I have felt studying the endocrine system with my daughter-in-law that I was plopped down in the middle of nowhere.

I was lost amidst the trees and hadn't a view of the forest. I didn't know where I was and couldn't get my bearings. I needed some kind of overview.

Today, I got on Wikipedia and got one. 

The endocrine system[1] is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. ...the hypothalamus is the neural control center for all endocrine systems. One of the most important functions of the hypothalamus...is to link the endocrine system to the nervous system via the pituitary gland.

Glands that signal each other in sequence are often referred to as an axis, such as the hypothalamic–pituitary–adrenal axis.

...

Major endocrine systems

editThe human endocrine system consists of several systems that operate via feedback loops. Several important feedback systems are mediated via the hypothalamus and pituitary.[4]

• TRH – TSH – T3/T4

• GnRH – LH/FSH – sex hormones

• CRH – ACTH – cortisol

• Renin – angiotensin – aldosterone

• Leptin vs. ghrelin
...
...The hypothalamus and the anterior pituitary are two out of the three endocrine glands that are important in cell signaling. They are both part of the HPA axis...
...
Hypothalamus: The hypothalamus is a key regulator of the autonomic nervous system.

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All of those in bold were trees that I recognized from study of minute, specific questions out of any context that I had. I have some overview now. Maybe I can help my beloved D-2 pass the USMLE. Great success.