Lecture 2: Endocrine Principles Intro to the endocrine system. Includes information on diabetes, obesity, metabolic disorders, some basics on hormones and positive and negative feedback loops.
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Physiology Lecture 2
The endocrine system controls bodily functions. Hormones such as insulin bind to
receptors, which trigger intercellular pathways. These pathways tell the cell to perform
an activity, and all the cells which received the hormone communicate between each
other to perform a bodily function.
Hormones can bind to receptors in completely different systems and still have the same
effect. For example, insulin, the hormone that controls the amount of blood glucose can
bind to the liver or the brain. If it binds to the brain, the brain sends a signal to the liver
along the efferent vagus nerve to decrease glucose production.
Two of the most common endocrine disorders are diabetes and obesity. Causes of these
include hypo-, which is a prefix denoting a lack of a certain hormone, or a resistance to
the hormone, which means that the hormone hasn’t enough effect on the victim.
Endocrine glands are identified through a series of steps. First, the removal of the gland
to create consequences, then the gland or its extract is replaced. Also, extra extract is
introduced, which should create the opposite consequences of removing the gland.
Finally, the extract can be tested using a biological assay.
Endocrine glands include: pineal, hypothalamus, pituitary, thyroid, parathyroid, thymus,
adrenal, pancreas, ovary and testes. A more recently discovered one is fat.
o Fat secretes leptin and adiponectin. The former lowers appetite and the latter
increases the effect of insulin.
Endocrine glands are named such because they secrete the hormones into the
Hormones can communicate over long or short distances. The longer ones use the
bloodstream or neurons, and the shorter ones just hop to adjacent cells. In the short
version, the hormones can even bind to the secreting cell in order to check the level of
said hormone in the body. Too much, and it’s cleared from the system.
Many tissues create hormones from specialized cells, such as the heart creating atrial
In summary, hormones are chemicals created by cells (either in tissues or specialized
endocrine glands) that communicate between cells. They do this by binding to specific
receptors which send signals that alter the activity of these target cells. They are meant
to maintain homeostasis of the body.
o For example, insulin maintains a healthy level of glucose in the blood by sending
a signal to the liver (either by direct binding to the liver or binding to the brain
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