Repro 1 Flashcards
What is the urogenital ridge?
A region of intermediate mesoderm from which the embryonic kidney and gonad arise
At this stage what is the gonad?
An indifferent collection of cells from the intermediate mesoderm and primordial extragonadal germ cells
What are primordial germ cells?
The “seed” cells arising from the yolk sac. They migrate to the retroperitoneum along the dorsal mesentry
What drives the development of the male?
The Sex Determining Region of the Y chromosome (SRY)
Name two duct systems involved in sexual development and where they end.
Mesonephric and paramesonephric ducts, both ending at the cloaca
What do the mesonephric ducts do?
Act in conjuction with the mesonephric tubules to form the embryonic kidney
What is the other name for the mesonephric ducts?
Wolffian Ducts
What is the other name for the paramesonephric ducts?
Mullerian Ducts
In males what happens to the mesonephric ducts?
They sprout the ureteric bud and then the prostate and prostatic urethra forms i.e. they don’t disappear
In females what happens to the mesonephric duct?
It sprouts the ureteric bud and then entirely regresses
How do the paramesonephric ducts appear?
Invaginate the epithelium of the urogenital ridge, make contact with the cloaca caudally and the abdominal cvity cranially
What do the Mullerian ducts form?
The uterus, cervix and the proximal 1/3 of the vagina
What are the male gonadal hormones collectively known as?
Androgens
What do the androgens do to the ducts involved in primary sexual development?
Support the mesonephric duct
What specific substance is produced by the testis to support male development?
Mullerian Inhibiting Substance (MIS; the function is in the name)
How then does the female embryo differ?
No androgens to maintain the mesonephrics and no MIS to act on the Mullerian ducts
What are the basic components of the undifferentiated external genitalia?
Genital tubercle (GT)
Genital folds
Genital swellings
In males what does the genital tubercle (GT) do?
Elongates
In males what do the genital folds fuse to form?
The spongy urethra
What hormone is key to the development of the male external genitalia?
Dihydrotestosterone
What doesn’t happen in the external genitalia of females?
Fusion, leaving the vestibule open
What is the 1st (of 4) stages of testicular descent?
The attached gubernaculum retracts pulling the testis retroperitoneally
Stage 2(/4) of testicular descent?
The processes vaginalis and scrotal swelling form as the testis reach the pubic symphysis
Stage 3(/4) of testicular descent?
They are pulled out from behind the peritoneum as they pass over the symphysis but are still cupped by the vaginalis
Stage 4(/4) of testicular descent?
The processes vaginalis receedes leaving the tunica vaginalis
Briefly describe the components involved in the descent of the ovary
Hint: 3 main points
GUBERNACULUM attaches ovary inferiorly to labio-scrotal folds
Ovary descends to PELVIS
Round LIGAMENT of UTERUS is present in inguinal canal
What cells secrete androgens, principally testosterone?
Leydig
Which cells secrete MIH (MIS)?
Sertoli cells (in the walls of the seminiferous tubules)
What structures come from the Wolffian Ducts?
Epididymis
Vas Defrens
Seminal Vesicles
What does the labioscrotal swelling become in the male and female?
Male - scrotum (obvioiusly)
Female - labia majora
What do the urethral folds become in the male and female?
Male - ventral aspect of shaft of penis
Female - labia minora
What does the GT become in the male and female?
Male - Glans penis
Female - clitoris
How long after conception do the germ cells appear?
3 weeks
Are germ cells haploid?
No
What are the 4 broad stages of gametogenesis?
- Colonisation of the gonad by germ cells
- Mitotic proliferation
- Meiotic division
- Cytodifferentiation into mature gametes
What are the 2 main functions of meiosis?
Reduce chromosome number tin gamete to 23
Ensure every gamete is genetically unique
What happens to the 4 daughter cells in females?
Only 1 becomes a mature oocyte - the others form polar bodies
What 3 processes contribute to genetic variation?
Crossing-over Random segregation (of chromosomes among four gametes) Independent assortment (of homologous chromosomes to separate gametes)
What are spermatogonia?
Male germ cells used in spermatogenesis
What is an Ap spermatogonium?
Diploid daughter cell of a spermatogonium that has undergone mitosis that will give rise to primary spermatocytes
What are Ad spermatogonia?
The diploid cells that do not differentiate any further after mitosis of spermatogonia i.e. maintain stock
What are primary spermatocytes?
The diploid daughter cells of an Ap spermatogonium after mitosis
What are secondary spermatocytes?
Haploid daughter cells of a primary spermatocyte after meiosis 1
What are spermatids?
Haploid daughter cells of a secondary spermatocyte after meiosis 2
What are spermatozoa?
The differentiated spermatids following spermiogenesis
Where does spermatogenesis occur?
Seminiferous tubules
Roughly how long is the spermatogenic cycle in humans?
16 days
Define spermiation
Release of the spermatids into the lumen of the seminiferous tubules
How are the non-motile secretions trasnported to the epididymis?
Peristaltic contraction
Which steps make up spermiogenesis?
HInt: 3
Spermiation
Remodelling of spermatids into spermatozoa
Presitaltic contraction to assist non-motile secretion
Describe the route of spermatids during spermiogenesis
Hint: 4 parts
Seminiferous tubules -> rete testis -> ductuli efferentes -> epididymis
Whci structures contribute to semen production?
Hint: 4
Seminal vesicles
Prostate
Vas defresn (deliver sperm)
Bulbourethral gland
What do the seminal vesicles actually secrete?
AAs, citrate, fructse, prostaglandins
What does the prostate contribute to semen?
Proteolytic enzymes, zinc
What does the bulbourethral (Cowper) gland secrete?
Mucoproteins to aind in lubrication and neutralise acidic urine in dstal urethra
How much semen is produced per ejaculate?
~2ml - most of which is from seminal vesicles
What is sperm capacitation?
Final step in maturation, only initiated by conditions in female genital tract - glycoproteins and cholesterol removed - sperm signalling pathways activated
What are oogonia?
Germ cells that have colonised the female gonadal cortex
How do oogonia initially develop?
Rapid mitotic proliferation (~3 months)
What are primary oocytes?
Oogonia that enter meiosis instead of mitosis (but stop at prophase of meiosis 1)
What happens at and by mid gestation
Maximun number of germ cells reached and cell death (both oogonia and primary oocytes) begins
What happens to the remaining primary oocytes by month 7?
They have entered meiosis 1 and are surrounded by follicular cells
What is a primary oocyte in meiosis 1 surrounded by follicular cells called?
Primordial follicle
Define atresia in relation to oocytes
The degeneration of the follicles which do not ovulate during the menstrual cycle
Describe the preantral stage of oocyte maturation
The once flat surrounding follicular cells grow into a stratified cuboidal epithelial layer of granulosa cells which create the zona pellucida
What are the components of the zona pellucida?
Glycoproteins
Describe the antral stage of oocyte development
Fluid filled spaces appear between the granulosa calls. They coalesce to form an antrum many times the size of the oocyte
Describe the preovulatory stage of oocyte development
Meiosis I complete
One of the daughters receives most of the cytoplasm (the other becomes a polar body) and enters meiosis II to stop at metaphase
What is needed to begin the preovulatory stage of oocyte development?
LH surge
What is needed to bring preovulatory stage oocytes out of meiotic arrest?
Fertilisation - otherwise cell degenerates from it’s position at metaphase of meiosis II
What is another name for a mature follicle?
Graafian follicle
What does the ovulatory surge in LH cause?
Increased collagenase activity
Prostaglandin initiated muscular contractions of the ovarian wall
What is the corpus luteum?
A collection of lutein cells derived from the now vascularised granulosa and theca interna cells
What does the corpus luteum do?
Secretes oestrogens and progesterone
Stimulates uterine mucosa to enter secretory phase
How long does the corpus luteum last if not fertilised?
14 days
How is the oocyte trasnported?
Hint: 3 main points
Fimbrae sweep it up-> uterine tube contracts -> peristaltic muscular contractions of the uterine tube and cillia
How long does a fertilised oocyte take to get to the unterine lumen?
~3-4 days
What is the corpus albicans?
Mass of fibrotic scar tissue left when unfertilised corpus luteum degenerates
Which main hormone decreases in production if fertilisation doesn’t occur and what is the consequence?
Progesterone - menstrual bleeding
What prevents the corpus luteum from degenerating if fertilisation occurs?
Human chorionic gonadotropin - secreted by the developing emryo
What does the corpus luteum grow into if fertilised?
corpus luteum graviditatis
What structure takes over from the embryo regarding progesterone secretion?
The placenta after ~4 months
What receptors do granulosa cells have?
FSH receptors
What receptors do thecal cells have?
LH receptors
