Lecture 10
Topic: General principles of evolution of organs. Phylogenesis of organs and functional systems in human. Phylogenesis of Heart and circulatory system. Phylogenesis of Urogenital system.
Plan of the lecture:
1. Principles of evolution of organs. Biogenetic law.
2. Evolution of heart and circulatory system in Invertebrates and Vertebrates.
3. Transformation of arteriousus (gill’s) arches in Vertebrates.
4. Excretory organs of Invertebrates.
5. Evolution of excretory and reproductive system in Vertebrates. Three stages of kidneys development (pronephros, mesonephros, metanephros).
1. The features of morphology and physiology of modern organisms are results of historical development or phylogenesis. The evolutionary history and relationship among organisms can be represented by a phylogeny. Meanwhile in individuals of every generation the features of structural-functional organization are reproduced in process of individual development, e.g. ontogenesis. Phylogenesis is consistently change of ontogenesis. Between historical and individual development exist connection.
Haeckel is author of “main biogenetic law”, which states that ontogenesis is short
and quick repetition of phylogenesis. Haeckel’s biogenetic law or recapitulation
theory states that life history of an animal reflects evolutionary history of the same.
Haeckel recapitulation theory states that ontogenesis repeats phylogenesis or embryonic development of an animal repeats the embryonic stages of ancestors.
Parallelism is adaptive convergence of closely related groups.
Analogous organs are different origin but similar functions (teeth of human and gorilla).
Homologous organs are similar origin with similar and dissimilar functions
(for example, paddle of whale, front legs of horse and arms of human/ legs of
duck, hindlimbs of pig, hindlimbs of kangaroo; wings of pigeon and arms of humans).
Evolutional morphology is science, which studies regularities of phylogenetic transformations. It appears in end of 19th century on base of three independent sciences:
1. Comparative anatomy is study structure of similar organs of animals of the different species;
2. Comparative embryology is study similarities of embryonic development of an organisms;
3. Paleontology or paleobiology is study of fossils animals that existed millions of years ago.
2. Unicellular organisms and most cells of multicellular organisms have intracellular circulation. This involves streaming of cytoplasm called cyclosis.
Multicellular organisms have some sort of extra cellular circulation also: extraorganismic in sponges and coelenterates and intraorganismic in other animals. Sponges circulate environmental water through an extensive canal system in their body with the help of choanocytes. Water brings food and oxygen to the cells, and carries away carbon dioxide and nitrogenous wastes from them.
Hydra circulates surrounding water in its central cavity, the coelenteron, with the help of flagellated cells of the cavity’s lining. Water provides food and oxygen to cells and removes carbon dioxide and wastes from them.
More active animals circulate body fluid or blood. Flatworms circulate tissue fluid in irregular parenchymal spaces. Roundworms circulate body fluid in the pseudocoel. Annelids, mollusks and Vertebrates circulate blood in blood vessels with the help of heart or hearts. Blood, blood vessels and heart form blood vascular or cardiovascular system.
Many Invertebrates, such as prawn and insects, have open circulatory system. In them blood pumped by heart comes out of the blood vessels and flows through spaces, the sinuses, present among the tissues and hence returns to the heart.
Annelids and Vertebrates have closed circulatory system. In them, blood remains within blood vessels throughout its circulation. Blood pumped by heart passes through arteries, arterioles, capillaries, venules, veins and returns to the heart. Valves in the heart and veins ensure flow of blood in a single direction. Exchange of material between blood and tissue cells occurs in the capillaries via tissue fluid.
Vertebrate heart is a muscular organ composed of cardiac muscle fibers. It receives blood from and pumps blood to the various organs and tissues of the body. The heart is divided internally into chambers, the number of which varies in different vertebrate groups. The heart in all Vertebrates has 1 or 2 auricles (atria) and 1 or 2 ventricles. These chambers are called true chambers. The heart of lower Vertebrates has additional chambers, namely, sinus venosus and conus arteriosus or bulbus arteriosus or truncus arteriosus.
Fishes. A fish heart handles only deoxygenated (venous) blood, and is often called venous heart. It is two-chambered, having a single auricle and a single ventricle. The accessory chambers, sinus venosus and conus arteriosus are present.
Fig.1. Heart and blood flow in a fish. Single type of circulation in fishes.
The heart receives the deoxygenated blood from all over the body, except the gills, into the sinus venosus and pumps it via auricle, ventricle and conus arteriosus into a short artery, the ventral aorta, which distributes it to the gills by breaking up into capillaries. Here the blood picks up oxygen. The oxygenated blood from the gills flows into the dorsal aorta, whose branches distribute it to the rest of the body by splitting into capillaries. The blood returns to the heart through the veins. The fishes have a single circulation. An advantage of single circulation is that the entire body receives oxygenated blood. A disadvantage is that the narrow gill capillaries slow down the blood flow and the body receives blood at low pressure. This slows rate of oxygen supply to the cells and limits the metabolic rate.
Amphibians. Amphibian heart receives both deoxygenated (venous) and oxygenated (arterial) blood, and is often termed the arteriovenous heart.
It is three-chambered, having two (right and left) auricles and a single undivided ventricle. Two accessory chambers: sinus venosus and conus arteriosus, are also present.
Fig.2. Heart and blood flow in Double circulation in amphibians.