CIRCULATORY SYSTEM -- VEINS

I. MAJOR COMPONENTS

A. Cardinals - anterior, posterior, and common.
B. Renal portal system.
C. Lateral abdominal veins.
D. Hepatic portal system: drains digestive organs of coelom and spleen into liver.
E. Two additional streams develop in lungfishes and tetrapods:

1. {Pulmonary veins.}
2. Postcava from kidneys.

II. EVOLUTIONARY TRENDS

A. Fishes (shark) = ideal blueprint of basic venous channels in vertebrates.

1. Cardinal veins:

a. Most blood returns to sinus venosus via common cardinals.
b. Anterior cardinal veins drain blood from head (not jaw).
c. Posterior cardinal veins: drain kidneys, body walls, and gonads.

2. Renal portal system develops, which is an advance over the primitive vertebrate condition (cyclostomes don't have one).

B. Amphibians.

1. Cardinal veins and precavae:

a. Common cardinals better known as precavae.
b. Anterior cardinals are called interior jugulars.

2. Postcava arises from subcardinal anastomoses; passes thru liver.

C. Reptiles.

1. Large systemic veins entering heart begin to shift to right. Why?
2. Renal portal system becomes less important.

D. Mammals.

1. Prominent shift of main venous channels to the right side.
2. Precaval and postcaval veins enter the heart directly because {the sinus venosus has been incorporated into the right atrium.}
3. No trace of renal portal system.
4. Cats and humans lose left precava (common cardinal), blood flows through brachiocephalic vein into right precava.