Hello everyone, welcome! Today we'll be doing a thorough review of the endocrine system, specifically for those who are getting ready to take the ATI-T's exam. First off, there are a few key points I want to go over before we jump into the glands and into the hormones. The endocrine system, in a nutshell, functions to maintain homeostasis in the body.
It keeps everything working within normal limits using negative feedback. So with the help of negative feedback, the endocrine system knows whether to secrete more hormones or inhibit them. The feedback mechanism is triggered by blood levels or more so the amount of substance in the blood.
So for example, hemoglobin or glucose, those are the substances. If there are low glucose levels in the blood, then the endocrine system will be triggered to release glucagon. And if there are high levels of glucose in the blood then the endocrine system will be triggered to release insulin to lower those blood level I mean to lower those glucose levels so that they're in within normal range. The endocrine system uses hormones to send messages throughout the body and much like the nervous system does except the nervous system sends quick impulses around the body and it usually generates a very quick result or response.
Also affect the effects are more sustainable or in other words they last longer. the endocrine system affects bodily processes related to growth, development, metabolism, immune function, reproduction, response to stress, water, and electrolyte balance. it secretes hormones directly in the blood system and as i mentioned this is the this is part of the reason why there is much lower sorry slower response than the nervous system Also, just want to mention the big difference between endocrine system and exocrine system is that the endocrine system deposits the hormones directly in the blood, while the exocrine system deposits secretions through ducts that eventually make their way outside of the body or into a lumen or opening into an organ. So endocrine system goes directly into the blood while exocrine system goes into ducts.
Cells that have specific receptors for a specific hormone will be affected by these hormones. So just to give you a visual of this, I like to think of like a lock and a key where the lock is the cell with a specific receptor and the key is a specific hormone. That lock can only be opened by a specific key. So when hormones float around in the blood and are dropped off to their destinations, they cannot connect to just any cell they'd like. They must connect with the cell that has a receptor specifically for that hormone and only that cell will be affected by the hormone and it will carry out the directions or whatever the hormone is asking it to do because these hormones are carrying around a message or instructions for the cells.
Okay so let's take a look at the glands and the organs that are most involved in the endocrine system starting off in the brain. Here we have a small area called the hypothalamus. Situated anteriorly near the cerebellum is the pineal gland and stemming off the inferior portion of the hypothalamus are two lobes.
These lobes make up the pituitary gland. Let's take a closer look at this pituitary gland. It consists of an anterior portion and a posterior portion.
Both these lobes receive messages directly from the hypothalamus sitting right on top of them. The anterior receives messages via a blood vessel. So how do we get messages from one place to another via blood?
Hormones, right? So hypothalamus sends hormones to the anterior pituitary gland and that's how they communicate with each other. The posterior on the other hand is connected by nerves. So therefore it does not need hormones to communicate because it communicates through these nerves. Okay, so let's move on with the other organs and glands in the body and then we will revisit the brain and talk specifically about the hormones here.
So if you are just here for the hormones, then you can go ahead and skip forward. But I highly recommend that you learn and associate these organs with the glands and the hormones first because it will help you understand so much better in my opinion. So next we have the thyroid and the parathyroid.
The thyroid hugs the trachea and the parathyroid glands are these tiny lobes that are the size of a grain of rice and they stick to the posterior or the backside of the thyroid. Next we have the thymus. This is located between the sternum and the heart. Normally it begins to get smaller after puberty and you'll see why once we look at the hormone that is secreted from here.
Next is the pancreas which is situated mostly posteriorly to the stomach. Next we have the kidneys and the adrenal glands. The brown here is the kidneys and the yellow are the pair of adrenal glands. So looking closely at the adrenal glands We will notice that it has two major components that are very relevant to the endocrine system because both these components they secrete different types of hormones.
So the inner layer is our medulla and the outer layer is the cortex. Next we have the gastrointestinal system which we know is inferior to the stomach and the lungs. Next is the liver that is in close proximity to the pancreas and the gastrointestinal system but The liver is on the right side of the body and the pancreas is mostly on the left side of the body. Next we have the adipose tissue which is also known as fat.
Next are the ovaries and the uterus in females and the testes in men. So these are known as gonads in both men and women. Ovaries and testes that is are known as gonads in men and women.
And these are all the major glands and organs associated with the endocrine system. So now let's go back to the top and take a look at the hormones that are excreted and the pathways that they take throughout the body. So starting again with the brain, we have the hypothalamus that is also known as the control center because it regulates much of the other hormones.
Specifically, it tells the pituitary hormone what to do. I'm sorry, the pituitary gland what to do. It is also the link between the nervous system and the endocrine system.
It secretes the following hormones. Thyropropin releasing hormone, corticotropin releasing hormone, growth hormone releasing hormone, prolactin releasing hormone, and gonadotropin releasing hormone. RH stands for releasing hormone and what that means is it these hormones will tell the pituitary gland to release a hormone.
So let's take a closer look at the different pathways each one of these hormones take. Starting with the thyrotropin releasing hormone. Thyrotropin releasing hormone is excreted by the hypothalamus and it travels to the anterior pituitary gland. Here the pituitary gland gets the message to release its thyroid stimulating hormone.
This thyroid stimulating hormone then travels to the thyroid gland and here the thyroid is stimulated to secrete its hormones. which are T3, T4, and calcitonin. So I've boxed all of the hormones I've mentioned and the ones that you need to know and I'll continue to do so for the rest of this video. T3 and T4 are responsible for both the development and the cellular metabolism. So in other words, the T3 and T4 regulate how fast a cell is able to work.
Calcitonin is responsible for decreasing calcium levels in the blood. Moving on to corticotropic releasing hormone. It is released by the hypothalamus and it travels to the anterior pituitary gland.
Here it tells the pituitary gland to release a hormone. That hormone is adrenocorticotropic hormone or ACTH for short. The pituitary releases this hormone and it travels to the adrenal glands. So here it has an effect on two areas of the adrenal glands, the cortex and the medulla.
In the adrenal cortex, it will stimulate the release of cortisol and aldosterone. In the medulla, it will stimulate the release of norepinephrine and epinephrine. So let's start with cortisol and what effects it has on the body. It is known as the stress hormone and the more stressed you are, the more cortisol will be released in the blood for you to use.
So it's sort of like a coping mechanism that your body does for when you're stressed out. Cortisol is going to increase fat metabolism, increase blood glucose. It's going to determine the fight or flight response. It's going to decrease your immune system and decrease your inflammation.
And basically all of these things are related to flight and fight response because they're going to kind of boost up things that are going to help you if you were to fight, like blood glucose, because that's going to give you energy. And they're going to decrease things metabolism of some things in your body that are not necessary for fight or flight. So they're going to put those things on hold and your body's going to going to conserve energy and metabolism for things that are needed for a fight or flight response.
So aldosterone increases the amount of sodium in your blood. So what happens when there is more sodium in the blood? Well we know where sodium goes, water follows.
So the more sodium we have in our blood, the more water content or water volume we will have in there too, which actually equals blood volume. So increased blood volume will result in increased blood pressure. So in short, aldosterone will increase blood pressure. so next norepinephrine and epinephrine.
they have similar roles and they work hand in hand to prepare our body for the fight or flight response, something similar to cortisol. so they have a ton of effects on the body and in fact they affect every single organ in the body. so we're just going to focus in on the most important effects that they have since there's just so many.
First off, they increase the heart rate, they increase your respiratory rate, and they also increase your blood sugar. So all of these responses will prepare a person for fight or flight. Again, I have boxed in all of the hormones for you that you need to know.
So next we have the growth hormone releasing hormone. This is also released by the hypothalamus and travels down to the anterior pituitary gland. Here it tells the pituitary gland to release its growth hormone.
This growth hormone goes directly into the blood and it travels all over the body. Nearly all cells have receptors for the growth hormone, meaning the growth hormone will affect almost all cells in the body. So the growth hormone stimulates growth in cells.
It also has a very important job when a person ages to maintain bone density and muscle mass. just by stimulating these types of cells, the muscle and the bone to grow. So next we have prolactin. It is also released by the hypothalamus and it goes down to the anterior pituitary gland.
Here it tells the pituitary gland to release prolactin hormone. Prolactin hormone then circulates in the blood and it is received by the mammary glands. Here it stimulates milk production.
So I do want to emphasize that this is milk production, not ejection, because prolactin only makes the milk or produces the milk, but there is another hormone that actually causes the ejection of the milk from the nipple. Lastly, we have gonadotropin-releasing hormone. Again, it is also released by the hypothalamus, and it makes its way down to the anterior pituitary gland.
Here it tells the pituitary gland to release its gonadotropin hormone. So there are two types of gonadotropins. One is the follicle stimulating hormone or FSH for short and the other is luteinizing hormone, LH for short.
Okay so these gonadotropins go to the gonads. In females the gonads are the ovaries and in males the gonads are the testes. The gonadotropins actually do a lot in the gonads and the process is tedious. But since it's not necessary to know the details of this process for the TEAS exam, I'm going to do a brief summary of what happens here in the gonads.
In the ovaries, LH stimulates the production of progesterone and ovulation. FSH stimulates the production of estrogen and follicle maturation. Again, I've highlighted the hormones for you here. Now the effects of both FSH and LH eventually prepare the uterus for implantation and fertilization. So that's the effects of the gonadotropin has on the ovaries.
Now let's look at the testes. LH produces leydig cells and these leydig cells produce testosterone. FSH produces cytoli cells and these cytoli cells produce androgen binding proteins.
Together the effects of LH and FSH in these testes produce sperm. So we have gone over all of the hormones produced by the hypothalamus and as you might have noticed they all begin with a very similar pathway to the anterior pituitary gland, right? And now we know all the hormones excreted by the anterior pituitary gland.
So now let's look at the posterior pituitary and don't worry there's only two important hormones you need to know here. First there's oxytocin So oxytocin gets released directly into the blood from the posterior pituitary. It causes smooth muscle contraction. So because it causes smooth muscle contraction, it causes milk to be ejected from the nipple and uterine contractions during childbirth. Next we have the antidiuretic hormone and if we break this down we can see its function or if we break this word down Sorry, if we break the word down we can see its function diuretic is related to diuresis, which is which means peeing or urinating so Antidiuretic is anti peeing in other words It tells you that it's going to tell the kidneys to hold on to the water and that water retention goes to the blood and increases the blood volume and the blood pressure.
So this can also keep somebody from becoming dehydrated because it's retaining fluid for hydration. Okay so now we know all of the hormones that are released from the anterior pituitary hormone and the posterior pituitary hormone. So let's go ahead and move on. We're gonna go to the brain again and here I have a picture just to remind you the hypothalamus, the pituitary gland, and up on the right hand side is your pineal gland so let's focus in on this pineal gland it releases an important hormone melatonin so melatonin regulates sleep and wake cycle in other words it regulates the karkadian rhythm also i've included here a picture of all of the the hormones that are released from the hypothalamus the pituitary gland and the pineal gland so Hopefully you can see the relationship between hypothalamus and pituitary gland hormones. Like thyrotropin hormone stimulates thyroid stimulating hormones.
So thyrotropin thyroid stimulating. So there's a similarity there. Corticotropin stimulates adrenocorticotropic. hormone so cortico that's the relation there growth hormone um stimulates the growth hormone obviously prolactin stimulates the prolactin and gonadotropin stimulates the gonadotropin so hopefully you're able to see these similarities and it makes memorizing these hormones much easier for you and remember the hypothalamus that's the one that's going to have the rh at the end the releasing hormone because it's telling pituitary gland hey it's time to release this hormone.
Okay, so next we have the thymus and the thymus is overlooked a lot of the time, but it is super important for the immune system because it secretes the thymocin hormone and this thymocin hormone stimulates T cell production. So this greatly influences the immune system. Next we have the heart and this secretes natriuretic.
peptides. Natriuretic peptides stimulate the kidneys to release sodium. Releasing sodium by that I mean peeing out the sodium. So remember what I said where sodium goes water follows.
So if we're releasing sodium from the body via your urine then we're also releasing more water from the body. So this in turn is going to decrease blood volume because there's less water in the blood and then it's also going to decrease the blood pressure. So natriuretic peptides, these are ultimately going to decrease blood pressure.
So next we have the digestive tract. This releases gastrin, secretin, and cck. So first off, gastrin stimulates the stomach to release hydrochloric acid.
Secretin and cck both stimulate the pancreas and the liver to secrete digestive enzymes and bile. Next we have the pancreas and this releases insulin and glucagon. These are both hormones and these actually help to regulate the blood sugar and they do opposing things.
So insulin is going to decrease blood sugar in the blood while glucagon is going to increase blood sugar. Next we have adipose tissue, which is also known as fat and this secretes leptin. Leptin is your hormone here.
Leptin suppresses appetite. Lastly, we have the kidneys. The kidneys excrete renin, erythropoietin, and calcitriol.
Renin is going to increase blood pressure. Erythropoietin stimulates red blood cell production. And calcitriol is going to increase reabsorption of calcium in the intestines.
Alrighty, my friends, we have finished. We have gone over every single hormone every gland and every tissue associated with the endocrine system that you're going to need for your t's exam so thank you for being here and happy studies everyone until next time