Our Endocrine System

Hi and welcome to our brief Journey through our Endocrine System. We will give you some basic notions, show how it is organized and how it works, and convince you that this is a delicate issue, important for our health. Our endocrine system a collection of glands within our body. This one that you see here is the thyroid. Our glands work in close connection and cooperation with the Nervous System (here you see a nerve cell) … ….and with the Immune System (here you see antibodies attacking a virus) Our endocrine system takes care of - for instance - Homeostasis and Adaptation, that is “to change something so that important things never really change”.

A sort of: maintain internal balance. .. or takes care of our Metabolisms, that is - the set of chemical reactions in our cells… .., or controls puberty, fertility and reproduction, including gestation .. … and control general physical, neurological and mental development. Many functions indeed ! We could not live happy without hormones, probably we could not live at all. Here you see the collection of our glands. When the cells that produce hormones – called endocrine cells – group together, This is a gland Some endocrine cells stay alone and scattered, in the Kidney, in the Lungs, in the Intestine, in the heart. They are also quite important.

To make things more complicated, one cell can produce more than one hormone, and sometimes the same hormones can be made by different endocrine cells. … OK but what is a hormone ? A good definition is “a natural endogenous substance that at low dose signals from one cell to another, and cause a response” The key words are ; Natural Endogenous, Substance, Low dose, Signals, From ..To…and Response Natural Endogenous means internal. Substance is for instance Peptide and Steroid Low Dose means very very low amount. Signals mean that cells talk to each other. …from … to… means that substances travel. Response means that something happens …. How do hormones travel and talk between cells.

,,, The producer cells injects the hormone in the blood flow, the hormone travels and reaches various organs and can leave the blood flow. The target cells are the responders; the non-target cells are non responders. This is called the Endocrine way …or the endocrine cell produce a hormone that directly reaches the target cells. This is called the Paracrine Way…., clearly these hormones don’t go very far. or… the endocrine cell and the target cell is …the same cell, so the hormone acts on the very same producer cell. This is called the Autocrine way. How do hormones talk? The target cells need to have receptors, sort of specialized “ears” only listen to one single hormone at a time.

Receptors come in two flavors: the membrane Receptors, like those for peptides, growth hormone and adrenalin, .. or the Nuclear receptors, that stay inside of cells. Such as the receptors for steroid hormones, thyroid hormones, retinoic acid. The hypothalamus is perhaps the center of all, and is part of the brain. Just under the hypothalamus we have the pituitary. The nerve cells of the hypothalamus do something special, they produce hormones, and export them in the blood flow. Many control the pituitary, that is very near. Others control appetite, thirst, temperature, sexual functions, sleep and emotions. This is the Pituitary. This small important gland receives instructions from the brain, and then produces several

hormones : the C, the G, the T, the L, the S… and others This is the list of the hormones that come from the anterior pituitary… …and this is the list of the hormones that come from the posterior pituitary. Isn’t this incredibly complex ? The thyroid gland is also very important and produces T3 and T4, two iodinated hormones. Thyroid hormons control body temperature, the accumulation and consumption of energy, the heart rate, and is very important for baby development when the baby is still in the uterus. The Pancreas is located near our digestive tube, and contains groups of cells that produce Insulin and Glucagone.

These hormones … … control the glucose in our blood, to make sure that it never goes too high or too low. If this is not working properly, we are at risk of diabetes or other serious conditions. Diabetes can be treated with insulin, in some cases. How is the complex set of hormons and receptors regulated ? To make it simple, it is like a self-regulation. One element produces a hormone that controls another element, but this in turn produces one hormone that controls back the first one. This type of control is called feedback ….

We can have short or long feedbacks, but the important fact is : the levels of hormone never go to high or too low, they oscillate. Think about Glucose, Insulin and Diabetes. Talking of OSCILLATIONS, do you kwow about biorhythms ? These are timely repetition of a biological event, at various frequencies. There is one in our brain associated with a main biologic clock located in the hypothalmus of our brain. One easy example, Think about our sleep-wake daily rhythms. .. or think about the woman’s cycle, during her fertile age … or think about hybernation in animals, seasonal reproduction….. etc. These are all controlled by the climate and the biorhythm together.

Our endocrine system is very delicate: many small glands, active for long times, very low doses of hormones, complex feedback regulations. Sometimes things can go wrong. Diseases due to altered hormones, or altered responses, are many. These are the most frequent or the best known ones. Now that you have learned this, you can see why exogenous chemicals may cause harm to our endocrine system.