Session 1 Flashcards
Label
Label
What is the urogenital ridge made of?
Intermediate mesoderm
What does the urogenital ridge give rise to? What does it require and where does it come from?
Embryonic kidney and gonad
Requires primordial germ cells which migrate from yolk sac into cloaca, then to the hindgut through the dorsal mesentery and finally into gonadal ridge
What happens to the mesonephric and paramesonephric ducts in male development? What part of the male DNA allows these changes to occur?
Mesonephric - becomes vas deferens
Paramesonephric - obliterated by production of mullerian inhibiting substance in males
SRY genes on the Y chromosome
What happens to the mesonephric and paramesonephric ducts in females? Why do these changes occur?
Changes occur due to lack of Y chromosome and therefore SRY genes
Mesonephric ducts - obliterated
Paramesonephric ducts:
- not obliterated due to lack of mullerian inhibiting substance
- Grow into abdominal cavity and use together to form uterus
- Forms bicordate uterus if PMD dont fuse
What are the mesonephric and paramesonephric ducts AKA?
Mesonephric - Wolffian duct
Paramesonephric - Mullerian duct
At what week do external genitalia begin to differentiate? What does it consist of at this stage?
At week 7
Consists of genital fold, swelling and tubercle
What happens to the indifferent stage to form the male external genitalia? What substance is required for this to occur?
Genital tubercle elongates and genital folds fuse to form the spongy urethra.
Requires dihydrotestosterone
What happens to the indifferent stage to form the female external genitalia?
No fusion occurs and urethra opens into the opening
Describe the descent of the testis
- Testis begin as a retroperitoneal structure
- Goes through deep inguinal and superficial inguinal ring to enter the scrotum
- Gets pulled by gubernaculum
Describe the descent of the ovaries
Ovary descends to the pelvis, pulled via the gubernaculum that becomes the ovarian ligament proper
Label
What occurs in Turner’s syndrome? When and how is it diagnosed? What is the chromsomal classification?
- 45,XO.
- Results in degeneration of ovaries at 15th week of gestation.
- Diagnosis only occurs post puberty, when a lack of a menstrual cycle and secondary sexual characteristics are revealed.
What are cloacal partitioning defects?
Failure of the cloaca to split into the reproductive/urinary system and digestive system.
What are hypospadias?
- Abnormally placed urinary hole in males and females. Defect of the urethra.
- Can open anywhere on the urethral groove (line which splits penis in 2)
What is a bicornuate uterus?
uterus fails to fuse, resulting in two uteri separated by a septum.
What is the function of GnRH?
Releases LH and FSH from Ant. Pit.
Where is LH and FSH released from?
Ant pit
What is the function of FSH and LH?
FSH - Stimulates maturation of germ cells
LH - Triggers ovulation and development of corpus luteum
What is the function of inhibin and oestrogen?
Inhibin - Inhibits FSH
Oestrogen - Promote and maintains uterus lining
What is the function of hCG and hPL (human placental lactogen)?
HCG - Promotes progesterone release form corpus luteum
hPL - Decreases maternal insulin and glucose utlitisation. Increases lipolysis.
Label
What is the tough fibrous outer layer of the testis called?
Tunica albuginea
What is the name of the visceral layer that covers the testis?
Tunica Vaginalis
How are the testes suspended in the scrotum?
Suspended by the spermatic cord
What is contained within the seminefrous tubules? What do they produce?
Sertoli cells - produce sperm
Where are leydig cells found? What do they produce?
found adjacent to the SF tubules. Produce testosterone.
What happens before birth with regards to spermatogenesis?
- Germ cells colonise sex cords in primordial gonad
- Germ cells proliferate by mitosis to form spermatogonia stem cells
- This self regenerating population of stem cells are maintained to allow continuous sperm production
What occurs at puberty with regards to spermatogenesis?
- Cords hollow out to form SF tubules where sperm is produced.
- Tubules empty into rete testis and from there form the epididymis.
What occurs post puberty with regards to spermatogenesis? How long does spermatogenesis take? How long does it take for new groups of spermatogonia to arise? What occurs during copuluation? Where do spermatozoa mature?
- At intervals, A1 spermatogonia emerge from population of stem cells, marking beginning of spermatogenesis in that part of the tubule.
- The A1 spermatogonia divide to produce more type A (stem) cells or Type B cells
- Type B spermatogonium divides to produce 64 clones of primary spermatocytes all linked together by a cytoplasm bridge
- Chain of primary spermatocytes push out of lumen of tubule and begin meiosis, producing 256 sperms per A1 spermatogonium.
- After meiosis complete, spermatids remodelled to form sperm by spermiogenesis and the cytoplasmic bridges are broken down. They are then released into the tubule lumen and washed down the rete testis by fluid secreted from Sertoli cells.
- Spermatogenesis takes 70 days and new groups of spermatogonia arise every 16 days.
- Production of sperm is continuous as different sections of the tubule begin the process at different times, therefore some part is always released sperm – Spermatogenic wave of production.
- Spermatozoa mature during progress through epididymis.
- During copulation, contraction of vas deferens sweep sperm to be mixed with seminal and prostate secretions.
Stem cells –> A1 Spermatogonia –> Type B spermatogonia –> primary spermatocytes (linked) –> Spermatids –> sperms (unlinked)
Distinguish between a spermatogenic cycle and a spermatogenic wave
Spermatogenic cycle – Development of A1 spermatogonia through to 256 sperms. Time taken for the same stage of the cycle to reappear in the same segment of tubule.
Spermatogenic wave – Different parts of tubule start the spermatogenic cycle at different times, so a constant ‘wave’ of production of sperm occurs. This can be thought of as the distance between 2 parts of the tubule on the same stage in the spermatogenic wave.
Describe the roles of the following:
a) Rete testis
b) epididymis
c) vas deferens
Rete testis – network of canals that SF tubules drain into
Epididymis – Duct in which sperms are stored and continue to mature
Vas deferens – continuation of epididymis. During copulation muscular walls of epididymis contract and force sperm along the tube to be mixed with other components of ejaculate.
Describe the roles of the following:
a) seminal vesicles
b) prostate
c) bulbourethral glands
Seminal vesicles – Secrete an alkaline fluid that is rick with fructose (energy for sperms) and a coagulating agent, makes up 60% of volume of semen. Seminal gland duct joins ductus deferens to form the ejaculatory duct.
Prostate – Prostatic fluid takes up 20% of volume of semen and helps activate sperms.
Bulbourethral Glands – Largely embedded in the external urethral sphincter. Opens into the proximal part of the spongy urethra in bulb of penis. Mucus like secretion enters urethra during sexual arousal.
How is the ovary suspended?
Mesentery called the mesovarium
What is the ovarian ligament a remnant of?
Gubernaculum
What is the name of the connective tissue capsule which surrounds the ovary?
Tunica albuginea
What happens ot the ovaries over time and why?
Epithelium of ovary becomes progressively scarred and distorted due to repeated rupture of ovarian follicles
What happens before birth in the ovarian cycle? What are the 3 stages that a follicle must go through to mature? Can a woman produce more oocytes, why?
- Primordial germ cells in the primordial gonad, AKA oogonia, proliferate by mitosis to form primary oocytes.
- Oogonia’s entry to meiosis 1 stimulated by mesonephric cells which surround the primary oocytes to form primordial follicles.
- Meiosis arrested at prophase due to oocyte maturation inhibitor (OMI) secreted by primordial follicles.
- A woman therefore has all the oocytes she will ever have at birth. The longer the oocytes remain in an arrested stage the increases chances there are of cell damage.
- A small number of follicles begin further development each day post puberty, formation of a mature gamete requires follicles to go through 3 stages.
3 stages are - primordial follicle, secondary follicle, pre-ovulatory follicle
What happens in the primordial follicle stage to form the primary follicle?
- The primary oocyte grows dramatically
- Squamous granulosa cells become cuboidal Granulosa cells
- Zona pellucida forms around oocyte
What happens to the primary follicle to get to the secondary follicle? What substance does the theca produce?
- Inner and outer theca forms
- Theca secretes oestrogens
- Fluid filled vesicles develop among granulosa cells
What happens in the secondary follicle stage? What cells do FSH and LH bind to?
- Fluid filled vesicles combine to make one antrum
- Continued development depends on reproductive hormones.
- FSH – Binds only to Granulosa cells
- LH – Binds only to Thecal cells
What happens in the pre-ovulatory stage? How many hours before ovulation does the phase start? After how many hours do unfertilised cells degenerate?
- Phase begins 37 hours before ovulation
- Oestrogen causes receptors for LH to appear on outer Granulosa cells
- LH surge stimulates these receptors, leading to rapid changes in the follicle
- Within 3 hours of the LH surge, the follicle restarts meiosis, and the first meiotic division is completed. This division is asymmetric; cytoplasm remains with one daughter cell and the other forms a condensed polar body.
- The secondary follicle then enters meiosis II and arrests again 3 hours prior to ovulation.
- LH stimulates collagenase activity leading to follicle rupture
- Ovum is carried out in the fluid and gathered up into the fallopian tube by fimbria
- Meiosis is not completed unless the ovum is fertilised
- Unfertilised cells degenerate 24 hours after ovulation
What happens to the remains of the follicle post ovulation? What is its function? How long does it live for before regressing?
Remains becomes corpus luteum, which secretes progesterone and oestrogen under the influence of LH.
In humans, the corpus luteum lives for 14 days before regressing spontaneously (in the absence of a fertilised ovum).
What does the labioscrotal swelling become in the male and female?
male - scrotum
female - labia majora
What do the urethral folds become in the male and female?
male - shaft of penis
female - labia minora
What would happen to an XY individual with genitalia that are insensitive to testosterone or DHT?
- Testes remain in abdomen but removed post puberty due to high risk of malignancy
- Well developed breasts, no pubic hair or menstruation
- Genital ambiguity
What would happen in an XX individual and excessive androgen secretion?
External appearance is male but genetically female with internal genitalia of both sexes
What would happen to an XY individual with resistance to MIH?
Genetically and gonadally male but internal genitalia of both sexes due to test promoting external genitalia and wolffian duct.
Testes will fail to descend
