Guyton and Hall Medical Physiology (Chapter 81) Male Reproduction || Study This!

hello and welcome to the review of chapter 81 of guyton and hall's medical physiology textbook in this chapter we're going to go over the male reproductive system now just before i get started i have to acknowledge it has taken a bit of time to actually produce these chapters and i'll be honest it's really centered around not knowing what youtube's policy is around the reproductive system and putting up videos about it it seems like it's going to be okay but that's why there's been a delay and there's been a lot of requests for these chapters so

we'll go through this chapter and the remaining chapters of guided hall and if you enjoy the videos please don't forget to give it a like and subscribe to the channel as it does help our channel grow if you want to support the channel you can do so through the patreon link within the description so to start off with there are three main functions of the male reproductive system number one is spermatogenesis which is the formation of sperm number two is the sexual act and then number three is the regulation by various hormones so we'll go

through each of these systems through this chapter but first before getting into that we should talk about the anatomy so sperm is produced within the seminiferous tubules within the testes they are then transported into the epididymis where they are temporarily stored before being laid out into the vas deferens which enters the body of the prostate gland it eventually passes into the ejaculation duct and into the internal urethra which is the last connecting link so the first function is spermatogenesis which is the production of sperm that occurs within the seminiferous tubules and it all starts off

at puberty where spermatogonia which is this original germ cell actually starts to divide via mitosis to increase the numbers of these cells within the testes these cells will then eventually be turned into sperm so once the spermatogonia have formed they actually cluster around these holy cells the sertoli cells are almost like a nutritional cell for the spermatocytes or the spermatogonia so once the spermatogodia cross into the and now surrounded by these sertoli cells they will undergo this mitosis and actually form primary spermatocytes these primary spermatocytes then undergoes meiosis remember meiosis is different to mitosis because

with meiosis you split your chromosomes in half and form two daughter cells whereas mitosis the two cells that form actually contain all of the chromosomes from before because you have duplicated the chromosomes so meiosis splits our 46 chromosomes in one cell to two separate cells which have 23 chromosomes each and these are now called spermatids and these are randomly divided up so then the sperm will contain half of the male characteristics or the half of the male genes which will then combine with the egg of the female which has half of the female genes so

then you end up producing a baby that has half of the female and half of the male characteristics in a random fashion so once these spermatids are formed after meiosis they then mature via differentiation into eventual mature sperm you can see that they have a different shape to them having this head and tail morphology now it's important to know that we have two sex chromosomes an x and a y for a male and an x and an x for a female now those get divided during meiosis so then one sperm will actually have the x

chromosome which is the female chromosome and that's called a female sperm and then the other sperm will have the y chromosome and the male chromosome so then that's now called a male sperm so the sex of the eventual baby actually depends on which sperm actually penetrates the egg because the egg can only ever be x so if you have the male sperm combining you get a male because it has that y chromosome whereas if you have the female sperm or the x chromosome combining with the egg you'll get a female now when it gets to

the actual anatomy of the sperm itself the head has this little portion right at the front called an acrosome the necrozome is formed from the golgi apparatus and it contains a lot of enzymes mainly hyaluronidases and also proteolytic enzymes and this allows the sperm to actually penetrate the wall of the egg because it releases those enzymes to basically digest down the wall of the egg so then the genetic material can actually enter other than this acrosome and this head we then have this neck and body portion which contains a lot of mitochondria to supply all

the atp and the energy for the tail or the flagellum the flagellum is nice and simple it's just the central skeleton or an axoneme of microtubules that then actually allows the sperm to form a whip-like movement to then move and be able to travel a distance the normal sperm can actually move around about one to four millimeters per minute which is relatively fast for such a small little structure so there's this little paragraph about some hormones that gets into more details later in the chapter just as a little summary testosterone is secreted by leydig cells

and this actually helps with the formation of sperm particularly the first stages luteinizing hormone released from the anterior pituitary gland that we covered in earlier chapters this stimulates the latex cells mentioned just previously to secrete the testosterone so that's a stimulation for testosterone and production fsh or follicle stimulating hormone is also secreted from the anterior pituitary gland and that stimulates the setoli cells and this actually allows the maturation of sperm estrogens probably also involved in spermatogenesis and then growth hormone helps to control the background metabolic functions of the testes so once the sperm is formed

within the seminiferous tubules it then passes into the epididymis they're actually non-motile and they can't fertilize anything at that stage and they need to be matured in order for it to actually be able to move and actually be able to fertilize the ovum so they develop this capability of motility within the epididymis and also once they have been ejaculated as well so in the epidermis they're stored they can be stored for up to a month and then once they are ejaculated they become motile and have this maturation process mainly because of the fluid that they're

surrounded in which contains hormones testosterone estrogens enzymes and also special nutrients as well they need a slightly alkaline medium to actually stay alive for as long as possible a very acidic environment will just rapidly kill the sperm so that's what this fluid actually contains is this alkaline environment to keep them alive once i've been ejaculated into the female genital tract they only last for one to two days so this fluid that keeps them alive and also helps to mature them that is formed in several different areas so one is within the seminal vesicles which secretes

the mucoid material so it contains fructose citric acid and other nutrient substances in addition to prostaglandins and fibrinogen so fructose nutrient substances they help to keep the sperm alive whereas prostaglandins actually helps to aid in fertilization of the ovum and fibrinogen actually as you'll see a little bit later that helps to keep the semen all held together a prostate gland produces milky fluid that contains calcium citrate ions phosphate ions and a clotting enzyme pro fibrinolysin so this helps to break down the fibrinogen from the seminal vesicles into fibrin and create a coagulant it also has

the slightly alkaline characteristic to keep the sperm alive with all this fluid into account including the sperm we end up with what's called semen so semen is the sperm and the fluid from the vas deferens which is only about 10 percent then the fluid from the seminal vesicles which is the majority at 60 percent and also fluid from the prostate gland at 30 percent then there's this very small amount from your mucous glands as well the average ph is very alkaline or little alkaline i should say at 7.5 and once again we contain this material

which is able to convert fibrinogen into fibrin to form this coagulum to kind of keep it all together this then breaks down after 15 to 30 minutes so then that coagulum dissolves and the sperm at this time becomes highly highly motile so that clearly occurs after ejaculation so once in the female reproductive tract the sperm actually goes through this process called capacitation and this is the final processes that allows the sperm to actually be able to fertilize the ovum what happens in the female reproductive tract the fluids within the uterine and fallopian tubes wash away

all the inhibitory factors within the male genital tracts or those inhibitory factors within the fluid it's trying to keep the sperm alive prevent them from being too motile and tire themselves out and die essentially while they're still in the male reproductive tract so the female reproductive tract is able to wash away all of those inhibitory substances we also get rid of this high cholesterol environment that's in the male reproductive tract which is functioning to actually harden that acrosome to prevent that acrosome from releasing its enzymes in the male reproductive tract but in the female reproductive

tract you don't have that cholesterol environment so then the head of the sperm becomes weaker and weaker as it starts to approach the ovum so then it's able to release all of those enzymes and then lastly the membrane of the sperm becomes more permeable to calcium ions which enters the cell activates the flagellum remember calcium activates muscles it's the easiest way to think about it so then the sperm increases its motility after that once it gets to the ovamer has to now dissolve the granulosa cell layers using these higher laronidases and also proteolytic enzymes as

well so once you get through that thick covering which is called the zona pellucida sperm's able to bind to receptor proteins that then releases these enzymes and creates a penetrating pathway the genetic materials then able to enter the oocytes form the new cell genome and we officially have achieved fertilization once that occurs calcium ions actually dissolve or diffuse into the oocyte's membrane and basically kick off all the sperm that are already there and harden the shell which prevents other sperm and other genetic material from entering the ovum since you only need two halves to form

a fetus obviously one half from the male one half from the female to create a baby so there's just a little portion here on the male sexual act it starts off with sensory nerve signals mainly coming from the gland's penis through the pudendal nerve to undefined areas of the brain and can also be stimulated from areas adjacent to the penis and also be stimulated if there's any infection or inflammation of the sexual organs and this is kind of how aphrodisiac drugs work by inducing inflammation of these areas and some congestion which kind of stimulates these

same nerve impulses there's a psychic element to kind of initiating the sexual act but it's not needed or necessary for performance because without the nerve signals from the brain the male sexual act or ejaculation is still able to occur so it starts off with erections which is through the parasympathetic nervous system and via the pelvic nerves which then causes the release of nitric oxide vasoactive intestinal peptide basically causes a dilation of the blood vessels and then the erectile tissue of the corpora cavinosa and corpus spongiosum basically fills with blood and then you end up with

an erection there is also the formation of mucus from your urethral glands and bobo urethral glands which helps to provide some lubrication during coitus but most of that is provided by the female sexual organs and then it ends with ejaculation which is actually secondary to sympathetic impulses rather than parasympathetic which originates from t12 and l2 via the hypogastric and pelvic nerves that then ultimately results in ejaculation via the contraction of the issue cavanosis and bulbocatinosis muscles at the end of the male orgasm then there is resolution of the male sexual act and then lastly here

we're going to talk about the hormones mainly talking about testosterone so there are other hormones as well collectively they're called androgens but the majority of them or the majority of the actions is from testosterone so that's really what we're going to talk about testosterone is formed from your latex cells or the interstitial cells of latex and then testosterone functions to basically give you the characteristics of the masculine body more specifically the formation and growth of the male sexual organs so as you can see we get testosterone formation and the fetus when you actually want to

form the male sexual organs and that occurs because of the y chromosome which has this region which encodes a protein called the sry protein this encodes some genes to then activate or cause the genital ridge to differentiate into cells that can produce testosterone and this region the genital region will then also eventually form into the sexual organs or the testes once the testes are developed at the last two to three months of gestation they will descend into the scrotum if there's enough testosterone you can then see that there's a little bit of testosterone produced in

the neonatal period but then in the childhood years you essentially produce no testosterone then those cells can lay dormant until you reach puberty so in puberty that's when you start to produce more testosterone that then results in growth of this male sexual organs in addition to these other side effects as well not necessarily side effects but these other effects of testosterone including the growth of hair so you start to become a lot more hairy as obviously everybody knows you end up with a lower or deeper voice and while that's occurring or why that occurs is

because of hypertrophy of the laryngeal mucosa and enlargement of the larynx and while that's occurring you can get cracking of the voice which then eventually ends up with the adult masculine voice testosterone also increases the thickness of the skin and increases secretion of your sebaceous gland so you start to sweat more and in the initial period you're going through puberty that can result in acne which eventually your body gets used to all that testosterone and the acne should resolve it also increases your muscle mass causes your bones to grow both thicker and also denser increases

your metabolic rate and also increases your red blood cells mainly because of the increased metabolic rate so these are just all the effects of testosterone in the normal male which creates these masculine characteristics it does that all through mainly just getting into the cells or the target cells and just telling that cell to increase the production of proteins those proteins then increase metabolism increase muscle building increases bone density causes the growth of hair the growth of the male reproductive organs etc so it just tells that target cell whatever its function is to increase proteins and

then that increases the function of that cell essentially these hormones get controlled actually way up in the brain due to the hypothalamus releasing you no detroit and releasing hormones gnrh as we've talked about in the previous chapters goes down to your anterior pituitary gland and causes the releasing of luteinizing hormone and fsh from your genetic tropes within your anterior pituitary gland lh is the primary stimulus for testosterone secretion in the testis whereas fsh stimulates spermatogenesis you can see that in this figure over here 8110 where we have the hypothalamus that releases gnrh causes release of

lh and fsh from the anterior pituitary in the testes lh causes testosterone release which has its androgenic effects we just talked about and also increases spermatogenesis from the sertoli cell and fsh is going to do the same thing now the cetoli cell actually releases inhibin that inhibits the release of fsh so with this negative feedback so you don't produce excessive sperm and testosterone has the same negative feedback both on the anterior pituitary gland and the hypothalamus so then you don't have excessive secretion of testosterone so we have this negative feedback to help prevent excessive secretion

and excessive function of the testes and then lastly in the placenta or in pregnancy i should say the placenta produces this hormone called human chorionic gonadotrophin or hcg which actually acts as a lh so it tells the fetus if it's a male to now produce testosterone so that's how the fetus releases that testosterone that we talked about earlier then in childhood the hypothalamus just isn't active 4g e and rh so then we don't get the production of testosterone so we're going to finish it there we're not going to flip the page over for obvious reasons

if you have the book if you have any questions feel free to drop it in the comments otherwise we'll see you in the next video