Tubulin we have centrioles one centriole keep on elongating and that is Dyenin, roll of
dynein proteins this is a complete spermatozoa so in the previous lecture we had discussed
how mature spermatozoa forms and you know the tail or flagellum of that sperm it forms
from the organelle called centriole in this video we will discuss in a bit more detail
that how flagellum forms and how flagellum Works, right, and we will start it with The,
with the discussion that how centriole, what is the structure of centriole, right? But
before that let me tell you an interesting thing. You know the only cell of human body
that contains flagellum is sperm we do not have any other cell that contains sperm, this
is contains, that contains flagellum. Right, so this is about a flagellum in human but
in other animals in small animals especially in bacteria, different cells there are lots
of flagellum they contain lot of flagellum, lots of Flagellum, right. So let's discuss
how centriole works? So here is the structure of centriole and you know centriole consists
of these tubules these tubes and this each tube, Right, this tubular structure, this
each tube is called microtubule and we have three microtubules forming a triplet. Right?
So triplet structure, three microtubules that form a triplet and we have nine such triplets
in one centriole one, two, three, four, five, six Seven, eight, nine you can count these
we have total nine triplets, Right, that forms this centriole and this is the structure of
one centriole similar to that we have an other centriole that lies perpendicular to this,
90 degree to this and both these centrioles they are called Centrosome. So a centrosome
consists of two centrioles that are arranged Perpendicular, that are arrange perpendicular
to each other, right, and if we look at a structure of a triplet it consists of three
microtubules and each microtubule, we will discuss structure of single microtubule. It
consists of, it is made up of these small beads bead like proteins you can see these
globular proteins, Right, it is made up of these globular proteins and these are called
tubulin proteins. Right, we have these tubulin proteins consist of two subunits alpha subunit
and beta subunit so this is alpha let's say alpha tubulin and this is beta Tubulin, Right,
so these alpha and beta tubulin They are arranged in a, they are arranged in a particular fashion
to form micro, micro tubule, right, and this micro tubules these three micro tubules are
ready to form a triplet and we have nine such triplets and they are arranged to form one
centriole and another centriole that is present perpendicular to this. Right, now let's see
how from the centriole flagellum arises? For this we will go to our beloved software blender
3d so here we have okay so this is a cross section of what is this spermatozoa, right,
and it consists of it is actually developing spermatozoa right now so it consists of what
is this thing across and behind the acrosome I as I have told you that this is nucleus,
nucleus is present. Right, and here we have centrioles, one centriole and the second centriole
and each of the centrioles they consist of what? Nine triplets one, two, three, four,
five, Six, seven, eight, nine interconnected with each Other, right, this is a structure
of Centriole. Now from this centriole from this centriole flagellum will Arise. How flagellum
will arise? You know these microtubules they can be elongated, they can further enlarge
if we add more tubulin proteins here and how tubulin proteins are added here very simple
just like any other tubulin* any other protein of the body tubulin proteins are also synthesized
by ribosome you know that from DNA mRNA is formed and from mRNA as we have discussed
previously, from mRNA ribosome transcribe them into mature protein or tubulin proteins
and then these tubulin protein they can come here and attach here, right, like this to
elongate any of these micro tubules. Right, they can elongate any of these Microtubules.
Now out of these triplets only two are elongated, right, like this only two are elongated let's
see how you see out of these three triplets One, three microtubules forming triplets One,
two, three only two elongate. One, two, right, here also one, two. Right, so now we have
in the flagellum, we have not triplets not nine triplets but we have nine doublet, we
have nine pairs of micro Tubules, and we do not just have pairs but we have two central
singlets, two central single micro tubules, don't worry I will 157 00:06:23,120 --> 00::26,240
discuss that what is their function very Soon, Don’t worry that what they are doing here
I will just discuss that. Right, so they keep on elongating and in the centre we have singlet’s
as well and they keep on elongating until a complete tail is formed. But before that
let me discuss another Thing. we do not just have, we do not just have these tubulin proteins
here, there are many other proteins that are associated with flagellum I will not discuss
each and every protein that is associated with flagellum because that way the lecture
will become very long I will discuss here the most important one and that is Dynein.
Let’s hide the mitochondria, you know mitochondrial sheath is also present here, right, surrounding
this, spirally arranged mitochondria here. Right, and we have rows of, two rows of what
is this? Dynein proteins, we have two rows of dynein proteins so they are also called
dynein arms. They have arm-like structure so this is outer layer of dynein this one,
this is outer layer of dynein, right, or outer row of dynein and this is inner row of dynein
so these two rows of dynein they are arranged along the long axis of, along the long axis
of these Doublets, these pairs of microtubules. Right, so this is the structure of Flagellum,
the cross section. Right, nine plus two, nine doublet and two singlets along with dynein
arms and some other proteins that keep them together. Right, and finally let's complete
this that it will form a complete tail. Right, and now we have what is this? This is a complete
Spermatozoa. So what is the structure of complete Spermatozoa? This is the acrosome, this is
Nucleus, this is centriole and this is flagellum and spirally arranged mitochondrial sheath
that surrounds the base and this tail like this inner mechanical part of flagellum, These,
these microtubules along with associated protein it is as a whole it is called axoneme. Now
axoneme along with this surrounded by this membrane is called flagellum or tail. Right,
and this is the structure of flagellum and this is the complete Structure, complete three-dimensional
structure of Spermatozoa. Right, now let's discuss how it works? Now we will discuss
what we will discuss that how this flagellum works? Right, and for this I will use my fingers
to demonstrate this. Now come here so these are my fingers of course you know this and
this finger let's suppose this is, this is one Microtubule, Right, and this is second
microtubule. So two microtubules form the doublet of flagellum and here also these two
microtubules they form doublet of what is this the doublet Of flagellum. So we have
nine such doublets but we are discussing here about two neighbouring doublets. What they
do to each other? These nasty neighbours, right, so These, these the this doublet it
is the one that is lying in front of this so this is front doublet and this is back
doublet. Right, and here these are dynein arm of this doublet. I have not shown dynein
arm here but these are the dynein of this doublet and with the help of this, these dynein
arms these doublets they can crawl on or climb on the neighbouring Doublet. Right, clear?
So let's suppose that this is the rest position, right, this is the rest position and in the
rest position the mid doublet, this dynein, this dynein, in the rest position this mid
dynein, Right, it is lying in the front of this, it is lying at the dot position. It
is lying at the dot position of this previous one, the one the doublet that is behind it.
Right, so this is the rest position and now when it crawls or climbs on this doublet,
the previous one and it will, it will what will happen? It will reach above from dot
it will reach this middle one, it will raise to star Position. So from dot position it
will reach the star position. Right, but while doing so it has risen upward, it rises Upward,
right? But fortunately this does not happen. Why it does not happen? Because all of these
doublets, they are anchored into the base, all these doublets they are anchored into
what into the centriole into the basal body and they cannot move up or down relative to
each other, right. They can, this cannot rise up or this cannot go Down, clear? So, This,
this middle dynein it still wants to touch this beautiful Star. So how it can touch the
star without rising upward? Normally you should rise upward to touch the star. Right, but
it cannot rise up so when it moves, when it crawls on this, when it crawls, so when it
crawls on this it can still do this but while doing so because it cannot rise up it bends
like This, it bends forward, it bends forward like this. Right, now it has touched the star
but it has caused a local bend forward and in this way a local bend backward can be generated
if this crawls on forward one. Right, so due to this local bends what will happen? The
flagellum will move forward and Backwards. And you know we also have two central singlets,
what is the role of this central, these central Singlets? It is not clearly known but it is
said that it controls this Mechanism. Right, it tells the doublet that which doublet should
move which doublet should rest and which doublet should crawl so due to the controlling mechanism
of those singlets some of the doublets they remain resting while other crawl on them and
vice versa. Right, so this is the mechanism of flagellum, Movement of flagellum. So you
have seen in that Analogy, in the fingers analogy that what happens is that these let's
suppose these three or four Doublet, these front one these three are four doublets at
one time they are resting and these previous those that are present behind these three
or four doublets they are moving they are crawling on those forward ones, on the forward
lying Doublets. And in this way due to this crawling of this previous one on the forward
one this causes backward bending and vice versa. That if front ones are crawling on
the back one then there is forward bending of flagellum. So and what controls this mechanism?
These central two Singlets. Right, so in this way forward bending and backward bending,
so forward and backward bending lead to a wave of movement. Right, it causes a wave
of movement in the flagellum that leads to motion of, that leads to the particular specific
motility of flagellum of sperm. So this was about how a sperm moves? Right, now finally
I would I would like to discuss another point that as we have discussed previously that
all the cells, as all the sperm precursor cell or spermatozoa precursor cells they undergo
incomplete cytokinesis. I have told you in previous lecture that they undergo incomplete
cytokinesis meaning that they are connected by cytoplasmic Bridges, so here also these
sperm they are also still connected by cytoplasmic bridges. Right, you can see here and finally
when they completely mature then what happens that they, they separate from each other.
Right, so sperm they are still embedded into the sertoli cells but they are now separate
from each other. Right, and finally when they are mature, what happens that they come out
of these sertoli cells, these furrows of seetoli cells, and they are released into lumen of,
what is this lumen of seminiferous Tubules. Right, so what happened here they were embedded
into these furrows and then they come out of these furrows and release into lumen of
seminiferous tubules and this process is called spermiation. what is spermiation? Spermiation
simply means release of Sperm, spermatozoa into the lumen of seminiferous tubules. Right,
then what happens that, Sorry, so finally when they are released into the lumen of seminiferous
tubules then from all these seminiferous tubules the spermatozoa they ultimately come into
epididymis. Right, they come into epididymis and then from epididymis through vas Deferens,
they are released with ejaculate into, they are, they are released outside the body through
the urethra. Right, so that's how spermatozoa Forms. Now I have a little question here that
I have told you that in seminiferous tubules these sperms they are protected from the hazard
of immune system with the help of blood Testes barrier, now what thing prevents, what thing
protects the sperm in epididymis from immune system? You got my question that in seminiferous
tubules there is blood Testes barrier, what is in epididymis That, that prevents it from
immune system? So I will address this question in next lecture. Meanwhile you have to tell
me the answer to this question in the comment section. So this was about spermiogenesis.
Finally, another point that I would like to highlight here is that the role of testosterone
I have told you that testosterone has very important role in maturation of sperm, testosterone
stimulates the sertoli cells, it causes the sertoli cells to release certain growth factors
that causes maturation of sperm but it has direct role in spermiogenesis as well. Right,
from that the processes of transformation of Spermatid to spermatozoa is called Spermiogenesis
and it directly causes spermiogenesis they have found certain receptors here in the spermatids,
they have found certain receptors and these are the receptors of, what is This? Testosterone.
So that is why scientists do believe that it has a direct role, testosterone has a direct
role in spermiogenesis as well. Thank you so much for watching this video. If you like
this video please press the thumbs up Button, please give your comments regarding this video
and please subscribe to my channel. Thank you so much.