Hello to you internet peeps!
I am going to be writing about the endocrine system and hormones today. I had no idea of what the endocrine system’s function was until I learned about it a few months ago! So crazy to think how little knowledge I had about the human body until I started university. I even thought I had more knowledge about the human body than the general public because I used to do ballet but I was so so wrong! I think it’s true when people say that the more you learn, the more you realize how much you don’t know about anything! But let’s embrace the fact we don’t know anything and learn something new today!
So what is the endocrine system? The endocrine system is basically hormonal communication. It is an important part of any animal’s internal communication system and any animal’s hormone producing cell constitutes its endocrine system.
What are hormones then? Hormones are chemical messages sent from endocrine cells through the bloodstream to target ‘cells’ where these messages are processed and integrated into a cellular response. These chemical messages play an important role in regulating the internal environment of the organism. But like sending any message to anyone, it is important to only send messages when required. We’ve all been there being annoying by texting tons of emojis to our loved ones which do no good to anyone really. And it is the same with hormones but with more serious physiological circumstances. All hormones are produced in endocrine glands (endocrine organs so to say) that usually have an effect in other parts of the body but in most cases, the endocrine glands are controlled by the hypothalamus via the pituitary glands. The messages that different hormones send to many different areas of the body are meant to be widespread and longer-lasting regulatory actions compared to the messages being sent in the nervous system. This is why even though the endocrine system has a similar job to the nervous system, it has completely different ways of communicating and functioning in the body. Hormones mediate responses to environmental stimuli, regulate growth, development, and reproduction while the nervous system responds to sensory stimuli.
How does the endocrine system communicate through hormones then? Well, it’s like sending a text message or sending a post via the Royal Mail. It’s as simple as that. Actually, not quite as simple but the general idea of communication is simple. The sender being myself in this instance sends a text message (the communication channel) to my sister, the receiver, asking for pictures of my dog Tory. She will then read the message and send me a few snaps of my adorable dog Tory like this one!
Apologies for the not so subtle photo attachment! More photos of my dog will pop up on this blog every once in a while as I am one proud dog mom! But going back to my point, the previous example was to help you understand the general idea of how the endocrine system communicates to the rest of the body.
Let me give you a more specific example of how the endocrine system communicates. You just had a delicious piece of chocolate cake and the beta cells in your pancreas detect your increase in blood glucose concentration. The pancreas being an endocrine gland, will send some insulin through your bloodstream to the liver telling it to increase its uptake of glucose. The liver will then receive that message through insulin and get to work by converting glucose to glycogen, resulting in your blood glucose level decreasing to its normal level.
But besides from insulin, there are so many different hormones that if I were to tell you about all the hormones, I would have to spend the whole day on my desk! But what I can tell you is the 3 major classes of hormones and a few examples of those hormones. The different classes depend on the hormone’s molecular structure. The first class is the amine hormones based on the amino acid tyrosine they have. A few examples of amine hormones are epinephrine, norepinephrine, and thyroxine which are all hydrophilic. The next class is the peptide hormones. Peptide hormones have very distinctive chains of amino acids and these hormones are also hydrophilic. Most hormones in our body are peptide hormones and few example of them are oxytocin, insulin, and growth hormone. Last but not least, the third class is the steroid hormones made from cholesterol and is the only class of hormone that is hydrophobic. Estrogen, testosterone, aldosterone are all examples of steroid hormones.
And as I mentioned earlier, peptide and amine hormones are hydrophilic while steroid hormones are hydrophobic. This makes a difference in how the hormones reach a cell. The membranes of cells are made of lipids which do not allow for hydrophilic molecules get across them. So as you can see in the diagram below, the left illustration is a target cell for hydrophilic hormones that has its receptor on the outside of the cell membrane so the hormone doesn’t have to go through the cell membrane. Hydrophobic steroid hormones, however, can go across the cell membrane so the target cells for steroid hormones have receptor proteins inside the cell. Once the hormones activate the target cell, it alters the activity of the target cell by increasing or decreasing some of its functions.
Because of these differences in water solubility, peptide-based hormone’s signals are often more transient and may sometimes alter gene expression. Steroid hormones, however, tend to be longer lasting and mostly alter gene expression.
Let’s move on to the endocrine system as a whole and learn about some of the endocrine glands that we have in our body.
Silly as it may sound, endocrine glands are glands of the endocrine system that produce hormones and secrete them directly into the bloodstream. Our endocrine glands are the hypothalamus, 2 pituitary glands, thyroid gland, parathyroid gland, 2 adrenal glands, gonads(testes or ovaries), and sort of the pancreas, the thymus, and the pineal gland.
The hypothalamus and the pituitary glands are located in our brain. This particular location links our endocrine system with the nervous system for certain situations. And the cells of the hypothalamus actually look like neurons in the nervous system. As you can see in this diagram, the hypothalamus kind of holds to the testicle looking pituitary glands. The pituitary glands looking like testicles means that there are two parts to it. The anterior pituitary gland and the posterior pituitary gland. The hypothalamus controls hormones produced by the pituitary gland so to remember this, I think of the hypothalamus having the upper hand on the pituitary glands since it is also anatomically above the pituitary glands.
Some of the hormones released by the hypothalamus are dopamine and corticotropin-releasing hormone. The anterior pituitary glands have 6 releasing and inhibiting hormones such as growth hormones and thyroid hormones. The posterior pituitary gland, on the other hand, acts as a storage to release oxytocin and antidiuretic hormones for when the body requires high amounts of it.
The next gland is the thyroid and parathyroid gland. The thyroid and the parathyroid glands are located by your larynx in your neck region. It produces hormones that help with increasing metabolism of most body tissues. It also plays a big role in providing you with normal growth and development. The thyroid glands produce thyroid hormones thyroxine and triiodothyronine, and also produce calcitonin and the parathyroid hormone which helps with decreasing or increasing calcium ions in your blood for homeostasis.
Moving on to the adrenal glands that sit on top of your kidneys. The adrenal glands respond to short-term and prolonged stress. When someone is experiencing short-term stress, the stress filled nerve impulses go to the hypothalamus in the brain where it sends signals down going through the spinal cord, down the preganglionic sympathetic fibers to the adrenal medulla in your adrenal gland. The adrenal medulla will then produce amine hormones called catecholamines that help increase your blood pressure and metabolic rate, convert glycogen to glucose for energy and releases that glycogen to the blood stream. The way in which the adrenal gland react to prolonged stress, however, is slightly different. When prolonged stress signals are sent to the hypothalamus, the hypothalamus will produce corticotropin releasing hormones to the anterior pituitary gland telling it to release corticotropin to the adrenal cortex of your adrenal glands. The adrenal cortex will then release mineralocorticoids which help your kidneys retain sodium and water while also increasing your blood volume and pressure. The adrenal cortex will also release glucocorticoids which help to convert protein and fats to glucose for energy, increase your blood glucose levels, and suppress your immune system.
Now the testes and ovaries, the gonads! Our precious reproductive organs! And yes you’ve probably guessed correctly that the gonads produce sex hormones. Estrogen and progesterone are examples of sex hormones produced in the female ovaries and the testes in men produce testosterone.
Although I mentioned the pancreas, the thymus, and the pineal glands, they are not really official endocrine glands so I won’t be talking about them today. I will when I properlly learn about them though!
Thanks if you’ve made it to this long post and I hope everything I said was east to understand. Next time I will be talking about our major food groups. Till then guys!