1. Origin Of The Sexes Flashcards
What is the embryonic kidney comprised of
What is the role of each component
Mesonephric tubules: primitive renal function
Mesonephric duct:
Describe primordial germ cells:
Where do they arise
When do they appear
Where do they migrate to
Special population of cells, separate from somatic cells
Arise in epithelium of yolk sac, near base of allantois
Allocated shortly after epic last folding in 2nd week
Migrate to retro peritoneum, along dorsal mesentery
Describe the Mesonephric ducts (Wolffian duct)
Part of embryonic kidney
Develops in both male & female
Runs causally
Makes contact with cloaca
Describe the paramesonephric ducts (Mullerian duct)
Develop near Mesonephric ducts
Develop in both males & females
Appear as invaginations of epithelium of urogenital ridge
Causally, make contact with cloaca (urogenital sinus)
Cranially, open into abdominal cavity
Grow into peritoneal cavity, taking gonads & fusing as a fold
Creates uterus & Fallopian tube
Describe the development of genetic male
Primordial germ cells carry Y chromosome
Expression of SRY gene
Mesonephric ducts reach urogenital sinus
Ureteric bud sprouts
Urogenital sinus expands as smooth muscle appears
UB & MDs make independent openings in UGS
MD now redundant but androgens retain it; involved in dev of testis
Testis secrete Mullerian Inhibiting Hormone from Sertoli cells
Paramesonephric duct degenerates
Describe the development of genetic female
Primordial germ cells do not carry Y gene: absence = female dev
Mesonephric ducts reach urogenital sinus
Ureteric bud sprouts from Mesonephric duct
Urogenital sinus begins to expand, Mesonephric duct begins to regress
As MD regression continues, UB opens into UGS
Ovary develops; no androgens = MD degenerates
No testis = no MIH
Describe the 3 basic components of the external genitalia in the indifferent stage
Genital tubercle
Genial folds
Genital swellings
Describe the development of the male internal & external genitalia
(What happens to basic components, descent of testis, hormone influence)
Genital tubercle elongates
Genital folds fuse to form spongy urethra
Retroperitoneal Testis descend thru inguinal canal & spermatic cord lies in inguinal canal
Influenced by dihydrotestosterone (metabolised testosterone)
Describe the development of the female internal & external genitalia
(Does fusion occur, descent of ovaries)
No fusion of genital folds: urethra opens into vestibule
Descent of ovaries:
gubernaculum attaches ovary inferiorly to labio-scrotal folds
Ovary descends into pelvis
Round ligament of uterus lies in inguinal canal
What are the common abnormalities of genital development
Genotype-phenotype mismatches
Structural defects:
Cloacal partitioning defects
Hypospadias (abnormally placed urinary hole)
Uterine structural defects (e.g. Bicornate uterus)
What are the reproductive hormones secreted by the hypothalamus
Gonadotropin Releasing Hormone
Prolactin Releasing Hormone
Prolactin Inhibiting Hormone
What are the reproductive hormones secreted by the posterior pituitary
Oxytocin
What are the reproductive hormones secreted by the anterior pituitary
Gonadotrophins:
Follicle stimulating hormone
Luteinising hormone
Prolactin
What are the reproductive hormones secreted by the testis
Gonadal steroids:
Inhibin
Testosterone
Mullerian inhibiting hormone
What are the reproductive hormones secreted by the ovaries
Gonadal steroids:
Inhibin
Oestrogen
Progesterone
What are the reproductive hormones secreted by the placenta
Human chorionic gonadotrophin
Human placental lactogen
Oestrogen
Progesterone
Describe the structural layers of the testis
Tunica vaginalis, which contains:
Parietal layer, adjacent to spermatic fascia
Visceral layer, covering surface
Small amt of fluid in between layers
Tunica albuginea: tough, fibrous outer surface
(thickens into mediastinum of testis which seminiferous tubules extend from)
What are the 2 types of cells in the testis
Where are they found
What do they produce
Sertoli cells:
Associated with seminiferous tubules
Produce spermatozoa
Leydig (interstitial) cells:
In the interstitial tissue, adjacent to seminiferous tubules
Secrete testosterone
Describe the course of sperm from testis to urethra
Seminiferous tubules Rate testis Epididymis Vas deferens (Through ampulla & ejaculatory duct) Urethra
Describe the urogenital ridge
What does it give rise to?
Region of intermediate mesoderm
Gives rise to:
Gonad (indifferent)
(also derived from primordial germ cells: extra gonadal)
Embryonic kidney (mesonephros)
Describe the differentiation of Type B spermatogonia into spermatozoa
Undergoes fixed number if mitotic clone divisions (usually 64)
A chain of primary spermatocytes push their way towards lumen of tubule
Begin meiosis:
1st division produces 2 haploid secondary spermatocytes
Each divides again to form spermatids
Spermatids re-modelled as pass down tubule to form sperm (spermatozoa) by spermiogenesis
Cytoplasmic bridges between them broken down
Released into tubule lumen
Washed down rate testis by fluid secreted by Sertoli cells
Spermatozoa mature during progress thru epididymis
Describe the process of spermatogenesis (from foetus to puberty)
Germ cells colonise sex cords in primordial gonad
Before birth: germ cells proliferate by mitosis - from spermatogonia stem cells
At puberty: cords hollow out to from seminiferous tubules
At intervals, A1 spermatogonia emerge from stem cells
Differentiate into either:
more Type A stem cells
Type B cells, committed to differentiation into spermatozoa
Define Spermatogenic cycle
Amount of time it takes for reappearance of same stage of cycle within given segment of tubule
Development of A1 spermatogonia through to 256 sperms
Define spermatogenic wave
Distance in tube between parts that are in the same stage
Different parts of the tube begin spermatogenic cycle at different times in a ‘wave’, so sperm production is constant
Describe the role of rete testis
Network of canals in mediastinum of testis
Seminiferous tubules drain into them
Describe the role of the epididymis
Convoluted duct where sperms stored & continue to mature
Describe the role of the vas deferens
Continuation of epididymis
Contracts in copulation, forcing sperm along tube to be mixes with other components of ejaculate
Describe the role of the seminal vesicles
Secrete thick, alkaline fluid rich in fructose & coagulating agent
Describe the role of the prostate
Fluid makes up 20% of semen vol
Role in activating sperms
Describe the role of the bulbourethral glands
2 pea-sized glands, largely embedded in external urethral sphincter
Ducts open into proximal part of spongy urethra in bulb of penis
Mucus-like secretion enters urethra during sexual arousal
Describe the development of oocytes in the foetus
Primordial germ cells colonise cortex of primordial gonad, becoming oogonia
Proliferate rapidly by mitosis
Most die, leaving approx 2 million
All enter meiosis 1 before birth to become primary oocytes
Stimulated by Mesonephric cells/follicular cells (somatic)
Single layer of somatic granulomas cells surround primary oocytes to form primordial follicles
Meiosis arrested at resting stage of prophase
Influenced by oocytes maturation inhibitor, secreted from follicular cells
Describe the 3 stages of ovulation that forma a mature gamete
Pre-antral / primordial follicle
Antral / secondary follicle
Pre-ovulatory follicle
Describe the pre-antral/ primordial follicle stage
Independent of hormones: occurs in ovary
Primary oocyte grows dramatically
Flat follicular cells become cuboidal granulosa cells
Granulosa cells secrete glycoprotein to surround oocyte with zona pellucida
Surrounding CT (stroma) cells from theca folliculi
Theca & granulosa cells collaborate to secrete oestrogens
Describe the antral / secondary follicle phase
Granulosa cells continue to proliferate
Fluid appears between them = Antrum
As more fluid forma, secondary / Graafian follicle expands
Further development depends on reproductive hormones
Under influence of LH, thecal cells secrete adrogens (oestrogen)
Describe the pre-ovulating follicle stage
37hrs before ovulation
Oestrogen cases receptors for LH to appear on outer Granulosa cells
LH stimulates these receptors = rapid changes in follicle
Within 3 hrs of LH surge, follicle starts meiosis
Secondary follicle enters meiosis II & arrests again 3 hrs prior to ovulation
Follicle size increases by increase in antral fluid
Structure begins to weaken
LH stimulates collagenase activity = follicle rupture
Ovum carried out into fluid & gathered up into Fallopian tube by fimbra
Meiosis not completed unless ovum fertilised
Describe the formation of the corpus luteum
Remains of follicle re-organise themselves
Secretes progesterone & oestrogen under influence of LH
Lives for 14 days before regressing spontaneously (in absence of fertilised ovum)
How long does it take for sperm to mature
How often are new groups of spermatogonia produced
How many haploid spermatids are produced by each spermatocyte
Approx how many spermatids are produced from one A1 spermatogonium
70 days
16 days (4 spermatogenic processes simultaneously)
4
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