Mammals

Mammals are vertebrate animals which feed their young on milk produced by mammary glands. All have hair at some point in their lives, even if they have only a few (like most whales). They are generally endothermic ("warm-blooded"), producing body heat internally. Some species, such as seals regularly also use the sun or other environmental heat sources in addition to the metabolic heat they produce. Most species give birth to living young - with the notable exception of the monotremes (the platypus and the echidnas) of Australia and the southern Pacific region, which lay leathery shelled eggs. The approximately 5000 species of mammals range in size from the 100 foot long (30m) blue whale to the 3/4 inch (30-40mm) long Old World hognosed bat. Various species of mammal can swim, climb, run and fly. Mammals are distributed worldwide, occurring on all continents and most islands. Even islands that are said to be without mammals will have whales in the nearby waters. One species has even begun to colonize local space off earth.

Neutrophils are a type of granulocyte that all mammals posses. Neutrophils are crucial to protecting mammals against infections. Because of this, 50 - 80% of white cells circulating in the blood are neutrophils. Neutrophils are produced in the bone marrow of mammals. The average adult Homo Sapiens manufactures 100 billion neutrophils per day.

Neutrophils take 1 week to manufacture, yet once they are released into the bloodstream of mammals, they only survive for 12 hourse at longest. Because of this, the bones of most mammals have vast reserves of neutrophils in the case of an infection.

Neutrophils are 12 - 15 micrometers long. As they are granulocytes, their nucleus is divided into 2 - 5 lobes.

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From something as small and complex as a chromosome to something as seemingly simple as the weather, sex determination systems vary significantly across the animal kingdom. Biologist and teacher Aaron Reedy shows us the amazing differences between species when it comes to determination of gender. Watch the Sex Determination: More Complicated Than You Thought video This video created by Aaron Reedy and Buzzco Associates and is available through the TED-Ed website.