CIRCULATORY SYSTEM

• The circulatory system consists of a blood vascular system and a lymphatic system.
• The blood vascular system consists of whole blood, heart, arteries, capillaries, and veins.
• Blood consists of plasma and formed elements. The formed elements are

  erythrocytes, granular and agranular leukocytes (the latter includes

  lymphocytes), and thrombocytes (platelets)
• Hemocytoblasts are precursors of all blood cells. Their initial source is

  blood islands of the yolk sac. Eventually they form in liver, kidney,

  spleen, and bone marrow.
• The lymphatic system consists of lymph, lymphatics, lymph hearts,

  lymph nodes, and miscellaneous lymphoid masses in one major taxon

  or another.
• Chyle is lymph collected in intestinal villi. Lymphatics terminate in a systemic vein.
• Fishes have a single circuit heart. Venous blood enters a sinus venosus,

  traverses an atrium, ventricle, and conus arteriosus, and then is discharged into a ventral aorta. The latter carries blood to aortic arches that

  supply gills, where blood is oxygenated. It then passes via arteries to

  capillaries everywhere in the body, gives up oxygen, takes on carbon dioxide, and returns to the sinus venosus.
• In vertebrates that breathe solely by lungs, a pulmonary circuit carries

  blood to the lungs and back and a systemic circuit carries oxygenated

  blood elsewhere and returns deoxygenated blood to the heart. This is a

  double circuit heart.
• Double circuit hearts have two atria and one or two ventricles. The right

  atrium receives deoxygenated blood from the systemic circuit, the left

  receives oxygenated blood from the pulmonary circuit.
• Mixing of oxygenated and deoxygenated blood in the ventricle of a

  double circuit heart is avoided by one of several adaptations, including

  spiral valves when there is a single ventricle, and trabeculae and ventricular septa.
• A complete interventricular septum separates the blood in

  crocodilians, birds, and mammals.
• Right-left shunts of blood (away from the lungs) are provided for in

  reptiles to meet metabolic needs imposed by certain behavioral patterns,

  including remaining underwater for long intervals without breathing.
• A sinus venosus is present in fishes, amphibians, and reptiles, serving

  the same function in all. It becomes partially incorporated into the wall

  of the right atrium in crocodilians, and totally incorporated in birds and

  mammals.

  true or false?
• The heart of adult amniotes has no conus arteriosus.
• The pulsations of the heart are autogenic, requiring no extrinsic neural

  stimulus. However, the rate of beat is imposed by the autonomic nervous system.
• The stimulus in fishes, amphibians, and reptiles is spread from the musculature of the sinus venosus. In birds and mammals it

  emanates from a sinoatrial (SA) and an atrioventricular (AV) node.
• The ventral aorta exhibits a swelling, the bulbus arteriosus, in teleosts

  and perennibranchiate urodeles. The ventral aorta is referred also as

  the truncus arteriosus in amniotes.
• In most reptiles the truncus arteriosus is split longitudinally into two

  aortic trunks and a pulmonary trunk. The two aortic trunks exit from a

  cavum venosum in the ventricle and supply all functional aortic arches

  except the pulmonary. The pulmonary trunk emerges from the right

  ventricle (cavum pulmonale) and supplies the pulmonary circuit. The

  left ventricle has been termed the cavum arteriosum.
• The ventral aorta in birds and mammals is split into only two trunks, a

  systemic trunk that emerges from the left ventricle and supplies all parts

  of the body except the lungs, and a pulmonary trunk that emerges from

  the right ventricle and supplies the lungs.
• Six pairs of aortic arches develop in vertebrate embryos. During ontogeny the arches are reduced in number, the third (carotid), fourth (systemic), and sixth (pulmonary) being the most persistent.
• The paired dorsal aorta between the third and fourth arches, when persistent, is the ductus caroticus. The dorsal segment of the left sixth aortic

  arch, when persistent, is the ductus arteriosus. The latter shunts blood

  away from the lungs and to the placenta of fetal mammals. The ductus

  arteriosus disappears at birth.
• The unpaired dorsal aorta of the trunk has paired segmental branches

  (somatic) to the body wall and appendages, unpaired visceral branches

  to the digestive organs within the coelom and to the spleen, and paired

  visceral branches to the urogenital organs and adrenal glands. The embryonic dorsal aorta of amniotes supplies an allantoic (umbilical) artery

  to the allantois or placenta.
• Retia mirabilia are localized skeins or networks of arteries, or sites of

  close proximity of arterioles and venules, performing a special function

  that varies with their location and with the species. In certain locations

  they provide a countercurrent flow of blood.
• Basic venous channels are anterior, posterior, and common cardinals,

  abdominals, renal and hepatic portals, hepatic sinuses, and coronary

  veins. Pulmonary veins and a postcava are added in tetrapods. Embryonic subintestinal and vitelline (omphalomesenteric) veins contribute to

  the hepatic portal system. Allantoic (umbilical) veins drain the allantois

  or placenta in embryonic amniotes.
• The renal portal system drains only the tail in fishes. It acquires connections with the hind limbs in amphibians. In crocodilians and birds this

  connection bypasses the kidneys and goes directly to the postcava.

  There is no renal portal system in adult mammals above monotremes.
• The postcava becomes increasingly important in tetrapods. Commencing as an alternate route from kidneys to heart, it eventually drains the

  tail, hind limbs, and most of the trunk.
• Remnants of embryonic vascular channels in adult mammals include

  the round ligament of the liver (remnant of left umbilical vein), ligamentum venosum (remnant of ductus venosus), ligamentum arteriosum

  (remnant of left ductus arteriosus), lateral umbilical ligaments (remnants of paired umbilical arteries from urinary bladder to umbilicus),

  and fossa ovalis (occluded interatrial foramen ovale of fetus).
• circulatory system is also called the blood vascular system
• the blood vascular system consists of the blood, heart, arteries, capillaries, and veins
• blood consists of plasma and formed elements
• Formed elements are erythrocytes, granular, and agranular leukocytes (the latter includes lymphocytes), and a thrombocytes (platelets)
• the hemocytoblast are the prercursor of all the blood cell and their initial source is the blood islands of the yolk sac, and eventually they form the liver, kidney, the spleen, and the bone marrow.
• sinus venosus receive blood from the body, especially in fishes, amphibians, and reptiles
• sinus venousus is partially incorporated in reptiles and totally incorporated in birds and mammals
• conus arteriosus receive blood from the heart. It is present in fishes and amphibians
• heart of the adult amniotes have no conus arteriosus
• bulbus arteriosus, which is a swelling in ventral aorta, only seen in teleost
• the ventral aorta is also called truncus arteriosus in amphibians and in some of the amniotes
• truncus arteriosum is split longitudinally into two aortic trunks and a pulmonary trunks in reptiles.
• The ventral aorta in birds and mammals is split into only two trunks