Cardiovascular System: Blood Vessels
Identify the superficial veins of the forearm and arm, and describe their anatomical location.
The superficial veins include the cephalic, basilic, median, and
median cubital veins.
The cephalic vein and basilic veins arise from the dorsal venous network. The cephalic ascends
the lateral forearm, whereas the basilic ascends the medial aspect. The median cubital vein
bridges these two veins; it runs obliquely across the cubital fossa from the cephalic to a more
proximal union with the basilic vein. The median vein ascends the center of the forearm before
passing the medial side of the cubital fossa.
Describe how blood flow is regulated (a) to whole organs, (b) within
tissues, and (c) to
Blood flow to groups of organs or to individual organs is regulated
by the muscular
arteries. Sympathetic vasomotor fibers innervating their walls constrict or dilate the arteries to
divert or enhance blood flow. A similar regulatory system occurs within tissues via
vasoconstriction of arterioles. Sympathetic stimulation can cause vasoconstriction of arterioles to
increase systemic blood pressure. Alternatively, local chemical conditions within metabolically
active tissues can cause local vasodilation of the arterioles. These chemical factors also cause
relaxation of the precapillary sphincters allowing greater perfusion of capillary beds within the
Define and explain the significance of vascular anastomoses.
A vascular anastomosis is a "coming together" of either
arteries or veins. Vascular
anastomoses are alternative pathways for blood flow. These pathways are called collateral
channels. Arterial anastomoses often occur around joints providing alternative pathways for
blood to flow when movement of a joint impinges upon flow through other vessels. The
anastomosis ensures adequate perfusion of the tissue. Venous anastomoses provide multiple
pathways for drainage. Blockage of a single vein rarely blocks blood flow or leads to tissue
Define the term portal system, and describe the significance of portal-systemic anastomoses.
A portal system consists of two separate capillary beds between the
arterial and venous
ends of the circuit. The capillary beds are joined to each other in sequence by a portal vein. In the
hepatic portal system, destruction of the hepatic sinusoids can lead to blockage of blood flow
through the liver, resulting in increased blood pressure throughout the liver and GI tract. Venous
anastomoses along the GI tract provide a "safety valve" through which venous blood can drain,
bypassing the blocked liver and relieving the hypertension.
Describe the function of the fetal shunts from the pulmonary circuit.
The foramen ovale is a shunt between the right and left atria of the
heart. This shunt
allows blood to bypass the entire pulmonary circuit. Only about half of the blood entering the
right atrium is diverted through the foramen ovale. Much of the remainder of the blood that
proceeds through the right ventricle and into the pulmonary trunk then enters the second shunt.
This ductus arteriosus connects the pulmonary trunk directly to the arch of the aorta. This blood
then continues to the systemic circuit. Only a small quantity of the initial blood entering the heart
goes to the developing lungs.