mammal

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mammal,

an animal of the highest class of vertebrates, the Mammalia. The female has mammary glands, which secrete milk for the nourishment of the young after birth. In the majority of mammals the body is partially or wholly covered with hair; the heart has four chambers, and only the left aortic arch is present; and a muscular diaphragm separates the chest from the abdominal cavity. Mammals are warm-blooded; that is, they have a relatively constant body temperature independent of the temperature of their surroundings. The mature red blood cells (erythrocytes) usually lack a nucleus. Except for the egg-laying monotremes (the platypusplatypus
, semiaquatic egg-laying mammal, Ornithorhynchus anatinus, of Tasmania and E Australia. Also called duckbill, or duckbilled platypus, it belongs to the order Monotremata (see monotreme), the most primitive group of living mammals.
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 and the echidna, or spiny anteater), mammals give birth to live young. A marsupialmarsupial
, member of the order Marsupialia, or pouched mammals. With the exception of the New World opossums and an obscure S American family (Caenolestidae), marsupials are now found only in Australia, Tasmania, New Guinea, and a few adjacent islands.
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 is born in a more undeveloped state than the young of other mammals, although all are relatively helpless at birth. In some marsupials and in higher mammals the young receive prenatal nourishment through a placentaplacenta
or afterbirth,
organ that develops in the uterus during pregnancy. It is a unique characteristic of the higher (or placental) mammals. In humans it is a thick mass, about 7 in. (18 cm) in diameter, liberally supplied with blood vessels.
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. The order Carnivora, or flesh-eating animals, includes terrestrial families such as the cat, dog, and bear as well as the aquatic seal, sea lion, and walrus. Other aquatic mammals are the whale, porpoise, and dolphin of the order Cetacea and the manatee and dugong of the order Sirenia. Unusual adaptations are also found in the bat (order Chiroptera); in the elephant (order Proboscidea); in the sloth, armadillo, and anteater (order Edentata); and in the beaver, woodchuck, porcupine, and squirrel (order Rodentia). The order Soricomorpha includes the shrew and the mole, and the spiny and hairy hedgehogs form Erinaceomorpha; both orders were formerly classed as Insectivora. There are two groups of ungulates, or hoofed mammals: most members of the order Perissodactyla, including the horse and the rhinoceros, are odd-toed, with the third digit the largest; those of the order Artiodactyla, including the deer, antelope, camel, pig, and cow, are even-toed, with the third and fourth digits symmetrical and functional. Humans, monkeys, apes, and lemurs belong to the order Primates. Some remains of mammals are identified as from the Jurassic period of the Mesozoic era, but mammals remained small creatures during the Mesozoic. The group became diversified relatively rapidly in geological terms in the Tertiary period of the Cenozoic era after the dinosaurs had become extinct.

Bibliography

See E. P. Walker et al., Mammals of the World (2 vol., rev. ed. 1968); S. Anderson, ed., Simon & Schuster's Guide to Mammals (1984); G. B. Corbett and J. E. Hill, World List of Mammalian Species (1986); H. H. Genoways, ed., Current Mammalogy (2 vol., 1987–89).

mammal

[′mam·əl]
(vertebrate zoology)
A member of Mammalia.

mammal

any animal of the Mammalia, a large class of warm-blooded vertebrates having mammary glands in the female, a thoracic diaphragm, and a four-chambered heart. The class includes the whales, carnivores, rodents, bats, primates, etc.
References in periodicals archive ?
How these prenatal programs could be activated in the adult heart as to be capable of generating new cardiomyocytes, are not elucidated.24 Genetic lineage tracing with 15N-thymidine labeling followed by imaging mass spectroscopy showed that the mammalian heart can be regenerated from preexisting cardiomyocytes however, being limited in potential.9 These cardiomyocytes might be involved in ongoing renewal, but their response to the extent of MI seems to be blunted.
Patek, "The morphology of the lymphatics of the mammalian heart," American Journal of Anatomy, vol.
Electrophysiological effects of antidepressants on mammalian hearts and crayfish giant axon.
Within the mammalian heart, the distribution of connexin43 (Cx43)-containing gap junctions is essential to facilitating the coordinated spread of electrical activation throughout the cardiac muscle cells (cardiomyocytes) and allowing the heart to contract properly.
One hundred or so of these toxins have been studied to date and have demonstrated such selectivity for specific receptors that some have been used, for example, to help characterize subtypes of nicotinic acetylcholine receptors in mammalian heart muscle, leading to a better understanding of the mechanisms that control heart rate and contractility (Bibevski et al.
Tissue-specific stem progenitor cells can be found in the adult mammalian heart. When cloned in suspension they form cardiospheres.
Glucose regulation of load-induced mTOR signaling and ER stress in mammalian heart. I Am Heart Assoc.
TEHRAN (FNA)- Up until a few years ago, the common school of thought held that the mammalian heart had very little regenerative capacity.
In a similar fashion, the researchers were able to induce comparable heart-rate growths in rats, indicating that the fatty acids have a similar effect on the mammalian heart.