Spermatogenisis Flashcards
Where is the sperm produced and stored?
Sperm produced in the testes and stored in the epidermis
What happens during ejaculation?
there’s contractions in the epidermis and the vas deferens that propel the sperm and epidermal fluid into the seminal vesicle.
What is the pathway for sperm during ejaculation?
- Sperm produced in the testes and stored in the epidermis
- During ejaculation there’s contractions in the epidermis and the vas deferens that propel the sperm and epidermal fluid into the seminal vesicle.
- Secretions from the seminal vesicles added to the mixture – continues to the ejaculatory duct.
- Secretions from the prostate and Cowper gland also added during that – this makes up the ejaculate
What does the ejaculate contain other than sperm?
- Epidermal fluid
- Secretion from the seminal vesicle
- Secretions from the prostate
- Secretions from the Cowper gland
What keeps the urethra open for semen?
Corpus spongiosum under it is very flexible and it keeps the urethra open to allow a passage for semen.
What is the function of testes?
- Produce sperm and store it.
* Produce hormones which regulate spermatogenesis ie tostesterone
Where are the testes found?
• Lie in scrotum outside body cavity – optimum temperature for sperm production 1.5-2.5oC below body. Overheating of testes reduces sperm count.
What is the structure of testes?
- Tubules lead to an area on one side called rete testis.
- Rete leads to epididymis (highly convoluted tubular structure) and that leads into vas deferens.
- Epididymis is made of 3 segments: head, body, and tail
- A Lot of lobes containing seminiferous tubules
- Testis is 90% seminiferous tubules - the site of spermatogenesis.
- 600m of seminiferous tubule in each testis. Tubules are tightly coiled.
What is the basal lining/basal laminar?
The outer lining of the seminiferous tubules
What is released in the lumen?
Spermatogenic cells/germ cells undergoing spermatogenesis and spermatozoa are released in the lumen.
Where are Sertoli cells found?
Between germ cell clusters
What is the function of Sertoli cells?
they respond to testosterone to regulate spermatogenesis and they provide sustenance for spermatogenic cells
Why is the mitotic division of primordial germ cells important?
Mitotic division of primordial germ cells is important because it means the male has a lifetime supply of sperm cells. Unlike females that a born with a fixed number of primordial oocytes.
What are the tight junctions?
- Exist between Sertoli cells forming blood-testis barrier.
* Are almost like a seal
What do the tight junctions do?
- Open to allow passage of spermatogonia prior to completion of meiosis
- Protects the spermatogonia/germ cells from immune attack – if they get exposed immune system will create antibodies against sperm/germ cells
- Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.
What are the two compartments in testes?
Basal and adluminal compartments - they’re separated by the tight junction/blood-testis barrier
Where are Leydig cells found and what do they do?
Leydig cells outside the basal line – produce testosterone that crosses the basal membrane to go to Sertoli cells
What are the different stages of sperms/spermatogenesis?
- Spermatogonia
- Primary spermatocyte
- Secondary spermatocytes
- Spermatids
- Spermatozoa
How are the sperm like during the spermatogonia phase?
Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid.
How many types of spermatogonia are there and how are they different from each other?
- There are 2 types of spermatogonia: A and B
- There are also 2 categories type A spermatogonia: Dark and pale
- Type A dark is capable of undergoing mitotic divisions to replenish itself or it could undergo differentiation to become type A pale
- Type A can further differentiate to become type B
How are the sperm like during the primary spermatocyte phase?
- Cell committed to differentiative pathway, primary spermatocytes are 46XY diploid.
- They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material and enter meiosis I – only type B can undergo this
How are the sperm like during the secondary spermatocyte phase?
Secondary spermatocytes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.
How are the sperm like during the spermatid phase?
Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation – end of meiotic divisions
How are the sperm like during the spermatozoa phase?
Maturation of the spermatids, extra cytoplasm is removed, acrosome and tail formed. Mature sperm extruded into the lumen. This is called spermiogenesis.
How long is the entire process of spermatogenesis?
74 days
When does a new cycle of spermatogenesis start?
Every 16 days
Summarise how sperm are made?
- Mitotic proliferation of spermatogonia.
- Meiosis and development of spermatocytes.
- Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents
What controls the movement into the lumen?
Sertoli cell secretions
What is the feedback of the HPG axis like in men?
In males there’s always a tonic level of production of the hormones – always constant and feedback is always negative
What receptors do Leydig cells have?
LH receptors
What is the Leydig cells function?
to convert cholesterol into androgens (testosterone)
What do androgens do in the testes?
Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis.
What receptors do Sertoli cells have and what do they do?
- FSH receptors
- FSH binding to Sertoli cells leads to production of androgen binding protein – it binds to testosterone and concentrates it within the epithelium to aid with spermatogenesis regulation
- InhibinB is produced primarily by Sertoli cells in response to FSH
What other purpose do the FSH and androgens have?
- FSH establishes a quantitatively normal Sertoli cell population, whereas androgen initiates and maintains sperm production.
- FSH also plays a role in helping the Sertoli cells plays their sustenance role
What does Inhibin B do in males?
Inhibin B reduces FSH production by the anterior pituitary
What is required for Inhibin B production?
Germ cells appear to be required for Inhibin B production
Why is the middle piece important in the sperm?
Middle piece has ion channels that are intracellular calcium signalling when the sperm is in the female tract
What is the normal ejaculate volume and how much of it is actual sperm?
Normal ejaculate volume is 1.5ml - 6ml.
Spermatozoa account for 1-5% of an ejaculate
Name 6 roles of the seminal fluid
- Transport of sperm through the male reproductive tract – sperm is non-motile is male reproductive tract
- Coagulation of the ejaculate and creating a sperm deposit in the vagina – allows the sperm to actually get into the female reproductive tract
- Creation of a neutral to slightly alkaline buffered milieu in the vagina to protect spermatozoa from the acidic vaginal milieu.
- Activation and augmenting the motility of the sperm cells.
- Coating the sperm cells with capacitation inhibitors.
- Supplying nutrients for the sperm cells.
What is analysed during semen analysis and what standards are used?
Seme analysis is carried out according to the standards set by WHO. Things that are analysed include: • Volume • Appearance/colour • Liquification • Sperm concentrate • Motility • Progressive motility • Morphology (normal forms) • Vitality (live) • pH • leucocytes
