Spermatogenesis 1&2 and male hormones Flashcards
What is the structure of the blood testes barrier
Sertoli cells, junctions with each other which is what forms the blood testis barrier
there is a basal compartment and an abluminal compartment, and an interstitual compartment to the blood testes barrier.
Why do males need reproductive hormones
general behaviour (find females) mating behaviour (successful mating) secondary sex characteristics (attract females) sperm production (successful fertilisation)
What is a hormone? (general definition)
Diverse group of signalling molecules, the messengers of the endocrine system.
Where are the major male reproductive hormones produced (origins - 3 main ones)
- hypothalamic
- pituitary
- gonadal
What hormones are produced in the hypothalamic region?
GnRH
Oxytocin
What hormones are produced in the pituitary gland
LH
FSH
What hormones are produced in gonadal region
testosterone
inhibin
estradiol
PGF2a (not focused as much)
What is the HPG axis?*
What does it regulate?
Hypothalamic pituitary gonadal axis regulated production of reproductive hormones in BOTH SEXES
- Production of hormones is controlled by positive and negative feedback*
- LH and FSH mainly by GNRH -> gonadotroph releasing hormone
Two parts of the pituitary gland
anterior pituitary and posterior pituitary
What is the role of GnRH? Where is it produced?
GnRH is produced in the hypothalamus and is going to act on the pituitary
- GnRH super important → acts on anterior pituitary → releases two gonadotropins (LH and FSH)
What are LH and FSH? Where are they produced? **
LH and FSH are gonodotropins (action in the testes)
- GnRH releases these hormones, which comes from the hypothalamus
- these hormones are released from the pituitary (anterior)
- LH = luteinizing hormone
- FSH = follicle stimulating hormone
What is the role of LH hormone? What cell do they bind too? (think L)
LH - bind to ILH receptors in leydig cells to produce testosterone (support leydig cell functions - hormone production)
What is the role of FSH? What cells to they bind to? (think S)
Binds to receptors on Sertoli cells and role is to support their function which is sperm production*
Gonadal hormones: what hormones do leydig cells and sertoli cells produce (separate)
Produce gonadal (sex) hormones
-
Leydig cells: testosterone and estradiol (important hormones*)
- Sertoli cells convert T to DHT and E2 and produce inhibin
Where are LH and FSH produced?
Anterior pituitary
Role of testosterone hormone:
Produced by leydig cells
- localised function - drive sperm production
- reproduction male characteristics (mating)
- increase muscle mass
- behaviour/libido
Role of DHT
- Produced by sertoli mainly
- development of repro anatomy and sexondary characteristics
- similar to T
Role of estradiol
produced by leydig and sertoli cells
- drive sperm production
- assists in fluid resorption in epididymis (become more concentrated in epididymis)
Inhibin = inhibiting*
Role of inhibin
produced by sertoli cells
- negative feedback on AP release of FSH → inhibits release of FSH in pituitary and reduces LH releasing hormone
What are the two negative feedback loops involved in the HPG axis feedback?
- inhibin - blocks FSH directly (in pituitary)
- Gonadal hormones block GnRH (in hypothalamus)
- Feedback mechanisms regulate hormone production
- ensures hormone synthesis remains active
Why do we need the HPG axis feedback mechanism (why can’t hormones be in high concentrations when they leave the gonad?)
High concentrations in gonad, but as soon as they leave they get dilated by about 500 times because if they were in really high concentrations in circulation, they would shut down the HPG access. So the concentration is enough to control GnRH being produced and ensure regulated hormone production along HPG access but not enough to shut down the axis.
Why does LH and FSH follow a GnRH release pattern?
because GnRH is causing them to be released → GnRH release by hypothalamus → acts on pituitary gland to release LH and FSH
- GnRH is short acting, and LH is higher peak than FSH due to inhibin dampening down FSH (inhibin inhibits FSH)
What hormones in the HPG axis inhibit the release of FSH?
Inhibin → directly limits FSH production
testosterone, DHT and ER → secreted by the gonads, negative feedback of the hypothalamus → so will decrease GnRH secretion and thus lower FSH secretion.
Why is cholesterol important for hormones?
cholesterol is the precursor to all steroid hormones
Role of cholesterol in testosterone (what is it converted into to become testosterone?)
Cholesterol → pregnenolone → progesterone → testosterone
- T can then ne aromatised to E2 (estradiol)
Basic steps of testosterone synthesis: (4 main steps)
- cholesterol important into Leydig cells then into mitochondria of cell
- cholesterol → pregnenolone → progesterone
- progesterone exported into cytoplasm
- progesterone → testosterone
What is the action of testosterone?
Acts by binding to the androgen receptor in the nucleus
This complex acts as a transcription factor to alter gene expression
Other male repro hormones: role of oxytoxin:
Produced by para-ventricular nucleus
- Oxytocin transported by reproductive tract and stimulates smooth muscle contraction and production of PGF2a (prostaglandin → not studied much in males..)
Summary: main actions of:
- GnRH
- LH
- FSH
- Testosterone
- Estradiol
- Inhibin
- Oxytocin
- GnRH → LH and FSH release
- LH → testosterone prod.
- FSH → sertoli cell func.
- Testosterone → spermatogenesis, anabolic growth
- Estradiol → sexual behaviour
- Inhibin → inhibits FSH release
- Oxytocin → pre-ejac sperm transport, PGF2A prod.
What occurs during meiosis in spermatogenesis?
Haploid cells are produced by dividing the cell
allows constant production of sperm
What happens during meiosis to create genetic diversity?
Crossing over of dna allowing recombination, get daughter cells that have a different mixture of alleles depending on which chromatid that daughter cell inherited.
What is the importance of the blood testis barrier In terms of immunity?
Preventing an immune response from occurring - haploid cells are being produced which look very different to diploid cell, so if the barrier wasn’t there then the immune system would attack the haploid cells
Third step in spermatogenesis is spermiogenesis. What occurs in this stage
Spermatids produced by meiosis 2
- go from round to elongated
round spermatids undergo spermiogenesis to form elongated spermatids that will eventually mature
what is the order of the 3 steps of spermatogenesis?
Mitosis (continual supply of cells) - meiosis (genetic diversity of haploid cells)- spermiogenesis (elongated spermatids)
In what stage would you see spermatogonia?
Mitosis
In what stage would you see spermatocytes in spermatogenesis
Meiosis
structurally, what will mature sperm contain
- a head with nucleus and acrosome
- tail with mid piece, mitochondria, principal piece and end piece
What are the cells that form tight junctions in BTB?
- leydig cells
- sertoli cells
- Extracellular cells
- Sertoli cells form tight junction between one another to form the BTB and protect non self haploid cells during sperm development
what are the ‘stages’ of seminiferous epithelium cycle referring to
the stages classify what is going on in the epithelium/classifying groups of cells in a section of the seminiferous tubule
What is the seminiferous epithelium cycle
Time taken for The reappearance of the same stage at a given location
What is a spermatogenic cycle
Full process from spermagonia to spermatozoa = 4.5 x seminiferous epithelial cycle
What are spermatogonia waves
Sequential order of stages along the tubule allowing sequential sperm release
What alters daily sperm production?
Testis size or spermatogenesis efficiency
What are factors that impact spermatogenesis
- breakdown of btb- if compromised then immune cells will attack developing sperm
- diet - vitamin deficiencies
- irradiation - e.g. cancer treatment, can cause permanent infertility
- excess heat *
- ‘drugs and toxic agents
- endocrine disrupting chemicals (EDCs) - pesticides
What causes excess heat of the testes?
- high environmental temperature
- fever
- cryptorchidism
