T2 L9 & 10 Short but happy life of a sperm Flashcards
What are the functions of the testis?
Production of spermatozoa
Production of hormones
What are the 2 compartments of the testes?
Seminiferous tubules
Vascularised stroma
Where does spermatogenesis occur?
In the seminiferous tubules
What is the structure of the seminiferous tubules?
Surrounded by myoid cells then a layer of basement membrane
Sertoli cells and spermatogenic cells within the tubules
Physiological barrier formed by gab and tight junction complexes between Sertoli cells
What is the purpose of the physiological barrier formed between Sertoli cells?
Creates basal compartment containing spermatogonia whilst spermatocytes, spermatids and spermatozoa are in a separate adluminal compartment
Where are Leydig cells?
In the vascularised stroma
What are the most important hormones in maintaining reproductive and sexual function?
Androgens
What is testosterone synthesised from?
Acetate and cholesterol by Leydig cells
How much testosterone is secreted daily?
4-10mg
What is testosterone converted to in Sertoli cells?
Dihydrotestosterone
What stimulates Leydig cells to produce androgens?
LH
What stimulates Sertoli cells?
FSH
What are the 3 stages of spermatogenesis?
1) Mitotic proliferation to produce lots of cells
2) Meiotic division to generate genetic diversity
3) Cell modelling to package chromosomes for delivery to oocyte
Describe the first stage of spermatogenesis
Germ cells of immature testis are activated at puberty undergo rounds of mitosis in basal compartment of tubule
From this self-regenerating population, a group of cells called A1 spermatogonia emerge
After last round of division, clone divides to form resting primary spermatocytes
Cytoplasmic division isn’t completed so all primary spermatocytes from division of spermatogonium are linked by cytoplasmic bridges
Describe the second stage of spermatogenesis
Resting primary spermatocytes push through Sertoli cell junctions into adluminal compartment
Enter meiotic prophase
Paired homologous chromosomes form contacts at pachytene, break and swap segments and re-join
First division ends with separation of homologous chromosomes to opposite ends of meiotic spindle, cytoplasm divides to form short-lived secondary spermatocytes
Quickly divide to form haploid spermatids
Describe the third stage of spermatogenesis
Cytoplasmic remodelling of spermatid Tail for forward propulsion Midpiece with mitochondria for energy Nucleus with package chromosomes Cap region forms for sperm-oocyte fusion Acrosome forms to penetrate oocyte
How many spermatozoa are produced per second?
300-600 per gram of testis per second
How long does spermatogenesis take?
64 days
Describe the spermatogenic cycle
Once the generation of sperm from a single spermatogonium has started, new stem cells at the same location don’t start generation of clones again for a few days
What would happen if all spermatogonia were activated on 11th birthday?
It would only produce mature spermatozoa every 16 days resulting in episodic fertility
Describe the later events in maturation of sperm
Spermatozoa wash into rete through vasa efferentia
Into the epididymis where fluid is absorbed and sperm is concentration
In the rete they can twitch
In the cauda epididymis they can swim
What are the final stages of maturation dependent on?
Androgen stimulation
What is semen?
Spermatozoa mixed with secretions from seminiferous tubules, epididymis etc.
What are the cellular components of semen?
Spermatozoa
Epithelial cells from tract
Spermatogenic cells
Leucocytes - risk of HIV etc.
