Repro Flashcards
(435 cards)
How is the development of secondary sex characteristics controlled?
Hormones: gonadotrophins + testosterone/oestrogen and progesterone
Describe the migration of germ cells that occurs embryologically.
The germ cells arise in the yolk sac then migrate along the dorsal mesentery to the urogenital ridge to reside within the primordial gonad.
How does development of the primordial gonad into the adult gonads differ according to genetic sex?
In males, germ cells colonise the medullary region and the cortex region atrophies. The germ cells allow rapid growth of the definitive sex cords which they subsequently invade. In the adult these give rise to the seminiferous tubules. The orignial mesodermal somatic cells form Sertoli cels, Leydig cells develop between the sex cords.
In females, germ cells colonise the cortex and so the medullary cords do not develop. The germ cells become surrounded by somatic mesenchymal cells which will eventually form primordial follicles.
Why can female genitalia be considered the “default”?
The cortex of the primordial gonad will develop even if no germ cells arrive.
How are the female internal genitalia formed?
The Mullerian / Paramesonephric ducts grow medially towards each other formining the uterus and its tubes, cervix, fornices and upper 2/3 of the vagina. The rest of the vagina is formed from the sinovaginal bulbs from the vaginal plate which grows from the urogenital sinus.
What is the function of Mullerian Inhibitory Hormone (MIH) and what is it secreted by?
MIH suppresses the growth of the Mullerian / Paramesonephric ducts in the male. It is secreted by Sertoli cells.
What is the genotype of an individual with true hermaphroditism?
Mosaicism of XY and XX or XO
Describe the important features of pseudo-hermaphroditism.
Occurs in individuals with XY genotypes but where foetal genitalia are insensitive to testosterone. The testis are undescended in the lumbosacral region, no internal genitalia will be produced and the external genitalia will be female. Undescended testes have an increased risk of developing germ cell tumours.
What genitalia (internal and external) will develop in an XX individual with congenital adrenal hyperplasia?
Female gonads but both male and female internal genitalia will develop. External genitalia will be male.
Describe the descent of the testes.
Testes start in the lumbosacral region, they then move caudally, crossing the inguinal canal obliquely and an invagination into the scrotum develops to form the processus vaginalis. Around 9 months gestation the testes migrate over the pubic bone to enter the scrotum.
What is the fate of the gubernaculum?
In females the guberaculum becomes the ovarian ligaments that join each ovary to the uterus.
In males the guberaculum becomes the scrotal ligament.
What is hypospadia and how does it develop? What is it associated with?
Hypospadias are where the urethral opening is on the ventral surface of the penis, they form due to incomplete fusion of the urethral folds. They are always associated with descended testes and sometimes with micropenis.
What is uterus bicornis? How does it develop? What are the consequences of it?
Uterus bicornis is where the uterus is “heart shaped” due to incomplete fusion of the paramesonephric ducts. It may cause menorrhagia but fertility is usually unaffected.
Describe the 4 main steps required for gametogenesis.
Colonisation of the gonad
Proliferation by mitosis
Introduction of genetic variation by meiosis
Cytodifferentiation
How does meiosis introduce genetic variation? MGD
Crossing over when pairs of chromosomes become bivalent
Random assortment as chromosomes line up at metaphase
Where does spermatogenesis occur?
In the seminiferous tubules
What is spermiogenesis?
Spermiogeneisis is the cytodifferentiation of spermatids into spermatozoa (mature sperm cells)
When do males start producing sperm?
At puberty
What is the spermatogenic cycle?
The spermatogenic cycle is the time taken for the reappearance of the same stage of spermatogenesis within a given segment of a seminiferous tubule.
What is the spermatogenic wave?
The spermatogenic wave is the distance along the seminiferous tubule between cells undergoing the same stage of spermatogenesis.
Where is the majority (by volume) of semen produced?
The seminal vesicle
What is the function of secretions from the bulbourethral (Cowper’s) glands?
To help lubricate the distal urethra and neutralise any acidic urine present
What is the source of the energy needed by sperm?
Fructose within semen is used to form ATP
What do the prostaglandins in semen do?
To increase sperm motility and to cause smooth muscle contraction within the female genital tract