Male Testicular Function Flashcards
Spermatozoa / Sperm
- Contains genetic material in nucleus
- Contains mitochondria (energy)
- Contains flagellum (movement to deliver genetics)
Processes that don’t occur in spermatozoa
- No transcription - no new proteins synthesised
- No endoplasmic reticulum
- No cytoplasm so cytoplasmic reactions
Post-translational modifications in Sperm
- Glycosylation
- Phosphorylation
- Disulfide cross-linking, Ubiquitination, Acetylation + Methylation
Changes to proteins on cell membrane surface
Sperm’s journey after ejaculation
(1) Cervix –> (2) Uterus –> (3) Isthmus –> (4) Oviduct (fertilisation) –> (5) Oocyte (egg cell)
Swims ~18cm in 30-60 minutes
What is Spermatogenesis?
Biological process of producing mature sperm and occurs in the male gonad
How does spermatogenesis work?
- Begins as a basic eukaryote with typical organelles (with acrosomal vesicle on the nucleus )
- Centrioles move to either end of cell
- From the centrioles, microtubules form the centriole
- Excess cytoplasm is pinched off and lost from around the nucleus + the acrosome grows
A specialised sperm cell
A Sperm Cell’s Journey
From the epididymis to through the vans deferens and arrives at the ampulla
Glands in the male reproductive organs
Seminal vesicle
Prostate
Bulbourethral gland
Purpose of the scrotum
Provides cooler environment compared to the body (35-36 degrees)
- aids sperm’s development due to sensitivity to high temperatures
Where spermatogenesis occurs + sperm maturation
Coiled seminiferous tubule (SFT) in the testis
- Primary spermatocyte (diploid) goes through meiosis to form secondary haploid spermatocytes
- Spermatids then mature to become spermatozoa (spermiogenesis)
- Sertoli cell supports process by providing necessary nutrients
When is spermatogenesis initiated?
At puberty - caused by initiation of pulsatile release of gonadotropin releasing hormone (GnRH)
How long does spermatogenesis take?
74 days
How much sperm does a human produce?
1000 per heartbeat = 100-200 million/day
95% is abnormally formed so only a small proportion are capable of fertilising an egg
In between seminiferous tubules - Interstitial cells
Leydig cells - androgen (mainly testosterone) producing cell
Sertoli Cells - Tight junctions
- Tight junction with adjacent Sertoli cells maintain spermatogonial stem cell niche
Sertoli Cells - Blood testis barrier
- Separate developing germ cells from the immune system
- Provides a controlled chemical microenvironment for spermatogenesis
Sertoli cells - Adherens junction
Form intimate associations with germ cells (40-50)
What are Sertoli cells + what do they do?
Form a syncytium-like epithelial monolayer that germ cells are embedded
- Phagocytose cytoplasm of spermatozoa - spermiation
- Secrete fluid into lumen of SFT that lush spermatozoa into rete testis + epididymis post-differentiation
- Secrete Inhibin + Androgen Binding Proteins to regulate spermatogenesis
What are spermatogonia?
Reservoir of self-renewing stem cells (maintain germ cell line) and remain in the basement of the seminiferous tubule as
undifferentiated spermatogonia
- Some type ‘As’ S will form type ‘A’ S + start the process of spermatogenesis
Miotic Proliferation of Spermatogonia
Each type ‘A’ S goes through mitosis to form type ‘B’ S
- Will divide again to form primary spermatocytes that will go through meiosis
- Then move towards lumen + through blood-testis barrier
- Enters resting phase where chromosomes duplicate ready for meiosis
Meiotic Divisions of Sperm
I: Primary spermatocyte divide to form secondary spermatocyte (diff arrangement of genetic material)
II: Secondary spermatocytes divide to form haploid spermatid (diff sections of genetic material resulting in variation)
1 primary S => 4 round spermatids
Sperm developmemt
Spermatogonia (base) -> spermatocytes -> spermatids -> spermatozoa (lumen)
- Spermatocytes + spermatids move into adluminal compartment disrupting junctions between Sertoli cells
Spermiogenesis / Cytodifferentiation
Round spermatids elongate to form spermatozoa
Requires the formation of specialised sperm structures - acrosome, centriole, flagellum, mitochondria, nucleus
What is the acrosome?
- Formed from the golgi apparatus which migrates to one end of nucleus
- Contains hydrolytic enzymes which are released when sperm binds to the zona pellucida of the egg to aid penetration and thus fertillisation
- Found on the head of the cell + envelopes the nucleus