12. (Image courtesy of Raj Paspulati, MD.)

Hepaticartery

Splenicartery

Left renalartery

Right renalartery

Aorta

Inferiormesentericartery

Left commoniliac artery

Rightcommoniliac artery

Left externaliliac artery

Left internaliliac artery

FIGURE 1-11. (Image courtesy of Raj Paspulati, MD.)


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Arterial System.pdf