Spermatogenesis Flashcards
Outline the journey of sperm through the male reproductive anatomy
1.Sperm is produced in the testes and store in the epididymis.
During ejaculation there are contractions in the epidydimis and the vas deferens and these will propel the sperm up and out through the vas deferens.
At this point the sperm will be mixed with epidydimal fluid.
This will make its way to the seminal vesicle where further secretions are added
As this mixture makes its way to the ejaculatory duct further secretions are added
from prostate and the calvus gland are added.
This becomes a complete ejaculate.
Corpus Cavernosum and Spongiosum fill with blood during an erection
Outline the role /function of the testes .
Where are the testes found ?
The testes produces sperm and also stores it.
It will also produce hormones which are important for regulating spermatogenesis .
The testes lie in the scrotum which lies outside of the body cavity.
This is the optimum temperature for sperm production (1.5-2.5 oC below the body temp)
Overheating of the testes will reduce the sperm count.
How is the testes adapted to its function ?
It is well vascularised , well innervated
The testes lie in the scrotum which lies outside of the body cavity.
This is the optimum temperature for sperm production (1.5-2.5 oC below the body temp)
This is the optimum as following ejaculation there is a spike of temperature which serves to activate the sperm
Overheating of the testes will reduce the sperm count.
What is the normal volume of testes ?
15-25ml and this can be measured using orchidometer
Describe the testicular structure
The testes contains tubules which lead to an area on one side which is the rete.
The rete will lead to the epididymis and vas deferens
The testis is 90% semineferous tubules and its the site of spermatogenesis.
600m of seminiferous tubule in each testis which are tightly coiled.
The tightly coiled tubules are all kept in a structure known as the rete-testis
What does the epidydimis lead into ?
It leads to the vas deferens
Describe the cross section of a seminiferous tubule
It has a outer lining known as the basal lamina.
There are different cell divisions of germ cells which take place towards the lumen.
The final products of these are to form spermatozoa.
In between each clusters of germ cells there are Sertoli cells and these provide sustenance to the sperm cells.
Describe the cross section of a seminiferous tubule
It has a outer lining known as the basal lamina.
There are different cell divisions of germ cells which take place towards the lumen.
The final products of these are to form spermatozoa.
In between each clusters of germ cells there are Sertoli cells and these provide sustenance to the sperm cells.
Describe each layer of division beginning from the germinal cell to form the spermatozoa
This begins with the germ cells which are diploid and these will begin division as the primary spermatocyte(diploid).
This will divide through meiosis 1 to form secondary spermatocytes (haploid).
Following this meiosis 2 will take place giving rise to spermatids (haploid) which will mature into spermatozoa.
Describe the seminiferous epithelium
These contain tight junctions which exist between sertoli cells which forms the blood-testis barrier.
It opens to allow the passage of spermatogonia prior to completion of meiosis.
Divides into basal and adluminal compartments
Protects the spermatogonia from immune attack
Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.
What is spermatogonia ?
Germ cell on basement membrane ,capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia through mitosis .They are diploid.
What are the two types of sperms and how do they divide ?
The two types are type a dark and type a pale.
It was found that type a dark was able to undergo mitotic divisions at any time to give rise to type A dark again or it can also differentiate to give rise to type A pale.
What is a primary spermatocyte?
Cells which are committed to differentiative pathway, primary spermatocytes are 46XY diploid .
They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exhange genetic material and enter meiosis 1.
What are secondary spermatocytes ?
Secondary spermatocytes have undergone meiosis 1 to give 23X and 23Y haploid number of chromosomes arranged as sister chromatids.
What are spermatids ?
Meiosis 2 occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.
What will take place following all the meitic divisions?
Following formation of spermatids these will not undergo a maturation process to give rise to spermatozoa.
Extra cytoplasm is gotten rid of.
This maturation process is known as spermatogenesis.
What is spermatogenesis
New cycle every 16 days ,entire process takes approximately 74 days.
Mitotic proliferation of spermatogonia
Meiosis and development of spermatocytes
Spermiogenesis ,elongation ,loss of cytoplasm ,movement of cellular contents
Movement into lumen controlled by Sertoli cell secretions.
Factors produced by Sertoli cells are required for development
Describe the process of androgen production in the testis.
Leydig cells contain LH receptors and primarily convert cholesterol into androgens .
Intra-testicular testosterone levels are 100x those in plasma .
Androgens cross over to and will stimulate the Sertoli cell function and will therefore control spermatogenesis.
Sertoli cells will contain FSH receptors and convert androgens to oestrogen.
Describe the effects of the hormones /androgens being produced in the testis
LH being produced by the anterior pituitary will act on the Leydig cells and this will produce testosterone which is take up by sertoli cells which will then regulate spermatogenesis.
FSH will act directly on Sertoli cells allowing it to sustain the spermatocytes.
FSH will also act on sertoli cell making it produce androgen binding protein which will bind to testosterone and binds testosterone and helps maintain a high concentration of testosterone within the testes; this is essential for spermatogenesis to occur.
FSH establishes a quantitivaely normal sertoli cell population , whereas androgen initiates and maintains sperm production
Outline the production of inhibin in the testis
Inhibin B is produced primarily by sertoli cells in response to FSH
Inhibin B reduces FSH production by the anterior pituitary.
Germ cells appear to be required for inhibin B production.
FSH and inhibin B in combination have been founf to correlate with testicular volume and spermatogenic activity .
Semen analysis is the gold standard.
This is the better way to assess male fertility.
Describe the cytoskeleton structure of a sperm cell
It is divided into two main sections: the head and the tail.
The tail is divided into three distinct sections.
The middle piece the principal piece and the end piece.
The head piece is made up of the acrosome and also contains the nucleus .
The middle piece of the sperm will house the mitochondria which is required for the tail to move .
It will also house ion channels which are important for intercellular calcium signalling which takes place when the sperm is inside the female reproductive tract.
Give a brief overview of the ejaculation and seminal components
There are around 300 million sperm being produced per day
Normal ejaculate volume is around 1.5ml -6ml
The initial portion of an ejaculate is the most sperm rich
99.9% of the is will be lost before reaching ampullaof the uterine tube.
Seminal fluid consists of secretions from:
Seminal vesicles ,
prostate ,bulbo-urethral gland (contains the calvus gland )and epidydimal fluid.
What is the role of the seminal fluid ?
This will transport sperm through the male reproductive tract
Coagulation (it will later liquify ) of the ejaculate and creating a sperm deposit in the vagina
Creates neutral -slightly alkaline buffered milieu in the vagina to protect spermatozoa from acidic vaginal millieu.(environment)
Activation and augmenting the motility of the sperm cells
Coating the sperm cells with capacitation (the process through which sperm goes through for it to be able to fertilise an egg) inhibitors
Supplying nutrients for the sperm cells
What sort of information can be collected through a semen analysis ?
This is a test which is requested when looking at male fertility.
Volume Appearance/colour Liquefaction Sperm concentration Motility Progressive motility Morphology Vitality pH Leucocytes
What are some abnormalities that can be identified in sperm?
Normal Condensed - has a large nuclear region Small head Large head Double headed Double tailed Abnormal middle piece (due to cytoplasmic droplets can occur during spermatogenesis)
What are some important adaptations of sperm production?
There is no male menopause -Sperm production will be continuous from puberty
Sperm is alsi highly specialised for its function
