Fat Tissue Expansion: Part II ~ Overview of How it Can Happen

In Part I, I laid out some terminology that we'll use in the discussion of how we get fat.  In this installment, I'm mostly going to list the various means by which fat tissue can expand, emphasis on the word can.  Because as future installments will lay out, while some of these mechanisms are plausible, some of these mechanisms contribute very little if at all to the fattening process. 

So what mechanisms might be involved in the expansion of fat tissue?  It is not controversial that fat tissue expands by two means:

• Adipocytogenesis:  The growth of new fat cells, increased fat cell number
• Adipocyte growth:  Increased size of adipocytes

Fat tissue also contains blood vessels and connective tissue, the amount and mass of which no doubt increases and decreases with expansion and contraction of the tissue.  I consider this to be a negligible component, or at the very least out of our control and proportional to adipocyte size & number, so won't really discuss this.  However there are two more related "components" of fat tissue that may be significant, likely moreso the greater the degree of obesity we're talking about:

• Adiposopathy:  Macrophage infiltration of "sick fat"
• Inflammation and lipid associated water (mostly extracellular)

Of the above, it is the adipocyte growth, often referred to as hypertrophy in the literature, that is likely the dominant factor in fat tissue expansion, especially in adults.  Fat cells grow when there is a net deposition of triglycerides in the fat cell.  So I'll be discussing:

• Factors favoring triglyceride deposition in adipocytes, including hormonal forces
• Factors suppressing lipolysis & NEFA release from adipocytes
• Sources of lipids for deposition.

There are several possible sources of the lipids that can accumulate in fat cells to make us fatter.  These are listed below 

• Dietary fat -- chylomicrons
• Lipoprotein particles containing lipids -- mostly VLDL triglycerides and chylomicron remnants
• Hepatic de novo lipogenesis -- the conversion of non-lipid substrates, mostly glucose, to fatty acids in the liver
• Adipose de novo lipogenesis -- the above, but within the fat cells themselves
• Recycled NEFA

My apologies that my HTML skills  do not allow a nested outline format for the topics of future posts.  I'll pretty much be going in order of the topics here ... and if at some point Blogger or my HTML skills allow, I'll come back and revise this.

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In Part III, I'll look at the role of adipocyte number in the growth of  fat tissue