1: Origin Of The Sexes Flashcards
What are the origin of germ cells? (3 points)
- Germ cells separate off from somatic (body) cells early in dev
(Primordial germ cells formed in epiblast @ 2nd embryonic week) - Germ cells then go to primordial gonads (which dev into testes/ovaries)
- @ Gonad germ cells interact w somatic cells
Germ cells multiply by mitosis then undergo meiosis -> haploid gametes (ovum / sperm)
(2 haploid gametes fuse -> diploid zygote)
How does gamete production differ between male and female?
Male: 7,000 sperms per second
Female: 400 ovums in lifetime
Describe the dev of gonads in general (not gender specific)
- Germ cells arise 3 weeks after conception
- Genetic cells derived by xsomes of germ cells
- Germ cells start near allantois - migrate -> genital ridge (@ back)
(This forms primordial gonad) - Gonad made from somatic cells from original primordium and germ cells
- Primordial gonad consists of cortex and medulla
What do primordial gonads consist of?
Cortex and medulla
Describe the dev of gonads in males (6 points)
- Male germ cells colonise MEDULLARY region of primordial gonad (CORTEX will atrophy)
- Germ cells allow sex cords growth (which they invade : means theres a mix of somatic and germ cells)
- Sex cords become seminiferous tubules in adults
- Original mesodermal somatic cells —> sertoli cells (only found in males)
- Sertoli cells express SRY gene —> influence masculinisation
- Leydig cells dev between sex cords —> secrete testosterone —> allows rest of body to become male
Describe the dev of gonads in females (2 points)
- Female germ cells colonise CORTEX region of primordial gonad (Medullary cords don’t dev)
- Germ cells become surrounded by somatic mesenchymal cells —> form primordial follicles (SRY gene not expressed)
What are the components of the male internal genitalia? (5 things)
- Testes
- Duct system
- Epididymis
- Ductus deferens (urethra)
- Seminal vesicles
- Prostate
- Bulbo-urethral glands
Why must males be continuously fertile?
To exploit the intermittent female fertility
Why is there a high production of sperm?
Only small proportion of male gametes survive journey through female reprod tract
What are the roles of the male internal genitalia? (2 roles)
- Collect + mature continuous sperm production
2. Prod other fluid components of semen
What are the components of the male external genitalia? (2 things)
- Penis
2. Scrotum
What is the role of the male external genitalia?
Deliver semen (ejaculate into vagina)
What are the components of the female internal genitalia? (2 things)
- Ovaries
- Duct system
- Fallopian tube
- Uterus
- Cervix
- Vagina
What are the roles of the male internal genitalia? (3 roles)
Provide environment for:
- Sperm to travel
- Conceptus to implant and form placenta
- Embryo to dev to term
What are the components of the female external genitalia? (5 things)
- Vagina
- Vestibule
- Labia Minora
- Labia Majora
- Clitoris
What are the roles of the female external genitalia? (2 roles)
- Prov means of introd sperm into female reprod tract
2. Allows formation of birth canal
How are the male internal genitalia developed? (3 points)
- Leydig cells prod testosterone —> stim. Wofflian duct
- Wofflian duct forms epididymis + rest of male internal genitalia
- Mullerian duct growth inhibited by “Mullerian Inhibitory Hormone” (secreted by Sertoli cells)
How are the male external genitalia developed? (3 points)
- Urethral folds —> Shaft of penis
- Labiosacral folds (genital swelling) —> Scrotum
- Genital Tubercle —> Glans of penis
All processes helped by testosterone from Leydig cells
How are the female internal genitalia developed? (2 points)
- Mullerian duct (para mesonephric) forms fallopian tube + rest of female internal genitalia
- Wolffian duct regresses naturally
How are the female external genitalia developed? (3 points)
- Urethral folds —> Labia Minira
- Labiosacral folds (genital swelling) —> Labia Majora
- Genital Tubercle —> Clitoris
Before the descent of male gonads, which region does the testes start at?
Lumbosacrial region
What are the testes tied to at the lumbosacral region and with what? (Before descent of male gonads)
Tied to labiosacral folds by male gubernaculum
What is the first stage of the descent of the male gonads? (2 points)
- Testes move caudal
2. Invagination of scrotum dev. —> forms processus vaginalis
What happens in the second stage of the descent of the male gonads? (Weeks 25-28)
- Testes migrate over pubic bone —> enter scrotum
Where does the processus vaginalis close? (And when?)
At the proximal end
Closes few weeks before or after birth
Where does the spermatic cord lie?
In the inguinal canal
What does the spermatic cord contain? (8 things)
- Pampiniform venous plexus
- Ductus (vas) deferens
- Cremasteric artery
- Testicular artery
- Artery to ductus (vas) deferens
- Genital branch of genitofemoral nerve
- Sympathetic nerve fibres
- Lymphatic vessels
What does the gubernaculum become in the descent of the male gonads?
Scrotal ligament
What happens in the descent of the female gonads? (2 things)
- Ovaries undergo slight caudal shift
- Gubernaculum becomes:
1. Ligament of Ovary (Minor)
2. Round ligament of uterus (Major)
Where does the round ligament of the uterus lie?
In the inguinal canal
What happens in Cryptochidism? (2 things)
- Testes fail to descend —> remain somewhere in abdominal cavity
- Causes one non-functioning scrotum
What is there an increased risk of in Cryptochidism?
Testicular cancer
What happens in Hypospadius?
- Incomplete fusion of urethral folds
2. So you get a slit on the shaft of penis (UNDER SIDE)
What happens in Epispadius?
- Incomplete fusion of urethral folds
2. So you get a slit on the shaft of penis (TOP SIDE)
What happens during development in spermatogenesis?
Spermatogonia migrate from yolk sac - remain dormant until puberty
What happens at puberty in spermatogenesis?
Spermatogenesis starts for real
What happens in the first stage of spermatogenesis?
Spermatogonia (diploid) undergoes MITOSIS
Becomes:
1. Type A Spermatogonia (diploid) OR
2. Type B Spermatogonia (diploid)
What happens to Type A Spermatogonia (diploid) in spermatogenesis?
Turn back into Spermatogonia (original diploid one)
What happens to Type B Spermatogonia (diploid) in spermatogenesis?
Become 1° Spermatocytes (diploid)
What happens to 1° Spermatocytes (diploid) in spermatogenesis?
Become 2° Spermatocytes (haploid)
What happens to 2° Spermatocytes (haploid) in spermatogenesis?
Become 4 spermatids (haploid)
What happens to the 4 spermatids (haploid) in spermatogenesis?
Undergo spermiogenesis and become 4 spermatozoa (haploid)
What happens during development in oogenesis? (3 things)
- Oogonia (diploid) migrate to developing gonads
- Undergo Mitosis —> 1° oocyte
- 1° oocyte undergoes Meiosis but halted at Prophase 1 until puberty
How is oocyte Meiosis reinitiated at puberty in oogenesis?
By GnRH
What happens after oocyte Meiosis is reinitiated in oogenesis?
Only one 1° oocyte completes Meiosis 1 —> 2° Oocyte + 1st Polar Body
What happens to the 2° oocyte in oogenesis?
Undergoes Meiosis 2 —> Ovum + 2nd Polar Body
What happens to the ovum in oogenesis?
Halted at Meiosis 2 until fertilisation
What happens to the ovum @ fertilisation? (2 things)
- Sperm penetrates 2° oocyte membrane
2. Ovum -> Zygote
