Week 1 RNU Lectures Flashcards
What two substance pass through the urethra?
Sperm and urine
What does the urogenital tract originate from?
Intermediate mesoderm
What are the three sets of kidney structures during development?
Pronephros
Mesonephros
Metanephros
Where are the pronephros found?
Cervical region
Where are the mesonephros found?
Abdominal region
Where are the metanephros found?
Pelvic region
How are the three sets of kidney structures formed during development?
cranial to caudal and chronological sequence
What are the pronephros?
Rudimentary and non-functional structures that begin to regress by week 4
How do the pronephros form?
Intermediate mesoderm starts to thicken and forms 7-10 solid cell groups in the cervical region
What are the mesonephros derived from?
Intermediate mesoderm from the upper thoracic and upper lumbar segments
What is the mesonephros?
A solid rod of intermediate mesoderm in the future abdominal area. It has everything needed to be functional but is not. Contributes cells to the genital ridge and eventually starts to regress
What is the metanephros?
The definitive kidney
When does the metanephros develop?
In week 5 and is functional by week 11
How do the excretory units of the metanephros form?
Develop from the metanephric mesoderm.
Formed from 2 parts at the bottom of the developing structure:
- Ureteric bud
- Metanephric cap
How is the metanephric cap formed?
Mesoderm around the ureteric bud forms mesenchyme which is the metanephric cap
What sources does the definitive kidney form from?
- Metanephric mesoderm (forms the excretory units)
- Ureteric duct (collecting system for excreted stuff)
What is the cloaca?
Posterior orifice that serves as the only opening for the intestinal, reproductive and urinary tracts at early stages
What is the ureteric bud?
A protrusion of mesonephric duct that allows urine drainage from the developing kidney
What does the cloaca begin as?
Hindgut (endodermal lining)
What divides the cloaca?
The Urorectal septum by fusing with the cloacal membrane
What does the division of the cloaca form?
- Anterior urogenital sinus
- posterior rectal/anal canal
What does the bladder form from?
the urogenital sinus and caudal parts of the mesonephric duct
What lines the bladder?
Endoderm
When is genetic sex determined?
At fertilisation
When do the gonads acquire morphological characteristics?
Week 7 of development
What are the three steps of the development of the reproductive tract?
- Genital duct development
- Gonadal development
- External genitalia development
What is present during the indifferent stage (weeks 5-6)?
2 pairs of genital ducts
- paramesonephric ducts (Mullerian) FEMALE
- mesonephric (Wolffian) ducts MALE
What is the function of the mesonephric ducts?
- drain urine from the mesonephric kidney
- an essential role in the development of the male reproductive system
What happens to the mesonephric ducts under the influence of testosterone?
forms the ductus deferens and ejaculatory duct when mesonephros vanishes
What happens to the mesonephric ducts in females?
almost completely disappears, leave a few non-functional remnants
What happens to the paramesonephric ducts in males?
degenerate due to the action of anti-Mullerian hormone. This is a protein made by the Sertoli cells of the testis
What do the paramesonephric ducts form in females?
- Cranial portion forms uterine tubes
- Caudal portion fuses to form the uterovaginal primordium (uterus and superior vagina)
What do the gonads initially appear as?
A pair of longitudinal ridges (on top of the urogenital ridge)
Where do primordial germ cells originate?
The yolk sac
How do primordial germ cells move from the yolk sac and to where?
To the genital ridge via the dorsal mesentery
What happens if the primordial germ cells don’t arrive into the gonadal ridge by week 6?
The ridges develop no further and the gonads don’t develop
What type of structure do the primordial germ cells form in?
A cord like structure - primitive sex cords
What does the Y chromosome encode?
SRY - Sex determining Region of Y chromosome
What does SRY act on and cause?
Acts on somatic cells causing proliferation of the sex cells
What happens to the primitive sex cords in male development?
They become horseshoe shaped and break up into tubules
What do Leydig cells produce?
Testosterone
What do Sertoli cells produce?
Anti-Mullerian hormone
What forms to separate cords from the surface epithelium (male gonadal development)
Dense connective tissue
- tunica albuginea
What happens to the testis cords in puberty?
- They acquire a lumen
- join with the rete testis
- join with efferent ductules
- rete testis and mesonephric duct link to form the ductus deferens
What does WNT4 do?
“ovary determining gene”
What happens to the primordial germ cells in female development?
They divide by mitosis creating a pool of oogonia
What happens to the oogonia at the beginning of the 4th month of gestation?
They enter meiotic arrest and are now oocytes
How are the external genitalia formed?
- a pair of cloacal folds develop around cloacal membrane
- join to form the genital tubercle at the cranial end – this will form the penis and the clitoris
- caudally the cloacal folds are subdivided:
• urethral folds in front - form labia minora in female
• anal folds behind
• genital swellings then appear on either side of the urethral folds
• form scrotal swellings in male, labia majora in the female
How is the urethra formed?
- From middle pelvic part of urogenital sinus
- In males, androgens from fetal testis cause genital tubercle to elongate into phallus
• phallus pulls urethral folds forward
• they form lateral walls of urethral groove and close over urethral plate to form penile urethra
• terminal part of male urethra (external urethral meatus) from surface ectoderm
What is hypospadias?
The urethra is open on the underside of the penis
How does the prostate gland form?
develops as outgrowths from the prostatic urethra
How do the bulbourethral glands form?
develop as outgrowths from penile urethra
How does the lower part of the vagina develop?
two outgrowths from urogenital sinus – sinovaginal bulbs – fuse to form a vaginal plate, hollows to form a cavity
How does the penis form?
androgens from fetal testis cause genital tubercle to elongate into phallus
o phallus pulls urethral folds forward
o they form lateral walls of urethral groove and close over urethral plate to form penile urethra
o terminal part of male urethra (external urethral meatus) from surface ectoderm
What are circulating oestrogens a mixture of?
Oestrone and oestradiol
Where is oestrone secreted from?
directly from the ovary or converted from androstenedione (via aromatase)
Where does oestradiol come from?
Produced by the ovary, derived by direct synthesis in developing follicles or through conversion of oestrone
What are oestrogens involved in?
Development of female secondary sex characteristics
What could happen if someone had issues with aromatase?
They could have issues with sexual development
What hormones do the ovaries produce?
androstenediol, dehydroepiandrosterone (DHEA) and small amounts of testosterone
Where does half of the daily production of androstenediol and DHEA and essentially all of the sulphated form of DHEA (DHEAs) come from?
The adrenal gland
What is DHEA?
An abundant circulating steroid hormone in humans and is a metabolic intermediate in the biosynthesis of androgens and oestrogens
What is DHEAs?
The sulfate ester of DHEA, catalysed by sulfotransferase in the adrenal, liver and small intestine.
In the blood, levels of DHEAs are 300x higher than DHEA and is more stable for measuring
When in the menstrual cycle are progestogens particularly important?
In the 2nd half
How are progestogens made?
From cholesterol via pregnenolone
Where are progestogens made?
Primarily in the corpus luteum, the adrenal glands, and, during pregnancy, the placenta
What are the roles of progestogens?
- Endometrial development
- smooth muscle control
- Maintenance of pregnancy - placenta (establishing and keeping pregnancy)
- Mammary gland development especially preparing breasts for lactation
What are some disorders relating to steroidogenesis?
- Congenital adrenal hyperplasia
- aromatase deficiency
- Aromatase excess
What causes congenital adrenal hyperplasia?
- 21-hydroxylase deficiency
- Deficiency in 11B- hydroxylase activity
What are the symptoms of Congenital adrenal hyperplasia?
- Ambiguous genitalia
- precocious puberty
- anovulation
- Hirsutism (excess hair)
- Steroid crisis
What happens in aromatase deficiency?
Prevents oestrogen synthesis
can lead to ambiguous genitalia
What happens in aromatase excess?
There is excessive conversion of androgens to oestrogens which can lead to the feminisation of male genitalia
What is the axis that regulates female reproduction?
Interactions between the Hypothalamic-pituitary-ovarian axis and the uterus
What happens when the hypothalamus secretes gonadotrophin releasing hormone (GnRH)?
GnRH –> anterior pituitary releases gonadotrophins (FSH and LH) –> target the gonads
What is the 2nd level of hormonal control of female reproduction?
The pituitary gland
What hormones does the anterior pituitary secrete?
FSH, LH
What does the posterior pituitary gland secrete?
Oxytocin