Lecture 17: Sperm and Fertility Flashcards
What is a Seminiferous Tubule?
tightly coiled tubules in lobules of the testes
What are the 2 types of cells in Seminiferous Tubules?
- Spermatogenic cells
2. Sertoli cells
What are spermatogenic cells?
most cells’ precursors to sperm cells –> different sizes
What are sertoli cells?
support spermatogenesis –> run longitudinally around cell
What part of seminiferous tubules look different?
looks different closed to the lumen = mostly tails of sperm
What is spermatogenesis?
Process occurring in male gonads from circular cell to elongated tailed cell
Where does spermatogenesis occur?
in the seminiferous tubules of testes.
When does spermatogenesis occur?
ONLY occurs after puberty,
-huge numbers of sperm are produced constantly by the mature male 300-600 sperm/gram of testes tissue/per second
-get smaller forming elongated cell –> which is capable of movement
there are 3 phases and takes about 65-75 days
What are the 3 phases of spermatogenesis and how long does it take to occur?
- Mitotic division 2n
- Meiotic division –> reduction division –> 2n–>n
- Cytodifferentiation
What is another name for spermatogonial stem cells?
Spermatogonium
primary germ cell reactivated at puberty
What is the five step process in forming mature sperm?
- Spermatogonial stem cells/spermatogonium (2n 46 chromosomes)
- Primary Spermatocyte (2n 46 chromosomes)
- Secondary Spermatocyte (n 23 chromosomes, 2 chromatids still attached to centromere)
- Spermatids (n 23 chromosomes)
- Sperm or Mature Spermatozoa
What happens during the first stem of sperm formation?
Division of Spermatogonial stem cells/ serpmatogonium
2n, 46 chromosomes, primary germ cells reactivated at puberty
Spermatogonia divided by mitosis
-these mitotic divisions occur in basal compartment of seminiferous tubules
-ASSYMETRIC division (1st division) - 1 daughter stem cell REMAINS undifferentiated - to maintain stem cells - basal - other daughter cell continues to divide by mitosis FORMING SPERMATAGONIA
-cells get smaller with each division =about 7 divisions
-spermatogonia held together by cytoplasmic bridges (different from other mitotic cells) - form series of 256 cells
Where does Mitosis occur?
Basal
Where does meiosis occur?
adluminal
Where does spermatogenesis occur?
lumen
note process also called cytodifferentiation
What happens during the second stage of sperm production?
- Primary Spermatocyte - 2n - 46 chromosomes
When the mitotic divisions are complete, the spermatogonia of between adjacent sertoli cells to the adluminal compartment of the seminiferous tubules - loses contact with the basement membrane
In adluminal compartment, 1 primary spermatocytes undergo meiosis
Dna content doubles - homologous pairs line up (crossing over) at metaphase
Undergo a REDUCTION DIVISION 2n –> n , spindle pulls to opposite poles
Yeild 2 secondary spermatocytes
What are 7 features of sertoli cells?
- support, nourish and protect developing spermatogenic cells
- nourish spermatocytes, spermatids and sperm
- phagocytose excess spermatid cytoplasm as development proceeds
- control movement of spermatogenic cells and release sperm –> into lumen
- secrete hormones
- form barrier and separates the(impermeable) basal and adluminal compartments
- held tougher by tight junctions - form blood-testis barrier (primary spermatocytes squeeze through)
What happens during the third stage of sperm production?
Secondary Spermatocyte (n 23 chromosomes , 2 chromatids, still attached at controller)
- no further replication occurs
-there are 2 secondary spermatocytes
very short phase- divide very rapidly
chromosomes line up in single file along (each one) metaphase plate , 2 chromosomes separate
results in 4 haploid (n) cells altogether called spermatids
What happens during the fourth stage of sperm production?
Spermiogenesis or cytodifferentiation
Spermatids (n 23 hormones)
Spermatids are round cells and still have round morphology
spermiogenesis or cytodifferentiation is the final process at spermatogenesis where the round spermatids differentiate and become spermatozoa
round cells are not hydrodynamically adapted to move through female reproductive tract, so differentiate into long, slender sperm cells
early spermatid is just after meiosis 2 and late spermatid undergoes differentiation
What happens in the fifth stage of sperm production?
Sperm or mature spermatozoa 23 chromosomes
sperm move into the lumen of seminiferous tubules with their tails projected in after they are shed from stroll cells (lose connection)
the excess cytoplasm of the spermatid is also lost into a structure called the residual body that is phagocytes by the sertolic cells after the spem leaves - cytoplasm wasteful and causes shape
sperm then enter the lumen of the seminiferous tubule - fluid secreted by stroll cells push sperm towards ducts of testes - sperm still CANNOT SWIM
What is the residual body?
Excess cytoplasm
buds off as don’t want to waste mitochondria, amino acids etc
What is the average length of sperm?
60 microns
What is the role of the principle piece of a sperms tail?
longest position of tail which is important for locomotion and propulsion of sperm through vaginal tract and uterus
What is the role of the mid piece of a sperm?
Midpiece contains mitochondria For Energy
What is the role of the nucleus of a sperm?
contains DNA
How many chromosomes does a sperm have?
23 chromosomes
What is an acrosome?
a cap like vesicle or compartment filled with enzymes (hyaluronidase) required to penetrate zone pellucid of secondary oocyte for fertilisation
Which enzymes do acrosomes contain?
hyaluronidase
enzymes required to penetrate zone pellucid of secondary oocyte for fertilisation
What is the role of GnRH in the hormonal control of spermatogenesis?
GnRH released from hypothalamus in a pulsatile fashion at puberty via hypothalamic neurosecretory cells
Travels via portal system and stimulates gonadotrophs in anterior pit.
secretes gonadotropins LH and FSH
What is the role of LH in the hormonal control of spermatogenesis?
LH stimulates Leydig Cells
Interstitial cells of testes –> outside of seminiferous tubules
involved in synthesis of testosterone
-lipid solubile so readily diffuses from Leydig cell –> interstitial fluid –> blood
-spermatogenia don’t develop into sperm without testosterone
-via negative feedback testosterone surpasses secretion of LH by anterior pituitary gonadotropidsand suppresses secretion of GnRH by hypothalamic neurosecretory cells
test–> diff in some target cells active metabolic of test
regulation of 2 sexual characteristics
What is the role of FSH in the hormonal control of spermatogenesis?
FSH with testosterone act on sertoli cells
- inside semnifererous tubules - in direct contact with spermatogonia
- produce androgen binding protein (ABP) into lumen if seminiferous tubule into interstitial cell around spermatogenic cell (nescessay for spermatogenesis)
-maintains concentration of androgen in seminiferous tubule –> locks testosterone inside tubule
indirectly stimulates spermatogenesis
What is male infertility?
male infertility has many causes
a common feature of fertile men is a reduced sperm count
What is IVF?
In-vitro Fertilisation
oocytes are harvested and fertilised ex-viro
requires approximately 50,000 motile sperm –> into media droplets with oocytes
Oligospermia low volume –> ‘some’ sperm
What is ISCI?
IntraCytoplasmic Sperm Injection
Sperm injected directly into oocyte –> just single sperm
sperm doesn’t need to be motile and can be collected from biopsy of testes –> immature sperm
asoospermia no sperm + immotile sperm cant swim
What is the two jobs of adapted reproductive organs?
to produce gametes (sperm and egg)
to produce reproductive hormones
How can you distinguish between a youth’s and adults seminiferous tubule?
Adults seminiferous tubule has sperm in it (as sperm production begins after puberty)
centre of the tubule
What is the seminiferous tubule’s structure?
circular tubule which is fully enclosed
sperm producing cells INSIDE the tubule
Which cells sit outside the seminiferous tubules and what is there role?
b/w tubules
involved in hormonal control
Leydig cells
When do females produce eggs?
BEFORE they’re born
have maimum amount of eggs BEFORE they’re born
ogenesis occurs PRIOR to birth
When does spermatogenesis occur?
AFTER PUBERTY
How many grams of sperm are produced in an adult man per second?
20grams
300–600 sperm, per gram of testis tissue, per second
How many sperm are produced in 1 minute in an average male?
1.2 million
How many sperm are produced in 1 hour in an average male?
72 million
What process occurs in every cell of your body?
Mitosis
same number of chromosomes 46
asymmetrical division
When does the chromosome number decrease from 46 chromosomes –> 23 chromosomes?
Meiosis
Is the process of spermatogenesis sporadic or continuous?
continuous
Where are spermatogonial cells located?
near basement membrane but still INSIDE
Where are all sperm cells derived from?
spermatogonial cells (near basement membrane)
Where is the basal compartment?
Between the basement membrane and spaces adjacent to one another in sertoli cells
When to spermatagonia become PRIMARY spermatoCYTES?
One they have left the basal compartment –> squeezed between little gaps between stroll cells –> into the adluminal compartment
now undergo meiosis
What is reductive cell division?
Meiosis I
Which cells undergo reductive cell division?
PRIMARY SpermatoCYTES
Why is there relatively few spermatocytes at the end of meiosis II?
as it happens so rapidly
such small phase
What happens as different round of reproduction occur?
The cells become progressively smaller (still round)
What is the name of production of elongated sperm cells –> round cells?
spermiogenesis
adluminal compartment in contact with stroll cells –> lumen
When are sperm close of sertoli cells?
when they’re in the alumni compartment 2-4
What is the role of sperm?
highly adaptive cells who try to fertilise a female’s egg
What is present in the head of a sperm?
just DNA
hardly any cytoplasm
shrunk down to make the sperm hyrdo-dynamically adapted (to swimming down the female uterus
Where is the energy generator of the sperm and what is its job?
midpiece
contains all the mitochondria
to power the tail for movement
How is the hard shell of a female human eggs pierces?
through the enzymes in the sperms acrosome
ZONA PELLUCIDA
How do you become more hydro-dynamically active?
shedding cytoplasm
(cheeding girth) around middle
What is cytoplasm full of ?
good proteins and fats
What are residual bodies?
buds of cytoplasm shed off by sperm
What happens to residual bodies?
phagocyted by sertoli cells as to not to water the good amino acids, proteins and fats in that cytoplasm from the sperm
When are sperm released released into the lumen?
at the end of spermatogenesis
released from sertoli cells into lumen
Where are spermatids most likely to be found?
near lumen
Where are spermatogonia most likely to be found?
near basement membrane
What does sperm need to deposit into a female’s egg?
DNA only
hence DNA is in the head at the front
What is a mature sperm essentially?
a swimming machine, with a powerhouse to engine the tail, with package to deliver and a delivering cap to wear
Do all sperm look the same?
No all sperm are different
When will a sperm not be able to penetrate an egg?
When it has undergone premature acrosome reaction
What shape are spermatids?
still circular
only mature sperm are elongated as transforming into this shape is the point of the final step!
how many chromatids do sperm have?
23 chromsomes
What are residual bodies pahgocytosed by?
sertoli cells
as to not to waste the fats, amino acids and proteins
What are the reproductive organs under the control of?
the brain
mainly hypothalamus, then second most pituitary
What does the hypothalamus do during puberty?
starts to secrete GnRH Gonadotropin releasing hormone (hormone that stimulate FSH and LH release)
How is GnRH transported directly to the pituitary?
via portal system
What does LH bind to?
receptors on the Leydig cells
Where are leydig cells found?
layer ADJACENT/OUTSIE the seminiferous tubule
-NOT INSIDE
What does LH stimulate the production of?
testosterone
What does testosterone do?
2 secondary characteristics
make proteins
What does testosterone convert into?
5 alpha dihyrdotestosterone
Where does LH operate?
inside seminiferous tubule
producing androgen binding hormone (water soluble) and carry hormones around the body
Where are androgen binding protein produced?
sertoli cells
What is an alternative function of androgen binding hormone?
locks some of the testosterone into the testes for spermatogenesis
-can no longer freely move as locked in
What are the compulsory things needed to make sperm?
Sertoli cells under the simulation of testosterone
make sperm
What is intimately related with sertoli cells?
spermatocytes and spermatids
What happens if you don’t have testosterone in the testes?
you can START to produce sperm
-mitotic division in basal
NO LATER DEVLOPMENT
What is the later part of spermatogenesis entirely dependant on?
presence of testosterone
everything outside of mitosis
What is the male voice regulated by?
testosterone
deep voice is one of the secondary characteristics
What are some the secondary characteristics mediated by testosterone?
deep husky voice agressive-male and females horny/libido- controlled by steroid hormones baldness hair growth
Is the levels of testosterone controlled? why or why not?
yes
via negative feedback systems
testes – -ve –> brain
turns DOWN (not off) GnRH production
+ turn down production of gonadtropins at pituitary
+INHIBIN, which specifically FSH production
What is in the overall control of spermatogenesis?
feedforward loop (GnRH –> testosterone)
Testosterone - - ve-> hypothalamus (GnRH) + pititary (FSH + LH)
Inhibin - -ve -> pituitary (FSH)
What is a come measure for intertility?
less than 20million sperm/mil
less than 3mL vol of ejaculate
Whatis a reduced sperm count/volume called?
oligospermia
What is no sperm in ejaculate called?
azoospermia
What is ejaculate with normal numbers of sperm but sperm which are unable to swim?
immotile
What makes a sperm unless?
sperm is immotile
What is the egg surrounded by in IVF?
cumular cells
How many sperm per egg in an IVF droplet?
50,000
fifty thousand
When will IVF not work?
when the sperm are immotile
still need to be able to travel to the egg
will just sit in the IVF droplet
What treatment do you do for Oligospermia?
IVF
What treatment do you do for Azoospermia?
ISCI
-only needs one to be injected into the cytoplasm of the oocyte
What treatment do you do for immotile sperm?
ISCI
-dont have to swim is injected into the cytoplasm of the oocyte
What is ISCI?
single sperm injected into egg
Which technique has overcome almost all of the problems which cause male infertility?
ISCI
IntraCytoplasmic Sperm Injection
