Spermatogenesis Flashcards
Where is sperm produced?
The testes produce and store sperm
Where in the testes is sperm stored?
Sperm stored in epididymis
How is sperm transported to the seminal vesicle?
During ejaculation, due to smooth muscle contraction of epididymis and vas deferens propels sperm up vas deferens where they connect to seminal vesicle
What is the role of the seminal vesicle?
Seminal vesicles produce semen containing enzymes for the sperm
Where in the genitourinary tract is the prostate located?
Prostate meets urethra below bladder
Where is the urethra located?
Urethra moves out the penis through the urethral opening
What are the 2 types of tissues that form the penis?
Corpus spongiosum
Corpus cavernosum
What do the testes produce?
Produce sperm and store it.
Produce hormones which regulate spermatogenesis
Where are the testes located?
Lie in scrotum: outside body cavity…. optimum temperature for sperm production 1.5-2.5oC below body
What is the significance of maintaining a cool temperature for the testes?
Overheating of testes reduces sperm count
Well-vascularised, well-innervated
What is the normal testicular volume?
Normal volume of testes approximately 15-25ml
measured by orchidometer
Describe the testicular structure
Tubules lead to an area on one side called rete.
Rete leads to epididymis and vas deferens.
Testis is 90% seminiferous tubules
600m long in each testis! Tubules are tightly coiled
What is the significance of the seminiferous tubules?
Site of spermatogenesis
Seminiferous tubules feed into epididymis and into vas deferens
Where among the testicular structures is sperm located during different stages of maturation?
Sperm move towards lumen as they develop and mature moving into epididymis when fully developed
Explain how the structure aids Sertoli cell function
Sertoli cells have tight junctions between them. The tight junctions form compartments for sertoli cells to secrete growth factors, signalling molecules, and hormones to control the environment in which sperm develops
What is spermatogonia?
Diploid cell produced during the early stages of sperm production
Where are spermatogonia found?
Germ cell on basement membrane capable of mitotic/meiotic division to produce spermatocytes or spermatogonia (by mitosis) - diploid
Which cells are the walls of the tubules composed of?
Walls of tubule made up of tall columnar endothelial cells Sertoli cells
Tight junctions between these form Adluminal compartment
What is the role of the tight junctions between sertoli cells?
Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells
What fills the spaces between tubules?
Spaces between the tubules are filled with blood and lymphatic vessels, Leydig cells and interstitial fluid
What surrounds the seminiferous tubules?
Seminiferous tubule surrounded by blood vessels, connective tissue and leydig cells. Leydig cells are male analogues of theca cells
What is produced by Leydig cells?
Leydig cells produce testosterone
Describe the inner structure of semniferous tubules
Inside seminiferous tubules contains basement membrane, sertoli cells, primary & secondary spermatocytes. Elongated spermatids are also present.
Developed mature sperm are in the lumen of the tubule
What occurs during S phase of meiosis?
During S phase chromosome is replicated
How are sister chromatids formed?
The replicated chromosomes stay attached to the originals forming identical sister chromatids
How are new chromosomes formed from homologous pairs?
Homologous chromosomes grow together in pairs and exchange genetic material
This gives rise to new chromosomes containing a mixture of maternal and paternal genes
How do sister chromatids end up differing in genes?
At this stage sister chromatids remain attached and differ from one another due to crossing over
Describe the events occurring in Meiosis I
Cell division occurs creating two haploid daughter cells, but each chromosome is two sister chromatids and these are no longer identical due to crossing over
What happens during Meiosis II?
Sister chromatids separate as cell divides giving haploid gametes
What is the role of primary spermatocytes?
Move into adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis I - 46XY diploid
What are secondary spermatocytes?
Have undergone meiosis I to give 23X + 23Y haploid no. of chromosomes arranged as sister chromatids
What are spermatids?
Meiosis II occurs to give 4 haploid spermatids, round spermatid → elongated spermatid differentiation
What is spermatazoa?
Mature sperm extruded into the lumen
How often does spermatogenesis occur?
New cycle every 16 days, the entire process takes approximately 74 days
What are the stages of spermatogenesis?
- Mitotic proliferation of spermatogonia.
- Meiosis and development of spermatocytes.
- Spermiogenesis, elongation, loss of cytoplasm,
movement of cellular contents
Why is each cell division in spermatogenesis incomplete?
Each cell division from a spermatogonium to a spermatid is incomplete - the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development
What is the role of the syncytia?
Syncytia at various stages of development throughout seminiferous tubule giving continuous supply for synchronous development
Compare Oogonia and Spermatogonia
Oogonia
- Oogonia all laid down in foetus.
- Begin meiosis to make oocyte
- Cannot make more oocytes by mitosis
- Limited supply
Spermatogonia
- Spermatogonia laid down in foetus
- Begin meiosis to make spermatocyte…OR
- Divide mitotically to make more spermatogonia.
- Lifetime supply
How does the male and female HPG axis differ?
Female HPG axis is cyclical
Male HPG axis isn’t
Testis produce testosterone which feeds back to the hypothalamus and pituitary
LH and FSH also produced
What do Leydig cells produce?
Leydig cells contain LH receptors and primarily convert cholesterol into androgens
Describe the intratesticular testosterone levels
Intra-testicular testosterone levels are 100x those in plasma
What role do androgens play in spermatogenesis?
Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis
What is the role of Sertoli cells?
Sertoli cells contain FSH receptors and converts androgens to oestrogen
What are the roles of LH and FSH in the male reproductive organs?
FSH establishes a quantitatively normal Sertoli cell population, whereas androgen initiates and maintains sperm production
What drugs interfere with the negative feedback on the HPG axis?
Anabolic steroids → reduces FSH/LH from pituitary leading to testicular atrophy
What causes an erection?
Vasodilation of the corpus cavernosum
Partial constriction of the venous return.
Autonomic nervous system causes coordinated smooth muscle contractions of vas deferens, glands and urethra.
What part of the CNS is involved in an erection?
Parasympathetic control
What controls the movement of sperm through the penis?
Sympathetic nervous system controls the movement of sperm into epididymis, vas deferens, penile urethra (emission)
What part of the nervous system regulates ejaculation?
Somatic nervous system (perineal branch of the pudendal nerve from nerve roots S2–S4) causes expulsion of the glandular secretions
& evacuation of urethra
Describe the blood flow during an erection
Arterial blood flow into penis dilates
Venous return is constricted giving an erection
How much sperm is produced ~1 day?
300 million sperm produced per day on average
How much sperm is expelled during ejaculation?
approximately 120 million in
average ejaculate
What is the normal ejaculate volume?
Normal ejaculate volume is 1.5ml - 6ml
around one third to just over a teaspoon full
Describe the sperm distribution in ejaculation
Initial portion of the ejaculate is most sperm rich.
99.9% lost before reaching ampulla of the uterine tube.
around 120,000 sperm get near to egg, only one enters
Where is the seminal fluid produced?
Seminal fluid consists of secretions from:
seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid
What does the Bubo-urethral gland produce?
Produces a clear viscous secretion high in salt, known as pre-ejaculate
What is the purpose of the fluid secreted by the bulbo-urethral gland?
This fluid helps to lubricate the urethra for spermatozoa to pass through, neutralizing traces of acidic urine.
How much of the ejaculate is from the seminal vesicles?
Secretions (semen) comprise 50-70% of the ejaculate
What does semen consist of?
Contains proteins, enzymes, fructose, mucus, vitamin C and prostaglandins
High fructose concentrations provide energy source.
High pH protects against acidic environment in vagina
How much of the ejaculate is produced at the prostate?
Secretes milky or white fluid roughly 30% of the seminal fluid
What does the prostate seminal fluid contain?
Protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen which are involved in liquefaction
High zinc concentration 500–1,000 times that in the blood is antibacterial
Outline typical results of a semen analysis
Volume 1.5 – 6.0 ml Sperm concentration >15million/ml Liquefaction <30 minutes Motility >40% Progressive motility >32% Vitality (live) >58% Morphology (normal forms) >4% pH >7.2 Leucocytes <1 million/ml
Describe the composition of a spermatozoon
Virtually no cytoplasm, carries DNA only, no ribosomes, mitochondria or cytoplasm derived paternally
Smallest cell in the body
What is the role of the acrosome?
Acrosome provides acrosome reaction due to the large no. of enzymes in the sperm head
What is the significance of the spermatozoon tail?
Base of the tail contains mitochondrial sheath with lots of mitochondria for energy (ATP)
