ADIPOCYTES, PHOSPHOLIPIDS & BIRDS

Solution Preview

Please see the attached MS Word document, 'QuestionsAnswered.doc,' for the complete responses to the submitted questions. Rather than paste them here, the answers are only attached in the document since I believe that the document's format will make it much easier to follow and understand the responses, and that format would be lost here.

"Questions Answered"

1. Animals that become naturally obese, do they have enormously increased numbers of adipocytes compared to their leaner relatives?
Briefly:
It depends partially on age (mostly on age or metabolic state)-
Neonates in humans & young in other animals: mostly an increase in number of adipocytes;
Mature/maturing humans and other animals: mostly an increase in the size of adipocytes;
Summary:
Adipose tissue mass depends on adipocyte number and adipocyte size. Increases in adipose mass can result from hyperplastic growth, an increase in the total number of adipocytes (by mitosis, simple cell division). Adipose tissue mass may increase by hypertrophic growth, an increase in the size of adipocytes by fat accumulation within the cell. In mammals, typical growth stages follow this example in rats:
1) From birth to 4 weeks of age, adipose tissue growth is hyperplastic. Overfeeding in this period can lead to permanent, lifelong increases (and tendency for weight gain) in body weight and total number of adipocytes .
2) From 4 to 14 weeks of age, adipocyte growth is hypertrophic AND hyperplasic.
3) After rats are 14 weeks old, adipose tissue growth occurs primarily by adipocyte hypertrophic growth.
NOTE: The adipose tissue growth in humans is less defined; the human newborn is already relatively fat. Two sequences of hyperplastic growth occur during the third trimester of pregnancy and later in life, just prior to and during puberty.
Hyperplastic growth may occur in mature animals, including humans and rats. Fat cells will fill with lipid to a critical size, then are stimulated to differentiate, and adipocytes increase in number. This critical size is probably not reached unless the ...