I have heard hypothyroidism, heavy metal, excess estrogen and diabetes can all cause hair loss in men. Can you let me know technically how it caues hair loss?

Hypothyroidism and diabetes decrease circulation, which can damage the hair follicles.  This is why minoxidil (Rogaine) is used to treat hair loss.  Minoxidil was originally being tested as an a hypertension drug, but failed.  As a side effect they noticed increased hair growth in some of the participants, so it got marketed as a hair loss treatment drug instead.  The reason it helps some people though is that it increases circulation to the scalp.  Massaging the scalp does the same thing though and is safer.

As far as heavy metals it would probably depend on the heavy metal, but I suspect most of them damage the hair follicles as they are generally detected in hair samples.

High estrogen does not cause hair loss in men.  Actually it can do just the opposite.  It is elevated dihydrotestosterone (DHT) formed from testosterone that kills the hair follicles or makes them go dormant causing the hair to fall out.  Estrogen can counter DHT formation.

And if you have any of these conditions how to limit the hair loss until you address the health issue?

Depends on the cause.  Increasing scalp circulation with massage and brushing with a boar bristle brush is a good start.  If there is elevated DHT then here is a post on that:

http://curezone.com/forums/fm.asp?i=1547772#i

Is it these conditions cause deficienices that are needed for healthy head of hair?

If so what deficienices?

Nutritional deficiencies can also lead to hair loss.  Here is an old post on that:

http://curezone.com/forums/fm.asp?i=1547772#i

There is an autoimmune alopecia as well, although it is rare.

Can ulcers/bacteria/yeast cause hair loss - if so how?

Infections of the scalp can lead to the hair falling out in patches.  How depends on the type of infection but is usually due to damage to the hair or hair shaft.

One other thing to keep in mind is that if the hair follicle is dead the hair will not come back.