Spermatogenesis Flashcards
Where does spermatogenesis occur and what is the optimal temperature?
- Occurs in the seminiferous tubules, lined with epithelium which are located in the testes
- 34 degrees
What are the other anatomical structures in the male reproductive system?
- Epididymis: Another network of tubules responsible for sperm storage and maturation.
- Vas deferens: Transports sperm from the epididymis to the urethra during ejaculation.
- Seminal vesicles: Secrete mucus to aid sperm motility.
- Prostate gland: Produces alkaline fluid to protect sperm from acidic urine.
What are the primary functions of the testes?
- Hormone production: Essential for normal sexual development and secondary sex characteristics.
- Sperm production: Development of mature sperm cells.
What are the Lobes of the testis and what do they locate?
- Composed of supercoiled seminiferous tubules, where sperm develop.
- Sertoli cells (somatic cells) support developing germ cells and produce hormones.
- Stroma (interstitial tissue between tubules) contains blood vessels, lymphatic vessels, and Leydig cells, which synthesize and secrete steroid hormones.
What is the pathway of released sperm?
Sperm are released into the rete testis, then travel to the vasa efferentia.
When do primordial germ cells (PGCs) appear in development?
- Early - PGCs appear at three weeks of gestation.
- Expand through mitosis and migrate to the genital ridge primordium by six weeks.
What is the second group of migrating cells called in development?
Sertoli cells (male) and Granulosa cells (female)
What is the maternal impact of smoking/ drug use during pregnancy?
Maternal smoking/drug use can affect Sertoli cell numbers and impact offspring development.
How many sperm are produced each day?
- 100 million sperm , requires extensive mitotic divisions for self-renewal and proliferation
Give an overview of spermatogenesis
Mitotic Division:
Some spermatogonia receive signals to differentiate into primary spermatocytes.
Meiotic Divisions:
- First Division → Produces secondary spermatocytes.
- Second Division → Produces four spermatids (genetically diverse, equal in size).
Spermiogenesis:
Spermatids undergo structural changes to become mature spermatozoa.
What is the fate of spermatigonial stem cells (SSCs) in terms of self renewal vs differentiation?
- SSCs can either self-renew or differentiate based on signals from their microenvironment.
- Type A spermatogonia form a clone of 16 cells, which undergo further mitosis and differentiation.
What is the role of cytoplasmic bridges in the fate of spermatogonial stem cells (SSCs) and what does this lead to?
- Cells remain connected by cytoplasmic bridges during division.
- Differentiation into Type B spermatogonia, then primary spermatocytes, followed by meiosis.
What determines whether SSCs divide or differentiate?
Growth factors in the microenvironment determine whether cells divide or differentiate.
How does centripetal development occur within the differentiation pattern?
- Differentiation occurs closer to the lumen of the seminiferous tubules.
- Immature cells are at the periphery, while mature sperm cells with tails are near the lumen.
What is spermiation?
- Release of spermatozoa into the tubule lumen.
- Not yet capable of fertilization; requires further maturation in the tubules.
What is the morphology of mature sperm cells?
Head:
Contains acrosome, derived from the Golgi apparatus, containing enzymes for sperm-egg fusion.
Condensed chromatin for efficient packaging.
Midpiece:
Contains mitochondria (<10) to generate energy for movement.
Tail:
Required for swimming.
Axoneme structure develops from spermatid components.
What is meant by spermiogenesis?
- Process of transforming round spermatids into functional sperm.
- Excess cytoplasm and mitochondria are removed by Sertoli cells before sperm release.
How does chromatin remodeling occur?
DNA repackaging:
- No active transcription occurs during this stage.
- Histones are replaced with protamines for tighter chromatin packing.
What are the structural characteristics of sertoli cells?
- Span the entire length of the seminiferous tubule.
- Form specialized gap junctions with developing germ cells.
How do sertoli cells keep the blood-brain barrier intact?
- Prevents immune system recognition of developing germ cells.
- If disrupted, autoimmune responses can cause infertility.
What is the timing of spermatogenesis?
- Each seminiferous tubule initiates a new clone of sperm every 16 days.
- Entire process takes 64 days.
How do sertoli cells regulate spermatogenesis and what is the evidence?
Precise communication:
Signals between adjacent Sertoli cells and Sertoli-germ cell interactions ensure synchronization.
Research evidence:
- Rat spermatogonial stem cells (SSCs) transplanted into mouse tubules followed rat-specific timing, indicating intrinsic germ cell control.
- Shows two-way communication between germ cells and Sertoli cells.
What happens to the fluid involved in spermiation?
- Spermiation occurs with excess fluid.
- 90% of fluid is reabsorbed in the vasa efferentia, regulated by oestrogen.
What is epididymal maturation?
- Sperm gain motility and fertilization ability, regulated by androgens.
- Takes 5-11 days.
Where are mature sperm stored?
Mature sperm are stored in the tail of the epididymis until ejaculation.
Give an overview of the hormonal control of spermatogenesis
- GnRH (Hypothalamus) → Stimulates anterior pituitary to release FSH & LH.
LH stimulates Leydig cells → Produces:
- Testosterone (spermatogenesis support, negative feedback).
- Progesterone (supports spermiogenesis & capacitation).
- Oestrogen (fluid absorption in vasa efferentia).
- Oxytocin (stimulates seminiferous tubule motility).
Prolactin enhances LH stimulation of Leydig cells.
What are the regulatory feedback effects of testosterone and progesterone?
Inhibit GnRH secretion via Kiss1 neurons.
What is produced when FSH stimulates Sertoli cells?
Androgens & oestrogens.
Androgen-binding proteins.
Activin (stimulates FSH production).
Inhibin (suppresses FSH, regulates Leydig cells, correlated with sperm count).
What are the effects of Activin?
- Autocrine impact on Sertoli cells.
- Paracrine effects on germ cells.
