Overview of the Endocrine System

hi everyone dr mike here in this video we're going to take a look at the endocrine system [Music] now the endocrine system is a collection of cells and glands that produce and release hormones these hormones are just chemicals that jump into the bloodstream and have their effect in distant areas of the body now it's a communication network similar to the nervous system that controls physiological activity but it's a little bit different it's different in the sense that the nervous system is very fast it's very direct and usually it's short acting the endocrine system is the

opposite so it's quite slow to have its effect it isn't direct because it jumps into the bloodstream and travels to very distant areas of the body and it can last a long time some hormones when they're released can have their effects that last hours to days to sometimes weeks so in this video we're going to go through some of the important cells or glands that produce and release hormones and go through what these hormones are and have a quick look at their activity or function in the body we're going to do this a top to

toe mechanism start at the top and move our way down so to begin we need to start at the brain specifically at the base of the brain there's something called the hypothalamus which is telling you it sits below the thalamus this is the hypothalamus it sits here we've taken it across here here's the hypothalamus and you can see that there's an extension of the hypothalamus that has two lobes to it or two parts this is called the pituitary gland and that's another endocrine tissue or gland that itself produces and releases hormones the hypothalamus produces another

a number of hormones that has its effect to control and regulate the endocrine system of many other tissues of the body so we call the hypothalamus the master regulator or the control center of the endocrine system now five important hormones that the hypothalamus produces and releases to control many other aspects of the endocrine system these hormones are thyrotropin releasing hormone corticotropin releasing hormone growth hormone releasing hormone prolactin releasing hormone and gonadotropin releasing hormone so a couple of points here releasing hormone tells you it goes somewhere else to release a hormone all right makes sense also

tropon as a suffix tropin sitting at the end of the word if you see a hormone with tropon as a suffix it means it's going to go to another tissue of the body to tell it to release another hormone all right so how does this work well the hypothalamus talks to both aspects of the pituitary gland posterior and anterior but interestingly the anterior is connected to the hypothalamus through a blood supply which means the only way the hypothalamus can talk to it is it releases hormones and they travel through this blood supply to tell the

anterior pituitary gland to release its hormones the posterior pituitary gland is connected to the hypothalamus through nerves which means the hypothalamus doesn't need to release hormones to tell the posterior to do it it just sends a nervous signal down to tell the posterior to release hormones all right these hormones that are named here that the hypothalamus produces moves through the blood supply to the anterior pituitary to tell the anterior pituitary to release a number of hormones number one the hormone that is told to be released from the anterior pituitary gland is thyroid stimulating hormone the

second hormone now there's no particular order i'm just ordering it here for ease basically but there's no particular order but the second hormone that's released is adreno cortico tropic hormone the third is growth hormone the fourth is prolactin and the fifth is the gonadotropin gonadotropins and there's two gonadotropins you need to know that is luteinizing hormone and follicle stimulating hormone all right what happens thyrotropin-releasing hormone released from the hypothalamus stimulates the release of thyroid stimulating hormone this is a hormone that now jumps into the bloodstream and goes to the thyroid to tell it to release

its hormone so let's have a look at this number one tells that one to be released that jumps into the bloodstream goes to the thyroid so let's have a look at the thyroid quickly the thyroid is endocrine tissue that hugs the front of your trachea your windpipe what you'll find is that the thyroid produces a couple of important hormones it produces t3 which is also known as tri-iodo thyronine and t4 which is known as thyroxine interestingly t4 well most of it is turned into t3 t3 is the most active thyroid hormone so when we talk

about thyroid hormones we're talking about t3 predominantly 80 percent 20 that's the ratio that we see here there's another hormone that's released by the thyroid called calcitonin calcitonin talk about that in a sec so thyrotropin releasing hormones released by the hypothalamus travels down this blood supply tells the anterior pituitary to release thyroid stimulating hormone that jumps into the bloodstream tells the thyroid to release t3 and t4 what do they do they play an extremely important role in metabolism development and catecholamine release what's catecholamine catecholamines are neurotransmitters these are things and hormones are things like adrenaline

or noradrenaline or epinephrine norepinephrine for example that's what thyroid hormones do calcitonin is interesting what calcitonin does is it decreases the amount of calcium in the bloodstream if there's too much calcium in the bloodstream calcitonin drops that calcium down helps us reabsorb and hold on to that calcium predominantly in our bony tissue that's the thyroid hormone what happens when corticotropin releasing hormone is released from the hypothalamus traveling through this blood supply stimulates adrenocorticotropic hormone to be released also known as acth that jumps into the bloodstream and travels to adreno adrenal adrenal gland cortico the outside

of the adrenal gland tropic is it's telling it to release another hormone so it's all in the name let's go to the adrenal gland now the adrenal gland now if we look at the adrenal gland you've got the cortex which is the outside of it like the shell of it and you've got the medulla which is the inside they release different hormones so for example adrenocorticotropic hormone will go to the cortex more specifically and release cortisol and it will release aldosterone and androgens we'll leave androgens out but androgens which are male sex hormones so cortisol

what does cortisol do cortisol increases blood glucose cortisol also suppresses the immune system and cortisol also stimulates our fight or flight response really importantly what does aldosterone do aldosterone increases our reabsorption of salt what does that mean increases our reabsorption of salt aldosterone travels to our kidneys and tells our kidneys don't pee out that salt or that sodium keep it in the blood this is important because wherever sodium goes water follows so if we reabsorb more sodium into our bloodstream water follows and it increases our blood volume which means it increases our blood pressure aldosterone

helps increase blood pressure increase blood volume and also maintain hydration really important what about the medulla well the medulla isn't stimulated very strongly at all by acth but the hormones that are released by the inside of the adrenal gland are predominantly noradrenaline and adrenaline what are they that's norepinephrine and epinephrine all right what else growth hormone okay growth hormone is released from the anterior pituitary gland and that stimulates growth unsurprisingly growth hormone stimulates growth increase growth things like increased protein synthesis for example increases growth increases metabolic processes all right prolactin prolactin lactin lactation the production

of breast milk pro-lactation so prolactin which is released by the anterior pituitary gland in response to prolactin releasing hormone from the hypothalamus that stimulates milk production increases milk production now it's not milk ejection which is let down through breastfeeding that's oxytocin which i'm going to talk about in a second and then the gonadotropins the gonadotropins so tropon it's going to the gonad so for the females the ovaries for the males the testes and these hormones go to both for females goes to the ovaries for males go to the testes and has their function what is

their function all right luteinizing hormone let's look at the ovaries first what luteinizing hormone does is it stimulates progesterone it also stimulates ovulation ovulation and progesterone follicle stimulating hormone stimulates follicle maturation what's that mean in the female reproductive cycle you've got these immature primordial follicles they ultimately turn into an oocyte or an egg that gets released so fsh released by the hypothalamus well specifically the anterior pituitary gland stimulates these follicles to start moving through the process to go towards the release of a mature egg the actual release of the egg is luteinizing hormone so follicle

maturation also leads to estrogen so two really important hormones that are released here in response to lh is progesterone and fsh estrogen what about in the testes let's have a look for males in the testes well luteinizing hormone stimulates a certain type of cells called latex cells and what they produce is testosterone that's the hormone produced here testosterone what about follicle stimulating hormone well there's no follicles in males but what it does is it stimulates a certain type of cells in the testes called setoli cells so both ladies and setoli cells are in the testes

lady produces testosterone so tole produces something called androgen binding protein and both of these bind together to promote sperm production so unsurprisingly the ovaries luteinizing hormone follicle stimulating hormone produced hormones here and what this does is it leads to uterus preparation so if you're preparing the uterus and producing sperm both of these things coming together is going to support reproduction that's going through the anterior hormones what about those are the posterior pituitary hormones there's only two you need to know here there's oxytocin and anti diuretic hormone known as adh also known as vasopressin all right

firstly hypothalamus doesn't produce any hormones to travel down to tell them to be released it's just a nerve signal in actual fact the hypothalamus produces these two hormones and sends them down and they're simply stored in the posterior pituitary gland now what oxytocin does is we know it's an important hormone for building relationships but it also tells smooth muscle to contract tells the uterus to contract and tells a smooth muscle in the breast to contract to eject milk so uterine contractions and milk ejection in addition to building relationships both positive and negative it's not that

feel-good hormone that everyone says anti-diuretic hormone diuresis means to release urine to release fluid from the body it's anti-diuresis so it stops the release of that fluid so it stops peeing so this hormone gets released in times of dehydration if we need to maintain water we release this hormone this travels to the kidneys and the kidneys hold on to water and we don't pee it out so it stops urination it's there to maintain hydration all right so that's the hypothalamus pituitary glands we've gone through the adrenal glands we also and we've gone through the sex

hormones and the thyroid there's a hormone or i should say there's a gland that sits behind the thyroid called the parathyroid gland and what the parathyroid gland is it releases parathyroid hormone and it opposes the activity of calcitonin so calcitonin decreases calcium parathyroid hormone increases blood calcium so if our calcium too low parathyroid releases parathyroid hormone calcium jumps up if calcium is too high calcitonin's released and it drops calcium levels can you see that what's happening here is the endocrine system maintains homeostasis maintains function for the body brilliant that's the parathyroid hormone the kidneys also

release some hormones renin for example and erythropoietin what renin does is it works in conjunction to aldosterone increases blood pressure increases blood volume erythropoietin increases red blood cell production why would the kidneys be in control of red blood cell production well because the kidneys need to maintain itself being fed oxygen because it's such a hungry tissue so red blood cell production the pancreas we can't forget about the pancreas the pancreas is both an endocrine tissue and an exocrine exocrine means it produces chemicals that get released into ducts these ducts are contained and this is part

of the digestive system so it releases digestive enzymes but it also releases hormones two really important hormones are insulin and glucagon and again these are opposing hormones so insulin drops blood glucose levels when they're high drops blood glucose glucagon increases blood glucose levels after a meal insulin's released pulls the glucose into the cells to be used for energy if we're not eating and it's been four to six eight hours and we haven't eaten glucagon's released and it releases stored glucose into the bloodstream and then the cells can use it for energy and so what we've

had a look at here is a relatively quick run through an overview of the endocrine system